Digging deep, 4th order bandpass subwoofer build

[Reid Malenfant]

Seeing as i have already started this project i thought i'd share this with anyone who is interested here on AoS :) This may take a bit of time due to me being compromised in the spinal department (multiple prolapsed discs, sciatica etc) but i'll get there in the end. I hope you enjoy the journey on the way ;)

A little background

I have been designing & building loudspeakers since about the age of 13 or 14, so the best part of 30 or so years :mental: Around 1990, or at least in that decade i used to buy a magazine called Electronics World & Wireless World. One day having bought the latest issue i came accross a design for a bass speaker or if you like - subwoofer of a type i had never heard of before. In the article it was called a "coupled cavity" & these are now more commonly known as a 4th order bandpass (though other orders such as 6th can be designed & built).

This speaker used a pair of Kef B139 bass drivers in two sealed boxes facing into a ported chamber with all the sound eminating from the port. The design itself had a -3Db bandwidth of 20 - 80Hz with no electronic augmentation. I was fascinated so i proceeded to analize how the thing worked, at the time there were no speaker design programs & very few PCs so i had to do this with a scientific calculator. Many hours & a good deal of paper later it began to dawn on me what was going on & how the thing worked.

The speaker itself used two sealed boxes, each with a volume of approximately 80 Litres & because of the free air parameters of the B139 drivers this gave a closed box Q (Qcb) of approximately 0.5. The drivers free air Q or Qts was approximately 0.36, so placing it in the sealed box raised the Q because the air in the box was stiffer than the drivers suspension in free air. Also because of this the drivers free air resonance (Fs) was also increased to 40Hz. Due to the fact that two of these drivers faced into the ported chamber & i was working out what was going on with just a single driver I had to divide the ported chambers volume in two. At that point i modelled what the B139 would do in a ported box of "X" volume which was tuned to 40Hz (the same as the drivers resonance in the closed box or Fcb).

So at this point in time i had the response of the sealed box modelled & also the response of the ported enclosure modelled, i could effectively design my own speaker :) Then i figured something out that would forever (or very nearly) put me off of bass reflex speakers & make me build bandpass bass speakers from then on. I looked at the overall size of this design which was near on 230L internal volume (which isn't small :rolleyes:) & realised that there could only ever be a maximum output from the design itself due to the drivers cone displacement at 20Hz.

Knowing this i decided to see if it was possible to get the very same output using a B139 in the same type of enclosure design, but a heck of a lot smaller :interesting: What i needed to do was sacrifice the holy cow of flat frequency response from the speaker itself & use electronics to make the response flat instead. I needed to test my ideas out so after designing a speaker that had a total internal volume of about 25L (less than a quarter the size of the magazine design for one driver) i proceeded to build it & make the electronic network needed to correct the response.

The result was that it worked :lolsign: What i did was use a special circuit called a Linkwitz/Riley network (or transform) to force the driver to behave like it had a closed box Q of 0.5 at 40Hz in my small sealed box. As i had to calculate the smaller ported enclosure to, i had to come up with what i call "imaginary" driver parameters (which aren't any such thing by the way) of free air resonance (Fs) & driver total Q (Qts) that would give me a closed box Q & Fcb that i wanted. There was only one important driver parameter that wasn't being changed & that was it's compliance equivalent volume or Vas. Because i knew this it wasn't difficult to calculate the Fs & Qts i'd need the driver to have to have a closed box Q of 0.5 & a 40Hz resonance. Using these imaginary parameters i worked out the precise volume i'd need to make the ported chamber to give the same response as it's much larger brother.

It turns out that was quite small, so small in fact that there would be no way of using a conventional port simply because to move enough air without causing turbulence it'd need to be a fair size & thus incredibly long to tune such a small box to 40Hz :eek: So i used a passive radiator instead, problem solved...

Here are a few pictures showing the original test enlosure that i built :)

You can see where the internal B139 resided & you may notice the external hole is the same shape, i used the BD139 from a pair of Kef Cadenzas as the passive radiator. Notice a 500ml pot of paint for size comparison purposes.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image5-1.jpg

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image6-1.jpg

Here is the Kef B139 or should i say what remains of one of them :lol: It died during a rather loud party unfortunately.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image7-1.jpg

If you know these drivers you'll probably notice that the frame has been cropped, this was because when i built the speakers properly i wanted to keep them as narrow as possible ;)

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image8-1.jpg

Finally a picture of one of the finished speakers. The bass speaker took up all of the volume behind the sloped baffle, on the front are two x Audax 5.25" & a Focal 1" inverted Kevlar dome. Electronics & amplification is sat on top, not pretty but it worked :rolleyes: Excuse the image quality, it's a picture of a picture...

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image9-1.jpg


I'll be back soon & i'll let you know what i'm planning & where i have gotten to so far. Lots of explainations & a few revelations & probably other boring stuff ;) Cheers for now...

[Reid Malenfant]

Ok, here is the plan & this will be the last upgrade i'll (hopefully :lol:) ever make to this systems speakers. Refer to them as subwoofers if you like, but essentially they'll be the bass speakers for a new pair of stereo speakers i'll also be designing & building in the future.

As i say, i'm not keen on bass reflex speakers due to the 24Db per octave rolloff below resonance for starters, there are a few other reasons such as transient response (difficult to get right but not impossible) & amplifier loading & these will be discussed as i go along :)

So what have i got & what am i planning on doing? Well i have 4 x 15" high excursion bass drivers, or in boy racer terms i have 4 x 15" competition subwoofers :lol: Have it whichever way you like it, i'm going to get some deep, clean & loud bass out of these drivers though it'll take some ingenuity. As i predominantly listen to stereo rather than watch films on my AV setup i'll be making a stereo pair of bass speakers. This doesn't matter a hoot to the AV setup anyway as i have never used the sub output on any 5.1 setup, turn the sub output off in the player & it forces the bass to the front left & right speakers which will be these babies ;)

I can't give you exact details of everything right now as i don't know all of the bass driver parameters, however, with what i do know i can predict a response & if things change slightly it's no big deal because all i'll need to do is subtly alter the equalisation. This being the Linkwitz/Riley network & another card i have up my sleeve as you'll see. In the case of the previously mentioned bandpass enclosures the -3Db points were 20 & 80Hz but these will be slightly different.

The drive units that i selected & bought for the left & right main speakers are 9" carbon fibre coned bass drivers (http://www.monacor.de/typo3/index.php?id=75&L=1&act=8&act_sub=25&artid=3734&spr=EN&typ=u) of rather good quality. In a sealed box with a Butterworth response the -3Db frequency will be 100Hz. So it's natural that i now make these bass speakers have a two octave response from 25 - 100Hz -3Db so i can use an active crossover (12Db per octave on top of the enclosures 12Db per octave) to get a 24Db octave rolloff from both enclosures, in other words a Linkwitz/Riley crossover which keeps everything in phase.

I really ought to add that these enclosures were very nearly never going to happen & i was going to build a pair of sealed box bass speakers, but fate gave me a hand. I'm a member on a few forums & one day i happened to be looking about on one that i'm reasonably regularly on & i found a chap selling 6 unused Exodus Audio 15" passive radiators. I quickly jumped on his thread & asked if he'd be willing to ship 4 of them to the UK from USA & if so how much would it all cost? Well he got back to me with a price i just couldn't resist so i sent him some money via paypal & the rest is history. To buy a new 10" Peerless passive radiator i was looking at somewhere near £80 each & i'd need at least 3 or possibly 4 per 15" driver as these drivers have a +/- 17.5mm excursion, 35mm pk-pk :eek: So for less than the price of 3 Peerless PRs i had exactly what i wanted & the project was implemented.

What i need to do is make sure than no matter what size sealed box these drivers go into is that i can get them to their full linear excursion without overloading them. With a power rating of 600W RMS that gives me quite a bit of choice & means the enclosure can be quite small. As i say, i don't know all of the drivers parameters yet but i did have something to start with, it looks horrible, but it's not a problem as you'll see.

Initial measurements of a single brand new driver netted me these results:- FS 35Hz, Qts 0.887 (yuck) Vas 58L (very small), as i say these are car subwoofers but that doesn't matter as the Linkwitz/Riley network not only corrects for output, but also for transient response :lol: Whatever i want these things to do, i'll be able to get them to do it...

With these parameters i went to work using WinISD a free program for bass enclosure design (available online) & i was rather surprised at what it predicted. Maximum volume level will be incredible right down to 25Hz, great says I simply because no matter how loud i turn things up i'll be straining the things.

Here is a graph of the predicted output of all 4 drivers in one box. Please remember that there will be 2 boxes of half the size of this one. I think you'll notice that the output compared to the box size is pretty incredible :)

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Peakoutput.jpg

If you look at the top right hand side you'll see a predicted 119.5Db at 25Hz from a total internal box volume of just under 250L. This will be split into 2 speakers which will each have the internal volume similar to an ATC SCM100.

You may notice that there is a slight skew of the response at the lower end, this is deliberate. While i may be able to totally deafen myself i happen to have a bit of a cunning plan (where's my turnip) :lol: If i use another Linkwitz Riley network i can equalise the speaker to go much deeper but at a lower volume level. So without further messing about here we have what i'll normally be listening to once it's completed...

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/boostedsub.jpg

Peak output at 111Db or there abouts & a -3DB frequency of 13Hz @ 108Db.


Back with more waffle soon ;)

[John]

Sounds a interesting project I look forward to seeing how it develops

[Reid Malenfant]

A rather interesting thing i found is that WinISD has problems predicting the response if i add the exact Linkwitz/Riley network i need to get the response that i want & for a long time i couldn't figure out why this was. It works perfectly if i use the "imaginary" driver parameters that i mentioned earlier, yet it really messes up if i attempt to do exactly what i'm going to do.

Eventually i figured out what the problem was :) You'll have to forgive me here as the nearest comparison i can get is nicked from a film most people will know :doh:

I finally realised what the problem was when i took a look at this graph. What you see here is a load of responses predicted by WinISD including the real output of the bass speaker, unfortunately it's not that clear colour wise so i had to label what each line on the graph represented.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/BandpassSealedresponses.jpg

You can see the single driver in the sealed box has a rather peaky response, this is due to the high driver Qcb & it should look orange. The same driver with the added helmholtz resonator (ported enclosure to make the bandpass) has a rather large dip in the middle of the passband, should be silver or white line on the graph.

To get the response i want i added a Linkwitz/Riley network to get exactly the closed box response i wanted from the speaker, graph line should be yellow but isnt, at least it's labelled :eyebrows: Now when the helmholtz resonator is added on top WinISD predicts the response will be as per the red line - bl**dy awful :eek: But in reality it'll be exactly as the "real response" graph shows, blue line. I couldn't figure it out until i saw this graph & then it hit me! All WinISD is doing is subtracting the difference between the two graphs of the closed box with & without the Linkwitz/Riley network :doh:

Much like the inside out baboon & the steak that was described as artificial in the movie The Fly, his computer wasn't getting excited by what it was doing looking at the flesh...
2346
WinISD isn't getting all excited about the way the bass driver rolls off in the sealed box with the addition of the L/R network, all it's doing is subtracting from the response rather than seeing a slower rolloff which is what the network is forcing on the driver. It can't see that the system is now behaving like it had a lower Qts & Fcb as it would be.

So given that i still have to input the so called imaginary driver parameters :rolleyes: Please remember though that these are the real driver parameters i'd need with a driver of that Vas to get the response i want, so in that respect they are real :lol:

What you may well notice is that with the L/R network in place i'll actually be cutting power to the bass driver all the way down to about 26Hz, only below this will i actually be boosting power & only by a few Db. All good news as far as i'm concerned as both the power amp & driver will have a much easier time.


Sounds a interesting project I look forward to seeing how it develops
Cheers John, just noticed your post as i'm writing this one :) These will be the last speakers of this kind of performance that i'll ever need to build. Probably won't stop me messing about with others though :lolsign: Bests to you chap!

Back again in a bit, i need another :cool:

[Reid Malenfant]

Finally an introduction to the drivers i'll be using to create these monsters ;) They are pretty cheap, the nasty parameters probably explain this, but as the drivers will be used in a sealed box with the L/R network it really doesn't matter in all honesty.

As i was going to use them previously in a standard sealed box i bought 4 x 8" dust domes to cover the originals that frankly advertise what they are. I do tend to like things looking a little more subtle ;) So here is the front of the driver with the new dust cap but not glued on. Thankfully i'll not need to paint the thing to make it black now either as it'll be out of sight inside the enclosure :)

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image2-1.jpg

Basket & magnet assembly...

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image3-1.jpg

At least the basket is cast & machined alloy, it'll need to be rather stiff. 220oz of magnet still doesn't help get that driver Q down :scratch:

At this point we attempt to find out the real driver parameters, the only way of doing this is to break the drivers in :lol: Out comes the Mackie M3000 power amp & i connected two drivers together with threaded rods & tightened everything up as best as possible. Feeding them a constant output at there resonance frequency that made the pair of drivers get to their maximum linear excursions (& getting the hell out of the room because of the noise) i proceeded to break them in...

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/2driverbreakin.jpg

The result was as i thought :doh: Driver resonance frequency dropped & because of this the Qts actually increased to about 1.18 :eek: No doubt Vas has also increased, however i can't find a damn test enclosure that's big enough to take a 15" driver & i don't know what i used to establish the 58L Vas previously...Need to make a new test enclosure :rolleyes:

While all that sounds bad in reality it isn't :) Now the driver Qts is even higher it means that when it's mounted into the sealed box i'll actually be cutting power to it even more to get the response i require. It looks like i'll be cutting power to well below 20Hz to get the response i want in the enclosure when it's built!

One thing i should mention at this point is that i realised that i couldn't use just the Linkwitz/Riley network. The reason for this is the speaker simply has too much output so the L/R can't correct for this & get the lower output that i need. Out comes the cunning plan again, though this one took a little more thought. Because the driver has too much output to get the desired response at 50Hz, IE a Qcb of 0.5 or there abouts i thought of the idea of using the L/R network to equalise to virtually DC, in this case i picked 0.12Hz. This would be suicide for amps & drivers alike, however, if i introduce a high pass filter with exactly the response i need & have the L/R network connected after this it'll be just what i want :lol:

So here is the even more peaky response of the run in driver & the response i require which is a gradual rolloff...

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/closedboxsystemresponses.jpg

Next up the near DC rolloff caused by the L/R network designed to run 0.12Hz at -3Db.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/closedboxwithlinkwitz.jpg

As soon as i introduce the high pass filter both traces merge, i have exactly what i want ;)

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/closedboxlinkwitzhighpass.jpg

To cap it all here is the filter responce of both the L/R network & high pass filter, i'm actually cutting power everywhere to below 20Hz to get the response i require :wow:

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/filterresponse.jpg

That's way too much waffle for today ;) I'll be back tomorrow to bring you up to where i am right now. Time to get a bit pickled :cool:

[Techno Commander]

I do like TCB's. Some years ago I was working on a couple of legs of the Minisrty Of Sound tour. They were using the (then) new JBL sound power system. It featured 4 of the 4688-4 TCB sub boxes.

http://i240.photobucket.com/albums/ff152/Fuzzylogic666/Westrex2080a067.jpg


They each featured 4 800W 18" drivers arranged like this. (yes I know this isnt the actual plan)
http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=4235&stc=1&d=1102741944

They produced enough bottom end to cause an interesting sensation in the trouser department. A number of young ladies were sat on them during the course of the proceedings and were sporting very intense facial expressions.
:eek:
About half way through the tour, the gig at Leicester university had to be delayed by an hour as the glaziers were still replacing the windows that were blown out during the sound check.:lol:

[Reid Malenfant]

I do like TCB's. Some years ago I was working on a couple of legs of the Minisrty Of Sound tour. They were using the (then) new JBL sound power system. It featured 4 of the 4688-4 TCB sub boxes.

They produced enough bottom end to cause an interesting sensation in the trouser department. A number of young ladies were sat on them during the course of the proceedings and were sporting very intense facial expressions.
:eek:
About half way through the tour, the gig at Leicester university had to be delayed by an hour as the glaziers were still replacing the windows that were blown out during the sound check.:lol:
2350 Yeah than can make an incredible amount of bass that's for sure ;) I remember wondering how Bose got so much bass out of their subs, not the home ones but the type used in clubs etc. Me being me i had my hands down both ports to attempt to work out what was going on :lol: They were 6th order bandpass with what felt like two 10 or 12" drivers in each cabinet.

Those speakers you have pics of look like they'll be 6th order bandpass judging by the way the ports are spread about. If they were fitted with 4 x 18" as you mention i'm not surprised they kicked out some bass. If they were arranged internally as you have pictured then effectively there will be 2 x 18" radiating as they look to be in an isobaric formation. This means you can effectively half the enclosure size but get the same volume level, you'd be stuffing double the power in though to do this ;)

6th order speakers are rather more difficult to design & roll off like a bass reflex at 24Db per octave. In fact they actually unload even faster due to the way the enclosure works, the upper frequency port adds mass to the bass drivers due to the big slug of air in the port itself. So when it goes below the lower port frequency it doesn't just have the drivers moving mass but this mass of air to. They'll usually need a steep cutting high pass filter so as not to kill the things with subsonic information :eyebrows:

Cheers for popping in Andy :)


Ok back to the subject at hand...

I mentioned in one of these posts that i'm not a huge fan of bass reflex speakers due to a couple of things. One was transient response & the other was amplifier loading.

Well the transient response of this speaker would be awful without the addition of the Linkwitz/Riley network, it'll be just the same as an optimal driver would be in this enclosure. In other words it'll behave just like a driver with the so called imaginary parameters & no electronics to get things flat.

Amplifier loading is an entirely different matter. In a reflex speaker & this speaker the highest amount of current is drawn at the port tuning frequency. This is due to the action of the port which provides incredible damping for the driver so it behaves much more like a pure resistance at the port tuning frequency. The consequence of this is that the impedance approaches the DC resistance of the voicecoil & it will draw lots of current from the amplifier. Another problem with this is that with this massive current, or if you like power draw the voicecoil will generate more heat. The big problem here is that the cone is severely damped & therefore not moving very much, it can't effectively pump air in & out over the voicecoil to cool itself. A recipe for self destruction if ever i heard of one :doh:

The very same problem can & does hamper the performance of a 4th order bandpass in most cases but not here with this one :lol: As i want a 25 - 100Hz bandwidth the port will be tuned to around 50Hz (46Hz in this models case), but if you look back at the way the Linkwitz/Riley network & high pass filter combine you'll see i'm cutting power by about 10Db at around this frequency. That is equivalent to 1/10th the power. The most each of these drivers will see is approximately 60W or a tad more at the port tuning frequency, they'll handle that with total ease ;)

An amplifier can easily supply loads of power at 50Hz as the capacitors are effectively be recharged at a rate of 100Hz in the UK & 120Hz in USA. They won't like to supply tons of power at really low frequencies though. A bass reflex that has a frequency response extending to 20Hz is likely to be tuned to about that frequency. This means that the peak power draw will be at a frequency that the amp can't supply as much power at as 50 or 60Hz, another brick in the wall for the reflex.

Here are a couple more graphs, one shows impedance & the second shows the load on the amplifier in VA (volt amps). As you can see the amplifier load for the reflex at 20Hz is rather high, for the bandpass it's vastly much lower.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Impedance.jpg

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Amplifierload.jpg

The above graphs need to be taken with a fairly liberal dose of salt ;) The reason for this is that these are the impedance readings of the driver with imaginary parameters. In the case of the real driver all the peaks & troughs will indeed be in the same positions, the peaks & troughs will be narrower due to the higher driver Qcb. Other than that they are a pretty good representation of what will be going on.


Because i can't resist fiddling with anything & because i felt that a drivers free air Q is a tad high at 1.18 i thought i'd try an old trick & see if i could lower it somewhat. Out came a decent sized ferrite ring magnet & i positioned it on the backplate of the bass speaker so that it was repelled by the backplate. This is the same kind of trick used on so called shielded drivers, though it has another & much more useful effect :idea: It forces more magnetic field into the voicecoil gap & lowers the driver Qts.

Having done a quick test i knew it'd have an effect so i went magnet hunting. Unfortunately i couldn't find a suitable magnet, what i was looking for was a ring magnet with an internal diameter of 105mm & an external diameter of 180 to 200mm, thickness wasn't an issue. I couldn't find one so i settled on a load of smaller magnets & i found a nice ebay seller with loads at a cheap price, i bought 30...

I did a quick test with 5 of them selotaped onto the backplate & discovered it lowered the Qts to about 1.05 :clap: as i'm planning on using 7 on each driver i'm at the present glueing them on with epoxy resin. Long job as the magnets try to force their neighbours off of the speaker :lol: So it's one at a time...

Here's the test setup

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/subdriverexperiment.jpg

Tools of the trade ;)

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/functiongenerator.jpg

That's where i am at the moment, i guess i'll be back with this once i have the driver parameters once all the magnets have been glued on :rolleyes:

Bests to all, cheers for now :)

[spendorman]

Seeing as i have already started this project i thought i'd share this with anyone who is interested here on AoS :) This may take a bit of time due to me being compromised in the spinal department (multiple prolapsed discs, sciatica etc) but i'll get there in the end. I hope you enjoy the journey on the way ;)

A little background

I have been designing & building loudspeakers since about the age of 13 or 14, so the best part of 30 or so years :mental: Around 1990, or at least in that decade i used to buy a magazine called Electronics World & Wireless World. One day having bought the latest issue i came accross a design for a bass speaker or if you like - subwoofer of a type i had never heard of before. In the article it was called a "coupled cavity" & these are now more commonly known as a 4th order bandpass (though other orders such as 6th can be designed & built).

This speaker used a pair of Kef B139 bass drivers in two sealed boxes facing into a ported chamber with all the sound eminating from the port. The design itself had a -3Db bandwidth of 20 - 80Hz with no electronic augmentation. I was fascinated so i proceeded to analize how the thing worked, at the time there were no speaker design programs & very few PCs so i had to do this with a scientific calculator. Many hours & a good deal of paper later it began to dawn on me what was going on & how the thing worked.

The speaker itself used two sealed boxes, each with a volume of approximately 80 Litres & because of the free air parameters of the B139 drivers this gave a closed box Q (Qcb) of approximately 0.5. The drivers free air Q or Qts was approximately 0.36, so placing it in the sealed box raised the Q because the air in the box was stiffer than the drivers suspension in free air. Also because of this the drivers free air resonance (Fs) was also increased to 40Hz. Due to the fact that two of these drivers faced into the ported chamber & i was working out what was going on with just a single driver I had to divide the ported chambers volume in two. At that point i modelled what the B139 would do in a ported box of "X" volume which was tuned to 40Hz (the same as the drivers resonance in the closed box or Fcb).

So at this point in time i had the response of the sealed box modelled & also the response of the ported enclosure modelled, i could effectively design my own speaker :) Then i figured something out that would forever (or very nearly) put me off of bass reflex speakers & make me build bandpass bass speakers from then on. I looked at the overall size of this design which was near on 230L internal volume (which isn't small :rolleyes:) & realised that there could only ever be a maximum output from the design itself due to the drivers cone displacement at 20Hz.

Knowing this i decided to see if it was possible to get the very same output using a B139 in the same type of enclosure design, but a heck of a lot smaller :interesting: What i needed to do was sacrifice the holy cow of flat frequency response from the speaker itself & use electronics to make the response flat instead. I needed to test my ideas out so after designing a speaker that had a total internal volume of about 25L (less than a quarter the size of the magazine design for one driver) i proceeded to build it & make the electronic network needed to correct the response.

The result was that it worked :lolsign: What i did was use a special circuit called a Linkwitz/Riley network (or transform) to force the driver to behave like it had a closed box Q of 0.5 at 40Hz in my small sealed box. As i had to calculate the smaller ported enclosure to, i had to come up with what i call "imaginary" driver parameters (which aren't any such thing by the way) of free air resonance (Fs) & driver total Q (Qts) that would give me a closed box Q & Fcb that i wanted. There was only one important driver parameter that wasn't being changed & that was it's compliance equivalent volume or Vas. Because i knew this it wasn't difficult to calculate the Fs & Qts i'd need the driver to have to have a closed box Q of 0.5 & a 40Hz resonance. Using these imaginary parameters i worked out the precise volume i'd need to make the ported chamber to give the same response as it's much larger brother.

It turns out that was quite small, so small in fact that there would be no way of using a conventional port simply because to move enough air without causing turbulence it'd need to be a fair size & thus incredibly long to tune such a small box to 40Hz :eek: So i used a passive radiator instead, problem solved...

Here are a few pictures showing the original test enlosure that i built :)

You can see where the internal B139 resided & you may notice the external hole is the same shape, i used the BD139 from a pair of Kef Cadenzas as the passive radiator. Notice a 500ml pot of paint for size comparison purposes.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image5-1.jpg

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image6-1.jpg

Here is the Kef B139 or should i say what remains of one of them :lol: It died during a rather loud party unfortunately.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image7-1.jpg

If you know these drivers you'll probably notice that the frame has been cropped, this was because when i built the speakers properly i wanted to keep them as narrow as possible ;)

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image8-1.jpg

Finally a picture of one of the finished speakers. The bass speaker took up all of the volume behind the sloped baffle, on the front are two x Audax 5.25" & a Focal 1" inverted Kevlar dome. Electronics & amplification is sat on top, not pretty but it worked :rolleyes: Excuse the image quality, it's a picture of a picture...

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Image9-1.jpg


I'll be back soon & i'll let you know what i'm planning & where i have gotten to so far. Lots of explainations & a few revelations & probably other boring stuff ;) Cheers for now...

Very interesting read (no pun intended). I can understand the B139 failing as they will probably need more power for a given sound level compared to a B139 in a conventional cabinet. The obvious replacement might be the later type KEF B139, which has larger power handing capability.

My own attempt at getting extended bass was much simpler, quite different and perhaps rather quirky.

The cupboard under the stairs has no door and in it is an air brick that goes into the adjacent garage (built on to the side of the house). I though that this hole in the wall would be an ideal "infinite baffle".

An old 8" RS bass unit of reasonable quality was tried. Pretty good results were obtained. The only snag with this strange set-up was that if the lounge door was closed. Not a real problem because the lounge door is normally left open and it is opposite the cupboard under the stairs.

The next step was to replace the 8" unit with an EMI 13x8" as used in the B&W DM3. This was an improvement, giving better bass attack. The next unit to be tried was a 12" bass unit from a Celestion Ditton 44. The results were very good, not a lot different from the EMI. I did not try KEF B139's although I have some, mainly because although good bass units they have some nasties in the midrange and as I was not filtering the input to them much.

[Reid Malenfant]

Sounds like you made an infinite baffle which often do give great results. Unlike a closed box which is often called an infinite baffle by those that don't really understand what's going on :eyebrows:

I'll be getting back to this project in due course. There is no way i'll be working out in a cold shed to build the cabinets over this winter, & right now i'm gradually clearing out a room of stuff i don't want. Once i have done that i'll be able to get to work, in fact i'll turn it into an electronics workshop along with a bench & test equipment. It'll be big enough to work on speaker enclosures as well :)

Nothing like being warm & dry & able to listen to some tunes whilst working away :eyebrows:

[Reid Malenfant]

Just bringing this up again as things have changed somewhat :lolsign:

Whilst browsing ebay today looking for something totally different I happened accross a few of the highest quality bass drivers i have ever seen this side of the Atlantic! It appears that someone imported a load of them just to get two & sell the others to kind of get a bit of money back on import duties & tax etc.

After my jaw picked itself up off of the floor i bought 4 of them very quickly knowing that they'll be vastly superior in any box application i care to mention ;)

They should be delivered tomorrow. Might appear to be a bit mad spending £900 on 4 bass drivers but if you want one of the best quality 15" drivers ever built then you have to pay for them ;) Lets not forget that a single Yamaha NS1000M tweeter costs about the same at over £200 each :eek:

Creative Sound Solutions SDX15 Subduction Subwoofer (http://www.creativesound.ca/pdf/CSS-SDX15-data-121107.pdf)

winISD is forcasting 122Db @ 20Hz with 3KW input power & 112Db @ 10Hz :mental: Bring on the bass depth... 4497


Looks like i might as well see if any OB builder wants some 15" drivers i no longer need :eyebrows:

[Welder]

Looks like an interesting Home Cinema project Mark :)

A bit of warmth and comfort is essential so having some room to dedicate to such projects is great.

[Reid Malenfant]

These will be the left & right bass speakers for the new enclosures John :eyebrows: 2 drivers per enclosure, probably mounted on the side to keep the front baffle as narrow as possible. I was going to build subs but decided against it, might as well have the whole lot in a couple of boxes rather than 4 boxes.

If you know anyone that wants some cheap 15" high excursion woofers send them my way. No point in keeping the old ones, just more clutter in the house :doh:

[Puffin]

I have built a coupled cavity sub in the past to very good effect and I still use a B&W acoustitune Coupled cavity sub. I think they sound as good as any other. The Acoustitune was originally a passive design with different length ports to tune the lower frequencies. I converted it to active operation.

[Reid Malenfant]

Hi Rob, yes i'm in 100% agreement if they are done right :) Done wrong like a lot of other speakers they can sound "one note" in nature.

Blimey, you just reminded me of that acoustitune thing! I has been years since i have heard that mentioned & if i remember right the only time i heard it mentioned was a test in a magazine? :scratch:


I'm not sure at all if these new drivers will be used in a coupled cavity, the others had to be or a sealed box simply because of the high driver Q. These new ones are spot on for anything, be it reflex, coupled cavity (4th order bandpass) or whatever. Some fiddling realises i can now squeeze 115Db 1M @ 10Hz with the SDX15 woofers :eek:

That's bloody crazy :D Well i guess earthquakes will feel more realistic!

[Puffin]

Nice thing about the B&W is the proper cast frame drive units. Unusual for a budget sub.

10 Hz, enough to mske you feel very queasy at the least and result in death at the worst :eek:

[Reid Malenfant]

Nothing like pushing the boundaries ;) I'm just about dead sure i'll never hear that kind of SPL at 10Hz as it'd be too much, but it also means that whatever volume level i listen at the speakers will take it & at a reduced level distortion will be negligible :)

It's not about making it go loud, but about getting the least distortion at any level i care to listen at..

I could happily listen at 100Db & know that absolutely nothing is stressed no matter what i throw at it, the resulting sound will have far less distortion than just about any speakers available unless you happen to have £50K+ to throw at some :eek:

[Reid Malenfant]

Well i have been messing about & got some results. If i happen to make a pair of 300L enclosures which is te same internal volume as ATC300A they'll certainly be blown to bits :eyebrows:

These graphs are for a 600L enclosure with 4 drivers, though i'll possibly be building 2 x 300L enclosures, i really haven't made my mind up yet :scratch: I don't have to please anyone except myself so a pair of coffins in here isn't a problem. All i have to decide is would i prefer to build a sealed box with fairly low Qtc (really clean bass), a reflex but very low tuning (should be damn clean still due to the low tuning frequency) or a 4th order bandpass :doh:

I think i'm going to go the reflex route :eyebrows:

First up maximum SPL @ 1M, 129Db is crazy :eek: I much prefer looking at the 115Db @ 10Hz :mental: Looks like well over 122Db @ 20Hz :clap: The blue trace is the 4 x 9" carbon bass mids i'll use for upper bass/lower mid duties. Green is in this pic combined with a red trace but you can't see the red trace, this is the 600L reflex tuned to 11.5Hz. The yellow trace (looks white :rolleyes:) is the same 4 SDX15 drivers in a 600L sealed box.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/SDXmaximumSPL.jpg

After a bit of fiddling with various filters that won't be difficult to make you can see how the SDX15s will combine with the bass/mids & cross over at 68Hz. As you can see from the box on the right system input power is 320W which results in 118.9Db @ 29Hz but with a -3Db frequency of 11.88Hz, -6Db @ 10Hz :eyebrows: There would be 320W RMS with no boosting, so assuming there is no silly frequencies (below 20Hz - which i love) the whole system can be driven to 129Db, however if there is silly stuff i can only go to a paltry 119Db :eyebrows:

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/SDX15600Lfrequencyresponse.jpg

Here is what the drivers would be doing being fed 3KW RMS (forget the bass mids ). As you can see they have a 30mm linear excursion but a 40mm mechanical limit. Now most people say that due to capacitors in equipment that a high pass filter isn't needed in an LLT sub. I guess that the fact that i'll never be able to handle the volume level that these things could kick out would make it even safer. But as you can see, with a high pass filter i can restrict the excursion to 39mm even if a full power signal at 1 - 5Hz came along (red trace again).

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/SDXconeexcursion.jpg

I guess if i try a single one of these subs in a 150L enclosure & feed it every bass heavy CD & blu ray i'll find out if i need that filter or not...


ATC SCM 300 AT (http://www.atcloudspeakers.co.uk/scm300at.php) eat your heart out :ner: :eyebrows: [B]Totally out monstered :cool:

[MartinT]

Anyone heard of Graham Holliman? :)

[Reid Malenfant]

Sounds like it's a bit room fussy (http://www.diyaudio.com/forums/subwoofers/3238-graham-holliman-velocity-coupled-infra-bass-speaker.html) ;)

These won't be :) They'll generate the pressure just like the response shows, well, as long as i make the enclosures well & you can be assured of that. Something tells me that they'll end up at about 200Kg each loaded with the drivers. Concrete floor, nothing to worry about :eyebrows: They'll sit on spikes to :lol:

Just don't get hand trapped under spike :eek:

[Reid Malenfant]

Oh well, as usual these things end up a pain in the proverbials :eyebrows:

If i port this thing the largest port i can get away with is 6" diameter for one speaker with two drivers & 300L internal volume. The port ends up 129cm long which is pushing things & the first port resonance is only 130Hz which is a bit close to 68Hz which will be the crossover frequency. Also the port air velocity is just a tad high at nearly 40M per second = noisy :eek:

If i use two passive radiators per speaker the ABRs will run out of excursion. I can't fit more ABRs even though i can buy them from the Netherlands simply because I'd need more mass than the PRs can handle to tune them low enough in the enclosure :doh:

I have considered using both passive radiators & a port, though i have no idea how they'd get along with each other? :eyebrows: If anyone happens to know then please let me know!

So it looks like i'm going to have to build my own passive radiators :rolleyes: It's not as difficult as it first appears, i have done this before though i can't honestly say i'm relishing the idea of doing it again! What would be used to do two large PRs would be a 1M^2 sheet of 5mm acrylic, 4 x 21" motorcycle innertubes, 2 new bolt up schrader valves, lots of evostik glue, MDF, woodscrews & M4 bolts, nuts & locking washers :mental:

In true Blue Peter style i'll show you one i made earlier :lol: I'll get my camera & fight my way into the garage...

[MartinT]

Mark - was the Graham Holliman infra-bass design or elements of any use to you?

[Macca]

I think some of the big B&W use ports and ABRs - 683 is a recent one I think

[Reid Malenfant]

Mark - was the Graham Holliman infra-bass design or elements of any use to you?
I found a huge thread on the subject Martin, did some prying but the jury is out right now. I have more investigations to do yet :)

As promised the Blue Peter ABR :lolsign: I'm hoping it's pretty self explainatory, but if you have questions then feel free to ask. I built this back in about 1996 :cool: It's 26" along the longest section & yes i made a round 16" innertube fit an oval :lol:

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/ABRfront-1.jpg

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/ABRfront2-1.jpg

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Corneredgeclose-1.jpg

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/ABRrear-1.jpg

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Rearclose-1.jpg

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/Innertubesandwich-1.jpg

Tuning is simply done by increasing the air pressure in the innertube & or adding more mass - simples :)

[MartinT]

Nice one! Must say, I'd never contemplate trying to make something like an ABR. I would probably try going ported the way of REL's resistive matrix design.

[Reid Malenfant]

The more difficult something is the more i often rise to the challenge :eyebrows: I'll look into that Martin, something tells me that i'll probably come back to something like this again though. If i do then they'll be round this time, i had to make it that shape due to the enclosure size & shape.

Round should be a damn sight easier to!

[Reid Malenfant]

Nice one! Must say, I'd never contemplate trying to make something like an ABR.
Well i have just discovered something of significance that is forcing my hand to make a couple of these big passive radiators :)

That big oval PR has a resonance frequency when mounted to the box of 40Hz. Now i was just giving the thing a good shake when i realised how low the unboxed resonance frequency was, it's approximately 2Hz give or take.

I just did some simple math & worked out that the PR has a VAS of over 5000L, this might not be significant in itself but it means that in any box the factor governing it's resonance frequency will always be the box & air inside of it. There is virtually zero mechanical losses unlike any other passive radiator i know of, in fact modelling it it behaves in almost precisely the same fashion as a ported enclosure. A standard PR will have significant mechanical losses due to the PR suspension & the whole speaker will suffer because of this :(

I'm off hunting for bits :eyebrows:

[MartinT]

Is what you are saying that the ABR will flop uselessly due to the effective volume being too large giving it virtually no stiffening?

[Reid Malenfant]

No, the Exodus Audio PR15 which i was going to use has a resonance frequency of 20Hz in free air. When it's put in any box (just like any driver or PR) the resonance frequency will be raised. To get the Exodus PR to resonate at 11.4Hz or so in the enclosure a lot of mass has to be added. The Exodus has a VAS of 245L.

Now you can see that because the free air resonance is 20Hz with no box that the PRs suspension will have a big effect on proceedings as it's already way above what i want it to be boxed. The big oval PR has a free air resonance at about 2Hz which is way lower than i'm after, which means that the box air stiffness & not the PR suspension will have a vastly greater effect & to all intents & purposes it can be factored out of the equation :)

I'll get some graphs up after i have finished buying stuff to do the job :cool: I always wondered why the heck that sub with the oval PR sounded so good :eyebrows:

Obviously i'll make these two new ones look a lot prettier :lol:

[Welder]

Interesting.

The first thing that strikes me is the difficulty of tuning. Given you have enclosed air as part of the suspension as the unit moves the air will heat up, tube expand etc.

Next, looking at the construction, it looks quite heavy compared to say a paper cone mounted on a traditional paper/pulp spider and that means a larger than practical moment of inertia I would have thought so response speed may suffer and from what I can see it looks difficult to control.
While you can tune roughly to a certain frequency roughly, in a sealed enclosure at least, ABR’s tend to vibrate within a range of frequencies and careful spider and suspension matching is needed to keep that range useful.
Because of the weight of what passes as a cone, won’t the unit tend to sink into the lower air tube?

Also, what sort of pressure wave will you get from a flat surface? Will such a wave propagate in a useful manner?

500 liters is a bloody big box and for digital media certainly any response below 20 Hz is wasted. An extra couple of Hz can be achieved by careful internal box configuration perhaps by using a pressure wave matrix but those who have tried this out haven’t met with a great deal of success without having a driver that goes down to the same frequency.

Anyway, I’ll be interested to see how it develops.
:popcorn:

[Reid Malenfant]

Interesting.

The first thing that strikes me is the difficulty of tuning. Given you have enclosed air as part of the suspension as the unit moves the air will heat up, tube expand etc.
Easiest thing ever to tune John, get it roughly right with mass & then final adjustment with a bicycle pump :lol:

Next, looking at the construction, it looks quite heavy compared to say a paper cone mounted on a traditional paper/pulp spider and that means a larger than practical moment of inertia I would have thought so response speed may suffer and from what I can see it looks difficult to control.
While you can tune roughly to a certain frequency roughly, in a sealed enclosure at least, ABR’s tend to vibrate within a range of frequencies and careful spider and suspension matching is needed to keep that range useful.
Because of the weight of what passes as a cone, won’t the unit tend to sink into the lower air tube?
Well i worked out that the aluminium weighs in at about 2Kg & considering the size of it that is naff all. Consider that i'd need to add 1.65Kg to one of the PR 15 drivers which has a smaller surface area now which do you think the air in a 300L box would have better control over? A bit more mass & over double the area or a small area & nearly as much mass? The diaphram does not sag at all fella, in fact if i turn it so it's horizontal it only sags a few mm. My guess is that the Exodus PR 15 with 1.65Kg would sag like a 80 year olds boobs :eyebrows:

Also, what sort of pressure wave will you get from a flat surface? Will such a wave propagate in a useful manner?
As good as a cone chap, there are one or two speakers out there with flat diaphrams (Kef, Technics) & lots of PRs (Celestion, Kef).

500 liters is a bloody big box and for digital media certainly any response below 20 Hz is wasted. An extra couple of Hz can be achieved by careful internal box configuration perhaps by using a pressure wave matrix but those who have tried this out haven’t met with a great deal of success without having a driver that goes down to the same frequency.

Anyway, I’ll be interested to see how it develops.
:popcorn:
I have a good deal of music with sub 20Hz high power signals, a good bit sub 15Hz. If you go to hometheatre shack (http://www.hometheatershack.com/forums/databass-movies-deep-bass-dmdb/) you'll find a list of films with deep bass & a good deal of those have strong signals right the way down to 10Hz :eyebrows: I like my movies & my music. This will be a pair of 300L speakers that will happily reproduce 123Db @ 20Hz & 115Db @ 10Hz (if required).

[Welder]

All I can say is air suspension has been tried before and its got problems but I think the experiment could be interesting so I’ll shut up and watch ;):popcorn:

[Reid Malenfant]

Ok, as threatened we have winISD take on things :) What we have here is three identical enclosures of 300L with two SDX15" bass drivers but with differing ways of tuning things.

Red graph trace is 300L tuned to 11.43Hz via two Exodus Audio PR15 ABRs.

White trace is 300L tuned to 11.43Hz via a 5000L VAS homemade ABR 21" piston diameter (not counting the suspension) so about 26" total :eyebrows:

Blue trace is 300L tuned to 11.43Hz via a dirty great reflex port.

First up we have the transfer function magnitude or if you like the predicted response.. As you can see the enclosure (red trace) loaded with the PR15s is not the same, the other two are very similar.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/transferfunctionmagnitude.jpg

Next up transfer magnitude phase. Oh dear look at those with the PR15, the phase goes nuts due to the mechanical compliance of the ABR itself as that has a strong effect due to have to it having a higher resonance frequency & low VAS.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/transferfuctionphase.jpg

Next up we have group delay, again the PR15s look bad & that kind of delay will effect the timing of bass in relation to everything else :rolleyes:

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/groupdelay.jpg

Impedance as seen by the amplifier, again the PR is vastly different from both the high VAS ABR & ported speaker.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/impedance-1.jpg

Oh here it gets messy, this is maximum SPL (sound pressure level). The PR15s just can't move enough even with a 40mm Xmax, so the SPL plummets. Can't add a couple more to the enclosure as i can't go over 1780G of added mass to the PRs :rolleyes:

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/maximumspl-1.jpg

Here is the ABR cone excursion just to put things into perspective.. No graph for the ported speaker as that has no passive radiator.

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/PRconeexcursion.jpg

Finally just to hammer things home we have the speaker cone excursion. As can be seen the PR15 loaded enclosure has a much more peaky nature to drive excursion & this is due to the PR15s mechanical effect having a much more pronounced effect on the response that the enclosure air controlled ported or homebrew ABR where only the air is in control...

http://i939.photobucket.com/albums/ad240/speakermark/subwoofer/coneexcursion.jpg

Fun innit :)

Already bought the aluminium & 4 x 21" motorcycle innertubes i need to make two of these beasts :eyebrows:

[Welder]

So what happens to the tuning frequency when you raise the temperature of the air inside the tubes by 15 degrees?
The suspension compliance must change with temperature mustn’t it? :scratch:

[Reid Malenfant]

How on earth is it going to get 15C hotter?

Besides which the resonance frequency is far more enclosure air volume dependant than the PR15 ABRs. I can certainly imagine that they will go out of tune as the mechanical side heats up, but the big homemade jobby is far more enclosure volume dependant & not on the mechanical side of things...

Think about it John, the PR15 would be far more affected than the beast :eyebrows:

[Welder]

Yeah but, as the temperature in the inner tube changes so does the suspension stiffness and thus resonant frequency; that isn’t so much of a problem for a usual rubber or neoprene roll surround.

[Reid Malenfant]

Yes John i agree fully. But the ABR will be so dependant on the volume of air in the enclosure because the VAS is stupendous that a little softening will have bugger all effect. As i mentioned the PR15s which are normal ABRs would be affected far worse as they are governed more by suspension compliance & not the air in the enclosure ;)

[Welder]

Hmm, I think you’re wrong mate for a number of reasons.
If your generating enough pressure to move the “cone” in a box of that size I think you’ll find a much larger temperature variation than you seem to be expecting and that’s going to play havoc with any attempts to tune the ABR.
I get a 15 degree rise in temp in my cabs easily if I give the bins a bit of stick.
But, one of the advantages of paper cones directly coupled to a neoprene/rubber suspension is that they both transfer heat with reasonable efficiency to the outside environment while air encased in rubber doesn’t.
Also, a plain neoprene roll for example has a reasonably uniform compliance over a fairly wide range of temperatures which is one of the reasons it gets used.

[Reid Malenfant]

& you don't think that aluminium will help radiate that heat John? :scratch:

Like i say you are looking at things the wrong way chap. The big ABR will be far more enlosure volume dependant than any normal ABR as they are generally mechanically (suspension) dependant. As the enclosure volume won't be changing they should be pretty stable. But an ABR based more on suspension compliance for resonance frequency would be affected far worse than one based on air volume due to heat & softening suspension...

Think about it fella, you'll soon see it makes sense ;)

[Welder]

"Think about it fella, you'll soon see it makes sense"

Thought about it and it hasn’t got any better :eyebrows:


I don’t need to think about it any more mate because I’ve had this debate before as have many manufacturers of drive units :doh:

It’s not that you cant get the ABR to vibrate its you cant keep it in tune and that means all the steady state models in the world wont predict the overall speaker response with sufficient degree of accuracy.
Yes, steady state models are used for all predictive speaker building but as you know yourself its all good at a particular temperature and goes to shite as the temperature changes. It’s the biggest problem in decent speaker building; having it all work as predicted at any given temp.

Anyway, build it and see innit ;)

[Reid Malenfant]

Anyway, build it and see innit ;)
Yes, you'll be most welcome to come round for a visit & be shaken & stirred :lol: Make it a weekend if you want ;)

Seriously though John this ABR will be far less effected by internal enclosure temperature as it is far more dependant on it's resonant frequency in that particular enclosure on the enclosure volume, rather than the ABR suspension...

Look at the graphs m8, they show it following a similar curve to a reflex port. Where as you can plainly see that a standard PR is governed more by it's suspension compliance.

What i'm getting at is this will be affected less by temperature & by suspension compliance as it is so high that the enclosure volume governs it because it has a VAS of over 5000L ;)

E2A:- Besides which i'm damn sure i'll never get anywhere near the full volume capability of these speakers, so they'll just be chugging along at a much lower level. So heat input is even more out of the window in a way :) The idea is i build something that can reproduce anything i can throw at it with more volume than i could ever take. So at normal levels distortion is out the window :cool:

[Welder]

If I can tear myself away from the tuneful bass I get here I may well do that one day Mark. I would like to meet you anyway.

You never know mate, I may just come equipped with a server so you can chuck your cd player out with the speakers :eek: :lolsign:

[Reid Malenfant]

:lolsign: All the best John, have a good weekend m8 :)

Weekend? I must be enjoying myself :eyebrows:

[Welder]

And you Mark :)

Cans time here methinks :doh:

[SPS]

i'm sort of with welder with my feelings about the quality.. but i cant help but admire your balls in attempting this project this Mark.
i also think heat is the least of your troubles

in my experence with hi fi its about understanding what gives



your clearly far more technical in your approach .. and I hope you succeed, so the best of luck to you

but when you have those very low notes you will have little to compare it too with regard to accuracy,

i was in precision devices's factory test room a few years ago, they have a wall of pa speakers and lots of good gear powering it up and the ability to cut/boost most frequencies , i was looking at their 22" drivers for an open baffle project, but got to hear only 15 & 18 units. He played me music that sounded like a concert.. but when he cut the (around) 70 hts upwards sounds, what an awfull sound came out of the speakers, sound full of distortions, in my view due to the amplification and port outputs, and the slowing of the cones movements due to the loading imposed from box speakers.

the design engineer sort of said whats the point.. look whats there?
but the whole picture sounded very impressive
and he was right to a point, if most people hear a little thunder through a system they are very impressed.

now, 2 years on.. in my system there's nearly the same drivers, with clean amplification and those low notes that have the sound like any real instruments that produce low notes. its very clean..

best of luck...

[Reid Malenfant]

Cheers for the luck Steve, it's nice to have it :)

Ok, so i'm not attaching accelerometers to the bass drivers & forcing them to follow the input waveform precisely a la motional feedback. So yes in that respect these & just about everything else isn't perfect. The drivers are very high quality units though, with a motor circuit designed to cut distortion in comparison with a standard motor unit by 75% up to about 75% of maximum linear excursion.

In that respect they should have lower distortion than something like the Precision Devices drivers, though i know these to be rather good with low thermal compression. They still don't have the XBL2 motor though ;)

The passive radiators are the only pain in the backside though. I don't mean what they'll do, but building the things :eyebrows: If you have read back from a page or two you'll know i couldn't port these things as the port would be either too small (causing turbulence & distortion) or too long in which case the first port resonance frequency would be in the passband :doh:

As it is i have sussed out a neat way of getting the passive radiators mechanical properties out of the window by giving them a huge VAS which will be totally swamped by the 300L of enclosure. Thus it'll only be the enclosure air volume that'll be in control of the PR which has the same effect as using a huge reflex port but with none of the problems associated with it..

It'll be interesting for sure, though as i have already pointed out (i think) i'll never hear them at full volume as i just won't be able to stand it. At lower volume distortion will be minimal :)

[SPS]

. So yes in that respect these & just about everything else isn't perfect. :)



to be frank thats my experence too,
most speakers can leave a lot to be desired, but most don't realise that

and there's just so many variables and viewpoints.... all valid enough,
the trouble is you cant imagine the improvements you can get in the sound quality when you give the driver less work to do, but as you know you need good drivers with just enough self damping for the job... and it sounds like that is what you have,

i've had a couple of pairs of ns1000's, as you know they dont have that ported sound, but the speakers sound is limited by the driver compressing the air in the box,
remove that aspect and speakers can spring into life,

i would make up a baffle board to compare

say a cheap W section board on hinges at the 3 joints, cut /mount the speakers on the two middle panels, well tape the joints so the dont leak
mount the speakers close to the floor on the boards & site next to a wall if you can, nothing too big... each board the width of the driver and say 30" high

they wont go as loud in the bass as you would like..but you can eq it a bit
without spoiling the sound too much,
but you will have a reference to what the driver will sound like on its own ( without a box or load)
and work from there..

hope you dont mind me interfering.. i too have been building speakers for a few years, but ended up in a totally different route, in the search of what i think is a realistic sound.

[Reid Malenfant]

hope you dont mind me interfering.. i too have been building speakers for a few years, but ended up in a totally different route, in the search of what i think is a realistic sound.
Steve, you aren't interfering in the least :lol:

To be perfectly honest i will say that i have never heard any open baffle speakers. Well that's not strictly true as i sure as hell heard the Pro Plus drivers breaking in :eek:

I'll be 100% honest & say that i was planning on going down the closed box route, rather than a reflex. The only reason i decided on the reflex is because i managed to get the box tuning so low (about 10Hz now :)). Because of that they should sound like a sealed box from 20Hz upwards as the port or in this case the ABRs PRs or whatever we shall call them will only operate up to approximately double the tuning frequency. For all intents & purposes that is now (supposedly) below audibility.

I still have 6 of the 15" Pro Plus drivers which are actually better suited to OBs due to the driver Q being higher. Maybe some day i'll experiment with some kind of OB & see what i get. Only a herd of charging rhinos will deflect me from building these as i designed them now as i have purchased the bits & pieces to build the ABRs :eyebrows:

You can't say you didn't try though ;) ATB!

[SPS]

it did look like i was trying to convert you to OB's mark.. that was not really what i had in mind, i was just thinking you could knock quick a test baffle up to compare to the speaker cabs you where planning,
you would easily be able to compare the sounds you where getting... and i just thought that may help...

but your minds set i can see...

cheers
steve