Building open baffles

[TBL]

I'm planning to try my hand at building a pair of open baffles speakers. To be honest its going to be a bit of gamble how it works out. But a bit of info needed first.

To get me started I have just ordered a pair of Markaudio CHP-70 drivers. Cheap as chips at under £50 delivered the pair.

66Hz ∼ 20kHz
Excellent linearity for this driver class
0.57 Qts

now I know that for open baffle I needed a driver with high Qts (even though I do not have a clue what it is)

My question is that although the frequency range goes down to 66hz I'll not get that in open baffle, so what can I expect to get. firstly in a standard flat baffle 48" x 15" and secondly would this be improved if I used an H frame (which is the plan) which would give side wings of appx. 12 "

Given the H frame option what sort of crossover frequency should I be looking at?

Many thanks

[Ali Tait]

You would get very little bass really. A better solution IMHO is to to use one or more 15 inch woofers as bass helpers-two is better than one per channel. It's not as simple as choosing a baffle size and chucking a speaker in, the baffle size has to suit the driver. Here is a pic of my OB's, which were designed and built by Steve (aquapiranha) who posts here. They use a Visaton B200 full range driver and a pair of Eminence Alpha 15" per side-

http://img689.imageshack.us/img689/423/imag0124ks.jpg (http://imageshack.us/photo/my-images/689/imag0124ks.jpg/)

[John]

Agree with Ali You can go active in the bass allowing you to alter how they interact with your speakers this is the eaisest way to overcome issues so you can have a valvae amp powering your full range driver and the sub plate powering your bass drivers. There are lots of bass drivers to choose from

[TBL]

Thanks Guys. Yes I know I need bass, I thought by asking about crossover points it would be obvious I was planning to add bass drivers, so sorry if that wasn't clear.

So my question still stands what would the range be of a 66hz-20khz driver in an H frame? (forget the flat baffle, as I'm def going H) given the dimensions quoted in the op.

[John]

Can you send us a link to the drivers you are getting

[AndrewR]

Another option is to build a pair of JE Labs baffles with a pair of full range drivers from Wild Burro Audio ($100 a pair). I've not heard the result, but the design and opinions are intriguing.

Or, as you have the Mark Audio drivers, a pair of Frugal Horn Mk3 cabinets (Toppsy on the audio-talk.co.uk forums can build them or provide flat packs for you) will suit them.

Andrew

[TBL]

Another option is to build a pair of JE Labs baffles with a pair of full range drivers from Wild Burro Audio ($100 a pair). I've not heard the result, but the design and opinions are intriguing.

Or, as you have the Mark Audio drivers, a pair of Frugal Horn Mk3 cabinets (Toppsy on the audio-talk.co.uk forums can build them or provide flat packs for you) will suit them.

Andrew

I want to build myself and have a play, so buying a kit is not an option

[TBL]

Can you send us a link to the drivers you are getting

These are the ones.

http://oaudio.de/Loudspeaker-chassis/NEW-SPEAKERS/Markaudio-CHP-70::755.html

[TBL]

Just to make it clear, I'm not trying to build the perfect open baffle speaker. I just want to play around and see what happens. I won't be using 15" drivers, simply because they take up too much room. I want to keep the baffle 15" max which will limit me to a 12" driver or I have a pair of active subs that could be used.

In the end if I don't like the sound I just take the drivers out sell on and bin the woodwork. not much cash not much effort and see what happens, well that's the plan anyway. I'm not that interested going down the scientific route of calculating optimum baffle sizes etc.

Yes the result may sound rubbish, but only a few quid lost and a bit of fun on the way I hope. If I like the result project 2 might be a bit more ambitious.

[Ali Tait]

Ok, well AFAIK, using an H frame will improve your bass response, but frankly, if you're going to use active subs, I wouldn't really bother, as long as you can adjust the subs high enough to match well to the CHP's linear response region.

One thing with doing it this way is that you won't get the OB bass you would get from some large woofers on the OB baffle. It's this that gives the special sound of an open baffle IMHO. If the subs are adjustable for frequency, I'd remove the woofers and mount them in the OB, running them from the plate amps in the subs. Should be easy to do, just unscrew the cones and add some longer wires. This should give you an idea if you like the way OB's do things.

Another way to do it is to buy a Behringer DCX2496 and run the baffles actively. You can usually pick up a secondhand one for a couple of hundred on the bay. It's a very versatile bit of kit and you can adjust crossover frequency on the fly, so great for experimenting. Only thing is you need an amp for each stereo pair of speakers, but if you have a spare amp or two lying around, this should give you a great basis for experimenting.

[AndrewR]

I want to build myself and have a play, so buying a kit is not an option

The plans for the Mk3 Frugal Horns are available on the Internet.

See here:http://homepage.mac.com/tlinespeakers/FH/beta/FH-Mk3-betaDoc-251010.pdf

Andrew

[Reid Malenfant]

The driver size & parameters aren't really the thing that govern the low frequency rolloff with a baffle that size. You'll often find that drivers are tested on what i think may well be known as an IEC baffle (yep i'm right), the dimensions of which you'll find here (http://www.diyaudio.com/forums/multi-way/80342-iec-268-5-baffle-dimensions.html) (post #2).

I'd expect any driver to start rolling off in an IEC baffle below 150Hz at about 6Db per octave until the driver hits it's resonance frequency. Below that it'll roll off steeper due to mechanical losses on top of the front to rear cancellations due to the baffle.

The one you are proposing will probably roll off from about 200Hz or a tad higher given it's dimensions & being longer & narrow, so as long as you can get some kind of sub to a frequency of 120Hz or a bit higher you should be able to integrate it without too much bother as the driver in the OB will roll off fairly slowly :)

[TBL]

Ok, well AFAIK, using an H frame will improve your bass response, but frankly, if you're going to use active subs, I wouldn't really bother, as long as you can adjust the subs high enough to match well to the CHP's linear response region.

One thing with doing it this way is that you won't get the OB bass you would get from some large woofers on the OB baffle. It's this that gives the special sound of an open baffle IMHO. If the subs are adjustable for frequency, I'd remove the woofers and mount them in the OB, running them from the plate amps in the subs. Should be easy to do, just unscrew the cones and add some longer wires. This should give you an idea if you like the way OB's do things.

Another way to do it is to buy a Behringer DCX2496 and run the baffles actively. You can usually pick up a secondhand one for a couple of hundred on the bay. It's a very versatile bit of kit and you can adjust crossover frequency on the fly, so great for experimenting. Only thing is you need an amp for each stereo pair of speakers, but if you have a spare amp or two lying around, this should give you a great basis for experimenting.

Thanks Ali,

Numpty alert, Behringers 2496 are way too complicated for me, bought one once looked at the controls and the manual put it straight back in the box and sold it on. Might be simple and straight forward to some, but to me the instructions might as well have been in Chinese.

One of my reasons for using active subs was to avoid the need to build crossovers (something else I don't want to try on this project) Taking them apart is also not on the agenda. I am planning on using Velodyne CHT-10q, 1 for each speakers they have a overall range of 17hz-240hz with 20-240hz +/- 3db they have inbuilt equalisation and variable crossover of 40-120hz (12dB octave, 24dB ultimate)


So knowing what the OB range of CHP-70's is will tell where to set the crossover. Of course I could just try different settings and do it by ear. However if in fact putting this driver in an H frame reduces the low frequecies to say 300hz then i have a problem of a gap in the frequency range.

I had sort of hoped that the DIY builders here could do a calculation based on the speakers specs and the baffle size and come up with an answer, maybe that's a bit too optimistic and I will have to suck it and see.

[John]

The best 10" bass drivers I know off is The Augees They ideal for cutting off around the 60 to 80hz region but if you wish for higher cut off of 120 then you need something a bit less stiff but not sure what going to give you this less than 15" so you have to do a bit of research and if it is quite high up and less than 15" diameter in the bass you bittom end bass will be a lot less but not sure how much that matters to you
Or you have go subwoofer in the bass this will give you more response but not give you that clean detailed sound of open baffle bass that is so additictive

[John]

I just tuned in my bass by ear on the active sub plate and everyone says it sounds great

[Ali Tait]

Thanks Ali,

Numpty alert, Behringers 2496 are way too complicated for me, bought one once looked at the controls and the manual put it straight back in the box and sold it on. Might be simple and straight forward to some, but to me the instructions might as well have been in Chinese.

One of my reasons for using active subs was to avoid the need to build crossovers (something else I don't want to try on this project) Taking them apart is also not on the agenda. I am planning on using Velodyne CHT-10q, 1 for each speakers they have a overall range of 17hz-240hz with 20-240hz +/- 3db they have inbuilt equalisation and variable crossover of 40-120hz (12dB octave, 24dB ultimate)


So knowing what the OB range of CHP-70's is will tell where to set the crossover. Of course I could just try different settings and do it by ear. However if in fact putting this driver in an H frame reduces the low frequecies to say 300hz then i have a problem of a gap in the frequency range.

I had sort of hoped that the DIY builders here could do a calculation based on the speakers specs and the baffle size and come up with an answer, maybe that's a bit too optimistic and I will have to suck it and see.

Just cross them at 200Hz initially, and adjust by ear from there.

[Ali Tait]

The Behringer does have a lot of features, but it's very simple to use as a two way crossover. Sounds great too IMHO.

[TBL]

The best 10" bass drivers I know off is The Augees They ideal for cutting off around the 60 to 80hz region but if you wish for higher cut off of 120 then you need something a bit less stiff but not sure what going to give you this less than 15" so you have to do a bit of research and if it is quite high up and less than 15" diameter in the bass you bittom end bass will be a lot less but not sure how much that matters to you
Or you have go subwoofer in the bass this will give you more response but not give you that clean detailed sound of open baffle bass that is so additictive

You obviously missed my post about using the Veodyne's and their crossover's.

[TBL]

Just cross them at 200Hz initially, and adjust by ear from there.


Am I missing something? isn't 200hz above the crossover level of the Veoldyne's? 120hz that I quoted in my post?

[Reid Malenfant]

:scratch: Anyone seen my post on here :scratch:

With an H frame you should extend the response i mentioned down some... Now go read my other post :eyebrows:

[TBL]

The Behringer does have a lot of features, but it's very simple to use as a two way crossover. Sounds great too IMHO.

Entirely possible but the current plan is to use active Velodyne subs (I have 2 spare)

[John]

Well the Velodyne will work fine
But to be honest one of the things I love about my open baffles is the bass The velodyne will give you good bass but its not going to give you the sense of real drums in the room
Just imho

[Ali Tait]

Yes I know, but as it stands you have no way of crossing the CHP drivers at the bottom end. Yes, you can just let them roll off naturally,but the problem with doing this is that you will be driving them pretty hard at times to match the subs, which will result in a lot of distortion at the bottom end of the range of the CHP's. Far better to cross over at about 200Hz or so, which will allow the drivers to play at higher levels without exceeding Xmax.

[TBL]

Yes I know, but as it stands you have no way of crossing the CHP drivers at the bottom end. Yes, you can just let them roll off naturally,but the problem with doing this is that you will be driving them pretty hard at times to match the subs, which will result in a lot of distortion at the bottom end of the range of the CHP's. Far better to cross over at about 200Hz or so, which will allow the drivers to play at higher levels without exceeding Xmax.

What is the bottom end, that's what I'm trying to find out.

[Reid Malenfant]

You probably wouldn't need to even if you could is what i'm saying ;) Without an H frame i'd expect the MA speaker in just the baffle you descibe go to about 150HZ -6DB (approximately), but the H frame will lower this due to the longer front to back distance..

You may well be able to integrate at 120Hz.

However, as Ali pointed out you'll soon run out of driver excursion from the MA as it'll be still be being fed with bass it can't reproduce. You just won't be able to go very loud, if that's not a problem then you should be ok.

If it is then you need to have a serious rethink :scratch:

[Ali Tait]

Exactly.

[TBL]

You probably wouldn't need to even if you could is what i'm saying ;) Without an H frame i'd expect the MA speaker in just the baffle you descibe go to about 150HZ -6DB (approximately), but the H frame will lower this due to the longer front to back distance..

You may well be able to integrate at 120Hz.

However, as Ali pointed out you'll soon run out of driver excursion from the MA as it'll be still be being fed with bass it can't reproduce. You just won't be able to go very loud, if that's not a problem then you should be ok.

If it is then you need to have a serious rethink :scratch:

Ok now that I understand :), so I'll just try it and see and set the crossover at max. Maybe it wont go as loud as I like but still no need to re-think. If it doesn't work it's no big deal. As I said its only for a bit of fun. If it's a total failure I could just convert to closed box and see how that worked.

[Ali Tait]

Yes, definately have a go. It's all good fun. you will like the drivers, they are very good.

[TBL]

MA drivers are on order and should be here in a couple of days, so should be able to start building next week.

I'll take some progress pics and post them up as I go along.

[Reid Malenfant]

You could always feed the MA CHP driver via a capacitor. With the right value it'll help roll off bass it can't reproduce & increase the power handling & hense volume it'd reproduce ;)

You might need to experiment a bit but i'm sure you could pick up a set of old crossovers with the appropriate approximate value caps for not a lot.

Once you have found the optimum value you could then invest in better quality capacitors, just a thought that might help :)

[Stratmangler]

You might well need to give the CHP-70 a helping hand up top - I have CHP-70s in my FH3 speakers, and I found the HF a tad soft.
A chat with my mate Colin (aka Toppsy) and this was the result http://www.diyaudio.com/forums/full-range/192083-frugal-super-tweeter.html

[TBL]

You could always feed the MA CHP driver via a capacitor. With the right value it'll help roll off bass it can't reproduce & increase the power handling & hense volume it'd reproduce ;)

You might need to experiment a bit but i'm sure you could pick up a set of old crossovers with the appropriate approximate value caps for not a lot.

Once you have found the optimum value you could then invest in better quality capacitors, just a thought that might help :)

Thanks mark, definitely worth looking at post build.

[TBL]

You might well need to give the CHP-70 a helping hand up top - I have CHP-70s in my FH3 speakers, and I found the HF a tad soft.
A chat with my mate Colin (aka Toppsy) and this was the result http://www.diyaudio.com/forums/full-range/192083-frugal-super-tweeter.html

That is just so cool:youtheman: Trouble is my hearing stops at about 10khz so not sure if I could hear the difference.

[Stratmangler]

That is just so cool:youtheman: Trouble is my hearing stops at about 10khz so not sure if I could hear the difference.

The supertweeter uses a corner frequency of 13.5 kHz, and it uses a 1st order hi-pass filter, so there's audible effect at 3.5 kHZ, which is inside your hearing frequency range.
One major area of improvement is in the attack of bass instruments.