View Full Version : Open Baffle Speaker With Active Bass
SteveTheShadow
31-10-2008, 15:11
Hi everyone.
I thought I'd post a bit of DIY on the forum. The design pictured below is an open baffle speaker I have been developing over the past couple of months. One reason I have for posting this is the fact that, in this month's HFW, Noel keywood, in answer to a reader's letter, and with some justification, talks about the fact that OB speakers are not for those with small rooms. I won't go into why here because Noel explains it in his answer, in the letters page.
http://homepage.mac.com/scress1958/.Pictures/birchbaffle2.gif
The design I have done is a bit of a cheat really as it is a hybrid design using active bass reinforcement, from a subwoofer bolted into the base. However what this means is that the delightful, fast open qualities of dipole midrange and treble can be enjoyed in a small room without the subsequent bass issues that a full dipole radiator would enforce. The laws of physics state that the speaker still needs to be relatively large to accommodate the big twelve inch lower midrange/upper bass driver, in this case a Goodmans Axiom 401, but not so large as to be overwhelming in a small space.
Why use such a big driver when there is a sub to handle the bass? The answer is that the sub needs to cross over at a relatively low frequency, certainly well below 200Hz, otherwise its monopole radiation pattern will interfere with the dipole baffle above and cause a discontinuity in the bass register, which will be audible at the listening seat. Plus the fact that a driver mounted on an open baffle needs to be at least 6dB more efficient than the upper mid/tweeter, otherwise searing treble and an overall tinny sound will result unless the tweeter is padded down. The large driver satisfies these requirements much easier than a small unit.
Personally I like to keep crossovers as simple as possible but this in turn means that you need very high quality drivers, matched for efficiency and radiation patterns otherwise you are wasting your time.
The monopole bass end also means that with a bit of tweaking for bass level, the speaker itself can be placed closer to the wall than would otherwise be the case for a full dipole radiator, again handy in a small space. My speakers are placed roughly half a metre from the rear wall and sound great in that position.
http://homepage.mac.com/scress1958/.Pictures/Birchbafflerear.gif
Here is a view of the rear of the baffle.
Looking carefully, one might see the slot at the base of the side wing through which the subwoofer vents to the sides.
There is one on the opposite wing too.
The towel is a temporary arrangement until I get some filling to put down the sides of the sub. This stops the sound, coming from the OB, above from resonating in the gap with the subwoofer output, until I eventually fit a board to isolate the sub chamber from the baffle.
The phase is set so that the sub radiates in-phase with the baffle's rear radiation. No direct front radiation of the out-of-phase bass from the sub is allowed. However, slots are cut into bases of the baffle wings to allow the bass to escape to the sides and of course the sub is free to radiate rearwards.
http://homepage.mac.com/scress1958/.Pictures/Birchbaffle1.gif
And here they are seen in-situ from, the wider angle, with my PX25 SE amp driving them. I like the look of them and so does the missus.
As to sound quality, they suit me down to the ground, with a beautiful, clear, open mid range that is fast and detailed without descending into shoutiness. the Fostex FE108EZ and the Goodmans Axiom 401 are a marriage made in heaven and together, produce a sound that is powerful and organic.
The presentation might be a little too "neutral" for rock music but given my diet of jazz, soul, blues, folk and classical, they suit me perfectly and are completely unfatiguing to listen to. The sub simply fills in the bottom octave from around 70Hz downwards and as a result, its radiation pattern causes no weird effects when combined with the dipole baffle.
I'm very pleased with them. If one is prepared to cast aside any prejudice one might have against subwoofers then they can be very successfully employed to give listeners the benefits of open baffle sound within a much smaller space than would be normal for such a speaker.
Steve
Hi everyone.
, in answer to a reader's letter, and with some justification, talks about the fact that OB speakers are not for those with small rooms. I won't go into why here because Noel explains it in his answer, in the letters page.
As to sound quality, they suit me down to the ground, with a beautiful, clear, open mid range that is fast and detailed without descending into shoutiness. the Fostex FE108EZ and the Goodmans Axiom 401 are a marriage made in heaven and together, produce a sound that is powerful and organic.
The presentation might be a little too "neutral" for rock music but given my diet of jazz, soul, blues, folk and classical, they suit me perfectly and are completely unfatiguing to listen to. The sub simply fills in the bottom octave from around 70Hz downwards and as a result, its radiation pattern causes no weird effects when combined with the dipole baffle.
steve these look great , and your room is not exactly big?
its funny what you say about being too neutral for rock,
I bough led zep 2 yesterday and it sounds very well with my baffles
and 3 watts /channel ..105db's my room was rocking..
but it was not the sound i expected.. i was used to hearing it with a level of distortion in the bass.. thickening it up... and without all the peaks in the music being heard..
but i was more than happy.. as i feel my system plays it fairly accurately
can't wait to hear them next week...
steve
SteveTheShadow
01-11-2008, 16:43
steve these look great , and your room is not exactly big?
its funny what you say about being too neutral for rock,
I bough led zep 2 yesterday and it sounds very well with my baffles
and 3 watts /channel ..105db's my room was rocking..
but it was not the sound i expected.. i was used to hearing it with a level of distortion in the bass.. thickening it up... and without all the peaks in the music being heard..
but i was more than happy.. as i feel my system plays it fairly accurately
can't wait to hear them next week...
steve
Hi Steve and thanks for the positive comments. Given your comments about trying Led Zep with your baffles I thought I might as well bite the bullet and try a bit of rock with them.
Using Thin Lizzy's "The Boys Are Back in Town" from their "Jailbreak" album The result was very impressive. Everything was separated out and as you say the bass was well portrayed without any thickening up, plus the track really moved along at a brisk pace. Much better than I remember it sounding on other systems I've had.
So it looks like my baffles are performing in a similar manner to yours.
That's what I like about baffles...you seem to be able to play anything you want on them.
Steve
Lovelly looking speakers Steve and I bet they sound great I heard the Bastanis Atlas and was blown away by them I wish had the room but alas only 4m by 3m
They really could play rock very well and did everything else as well
SteveTheShadow
01-11-2008, 20:36
Hi John,
They really work well.
I guess the hardest part about building them was the crossover.
Trying to marry together two ostensibly full-range drivers with rising responses meant I had to throw the crossover rule book out the window, by putting a big hole in the mid-range, so that the rising responses would flatten, come together properly and fill that hole back in again.
The results however have been well worth the effort.
Steve
Lovelly looking speakers Steve and I bet they sound great I heard the Bastanis Atlas and was blown away by them I wish had the room but alas only 4m by 3m
They really could play rock very well and did everything else as well
I would think steves listening room is about 4x4m.. so would not be put off too much, the real issue for many is can you accept the size of the speakers in the room,
open baffles can be very good ..i have not heard the bastinis but i would guess they would have a similar sound to steve's and my own..
steve
aquapiranha
02-11-2008, 22:02
Lovely! I especially like the Fostex drivers.....just kidding.. I have done a very modest amount of diy audio myself but I have never tried an OB - perhaps it is time I gave it a go? I do like the look of the Hemp acoustics drivers, but they woulod be best in a cab..then there is the Siver Iris...now I have started myself off again!
Like I said, they look brill and I bet they sound it too!
steve.
SteveTheShadow
03-11-2008, 13:12
Hi Guys,
To give an idea of the size..they are 41 inches high by 16 inches wide by 13 inches deep, at the bases, where the wings are at their widest. The measurement from the back of the Fostex driver to the rear wall is around 2ft, which means that the subs at the base are positioned about a foot from the rear wall.
In a 4m x 4m space, the baffles become a feature of the room... no getting away from it, so they have to be designed to look good, otherwise the better half will not accept them (and you can't blame her either)
Steve has bigger baffles in his room with 2 x 12 inch Goodmans drivers below a Lowther EX4 full ranger. I think his are about 2ft 6in across the front and about 4 feet high with foot deep side wings. Although he has a bigger room than I do, his baffles still become a feature of his room, simply because of their increased size compared to mine. But he has also designed his to look good to minimise complaints from the distaff side.
That I think is the secret of getting open baffles into a room that is shared with the family, make them look good, complement the fixtures and fittings, put a few pot plants around to soften the impact and half the battle is won. The sound takes care of the rest, because even the most cloth-eared person can tell that, in the right circumstances, open baffles will blow away most box speakers.
Steve
The sound takes care of the rest, because even the most cloth-eared person can tell that, in the right circumstances, open baffles will blow away most box speakers.
Hi Steve,
Nice speakers, btw!
Much as I like good open baffles (and there's plenty to admire in their presentation) the ones I've heard so far (at Owston, etc) lack the sort of scale and visceral bass I get with my Spendor SP100s (with 12" bass units) when playing music at the sort of silly loud levels I do when friends pop round. It's that gut-wrenching, feel it in your chest, 'physical' quality to the bass that I miss with the open baffles I've heard so far, and I want that, big time! :fingers:
I find almost every other aspect about the presentation of open baffles better than large well-sorted box speakers (and otherwise), apart from the above. I also find much the same thing with good push-pull amps compared to SETs, but that's for another discussion.
Like always though, I'm always open-minded about these things and if or when I hear a pair of open baffles which do the 'visceral' thing in the bass that I like I'll openly acknowledge it!
If you're bringing your speakers to Owston this weekend then I'll bring my p/p 30W Class A Copper amp and some suitable music to see whether your babies do it for me in the bass and scale department :smoking:
Marco.
SteveTheShadow
03-11-2008, 14:55
Hi Steve,
If you're bringing your speakers to Owston this weekend then I'll bring my p/p 30W Class A Copper amp and some suitable music to see whether your babies do it for me in the bass and scale department :smoking:
Marco.
You know of course they won't :lol:
Notice I said most box speakers. There's no way a 12 inch driver on an open baffle will hit the chest like a 12 inch driver in a box will. Laws of physics innit?:) I'd probably need a pair of 15s to get anywhere near.
You're welcome to have a go with your amp but we need to remember that these things are efficient, so the power handling is not that of a modern driver. The Goodmans Axiom 401 will only take 15W before it blows up and I love these drivers too much to risk them in any way. Also they are not mine (not yet anyway :) )
The Fostex FE108EZ driver is nominally an 8W max power speaker with a 0.28mm xMax and again I'm not prepared to risk destroying them in a power game.
I'm not trying to be awkward or anything Marco, but you can see the problem. :)
Steve
greenhomeelectronics
03-11-2008, 16:26
Wow, nice looking job. There is nothing more satisfying than building a pair of speakers that sound just right in your environment. If you are looking for material to replace the towel you might like to try some stuff called sorbo - it's a very dense foam rubber type substance that has excellent absorbtion characteristics, I have used it myself many times.
Dave.
You know of course they won't :lol:
Notice I said most box speakers. There's no way a 12 inch driver on an open baffle will hit the chest like a 12 inch driver in a box will. Laws of physics innit?:) I'd probably need a pair of 15s to get anywhere near.
You're welcome to have a go with your amp but we need to remember that these things are efficient, so the power handling is not that of a modern driver. The volume must be kept down so your proposed experiment is really a non-starter. The Goodmans Axiom 401 will only take 15W before it blows up and I love these drivers too much to risk them in any way. Also they are not mine (not yet anyway :) )
The Fostex FE108EZ driver is nominally an 8W max power speaker with a 0.28mm xMax and again I'm not prepared to risk destroying them in a power game.
I'm not trying to be awkward or anything Marco, but you can see the problem. :)
Hey, Steve, no worries mate. I completely understand :)
However, for that reason you can probably appreciate exactly why I don't use open baffles and SET amps! ;)
Marco.
SteveTheShadow
03-11-2008, 17:18
Wow, nice looking job. There is nothing more satisfying than building a pair of speakers that sound just right in your environment. If you are looking for material to replace the towel you might like to try some stuff called sorbo - it's a very dense foam rubber type substance that has excellent absorption characteristics, I have used it myself many times.
Dave.
Thanks Dave I'll certainly look into that.
No probs Marco :)
Steve
Hi Steve,
Nice speakers, btw!
Much as I like good open baffles (and there's plenty to admire in their presentation) the ones I've heard so far (at Owston, etc) lack the sort of scale and visceral bass I get with my Spendor SP100s (with 12" bass units) when playing music at the sort of silly loud levels I do when friends pop round. It's that gut-wrenching, feel it in your chest, 'physical' quality to the bass that I miss with the open baffles I've heard so far, and I want that, big time! :fingers:
I find almost every other aspect about the presentation of open baffles better than large well-sorted box speakers (and otherwise), apart from the above. I also find much the same thing with good push-pull amps compared to SETs, but that's for another discussion.
Like always though, I'm always open-minded about these things and if or when I hear a pair of open baffles which do the 'visceral' thing in the bass that I like I'll openly acknowledge it!
If you're bringing your speakers to Owston this weekend then I'll bring my p/p 30W Class A Copper amp and some suitable music to see whether your babies do it for me in the bass and scale department :smoking:
Marco.
Interesting points Marco
i would have agreed with you a couple of years ago
the bass is one of the real weak points with most home audio speakers
there is no way to get really clean bass from a box, with every type of speaker there are trade offs to some extent..
but less so in the sound deptment, if the low bass can be achieved with a baffle
it would be great if you could get your spendors in the car too..
as you know the only way is to a/b..
if your playing at loud levels say 109 dbs.. you need to be using say around 60watts.. if you are getting those levels from your existing amp you will be well into clipping.. so you will have fair bit of distortion going on.. and probably not getting the 'scale' as much as you think.. as its the peaks that clip.
with high watts into speakers like that, the voice coils will be getting very warm causing further clipping..
add to that the port output .. which is with bass reflex is slightly delayed to avoid the low notes being cancelled, and to achieve reasonable levels from the single bass driver...this is not accurate bass.. but one easily get used to the sound of it..
all the above has the effect of thickening the sound.. giving it more body.... more than it should have ? .. and of course, masks some of the finer details
the real advantage of high eff is that one can get those sound levels with 4 or 5 watts, all class A, no feed back, triodes
and the voice coils are are not being warmed up too much..
and scale...the sound is clean.
steve has a few trade offs.. the main one with smaller baffles is that he's using subs.. for the very low bass only.. and only below 60 hz
steve
Filterlab
03-11-2008, 20:40
Steve, I love your speakers and I bet they sound superb. The sound from an open baffle arrangement is so liberating and airy, although I'm partial to the thump from a speaker with a small enclosure as well. However experience from using electrostats has taught me a lot about choosing speakers to suit the music one listens to the most, and these sound like they're exactly right for their purpose. That's pretty well the reason I sold my electrostats and went back to stand mount speakers, they're exactly right for me.
However, tastes change over the years and I may well look into open baffle speakers in the future. :)
Excellent work, they look gorgeous and the idea of combining a bass enclosure with the open baffle arrangement is something that captures the best of both worlds, much like the hybrid electrostats. Lovely stuff. :)
Hi Steve,
the bass is one of the real weak points with most home audio speakers
there is no way to get really clean bass from a box, with every type of speaker there are trade offs to some extent..
I completely agree. Hi-fi is all about choosing your compromises and the Spendors are by no means perfect - there is no such thing as a perfect loudspeaker. However they get the important things right (for me); it's not just about realistic, tightly controlled, musical sounding bass, which they do extremely well, but also the way music is communicated overall via other parts of the frequency range. The Spendors give great insight into music and have clarity and definition without any fatigue factor whatsoever.
Open baffles sound absolutely fantastic in the midrange with a 'freedom' and expressiveness that no box speaker can match - I love that about them - but I've yet to hear a pair that can do deep, 'visceral' bass in the way of a large box speaker; and there is very little coloration, believe me, when you get it right. There's no audible distortion, clipping, or thickening of the sound whatsoever in my system when music is played within the capabilities of the amplifier and speakers - and you have to go some to exceed that level! You must come round and visit sometime :)
A friend of mine has recently bought a pair of (huge) 96db Tannoy Canterburys with 15" dual-concentric drivers and the sheer scale that these produce with his 40w p/p valve amp is frightening. Your ears will give in long before they do! That's the way I like it as I couldn't be bothered worrying about blowing drive units, etc, as seems to be the case with open baffles. And SET amps, as lovely as they sound, are too 'weedy' for me. All the guys at Owston seem forever to be worrying about the volume music is played at, as there appears to be a finite level of loudness one can achieve before things go pop. That's just not my 'thang'. I go to a fair few gigs throughout the year and I can tell you that Ian's Tannoys produce a sound that's as near as I've heard to live music, which is where it's at for me with hi-fi, and I'm sorry, a world apart from what I've heard so far from any open baffle design and SET amp.
These are just my honest observations to date. Feel free to convince me differently at Owston! ;)
Marco.
I would think steves listening room is about 4x4m.. so would not be put off too much, the real issue for many is can you accept the size of the speakers in the room,
open baffles can be very good ..i have not heard the bastinis but i would guess they would have a similar sound to steve's and my own..
steve
Thanks for the info its good to know that open baffle can work in my room, at the moment I use Wharfedale Opus 3 lovelly speakers abd really big
Hi Steve,
I completely agree. Hi-fi is all about choosing your compromises and the Spendors are by no means perfect - there is no such thing as a perfect loudspeaker. However they get the important things right (for me); it's not just about realistic, tightly controlled, musical sounding bass, which they do extremely well, but also the way music is communicated overall via other parts of the frequency range. The Spendors give great insight into music and have clarity and definition without any fatigue factor whatsoever.
Open baffles sound absolutely fantastic in the midrange with a 'freedom' and expressiveness that no box speaker can match - I love that about them - but I've yet to hear a pair that can do deep, 'visceral' bass in the way of a large box speaker; and there is very little coloration, believe me, when you get it right. There's no audible distortion, clipping, or thickening of the sound whatsoever in my system when music is played within the capabilities of the amplifier and speakers - and you have to go some to exceed that level! You must come round and visit sometime :)
A friend of mine has recently bought a pair of (huge) 96db Tannoy Canterburys with 15" dual-concentric drivers and the sheer scale that these produce with his 40w p/p valve amp is frightening. Your ears will give in long before they do! That's the way I like it as I couldn't be bothered worrying about blowing drive units, etc, as seems to be the case with open baffles. And SET amps, as lovely as they sound, are too 'weedy' for me. All the guys at Owston seem forever to be worrying about the volume music is played at, as there appears to be a finite level of loudness one can achieve before things go pop. That's just not my 'thang'. I go to a fair few gigs throughout the year and I can tell you that Ian's Tannoys produce a sound that's as near as I've heard to live music, which is where it's at for me with hi-fi, and I'm sorry, a world apart from what I've heard so far from any open baffle design and SET amp.
These are just my honest observations to date. Feel free to convince me differently at Owston! ;)
Marco.
to be honest Marco, i had heard open baffles quite a few times at various meets, and was never convinced.. i liked my big lowther horns..
It was not until Nick brought his baffles around to my house about 2 years ago now.. and we did a lot of a/b testing, then i heard the difference in the bass..
once i started to reconised what Nick had been pointing out to me .. my view of boxed speakers changed..
the Se / push pull thing is a matter of opinion, there are very good examples of each type..
the speakers you own or use, dictate how many watts you need.
I would love listen to your kit at your place..we'll speak at the weekend and try to arrange something?
I have no worrys about blowing drive units and will happily crank mine up
i could get 120db peaks from 5 watts of px25 but is was not as clean as it could be with the old horns,
The baffles give about another 3 dbs due to the doubling up of the drivers
but much cleaner in the bass..
with open baffles there is no load from a box or horn.. so you have to keep well in the rated wattage.. but there's the advantage of the fact that there is less compression or expansion from the box to deal with for the driver..
Briggs in the 50's documented these effects in his books
last time at owston I had fitted a new driver the day before the meet, so was taking things steady in the room... and i was only using a 2 watt amp most of the time
I'll be bring the other amp only this time it makes about 3 watts or so so we can really blast it...:guns:
the valves in it now are real vintage stuff.. very different from last time..
steve
Sounds great, Steve! I'll look forward to it :eyebrows: :)
Owston is always good because apart from the social aspect you always come away having learnt something.
Marco.
Sounds great, Steve! I'll look forward to it :eyebrows: :)
Owston is always good because apart from the social aspect you always come away having learnt something.
Marco.
Yes I agree, and it is especially pertinent when the listening environment is very compromised. I'm sure a listen to O/B speakers with a low wattage SE amp is a very different and fulfilling experience in the domestic situation. Organising small minifests is the way to trial properly really. The big events however as so much fun in all aspects. Looking forward to seeing y'all (trying to be topical ;)) at the weekend.
Best wishes,
Greg
I'm sure a listen to O/B speakers with a low wattage SE amp is a very different and fulfilling experience in the domestic situation. Organising small minifests is the way to trial properly really.
I'm certain that's the case as some of those little amps and speakers seriously struggle in such a huge room. They definitely need a more intimate environment :)
Yes, I'll look forward to downing the beer that's been left on the counter for me since the last time - jeez, it'll be as flat as a pancake now! :lol:
Never mind :cool:
Marco.
Sounds great, Steve! I'll look forward to it :eyebrows: :)
Owston is always good because apart from the social aspect you always come away having learnt something.
Marco.
me too, i had the same equipment for around 7 years.. and since these meets it has all changed and improved(i like to think..)
but not from what people said about it.. it's from what they didn't say...
Indeed. I was honoured that my Sony DAC and modified SL-1210 went down so well first time around! ;)
Marco.
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