Open baffle drivers configuration: time to ask the experts

Recently I got inspired by an open baffle system from http://www.warco.com.au/awar.htm. It is using Raven 3 ribbon and 2 Cabasse woofers 21NDC. It seems that it got good response from the listeners.
 

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I was thinking about building something similar, since I have Cabasse woofers. Instead of Rven 3 I want to use Raven 2 and Triangle 5" midwoofer. Cressovers would be around 200 and 10K and probably active. Would this configuration work well? It's not MTM, but something slightly modified. Also is it better to place woofers as close as posible to tweeter and midrange or better space them?

The drivers would be mounted in a wall separating two rooms, so it's sort of infinite baffle design. Your input greatly appreciated.
 

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gilid

Member
2002-01-25 9:28 pm
France
Open baffle speakers

Proac recently launched an open baffle series, the 'Futures'. I have heard only excellent things about them, so they can serve as a good starting point for inspiration.
Check out www.proac-loudspeakers.com/proacfut.htm for info.

Very expensive (more than the usual proac stuff), and they do not appear to use any propriatary 'black magic' techniques. They appear to be well within the reach of a determined DIY'er.
 
Keep the woofers as close as possible to each other, otherwise you will get comb filtering effects off axis vertically. Also cross over as low as possible. Another option is to put both woofers on the bottom. Your IB idea should work well, realize that the overall Qtc will be quite low, and therefore the bass will be on the thin side of things ;)

Should be a nice system, you don't have to worry about baffle step response, edge diffraction, etc. Good luck and let us know how it turns out.

RonS
 
Proac Futures

It's unfortunate that Proac chose to only use a dipole open baffle midrange, since it's in the bass region that the concept really shines, in reducing room/speaker interaction. I would imagine that the omnidirectional bass radiation coupled with the dipole midrange and line source forward radiating tweeter would make for a weird power response curve. Not my choice. I'd do something like the Linkwitz Phoenix or Orion. Peter's IB approach should make for a fine speaker as well, and get rid of many problems associated with box speakers. Of course it will do nothing for reducing room interactions, and he won't be able to move the speakers closer or wider for positioning :D

RonS
 
transducer said:
Keep the woofers as close as possible to each other, otherwise you will get comb filtering effects off axis vertically. Also cross over as low as possible. Another option is to put both woofers on the bottom.
RonS

Looking at Proac it seems very similar driver choice.;) They place the woofers at the bottom. Somehow I lean towards WTMW arrangement. What is better?
What do you mean by crossing as low as possible? I could cross mid-woofers at any frequency but ribbons can't go lower than 7-8k, they just blow when pushed too much (18dB slope).
 
Reminder

Hi Peter, your picture reminded me that I have not caught up with Pat for at least a year he is only about 10 miles away and has made some really good stuff.
I've heard the speakers that you mention and they really are very good.
Those boards are HEAVY, and the sound is solid and open and very nice depth and L/R imaging.
In a search I found these, http://www.enjoythemusic.com/ces2002/bonus/glackin.htm but have not seen or heard them, so cannot comment on these.

Eric.
 
cloning the future?

I still have vivid memories from listening to the mid model of the Future range late last year. Open baffle has always been an attractive concept and cloning these ProAcs may be very rewarding if you like electrostatic type of sound coupled with reasonable impedance and efficiency. The bass is a bit weak but integrates very nicely. E-speakers claim the ribbon tweeter to be ATD LeRibbon. Any idea what are the other drivers?

cheers

peter
 
open baffle with Manger?

The Manger Zeroboxes (www.manger-msw.de or www.espeaker.com) have side drivers to deal with the limited baffle size (any idea why these would be more affected than other speakers?).

Using a very large baffle might be a neat way to deal with the problem using only one of these pretty expensive drivers. I've been dreaming about putting one to the wall that would hang there like a picture. My girl-friend would no longer complain about monstrous tower speakers in the living room...

However, they seem to require a damped volume of about 15 liters (don't remember the exact number). So even if I try to get spread this volume over a large area, they'd still have to be 5-10 cm thick.

Eric
 
Actually, it should be measured from the centre of the woofer to the centre of the tweeter according to D'Appollito's work.

But you should read the info at this link: http://www.birotechnology.com/articles/VSTWLA.html for another look at this topic. Do the calculations and then you'll know how far apart you can space the woofers. I'd still put both woofers on the bottom.

RonS
 
I'm coming in late, so will comment on a couple things.

These aren't really open baffles, but infinite baffles (or at least a box=room that is large enuff to not care). With an XO at 200 Hz between mid & tweeter you don't have to worry much about comb-filtering. This dipole concept was to have an XO at 150 Hz and the wavelengths are long enuff that they essentially act as a single source.

You have midbasses that go way up for the bottom, and the triangle, if the same as the ones you mentioned before are essentially full-ranges so this gives you a lot of XO flexibility. I'd be playing with 100-300 Hz and wouldn't be afraid to try 1st order (RC in front of the amps). Let your ears tell you what works best.

With the wall as baffle you will have no baffle-step problems, but sometimes the wall can get in the way of really good imaging.

dave
 
Thanks Dave for your comments.

I think I found the link to WAR Audio in one of your posts actually.;) I was thinking recently about building a nice system in a basement ( maybe even home theatre), but somehow didn't want to use the drivers from my open baffle speakers because I was indeed concerned that with the wall I might loose some of the imaging. So seeing the open baffle design with Cabasse woofers and Raven came really handy, especially when I kept them in a storage for last 4 years. And Triangle woofer which is full range driver fills the gap between the other two drivers ( Raven 3 is out of reach considering its pricing). I also don't want to use anything over 3rd order slope on a tweeter and they really need 6th order if not to break when pushed (I changed ribbon on mine at least 3 times).

My main concern now is should I go with WTMW configuration (like WAR kit) or place the 2 woofers at the bottom. Something tells me that first option might be better after all.;)
 
Dave: Yes, this is IB, as I've said before. The comb filtering will not be between the mid and tweeter, but rather between the two woofers if they are placed in a WMTW configuration. The comb filtering will occure above and below the design axis, which most likely is the tweeter axis. Say at +/-45 degrees. This is a matter of physics, see the paper I refered to in an earlier post. The comb filtering will alter the power response, affecting the overall frequency response. Only way to avoid this is to cross over very low, and keep the two woofers close to each other.

Peter: It seems like you've got your mind made up even before you've asked the question, so why bother asking? I've refered you to sound physics information that shows the potential problems you will have, and pete maze has also recommended TMWW. Here is a piece of software which you can play with to show you what will happen in a WMTW situation. http://www.pvconsultants.com/audio/radiation/downloadarpe.htm I'm not saying it won't work, but be aware of the potential problems. Or don't bother asking and just do what you want.

As to the whole IB idea, I'd be tempted to do a proper dipole with correction for the bass cancellation of front and back waves. You'll get much less room interaction that way. I know you've seen Linkwitz' web site and think it's too much circuitry, but it's sound scientific stuff and works. I've built a dipole sub based on his work and can tell you that it is the most natural sounding bass that I've heard, ever.

RonS
 
Peter Daniel said:
My main concern now is should I go with WTMW configuration (like WAR kit) or place the 2 woofers at the bottom. Something tells me that first option might be better after all.;)

The WTMW (or WMTW) would be my 1st choice, but a mirror image square 4 (WW||MT) configuration also strikes me as a real possibility.

dave
 
transducer said:
The comb filtering will not be between the mid and tweeter, but rather between the two woofers if they are placed in a WMTW configuration.

Ron,

I understood this. I just figure that with an XO at 200 (i suspect Peter will find that a more optimal XO point will be lower, but i left it for him to play and discover what works best), a 1/4 wave allows c-c of about half a metre, and i figured that made it low enuff not to worry too much about it -- i could be wrong, maybe that is why the square-4 config kept poking at me.

The paper you mention is a very good one, i ran across it at least a couple years ago and a print-out is somewhere in my library. It really puts the question marks to MTMs with big spacing.

dave
 
Dave, yeah, that paper is really making me stop and think about MTMs, especially since I'm in the middle of designing one! There's no problem with comb filtering ON AXIS, it's the vertical off axis that proves to be a problem. I'm eager to see what happens with my design, but it will be some time before I know for sure. The question of how much this affects the overall power response is also raised, as this is only one part of the equation. Maybe the raged response in the vertical plane will prove to be somewhat acceptable, who knows.

The flip side is this, with a WMTW, what is the benefit of spacing the woofers as opposed to doing a WWMT?

Cheers,
RonS
 
transducer said:


Peter: It seems like you've got your mind made up even before you've asked the question, so why bother asking? I've refered you to sound physics information that shows the potential problems you will have, and pete maze has also recommended TMWW. Here is a piece of software which you can play with to show you what will happen in a WMTW situation. http://www.pvconsultants.com/audio/radiation/downloadarpe.htm I'm not saying it won't work, but be aware of the potential problems. Or don't bother asking and just do what you want.

As to the whole IB idea, I'd be tempted to do a proper dipole with correction for the bass cancellation of front and back waves. You'll get much less room interaction that way. I know you've seen Linkwitz' web site and think it's too much circuitry, but it's sound scientific stuff and works. I've built a dipole sub based on his work and can tell you that it is the most natural sounding bass that I've heard, ever.

RonS

If I had my mind made already I wouldn't bother asking for shure.;) It's just that I'm leaning towards certain type of design (proven BTW, if you see the first picture and read reviews, and check the track record of a designer). I was rather lookin for confirmation and was open for other suggestions as well, after all I'm not the expert.;)

As to correction for bass cancellation: is it really necessary if the speakers are located in a wall and front and back waves are separated? I guess you've seen my other open baffle speakers and even there I didn't use any correction and it is indeed the most natural bass I've heard going down to 25Hz.

Probably the best solution would be checking few different configurations sonically and then deciding, but I'd rather wouldn't like to go through all this trouble.