Open baffle drivers configuration: time to ask the experts

[Peter Daniel]

Like 80 Hz or lower? Those Cabasse units are almost flat up to 2K.

[Pete Mazz]

You should keep the xover point less than the wavelength of your ctc distance. If, say 20" ctc, then 13560/20=678 Hz. This will reduce comb filter effects in their passband.

I think you'd be better off trying a TMWW, also.

Pete

[transducer]

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

[planet10]

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

[Peter Daniel]

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.

[transducer]

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/r...wnloadarpe.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

[planet10]

Originally posted by Peter Daniel
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

[planet10]

Originally posted by transducer
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

[transducer]

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

[Peter Daniel]

Originally posted by transducer


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/r...wnloadarpe.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.