d'Appolito configuration

[planet10]

By push-push you mean that drivers are connected in phase and move in opposite direction so the enclosure is more pressurised?

I guess so... i would phrase that last bit as move in the same direction wrt the inside of the box. They act as one driver, but are physically oriented to cancel the majority of the "equal and opposite reaction"

I am actually thinking about mounting drivers in the wall, using the room on the other side as enclosure. Is there a way to use that bi-pole setup in this case?

You are talking here about an infinite baffle, hard to make that a bi-pole, but you can take advantage of push-push for the bass.

dave

 

[Peter Daniel]

You are talking here about an infinite baffle, hard to make that a bi-pole, but you can take advantage of push-push for the bass.

dave

It is an infinite baffle indeed and that's what I'm after. The question is what's bigger advantage: avoiding box coloration in an open baffle or using p-p setup for increased dynamics and distortion cancellation?

 

[planet10]

It is an infinite baffle indeed and that's what I'm after. The question is what's bigger advantage: avoiding box coloration in an open baffle or using p-p setup for increased dynamics and distortion cancellation?

I guess you could mount an identical driver in the "box/room" in an open frame to act as a force canceller, then connect or not connect it to see how much improvement it makes. Given a secure connection to the mass of the house, and a secure mechanical connection of that mass to the back of the magnet as well as the frame at least some of the benefit of push-push could be achieved.

dave

 

[taufern]

dave i think peter was trying to ask a tradeoff question more along the lines of "is it more advantageous to go the push push route to avoid newtonian forces coloring the sound or to go the dipole route to avoid box coloration...at least that was my impression...i dont know the benefits of push push dipoles, if there are any...i feel that the whole idea of a dipole is to use the back wave to reduce reverberant (did i spell that right??? who cares) sound waves and receive more of the direct wave...with the push push type it would seem to defeat this purpose by counteracting the rear wave and adding to it an in phase wave that would lead me to think about things like time smear...plus the impedance would seem to sky rocket as the woofers/mids both being dipole and push push...just my two cents but thats the way i see it

 

[planet10]

i think peter was trying to ask a tradeoff question more along the lines of "is it more advantageous to go the push push route to avoid newtonian forces coloring the sound or to go the dipole route to avoid box coloration...

That is a good question...

dave

 

[taufern]

peter, just a thought but have you ever given any consideration towards an infinite box (not baffle)??? it will take a little more work in the x-over section but im sure youre pretty comfortable with active filters and should be able to eq it...somewhere along the lines of 5-10 times the Vas...I've had great results mounting the peerless 7" HDS driver in such sort of an arrangement...you just have to be able to completely kill the back radiated wave...the box coloration can be avoided and the problems surrounding dipole design could be thrown out the window as well...so you have an uncolored driver that can go as low as a vented box with no time smear since the front wave will be the only one listened to...you could probably go as big as a 8" driver without the box becoming too big of an eyesore...just make sure to have no parallel walls and ever increasing density of the stuffing...maybe you'll find something you really like...

 

[planet10]

just a thought but have you ever given any consideration towards an infinite box (not baffle)???

If his plan is to use the room next door as the box this is essentially what he is doing.

Thot quite a bit about doing that with mt ESLs but alas the call of some iron sent them to california.

dave

 

[Peter Daniel]

I want to use the wall dividing two rooms as a baffle and one room as enclosure. I have 2 midbass drivers that I have to use together in parallel (because they are 12 ohms ea.), but started to have doubts about advantages of MTM config after listening to some simple TM systems. So one other option would be using two drivers in push-pull or push-push setup to somehow improve single driver performance. But doing this requires sort of enclosure, so my next concern was is it advantageous comparing to open baffle (infinite baffle)?

I was thinking about mounting both drivers in a 6" pipe, magnets together, and spaced closely, firing in push-pull config, but have no idea if it's good or not?😉

Those drivers can operate up to 10k, so tweeter basically would cover everything above. Since it's Raven 2, the spacing between midbass units would be more than usually, and that's another reason against MTM. I'm planing on not using crossover in midranges and a ingle cap only in a tweeter, or going active.

 

[SY]

Many years ago, I played with some wall-mounted drivers with the next room being the "enclosure." The big advantage was that there was no spreading loss from the baffle; I didn't really need all that volume, I just wanted to get a true 2pi loading. It's tricky to avoid cavity resonances from the interior of the wall. And on the woof end, you need drivers with high Qts- I used Dynaudio 17Ws.

All in all, it was not a great success. I got it to work by carefully shaping some plaster and mesh to line the holes in the wall. But the system didn't really give me anything that my box speakers didn't (when my xover was designed to get rid of spreading loss), there was clearly no placement flexibility, I couldn't use that wall for anything else, and I had to patch those damn holes when I moved.

I didn't try this with a big woofer, and the nightmare of acoustically isolating that backwave and rigidizing that entire wall makes me grateful that I wasn't feeling too ambitious! I explained Dave's idea of doing this with ESL panels to my wife. She explained the idea of a divorce lawyer to me.

 

[kimbo]

D'Appolito and active crossovers

Hi All,

I know that this thread has wandered a little from it's original topic, but I'm pretty new to speaker design and I'm wondering if any of you can straighten me out with regards to the MTM or D'Appolito configuration.

I'm about to make a start on a pair of tall two way bass reflex boxes with a pair of 8 inch drivers and a single tweeter in each box. The D'Appolito configuration appeals to me, mainly as I can see that to a listener sitting close to the horizontal plane of the tweeter, the sound of both the bass and the higher frequencies would appear to be coming from the same point. I understand that if the drivers are too far apart, and if the crossover is not of a high order, then when your head (still attached to it's body I hope) moves off axis vertically, there will be pronounced lobing or uneven freq response. I have seen some software that provides a figure for the driver spacing, however it is not clear if this is an absolute value or a recommended maximum value.

My thinking is that the closer the drivers are the better, as this will minimise this effect. Yes?

Also, as noted in an earlier post, D'Appolito uses 3rd order (or higher) crossovers. Is this just to minimise the width of the frequency band that would show this effect?

I am considering using a couple of stereo amps and an active crossover that uses paired Linkwitz-Riley filter stages providing 24dB/Octave slopes, ( in particular the "Silicon Chip" crossover from the Jan 2003 issue http://www.siliconchip.com.au/cms/A_30278/article.html . ) Does anyone have any thoughts about this approach?

Any comments are greatly appreciated.

Kim