Question about d'appolito configuration

[Leeuwarden]

Hello everyone!

I have an Alcone AC8 HE woofer together with a Dynaudio D-260 Esotec tweeter in the cabinet of an Alcone Fourier design.
(see www.rcmakustik.com or www.lautsprechershop.de))

As far as I know a M-T-M configuration is the best way to create the best holografic image de tweeter can give wich is important to me.

I've got the following questions:

The AC-8 HE needs (in the Fourier) a volume of 75 liters. What happens to the volume if I add a second AC-8 HE? Do I have t increase the volume? (150 liters???)

How do you active filter a d'Appolito system?

Does the tweeter needs to be in a sealed enclosure within the cabinet?

Are there any site's wich can tell me more about d'Appolito configurations?

Are there any other things I need to know but might have overlooked? ( )

Thanks!

Greetings from the Netherlands
Jan

[Pan]

MTM layout is not automatically the best way to good 3-d.
The best soundstaging I have heard have been on "point sources" or TM layouts.

And yes, you would need the double volume for two bassdrivers.

The tweeter has its own sealed chamber so no need for a "sub-enclosure" within the cabinet.

As for active x-ing, every speakers needs a specific designed crossing so it is hard to give you a short answer to that q.

Good luck :-)

/Peter

[SY]

What MTM will get you is a polar pattern which is symmetrical about the tweeter axis. The vertical dispersion will also be narrower than with a "normal" TM or MT. Whether or not that's a good thing is very dependent on the overall design; I've heard great imaging MTMs and coventional speakers both, I've also heard lousy imaging from MTMs and conventional arrangements- MTM is just one design choice amidst many others.

FWIW, MTM is what I'm using in my current speakers. But there's nothing magic about it- my speakers sound good (to me, at least) because I paid attention to a lot of design details.

[Pan]

Agree with SY.

My current set up is also MTM, will put it aside any day for another high priority project.

What most people tend to forget about MTM´s is that what happens around the x-over point is one thing, and what happens in the lower mids, (vertically off axis) is another.

Often people mention the uneven power response/verticall off axis response as something very good, I´m not so sure about that. As SY said, obviously it can be made to sound very good and function just fine, however for my own systems I tend to "believe" more and more in either point source or line source solutions.

IMO, even if I tend to sit down in the sweet spot mostly when listening, I feel the difference in sound when standing up is to much from an MTM.

The lobing from the x-over at 2k-3k is not nearly as noticable IMO as compared to what happens between the two mids in an MTM.

/Peter

[jimbo149]

I'm new to this forum but not to DIY speaker building. I subscribed to SB from '82 till '97 and have built quite a few projects over the years. Not bragging, just introducing.
When the D'App MTM's parameters and properties were first published in the mid eighties, their stated chief advantage was a relatively stable vertical polar response, both at XO and at XO +1octave. The pattern is STABLE, but not very flat. It varies by plus and minus 3dB at various vertical angles, but with NO 'lobing'. It is back to zero on axis. The advantage to this pattern is the realtive insensitivity to listening position, i.e. no really strong 'sweet spot'. I tend to prefer arrangements other than MTM for critical listening but think MTM is ideal for HT. Other configurations have 'flatter' vertical polar responses, albeit with some lobing farther off of the vertical axis. These arrangement are better for soundstaging and imaging but have a definite sweet spot. The M-T with third order is such an arrangement. It is virtually flat in vertical polar response from about 20 degreees above axis to about 45 degrees below. There is a big, sharp lobe on top but who listens at a position above their speakers, anyway? See the SB back issues with the articles by Bullock on XO's for more details.

Jimbo

[apassgear]

Agree with most have to say about MTM.

In the 80 I built the original D'Appolito and tested every XO possibility but didn't like it , though I know that today there are better implementations, so, no way Jose I would go again through that road.

I preffer full range speakes for 3D.