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Old 28th February 2010, 04:42 PM   #502
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Crazy is easy.......

Crazy + good sound; not so easy.

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Old 28th February 2010, 04:49 PM   #503
pol_bct is offline pol_bct  Reunion
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you're really quick on react!
already done a try to this one?

I have an ethic
I would not post a design who does not sound


Last edited by pol_bct; 28th February 2010 at 04:55 PM.
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Old 18th March 2010, 10:43 AM   #504
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Originally Posted by LineArray View Post
Hi Markus,

yes modal density increases faster with frequency,
due to c being frequency dependent.

This effect allows sufficient reproduction quality in
the range > 10 modes/ocatve and above as a rule of thumb.
Unfortunately this statement is wrong.

Modal density would increase even more with frequency if c
(propagation velocity of bending waves)
would be frequency independent.

I took over this opinion from a paper without having
thought about it sufficiently.
Oliver, RFZ believer (?)
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Old 9th June 2010, 01:07 PM   #505
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Hi guys!

I'm a new poster on this forum, but have done some extensive builds on a dutch forum: forum.zelfbouwaudio.nl • Toon onderwerp - Proof of concept (8x 2" Tangband) and forum.zelfbouwaudio.nl • Toon onderwerp - Jordan JX92s / CSS SDX7 ontwerp (for you, just watch the pretty pictures, as all is in Dutch )

Okay, so I'm a big fan of full range drivers and came across the "Podium Sound" speakers. I bought 7 pairs of Dayton Daex 25's and started testing (after first reading through to page 26 of this topic!).
I like the challenge and different style speakers.

It seems that I got a hold of some sort of "Gatorboard". It's a dence foam type core with 1mm of paper on the front and back. When you tap it, it sounds dry and solid. The board cannot easily be bent. The exciter was placed 1/3th of the hight of the board.

I've also done some measurements and see that with one exciter there is WAY to little highs. See the meaurement (red graph). One corrections have been made with a DSP the curve lookes like (green graph). Mind you: this measurement was done in the dead center, close proximity.

Do any of you use DSP? Do any of you do measurements? I would be very interested to see what kind of frequency response the large panels have.

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Old 9th June 2010, 09:49 PM   #506
jonners is offline jonners  United Kingdom
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Hi Mikesbmw.

Interest in this topic seems to have fizzled out here, but it is still happening on the open baffle forum at Audiocircle. The current fave is expanded polystyrene sheet in a high-density grade. Paper-backed foamcore board has serious shortcomings, as you have discovered.
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Old 12th June 2010, 03:31 AM   #507
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I saturated the paper of my foamcore with lacquer to harden it.
Improved, but still not hard like real Gatorboard... Which has an
almost veneer feel to the coverings. Gator paper shatters like a
thin layer of wood, if torn. Looks same at first glance, but made
of totally different stuff.

Last edited by kenpeter; 12th June 2010 at 03:34 AM.
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Old 12th June 2010, 08:13 AM   #508
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What was your listening impression, especially when comparing the
"pure" and the DSP version ?

Kind Regards
Oliver, RFZ believer (?)
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Old 12th June 2010, 01:32 PM   #509
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True, this core is softer. A collegue of mine pointed this out to me...


A totally different league!
Without DSP it sounded dull, lacking highs and voices sounded to much 'in your face'. Basically it would be okay for ambient sound, but not for everyday use. This is all easily seen in the first graph.

I'm definitely going to stick with DSP. All speakers I've build so far sounded better with it. True, you have to stick to the basic principles of speaker building or DML building, but that speaker or DML should always be assisted by DSP.

I for one, think that the 'Podium Speakers' could sound nice (haven't listened to them though), but they can and will sound better with DSP. I agree with Katz that you shouldn't use crossovers! Crossovers suck, even the digital ones. (if they are necessary try to cross as low as possible)

DSP has and will remain my holy grail

To bad I can't find what Gatorboard is called in the Netherlands...

Last edited by mikesbmw; 12th June 2010 at 01:54 PM.
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Old 12th June 2010, 03:09 PM   #510
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In the "Loudspeaker and room as a system" thread we had also
a discussion on DSP.

For the low frequency range below the schröder frequency of the room
DSP can be used to compensate for room modes but will be restricted
for optimizing the transfer function for a certain listening position.

A compromise can be found when averaging over more than one
listening position.

With DML you have strong deviations in the fine structure of the transfer
function even when the angle is only changed by small amounts.

The "ruler flat" result with DSP can - even for mid to high frequencies -
only be achieved for a certain listening position. The deviations of the
transfer function at small changes of angle are typical for DML and go
together with their virtues of radiating in an uncorrelated manner
especially in the off axis directions.

So i doubt that - given a DML which is somewhat more tamed and maturated
than your prototype - compensating the fine structure of the transfer function
above the schröder frequency of the room will really help that much.

The listener not being nailed to a sweet spot is one of the DML virtues,
but the fine structure can only be compensated for one listening position,
possibly making things worse for other positions.

Don't get me wrong: I am interested in DSP too. But currently i think
maybe a compromise is to be found:

For a conventional or DM- Loudspeaker operating below the schröder
frequency a DSP can be used to flatten the response over a couple
of preferred listening positions.

In the non modal range above the schröder frequency of the room, i guess
best for a DML is a smoothed compensation of the overall radiated power
into the room.

But this tends to be rather flat with a matured DML anyhow, because the
frequency dependent beaming does not occur like with a conventional

Kind Regards
Oliver, RFZ believer (?)
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