I know. But as I mentioned before I didn't want to risk to damage my xps panels by removing the exciters as I cannot buy new ones right now. Therefore it's not a fair comparison, I'm very aware of that fact.
Both plywood panels do have frames and a spline right now - for damping I use 6mm window insulation foam. I've used 7x50mm strips - 5 of them on the long side and 3 on the short side of the panel. I noticed how easily a panel gets overdamped and thus loosing all the magic. This worked out quite well.
The XPS panels are without a frame as they immediately change their characteristics when I frame them. But I'm sure this can be improved.
The wood panels are both 4mm.
We also don't have this exact product here in middle europe. But I'm sure if you search for "hollow chamber plate polypropylen" you will find alternatives. I'm really curious to try those.
I want to add another patent, in my opinion it is the most informative and voluminous:US7916878B2 - Acoustic device and method of making acoustic device
- Google Patents
- Google Patents
To clarify, I think a panel should be designed to be modal above the room's Schroeder transition frequency range.
Distributed Mode Panel: frequencies above Schroeder.
Bending Wave Infinite Panel: frequencies below Schroeder.
In small rooms, there's no advantage in trying to combine the two conflicting methods into a single speaker. But there is an advantage is separating a DML source from a bending wave source.
I am confused by burncoils response. Could someone provide a succinct definition of a BMR and a DML? Define differences?
I have seen many DMLs driven by frame mounted exciters and many with suspension methods (AER for example). Is it a matter of size of the panel relative to the drive linear motor( voice coil or moving magnet)? Is it a matter of how the wave propagate through the panel that defines a DML?
For that matter is the dynamic speaker KEF B-139 a BMR( co cone, solid styrofoam planar piston)?
I think we could use good definitions here.
Thanks
I have seen many DMLs driven by frame mounted exciters and many with suspension methods (AER for example). Is it a matter of size of the panel relative to the drive linear motor( voice coil or moving magnet)? Is it a matter of how the wave propagate through the panel that defines a DML?
For that matter is the dynamic speaker KEF B-139 a BMR( co cone, solid styrofoam planar piston)?
I think we could use good definitions here.
Thanks
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From the patent
Does anyone know where the low frequency problem happens, what frequency range do DMLs start struggling?
Yes, it is about how the wave moves through the panel.
DML = vibrating surface with many reflections/modes.
Bending Wave = vibrating surface without reflections/modes.
BMR = a surface that vibrates and moves forward and backward like a piston; DML + traditional speaker combination.
Can someone describe the physical differences that produce these effects? Seems as though most of this thread is based on DML examples?
Thanks!
BMR is a term coined by NXT/T.E. They basically converted a DML into a BMR as its just based on design with a few modifications to the exciter.
DML exciters have strong plastic adhered to the voice coil so it can hold up the panels weight as well as the exciters own magnet weight. With BMR's since most don't go over 3 inches with a diaphragm less then 1mm thick the BMR's voice coil is very thin and not as strong or heavy as the plastic voice coil on the exciters used for DML. Because BMR's voice coil is lighter and the diaphragm material is very ligh the voice coil should have more excursion (due to being more efficient) with higher pistonic motion aka Xmax.
Certain high power high excursion exciters used for DML can reach around 2-4mm of Xmax but need more power or boost to do so then a BMR due to being less efficient in pistonic motion.
One can even turn a exciter into a BMR and vice versa as they are that similar and based on design.
DML exciters have strong plastic adhered to the voice coil so it can hold up the panels weight as well as the exciters own magnet weight. With BMR's since most don't go over 3 inches with a diaphragm less then 1mm thick the BMR's voice coil is very thin and not as strong or heavy as the plastic voice coil on the exciters used for DML. Because BMR's voice coil is lighter and the diaphragm material is very ligh the voice coil should have more excursion (due to being more efficient) with higher pistonic motion aka Xmax.
Certain high power high excursion exciters used for DML can reach around 2-4mm of Xmax but need more power or boost to do so then a BMR due to being less efficient in pistonic motion.
One can even turn a exciter into a BMR and vice versa as they are that similar and based on design.
Basically a bmr is designed to go in a box and i have seen it in a rear firing horn , only the front radiation is used , similar to a cone type unit (I haven't read the patent) so at some point there is a transition between a dml into a piston mode type radiator,and obviously for a period will be radiating both dml and piston type motions at the same time.
It is designed to be pretty much full range down to 60hz or so in one driver.
Steve
It is designed to be pretty much full range down to 60hz or so in one driver.
Steve
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In the Loudspeaker and Headphone Handbook, Graham Banks writes that
For a typical panel whose lowest mode is set at f0, then useful output is available from 2.5 x f0...
And f0 can be calculated using FEA, or estimated from:
f0 = (PI/A)*(B/m)^1/2
where f0 is the lowest natural frequency of panel, A is the panel area, B is the panel bending stiffness and m is the "area density" in Kg/m2.
Eric
From experience I have found , depending on the type of panel and room response dml can start to struggle at about 300hz or so ,this is why I usually run my cone type LF drivers to cover this area.
Steve
BMR's are nothing new as they have been used in many big name brand speakers like Sony's APM line of speakers, Technics SB series, Akai and many other brands.
The reason why BMR's are small (under 4") is because if they were to make them any larger the high frequencies would suffer which would make them no longer full range. Sony knew this so they designed each BMR driver for a certain frequency by making it a 2-3 way with a 1-2inch BMR tweeter, 3-4inch BMR midrange and 6-10inch BMR woofer.
One could also build a 2-3 way DML panel stacking panels on top of each other with each panel having there own frequency response to prevent comb filtering. Yes even DML's have comb filtering but since the sound is more diffused the comb filtering is not at prominent as conventional cone speakers but its there.
The reason why BMR's are small (under 4") is because if they were to make them any larger the high frequencies would suffer which would make them no longer full range. Sony knew this so they designed each BMR driver for a certain frequency by making it a 2-3 way with a 1-2inch BMR tweeter, 3-4inch BMR midrange and 6-10inch BMR woofer.
One could also build a 2-3 way DML panel stacking panels on top of each other with each panel having there own frequency response to prevent comb filtering. Yes even DML's have comb filtering but since the sound is more diffused the comb filtering is not at prominent as conventional cone speakers but its there.
Thanks. That chapter and book is a good source of information. And that equation gives me an idea of which direction to head.
In that case, it's good news because that's around where small rooms run into the Schroeder range. There's no benefit in trying to improve the DML's low frequency performance.
With full range DML panels most people boost the bass which in turn will make the frequency response uneven and cause other sorts of problems.
Enter the DML sub. A DML sub is a DML panel specifically for low frequencies only and used with a Sub amp powerful enough to drive the exciter into pistonic motion. Combined that with adjustable sub cross over you can blend them to your main DML panels and use them like Satellite DML panels for the higher frequencies. I have used this combo for the past 3 years or so and it works great.
A DML sub wont slam like a conventional cone driver or play as low mostly because exciters are limited and made for full range duty. I wish they would make specific exciters that could be used for sub duty by making them more powerful and able to handle at least 100 watts rms.
On the other hand a DML sub blends the best with a DML panel because its like a open baffle subwoofer but with a flat diaphragm. I've tried 5 different conventional cone boxed subs and none of them can beat the DML sub in terms of blending with DML panels. A DML sub also sounds more articulate and life like then a conventional cone boxed sub in which they appear to disappear just like with most Open baffle subs/speakers.
Enter the DML sub. A DML sub is a DML panel specifically for low frequencies only and used with a Sub amp powerful enough to drive the exciter into pistonic motion. Combined that with adjustable sub cross over you can blend them to your main DML panels and use them like Satellite DML panels for the higher frequencies. I have used this combo for the past 3 years or so and it works great.
A DML sub wont slam like a conventional cone driver or play as low mostly because exciters are limited and made for full range duty. I wish they would make specific exciters that could be used for sub duty by making them more powerful and able to handle at least 100 watts rms.
On the other hand a DML sub blends the best with a DML panel because its like a open baffle subwoofer but with a flat diaphragm. I've tried 5 different conventional cone boxed subs and none of them can beat the DML sub in terms of blending with DML panels. A DML sub also sounds more articulate and life like then a conventional cone boxed sub in which they appear to disappear just like with most Open baffle subs/speakers.
Perhaps not 100W RMS, but have you tried any of these yet?
https://www.digikey.com/en/product-highlight/p/pui-audio/subwoofer-exciters
And not sure if they will go into pistonic mode either?