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A Study of DML's as a Full Range Speaker
A Study of DML's as a Full Range Speaker
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Old 8th April 2020, 08:02 PM   #1721
bradleypnw is offline bradleypnw
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Join Date: May 2019
Quote:
Originally Posted by gapmedia View Post
Hi bradleypnw. Are you using REW for the above? I'm not (that) familiar with HolmeImpulse if you're using that, as 'dbjohns' mentioned. I tend to use REW for measurements, DRCDesigner to play with DSP/DRC, and then playback through JRver to test measurements and implement any DSP/DRC. Not saying these are the best software to use, just don't cost that much (some free) and work well for me.

I have started to look into room diffusers and bass traps, but these really have a low WAF. But in the end, would probably, in terms of performance increase be worth the grief.
I use REW for equalization. If you build a DML you probably won't need room diffusers because DMLs solve room reflections above the Schroeder transition frequency due to the type of soundfield they generate.
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Old 8th April 2020, 11:55 PM   #1722
spedge is offline spedge  United Kingdom
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Originally Posted by bradleypnw View Post
I use REW for equalization. If you build a DML you probably won't need room diffusers because DMLs solve room reflections above the Schroeder transition frequency due to the type of soundfield they generate.
I'm glad you used the word probably,all panels that I know of ,use a primary drive area to drive the dml mode ,my exciters have a 1inch voice coil plus the foot mounting ,and the coil drives the area outside the coil to some extent ,I have not measured this but at a guess depending on materials ,the drive area could be about 2inches ,this can easily be measured by moving a microphone across the panel .
So basically you have a 2inch full range driver in the middle (or whatever you put it) of your panel,this is a pulsed direct radiator,not dml,the dml comes after.
I have mentioned this over the years ,but it seems to be ignored for some reason?
There is also the problem with the tin can effect,but i will not go into that now.

If like me you have a narrow room , reflections will sometimes give a false impression of a harshness in say the vocals,in the past I have spent ages trying to cure a problem I never had,it was only after playing the offending piece of music over and over again while playing around with the panel,that I realized it disappeared when i was up close to the panel,now when I hear what can be a painful noise ,I just turn my head to one side so that my ears are not receiving the full blast from the walls and ceiling and hey presto it is gone.
A panel can never (unless someone can show otherwise) be 100% dml, how much dml and how much postonic(oh no not again) depends on material (flexibility).
I think that's enough for now,just thought I'd mention this.
Steve

Last edited by spedge; 8th April 2020 at 11:57 PM.
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Old Yesterday, 08:46 PM   #1723
bradleypnw is offline bradleypnw
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Join Date: May 2019
I modified my plastic honeycomb polyester skin panels to see what would happen.

1) one side resin other side original polyester fabric
2) both sides resin
3) Number 2 plus exciter side cut with hacksaw between exciters to form alternating trapezoid shaped surfaces for each exciter - simple angled cuts with the hacksaw. (see image)
4) Number 3 plus holes punched into resin side opposite exciters (see image)

They all sounded bad without DSP equalization. Number 2-4 required more high frequency reduction at a large bandwidth than the Number 1.

My subjective perception was number 1 and 4 sounded the best. I'm thinking that a single modal radiating surface is better than two. Which might be a reason to ditch foam.

I'm going to build a new set. I'll use the same plastic honeycomb polyester skinned material. I'm going to use carbon fiber on the active side. I will probably cut the active side like Number 3. I will not punch holes in the polyester fabric side. Which is too bad because the polyester is ugly and difficult to dye.

Honestly, I don't know if I'm imagining things or not between one hard modal surface vs two. I'd describe the difference in sound as "closed" with two surfaces and "open" with one surface. It's such a subjective observation that I'm embarrassed to say it. I notice it most clearly on piano solo music. The single surface sounds more like a real piano.
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Old Yesterday, 09:07 PM   #1724
tagis is offline tagis  United States
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Hi Dave,
How is the honeycomb CF coming along I saw your last result wich was kind of a bummer but Like you say it a learning curve point. Here is a bit of some information that may be enlightening to the group. I cant up load it exceeds the limit of the file space I will see if I can break it into smaller pieces Structure-Borne Sound
Cheers,
Steve
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Old Yesterday, 09:26 PM   #1725
tagis is offline tagis  United States
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Here is the link to the chapter on Structure-Borne Sound Sci-Hub | Structure-Borne Sound. Foundations of Engineering Acoustics, 270?314 | 10.1016/B978-012247665-5/50011-4
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Old Today, 02:57 AM   #1726
Veleric is offline Veleric  United States
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Quote:
Originally Posted by tagis View Post
great link tagis. Thanks.

Dave, see the second full paragraph on page 273 of tagis link. That's what I was trying to explain in my PM:

Over much of the audio-frequency range, bending waves in thin plates and shells have the lowest mechanical impedance of the structure-borne wave family; they therefore tend to be most strongly excited by vibrational forces. Per unit of energy density, they also impose the largest normal displacements on contiguous fluids. For these two reasons, acoustic interaction between fluids and structures tends to be dominated by flexural waves.

in the context of a DML speaker, the fluid is air and the structure is the plate.

For clarification of the difference between transverse flexural (i.e. bending) waves and transverse shear waves, see sections 10.6 and 10.7 respectively.

Eric
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Old Today, 03:15 AM   #1727
davelang is offline davelang  United States
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A Study of DML's as a Full Range Speaker
Awesome, thanks.
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Old Today, 03:32 AM   #1728
Veleric is offline Veleric  United States
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Quote:
Originally Posted by bradleypnw View Post
I'm going to build a new set. I'll use the same plastic honeycomb polyester skinned material. I'm going to use carbon fiber on the active side.
Do you have enough of the core to try carbon fiber or fiberglass on both sides?
How thick is your carbon cloth?
When I finally get my pp honeycomb (back ordered, drat), I'm planning to try one or both of the above. My CF is 3K that finishes out to about 9 mils which I think is way too stiff with that core. But thinner FG is cheap and easy to get so that may be a better choice.
I know what you mean about having two radiating surfaces possibly not being ideal. But my thinking is that it's probably fine if both surfaces are actually doing the same thing. Seems to me the problem would come in if they are not.
Eric
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Old Today, 06:27 AM   #1729
bradleypnw is offline bradleypnw
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Quote:
Originally Posted by Veleric View Post
Do you have enough of the core to try carbon fiber or fiberglass on both sides?
How thick is your carbon cloth?
When I finally get my pp honeycomb (back ordered, drat), I'm planning to try one or both of the above. My CF is 3K that finishes out to about 9 mils which I think is way too stiff with that core. But thinner FG is cheap and easy to get so that may be a better choice.
I know what you mean about having two radiating surfaces possibly not being ideal. But my thinking is that it's probably fine if both surfaces are actually doing the same thing. Seems to me the problem would come in if they are not.
Eric
I don't know. And I don't know how to measure what I perceive as better sound. I hope people try different things and give their feedback so I can see if I'm imagining something that isn't there.

At this point I think I'm biased in one direction and can't give objective feedback. Also, a traditional rectangle DML similar to Tectonic might sound better with both sides covered in CF.
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