A Study of DMLs as a Full Range Speaker

[toddincabo]

Sure we can all hear the difference between two very different speakers, but when taking about things like plate dimensions, exciter placement, material choice, etc, the differences when tweaking is much smaller than the ability we have to alter our subjective impression of sound.

I'm not saying that you should rely completly on graphs, and especially blind listening tests are very valuable, but it is a lot of work and impractical to guide a design all the way.

I agree, testing and graphs are valuable. Chasing the flat line is not a folly, it's just simply a choice. Nothing wrong with that if that's someone's thing, that's a lifetime of hobby right there. I hope they hit the magic combo and share it because I will definitely try to reproduce it and thank them for it if it's pleasing.

I just don't like when certain folks believe their method is the end all and people who don't subscribe to it are inferior or whatever.

 

[xsuper9988]

I think that's exactly what I said.

See, anybody can spend a few weeks to knock together a tin can onto an old apple crate and then try really really hard to convince themselves that it "sounds good to them", and bugger anyone else.
That's great! We need more people like that.

Hi Andre

I'm just testing with an "old apple box" right now
Like I said before the sound is a bit extreme
Then I use "Corrected Microphone" + "DSP EQ" + "DSP Crossover" + "White Noise" to do frequency adjustment
In the end I found that it doesn't sound good when the frequency is even and flat
I refer to the curve of the "headphone" to make adjustments and the effect has improved a lot
If it's a tweaked "old apple box" it sounds good

Then I want to ask everyone
Is the material of the old apple box "EPS"???
Sounds really loud if it's EPS
Later I also want to test "PC hollow board"
The material seems to be loud too?

I can't understand what is the situation that the "Passive Crossover" destroys the DML???
I use the "DSP Frequency Crossover" to make adjustments, and there is no sense of unsmooth listening
I'm using two-way
I want to test the three-tone road these days
I feel like each speaker is responsible for less bandwidth
Does this seem to improve the resolution?
I'm not sure but I'll test it out

In the end, I want to conclude that both "microphone" and "ear" are indispensable
I also tried making adjustments without using the microphone
The difference is that the number of adjustments needs to be more
Of course, if you have a microphone, you can also use software to measure it. It is an additional auxiliary tool.
In the end, I want to say that the most important thing about playing audio is to make yourself happy

 

[xsuper9988]

@Leob thank you that’s a good tip for the high pass being at 7khz+

When I do use the crossover it does sound good to my ears though. Which has added impetus for further discovery in that area.

The comparison being three separate panels that get no crossover filtering, or a single panel.

It seems quite common for hifi DML setups to have multiple panels, which help cover each others peaks and troughs on the spl graph, but uncommon to split the panels for frequency band responsibility.

Question to the group:
If you were going to this (in a universe where you too wanted to see the experimental outcome) what kind of crossover would you choose to go with?

1. Butterworth
2. Linkwitz-Riley
3. Bessel
4. Combination of above
5. Achieve the outcome via another method, which is…

Hi Jamienelson

The forum mentions that "passive crossover" can break DML
I have no test or experience with this
But I think you can try to test with DSP first
After the test is completed, use the DSP results to make a "passive frequency crossover"
This may be a faster way

 

[Audiofrenzy]

@Leob thank you that’s a good tip for the high pass being at 7khz+

When I do use the crossover it does sound good to my ears though. Which has added impetus for further discovery in that area.

The comparison being three separate panels that get no crossover filtering, or a single panel.

It seems quite common for hifi DML setups to have multiple panels, which help cover each others peaks and troughs on the spl graph, but uncommon to split the panels for frequency band responsibility.

Question to the group:
If you were going to this (in a universe where you too wanted to see the experimental outcome) what kind of crossover would you choose to go with?

1. Butterworth
2. Linkwitz-Riley
3. Bessel
4. Combination of above
5. Achieve the outcome via another method, which is…

The question should be who here has used crossovers in there DML designs.

I've used 2nd order linkwitz and Butterworth. The Butterworth sounds better but the best is from using just a single (1st order) cap for high pass and a single inductor for low pass as this will have the least amount of filtering including other issues.

I also suggest instead of using electrolytic caps and iron core inductors its better to use metalized poly caps and Air core inductors as they actually sound better.

 

[xsuper9988]

I want to test the three-tone road these days
I feel like each speaker is responsible for less bandwidth
Does this seem to improve the resolution?
I'm not sure but I'll test it out

I used "Google Translate" and didn't pay attention to it
I correct the text
"I want to test the three-tone road these days" >>> "Recently I will be testing three-way"

The three-way I said refers to "DML two-way" + "<80Hz Subwoofer"

 

[xsuper9988]

The three-way I said refers to "DML two-way" + "<80Hz Subwoofer"

Human voice is rarely below 80Hz
I think the subwoofer frequency is too high
It can cause the human voice to sound less clear
The above refers to the sealed box
If you use an OB subwoofer, there should be no problem
But the pressure on the OB subwoofer doesn't seem to be enough???
I think it sounds empty, no space
This is purely my opinion
I will test and see the OB class subwoofer later
Those who have tested the OB subwoofer can share their feelings

 

[spedge]

All my DML panels built using only my ears , no measurements involved.

Once again, a very nice sounding recording, the rug makes all the difference 😀
This is a very familiar sound to me, very close to my EPS panels.
I enjoyed listening to this recording.
Steve.

 

[Eucyblues99]

This seems to be a constant issue of contention especially in the HiFi and DIY audio community, and I should stay out of it and focus on DML speakers instead...
But I think no one is saying that it doesn't matter if something sounds good to you. In the end that is the end goal for everyone, an amazing audio experience, not seeing a flat line or a really nice RT60 waterfall.

But even if we have the same goal, a good listening experience, it doesn't mean that listening tests is the best way to guide a design. I think you need both, but I am in the "measurement trumps subjective listening experiences" camp, and the reason is that have learned how subjective our hearing is through the years working with audio in different ways (producing, mastering, sound reinforcement, sound design, etc). I don't trust that anyone, myself included, can accurately assess audio quality without a proper procedure to ensure no subjective bias. I just seen so many times people claming to hear differences that they fail to identify in blind tests.
It is not an attack on anyone or accusing them of being incapable to hear things. Sure we can all hear the difference between two very different speakers, but when taking about things like plate dimensions, exciter placement, material choice, etc, the differences when tweaking is much smaller than the ability we have to alter our subjective impression of sound.

Another issue with doing subjective judgements is that how the speaker sounds will vary a lot on source material. For example I find that a free hanging plate can add a chorus like effect that sounds amazing on some material, and just makes other songs blurry and undefined. Or an uneven frequency response can highlight interesting parts in some tracks. To get an accurate picture when making a change you need to test every change on a lot of material, which just becomes unfeasible. Even if you did take the time, your ears would fatigue before you can reach any conclusion.

I'm not saying that you should rely completly on graphs, and especially blind listening tests are very valuable, but it is a lot of work and impractical to guide a design all the way. Instead you both measure and listen and learn to correlate measurements with how it sounds, and eventually you will find that addressing eventual peaks or throughs in the graph or reducing phase/delay issues will make things sound better, and is a lot more efficient to guide your design than trying to iterate through listening tests. Not only does blind listening tests take time to perform, but without being able to correlate the listening experience to measurements it is usually harder to know exactly what the problem you are hearing is, which makes it slower to fix.

Just some friendly advice...my intention is only to help trying to avoid traps that I have myself fallen in to before, and not to put anyone down. If you prefer working with listening tests, and think chasing a flat line through measurements is folly, that is fine with me.

A sensible balance of measurement and listening is quite sensible quoteth I
Eucy the sage 😜

 

[jamienelson]

Hi All,
I'm back after the weekend and have been testing some new changes to panels after reading a paper on 'resonance phenomena in acoustic wood boards'.
As per my other posts my current short term goal is finding a way to make a dml tweeter, and near the start of that article i read that they had noticed that that the resonant frequency of the board moves to a higher frequency on their perforated test board.

So i read on.

In addition, it was determined that the mode shape of perforated lightweight boards remained virtually unchanged.

well that's positive...

It was determined that when boards undergo perforation, the vibrational amplitude decreases by up to 1.5-2.6 times on average and there is no significant change in the first vibrational mode of boards. The frequency range of boards tends to become wider. It was determined that, in general, separate frequency ranges change in different ways. After the perforation of boards, there is a decrease in the value of the first resonant frequency, whereas the one of higher resonant frequencies tends to increase.
There is a noticeable change in the coefficient of damping of boards, which reaches up 20-100%.

This is what I am after I thought, and went and made up a series of tests...

I don't know if any of you have tried this before, but the results are very repeatable.

Here is an example of the difference it makes:
In the image below looking at the results over 3khz, you will see a large improvement in higher-frequency amplitudes, AND in its smoothness. The many ups and downs that you see in the red graph shrink to almost nothing in the green graph.

And the same with Popcicle sticks (which are the best tweeters i have found yet)

0 holes vs 4 holes:

0 holes vs 7 holes:

0 holes vs 23 holes:

0 holes vs 24 holes that are 2x larger.

I further experimented on another small piece of basswood cut in a triarm shape (whatever that shape is called, i label it triarm here)
This is the 'before'.

0 vs 4 perforations per arm.

0 vs 6 perforations per arm:

0 vs 11 perforations per arm:

The trend is that the SPL variation is reduced, the peaks and troughs are flattened, and the amplitude of the SPL is increased.

 

[jamienelson]

I also tested a 6inch diameter circle of basswood, and a 6inch diameter 3/4ths inch XPS board circle - same trend. I can post those results too on request.

So the good news is by having a strip of basswood cut with a lattice, I now have the tweeter that can give me an SPL of ~80 from 6000hz to 15000hz.

 

[jamienelson]

So this company has just released a panel speaker that works from 20hz all the way up.
It only costs €44,000

 

[Eucyblues99]

I also tested a 6inch diameter circle of basswood, and a 6inch diameter 3/4ths inch XPS board circle - same trend. I can post those results too on request.

Yes please 👍

And I'm wondering what, if any, the effect would be if you glued a thin membrane over the perforated panels... Maybe with one or more larger holes, say around 15 -20 mm dia. Something like doped tracing paper or scrim cloth

Eucy

 

[Eucyblues99]

And good luck doing a Chladni test with those holes 🤭🤗

 

[Andre Bellwood]

I saw somewhere here, and I did experiment at some stage with holes drilled randomly around the exciter.
Can't find the posts...

However!
The perforations, sizes, spacing, positions in a panel, and the resultant efficiency and FR are directly related to the speed of sound in the associated material.
This is something that must be investigated closely.

 

[Andre Bellwood]

And good luck doing a Chladni test with those holes 🤭🤗

Having said that...
The way, apparently, to approach the solution is to do Chladni tests on a raw panel, and then put holes into the antinodes. I suspect this should decrease the peaks in FR. not sure how it will effect the dips.

 

[homeswinghome]

So this company has just released a panel speaker that works from 20hz all the way up.
It only costs €44,000

Those speakers are isodynamic type (12µm mylar membrane) not DML. See DyptiqueAudio web site

 

[jamienelson]

Yes please 👍

And I'm wondering what, if any, the effect would be if you glued a thin membrane over the perforated panels... Maybe with one or more larger holes, say around 15 -20 mm dia. Something like doped tracing paper or scrim cloth

Eucy

I’ll test it. I also want to know this. As I can’t have a trypophobia inducing tweeter.

 

[jamienelson]

Having said that...
The way, apparently, to approach the solution is to do Chladni tests on a raw panel, and then put holes into the antinodes. I suspect this should decrease the peaks in FR. not sure how it will affect the dips.

The dips and peaks caused by coincidence frequency overlap seen in a whole panel will be reduced if not removed.
The dips caused by inefficient modes will still exist.

 

[Eucyblues99]

I’ll test it. I also want to know this. As I can’t have a trypophobia inducing tweeter.

Dark glasses may help .🤭

 

[Audiofrenzy]

I also tested a 6inch diameter circle of basswood, and a 6inch diameter 3/4ths inch XPS board circle - same trend. I can post those results too on request.

So the good news is by having a strip of basswood cut with a lattice, I now have the tweeter that can give me an SPL of ~80 from 6000hz to 15000hz.

Just curious where did you get the concept of putting holes in the diaphragm?