Hello Andre,Yes I saw their curves. That's the first thing that made me look again... It's just not physically possible for a driver with the same BL, Re and similar Cms to all the other drivers, to have 20db better sensitivity.
That's why I doubt the Dayton measurement.
Here's the formula to find efficiency (in %) given BL, Re and Cms for any magnet/voice-coil motor:
View attachment 1255361
Plugging in the values from the Dayton datasheet, one gets an efficiency of over 8,500%. I think this is inaccurate.
The Cms figure on the datasheet is 0.0001mm/N. And I think this is why the above is inaccurate.
However, the Billionsound factory data figure for Cms for the same driver is 133.6mm/N.
This results in an efficiency of 0.64%. And THAT sounds accurate!
I suspect Dayton Audio needs an audio engineer on their staff.
Could you document the source of this formula please? I have found in acoustics book some efficiency expression for pistonic loudspeakers based on the flow of a mass controlled piston. In addition of Bl and Re, the mass is involved with the diaphragm surface. For DML, I don't have in mind to have seen the exciter stiffness in the significant data and I don't see how it can be involved. We saw in previous posts that the Young modulus and the panel density are key factors... but the material can be supposed as a constant in exciter comparison.
Christian
I spent nearly a decade in Audio Mastering, with a plethora of audio devices at my disposal,
things that are just not used in home audio. I find the use of DML's in PA quite interesting,
however, none of the above really plays a significant part of the project I am going to build.
I still intend to use Top & Bottom suspension only. No side 'fixing' at all.
The MASS of a panel surely relates to "Stored Energy".
What I really want to see in this 'thread' is more details of Cumulative Spectral Decay and THD.
things that are just not used in home audio. I find the use of DML's in PA quite interesting,
however, none of the above really plays a significant part of the project I am going to build.
I still intend to use Top & Bottom suspension only. No side 'fixing' at all.
The MASS of a panel surely relates to "Stored Energy".
What I really want to see in this 'thread' is more details of Cumulative Spectral Decay and THD.
Also the energy needed to "excite" it to some SPL level which also relates to other factors concerning the material used to produce the panel.
DML's are said to be tricky as they have too many degrees of freedom. A fact as all sorts factors inter react and more variations can be added over and above the basics. The 1st post in the thread indicates this and also shows distortion levels. Impulse response is seen as important by many. Maybe tone bursts would be a better option concerning decay.
This is from the article I posted earlier, I have no problems with measuring dml panels , as long as we understand the outcome.
But the panel itself operates wholly in resonance of course, which is one of the features of
NXT that most concerns audio people raised to regard resonance as anathema. Doesn't all
this resonance in the panel color the sound unacceptably? The surprising answer is no, it
doesn't, because of the highly complex nature of the panel's vibration. The impulse
response of an NXT panel (Figure 4) displays a long resonant `tail' which would damn any
conventional loudspeaker, but in fact the sound quality has extraordinary clarity and
transparency confirming the measured flat frequency response (Figure 5).
Of course a large 6ft x 4ft freely floating panel will have a very large tail, but even this can be reduced with various shapes and angles.
Or a panel with its own self damping properties (JohnnoG) 😉
Steve.
But the panel itself operates wholly in resonance of course, which is one of the features of
NXT that most concerns audio people raised to regard resonance as anathema. Doesn't all
this resonance in the panel color the sound unacceptably? The surprising answer is no, it
doesn't, because of the highly complex nature of the panel's vibration. The impulse
response of an NXT panel (Figure 4) displays a long resonant `tail' which would damn any
conventional loudspeaker, but in fact the sound quality has extraordinary clarity and
transparency confirming the measured flat frequency response (Figure 5).
Of course a large 6ft x 4ft freely floating panel will have a very large tail, but even this can be reduced with various shapes and angles.
Or a panel with its own self damping properties (JohnnoG) 😉
Steve.
Another quote, this time from Peter Napp.
Provided that they are correctly designed, distributed-mode loudspeakers do not sound colored as might be expected. This is due to their complex radiation and its decorrelated nature.
Distributed-mode panels also exhibit an unusual impulse response that display a fast rise time or initial transient but incorporates a decaying resonant tail. This impulse response can lead to a flat frequency response and a flat acoustic power output. An interesting outcome of the unique sound-radiating properties of the distributed-mode loudspeaker is that it can be used un-baffled as a free-standing loudspeaker.
Steve.
Provided that they are correctly designed, distributed-mode loudspeakers do not sound colored as might be expected. This is due to their complex radiation and its decorrelated nature.
Distributed-mode panels also exhibit an unusual impulse response that display a fast rise time or initial transient but incorporates a decaying resonant tail. This impulse response can lead to a flat frequency response and a flat acoustic power output. An interesting outcome of the unique sound-radiating properties of the distributed-mode loudspeaker is that it can be used un-baffled as a free-standing loudspeaker.
Steve.
I think you are missing some nuance Steve. Because a DML speaker naturally has a prolonged impulse response and still sounds good doesn't mean that IR doesn't matter and longer is better.
Same with FR...we don't aim for as bumpy FR as possible because bumpy FR tends to be part of the nature of DML.
My dampened plates still have all the attributes of a DML speaker with a phase incoherent waves with broad dispersion, low distortion and excellent spatial separation.
It just doesn't have the extra ringing and interference that a free plate gives.
Are you trying to say that NXT are referring to free plates rather than suspended?
Same with FR...we don't aim for as bumpy FR as possible because bumpy FR tends to be part of the nature of DML.
My dampened plates still have all the attributes of a DML speaker with a phase incoherent waves with broad dispersion, low distortion and excellent spatial separation.
It just doesn't have the extra ringing and interference that a free plate gives.
Are you trying to say that NXT are referring to free plates rather than suspended?
twocents,
I'd be surprised if you could get away with less than 12" wide and and still get down to 100 Hz, at least with any of the 5 ply plywoods I'm familiar with, which are all nominally 1/4" thick (typically closer to about 0.20" actually thickness).
I too would like to use a smaller panel (and still get down to 100 Hz) and wish I could find a thinner 5 ply for that reason. But they are hard to come by.
I've also been contemplating making a very thin (say 1 mm) CF/balsa sandwich panel, but the CF I need is always out of stock!
Revply is okay, but not really all that special. It's actually a bit on the dense side. The best things about it are that it's inexpensive and surprising good looking for something that's intended for underlayment.
Eric
All right Eric, I have an update. Long day in the shop today, half for DML and half for other stuff. I got diverted from the Birch project because you posted that DML equation, and I became interested in trying to make a smaller panel with the same output as a larger one. So I resawed a 12 x 17 x .25 " piece of XPS and built a frame and applied a thruster, and the result seems to confirm it's capable of about the same low frequency as my bigger panel, but other than that, it doesn't sound nearly as good. I tried numerous configurations; enough to cool off from the idea. I was about to call it a night, but since everything is out, I figured I'd at least get a simple test in on the 24 x 48 piece of plywood just to get a basic idea. So I put a dab of double-sided tape slightly off-center and applied the thruster.
Yeah, it has nowhere near the efficiency that the XPS does, but holy f. Have you tried your Birch with a thruster? I wouldn't have understood what my thrusters were truly meant to do without this test, because up until 20 minutes ago, they've been idling. I put on one of those "deep bass" jazz tracks on youtube, and the board is resonating like a woofer. I have to stand up and hold it in place with one finger -- it's vibrating like crazy. The bass is unreal. I don't have a test mic yet (I have ordered one from PE though so a couple weeks), but I do have the simple decibel x app on my phone, and when that booming bass drum slams, it's jumping to 65 db dead even from 50hz - 100hz. It's already the single best sounding speaker I have in my house.
I see what you're saying about the frame using the double-sided tape but I have a hard time believing the role of the frame is the same in the context of the birch plywood as it is for the xps. It's not really believable to me that by applying a frame, my birch plywood will have MORE bass than it has now. The plywood is the medium that I think you could hang from a piece of fishing line and call it done. But if you were going to make a frame, I totally understand now why you'd need a couple layers of tape because this thing resonates like a salmon on crack, so yeah, gluing it to a frame would obviously ruin it. But totally different for XPS, I can't visualize what's going on with XPS and the frame.
Now if I'm wrong and the frame adds more bass, so be it, but at this point, bass isn't the weakness, it's the overall output. Granted, it sounds epic, and you can't compare the 70db it's putting out to the 70db of the .25" xps speaker I built earlier today. I mean, just the single board sounds so good that it's like full system already. My other removable-bass thruster has a spine attached to its xps panel, I've got to figure out how to rip that off so I can attach to the second birch board. I've got to find a temp way to hold them up so I can hear these in stereo.
I'm sure those other exciters you recommended are good, I've got 6 coming in, but I have a feeling I'll be buying more thrusters. lol. Or maybe put those on my xps panels. I've also got one of the new mid-bass exciters coming that's double the price of the thruster (had to make it 100$ for shipping) with that mic so interested in what that will do.
Yeah, it has nowhere near the efficiency that the XPS does, but holy f. Have you tried your Birch with a thruster? I wouldn't have understood what my thrusters were truly meant to do without this test, because up until 20 minutes ago, they've been idling. I put on one of those "deep bass" jazz tracks on youtube, and the board is resonating like a woofer. I have to stand up and hold it in place with one finger -- it's vibrating like crazy. The bass is unreal. I don't have a test mic yet (I have ordered one from PE though so a couple weeks), but I do have the simple decibel x app on my phone, and when that booming bass drum slams, it's jumping to 65 db dead even from 50hz - 100hz. It's already the single best sounding speaker I have in my house.
I see what you're saying about the frame using the double-sided tape but I have a hard time believing the role of the frame is the same in the context of the birch plywood as it is for the xps. It's not really believable to me that by applying a frame, my birch plywood will have MORE bass than it has now. The plywood is the medium that I think you could hang from a piece of fishing line and call it done. But if you were going to make a frame, I totally understand now why you'd need a couple layers of tape because this thing resonates like a salmon on crack, so yeah, gluing it to a frame would obviously ruin it. But totally different for XPS, I can't visualize what's going on with XPS and the frame.
Now if I'm wrong and the frame adds more bass, so be it, but at this point, bass isn't the weakness, it's the overall output. Granted, it sounds epic, and you can't compare the 70db it's putting out to the 70db of the .25" xps speaker I built earlier today. I mean, just the single board sounds so good that it's like full system already. My other removable-bass thruster has a spine attached to its xps panel, I've got to figure out how to rip that off so I can attach to the second birch board. I've got to find a temp way to hold them up so I can hear these in stereo.
I'm sure those other exciters you recommended are good, I've got 6 coming in, but I have a feeling I'll be buying more thrusters. lol. Or maybe put those on my xps panels. I've also got one of the new mid-bass exciters coming that's double the price of the thruster (had to make it 100$ for shipping) with that mic so interested in what that will do.
Leob.
I should have mentioned that this quote was from HENRY AZIMA.
I agree with these statements from Azima and Napp, as I also hear a clean clear sound from my panels.
The use of damping, for the sole purpose of removing the long tail , is detrimental to the distributed modes .
Carefully placed weights or mountings can help a panel with frequency response problems, but I have no idea how this affects the IR.
I listen carefully after each step, to make sure I have not impinge on the sound quality, or as little as possible.
For PA work , I think this sort of detail is unnecessary.
I talked about this many years ago, over on AudioCircle.
It is more important to control and stabilise the PA panel and exciters .
Which is what I believe , tectonic do ,to protect their panels.
As far as ringing is concerned, I seem to remember the designer of the podiums, stating that he wanted his panel to ring like a bell.
I'm not sure that was the best analogy, I would have said freely vibrate .
He is a well-known conductor and pianist , so the sound is very important to him(as it is to me) and I would believe he would be very finicky (as I am) about the sound reproduction.
His panel sounded very good although I believe the panel was too heavy for the ultimate sound quality that I desire.
At least you are using EPS , which I recommend well over 10years ago, over on AudioCircle .
EPS is still my favourite panel material (not XPS !) for home use, as it produces , for me, the best sound quality , and can fill my whole house (and street) from a small 10watt amp.
We also seem to be taking at cross purposes about PA and home audio, and what is best for each type.
Maybe we should keep this in mind ,when discussing DML panels.
Steve.
@AjohnL
I think that can work reasonably well considering that DML speakers blend easily. With the phase incoherent signal I att least find them easier to cross over with the subs.
But I'm not really sure what would be gained? The fact that you do not need any crossover in the sensitive mids is one of the nice things about DML. With the right plate there is no issue to reproduce 100Hz and upwards, so why split them and introduce a extra crossover?
For HiFi purposes, I guess it could make sense if you really like the sound of a certain material or exciter that doesn't perform well in the full range.And if you want really flat treble up to 20k, it could be a solution.
But it will affect fidelity of your mids adding a crossover, and that usually is more important than that last fraction of an octave of perfect hearing range. I might hear an xover at 10k or lower, but certainly not a rolloff over 16k, as many DML plates will have.
I also considered if it could be useful to improve efficiency or power density for PA use, but cannot really see that, but would increase complexity of the system a lot.
So question is really what you want to achieve and off you think it is worth the tradeoffs that comes with it. The broad range of a DML is one of the big advantages, and to sacrifice that I would need a very strong alternative advantage doing so, and nothing tells me a multiway DML would sound better, be cheaper or easier to construct, be more efficient or offer better power density. Only a little more power in a band that most people cannot hear, and those that can won't really miss.
If you do hear to 20k and find that it is important to you with full response, then it is probably better than using a conventional tweeter to supplement.
I think that can work reasonably well considering that DML speakers blend easily. With the phase incoherent signal I att least find them easier to cross over with the subs.
But I'm not really sure what would be gained? The fact that you do not need any crossover in the sensitive mids is one of the nice things about DML. With the right plate there is no issue to reproduce 100Hz and upwards, so why split them and introduce a extra crossover?
For HiFi purposes, I guess it could make sense if you really like the sound of a certain material or exciter that doesn't perform well in the full range.And if you want really flat treble up to 20k, it could be a solution.
But it will affect fidelity of your mids adding a crossover, and that usually is more important than that last fraction of an octave of perfect hearing range. I might hear an xover at 10k or lower, but certainly not a rolloff over 16k, as many DML plates will have.
I also considered if it could be useful to improve efficiency or power density for PA use, but cannot really see that, but would increase complexity of the system a lot.
So question is really what you want to achieve and off you think it is worth the tradeoffs that comes with it. The broad range of a DML is one of the big advantages, and to sacrifice that I would need a very strong alternative advantage doing so, and nothing tells me a multiway DML would sound better, be cheaper or easier to construct, be more efficient or offer better power density. Only a little more power in a band that most people cannot hear, and those that can won't really miss.
If you do hear to 20k and find that it is important to you with full response, then it is probably better than using a conventional tweeter to supplement.
AjohnL.
There is also the problem of materials, if you have the two panels using the same material, then the hf is going to be very similar.
Using a panel for the hf which can actually reach 20k and maybe the lower panel which might only go up to say 8k ,apart from the XO problem you will also have efficiency and power handling problems to take care of.
You might as well use two identical panels.
There are panels with rising hf above 10k and there are panel with roll off above 10k.
Some have a naturally flat response, some need a little help with a little jiggey pokery .
It all depends on panel materials and exciters used.
I did use a piezo horn at one point, to improve the hf of the panel I was testing at the time, this was without an XO, but with a volume control to match the efficiencies.
Steve.
There is also the problem of materials, if you have the two panels using the same material, then the hf is going to be very similar.
Using a panel for the hf which can actually reach 20k and maybe the lower panel which might only go up to say 8k ,apart from the XO problem you will also have efficiency and power handling problems to take care of.
You might as well use two identical panels.
There are panels with rising hf above 10k and there are panel with roll off above 10k.
Some have a naturally flat response, some need a little help with a little jiggey pokery .
It all depends on panel materials and exciters used.
I did use a piezo horn at one point, to improve the hf of the panel I was testing at the time, this was without an XO, but with a volume control to match the efficiencies.
Steve.
I saw images of one, Russian I assume that used a small panel above a larger one but it's an area I have wondered about anyway.
People mention HF drop off. A possible solution.
Maybe panels can be "designed" to have better bass response at the loss of HF.
Me - people do use woofers with them so at what F would a dml panel need to come in? I start wondering about 2 ways using DML instead of a tweeter. Crossing over at anything in say in the range of 500 to 1Khz wouldn't be suitable for a separate woofer but smaller woofers can work in that range.
Ideally the dml would be mounted directly on the baffle but it could just sit on the top of a cabinet. Xover, for various reasons I feel circa 500Hz may be a good choice. Depends on the size of the panel needed.
LOL I am at odds with the general forum feelings about what the bass end needs but my opinion is based on what I have listened to. For instance my PC speakers that use a 120mm woofer can easily play way to loud for our lounge. This comes in rather rapidly at 40Hz. Seems according to some that this is impossible.
AjohnL, my 2.5 day holiday sound competition between my floor-standing speakers and DMLs here:
https://www.diyaudio.com/community/...ll-range-speaker.272576/page-570#post-7552214
Basically revealed the one deficiency of my panels compared to the c5s was high frequency. I happened to have a couple of experimental coin-based small panels (pink in pic) that pour out HF, and disconnected one of my two amps, the one going to the top panel, and connected that to the coin speakers, and problem solved. No crossover or anything needed, the trick seemed to be -- as I'd tried to do this in the past but without the reference speakers -- that it needed precious little from the 'tweeters' to complete the sound.
https://www.diyaudio.com/community/...ll-range-speaker.272576/page-570#post-7552214
Basically revealed the one deficiency of my panels compared to the c5s was high frequency. I happened to have a couple of experimental coin-based small panels (pink in pic) that pour out HF, and disconnected one of my two amps, the one going to the top panel, and connected that to the coin speakers, and problem solved. No crossover or anything needed, the trick seemed to be -- as I'd tried to do this in the past but without the reference speakers -- that it needed precious little from the 'tweeters' to complete the sound.
That is another question really. Are there panel arrangements that significantly improve the bass end without needing huge panels which I feel probably mess up the HF end.
Another option but can't be certain. A Russian group that may well have been playing through a bank of dml's
AjohnL.
I have not found that large panels mess up the hf , but what I would say is, that I do not play my panels down to 40hz , even though many of them can.
It saves my exciters from excessive movement and overheating.
I usually roll them off at about 100hz, depending on the panel .
My TLs go lower than most subs I have seen and can go up to about 350hz with no problems.
A small panel can easily do 500hz to 20k for home use, as shown in my videos on YouTube(Leob) 😃9x6inch panel.
Although I actually cut the panel off at about 125hz.
Steve.
I have not found that large panels mess up the hf , but what I would say is, that I do not play my panels down to 40hz , even though many of them can.
It saves my exciters from excessive movement and overheating.
I usually roll them off at about 100hz, depending on the panel .
My TLs go lower than most subs I have seen and can go up to about 350hz with no problems.
A small panel can easily do 500hz to 20k for home use, as shown in my videos on YouTube(Leob) 😃9x6inch panel.
Although I actually cut the panel off at about 125hz.
Steve.