These are them.... I added this material after attached post address to cut back on some harshness, I like warm sound https://www.diyaudio.com/community/...ll-range-speaker.272576/page-489#post-7308031 post 9,774
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Last week I shared details of various methods of evaluating and comparing the damping level in panel speakers. Here I'll share how the frequency response of the various constructions compared.
As you may recall, I tested the same panel in five different mounting configurations.
The panel is a three layer composite with a balsa core and carbon fiber skins, about 2.1 mm thick and with dimensions of 16" x 23.5". In all tests the panel was oriented with the long direction horizontal. The different mountings are described below. Note, I added a new one (#5) similar to 3,4 and 6 with full surrounds, onl;y using butyl rubber between the panel and frame.
The five mountings are as follows:
1.Hanging Free: Panels were hung from wires attached with small alligator clips, about 5" from the two ends of the panel.
2. Four Points 3M Indoor: Panel attached at four points to a frame using 3M Indoor double sided foam mounting tape. The four points were along the two long edges, about 5" in from the corners. The tape pieces were each approximately 3/4" square. This foam tape is quite soft and rebounds quickly when compressed.
3. Full Surround 3M Indoor: Panel attached to frame around the entire perimeter, excluding about 2" from each corner. The width of tape in contact with the frame and panel was about 0.5" wide.
4. Full Surround 3M Extreme: Similar to directly above, except using 3M Extreme double sided mounting tape. This foam tape is much firmer, and has much slower rebound than the 3M Indoor used in mountings 2 and 3 above.
5. Full Surround Butyl Rubber: Similar to 3 and 4 above, only using a strip of butyl rubber between the panel and frame, excluding 2" from each corner. The butyl rubber strip was 1/2" wide and 1/8" thick.
6. Full Surround Poron 92: Similar to 3, and 5 above except the panel was attached to the frame using Poron 92 foam (about 0.25" thick). This foam is very soft, with very slow rebound. The width of foam in contact with the panel and frame was in this case was about 1.25" wide.
Since I added mounting 5, see below the impedance plots comparing all six mountings. As you can see, the results show that the butyl rubber provides a bit more damping than the 3M Extreme (esp at low frequencies) but not as much as the Poron 92.
The figure below compares the the SPL frequency response for mounting conditions 1, 2, and 3. These are the three mountings with minimal damping All are plotted with 1/1 octave smoothing. I choose this smoothing only because it is very hard to compare these responses with less smoothing, as they bounce around a lot and cross each other so much it's hard to make comparisions.
The results show that "Full Surround-3M Indoor" mounting provides considerably higher SPL than either the "Free Hanging" and "Four Points" mountings from 50 Hz up to over 1000 hz. But while the "Full Surround-3M Indoor" has a little more damping than the other two (based on the impedance plots), I would not suggest that higher damping is the reason for the higher SPL for the "Full Surround" case. Rather, I suggest that it's because the constraint around the perimeter makes the fundamental mode in particular much more efficient. I have seen this difference everytime I compare free hanging panels to panels with support around most or all of the perimeter. That is, more SPL at low frequencies with more perimeter constraint.
The next plot below compares case 3 (Full Surround-3M Indoor) to the other panels with full surround with increasing levels of damping.
Perhaps the most obvious difference is the the 3M Indoor (lowest damping) provides the highest SPL below about 80 Hz. The 3M Indoor is the softest of the surrounds, resulting in a fundamental frequency of 60 Hz, (compared to about 85 Hz for the others) and resulting in stronger SPL at the very lowest end of the range.
But above 80 Hz, the low damping 3M Indoor mounting has no higher SPL than the much higher damping 3M Extreme, or even that of the even higher damping Butyl Rubber.
The Poron 92 mounting, with the highest damping, finally does exhibit some reduction in SPL, particularly above about 1000 Hz.
Overall, I believe these results suggest that you can add lots of both constraint and damping before you have to worry about significant loss of SPL.
Also, of course, onother aspect of response is in the time domain, which is not revealed by the SPL curves. But the spectrogram view shows the time domain and shows the extent of "ringing", or delayed response. I won't show all the spectrograms, but the two spectrograms (measured at 1 meter) below compare the mounting with the lowest damping ( #1, Free Hanging) to that of the mounting with the highest damping (#6, Full Surround, Poron 92). While the differences are less dramatic in the 1 meter test than they are inthe Close Mic spectrograms, it's clear that the Free Hanging mounting shows much more ringing than the Poron 92 mounting.
Eric
Free Hanging
Full Surround-Poron 92
As you may recall, I tested the same panel in five different mounting configurations.
The panel is a three layer composite with a balsa core and carbon fiber skins, about 2.1 mm thick and with dimensions of 16" x 23.5". In all tests the panel was oriented with the long direction horizontal. The different mountings are described below. Note, I added a new one (#5) similar to 3,4 and 6 with full surrounds, onl;y using butyl rubber between the panel and frame.
The five mountings are as follows:
1.Hanging Free: Panels were hung from wires attached with small alligator clips, about 5" from the two ends of the panel.
2. Four Points 3M Indoor: Panel attached at four points to a frame using 3M Indoor double sided foam mounting tape. The four points were along the two long edges, about 5" in from the corners. The tape pieces were each approximately 3/4" square. This foam tape is quite soft and rebounds quickly when compressed.
3. Full Surround 3M Indoor: Panel attached to frame around the entire perimeter, excluding about 2" from each corner. The width of tape in contact with the frame and panel was about 0.5" wide.
4. Full Surround 3M Extreme: Similar to directly above, except using 3M Extreme double sided mounting tape. This foam tape is much firmer, and has much slower rebound than the 3M Indoor used in mountings 2 and 3 above.
5. Full Surround Butyl Rubber: Similar to 3 and 4 above, only using a strip of butyl rubber between the panel and frame, excluding 2" from each corner. The butyl rubber strip was 1/2" wide and 1/8" thick.
6. Full Surround Poron 92: Similar to 3, and 5 above except the panel was attached to the frame using Poron 92 foam (about 0.25" thick). This foam is very soft, with very slow rebound. The width of foam in contact with the panel and frame was in this case was about 1.25" wide.
Since I added mounting 5, see below the impedance plots comparing all six mountings. As you can see, the results show that the butyl rubber provides a bit more damping than the 3M Extreme (esp at low frequencies) but not as much as the Poron 92.
The figure below compares the the SPL frequency response for mounting conditions 1, 2, and 3. These are the three mountings with minimal damping All are plotted with 1/1 octave smoothing. I choose this smoothing only because it is very hard to compare these responses with less smoothing, as they bounce around a lot and cross each other so much it's hard to make comparisions.
The results show that "Full Surround-3M Indoor" mounting provides considerably higher SPL than either the "Free Hanging" and "Four Points" mountings from 50 Hz up to over 1000 hz. But while the "Full Surround-3M Indoor" has a little more damping than the other two (based on the impedance plots), I would not suggest that higher damping is the reason for the higher SPL for the "Full Surround" case. Rather, I suggest that it's because the constraint around the perimeter makes the fundamental mode in particular much more efficient. I have seen this difference everytime I compare free hanging panels to panels with support around most or all of the perimeter. That is, more SPL at low frequencies with more perimeter constraint.
The next plot below compares case 3 (Full Surround-3M Indoor) to the other panels with full surround with increasing levels of damping.
Perhaps the most obvious difference is the the 3M Indoor (lowest damping) provides the highest SPL below about 80 Hz. The 3M Indoor is the softest of the surrounds, resulting in a fundamental frequency of 60 Hz, (compared to about 85 Hz for the others) and resulting in stronger SPL at the very lowest end of the range.
But above 80 Hz, the low damping 3M Indoor mounting has no higher SPL than the much higher damping 3M Extreme, or even that of the even higher damping Butyl Rubber.
The Poron 92 mounting, with the highest damping, finally does exhibit some reduction in SPL, particularly above about 1000 Hz.
Overall, I believe these results suggest that you can add lots of both constraint and damping before you have to worry about significant loss of SPL.
Also, of course, onother aspect of response is in the time domain, which is not revealed by the SPL curves. But the spectrogram view shows the time domain and shows the extent of "ringing", or delayed response. I won't show all the spectrograms, but the two spectrograms (measured at 1 meter) below compare the mounting with the lowest damping ( #1, Free Hanging) to that of the mounting with the highest damping (#6, Full Surround, Poron 92). While the differences are less dramatic in the 1 meter test than they are inthe Close Mic spectrograms, it's clear that the Free Hanging mounting shows much more ringing than the Poron 92 mounting.
Eric
Free Hanging
Full Surround-Poron 92
Hi Eric
Many thanks for this very useful and informative post.
And I guess the main takeaway is that a slow rebound mounting is not really necessary??
What is the cross section size of the 3M indoor tape...I can find Scotch mount indoor double sided tape here but I don't know if it's the same as yours.
Also, so you think the thickness of the tape comes into play...ie.. Added absorption, resilience etc.?
Was reason you tested horizontal purely practical?
Did you perchance do a subjective listening test of each mounting with music?
Thanks again
Eucy
Many thanks for this very useful and informative post.
And I guess the main takeaway is that a slow rebound mounting is not really necessary??
What is the cross section size of the 3M indoor tape...I can find Scotch mount indoor double sided tape here but I don't know if it's the same as yours.
Also, so you think the thickness of the tape comes into play...ie.. Added absorption, resilience etc.?
Was reason you tested horizontal purely practical?
Did you perchance do a subjective listening test of each mounting with music?
Thanks again
Eucy
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Eucy,
As I said before, what I was intending the main takeaway to be was simply the fact that there are several pretty simple ways to assess the amount of damping that any mounting provides. But that's really not what yo are referring to, is it?
In answer to your actual question, I guess I would say both yes and no. If your goal is simply to maximize the low frequency output, without regard to any control over extended ringing in the time domain, then yes, slow rebound mounting is not necessary. I forgot to include in my last post a link to this earlier post, which explains what I believe is the reason that constraining the perimeter is good for maximizing low frequency output:
https://www.diyaudio.com/community/...s-as-a-full-range-speaker.272576/post-7515774
And what I mean by "constrained" in this case is a perimeter that acts approximately like a hinge, i.e. a so called "simple support".
But if you want to control ringing, then slow rebound mounting can be very effective.
The 3M Indoor tape is about 3/4" wide and 1 mm thick and looks like this:
This link shows both the 3M Indoor and 3M Extreme.
https://www.scotchbrand.com/3M/en_U...245799821!e!!g!!3m mounting tape&gad_source=1
I have played around a bit with different dimensions of the tape. It effects the damping of different tapes in different ways. See this post:
https://www.diyaudio.com/community/...ing-of-dml-speaker-panels.394465/post-7279558
Yes, no other real reason.
Only for the ones with the higher damping levels. I have listened before to the ones lacking significant damping and I know already that I don't like them, at this point I can tell just by listening to the frequency sweeps! And while I did spend some time listening to the more damped versions, I'm not very good at subjective descriptions and rarely find the subjective descriptions of others very useful. That's just me.
But also, my intention with this series of posts was never was to compare how the various builds actually "sounded", but rather to demonstrate tools that I thought were useful at assessing damping levels, so others could use the same tools and assess the extent to which any change in panel mounting etc. actually impacted damping, as opposed to simply adding weight or changing the distribution of natural frequencies.
Eric
I guess that's why it's called subjective Eric 😁.
Nevertheless, would you have preferred the Poron option based on those listening tests? And do you think that effective edge damping, in your case at least, removes the need for selective panel damping?
From your comments, I assume that the test plate exhibited audible ringing before damping, even with the balsa core.
Thanks, that's a handy reminder, there are so many posts... we need a librarian.. It's interesting, thicker tape would produce a more flexible "hinge" so a thinner tape could constrain flexural rotation more and add to damping over that of a thicker tape, but the absolute rotations are so small that the effect of the thickness is also small, and I guess ditto with the tension and compression components.
Thanks again Eric.... All grist to the mill
Eucy
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Hi again Eric
I was wondering if you'd be prepared to try a felt strip for mounting...3 to 4 mm thick single sided adhesive felt is available here in sheets. Cut in strips, glue to frame and stick to panel or vice versa... Seems to me it could be a good candidate for damping. I'll also try it but I don't currently have an impedance rig to test it.. It's on the list.
Cheers
Eucy
I was wondering if you'd be prepared to try a felt strip for mounting...3 to 4 mm thick single sided adhesive felt is available here in sheets. Cut in strips, glue to frame and stick to panel or vice versa... Seems to me it could be a good candidate for damping. I'll also try it but I don't currently have an impedance rig to test it.. It's on the list.
Cheers
Eucy
Not sure about Poron vs. say Butyl or 3M Extreme. I currently have identical panels built with Poron and Butyl Rubber surrounds, I may spend some more time comparing them. Yes, I think effective edge damping removes the need for selective panel damping.
Oh yeah. Rings like crazy. About the same as EPS and XPS.
Let me see what I can find.
Eric
Moray James.
I came across this post with recordings I made with the panels pointing at each other.
I should have spent more time recording the panels at a distance, but I was more interested in the sound produced by the panels in headphone mode.
It reminded me of the experiments I made many years ago trying to imitate GA Briggs upwards firing mid tweeter on an open baffle .
I remember preferring to have the panel tilting forwards for a better direct sound.
Pointing straight up sounded fantastic with orchestral music, but with rock music, the guitar sounded like it was behind the wall in my neighbours house 😅
I ended up having two mid tweeter units point at each other, slightly tilted towards to the front, this is with one above the other about 2 to 4 ft apart.
I could stand in the far corner of the room and still have perfect imagery, I still remember , at being amazed at the sound of a saxophone sounding so real.
I'm not sure how this would work using small dml panels, but it would be interesting to find out.
I gave up this idea as my wife was not very happy with wires and speakers hanging from my living room ceiling, hence me having to move audio out of the living room 😳😭 or else 😱
The drive units I used at the time were bandor 2inch full range drivers (almost full range).
Steve.
Sorry Steve but I am confused, are you saying that you used two mid / tweeter units per channel for a total of four in stereo? I think where I am getting confused most is when you say that one was above the other so I then get the impression that you only used one mid tweeter per channel and that they were positioned anywhere from 2 - 4 feet apart (left / right) but one channels mid /tweeter was positioned vertically above the mid / tweeter of the opposite channel. Can you set me straight please? Thanks for the post with the two recordings and for helping me to understand.
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Eric
I changed one panel to the felt and did an A-B test with it's partner (my modified foam mount). Hard to tell but I think it's a teeny bit more damped. The felt is 3mm thick. It's a strange beast, quite mobile... You'll see what I mean if you try it. Works out ok though.
To make the mounting easier, I used thin double sided self adhesive foam struck to the felt, giving peel layers on each side, then cut the strips. The felt layer went to the panel, the foam to the frame. It's much easier to use scissors when you're not exposed to the adhesive side. Instead of full length strips, I used shortish ones with small gaps (easier to cut one or some out should I fiddle about with it)
I'll be very interested in seeing results if you do test it.
Eucy
Moray.
I decided to take a picture rather than trying to explain.
These are the same sort of size as the bandor 2inch units, as you can see I am holding on above the other for one chanel.
By moving the top speaker up and down you could hear the units coming in phase and out of phase with each other, all I had to do was pick which position I preferred.
Over the years I have seen various manufacturers using the same techniques, with varying amounts of success.
I hope this makes it clearer to you ?
Steve.
I decided to take a picture rather than trying to explain.
These are the same sort of size as the bandor 2inch units, as you can see I am holding on above the other for one chanel.
By moving the top speaker up and down you could hear the units coming in phase and out of phase with each other, all I had to do was pick which position I preferred.
Over the years I have seen various manufacturers using the same techniques, with varying amounts of success.
I hope this makes it clearer to you ?
Steve.
Attachments
Yes it does help Steve thank you very much. Have you considered or tried a similar experiment using a pair of small DML panels? Thanks.
Moray.
Yes I have considered ,in the past using two panels in this configuration, but I have not tried it.
Probably because I manage to get such a good sound from single panels.
I'm not sure if it would be worth the extra effort, and if it would be advantageous or not ?
Steve.
Yes I have considered ,in the past using two panels in this configuration, but I have not tried it.
Probably because I manage to get such a good sound from single panels.
I'm not sure if it would be worth the extra effort, and if it would be advantageous or not ?
Steve.
Moray.
In a moment of madness I decided to glue two pieces of veneer together, with the grains going in the same direction.
The pieces have been lying around for years waiting for me to make up my mind what to do with them.
I have an idea of what this panel will sound like, but am more interested in how it performs with the varying flexibility in different directions 🤔
I will probably have to add my dome to the centre to stop the exciter panel distortions, although I might try a thin film Coating first ?
We shall see.
If nothing else, I have finally got rid of the veneer that has been knocking around for so long 🙄
The panel is 34x28cm x 1mm.
I could cut this in half later on to make even smaller panels.
Steve.
In a moment of madness I decided to glue two pieces of veneer together, with the grains going in the same direction.
The pieces have been lying around for years waiting for me to make up my mind what to do with them.
I have an idea of what this panel will sound like, but am more interested in how it performs with the varying flexibility in different directions 🤔
I will probably have to add my dome to the centre to stop the exciter panel distortions, although I might try a thin film Coating first ?
We shall see.
If nothing else, I have finally got rid of the veneer that has been knocking around for so long 🙄
The panel is 34x28cm x 1mm.
I could cut this in half later on to make even smaller panels.
Steve.
Attachments
I have turned the bottom board over to help the moisture evaporate into the plasterboard.
I tried to let it dry naturally but the sides started to bend upwards.
Hopefully when dry the veneer will stay fairly flat ?
I think I will add some more undiluted pva to the short edges , just to make sure the edges do not split along the grain.
Steve.
I tried to let it dry naturally but the sides started to bend upwards.
Hopefully when dry the veneer will stay fairly flat ?
I think I will add some more undiluted pva to the short edges , just to make sure the edges do not split along the grain.
Steve.
Attachments
Eric
I attempted some tap testing today with mixed results I think...
Panels were..
1/ 10mm high density EPS 600x300 raw
2/ ditto material and size but sanded and 2 coats of latex, then a 3mm poplar ply backing approx 150x300 centrally fixed to one side.
3/ Blackwood panel 900x300x2 with foam mounts...Foam being sponge modified with mastic/silicone mix massaged in.
4/ Partner panel to above with felt mounts as previously described
I held the unmounted foam between two fingers and after testing a few different hammers, ended up just using my finger.
The Blackwood panels I tried both finger holding and resting the frame edge on a padded table... Finger hammer again
I found the results to be variable, but it did indicate that both forms of mounting of the Blackwood panels were damping peaks.
The foam/ply panel image shows the result of striking from either side.
Eucy
I attempted some tap testing today with mixed results I think...
Panels were..
1/ 10mm high density EPS 600x300 raw
2/ ditto material and size but sanded and 2 coats of latex, then a 3mm poplar ply backing approx 150x300 centrally fixed to one side.
3/ Blackwood panel 900x300x2 with foam mounts...Foam being sponge modified with mastic/silicone mix massaged in.
4/ Partner panel to above with felt mounts as previously described
I held the unmounted foam between two fingers and after testing a few different hammers, ended up just using my finger.
The Blackwood panels I tried both finger holding and resting the frame edge on a padded table... Finger hammer again
I found the results to be variable, but it did indicate that both forms of mounting of the Blackwood panels were damping peaks.
The foam/ply panel image shows the result of striking from either side.
Eucy
Attachments
Eucy,
For the foam panels, you could try hanging the panel with a pair of strips of painters tape. When you hold with your fingers you introduce a lot of damping just with your fingers, and it's pretty hard I imagine to have the mic in a particular place, and also very close to the panel, when you are trying to hold it with one hand and strike it with the other. Despite that your EPS panel shows the sharp peaks characteristic of an undamped panel. Painters tape shouldn't stick to the plate and cause any damage to the foam or coating.
For framed panels, I clamp the frame to a table, but making sure that the table contacts only the frame and not the panel itself.
Eric