Quad ESL (the original from the fithties) has felt on the back but it is on the outside covers a small distance away from the esl drivers. Removing it will change the tonal balance, more acoustic output will reach the wall behind the speakers. In some cases this will force you to increase the distance to the wall.
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I'm not familiar with the Monsoon design, but builders are cost conscious and only include parts as required. My guess is that if there's felt applied, it prevents the membrane from touching some part of the assembly, probably where the membrane has the least controlled movement.
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A diaphragm hitting the magnets or anything else use to be a bad thing. There can be a cavity resonance inside push-pull drivers that can be disturbing. I have seen planar tweeters being lined inside (Technics) to reduce resonances. The Strathearn and similar ones also had felt inside. Infinty EMIM also had some stuff inside.
the "felt" is used as diaphragm damping mechanism.
The felt adds a bit of resistance to air movement to help tame resonances in the diaphragm, particularly below about 500 hz.
Planer diaphragms have mechanical properties that result in about zero damping of large lower frq movements that move a lot of air. The majority of their control comes from the resistance to air movement that the magnet array represents. Often however they need a bit more.
Planers tend to have issues with diaphragm movement in the lower freqs. The biggest issue is main resonance wich can peak up diaphragm movements to the point were max travel is used up long before a reasonable volume is achieved. So adding a bit of resistance to air movement can damp this main resonance out and often can help control some issues above main resonance for a few octaves.
Stratherns actually used aprox 2 inch thick layer of fiberglass compressed down to about 1 inch on back side of their planer. There were mods that allowed you to eliminate this.
In fact many have found that using a bit of this type of material attached solid to the back side of planer bass diaphragms can "tune" the bass of these design wich can often be a bit heavy around main tune. This was quite effective on Apogee ribbons as well as others. The result is less "boom" and a fast bass decay. Fine line to get it all match to room etc.
In practice you can vary the "felt" thickness/density/size/area covered, to get desired result. Ive used everything from bed sheets to nylon stockings.The ideal construction seems to be solid materials with just the right amount/ size holes. The flexable felts/cloths etc work best is tacked down so cant move like when glued to the perforated metal on backside of planers. If the "felt" or whatever is left loose and can easily move there can be some loss of dynamics
I suspect the monsoon is used low enough and it needs this restriction so avoid diaphragm overtravel and possibly some coloration for a few octaves above main tune.
Even planer tweeters will use this method. It can sometimes have effect on a response bump in band BUT I suspect even in these its for diaphragm control around the crossover region wich may be getting enough low freq energy to excite the rather high resonance of that small diaphragm.
The felt adds a bit of resistance to air movement to help tame resonances in the diaphragm, particularly below about 500 hz.
Planer diaphragms have mechanical properties that result in about zero damping of large lower frq movements that move a lot of air. The majority of their control comes from the resistance to air movement that the magnet array represents. Often however they need a bit more.
Planers tend to have issues with diaphragm movement in the lower freqs. The biggest issue is main resonance wich can peak up diaphragm movements to the point were max travel is used up long before a reasonable volume is achieved. So adding a bit of resistance to air movement can damp this main resonance out and often can help control some issues above main resonance for a few octaves.
Stratherns actually used aprox 2 inch thick layer of fiberglass compressed down to about 1 inch on back side of their planer. There were mods that allowed you to eliminate this.
In fact many have found that using a bit of this type of material attached solid to the back side of planer bass diaphragms can "tune" the bass of these design wich can often be a bit heavy around main tune. This was quite effective on Apogee ribbons as well as others. The result is less "boom" and a fast bass decay. Fine line to get it all match to room etc.
In practice you can vary the "felt" thickness/density/size/area covered, to get desired result. Ive used everything from bed sheets to nylon stockings.The ideal construction seems to be solid materials with just the right amount/ size holes. The flexable felts/cloths etc work best is tacked down so cant move like when glued to the perforated metal on backside of planers. If the "felt" or whatever is left loose and can easily move there can be some loss of dynamics
I suspect the monsoon is used low enough and it needs this restriction so avoid diaphragm overtravel and possibly some coloration for a few octaves above main tune.
Even planer tweeters will use this method. It can sometimes have effect on a response bump in band BUT I suspect even in these its for diaphragm control around the crossover region wich may be getting enough low freq energy to excite the rather high resonance of that small diaphragm.
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All of you guys might want to do a little bit of math on the required excursion versus SPL attained on a planar diaphragm.
Some of what has been stated is true. But not all of what has been stated in this thread is true.
There is a reason why planars of moderate size are bandwidth limited.
There are also simple reasons why they are designed the way that they are.
If I have time I can point you to some useful tools to calculate some of the vital parameters.
If you want a head start go to Linkwitzlab and look for his dipole excursion calculator.
That will get you started.
sengspielaudio also has some very useful calculators. But be sure to find ones that are appropriate for the loading conditions. If the planar has a closed back it is effectively a system, closed box. If it is open to the atmosphere on both sides it is effectively a dipole.
As a bit of a question to think through. If you believe that the felt or other absorbing material protects against over excursion why is it on only one side of the diaphragm? It's a push pull system in most planars.
Some of what has been stated is true. But not all of what has been stated in this thread is true.
There is a reason why planars of moderate size are bandwidth limited.
There are also simple reasons why they are designed the way that they are.
If I have time I can point you to some useful tools to calculate some of the vital parameters.
If you want a head start go to Linkwitzlab and look for his dipole excursion calculator.
That will get you started.
sengspielaudio also has some very useful calculators. But be sure to find ones that are appropriate for the loading conditions. If the planar has a closed back it is effectively a system, closed box. If it is open to the atmosphere on both sides it is effectively a dipole.
As a bit of a question to think through. If you believe that the felt or other absorbing material protects against over excursion why is it on only one side of the diaphragm? It's a push pull system in most planars.
one sided application is all thats needed. You can put on both sides but to get the same resistance to air flow you would need to cut the restriction in half. Will do same thing BUT with twice the work. Its ok but not necessary, at least for the lower freqency problems.
Diaphragm excursion calcs dont tell the whole story
Large amplitude resonances in planers that can often peak up sharply will get ya if there in your passband. Its not the amplitude needed to achive a certain volume BUT the over excursions of strong high Q resonances.
Sometimes these resonances can be excited by the output from other drivers in the system so even if your not using the planer near its resonance, it can still be excited.
The other area the restriction helps with is a few multiples above the main resonance. A particular problem on larger planers tends to be around 200 Hz. Standing waves here tend to give a thickening to the sound. The restriction can help here too. Give a nice , fast clean attack. Lower mids are clearer and bass notes have faster decay.
Some food for thought. I do not speak from theory. I speak from experience. Have design/built/tested literally hundreds of planer and ribbon designs over last 30 yrs. No exaggeration. Have played extensively with magnet spacing's and the "open area" of planer designs as well as experimented with many air flow restriction methods on all as well as a number of commercial designs. From full sized planer bass/ mids/ and tweeters.
ALL "thin film" designs behave similarly
Diaphragm excursion calcs dont tell the whole story
Large amplitude resonances in planers that can often peak up sharply will get ya if there in your passband. Its not the amplitude needed to achive a certain volume BUT the over excursions of strong high Q resonances.Sometimes these resonances can be excited by the output from other drivers in the system so even if your not using the planer near its resonance, it can still be excited.
The other area the restriction helps with is a few multiples above the main resonance. A particular problem on larger planers tends to be around 200 Hz. Standing waves here tend to give a thickening to the sound. The restriction can help here too. Give a nice , fast clean attack. Lower mids are clearer and bass notes have faster decay.
Some food for thought. I do not speak from theory. I speak from experience. Have design/built/tested literally hundreds of planer and ribbon designs over last 30 yrs. No exaggeration. Have played extensively with magnet spacing's and the "open area" of planer designs as well as experimented with many air flow restriction methods on all as well as a number of commercial designs. From full sized planer bass/ mids/ and tweeters.
ALL "thin film" designs behave similarly
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one sided application is all thats needed. You can put on both sides but to get the same resistance to air flow you would need to cut the restriction in half. Will do same thing BUT with twice the work. Its ok but not necessary, at least for the lower freqency problems.
Diaphragm excursion calcs dont tell the whole story
The other area the restriction helps with is a few multiples above the main resonance. A particular problem on larger planers tends to be around 200 Hz. Standing waves here tend to give a thickening to the sound. The restriction can help here too.
Some food for thought. I do not speak from theory. I speak from experience. Have design/built/tested literally hundreds of planer and ribbon designs over last 30 yrs. No exaggeration. Have played extensively with magnet spacing's and the "open area" of planer designs as well as experimented with many air flow restriction methods on all as well as a number of commercial designs. From full sized planer bass/ mids/ and tweeters.
ALL "thin film" designs behave similarly
Nice.
So planar design is something we have in common.
Although I do not have 30 years of design experience.
You bring up points that I am well aware of in terms of structural resonance and how a stretched diaphragm really behaves. It was not in the thread discussion yet.
But all great points.
I have done a lot of AMT design work and am transitioning into Large format planars. It is indeed very different from cone and dome driver design. And I enjoy the challenge.
Just checked out your website. Nice.
I like the diagonal stiffening method you use.
The planar work I do is much higher efficiency, and stretched membrane types. Pro sound stuff. Large area and very high SPL is required. 100db/watt efficiency is the normal minimum.
And you are working with single ended designs I'm working with push-pull designs.
I see your planars are free on the sides. So you are completely correct in stating that the resonances are a multiple of the length. A wavelength calculation in 1/4 and half wavelengths will give the ball park areas of concern. Then the stiffness generated by the forming process will address some of those, but raise the strongest resonances higher in frequency. If you gain enough stiffness you can raise the primary resonance well above the hearing range.
Nice idea!
I like the diagonal stiffening method you use.
The planar work I do is much higher efficiency, and stretched membrane types. Pro sound stuff. Large area and very high SPL is required. 100db/watt efficiency is the normal minimum.
And you are working with single ended designs I'm working with push-pull designs.
I see your planars are free on the sides. So you are completely correct in stating that the resonances are a multiple of the length. A wavelength calculation in 1/4 and half wavelengths will give the ball park areas of concern. Then the stiffness generated by the forming process will address some of those, but raise the strongest resonances higher in frequency. If you gain enough stiffness you can raise the primary resonance well above the hearing range.
Nice idea!
Just checked out yours! Impressive array of things going on, very nice.
It is fun. Planers are fundamentally easy to build yet there really is a world things left to try with planers.
The last few yrs have been focused on bringing a new ribbon technology to market. Patent is still pending so cant say much about how it works (even in the web site ha) but its finally "out there" . The pics and words dont really disclose the ribbons construction completly but the technology has a powerfull effect on ribbon trashing standing waves below 500hz or so allowing a smaller ribbon to be used lower in freq. I have a bass panel planer design that i think is worthy of the same effort if can get to it Ha.
I think you will have a blast with the planer. Sooo much that can be done yet there IMO for those thinking outside the box
The AMT certainly has some very strong points. Im not sure its potential has been realized yet. I see unique materials AND unique conductor trace designs possably taking them to next level??
High sens Pro sound, Are U using any wave guides/horns??
It is fun. Planers are fundamentally easy to build yet there really is a world things left to try with planers.
The last few yrs have been focused on bringing a new ribbon technology to market. Patent is still pending so cant say much about how it works (even in the web site ha) but its finally "out there" . The pics and words dont really disclose the ribbons construction completly but the technology has a powerfull effect on ribbon trashing standing waves below 500hz or so allowing a smaller ribbon to be used lower in freq. I have a bass panel planer design that i think is worthy of the same effort if can get to it Ha.
I think you will have a blast with the planer. Sooo much that can be done yet there IMO for those thinking outside the box
The AMT certainly has some very strong points. Im not sure its potential has been realized yet. I see unique materials AND unique conductor trace designs possably taking them to next level??
High sens Pro sound, Are U using any wave guides/horns??
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Thanks a million for the clarification! I just wished to know the following...as the planar is a dipole transducer, with no felt in the front & felt at the rear, will not the frequency characteristics change between front & back sides?
Would it be right to conclude that with felt at the back, while it resolves the issue of cavity resonances it would be at the expense of the frequency characteristics being different between the front & the back?
Any/all advise on the above would be greatly appreciated!
Thanks,
Would it be right to conclude that with felt at the back, while it resolves the issue of cavity resonances it would be at the expense of the frequency characteristics being different between the front & the back?
Any/all advise on the above would be greatly appreciated!
Thanks,
Well I have an AMT that both measures better and sounds better than the Mundorf. It's basically a material choice and construction issue.
Horns and waveguides?
That I have been doing since 1994.
The front side you see is loading into a space that is very different from the rear side. The rear of the diaphragm it relatively close to reflective surfaces when compared to the front side.
That is why you see attention to the damping on the inside.
I'll through in another point. I know many parts are manufactured in China. Some are simply copies. And parts are included and stuck in that are done with little understanding as to what they do, or what they potentially could do. This is not conjecture. I know of one well designed planar that has been copied by quite a few OEM companies in China and sold to many clients.
I would like to hear what Mark has to say but In my experience this is only an issue in the higher freqs.
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