inertial said:Hi Critofu,
Yes I know thermos.
Excuse me, but do you know structural-vibrations propagations?
No offence , perdone my basic language .
Cheers,
Inertial
Sound doesn't travel through a vacuum. If you constuct an air-tight two walled speaker cabinet and between the walls is vacuum, then it will be a very excellent enclosure.
Having just read through all the posts here it is very intersesting. I just want to throw in my 20 cents worth.
About 12 months ago I built a pair of speakers that used some very cheap drivers that originally came in some moderate bookshelf sized cabs. The complete speakers cost me just $30.00 per pair (two 6.5s ad two tweeters).
The long and short was I built these into cabinets that had a front baffle 45mm thick, and side walls comprised of 3 thicknesses of MDF with non slip rubber matting between the layers, and concrete slabs top and bottom of the cabs. Basically they are meant for my surround sound home theatre. Each speaker weighs at least 80kg probably more, it takes two to lift them anyway. There were many other measure taken to address much of what has been mentioned here as well.
End result virtually no cabinet resonance and as far as I can tell very little colouration, compared to other speakers I have they sounded very live. pure and detailed and far far better than such a cheap set of drivers should..... a comparison. Not dead and lifeless as some people seem to think they would.
Well I have some B and W 602S3s in my office and by comparison they sound very very coloured and dead and most folk think they are quite OK speakers, including me until I built the incredible bulks.
I have since moved on the full range driver setups but that another story all together.
In my opinion far too little attention is paid to the issues of this thread, probably because to do so commercially would be difficult and expensive........ but that doesn't dimish the importance of these issues for good sound. I think it is very odd that DIYs often spend massive amounts of money on very pricey drivers and then put them into cabs that are actually very compromised. I am very much of the opinion that a average or even cheap drivers in a really solid well built cab can kill an expensive drivers in an average box.
About 12 months ago I built a pair of speakers that used some very cheap drivers that originally came in some moderate bookshelf sized cabs. The complete speakers cost me just $30.00 per pair (two 6.5s ad two tweeters).
The long and short was I built these into cabinets that had a front baffle 45mm thick, and side walls comprised of 3 thicknesses of MDF with non slip rubber matting between the layers, and concrete slabs top and bottom of the cabs. Basically they are meant for my surround sound home theatre. Each speaker weighs at least 80kg probably more, it takes two to lift them anyway. There were many other measure taken to address much of what has been mentioned here as well.
End result virtually no cabinet resonance and as far as I can tell very little colouration, compared to other speakers I have they sounded very live. pure and detailed and far far better than such a cheap set of drivers should..... a comparison. Not dead and lifeless as some people seem to think they would.
Well I have some B and W 602S3s in my office and by comparison they sound very very coloured and dead and most folk think they are quite OK speakers, including me until I built the incredible bulks.
I have since moved on the full range driver setups but that another story all together.
In my opinion far too little attention is paid to the issues of this thread, probably because to do so commercially would be difficult and expensive........ but that doesn't dimish the importance of these issues for good sound. I think it is very odd that DIYs often spend massive amounts of money on very pricey drivers and then put them into cabs that are actually very compromised. I am very much of the opinion that a average or even cheap drivers in a really solid well built cab can kill an expensive drivers in an average box.
After a lot of experimenting, I have come to the conclusion that most of the sound (=unwanted coloration) from the walls of the typical box has its origin in the mechanical transfer of vibration from the drive units. Perhaps this is the second most overseen factor in loudspeaker construction.
The MOST overseen factor has probably to do with sound leakage (from the -sometimes enormous- sound levels which are reached inside the enclosure), and its leakage through the weakest spot of the speaker cabinet, seen as a whole. What is this spot? The weak spot is not the walls, but the thin membrane + surround of the typical mid/bass drive. The leakage here does not stop because the membrane itself is moving and producing the sound in the first place. The reflected sound from the inside does not care about this. The result would be the same if one cut out a big round circle in the middle of a side panel and covered it with a thin membrane of paper or plastic, or whatever.
There is a reason why the speakers which are constructed to absorb a maximum of the sound energy –not only at bass frequencies- from the rear side of the membrane often has such a clean sound. (say, TL cabinets with lots of absorbing stuff along the internal walls).
The MOST overseen factor has probably to do with sound leakage (from the -sometimes enormous- sound levels which are reached inside the enclosure), and its leakage through the weakest spot of the speaker cabinet, seen as a whole. What is this spot? The weak spot is not the walls, but the thin membrane + surround of the typical mid/bass drive. The leakage here does not stop because the membrane itself is moving and producing the sound in the first place. The reflected sound from the inside does not care about this. The result would be the same if one cut out a big round circle in the middle of a side panel and covered it with a thin membrane of paper or plastic, or whatever.
There is a reason why the speakers which are constructed to absorb a maximum of the sound energy –not only at bass frequencies- from the rear side of the membrane often has such a clean sound. (say, TL cabinets with lots of absorbing stuff along the internal walls).
I agree with his opinion, a small ring joining the inner and outer boxes does not have enough area to be significant. Factoring in losses and the inability to transmit vibes perfectly plus the fact that he would design it with a well damped material, I doubt very much would get through. Plus, most acoustic energy from the enclosure is due to large surface area panel vibration as he stated, and the comparing the two values I would say that the joint is insignificant. Especially with a well damped and thick baffle, the one face that will radiate most of the transmitted energy.
As to the math that pinkmouse and poobah did awhile back I, for some reason looked over this whole post again, noticed that I disagree with the methods used. Mainly conservation of momentum which I believe should only be used for unconstrained objects. Since the box is constrained by the floor I decided to try a force balance and determined that the base wont move(using your numbers guys) and tipping will have to occur, see attachment one, or with spikes on carpet I did a loose analysis of carpet compression that could result in angular rotation of the box about the base, see attachment 2 (next post).
Anyways, unless I missed something I believe these number to actually represent a real world scenario and feel free to question any part of it
Attachments
An externally hosted image should be here but it was not working when we last tested it.
and
An externally hosted image should be here but it was not working when we last tested it.
and
An externally hosted image should be here but it was not working when we last tested it.
and ...
no vibration what so ever. Even at near xmax, one can't feel any vibration in the cabinet.
pinkmouse said:Simple Newtonian physics.
Lets say a cone weighs 50 grammes, and the enclosure weighs 10 kilos, a not unreasonable assumption I feel. If the cone is moving, by Newton's conservation of momentum the forces must balance. The ratio of cone movement to to enclosure movement is therefore 50/10 000, which gives us a maximum possible movement in the box of 0.005% of the movement of the cone. And that's with a box that's not coupled to anything, and is completely free to move. I'm not that worried.
Cal Weldon said:
pinkmouse said:
.5% is equivalent to -23db.
Things get more interesting when you consider the swept volume of the vibrating enclosure compared to the diaphram. Since the front and back of the enclosure can easily be 10x the area of the diaphram, the volume would be 5%, or -13db. For low frequencies it doesn't matter, because the front and back are out of phase. For frequencies where the quarter wavelength is less than the enclosure depth it starts to matter.
Since the box is not completely rigid and free to move, the real effect is much lower. Now the question to ask yourself, is it less than -20db? -30db? When is it ok to start ignoring it? I don't have the answers, but I'm definately interested in further discussion on the subject.
Dan
Edit: TNT - fantastic! I want to try something similar, but using aluminum rods and sonotube. Any chance you've taken nearfield distortion measurements with one vs. both drivers active?
owdi - I don't have distorsion measurement possibilities unfortunantly. I am planning to use metal parts for joining the drivers, this was a prototype. However so good I will finish the second one.
This is in my sofa and Eq'd ...
I'm really satisfyed. I cant feel *anything* when laying my hand on this cabinte - it's almost scary.
/
This is in my sofa and Eq'd ...
An externally hosted image should be here but it was not working when we last tested it.
I'm really satisfyed. I cant feel *anything* when laying my hand on this cabinte - it's almost scary.
/
(The weak spot is not the walls, but the thin membrane + surround of the typical mid/bass drive. The leakage here does not stop because the membrane itself is moving and producing the sound in the first place) Sletol
Absolutely in my opinion, I did some tests on one of my 4 inch full range driver systems, it has cloth surrounds, I found that if I fabricated a circular shield with a non reflective rubber neoprene caoting that when it was set up to cover the surround with the neoprene side facing the speaker there was a substantial improvement in the sound. Basically the whole thing sounded less congested and there was an improvement in the lower mids. It didn't help the bass of course but I didn't expect that either.
Likwise doping of paper cones on many full range drivers seems to bring about vast improvments in sound quality for a few reasons, but one of those I feel is it is less likely to re-vibrate in sympathy with the reflected sound waves when they hit the back of the cone, however I don't think this applies to bass reprduction. IN this case Bass reproduction is often improved just because the stiffer cone doesn't flex as much on long excursions.
Once again my experiments have shown me that damping the back of the box internally helps a lot in stopping the reflection in the first place, additionally having an angled false rear panel can diffuse the sound waves a bit so the bounce into the side walls before re-reflected to the back of the driver. I sure most of us are aware of this but its worht mentioning perhaps.
I imagine the design of the basket will cause some issues also, by its nature it presents a more restrictive path to the rear firing soundwaves and this must cause some reflection issues, one of the problems with some small full range drivers is the rear is almost strangled. I'd say that a small driver with its basket supported on small solid arms shaped in a teardrop cross-section rather than flat metal would work better but I have never seen such a driver.
Yep I reckon theres lots too work on and it is pretty much all vibration and reflection.
Absolutely in my opinion, I did some tests on one of my 4 inch full range driver systems, it has cloth surrounds, I found that if I fabricated a circular shield with a non reflective rubber neoprene caoting that when it was set up to cover the surround with the neoprene side facing the speaker there was a substantial improvement in the sound. Basically the whole thing sounded less congested and there was an improvement in the lower mids. It didn't help the bass of course but I didn't expect that either.
Likwise doping of paper cones on many full range drivers seems to bring about vast improvments in sound quality for a few reasons, but one of those I feel is it is less likely to re-vibrate in sympathy with the reflected sound waves when they hit the back of the cone, however I don't think this applies to bass reprduction. IN this case Bass reproduction is often improved just because the stiffer cone doesn't flex as much on long excursions.
Once again my experiments have shown me that damping the back of the box internally helps a lot in stopping the reflection in the first place, additionally having an angled false rear panel can diffuse the sound waves a bit so the bounce into the side walls before re-reflected to the back of the driver. I sure most of us are aware of this but its worht mentioning perhaps.
I imagine the design of the basket will cause some issues also, by its nature it presents a more restrictive path to the rear firing soundwaves and this must cause some reflection issues, one of the problems with some small full range drivers is the rear is almost strangled. I'd say that a small driver with its basket supported on small solid arms shaped in a teardrop cross-section rather than flat metal would work better but I have never seen such a driver.
Yep I reckon theres lots too work on and it is pretty much all vibration and reflection.
Hi all,
kind nunayafb,
thanks for your accurate analysis.
I see two separate arguments
one: "the vacuum " ; two : " cabinet reactions"
for the first point, we wait a answer by Critofur in form of drawing.
My skepticism is motived because I suspect a issue called
" acoustic-bridge ".
In a normal double-layer structure ( like rec studio, for example)
we have good solutions.
In this particular situation, I suspect the vacuum can be not
compatible. In others words, a good structural decoupling
obstruct a good vacuum.
This is my impression. Maybe I have missed something.
for the second point,
maybe I was not much clear :
The "whole movement" of the cabinet is not my trouble!
All my "bla bla bla" is about modal exitations of cabinet .
Aerial transmission and structural transmission.
This is not 50 and 50. Do you agree ?
Structural is our worst/biggest hostile . Do you agree?
What is our medicine?
Thanks to all for yours precious contribute .
Inertial
kind nunayafb,
thanks for your accurate analysis.
I see two separate arguments
one: "the vacuum " ; two : " cabinet reactions"
for the first point, we wait a answer by Critofur in form of drawing.
My skepticism is motived because I suspect a issue called
" acoustic-bridge ".
In a normal double-layer structure ( like rec studio, for example)
we have good solutions.
In this particular situation, I suspect the vacuum can be not
compatible. In others words, a good structural decoupling
obstruct a good vacuum.
This is my impression. Maybe I have missed something.
for the second point,
maybe I was not much clear :
The "whole movement" of the cabinet is not my trouble!
All my "bla bla bla" is about modal exitations of cabinet .
Aerial transmission and structural transmission.
This is not 50 and 50. Do you agree ?
Structural is our worst/biggest hostile . Do you agree?
What is our medicine?
Thanks to all for yours precious contribute .
Inertial
I however am not waiting for a drawing, I have contemplated vacuum paneled enclosures several times, both for speakers and for cold food storage(coolers). Just picture a box suspended inside of a box like he drew, the gap size is not crucial, 1 milimeter will perform the same as 1 meter. Now the inner box has to mount somehow, this could simply be a ring of wood around the speaker cutout, maybe a 1in larger radius. Since this is the only point of transmission the five other faces of the box will not be subjected to any force and therefore will not resonate. The baffle will however have to damp out a small amount of energy but this is true for any enclosure type.
We have a "lost in translation" problem here, Im not sure what you mean by double-layer structure, rec studio, and solutions?
In addition, how do you see a compatibility problem with vacuum here? Also I looked up the acoustic bridge and the only relevent hit was for measuring surface area, could you elaborate on this please.
The second point, the analysis had nothing to do with your statements.It was a response to some older posts, in fact the purpose was to show that you have to cross a threshold before box motion surpasses zero. In my opinion a properly designed enclosure will never move and panel resonance is the key issue. According to Loudspeaker Design Cookbook, bracing a panel doesnt reduce magnitude of vibration it simply raises the frequency of resonance. I didnt believe it when I read it but until I run my own tests I am going to assume it is true. It really illustrates the importance of proper bracing and damping though doesnt it?
nunayafb,
Lost in traslation? Sure , perdone my poor english.
about the first point,
rec-studios, normally are a inner room floating into another external room. Sometimes is sufficient a bad mounting of a 110volt intake
to compromise the isolation inner/external.
For analogy, "the little ring of wood" is the easy way through the
inner box ( that is vibes) transmit his movements to the external
box.
The story can will be different if you decoupling totally the two boxes
with Fr below your audio band. Sure you can. And the vacuum?
Am I wrong?
about second point, excuse me, I need a lot of time for translate.
Thanks for your reply,
Inertial
Lost in traslation? Sure , perdone my poor english.
about the first point,
rec-studios, normally are a inner room floating into another external room. Sometimes is sufficient a bad mounting of a 110volt intake
to compromise the isolation inner/external.
For analogy, "the little ring of wood" is the easy way through the
inner box ( that is vibes) transmit his movements to the external
box.
The story can will be different if you decoupling totally the two boxes
with Fr below your audio band. Sure you can. And the vacuum?
Am I wrong?
about second point, excuse me, I need a lot of time for translate.
Thanks for your reply,
Inertial
nunayafb,
about second point,
I have looked at book of Vance D.
If you look belove 100 Hz, you have -62 dB medium versus
- 78 dB medium. I think this is in good agree with the increase
of rigidity ( due to the bracing , I suppose).
My version is a bit old and in italian language, capitolo 5,
fig. 5.6 and 5.7
Rigidity is welcome!
Cheers,
Inertial
about second point,
I have looked at book of Vance D.
If you look belove 100 Hz, you have -62 dB medium versus
- 78 dB medium. I think this is in good agree with the increase
of rigidity ( due to the bracing , I suppose).
My version is a bit old and in italian language, capitolo 5,
fig. 5.6 and 5.7
Rigidity is welcome!
Cheers,
Inertial
A very interesting topic here, glad to see it getting some technical discussion on this forum. I have experimented with mounting drivers using rubber washers between the frame and screws, and have found that if you don't overtighten the screws, this seems to lower the vibration transmitted to the box by a good deal.
However, since the driver is in that case not rigidly coupled to the box, I wonder if it is 'rocking' back and forth more because of this, and if so, if that is creating more problems/distortion than was previously caused by the energy transmitted to the box walls?
Can it be that as in so many other areas of speaker design, we trade off one for the other (driver rocking vs. mechanical vibration transmitted to cabinet) and if so, how do we determine the best compromise between the two?
For example if one has a particularly dead enclosure with CLD panels, would one be better served by rigidly coupling the driver to the box so that the enclosure can dissipate most of that energy? And vice versa if the enclosure is a bit resonant or 'flexy' in the panels, would one be best served with a lossy coupling between driver/baffle so as to dissipate as much of that energy by friction rather than in the panels (where it may be audible)?
However, since the driver is in that case not rigidly coupled to the box, I wonder if it is 'rocking' back and forth more because of this, and if so, if that is creating more problems/distortion than was previously caused by the energy transmitted to the box walls?
Can it be that as in so many other areas of speaker design, we trade off one for the other (driver rocking vs. mechanical vibration transmitted to cabinet) and if so, how do we determine the best compromise between the two?
For example if one has a particularly dead enclosure with CLD panels, would one be better served by rigidly coupling the driver to the box so that the enclosure can dissipate most of that energy? And vice versa if the enclosure is a bit resonant or 'flexy' in the panels, would one be best served with a lossy coupling between driver/baffle so as to dissipate as much of that energy by friction rather than in the panels (where it may be audible)?
Thanks! I migth do a description of them later anf post some drawings. They are based on Seas 8" aluminum drivers (H.1208, 100 USD per driver) and IKEA (yepp, the furniture company) Blanda Blank (to keep food in) cost in sweden appr. 15 USD and plumming pipes (15USD).
Some expoxi glue + marine compund and thats it really.
I call them BBOLL and tahts a palindrome but so is also the design mechanically - compleatly symetrical and thus, vibration free - that's why I posted in this thread.
/
Some expoxi glue + marine compund and thats it really.
I call them BBOLL and tahts a palindrome but so is also the design mechanically - compleatly symetrical and thus, vibration free - that's why I posted in this thread.
/
panomaniac said:
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