I am a bit skeptical that any of the elaborate methods to absorb/diffuse the driver back wave have any real world benefit over the simple solution of just using acoustical absorption (fibrous stuffing and foams) in a simple box shaped cavity.
j.
j.
Yes. An infinite baffle is perfect, but not usually possible without some creativity.
mpdaudio, that reflector also reflects the midrange back on to the cone when it returns. You can have a standing wave that goes around a corner.
mpdaudio, that reflector also reflects the midrange back on to the cone when it returns. You can have a standing wave that goes around a corner.
As a I said in my initial description, the reflected sound goes into a heavily damped lower part of the cabinet to minimize further reflections.
Hello Krivium,
Thank you for the feedback. It is more a less where I am but always interesting to get new inputs. I will probably start some experiments with the Metisse coton wool to see if it can mitigate some effects...
As reading the posts after, I didn't kwon about Kef metamaterial. Here is a Kef Metamaterial AES paper
Christian
Hi Christian,
Yes experiment by yourself this is ime the only way to discover what you need/want.
Another approach is to use reflectors as mdpaudio presented, to redirect energy.
The size of reflector is linked to the lower freq of intended use here again... but it is very effective.
Why do you focus on absorbing? I mean it is the 'simpler' and most used technique ( because it is simple) but it's not a panacea. The main issue i have with it is linked to the fact that once you start putting absorbers people very often overtreat with it. And for a room to sound nice it have to be balanced between absorbing/diffusing/ reflecting. This have to be kept in mind. It can bring imbalance to te diffuse field too which in turn can bring it's own set of nastys.
I repeat try diffusors. If you find a Schroeder to be daunting to build other solution are possible: make a search for B.A.D. panels ( Binary Amplitude Diffusors). They use absorbsion and reflection to produce diffusion (!), don't take a lot of space and are effective in closer proximity than a typical Schroeder diffusor.
This have the other benefit to make our brain believe the room is bigger.
I always fear winter because my kids wants a christmas tree which is invariably located on one side of my stereo: it make some very effective diffusors! And i can hear it! ( next year i will impose two, one on each side... i will tell one for each kid! But in reality it will be to have symmetry in rendering!).
To give you the rule of thumb used to define the reflectors diffusor effectiveness:
For reflectors: the size ( width) of panel must be 3x the wavelength of the lower freq you want to treat: for 1khz lower freq you need 1m width panel ( 1khz wl~ 30cm)
For diffusors: the distance between you and the diffusor should be 3 time the lowest wavelength of efficiency ( if you are located 2m away from the diffusor it could act to approximately 550hz/600hz).
Bad panels are differents though but it is explained into their patent which is accessible if you search (there is everything you need into the patent to build one).
With absorbers the effectiveness depend of material of course but the angle of incidence of wave play a role too. And the distance ( too bad but true, you often loose much more from the distance the sound have to travel to bounce back than from the absorbsion by itself ( you loose 6db each time you double traveling distance)... why size does matter in acoustic).
Yes experiment by yourself this is ime the only way to discover what you need/want.
Another approach is to use reflectors as mdpaudio presented, to redirect energy.
The size of reflector is linked to the lower freq of intended use here again... but it is very effective.
Why do you focus on absorbing? I mean it is the 'simpler' and most used technique ( because it is simple) but it's not a panacea. The main issue i have with it is linked to the fact that once you start putting absorbers people very often overtreat with it. And for a room to sound nice it have to be balanced between absorbing/diffusing/ reflecting. This have to be kept in mind. It can bring imbalance to te diffuse field too which in turn can bring it's own set of nastys.
I repeat try diffusors. If you find a Schroeder to be daunting to build other solution are possible: make a search for B.A.D. panels ( Binary Amplitude Diffusors). They use absorbsion and reflection to produce diffusion (!), don't take a lot of space and are effective in closer proximity than a typical Schroeder diffusor.
This have the other benefit to make our brain believe the room is bigger.
I always fear winter because my kids wants a christmas tree which is invariably located on one side of my stereo: it make some very effective diffusors! And i can hear it! ( next year i will impose two, one on each side... i will tell one for each kid! But in reality it will be to have symmetry in rendering!).
To give you the rule of thumb used to define the reflectors diffusor effectiveness:
For reflectors: the size ( width) of panel must be 3x the wavelength of the lower freq you want to treat: for 1khz lower freq you need 1m width panel ( 1khz wl~ 30cm)
For diffusors: the distance between you and the diffusor should be 3 time the lowest wavelength of efficiency ( if you are located 2m away from the diffusor it could act to approximately 550hz/600hz).
Bad panels are differents though but it is explained into their patent which is accessible if you search (there is everything you need into the patent to build one).
With absorbers the effectiveness depend of material of course but the angle of incidence of wave play a role too. And the distance ( too bad but true, you often loose much more from the distance the sound have to travel to bounce back than from the absorbsion by itself ( you loose 6db each time you double traveling distance)... why size does matter in acoustic).
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Reversed horn? Let backside of driver play into the mouth of an exponential horn - open and damped throat...? There are (old?) patents on this...
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Yes, that's Terman's 'Sound Absorbing Apparatus' (US patent 2293181 granted 1942). It works well; generally the easiest approach however is simply (and by definition) a maximally flat impedance TL, which doesn't need to be more complicated than an open-ended rectilinear box, although you can do variations as desired of course.
TNT, the 'Dagger' member XRK used is not very different of what you purpose ( coupled to absorber material).
Xrk used a five side approach to not have axial symetry though ( less HOM if closed box ... if i can make a coarse shortcut).
Xrk used a five side approach to not have axial symetry though ( less HOM if closed box ... if i can make a coarse shortcut).
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It was my first reflex too but no, 3, 9, 15 ,... have axial symmetry: choose an angle, draw the tangent to the other facing side and you have two identical triangle: there is symetry).
5,7,11 don't have this.
5,7,11 don't have this.
Thanks again Krivium
I am not focusing on absorbing. I am at a step I collect possible solutions. In the absorbing family, you opened to the possibility of tests with the Metisse panel. This second post opens the branch of the diffusor solution. I am going to dig around B.A.D.
Christian
Christian,
Metisse is nice because it is clean to work with ( doesn't hitch) and the whole approach they have is win win ( recycling, giving job to reinsert people into society,...). But in no way it is cheap. Compare to rockwool.
If you want to experiment cheap Rockwool is your best bet ( the fiber are coarser than glassfiber so not as an health hazard and they don't hitch a lot when manipulated). And it can be used for basstrap if you want ( Metisse isn't as good for that matter).
For reflectors plasterboard ( placoplatre). Ba10 is sufficient but britlle. Ba13 is ok and cheap. Cut it with a knive and it is clean.
For diffusors try christmas trees. They'll give you the effect without anything to do and won't pollute. And don't cost a lot. I'm not joking it is effective ( but random, diffusors based on math sequence have a pattern. It might or not be an adantage).
Metisse is nice because it is clean to work with ( doesn't hitch) and the whole approach they have is win win ( recycling, giving job to reinsert people into society,...). But in no way it is cheap. Compare to rockwool.
If you want to experiment cheap Rockwool is your best bet ( the fiber are coarser than glassfiber so not as an health hazard and they don't hitch a lot when manipulated). And it can be used for basstrap if you want ( Metisse isn't as good for that matter).
For reflectors plasterboard ( placoplatre). Ba10 is sufficient but britlle. Ba13 is ok and cheap. Cut it with a knive and it is clean.
For diffusors try christmas trees. They'll give you the effect without anything to do and won't pollute. And don't cost a lot. I'm not joking it is effective ( but random, diffusors based on math sequence have a pattern. It might or not be an adantage).
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AllenB
There isn't yet a project in plan... but this kind of stuff keeps me awake on the highway (autobahn)
Excellent.
The ideal is the infinite baffle where sound goes and never comes back, an abyss. You can emulate this in a more practical box by creating your own losses.
The ideal is the infinite baffle where sound goes and never comes back, an abyss. You can emulate this in a more practical box by creating your own losses.
Redirecting doesn't make the energy go away, it isn't a loss.
We agree Allen but the quote was aimed at room acoustic not what happen within a box.
It is the same principle than BBC's C.I.D. or RFZ implemented using complex room shape rather than absorbers i talk about.
The incidental loss comes from distance sound have to travel ( and if there is diffusors implemented to receive the 'redirected' wave you can make them non specular at same time).
https://images.app.goo.gl/oSzAArMM9x1NGM8q9
It is the same principle than BBC's C.I.D. or RFZ implemented using complex room shape rather than absorbers i talk about.
The incidental loss comes from distance sound have to travel ( and if there is diffusors implemented to receive the 'redirected' wave you can make them non specular at same time).
https://images.app.goo.gl/oSzAArMM9x1NGM8q9
It finds specific use in a real room, based on audibility.
However in theory it still isn't minimum phase interaction. It can also permit modal behaviour. Like similar situations, damping can become necessary.
Yes it still is but much less than a typical control room treatment.
It was the initial motivation of Robert Walker: less amount of damping to have a more user friendly environment. Worth a read and regularly used technic in 'new school' approach to control room treatments (iv'e seen pictures of T.JouanJouan's room ( northward acoustic) where he used this principle for freestanding loudspeakers. Easy to identify as front wall have a particular shape)..
Like this:
https://images.app.goo.gl/R1UBBtdCdXEkNgQ47
It was the initial motivation of Robert Walker: less amount of damping to have a more user friendly environment. Worth a read and regularly used technic in 'new school' approach to control room treatments (iv'e seen pictures of T.JouanJouan's room ( northward acoustic) where he used this principle for freestanding loudspeakers. Easy to identify as front wall have a particular shape)..
Like this:
https://images.app.goo.gl/R1UBBtdCdXEkNgQ47
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I suppose, absorb it, either down an acoustical-impedance matched transmission-line, or possibly within an A.R. Bailey style acoustic-labyrinth. The two not being the same. In Bailey’s article, within the October, 1965 issue of Wireless World, it interestingly depicts a closed box, filed with a series of differently sized internal baffles, reminiscent of a car muffler except without an exit. Which are intended to reflect the driver’s back waves internal to the enclosure, until they are finally absorbed (dissipated to heat). I never experimented with his design to gain understanding of it’s effectiveness.