I've read and received a lot of advice about stuffing or lining a speaker cabinet. Some positive some negative. I've also read a lot about materials that should be used. This leads me to my question.
I happen to have a large amount of perforated foam laying around. The kind you can tear out square pieces to form a shape around an object, usually for shipping or storage. My question is would this be suitable to line the interior of a box with. If so are their any suggestions on what to do and not to do?
I'll include a pic of the foam for reference. Thanks!
I happen to have a large amount of perforated foam laying around. The kind you can tear out square pieces to form a shape around an object, usually for shipping or storage. My question is would this be suitable to line the interior of a box with. If so are their any suggestions on what to do and not to do?
I'll include a pic of the foam for reference. Thanks!
Can you blow through it? (Open cell)
Will the 1" squares come loose and jam the back of the cone? (You can try burlap around the frame.)
My own preference is wool; old blankets and socks. But mostly-wool is getting hard to find free. Most "wool" is largely adulterated with Orlon and such, which is not the same. You can tell if it is some-wool by burning a scrap for burnt-hair smell. You can tell large plastic content by burning making a very sooty flame.
Will the 1" squares come loose and jam the back of the cone? (You can try burlap around the frame.)
My own preference is wool; old blankets and socks. But mostly-wool is getting hard to find free. Most "wool" is largely adulterated with Orlon and such, which is not the same. You can tell if it is some-wool by burning a scrap for burnt-hair smell. You can tell large plastic content by burning making a very sooty flame.
For what it's worth, my limited experience with foam which in my case was the type of foam used in mattresses which I guess is an "open cell" is that it didn't work well at all for a bass box I built.
I go to Goodwill and look for old wool sweaters. Ugly green ones and such. Buy them for $1 and cut them into pieces for stuffing.
I normally use the ' hollowfibre ' stuffing from old pillows and duvets ,seems to work as well as the expensive ' pro ' material and for the actual cabinets themselves noise reduction panels from car accessory outlets.
What I have found quite effective is the fibrous cotton material used as the under-linning for carpet in cars. It is a tight mixture of cotton waste material compacted to form a mat about 1/2 inch in width. A couple layers is all that is needed and it is not at all expensive to implement.
C.M
C.M
What type / size of enclosure? That might well factor in to the choice of damping schemes and materials. Search the forums for recent posts by Earl Geddes on the subject.
I like to use a product called UltraTouch for lining of cabinet walls. It's 1/2" thick recycled denim fibre. For loose fibre fill, I think the consensus is that Acoustic-Stuff is at least the equal to carded lambswool.
I like to use a product called UltraTouch for lining of cabinet walls. It's 1/2" thick recycled denim fibre. For loose fibre fill, I think the consensus is that Acoustic-Stuff is at least the equal to carded lambswool.
I can't remember the exact equation. but in general, lining a box with rubbery foam only affects frequencies above a 1/4 of the wavelength of the foam thickness.
At 3kHz, a quarter wavelength is about 2.5cms. So really you will just be damping the upper harmonics of voices or a guitar. This IS worth doing IMO. A less peaky sound on the upper midrange.
This is called volume damping. It is quite separate from cabinet damping. Cabinet damping is about stopping the wooden sides rattling. Which is done by sticking heavy rubbery stuff to the panels.
Interesting read I found on Lossy Cabinet designs by Harbeth
The third option, which mainly applies to closed box designs, is filling the whole flippin' volume with heavy fibres. This works much lower in frequency. It's a realistic option for high, tall cabinets which might otherwise have some horrible resonant standing waves on the long axis.
At 3kHz, a quarter wavelength is about 2.5cms. So really you will just be damping the upper harmonics of voices or a guitar. This IS worth doing IMO. A less peaky sound on the upper midrange.
This is called volume damping. It is quite separate from cabinet damping. Cabinet damping is about stopping the wooden sides rattling. Which is done by sticking heavy rubbery stuff to the panels.
Interesting read I found on Lossy Cabinet designs by Harbeth
The third option, which mainly applies to closed box designs, is filling the whole flippin' volume with heavy fibres. This works much lower in frequency. It's a realistic option for high, tall cabinets which might otherwise have some horrible resonant standing waves on the long axis.
Steve - note that following the wonderful contribution to the DIY arena by Martin King, the action of those standing wave resonances are taken well into account in some vented enclosure designs. I'm living with a couple of pairs of them now.
That is brilliant. Cheap wool, recycling, and ridding the world of ugly sweaters by destroying them and hiding the evidence in speakers. 🙂 +1
What are we trying to achieve here. Are we fixing the cabinet or adjusting the speaker response?
Sound waves have to move through the filing material to dampen their movement. The filing needs to be at least in the center for this. There is no wave movement at the walls.
Adding a coating or a layer onto the speaker walls can dampen speaker wall vibrations or radiation from the walls.
Sound waves have to move through the filing material to dampen their movement. The filing needs to be at least in the center for this. There is no wave movement at the walls.
Adding a coating or a layer onto the speaker walls can dampen speaker wall vibrations or radiation from the walls.
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True enough Don - the fun comes in trying to locate loose fibrous material to only the centre of enclosure. If the box is large enough, it helps if there's at least a couple of stick braces to which the material can be adhered.
What I understand as to why low frequencies are poorly attenuated within a damping material in a box is due to the way sound is propagated through air. At low frequencies sound waves essentially propagate as a pressure wave whereas at the higher frequencies the propagation has transistioned into a velocity wave. Low frequency sound confined within an enclosed box actually causes changes in pressure (amplitude) within the damping material with little friction with the fibres of the material. Whereas, at the higher frequencies there is a velocity change in the waveform and this causes much more friction within the fibres as the fibre length is more akin to wavelength. It is the lower midrange that seems to be most impacted audibly by this containment of sound within a box.
So different approaches are needed to attenuate the sound trapped within a box for different ranges of frequencies. For lower frequencies, maybe no box at all (i.e an OB) or maybe a small, rigid box with low frequency equalization. For the rest of the system from low to midrange + tweeter possibly a separate box with heavy damping material or an open baffle. Finding the right amount of damping material needed is experimental and requires some listening time to optimize.
C.M
So different approaches are needed to attenuate the sound trapped within a box for different ranges of frequencies. For lower frequencies, maybe no box at all (i.e an OB) or maybe a small, rigid box with low frequency equalization. For the rest of the system from low to midrange + tweeter possibly a separate box with heavy damping material or an open baffle. Finding the right amount of damping material needed is experimental and requires some listening time to optimize.
C.M
But there is movement a short distance from the walls. All that is required is for a suitably dense (and fairly thick) material to be used to line the cabinet walls. Density should be progressively be reduced as you move away from the walls - in an ideal world. In practice, you'll have something like thick felt lining the walls, and traditional stuffing material filling the cabinet (assuming a closed box).
Think about a room with bare walls and solid floor. Now add a nice thick carpet, and wall coverings, such as Persian carpets, drapes or tapestries. You'll find a huge difference in the room acoustics.
I agree with you that adding materials to the walls and floor can reduce reflections. There are 2 different effects taking place here (reflection + transmission) and 2 different fields (near and far).
The room is far field and reflections / diffractions are taking place off the walls and furniture. The surface absorption is freq dependent and can be relatively low maybe 20-30% and most of the energy (80%) just bounces off. It makes a difference but you still hear most of the sound. More importantly the reverb time is reduced as it looses energy on each bounce.
Compare that to being on the other side of the wall, especially when it has insulation, and sound has to transmit though it. Maybe 1% of the sound will get through a well insulated wall. Same goes for acoustic tile in a ceiling, some is absorbed but you still hear sound in the room. Go on the other side of that acoustic tile and you'll hear alot less. So putting the filling in the center of the cabinet forces the wave to transmit through it and attenuate more.
I tried a few experiments, with a cabinet that had a strong reflection from the bottom. I used an acoustic tile with a published characteristic to attenuate my reflection freq by -30db. The tile was place on the bottom and it made a measurable but tiny difference. Stuffing in the middle worked, as the wave was forced to move through it (transmission) not just bounce off it (reflection). A tile in the middle is too dense and just caused the reflection point to move to the middle, but I'm sure the sound in the space below the tile was reduced.
The room is far field and reflections / diffractions are taking place off the walls and furniture. The surface absorption is freq dependent and can be relatively low maybe 20-30% and most of the energy (80%) just bounces off. It makes a difference but you still hear most of the sound. More importantly the reverb time is reduced as it looses energy on each bounce.
Compare that to being on the other side of the wall, especially when it has insulation, and sound has to transmit though it. Maybe 1% of the sound will get through a well insulated wall. Same goes for acoustic tile in a ceiling, some is absorbed but you still hear sound in the room. Go on the other side of that acoustic tile and you'll hear alot less. So putting the filling in the center of the cabinet forces the wave to transmit through it and attenuate more.
I tried a few experiments, with a cabinet that had a strong reflection from the bottom. I used an acoustic tile with a published characteristic to attenuate my reflection freq by -30db. The tile was place on the bottom and it made a measurable but tiny difference. Stuffing in the middle worked, as the wave was forced to move through it (transmission) not just bounce off it (reflection). A tile in the middle is too dense and just caused the reflection point to move to the middle, but I'm sure the sound in the space below the tile was reduced.
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Low frequencies don't move through the stuffing material of a box as their wavelengths are too long for the dimensions of a typical box, they just pressurize the box. Thus the stuffing material is ineffective at low frequencies. Upper midrange frequencies whose wavelengths are short enough to allow propagation (movement of the wave) within the dimensions of the box encounter friction within the fibres or the used material and thus a noticable attenuation.To attenuate the lower midrange frequencies where the audible problem lies one needs a suitably large box to accommodate those wavelengths so propagation can take place, or for at least a 1/2 wavelength. When that is achieved the stuffing will work as it should.The lower midrange should start around 300c/s which would give a wavelength of 45 inches, so a halfwave length is 22.5 inches thus a box 24 inches wide externally and with stuffing would give a nice sounding loudspeaker.
C.M
C.M
Disagree about your differentiation between "reflection" and "transmission". Both locations of absorptive material will cause reduction in the reflected wave by absorption. The material next to the wall just needs to match the low-velocity/high-pressure nature of the wave, and the material further away from the wall needs to match the high-velocity/low-pressure nature.
Hence the use of dense felt to line the walls, and significantly less dense stuffing for the rest of the cabinet.
In my example of the room with carpets, the carpets are not somehow treating the hard surface so that it reflects less, they are attenuating sound waves just before they hit the hard surface, and just after they leave.
What I have found.
So I will answer with what I have found, understanding this is an old thread. But bear with me. 2 very different sets of speakers. A set of Micca MB42 and BestBuy brand Insignia NS-SP213 5.25 2 way speakers.
I will start with the Micca's. This speaker originally came with a single capacitor that allowed the woofer to run full range and cutoff the tweeter somewhere around 5500hz. This created undesirable sounds at mid/high volumes. We had a hot summer so I had AC panel foam from walmart. I did 2 things. I ordered a cheap crossover from Amazon and installed it. While the boxes were open I cut the foam up and lined the inside of the box. This changed the character of the speaker entirely! The woofer now crossed with the tweeter at 3500hz and put a much needed 2 ohm resister on the tweeter side to help keep it from running away as soon as real power was applied. So now the foam gave a very drastic effect. The enclosures are roughly 0.08 cu.ft. and are tuned by BTC specs on android, at around 57hz. Bass was kind of sloppy sounding, not very tight. After putting the foam in the speaker had very tight punchy bass. Very distinct. It helped that now I could now drive them without the tweeter going way out of control.
So now I decided to check over the Insignias which were a steal when I bought them at 60 dollars on clearance around 2011 or so. These were always really good sounding, although the bass suffered the same sloppiness that plagued the Micca MB42's. I was surprised to see a real 2 way crossover installed. So I lined these speakers with the foam and put them back together. These speakers are now my favorite speakers. They are so balanced and the the tweeters are perfectly matched. They are voiced just right. I have them hooked to my Yamaha Avantage amp in the living room.
I am building a new set of speakers built around Daytons Aluminum dome midrange. And when these panels finally get in, will 100% be using them to clean the bass up in the enclosures.
So I will answer with what I have found, understanding this is an old thread. But bear with me. 2 very different sets of speakers. A set of Micca MB42 and BestBuy brand Insignia NS-SP213 5.25 2 way speakers.
I will start with the Micca's. This speaker originally came with a single capacitor that allowed the woofer to run full range and cutoff the tweeter somewhere around 5500hz. This created undesirable sounds at mid/high volumes. We had a hot summer so I had AC panel foam from walmart. I did 2 things. I ordered a cheap crossover from Amazon and installed it. While the boxes were open I cut the foam up and lined the inside of the box. This changed the character of the speaker entirely! The woofer now crossed with the tweeter at 3500hz and put a much needed 2 ohm resister on the tweeter side to help keep it from running away as soon as real power was applied. So now the foam gave a very drastic effect. The enclosures are roughly 0.08 cu.ft. and are tuned by BTC specs on android, at around 57hz. Bass was kind of sloppy sounding, not very tight. After putting the foam in the speaker had very tight punchy bass. Very distinct. It helped that now I could now drive them without the tweeter going way out of control.
So now I decided to check over the Insignias which were a steal when I bought them at 60 dollars on clearance around 2011 or so. These were always really good sounding, although the bass suffered the same sloppiness that plagued the Micca MB42's. I was surprised to see a real 2 way crossover installed. So I lined these speakers with the foam and put them back together. These speakers are now my favorite speakers. They are so balanced and the the tweeters are perfectly matched. They are voiced just right. I have them hooked to my Yamaha Avantage amp in the living room.
I am building a new set of speakers built around Daytons Aluminum dome midrange. And when these panels finally get in, will 100% be using them to clean the bass up in the enclosures.
Not an expert but why do you stuff the line in a TL enclosure!
To stop the HF and allow the LF thru 🙂
So my monies with the voices that say stuffing only significantly affects the mid and high Hz's...
As for carpet, old sweater or foam, well i used some cushion filler in my last pair of TL's and tweaked the amount until it sounded ok.
Am about to try same on pair of 9lt sealed unit for the DQ40TZF-02 i just completed.
As for sticking foam I use Double Sided tape.
To stop the HF and allow the LF thru 🙂
So my monies with the voices that say stuffing only significantly affects the mid and high Hz's...
As for carpet, old sweater or foam, well i used some cushion filler in my last pair of TL's and tweaked the amount until it sounded ok.
Am about to try same on pair of 9lt sealed unit for the DQ40TZF-02 i just completed.
As for sticking foam I use Double Sided tape.