Hello.
I am really puzzled about acoustical materials like foam on walls, polyfil or other materials, that supposed to remove standing waves from enclosure.
I tried reading lots of threads about it, but I never succesfuly reached decision what to do 😕
I am building little ported subwoofer with 8" driver. Box will have 20L (0.71cu ft) It will not play higher than 90hz. Do i need anything on walls?
I am really puzzled about acoustical materials like foam on walls, polyfil or other materials, that supposed to remove standing waves from enclosure.
I tried reading lots of threads about it, but I never succesfuly reached decision what to do 😕
I am building little ported subwoofer with 8" driver. Box will have 20L (0.71cu ft) It will not play higher than 90hz. Do i need anything on walls?
Where did you find the directions for your box ? As a general rule in a ported box you just use damping on 2 walls. The rules change when using a sealed box where you may almost fill the box because here you don't just kill standing waves all the damping material will also make the box look as if the volume is larger.
I don't recall ever seeing a manufacture damping only two walls in a ported box. Whereabouts did this "General Rule" come about?
It was very common over the years to have only one of each opposing side damped. (3 walls in total)
Valtra, If 90 Hz is the highest the woofer will be going then the typical materials used for damping aren't going to have much if any effect so try it both ways and see which you like.
Valtra, If 90 Hz is the highest the woofer will be going then the typical materials used for damping aren't going to have much if any effect so try it both ways and see which you like.
You want to conceal all box sounds including that precious resonance that your sim so carefully cultivated mathematically so as to get a flat output curve. So go to your local dry-goods store and ask for pillow stuffing and stuff the whole box lightly. That's the way Rudy Bozak always did it and everybody gushed over the sound of his speakers*.
Will your output droop, just as the sim predicts? Maybe so, but your sound will be better.
In light of these thoughts, would it not be correct to say the sim is wrong? Wouldn't it be logical to start with a sim that assumes you want to stuff the whole box?
Ben
*From Wikipedia,"Rudy Bozak was not in favor of using ports or vents to tune loudspeaker enclosures for greater low-frequency output from a smaller box. He was a purist; he felt that the impulse and transient response of ported designs was inferior and that the augmented bass was too boomy."
Will your output droop, just as the sim predicts? Maybe so, but your sound will be better.
In light of these thoughts, would it not be correct to say the sim is wrong? Wouldn't it be logical to start with a sim that assumes you want to stuff the whole box?
Ben
*From Wikipedia,"Rudy Bozak was not in favor of using ports or vents to tune loudspeaker enclosures for greater low-frequency output from a smaller box. He was a purist; he felt that the impulse and transient response of ported designs was inferior and that the augmented bass was too boomy."
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I am rebuilding logitech z-2300 subwoofer. I am getting rid of integrated amplifier. And original box had too much leaks. I really liked how it sounded in original system, so now i decided to repurpose it to use with my speaker system. New box will get rid of all leaks, and have port and woofer on same wall.
Original box don't have anything on walls. It is bare wood. So i don't know if it was because of cost cutting, or damping is not needed. Like i said it sounded very good, without any problems or resonances.
Filling the box with fibers will convert the bassreflex ( deeper bass but poorer transient response) to a closed box with a large leak, not that useful. I see no point in having damping material in a subwoofer.
Thank you all for help.
I decided not to put anything.
But one more question, which is very unclear for me 😀
How eggcrate open cell foam affect volume that woofer see in ported design? Reduce it? Enlarge it?😕
I decided not to put anything.
But one more question, which is very unclear for me 😀
How eggcrate open cell foam affect volume that woofer see in ported design? Reduce it? Enlarge it?😕
It should enlarge it some. As the speaker cone moves in the air pressure goes up some. Any time you compress a gas it heats up some making it even harder to compress. The added thermal mass of the damping material minimize this effect. There is a fancy term
for this.
for this.
I know I've seen bjorno post a rather large mathematical breakdown for stuffing in enclosures, and his opinion at the time was that it's always necessary for hifi applications. Whether that was restricted to just the design we were talking about at the time, I do not know. Personally, I've always found stuffing / lining absolutely required.
My latest cabs are actually sporting carpet pad lining, which seems to work rather nicely.
My latest cabs are actually sporting carpet pad lining, which seems to work rather nicely.
The rule is quite simple: stuffing a closed box has benefits. It introduces losses to ported box so it has to be avoided there. Dampening the walls or bracing is beneficial for both types in order to reduce unwanted resonances.
Hi Ben. It would be 100 percent incorrect to say the sim was wrong. It would be very correct to say the user used the simulator wrong.
As I've pointed out to you 3 or 4 dozen times a simulator doesn't suggest an alignment, the user is in control. There's no requirement that says a flat response is best, in fact it's usually not a good idea. It sounds like Bozak made a badly designed ported box and had to fix it with stuffing. What he was hearing was a bad frequency response, not bad impulse or transient response.
It's trivially easy to design a ported box that has the exact same frequency response as a sealed box, and when you listen to them blind you will not be able to tell which is which until the volume level gets high enough that the sealed box falls on it's face and the ported box has plenty of output left.
Resonant alignments often benefit from a very small amount of stuffing or lining to clean up the higher frequency harmonics but if the box requires stuffing throughout it was designed wrong.
One more note about this. Your beloved K-horn, the cornerstone and foundation of your system, like all front loaded horns, is just a bandpass box with a very large expanding port. The entire output of your horn is a series of undamped spiky resonances. If it wasn't for resonances your horn would have no output at all, the entire output is resonant.
In this light, your unrelenting war against resonance is both confusing and amusing.
How much stuffing is in your highly resonant K-horn? Why is resonant output ok in your horn but not ok in every other design on the face of the earth? Tapped horns are bad, ported boxes are bad, but a badly designed antique K-horn that produces the same "bad" resonances is good?
Luckily, "to stuff or not to stuff" is a very simple affair that requires only a few dollars / minutes to check out.
I always use the amount that I've always used, which granted isn't much (for subs) but should the mood strike me to check it out, I could have it out and re-measured in about 15 minutes.
Stuffing is pretty non-committal, tbh, since it's fairly obvious that a consensus will probably not happen in this thread, the best advice would probably be "try it both ways".
I always use the amount that I've always used, which granted isn't much (for subs) but should the mood strike me to check it out, I could have it out and re-measured in about 15 minutes.
Stuffing is pretty non-committal, tbh, since it's fairly obvious that a consensus will probably not happen in this thread, the best advice would probably be "try it both ways".
Thank you all. I am getting lots of useful information.
So it is nearly impossible to predict how putting something on walls will affect volume that driver see? So if one decides to put some damping on ported enclosure walls, only way is trial and error?
Because if box is designed to have theoretical flat response without anything inside, when foam put in, volume seen by driver will increase, like someone said, and goodbye precisely tuned box? Only way i see, is to build box calculated size and leave some corner for wood block or something to reduce volume depending on measurements till flattest response is achieved. I hope foam on walls won't actualy reduce volume, because then it is really bad, because box would become too small. 🙁
So it is nearly impossible to predict how putting something on walls will affect volume that driver see? So if one decides to put some damping on ported enclosure walls, only way is trial and error?
Because if box is designed to have theoretical flat response without anything inside, when foam put in, volume seen by driver will increase, like someone said, and goodbye precisely tuned box? Only way i see, is to build box calculated size and leave some corner for wood block or something to reduce volume depending on measurements till flattest response is achieved. I hope foam on walls won't actualy reduce volume, because then it is really bad, because box would become too small. 🙁
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