So, I have a WtmW speaker with front ports. I managed to walk out the ports with a screwdriver handle and stuffed them with 2 tightly rolled up socks.
The bass sounds like it rolls off at a higher frequency and has a little too much gain, but not quite boxy or resonant. I will have to play with the vent stuffing.
What strikes me is the sort of disembodied rumble that would normally accompany the music is gone (not like peaking, but just how it sounded). The bass that is left still goes acceptably low but now it stops and starts abruptly and sounds more like a component of the instruments.
Speaker excursion seems to have increased, although I could be completely wrong about that not having made any comparisons. It does sound like I may be getting distortion from excursion now. I'll see if I can change the effect with vent stuffing.
The bass sounds like it rolls off at a higher frequency and has a little too much gain, but not quite boxy or resonant. I will have to play with the vent stuffing.
What strikes me is the sort of disembodied rumble that would normally accompany the music is gone (not like peaking, but just how it sounded). The bass that is left still goes acceptably low but now it stops and starts abruptly and sounds more like a component of the instruments.
Speaker excursion seems to have increased, although I could be completely wrong about that not having made any comparisons. It does sound like I may be getting distortion from excursion now. I'll see if I can change the effect with vent stuffing.
Not teaching anyone so wind your neck in!!
Suggest you "suck it and see" if you are not prepared to work to the guidelines, originally suggested by North Creek Audio. Both the designs I have build, both single and dual chamber measure as expected and as advised by North Creek..
Don't know of any simulation programmes that can plot this for you and it will depend on many factors, including amount and type of stuffing.
So go build and measure for yourself and don't expect others to do the work for you. Get a DATs and measure it yourself...I only offered guidelines which you are welcome to ignore....
That post was made on the 20 December 2017, and the last one on this thread was 26 May 2018, so presumably necks have had much better things to be doing in the intervening two years. Either way, reactivating a thread that has lain fallow since late spring 2018, apparently to object to comments made six months before that, does not seem very productive.
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Guys, I'm going to resurrect this thread. Not because I have any interesting science to discuss about the aperiodic enclosure but because I have found an easy way to make a pretty good aperiodic vent that is easy to adjust and experiment with.
I think that a lot of guys are not interested in this approach to cabinet design because they prefer the extra amount of bass that is contributed by the ported vent. And if that is what they like, then that is the kind of cabinet that they should build.
I have found the the improvement in transient response in the bass also translates into some improved naturalness in sound and timbre in the lower mid-bass and midrange. Also, the well designed aperiodic enclosure does not call attention to itself unless the bass is really there in the music. This is not the best selling point for a commercial speaker which needs to sound like it has good bass on the showroom floor.
Anyway, this is how I made the last aperiodic vent and it worked pretty well.
You need some aluminum sheet 1/8 to 1/4 inch thick. You will be drilling 4-6 holes around the outer edge to screw this plate with drilled holes in it to the back of the speaker cabinet. I will not go into the sizing of the holes or how big the plate is because it depends on the cabinet and the drivers. Basically, the more cone area you have the more vent area you need, but it always must be quite a bit less than the cone area.
So the aluminum plate it then drilled with many holes like a speaker grill but spaced out enough to keep
some strength to the plate. Then you place it on the back of the cabinet in the place you want and use it as a template to route out an area the same depth as the plate. This is optional but makes it easier to capture the vent material in place. It can also be surface mounted
if the cabinet material is not very thick.
After you route out the area, screw the plate to the cabinet and use it as a template to drill out the holes in the cabinet in all of the little holes in the plate. Except the one you are using to hold the plate to the cabinet of course.
You can experiment with different materials and squeeze them to different amounts to get the right resistance you need.
I found that coffee filters can work pretty well. Pretty resistive so I just used one for that speaker. You can use just one or a couple or use that piece of 1 inch fiberglass you have around from those old speakers you tore apart. Or maybe you have a better idea on what to use than I do.
Thin hobby felt come to mind and can be easily layered.
I think that a lot of guys are not interested in this approach to cabinet design because they prefer the extra amount of bass that is contributed by the ported vent. And if that is what they like, then that is the kind of cabinet that they should build.
I have found the the improvement in transient response in the bass also translates into some improved naturalness in sound and timbre in the lower mid-bass and midrange. Also, the well designed aperiodic enclosure does not call attention to itself unless the bass is really there in the music. This is not the best selling point for a commercial speaker which needs to sound like it has good bass on the showroom floor.
Anyway, this is how I made the last aperiodic vent and it worked pretty well.
You need some aluminum sheet 1/8 to 1/4 inch thick. You will be drilling 4-6 holes around the outer edge to screw this plate with drilled holes in it to the back of the speaker cabinet. I will not go into the sizing of the holes or how big the plate is because it depends on the cabinet and the drivers. Basically, the more cone area you have the more vent area you need, but it always must be quite a bit less than the cone area.
So the aluminum plate it then drilled with many holes like a speaker grill but spaced out enough to keep
some strength to the plate. Then you place it on the back of the cabinet in the place you want and use it as a template to route out an area the same depth as the plate. This is optional but makes it easier to capture the vent material in place. It can also be surface mounted
if the cabinet material is not very thick.
After you route out the area, screw the plate to the cabinet and use it as a template to drill out the holes in the cabinet in all of the little holes in the plate. Except the one you are using to hold the plate to the cabinet of course.
You can experiment with different materials and squeeze them to different amounts to get the right resistance you need.
I found that coffee filters can work pretty well. Pretty resistive so I just used one for that speaker. You can use just one or a couple or use that piece of 1 inch fiberglass you have around from those old speakers you tore apart. Or maybe you have a better idea on what to use than I do.
Thin hobby felt come to mind and can be easily layered.
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Depends how you define information as it wasn't an overly precise derivation; you should be able to find it on-line. However, to forshorten, they used a small driver sub-chamber sized per the standard acoustic suspension Vb alignment, then resistively vented to a larger secondary volume, usually aiming for an overall system Q lurking somewhere between Butterworth and about 1.1, according to personal taste.
Yes. If you are using the staggeringly expensive scan speak acoustic resisters, one for cabinets up to around 40 litres. 40-80+, two per cabinet.
Not an exact science. Start with drivers with a relatively high qts, certainly above .35 and decent excursion. The original Dynaudios used the 10" Seas drivers, long gone. Peerless sls 10 and 12 are good drivers for this application.
For measured results used Dats software which will give you the impedance curve, the qts and fs, etc. Adjust stuffing amount to tune to qts of around .7...
A simple "ported" to atmosphere gives you around a 15db/octave roll off and not the same power handling as the dual chambered aperiodic cabinet design but does have the "advantage" of utilising a small cabinet volume. To establish cabinet volume, design for a qts of around 1.2 assuming a sealed cabinet. Your qts will drop of course with the damped port.
The twin chambered aperiodic is a very good way of achieving superb bass performance but comes at the cost of a large cabinet. Always a good thing for bass!! You split the cabinet internally into two chambers. The smaller one is around 1/3rd the vas of the driver. The driver is loaded into this one, benefits include a non symmetrical small cabinet which is great for mid reproduction. The small cabinet is "ported" using the acoustic resister into the larger chamber which is between .75 and 1 x the driver vas.
Loading this way gives you the 12 db/oct roll off of a sealed cabinet and an f3 approaching the fs of the driver. Superb, damped, great power handling, optimised mid range cabinet, low group delay associated with sealed box.
But a big box....
Not an exact science. Start with drivers with a relatively high qts, certainly above .35 and decent excursion. The original Dynaudios used the 10" Seas drivers, long gone. Peerless sls 10 and 12 are good drivers for this application.
For measured results used Dats software which will give you the impedance curve, the qts and fs, etc. Adjust stuffing amount to tune to qts of around .7...
A simple "ported" to atmosphere gives you around a 15db/octave roll off and not the same power handling as the dual chambered aperiodic cabinet design but does have the "advantage" of utilising a small cabinet volume. To establish cabinet volume, design for a qts of around 1.2 assuming a sealed cabinet. Your qts will drop of course with the damped port.
The twin chambered aperiodic is a very good way of achieving superb bass performance but comes at the cost of a large cabinet. Always a good thing for bass!! You split the cabinet internally into two chambers. The smaller one is around 1/3rd the vas of the driver. The driver is loaded into this one, benefits include a non symmetrical small cabinet which is great for mid reproduction. The small cabinet is "ported" using the acoustic resister into the larger chamber which is between .75 and 1 x the driver vas.
Loading this way gives you the 12 db/oct roll off of a sealed cabinet and an f3 approaching the fs of the driver. Superb, damped, great power handling, optimised mid range cabinet, low group delay associated with sealed box.
But a big box....
Ok, thanks, was hoping that their work would reveal more info than what I’d found already.
I have some great sounding speakers, Dahlquist DQ8, that use that two-chambered approach. The two chambers are merely a common volume with a panel of open cell foam functioning as a divider. The outlet to atmosphere is a 2” X 5” port.
I have some ideas for a pair of smaller (.3 cubic feet) sized woofer cabinets, am considering the Tang Band W8-2282, shallow 8” for these, have a qts of .66, plenty of excursion, and a max power rating of 400w each.
My vent plan is to use a block of open cell foam (or felt, etc.) under the driver, followed by a replaceable aluminum panel with breather holes. The remainder of the box would be filled with fiber material. The boxes would be made to fit underneath the front seats, and have three studs anchored to the floor to attach them. That would allow for a means to level the boxes, provide an air gap for the vents, as well as control the coupling/isolation to the car via rubber washers. These could also hopefully be tuned for use under a couch if the effect is just too much in the car.
It may be worth getting something set up to use to measure both the sound, and impedance, then keep fiddling until I can achieve something that is a balance between extended lower frequency, flatter peak.
I have some great sounding speakers, Dahlquist DQ8, that use that two-chambered approach. The two chambers are merely a common volume with a panel of open cell foam functioning as a divider. The outlet to atmosphere is a 2” X 5” port.
I have some ideas for a pair of smaller (.3 cubic feet) sized woofer cabinets, am considering the Tang Band W8-2282, shallow 8” for these, have a qts of .66, plenty of excursion, and a max power rating of 400w each.
My vent plan is to use a block of open cell foam (or felt, etc.) under the driver, followed by a replaceable aluminum panel with breather holes. The remainder of the box would be filled with fiber material. The boxes would be made to fit underneath the front seats, and have three studs anchored to the floor to attach them. That would allow for a means to level the boxes, provide an air gap for the vents, as well as control the coupling/isolation to the car via rubber washers. These could also hopefully be tuned for use under a couch if the effect is just too much in the car.
It may be worth getting something set up to use to measure both the sound, and impedance, then keep fiddling until I can achieve something that is a balance between extended lower frequency, flatter peak.
Any method of making a leaky cabinet is appropriate. What we don't know, with any of them, is how linear wadding/felt/cellular foam is at power levels. Linkwitz has suggested metal felt which is available with different hole sizes to be a more linear option. Again all tests would be empirical.
Oh cool!
Thanks!
I didn’t think about the wayback machine...
I wanted to leave a means of quickly changing variables in order to hopefully arrive at a more linear or at least a subjectively desirable solution. With the similar T-line arrangements, it has been noted that a more restrictive initial path, followed by a gradual transition to looser filling is best, subjectively anyways.
Thanks!
I didn’t think about the wayback machine...
I wanted to leave a means of quickly changing variables in order to hopefully arrive at a more linear or at least a subjectively desirable solution. With the similar T-line arrangements, it has been noted that a more restrictive initial path, followed by a gradual transition to looser filling is best, subjectively anyways.
The original papers were done by Ted Jordan for Goodmans (1956).
http://p10hifi.net/TLS/downloads/TedJordanAperiodic.pdf
dave
http://p10hifi.net/TLS/downloads/TedJordanAperiodic.pdf
dave
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