Well i didnt think this would be a problem but....
When i add stuffing to my sub the resonant freqency of the drivers (2 in series) becomes really hard to measure, the impedence just doesn't really peak anywhere close to when there's no stuffing in the box
Im wondering if ive over stuffed it or something, orignally i tried the whole box, loosely packed with fiber glass loft insulation (I hate working with this stuff!) I couldnt even find anything near a RF then, then took out a good portion of it leaving only stuffing stapled to the edges and now i get a sort of tiny impedence peak at 50hz (57 w/o stuffing) and a kind big lump between 49 and 54 hz
Is this just a characteristic of adding this kind of stuffing or have i missed something.
Thanks (a little itchy) Beggar.
When i add stuffing to my sub the resonant freqency of the drivers (2 in series) becomes really hard to measure, the impedence just doesn't really peak anywhere close to when there's no stuffing in the box
Im wondering if ive over stuffed it or something, orignally i tried the whole box, loosely packed with fiber glass loft insulation (I hate working with this stuff!) I couldnt even find anything near a RF then, then took out a good portion of it leaving only stuffing stapled to the edges and now i get a sort of tiny impedence peak at 50hz (57 w/o stuffing) and a kind big lump between 49 and 54 hz
Is this just a characteristic of adding this kind of stuffing or have i missed something.
Thanks (a little itchy) Beggar.
Hi I proded around a bit more in the sub, experimenting, got some particularly itchy arms, doh should have worn a long sleeve shirt! And it seems that indeed i had way to much stuffing in there, i was suprised actually just how little u need 🙂
Well got my a nice Qtc of 0.68, effective volume 75 litres, Rf of 52.8 hz yey, bring on the sattellites.
Thanks to anyone who was thinking of answering this thread 🙂
Well got my a nice Qtc of 0.68, effective volume 75 litres, Rf of 52.8 hz yey, bring on the sattellites.
Thanks to anyone who was thinking of answering this thread 🙂
Well, guess I'm a little late 😉
But don't be afraid to do some ear tuning, now that you've got a known starting point. The interaction of the woofer with your room is not well-predicted by simple equations (unless you're living within rigid walls of known linear reflectivity and a rectangular shape), so trust your ears here.
But don't be afraid to do some ear tuning, now that you've got a known starting point. The interaction of the woofer with your room is not well-predicted by simple equations (unless you're living within rigid walls of known linear reflectivity and a rectangular shape), so trust your ears here.
Beggar said:
A flatter impedance curve is better. The 50 vrs 57 hz is an example of the stuffing making the box function as if it were larger than it is.
dave
fdegrove said:
I always try to build in asymmetry wherever i can to combat resonances... from building at least non-parallel walls to assymetrical bracing to assymetrical distribution of damping as well as different kinds of damping in the same box.
dave
Hi,
That's exactly what I meant, Dave.
In it's simplest form, when you have a basic rectangular box, applying damping material in an asymmetric way will help preventing standing waves.
It's also a cheap and cheerful technique that helps prevent a monotonous resonance frequency of the cabinet.
As an example:
In a rectangular woofer cabinet:
Put damping on the backwall, the bottom an on one of the sidewall.
Leave the remaining walls untouched.
Anything else I'll leave to your creative imagination, just know that this works well for anything else as well: TTs, amp and preamp chassis, room acoustic treatment, you name it.
Cheers,😉
That's exactly what I meant, Dave.
In it's simplest form, when you have a basic rectangular box, applying damping material in an asymmetric way will help preventing standing waves.
It's also a cheap and cheerful technique that helps prevent a monotonous resonance frequency of the cabinet.
As an example:
In a rectangular woofer cabinet:
Put damping on the backwall, the bottom an on one of the sidewall.
Leave the remaining walls untouched.
Anything else I'll leave to your creative imagination, just know that this works well for anything else as well: TTs, amp and preamp chassis, room acoustic treatment, you name it.
Cheers,😉
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Beggar: Glad to see you've solved your problem with stuffing. From whatI have learned talking with various people, a good place to start stuffing a closed sub is approx 1 pound of stuffing for each cubic foot of the enclosure. Then, tweak up or down from there.. I know I'm late, but figured it was worth a stab.
I'm assuming that the subwoofer will only have to carry up to around 100Hz maximum. Therefore the only function of the stuffing is to give an apparent increase in cabinet volume.
Are we agreed on this?
Are we agreed on this?
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Joined 2000
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... So, what is happening when the impedance peaks are dampened?
I believe that the stuffing should lower the frequency of the peaks. If the peaks are being dampened does this mean that the cabinet is too small (higher Qtc) without the stuffing?
I believe that the stuffing should lower the frequency of the peaks. If the peaks are being dampened does this mean that the cabinet is too small (higher Qtc) without the stuffing?
nonparallel walls won't do the job. following pics are taken from german speaker manufacturer Visaton.
they took a 4" driver with titanium cone. the cabinets were unstuffed. it is quite obvious, that the tapering walls do not reduce standing waves. reflections appear always, when two medias travelled by the wave have a significant difference of the acoustical impedance!
they took a 4" driver with titanium cone. the cabinets were unstuffed. it is quite obvious, that the tapering walls do not reduce standing waves. reflections appear always, when two medias travelled by the wave have a significant difference of the acoustical impedance!
Hi,
That Visaton test only proves what Visaton was proving, not that:
Tapering walls are nothing more than parallel walls converging, the closer they get together the worse they're going to behave.
Cheers,😉
That Visaton test only proves what Visaton was proving, not that:
but that tapering walls aren't reducing standing waves.
Tapering walls are nothing more than parallel walls converging, the closer they get together the worse they're going to behave.
Cheers,😉
The original question was about subs, wasn't it? Something with an upper cutoff frequency of about 100 Hz?
100 Hz has a wavelength of 3.43 m. For a standing wave, you need at least lamda/2, which is 1.715 m. For any box which doesn't have any dimension which approaches this length, there is no need to do anything against standing waves.
Regards,
Eric
100 Hz has a wavelength of 3.43 m. For a standing wave, you need at least lamda/2, which is 1.715 m. For any box which doesn't have any dimension which approaches this length, there is no need to do anything against standing waves.
Regards,
Eric
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