Measure impedance of a raw woofer driver unstuffed vs. stuffed. Internal cabinet height (assuming 1m) will produce a standing wave around 170 Hz.
So will the depth and width contribute.
So will the depth and width contribute.
Measure close range (2cm from the woofer cone) and make a burst decay plot from both.
So you are measuring left and right speaker on listening position? That does show a lot but not for investigating the internal dampening ;-).
You need to get very close with your mic to the membrane of the low frequency driver - 1cm max. It's only that frequency range we are interested in - not the tweeter cause cabinet dampening doesn't influence the tweeter. Turn down the level of your microphone if it overdrives.
Best is to measure one speaker, chenge the dampening and measure that speaker again. But for a quick test you can also use left and right speaker.
Show us these measurements and we can take the next step.
You need to get very close with your mic to the membrane of the low frequency driver - 1cm max. It's only that frequency range we are interested in - not the tweeter cause cabinet dampening doesn't influence the tweeter. Turn down the level of your microphone if it overdrives.
Best is to measure one speaker, chenge the dampening and measure that speaker again. But for a quick test you can also use left and right speaker.
Show us these measurements and we can take the next step.
Did you measure in front of the dustcap? Try to go directly to the lf driver membrane, somewhere off center. Try at the edge of the dustcap and one even further. It seems you still have some room influence in your measurement - get closer! The mic just barely shouldn't touch the membran when the speaker is moving.
With these measurements it doesn't look like a very low Q speaker with low resonance frequency btw. Looks like a way higher resonance frequency and nice 12dB slope after 60Hz. Impedance measurements would be very helpful.
With these measurements it doesn't look like a very low Q speaker with low resonance frequency btw. Looks like a way higher resonance frequency and nice 12dB slope after 60Hz. Impedance measurements would be very helpful.
And again, mic placed 1cm from the face of woofer cone, mid-way between the edge of the dust cap and the surround:
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That resonance at 1kHz ... that shouldn't be there and I don't think it's part of the stuffing. Units are 100% ok?
I'm afraid you need to do this test with ONE unit, there are to much differences. Mark/remember the place on the membrane and put the speaker at exactly the same spott in the room.
But stuffing of a closed box is nearly always a good thing, even when you already put in quite a lot (depending on the density of teh material - when it's "fluffy" it's fine).
I'm afraid you need to do this test with ONE unit, there are to much differences. Mark/remember the place on the membrane and put the speaker at exactly the same spott in the room.
But stuffing of a closed box is nearly always a good thing, even when you already put in quite a lot (depending on the density of teh material - when it's "fluffy" it's fine).
Classic Tannoy drivers like your MG15 are not really suitable for sealed cabs.
For best results you need a large cab which you have and a port tuned to Fs which in your case is 26Hz.
In return you will get a EBS (Extended Bass Shelf) alignment ie the bass drops about 3-6dB around 100Hz and will stay there down to 26Hz.
For best results you need a large cab which you have and a port tuned to Fs which in your case is 26Hz.
In return you will get a EBS (Extended Bass Shelf) alignment ie the bass drops about 3-6dB around 100Hz and will stay there down to 26Hz.
Thanks, I'm coming round to the idea of a port but worried that it will exacerbate the room modes even further.
Just did a little more stuffing behind the drivers and re-measured:
Finally, with each speaker in the same spot in the middle of the room and the mic at 1m on-axis:
Finally, with each speaker in the same spot in the middle of the room and the mic at 1m on-axis:
If it was me, I would completely fill the cab with cotton wool. That's what I do on my enclosures, being Closed-Box or Bass-Reflex. Below, the example of my DIY 3-ways model 375L monitors :
"This increases the acoustical apparent / equivalent volume up to +41% over the empty box, in theory. In practice, +25-30% are easily obtained." Doing this, you increase the acoustic compliance of the box CAB, lower the QTc and increase the bass extension, while adding neutrality in the bass-midrange area.
(source : Vance Dickason "the Loudspeaker CookBook" / Martin Colloms "High Performance Loudspeakers" / Joseph D'Appolito "Testing Loudspeakers").
A Qts at 0.2 is usually not premium for a sealed enclosure, where Qts of 0.4-0.5 are better suited... A Qts=0.2 would probably better served by a BR enclosure.
But it's me, OK ? 😉
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No kidding. I am missing the point of adding extra stuffing to an oversized cabinet with a seriously low Q driver without adding a port. It seems so counterintuitive. I am hoping to learn something new here. Something that up to this point has made no sense.
My ears and eyes are wide open.
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I’m far from knowledgeable enough to answer that question but I wouldn’t say that these cabinets are oversized. As I understand it, ideal cabinet volume (Vas) is 350L, these are closer to 160L after bracing and driver are deducted.
I can say that I am hearing an improved sound (to my ears) after stuffing them, bass response seems fuller and less hollow. Thats not to say that adding a port wouldn’t improve things further, however, my trepidation is that it wouldn’t improve things, possibly even make things worse and cannot be easily undone.
I can say that I am hearing an improved sound (to my ears) after stuffing them, bass response seems fuller and less hollow. Thats not to say that adding a port wouldn’t improve things further, however, my trepidation is that it wouldn’t improve things, possibly even make things worse and cannot be easily undone.
Do you have the possibility to measure the speaker with open port and in comparison with closed/dampened port? (a cosy winter sock will do the trick ;-))
Normally when you fill a ported volume that strong there is very little effect left of the port.
But the filling itself looks very good!
The low Q is irrelevant to enclosure cavity resonances that mess up a lot above 100Hz. Addressing this is often ignored (have a look at Troels G), but of quite some importance.
Yes. If I plug the port (using a foam ball), the bass extension disappears - it's clearly audible.
No, the port (or vent) is as efficient as if the enclosure was empty, without filling material - the only point to check is that nor the port, nor the woofer, is plugged by the filling material itself. I mean : there must be some "free channel" between the port and the back of the woofer, even if it is not in direct sight, as shown below :
Another example on my DIY little bookshelf 2-Ways (222L) :
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The stuffing strategy that @tubelectron used in the 375 liter box seems very reasonable to me. I don't think the insulation would provide any flow resistance to the air around the woofer or the port tube.
375 liters... that is bigger than the refrigerator my family had when I was a kid (!) Big speaker !
375 liters... that is bigger than the refrigerator my family had when I was a kid (!) Big speaker !
Thanks @hifijim !
Yes. Assuming that the port and the woofer are not plugged or muffled, you do not change the operating mode of the bass-reflex enclosure, plus you have the benefit of increasing the acoustical volume (theorically 40, in practice 20-30) and obtaining neutrality in the bass-mide range of tones.
375L indeed doesn't mean 375 Liters ! 😆😉
3 = 3-ways
75L = approx. projected 75Liters neat volume (all internal volumes deducted, stuffing increase not counted).
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