Aguilar DB112 stuffed with foam????

[Bill Fitzmaurice]

[quote name='stevie' post='621899' date='Oct 9 2009, 01:30 PM']His explanation about how stuffing works may be incorrect (although I think if you slag off Richard Small the least you could do is provide some supporting references) but the practical consequences of stuffing a sealed box are the same – you increase the effective box size! Call it increasing the compliance of the enclosure or lowering the system Q - these are both things that happen when you increase the size of the box.[/quote]When stuffing is used to achieve a lower Q overall system sensitivity and extension will be minimally altered, if at all. When a larger box is used system sensitivity will go up and extension will go lower. Using stuffing to lower Q can mimic the flatter response of a larger box, but it won't give the greater sensitivity and lower extension of a larger box.

[stevie]

Interesting, but without any citation it’s a bit difficult to comment. Thiele and Small’s work has been constantly refined over the years and the effects described could easily be classed as ‘system losses’ in TS theory, which may be what Alex was referring to earlier.

[url="http://web.archive.org/web/20041027051204/http://www.integracaraudio.com/caraudio/resources/fiberfill/"]http://web.archive.org/web/20041027051204/...rces/fiberfill/[/url] is a much-quoted experiment by Tom Nousaine which demonstrates that stuffing a sealed box can lower Fb by at least 10 percent. He also, interestingly, shows that stuffing is less effective with larger boxes and that overfilling is counterproductive. Countless speaker engineers have observed the same (Ken Kantor here: [url="http://www.lungster.com/l/speakers/BassListArchive.shtml)"]http://www.lungster.com/l/speakers/BassListArchive.shtml)[/url].

As resonant frequency is a function of mass and compliance and stuffing does not change the mass of the speaker, a drop in resonant frequency means an increase in compliance. This is the proof of Small’s statement as I see it. To disprove it would require some other explanation or a demonstration that the drop in resonant frequency does not in fact occur. I don’t think Small went any further than to observe this increased compliance and so I do not see how his theory has been ‘debunked’.

Is there any accessible published data on the AES position?

Edited October 12, 2009 by stevie

[alexclaber]

[quote name='stevie' post='623926' date='Oct 12 2009, 01:20 PM'][url="http://web.archive.org/web/20041027051204/http://www.integracaraudio.com/caraudio/resources/fiberfill/"]http://web.archive.org/web/20041027051204/...rces/fiberfill/[/url] is a much-quoted experiment by Tom Nousaine which demonstrates that stuffing a sealed box can lower Fb by at least 10 percent. He also, interestingly, shows that stuffing is less effective with larger boxes and that overfilling is counterproductive.[/quote]

Interesting. If the increase in compliance was due to a lowering of the speed of sound one would expect this to be consistent with larger boxes - so does this suggest that a larger box is inherently more isothermal due to the greater heat capacity of the air within it and the greater radiating area of the enclosure? I presume overstuffing is counterproductive because the increase in compliance due to heat absorbtion is offset by the decrease in actual net volume.

Alex

[stevie]

[quote name='alexclaber' post='623937' date='Oct 12 2009, 01:28 PM']Interesting. If the increase in compliance was due to a lowering of the speed of sound one would expect this to be consistent with larger boxes - so does this suggest that a larger box is inherently more isothermal due to the greater heat capacity of the air within it and the greater radiating area of the enclosure? I presume overstuffing is counterproductive because the increase in compliance due to heat absorbtion is offset by the decrease in actual net volume.

Alex[/quote]
I've never seen an explanation for it, Alex, and I doubt I'd understand it if I did. But his big enclosure was 5 cubic feet, which is not a very practical size. Did you have a look at the Kantor link? (oops, no, this was in the Nousaine piece) There was quite a useful tip for optimizing midrange cabinet stuffing by measuring the impedance, I thought.

Edited October 12, 2009 by stevie

[Bill Fitzmaurice]

[quote name='alexclaber' post='623937' date='Oct 12 2009, 08:28 AM']Interesting. If the increase in compliance was due to a lowering of the speed of sound one would expect this to be consistent with larger boxes - so does this suggest that a larger box is inherently more isothermal due to the greater heat capacity of the air within it and the greater radiating area of the enclosure? I presume overstuffing is counterproductive because the increase in compliance due to heat absorbtion is offset by the decrease in actual net volume.

Alex[/quote]The changes offered by stuffing have nothing to do with either lowering the speed of sound or heat. They're the result of the alteration of system impedance by the higher mass load of a stuffed rear chamber versus unstuffed. And that's why the response of a larger box is impossible, because stuffing is a passive component, and passive components can never add energy, they can only consume or reallocate it. Depending on system Q stuffing can reduce a midbass peak with little alteration otherwise to broadband response, and it can lower system Fsc while lowering broadband sensitivity. But what it cannot do is lower system Fsc while maintaining or even increasing broadband sensitivity, wheras a larger box can do just that.
As to the heat increase exhibited in a stuffed box, there are two sources. One is the higher coefficient of friction offered by stuffing versus air to the rear wave, and where there's friction there's heat. The other is the insulation value of the stuffing, which retains not only the heat created by the stuffing but that of the driver motor. Measuring a higher temperature within a stuffed versus unstuffed box isn't the least bit unexpected, it would be inexplicable not to.

[stevie]

In other words, a free lunch there is no such thing as!

[Count Bassy]

I've read through this thread and am still a bit confused.

Am I right in thinking then that ported cabs should be lined and that sealed cabs should be 'stuffed'.

I've suddenly become interseted as I've just opened up my Marshall combo (to fix an amp problem) and notice that the (sealed) cab part has no lining or stuffing of any sort. Should I be looking to do something about this, and if so what?

Thanks in advance.

[Bill Fitzmaurice]

[quote name='Count Bassy' post='627478' date='Oct 15 2009, 06:44 PM']I've read through this thread and am still a bit confused.

Am I right in thinking then that ported cabs should be lined and that sealed cabs should be 'stuffed'.[/quote] Not necessarily, sealed cabs only need to be stuffed when they're too small for the drivers within. But that situation probably applies to 99% of the sealed cabs made. For instance, the SVT ten inch drivers are happiest in 6 cubic feet...each.

[quote]I've suddenly become interseted as I've just opened up my Marshall combo (to fix an amp problem) and notice that the (sealed) cab part has no lining or stuffing of any sort.[/quote]I'd call that unbelievable if I didn't know better. Line or stuff it, based on ported or sealed.

[Lfalex v1.1]

For all those of you that gig a lot, there's one other related point to consider with lined/stuffed cabinets;

Since the inception of the ban on smoking in public places, cabinets will no longer smell of 40,000 smoked cigarettes when you remove the drivers.
Those were the days!