When designing a ELF type subwoofer, does the cabinet size matter?

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#21
Ken Newton said:
Just an anecdotal observation about the subjective effect of an extended deep-bass sub response in general. I once owned a 15-inch acoustic-suspension subwoofer, which produced an interesting listening sensation which I hadn't expected. It provided a definite feeling of increased ambience to many orchestral performances. To be clear, this wasn't a sensation of added orchestral bass, but a sensation of much greater ambient space. Perhaps paradoxically, my listening room felt less 'pressurized' to my ears, rather than feeling more pressurized, as is often provided by adding a subwoofer. I suspect that a sensation of greater acoustic pressure has more to due with mains-to-sub mid-bass integration.

I presume that the aural sensation of a reduced room pressure was due to a more accurate reproduction of the recording venue's acoustic ambience, but I'm uncertain. In the end, I didn't keep that 15"sub because I couldn't get it to satisfactorily integrate with the satellite speakers which I had at that time. I eventually settled on a 12-inch vented-sub that did integrate well. It didn't, however, provide that same feeling of increased ambience which the 15" A.S. sub did. I've been using full-range speakers for decades now, but am occasionally tempted to experiment with integrating a true deep bass sub in pursuit of that sensation of increased venue ambience. As we all know, those are the most expensive subs. While I've never auditioned it, BAG END's ELF subwoofer approach seems like it could be the most cost effective deep-bass solution, due the relatively very small enclosure needed.
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The closed-box sub can pressurize the room, and the vented one cannot. Thus the CB sub can provide that "sense" of VLF energy. IMHO vented subwoofers are not a great way to make one, for just this reason.
 
#22
Hi Charlie,

The sensation I had felt was that the 15" CB sounded like it pressurized the room LESS (made the room feel larger), and the vented-sub pressurized it MORE. Which is why I'm guessing that the effect had more to do with mid-bass integration than with deep-bass reproduction. The CB sub has seemed to have less obvious bass much of the time, until something like a tympani of bass drum thwack came along. Then, it obviously reproduced the more instrumental based deep-bass than the vented-sub did. Even while there wasn't any music based deep-bass, the CB sub felt like it revealed something of the open ambience of the recording venue. It don't know whether it was doing that, or not, but it gave the sensation that it was.
 
#23
The key to the Bag End is the limiter or concealer circuit; instead of the VCA in a normal limiter, it has a voltage-controlled high-pass filter which removes the bass to prevent amp clipping and over-excursion. The result is that it's only flat to 8 Hz at inaudible SPLs, but you have high sensitivity for the kick drum. So it's great for parties, not so much for home theatre or full-range music.
The 21" Bag End is in part 2 of the "Way Down Deep" series of subwoofer reviews.
https://www.soundandvision.com/content/way-down-deep-i
https://www.soundandvision.com/content/way-down-deep-ii
 
#24
The limiter in the Bag End limiter circuit used an LED acting on light dependent resistors in the integrators to reduce boost. When I was playing around with analog circuit design I came up with some ideas like this using a Vactrol LED/LDR but never built them.

The circuit is right there in the patent, which I have attached. It's quite simple.
 

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#25
Using speakers that weren't specifically designed for teeny enclosures can get...interesting.
I've had drivers physically give out in one way or another...a very shallow cone can buckle under the pressure of moving in a small volume (think high compression pistons) even before getting close to Xmax. Also, I've had a passive radiator surround invert itself under those same pressures.
But anyway, the main thing to look for is this: can your speaker take the power required to reach xmax (at 16hz specifically, in your case) in the box size you've chosen? If so, can you provide that kind of power?
 
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#27
Those woofer should work fine. Look at using the Linkwitz transform. WinISD can model a Linkwitz transform so you can predict the end response. This filter will simply cancel out the high Q of the driver in the box and substitute in the low frequency response you desire with a low Q. If the drivers have sufficient Xmax to produce the bass you desire the other parameters really don't matter that much. I would build a half cube shaped box segment for each driver. Maybe go with 1 to 1.5 cu ft for each 10" driver. You can use a series parallel combination to get an impedance that is easy for an amplifier to drive.
 
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#28
Here I modeled a single woofer in a 1.5 cu ft box with the Linkwitz transform parameters shown in the window. I wasn't sure what the Xmax was so the maximum SPL is not known.

Woofer10InchHiQ.jpg
 
#30
I think the EQ is accomplishing the same thing. The previous calculation indicated using 80V to drive an individual woofer (if that was 80V RMS that would be 533 Watts) That seemed high to me. The maxSPL calculation in WinISD fails with this woofer. The SPL plot shows it hitting X max at 16 Hz at very low power levels. In any case, a typical 10" woofer can handle 100 - 200 Watts and in a 1.5 cu foot box I expect such power will easily drive these woofers past the Xmax at low frequency, in this case 15 or 20 Hz. So that's all the SPL you can get out. You don't get more than Xmax. So it takes 150 or 200 watts per woofer. That's exactly how every small volume sealed subwoofer works. Go find an amp that can supply 150 - 200 Watts for each woofer and you have a good solution as far as I can tell. Building a single 1.5 cu ft box could verify the design at low expense.
 
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