how low can u go? (1 Viewer)

[MichaelAngelo]

Dave,
In a review of the JL 12W7 in Apr02 Mobile Entertainment, Tom Nousaine states that his eight 15-inch subwoofers "can produce 120db spl average from 12 to 62 hz at 2 meters."
I don't know Mr. Nousaine well enough to demo his setup, but I'm dying to feel what 115 or 120 db at 12hz is like !!!

I'm just a bass nut. But rather than pump 1000 watts into 2 L7 squares, theres gotta be a cleaner, better way. Not a Rockefeller way tho lol.
Example; the 16 foot box helps with all the deep bass in HT. But theres a sacrifice in power handling. Ok, get a better driver. But do I do it with more power to the drivers, or more drivers with the same power? 2 subs with 1500 watts each, or 8 subs with 375 each?

BTW, what does the word "compression" signify in relation to subwoofers? Ex: the AWT series from Audiobahn, they saay compression subs, the hi-level Flame subs say it too, is it just marketing?

 

[Brian Bunge]

For a ported enclosure (for HT use) I'd prefer something with a little lower Fs and greater Xmax. If you start running too much power to the L7's and tune much below Fs you risk destroying the drivers. The upside is that it will be possible (notice I didn't say easier) to get a much smoother in-room response with 2 or 4 separate enclosures positioned properly and overall efficiency goes up so less power is required.

 

[MichaelAngelo]

Thanks again Mr. Bunge. Can you suggest a driver? After some experimenting, I've seen the benefits that multiple subs can give, PITA to get phasing right lol, but I could build 2 or 4 cabs, or tubes.Looking at diff amps too.

Thanks,
Mike

 

[Brian Bunge]

The new AV12's and AV15's from Stryke look good. But 4 Tumults look better!
Actually, I was talking with a gentleman last night that set up 4 Shiva enclosures in a dedicated room. He used measurement software (I think LEAP) to properly position the subs and integrate them into the room. IIRC, they were all wired together to achieve a 4 ohm load and were running off of a monoblock Adcom running around 450W. It may not be capable of TN's levels of bass, but we're only talking $500 worth of drivers. Not bad in my book!

 

[MichaelAngelo]

Very interesting! Integration of multi subs can drive you nuts, or be the most fun you can have.

 

[Greg Monfort]

>Ok, get a better driver. But do I do it with more power to the drivers, or more drivers with the same power? 2 subs with 1500 watts each, or 8 subs with 375 each?
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There's no replacement for displacement where reproducing LF is concerned, and the more efficient it is, the lower the distortion, so enough high displacement drivers to keep power to each of them down to >1/4 of their continuous rating is the Hot Ticket.

GM

 

[MichaelAngelo]

Greg!
thanks for the reply. As a one-time gearhead, that maxim sounds familiar, so displacement it is.

cubic inches over RPM any day, so
I guess cone area over excursion

I referred to Mr Nousaines system earlier, and seldom would be the times I'd have to listen at those levels. But, how tight, how THERE, the impact his sys must have, at low levels! If hes doing 120+from 12-62, how does it sound at 75-85??

 

[ThomasW]

Trying not to spoil the party, but square/rectangular drivers and driver frames may look cool but aren't a good idea for high output use. Why???

It's physically impossible to equalize the pull of the suspension on the cone as it turns the corners of the frame. Drivers built this way are prone to unequal loading on the cone (not a good thing Martha....) So when possible stick with ROUND drivers for the best overall performance and longest driver life.

 

[Greg Monfort]

>cubic inches over RPM any day, so
I guess cone area over excursion
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Yep, though with the new low distortion/high excursion drivers available now you can have your cake and eat it too, so I'll amend my ideal of >1/4 power to the manufacturer's rated power at which thermal power compression rears its ugly head.
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>If hes doing 120+from 12-62, how does it sound at 75-85??
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With this amount of efficiency I'm sure it's impressive except for the organ pipe resonances the long plenum he used creates.
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>So when possible stick with ROUND drivers for the best overall performance and longest driver life.
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For sure! When he said square, I assumed he was referring to the frame and not the diaphragm!

GM

 

[ThomasW]

http://a763.g.akamai.net/7/763/1644/3/app.infopia.com/cgi-bin/image/VPID/569303
Looks sort of cool but.......

 

[Dave_Gib]

the L7's are as reliable as any subwoofer, the physics arguement always seems to come up, but have you ever used them?

I'm a big fan of displacement too, the 18" brahma would have to have an xmax greater than 60mm to outdisplace 4 of the L7's, to me it's easy, you already got 2 of them, but I also know how audiophiles enjoy collecting equipment, I'm guilty myself

 

[ThomasW]

I used to design loudspeakers for a international company. So I'm reasonably well versed in the physics of their design and construction.

Asymetrical surrounds = unequal tensions on the cones = non-pistonic cone performance. That's fine for car audio where high SPL's and cool looking products are the primary goal. But it's not a good idea for getting the highest overall sound quality and the longest life from the product.

 

[MichaelAngelo]

Thomas,

I have to say I question the usefulness of the corners on these subs as well. But they were what I had, so I used them.

 

[Greg Monfort]

Yeah, way cool, but it would be interesting to see a distortion plot at rated Xmax........
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>But they were what I had, so I used them.
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Understood. We just wanted to point out to anyone who may want to buy these based on looks be forwarned that for best high SPL performance there are better driver designs available in this price range.

GM

 

[MichaelAngelo]

.

 

[Rusty Boudreaux]

There's no replacement for displacement...

Guys, don't forget what we are looking for is maximum volume of air displaced. In terms of T/S this is Xmax*2*Sd (be sure to use consistent units). It's not a simply Xmax or cone area...it's the product.

Also, Xmax should be used instead of Xsus. Calculating with Xsus is nice for marketing (i.e. Kicker info shows larger displacement) but the distortion at Xsus can be huge. Xmax is a realistic distortion limit.

So,

Tumult = 34*2*749/10000 = 5.09 liters
Brahma 15 = 4.09 liters
AV15= 4.04 liters
Solobaric S15L72 = 3.4 liters
Solobaric S15L5 = 3.27 liters
Tempest = 2.56 liters
Dayton DVC15 = 2.44 liters

Now look at value:
Tumult = $98/liter
Brahma 15 = $59/liter
AV15= $41/liter
Solobaric S15L72 = $77/liter
Solobaric S15L5 = $61/liter
Tempest = $59/liter
Dayton DVC15 = $54/liter

So, in terms of sheer output per dollar the AV15 is it.

I've ordered four AV15 for an infinite baffle setup in my HT. Assuming no room gain I calculate 127.5 dB at rated power but Xmax limited to roughly 120dB at 20Hz and falling to about 109dB at 10Hz, 96dB at 5Hz, 84dB at 2.5Hz, 60dB at 0.6Hz, etc..

 

[MichaelAngelo]

Rusty,
Sounds like you're gonna have a heavy hitter

 

[Chris James]

So, in terms of sheer output per dollar the AV15 is it.

First of all, according to Kyle's website (Acoustic-Visions), the displacement of the AV15 is 3.8L.

Now, with my "limited" knowledge, here's my take on this point. Sure the Tumult is $98/L, but thanks to the excellent motor design (XBL2), almost all of that displacement can be used with little distortion. The AV15 will start to show distortion earlier, due to the differences between motor structures of the two drivers. I'd probably pay the money for the extra 1.3L of displacement. I guess what I am trying to say is that there is more to look at besides displacement...i.e. BL numbers, etc. I'm sleepy.

 

[Dan Hine]

I agree with Chris, there is more than just displacement. Like the quality of that displacement. Also, for some of us, the amount of space a sub takes up is important. I don't have the luxury of space so I would definitely give up 5-8db in order to only take up 1/4 of the space.
Thomas and Greg,
So with the square shaped driver, would that mean the "usable" Vd would not quite be its Sd * Xmax since the entire cone does not move evenly all the way across? I guess, in other words, are the specs inflated as they most likely don't take into account the setbacks of a square shape?
If I'm off base then would one of you mind explaining a little more about why such a design is not optimum. Or point me to some "light" reading somewhere? Thanks.
Dan Hine

 

[ThomasW]

Dan

It's just simple physics. With a circular driver shape the tensions (stresses) are equalized across the surface of the cone as a function of the shape (round). That can't occur with an asymetrical shaped driver.