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Old 15th February 2010, 01:41 AM   #1
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Default High output true subwoofer

So all this playing around with a cheapie JBL sub has me thinking once again about building a good sub or set of subs for my Hales Revelation 3's. The problem i have with most subs is that they don't seem to play well down where i think they should. most store bought types seem to be designed to have lots of 40-50hz boom. The hales -3db point is 29hz reportedly and they do play very VERY well down low and CLEAN! to the extent that i have never really felt a need to have sub. however playing with these crappy subs has me wondering if I could actually build a high quality sub that would start where the Hales start falling off and continue down to the seismic range??

Years ago when i considered this. my thinking was a pair of subs each with 2x 12" drivers. something like the Dayton high output subs. But looking at the specs. the 20hz FS point makes me wonder if they are really up to the task?

I once saw the specs for the custom drivers Hales used in the Rev 3's and they are a 10" with a FS of 14hz! So that makes me wonder what the -3db point would be with a FS of 20hz?? granted i am leaving a lot out here. My first thoughts would be to build sealed cabs like the Rev's to keep that ultra clean low end. But if we are only talking about a small range of what? 20-30hz? a ported system might be the best option.

Or maybe a single 18"???

Or maybe i just buy a Bag End ELF system??


Zc
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Old 15th February 2010, 02:02 AM   #2
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Default getting good bass...

Maybe you should consider building a free-air sub. There are many good drivers available for this purpose - one that I have experience with is the Exodus Audio DPL-15. But there are other options.

Avantages: excellent extended bass response, well below 20 Hz. Reduced distortion. No need for fancy electronics or boost circuits. Good transient response (e.g. similar to a Q=0.707 sealed box).

Disadvantages: you will need to do some "remodeling" and the subwoofer becomes part of your home, more or less. You will need a large space adjacent to the listening space (this could be outside the house if the climate is moderate). I use a large attic space for my free air sub. You need to securely mount the driver - often people mount it in to the wall studs, however I have found that this does not provide all that much bracing.

The idea is to take a high-excursion, high Qts (e.g. around 0.7 or even higher) low Fs driver and mount it in such a way that it is in an infinte baffle "enclosure" where Vb >> Vas. In that limit, Q and Fs are approximately what you get in free air, thus the name. If you use a wall, be prepared to add bracing and/or mass damping to the wall separating the listening space and the "box". A wall in a typical home in the USA is NOT like a MDF enclosure and is easy to "excite", which is not desirable! To reduce vibration somewhat, you can use pairs of drivers mounted face to face so that vibrations cancel.

This might get you the type of bass response that you are after, if you can build it. Good luck

-Charlie
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Old 15th February 2010, 07:57 AM   #3
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Something I've heard of, but never tried:

Get a driver with a rubber/foam surround, (around 8-10"), then cut out triangles from the spider (maybe 3/4" equilateral triangles, on in each quarter). This greatly reduces Vas, and lowers resonance too, making for a very small box that goes very low. The disadvantage is that you'll quickly bottom out the driver at anything more than normal listening levels.
Disclaimer now - I've never tried that, only heard of it.

You say you want to go from 30Hz down, so I immediately thought "bandpass enclosure" - they have good efficiency over a fairly narrow band, so it may be worth a look......

Chris

Edit - just noticed - you're after high output, which discounts the first idea...
Some PR cabinets would probably do what you're asking...
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Last edited by chris661; 15th February 2010 at 07:59 AM.
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Old 15th February 2010, 02:53 PM   #4
GM is offline GM  United States
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Double the compliance, double the Vas and Fs drops ~26% if I did the math right, so cutting up the spider increases compliance, ergo *increases* Vas which in turn lowers Fs for a given moving mass and *increasing* cab Vb proportionately for a given Fb same as when multiple drivers are used in a common cab, i.e. double the drivers, double the net Vb required for a given alignment. Taken to its extreme is to make a string weave spider like some DIYers do to make super high compliance PRs from blown drivers once the magnet assembly is removed.

GM
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Old 15th February 2010, 03:21 PM   #5
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How large can it be?
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Old 15th February 2010, 03:22 PM   #6
GM is offline GM  United States
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Quote:
Originally Posted by Zero Cool View Post
The hales -3db point is 29hz reportedly and they do play very VERY well down low and CLEAN! to the extent that i have never really felt a need to have sub. however playing with these crappy subs has me wondering if I could actually build a high quality sub that would start where the Hales start falling off and continue down to the seismic range??
There's more than one way to approach this, so Charlie's IB and the BagEnd alignments are both viable, but once you've experienced compression horn (sub) bass there really is no other alignment if space, budget isn't an issue, so until recently this option was only for the wealthy few and/or really serious DIYer. Second best is 4th order BP, then IB or TL alignments that mimic them.

The tapped horn and tapped TQWT (6th order BPs) or even the basic tapped pipe has changed the pecking order by merging the 4th order BP with the TL to create hybrids that can yield high SQ compression (sub) bass horn performance over a relatively narrow BW in a much smaller bulk, so ideal for filling the lowest octaves of a typical sound system, though still relatively large if designed for true sub bass output at ~live levels for music or DD/DTS/THX HT reference levels.

GM
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Old 15th February 2010, 04:47 PM   #7
tb46 is offline tb46  United States
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Default High output true Subwoofer

How about the new Eminence LAB15 as a single or dual in a tapped horn?

Regards,
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Old 15th February 2010, 05:00 PM   #8
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I live in a rented townhouse so mounting drivers in walls just isn't an option! There is a permanent residence in my future but I still would want the subs to be a contained type system. I once had a JBL B460 sub. single 18" in a 8cu cab. that's about as large as i would want to go for a single sub. For a pair I was thinking something maybe 30-36" high by 14-16" wide by 24-36+ deep. and those numbers are just thinking aloud. no real math done.

The Rev 3's aren't real efficient. But they will get to 100+ db easily. i forget what the actual numbers are but I think it was around 84-86db 1 watt 4 ohms. and I run them with a 200wpc amp and have seen the clip lights flash...well...often LOL! So for a design goal i would want to be able to hit at least 105-110db at 20hz clean. no huffing, chuffing, puffing sounds. just suddenly the whole room moves sort of thing.


Zc
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Old 15th February 2010, 06:24 PM   #9
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You're looking to moving lots of air very far if you want any output at all at 20Hz.
Seeing as you're in rented accomodation, hitting those SPLs at that volume may not be a good idea. Think structural damage if you're not careful.

I'd still insist that a bandpass design is the way to go. Or some kind of super-horn. You could even paint a big S on it........
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Old 15th February 2010, 07:19 PM   #10
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