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Old 13th December 2009, 06:15 PM   #1
pjanda1 is offline pjanda1  United States
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Default OB project: thinking out loud

I'm contemplating jumping on the OB/helper woofer bandwagon. I do really like the idea of 'Zilla's Betsy +Boomer kit, but I am bad a jumping on bandwagons. I am often attracted to the prevailing popular idea (OB's and helper woofer certainly are popular right now), but I usually feel most gratified by putting my own spin on it.

I really like the idea of the OB's the Nelson Pass appears to have in his personal system, and the OB's he and JVH used with the Lowther Field Coils. They use lower QTS woofers on U baffles, presumably with some EQ. Obviously, active crossovers like the B4 pose a ton of advantages. We can certainly talk more about that, but in the true WBAL fashion, I'm thinking about even simpler and easier.

But first, I'm looking at the Jensen 15" woofers Jack Hidley sells. That seems like an awfully nice woofer for $60. But these Eminence 12's from the Swap Meet some like an awfully good deal. One could even use 2 per side! Either way, I'm thinking of a baffle around 18" wide, with maybe 10" or 12" wings beside the woofer(s).

I'll biamp no matter what. Obviously, the lower Qts woofers need some EQ. Fancy solutions like NP's B4 presumably take care of that. However, it also looks like the built-in "spectral tilt" on Hidley's $35 plate amp (see same link as 15" woofers) might do the trick. I've done some quick sims, and 10db should be enough. One could futz with the exact contour as the tilt is adjustable, but so is the built in high pass filter. Then, the crossover is the only problem.

That plate amp has a 4th order LR adjustable low pass. Depending on the crossover point, the woofer rolloff could be pretty complex. On the baffle by itself, the 15" rises up to 200hz or so and then drops. So, I'm not quite sure what sort of acoustical slope I'd get. It seems like one could lose 30 db between 200-400hz, right?

Of course, the fullranger could use a high pass as well. Passive first order crossovers would be easy. I figure that I could get up to a 3rd order acoustic roll-off with nothing but caps. The driver would be rolling off at 6db/octave on the baffle. Then, I could put a first order HP on the amp input, the driver, or both. If those first orders were at around 200hz, I imagine excursion would be controlled well enough for my taste.

So, though several acoustical slopes are possible, the easy options I can think of produce potential phase problems. I don't really want to build an active crossover, but I might have to. To even do a higher order line level XO, I'd need to build a tube pre of some sort to counter the insertion lose. I might enjoy that, but it wouldn't be as simple!

I think I'll be able to do some interesting crossover simulations with Passive Crossover Designer, but I don't have it running yet. In the mean time, I figured I'd throw this out for comment.

Paul
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Old 13th December 2009, 06:29 PM   #2
tinitus is offline tinitus  Europe
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Sounds more like its fore your own personal use, or ?

Should I do a dipole, I would look at AEs Dipole15, or the 12", but cost more
Its 90db woofers
If you choose the higher SPL semipros, then yes you will have to deal with the rising response one way or the other

Active, could be crossed low
Passive, higher
Higher crossing give the advantage to deal with some of the dipole rolloff and baffle step loss

Last edited by tinitus; 13th December 2009 at 06:33 PM.
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Old 13th December 2009, 07:51 PM   #3
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since an OB is on my list of things to gather money for, i'm looking with interest at this and others alike DSP based active XO: have a look, i don't know how good this could be a solution

Low cost dsp based crossover module
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Old 13th December 2009, 08:39 PM   #4
pjanda1 is offline pjanda1  United States
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The AE speaker site (AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.) is fun. I hadn't been there in awhile. I think the dipole woofers would be overkill for me. The IB woofers would be fun with a bigger amplifier. You've got to have some EQ no matter what. With the dipole woofer I could see adding 6db at 40hz to get dead flat into the bottom octave. Fun stuff.

However, I can't see even approaching the limits of either of the cheap woofers (the 15" is evidently well behaved to +/- 8mm excursion), and solving the bass EQ problems shouldn't be as difficult as getting the crossover right.

That DSP solution look neat, but it ain't for me. I suppose DSP crossovers could really be fun for a computer based source, prior to a pair of DACs. I'm not inclined to even add a couple of op amps into the system. I'll only consider discrete SS if I have to!

Based on the quick and dirty sims I've done, I'm anticipating a crossover around 200hz (acoustic/actual, the sub crossover might need to be as much as an octave lower, electrically, with that 15" to end up flat to 200hz), preferably not higher.

Thanks for the thoughts! I would love to hear an implementation of those AE drivers.

Paul
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Old 13th December 2009, 10:26 PM   #5
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by pjanda1 View Post
The AE
I think the dipole woofers would be overkill for me.
Goldwood have become relatively popolar low budget OB woofers
PE even have a Jamo listed now
15" they are
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Old 14th December 2009, 12:13 AM   #6
pjanda1 is offline pjanda1  United States
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The Jamo 15" at PE is probably the best candidate for an ultra-budget build with the NHT amps. It also might be the ugliest speaker I've ever seen.

I really don't think that Jensen/Foster 15" can be beat in price/performance. It is much more woofer than the Goldwood's, and not more expensive. Of course, it needs EQ, unlike some of the popular high Qts designs. But like I said, that is the direction I'd like to go.

Paul
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Old 14th December 2009, 12:23 AM   #7
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by pjanda1 View Post
The Jamo 15" at PE is probably the best candidate for an ultra-budget build with the NHT amps. It also might be the ugliest speaker I've ever seen.
I didnt see that one
There a more expencive Jamo at 25USD
Looking at specs on both, it could seem like they have got them mixed around
Well, they are what they are, leftovers
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Old 14th December 2009, 12:31 AM   #8
pjanda1 is offline pjanda1  United States
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That's funny, I didn't see the other one! It would make a great of sense if the specs are swapped from driver to driver.

Paul
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Old 14th December 2009, 12:34 AM   #9
pjanda1 is offline pjanda1  United States
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I should add that I'm following this thread in the event an active crossover is necessary.

Paul
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Old 21st January 2010, 03:51 PM   #10
pjanda1 is offline pjanda1  United States
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For the record, I'm starting this project. I ordered the Jensen 15"'s from Jack Hidley. Instead of the plate amps, I'm going to biamp with tubes (which I'm discussing in another thread). I am planning to control the woofers with a miniDSP from my next door neighbors on the manufacturer's forums. It will be much, much more flexible than the plate amps or the DSP's I was considering (Behringer Feeback Destroyer or used 8024).

Paul
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