Dual woofers in OB v single - diyAudio
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Old 13th December 2008, 12:11 AM   #1
Stuey is offline Stuey  Australia
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Default Dual woofers in OB v single

Howdy,

I've been trying to decide on the compromises before I start buying drivers for a pair of OB's as only my third ever pair of DIY speakers. The main sticking point is probably size.

I'd like to go for a 15" (say the ubiquitous Eminence, although I have been thinking Beta rather than Alpha) but it may be too wide for a reasonable baffle size for both fit and WAF. So I've been considering a pair of cheap 12"ers versus a slightly more expensive 12" on its own (say, an Eminence 12).

I'm thinking of a simple full ranger plus woofer(s) crossed down around 150-300 Hz.

A question that has arisen in my mind is the comparison between dual and single woofers. My understanding is that dual woofers will give 3dB more relative output, same Qts, 1/2 the impedance and 1/2 the excursion when compared to a single of the same specs.

However, if the single is nominally ~6dB more efficient, is it mainly the excursion factor that is of concern when comparing? And I guess reduced distortion in the duals due to the cones staying closer to their linear range?

I'd welcome some comments. I'm a real novice on this stuff.

Cheers

Stuey
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Old 13th December 2008, 01:08 AM   #2
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when it comes to OB, the more surface area the better...
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Old 13th December 2008, 01:23 AM   #3
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Several designs using two 15" woofers, an 8" or 10" wide BW midrange, and an efficient tweeter have gotten good reviews because the large cone areas provide good dynamics. If you want a modest width baffle, large woofer area is necessary.
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Old 13th December 2008, 03:08 AM   #4
2litre is offline 2litre  United States
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Reading your question(s)

Quote:
A question that has arisen in my mind is the comparison between dual and single woofers. My understanding is that dual woofers will give 3dB more relative output, same Qts, 1/2 the impedance and 1/2 the excursion when compared to a single of the same specs.
Quote:
However, if the single is nominally ~6dB more efficient, is it mainly the excursion factor that is of concern when comparing? And I guess reduced distortion in the duals due to the cones staying closer to their linear range?
I believe it would depend on how low you'd like the system to go (baffle width, driver size, low Fs and highish Qts help here) and how loud do you expect to use them (might be louder than one driver can effectively handle).

Depending on application (room size, wall stand off, 70-80db SPl at the chair) a modest single 12" / FR can still surprise you.

R/

Jim
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Old 13th December 2008, 04:23 AM   #5
Stuey is offline Stuey  Australia
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Thanks guys.

I forgot to say in the first post, the duals would be in parallel.

Yeah, I had thought that cone area must give that extra something to the party. I'm verging on getting the 15 and just dealing with how it'll fit in later.

I only occasionally like to crank it up. Most listening is at modest volume. But we all like to show off to the family when they come to see what you've built...

They'd be about a metre (3') from the wall.

I'd like reasonable output at say 40 Hz.

I've even considered the Peerless 830669 like used in the Manzanitas, despite its relatively low Qts and efficiency, as it seems to have acquitted itself well in this project. It does have a low Fs though.

As you've probably guessed, there are budget considerations here too. Big school fees are due for the kids. Mrs Stuey doesn't want me spending on frivolous hobbies right now. So I might even try a single quality 12 on a baffle capable of modification to a dual later on.

Decisions...

Stuey
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Old 13th December 2008, 04:37 AM   #6
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How big is your room?

Dual 12" should be okay provided you do active equalisation.
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Old 13th December 2008, 04:43 AM   #7
Stuey is offline Stuey  Australia
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Ahhhh, now that's the problem. Room is 65 square metres, and I don't really want to go active (but I guess I could if I have to...).
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Old 13th December 2008, 06:24 AM   #8
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Stuey , even with 4 of those 12inch woofers if I want high SPL in those frequencies below 35Hz ( ie more than 105dB ) I'm going to have to use subs activelly crossed at 40. and then I will need three or four 15inch subs to keep up.
But most of the time I'll probably be happy with 5 watts and 100dB
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Old 13th December 2008, 06:34 AM   #9
Stuey is offline Stuey  Australia
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Okey dokey, thanks. I'm not the best at visualising dB in terms of 'loudness'. But, I don't think my requirements are up there with yours, Ted !!!

I might have to seriously consider the 15".

Cheers

Stuey
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Old 13th December 2008, 07:12 AM   #10
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What kind of baffle width are you planning for the 12s ? I would think it would be not much difference with 15s.

With 15" I'm happy with 45cm, stock size from bunnings!
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