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Multi-Way Conventional loudspeakers with crossovers

Multiple 12-ish ohm drivers in a 2.5 way? no way?
Multiple 12-ish ohm drivers in a 2.5 way? no way?
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Old 10th July 2018, 04:12 PM   #1
G Speakers is offline G Speakers  United States
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Default Multiple 12-ish ohm drivers in a 2.5 way? no way?

I've been given 12 of some B&C 10" woofers that came out of a d&b line array. Attached is the impedance plot of one. Would you call it 12 or 16 ohm? Currently my best option is a TMM 2.5-way. I want to know if it's possible to do a TMMM 2.5 way, where the 2 drivers that are in series is the .5. I'm fairly confident in the wiring here, my concern is won't the .5 section only be taking 1/3 of the power due to its higher impedance, which sort of diminishes the whole point of doing a 2.5? These drivers have a sensitivity somewhere around 97dB but won't get any lower than 80Hz or so. I just think having more surface area would be more fun if I can do it (they were free after all) and also help with bass extension. Secondly, am I missing anything with getting more LF extension? I can't afford the size/power sub that would be needed to make them a 3-way.

Since they're so sensitive I don't think want the impedance lower than 8ohms, unless I'm missing something there.

I need the horns on top for this build so please don't suggest a MTM.

FYI I already have some Selenium D220Ti. Didn't want to break the bank on some free woofers.


PS - I tried modeling some passive radiators but vents looked quite a bit better.
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Old 10th July 2018, 04:24 PM   #2
DPH is offline DPH  United States
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DCR looks around 12 ohms, but nominally "8 ohm" speakers have DCR's in the 6 ohm range. Certainly most competent amplifiers will not struggle with the load of the pair in parallel.

As far as I know, you've stated you have:

2x Selenium D220TI in some sort of horn
12x B&C 10"

Before getting ahead of ourselves on topology, what's the end-goal? Will this be an active setup? What are the volume constraints? There's a lot of things that could potentially be done here, depending on what sort of goals/objectives you're aiming for.
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Old 10th July 2018, 04:31 PM   #3
1audiohack is offline 1audiohack  United States
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You wouldn’t be in bad company. One of the JBL Everest DD (6500?) series uses two 12 Ohm woofers in .5 configuration.

Barry.
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Old 10th July 2018, 04:45 PM   #4
G Speakers is offline G Speakers  United States
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Quote:
Originally Posted by DPH View Post

2x Selenium D220TI in some sort of horn
12x B&C 10"

Before getting ahead of ourselves on topology, what's the end-goal? Will this be an active setup? What are the volume constraints? There's a lot of things that could potentially be done here, depending on what sort of goals/objectives you're aiming for.
Correct on what drivers I have. Goals are vague at best (SMH). Big, open sound, with plenty of headroom. Passive for sure. Might replace some ribbon tweeter bookshelves that aren't filling my living space. Or maybe they'll replace my POS Polk towers. Certainly I favor fidelity over power or whatever, these can probably be a small PA, but will stay inside. Maybe they'll just be an experiment and I'll destroy the evidence when the build is done. Who knows (Yes, I know that makes the design process more difficult).
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Old 10th July 2018, 05:30 PM   #5
DPH is offline DPH  United States
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Okay, so you have WAY more oomph in drivers than you should really need, but that's a better problem to have than the alternative. And frames your ideas better as well.

A 2.5 way TMM would certainly let you rock the house. Mating the 10" to the tweeter/horn will require a relatively low xover, which might be ultimately close to the baffle step anyhow. I haven't plugged your woofers into a modeling to see what that gets you, but 2x10, even with an open air FS of 50-55 Hz, can be used in a low-low tuning alignment and have enough displacement to look at a bit of bass boost to compensate.
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Old 10th July 2018, 05:56 PM   #6
G Speakers is offline G Speakers  United States
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Default The real question then-

So is a TMMM (note the 3 Ms) just a waste of time since the .5 section would have a higher impedance? Or will it actually contribute to the low end? I generally like how speakers with more surface area feel, but don't want to waste drivers if they're not going to ask for it from the amp. I guess what I'm getting at is is it possible to avoid a passive bass boost. I know the drivers can take it, but we all want the best sound before EQ is necessary.
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Last edited by G Speakers; 10th July 2018 at 05:58 PM.
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Old 10th July 2018, 06:36 PM   #7
DPH is offline DPH  United States
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With active, I could see making a case for said speakers, or, some sort of dipole loading (if you're placing them far enough into the room). It'll be REALLY awkward getting the balance right to have some sort of (tm)(mm) with the latter coming in as baffle step.

Similarly, you *could* try some form of bandpass/tqwtp alignment as sub(ish), too, that come in lower. I mean you do have 12 of 'em.
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Old 10th July 2018, 07:50 PM   #8
G Speakers is offline G Speakers  United States
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I think I know that tqwtp is like a backwards horn?? Any more info on that (not to redirect this thread). I'm interested in diving into long horns more. I don't know what the letters mean!
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Old 10th July 2018, 11:15 PM   #9
hollowboy is online now hollowboy  Australia
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Quote:
Originally Posted by G Speakers View Post
I've been given 12 of some B&C 10" woofers that came out of a d&b line array.

[...]

I can't afford the size/power sub that would be needed to make them a 3-way.

[...]

Didn't want to break the bank on some free woofers.
It seems odd to cry poor when you have all these surplus drivers
You could sell some of them, and use the money for parts for make a 3-way.

OR

Using a couple of assumptions:

1) You need the midbass section to be ~80cm tall to get the horn to ear height, so an enclosure volume of about 100 litres seems reasonable.
2) The drivers probably have a VAS of only 25-30 litres (the other B&C 10" drivers have values in that region). You'll be able to pack a lot of these into a 100 litre cabinet.

...so why not make a 2.5 way using five of the 10" woofers per cabinet?

- one 10" (nominally 16 ohm) running as a midbass, up to ~1.5kHz

parallel that with:

- four x 10" (in series-parallel, nominally 16 ohm), bass only.

That'd give you a 'normal' nominal 8 ohm load. The crossover on the bass quad could possibly be as simple as one humungous inductor.

You wouldn't have to mount the 5 drivers woofers on the front panel. The bass quad (or half of it) could go onto the sides.
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Old 10th July 2018, 11:22 PM   #10
DPH is offline DPH  United States
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I was thinking something similar in terms of dipoles, Hollowboy.
Do think this requires some active to leverage the extra surface area down low.

I'm on my phone, G, so I'll dig up some material soon. Look up tapered quarter wave pipes. They're yet another helmholz resonator.
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Last edited by DPH; 10th July 2018 at 11:24 PM.
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