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Qts in OpenBaffle - How low can you go?
Qts in OpenBaffle - How low can you go?
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Old 26th May 2017, 06:19 PM   #51
Scott L is offline Scott L  United States
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Qts in OpenBaffle - How low can you go?
Quote:
Originally Posted by JungDA View Post
I am researching OB speakers because I am thinking about building some. I haven't listened to any, so what aspect do people dislike about them?
Here, please see the link for the longest discussion I could find. Bear in mind, these are just opinions. You will find that "pro OB" far outweighs the detractors.

So, since OB is the more popular, it must be right. Right ?

So - why DON'T people go with open baffle? - Techtalk Speaker Building, Audio, Video Discussion Forum
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Old 13th February 2018, 06:51 PM   #52
CharlieM is offline CharlieM  United States
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Hi all,
I came across this thread in a search for “low Qts woofer on OB” --- in reference to a speaker project I’m working on which mates a 12” woofer with a 10.5” x 46.5” ESL on a modified H-baffle, as shown here:
https://4.bp.blogspot.com/-xtBTeBU6b...B12%2BSLS.jpeg

I’ve read many of MLK’s posts and MATHCAD simulations but I’m afraid they’re mostly over my head.

Anyway; I drew up this modified H-baffle hybrid ESL design for a friend who needs to go OB so that the speakers can be broken down to fit into his car with the seats folded down (big woofer boxes won't fit).

I/we are conflicted about the woofer choices in this application. My experience in building many hybrid ESL's is that a woofer optimized to blend with an ultra-low Q ESL crossing over at around 250Hz needs a low Qts( <0.4) and low inductance (< 0.7 mH). However, I'm reading that low Qts doesn’t work well on an OB-- at least, not without a lot of EQ’ing.

My friend has awesome subs, a DSP crossover and big Sunfire amps so there’s plenty of power and flexibility for EQ’ing and whatever woofer we choose can be unloaded to the subs below [let’s say] 60-80Hz. This may allow going with a lower Qts.

Even having subs, it would be nice if the speakers could be at least listenable without them. But I’ve never built an OB so I don’t really know what’s reasonable in this case for the woofer’s Qts and EQ’ing.

How low can I go??

I’m thinking we might need to split the difference—not optimal for either the ESL or OB but somewhere in between. My friend is looking at some AE woofers (IB type) but I’m leaning towards one of the two Eminence woofers below, with added EQ’ing as required (I especially like the BL product on the Kappa-Lite 3012LF -- should really thump):
Speaker Detail | Eminence Speaker
Speaker Detail | Eminence Speaker
Opinions and advice are appreciated… and if anyone thinks I’m nuts, I would need to hear that too.

Thanks!
Charlie (a.k.a. Jazzman)
Jazzman's DIY Electrostatic Loudspeaker Page)
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Old 13th February 2018, 08:03 PM   #53
scottjoplin is offline scottjoplin  Wales
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Hi. Normally a very shallow H-frame like yours is going to need all the help is can get. If you use something deeper it won't need as much EQ, though with a crossover at 250Hz you may have a problem with cavity resonance and since you only want to hit 80Hz you could probably get away with your design. A simulation would be your best bet
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Old 13th February 2018, 08:50 PM   #54
multi is offline multi  Australia
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I am thinking of trying OB I have Chinese 15 and 18 speakers with QTS OF .7 would I need EQ I had the drivers tested; the Quoted QTS from Maker was much lower .3 from memory.
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Old 13th February 2018, 11:38 PM   #55
CharlieM is offline CharlieM  United States
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Quote:
Originally Posted by scottjoplin View Post
Hi. Normally a very shallow H-frame like yours is going to need all the help is can get. If you use something deeper it won't need as much EQ, though with a crossover at 250Hz you may have a problem with cavity resonance and since you only want to hit 80Hz you could probably get away with your design. A simulation would be your best bet
Thanks for your reply. I've modified my drawing slightly and added some dimensions. Unfortunately, I have no idea how to use any of the simulation software or calculate the cavity resonance. Absent the ability to model it, I'm left with only the trial and error approach.
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Old 14th February 2018, 04:17 PM   #56
KSTR is offline KSTR  Germany
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Woofer Qts doesn't matter much as long as have enough voltage headroom in the power amp for EQ.

Its a myth that a low Qts woofer eats more power than a similar one with higher Qts. It needs more voltage (to overcome the higher motional "back EMF" voltage) but way less current (because of the better force factor).
Remember that Qts is a parameter *external* to the woofer as it mainly depends on the output impedance of the amplifier. If you have a current-drive amp then Qes (normally dominating the Qts) goes infinite and Qts equals Qms. To make the same movement the driver always needs the same terminal voltage no matter what the driving impedance is, hence the exact same power is dissipated in the voice coil resistance regardless of effective Qts.
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