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Old 18th October 2006, 12:57 PM   #21
bigwill is offline bigwill  United Kingdom
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Quote:
Originally posted by AndrewT
Hi Bigwill,
you think BIG!
Each 18inch with 12mm Xmax is equivalent to about 4 of my 15inch Tannoys.
You want a pair per side.

That is equivalent to 16off 15inch drivers in one room.

How long will the room last!

I love big speakers! I think I'll settle with 4 15s per side eventually (in OB)

That should be punchy enough...

If I had the money and room I would seriously consider 4 high efficiency 18"s per side!! All in the name of headroom
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Old 18th October 2006, 03:36 PM   #22
AndrewT is offline AndrewT  Scotland
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But there would be no room left for your head.
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Old 18th October 2006, 10:12 PM   #23
bigwill is offline bigwill  United Kingdom
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Quote:
Originally posted by AndrewT
But there would be no room left for your head.


(sorry about my slight derailing of the thread)
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Old 19th October 2006, 12:58 AM   #24
Ron E is offline Ron E  United States
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Quote:
Originally posted by johninCR
Ron,

That's just semantics. There's a direct correlation between Vas and CMS, and an inverse relationship between Vas and RMS.

I must take exception to your statement regarding the source of damping, because I've yet to hear a low Qms (high mechanical damping) driver that sounds really good, and I can say the same for drivers with low Vas in relation to their size. IME stiff suspension corresponds directly to poor sound.

It isn't semantics, really. There is a direct correlation between the speed of sound and wavelength , but which is a physical constant? The speed of sound is the real quantity, and wavelength is just a consequence of it. Cms is the compliance of the suspension. That is the physically real quantity.

Sorry to say, but Rms has no inverse correlation WRT Cms that is always true.

In regards to Qms, many tweeters have a dominant (or prominent ) Qms I am almost certain that you didn't hold that opinion before reading a certain article by a certain successful designer.....
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Old 19th October 2006, 02:52 AM   #25
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Ron,

If you keep everything else the same for a driver and decrease the Vas, the CMS decreases and/or the RMS increases. That's what I meant by direct or inverse relationship.

We weren't talking about tweeters. Anyway there are exceptions to any generalization.

I don't read articles, so I don't have a clue about the article to which you refer. I discussed it once with someone on another forum, who may have been influenced by the article in question. I agreed with him because it corresponded with what I found from listening to literally hundreds of different cheap drivers while I was trying to find bargains locally for OB use. After quite a few direct listening comparisons, I stopped even bothering to listen to drivers with stiff suspensions. I just never really though about it in terms of specs until the forum discussion, because I was dealing with drivers for which I had no specs, only feel and guestimate. If some famous designer says the same thing, then I agree with him.
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Old 19th October 2006, 03:04 AM   #26
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Default cheap drivers Vs expensive (good) ones...

worth considering the quality of driver you are using as a base reference. Low cost drivers by thier very nature are made with every cost cutting tatic there is. If you look at quality pro drivers for example you will not have a hard time finding units with stiff suspensions. Very high efficiency stiff suspension units with only a couple of mm xmax designed for horn loading or sealed boxes will often have an xlim of 20 mm or more. I dont think that these two stiff suspension driver will sound anything alike do you? Regards Moray James.
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Old 19th October 2006, 03:55 AM   #27
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Moray,

High efficiency or low Xmax doesn't mean stiff suspension at all. I'd suggest looking at the T/S parameters of Eminence and JBL units. Low Vas is out the window. That's why pro sound doesn't come in small packages.

BTW, drivers don't have to be expensive to sound good. It's higher efficiency and lower Qes that cost more money due to more refined manufacturing tolerances and larger motors being required.
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Old 19th October 2006, 08:48 AM   #28
AndrewT is offline AndrewT  Scotland
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Hi John,
Quote:
High efficiency ......... doesn't mean stiff suspension at all
I don't think this is right.
I think Fs is one of the determining factors in efficiency. High Fs comes from low Vas and stiff suspension as well as lightweight moving mass.

High efficiency does mean stiff suspension.

That was my point in post 18, but no-one picked up on it.
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Old 19th October 2006, 09:07 AM   #29
Svante is offline Svante  Sweden
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Hmm. Efficiency is generally defined as the ratio between output ant input power to the loudspeaker at mid frequencies, ie an octave or two above the system resonances. That means the mass-controlled region, where stiffness has very little effect.

Here is a formula that is frequently used to calculate the efficiency of a driver in half-space:

eta=rho0/(2*pi*c) * (Bl)^2/Re * Sd^2/Mms^2

Neither of Cms or fs are there. The equation assumens, however, that the frequency is well above fs.
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