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Old 13th March 2016, 10:37 PM   #1
tbolk is offline tbolk  Kazakhstan
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Default Why do high-Q drivers exist?

Low Q drivers are very useful in that they can be put into horns, vented boxes, APs, etc. Semi-high Q (0.4-0.8) speakers can be put into sealed boxes, TLs, TQWTs, open baffles, etc. What I don't get are High Q speakers (0.9-1+). You can't really build a proper enclosure for these, and whatever you make the system Q will never be lower than that. Considering the optimal Q is 0.707, why would anyone make a driver with Q higher than that? I feel like I'm missing something here...
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Old 13th March 2016, 10:57 PM   #2
POOH is offline POOH  United States
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They are cheap to manufacture and of course have the infamous bass bump that a lot of people like. You can put them in tiny boxes and they sound "full"
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Old 13th March 2016, 11:22 PM   #3
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Short & sweet answer: because people buy them. That literally is, it. Forget performance. Forget sound quality. Forget all that. It's irrelevant. It is purely a question of commercial manufacturing reality and profit. If people, whether they be DIYers like here, or large brands purchasing OEM units, didn't buy them, they wouldn't be made.
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Old 14th March 2016, 12:32 AM   #4
lauda is offline lauda  United States
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In the case of home and pro audio, there is something of a corner case "legitimate" application of high-Q drivers. A Butterworth third order alignment uses a high Q (= 1 IIRC) 2nd order section in series with a first order section. Many higher order alignments are similarly constructed (i.e., an under-damped 2nd order section in series with additional sections). Thus, high-Q drivers can be of use in constructing hybrid acoustic/electronic alignments.

In the case of guitar amplification, a high-Q driver can add some of the body that the guitar, er, body doesn't.
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Old 14th March 2016, 01:49 AM   #5
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It is true that any driver with a high or low Qts can be equalised to provide any arbitrary final target Q when filtered via a high pass. The B&W FST midrange driver is a prime example of this, with at least the old generation with the Kevlar cone having a Qts of around 1 and these aren't inexpensive. It isn't just midrange drivers mind you many tweeters have high Qts figures too. Most of the time it's the small neo tweeters that have very little in the way of air space. The high Qts is of very little consequence when the tweeter is correctly filtered.

If we're talking about drivers that aren't going to have a high pass fitted then it's as POOH says, they are cheap. To lower a drivers Qts you usually need to increase its magnet strength and doing so requires either more magnet material or a higher grade of material. Both of these cost money.

There is most likely an element of creating a sound with more fullness too, but if you're using the loudspeakers in an open backed enclosure, such as some TVs etc you're going to get dipole cancellation occurring at some point and theoretically the rising response could counter that but that'd require a lot of correct design elements being put together, which is unlikely when a loudspeaker of such low cost is being used.
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Old 25th March 2016, 08:16 PM   #6
Retsel is offline Retsel  United States
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Default Open Baffle and high Q drivers

When trying to adjust for baffle step loss, high Q drivers are useful, and often times more efficient, than lower Q drivers, when used as open baffle speakers.

I myself have not done a critical sound review of low vs high Q drivers. Thorsten Loesch apparently did such a review and found that, despite the use of smaller magnets, the sound quality of high Q drivers did not suffer, compared to low Q drivers, until the Q of the driver exceeded 1.3.

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Old 25th March 2016, 09:17 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

High Q drivers are well suited to open backed guitar speaker cabinets.

In HiFi they are old school, giving a Bass bump to speakers
designed with no BSC (baffle step compensation). They
still proliferate in the budget markets of the world.

Many budget drivers are not built for the "rich" markets.

rgds, sreten.
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Old 25th March 2016, 10:17 PM   #8
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Default Flow resistance damping and clang

Hi,

a high ratio between air loading and motor strength reduces harmonic distortions ("clang"), because air load usually is more linear than electromagnetic motor. Therefore, high-Q drivers have less clang than low-Q drivers.

Low-Q drivers can become current-driven, raising Q and lowering clang, see also current-feedback amplifiers.

High-Q drivers can often be damped by flow resistance damping, in explanation providing for a low mechanical Q by letting back sound press thru wool. In order for this to work, enclosure must be a compression chamber, say smaller than lambda/2Pi.

Flow damping raises efficiency: While electric damping transforms all power loss at resonant frequency to power gain above it, mechanical damping transforms at least and most half of that.

Backdraws: For one, vegetable and to a lesser degree animal and synthetic wool changes characteristics with temperature, humidity and smoke. For another thing, if flow resistance becomes too great, it saturates. This is, why, if full level is transmitted at resonance frequency, port should be big but may be smaller, if an electric highpass runs over it.

Cut short, high-Q need not be a problem but may be a challenge or even blessing.

Uli
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Old 25th March 2016, 10:19 PM   #9
bwaslo is offline bwaslo  United States
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The Carver ALS used high Q woofers as a counter to the dipole cancellation too.
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Old 25th March 2016, 10:27 PM   #10
Jsixis is offline Jsixis  United States
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pretty obvious no one here has tested the old speakers of the tube era.
Almost every one I have tested (pushing 100) have just stupid high Q.
I've seen them in open back and 2 foot square cubes.
One thing nice about them is they sound better then what software claims.
Makes me wonder about speaker modeling software.
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