what exactly is Q?

I've heard a lot about building a system to the Q of .7 or 1.1 or whatever, but what exactly is that.  Is that the enclosure design or the all around system design.  When I had heard about it, it was someone design an enclosure for SQ and they said they were building their box to the Q of .7. Can someone expalin this to me.

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what!?!?! you want some??

Generally speaking, the lower the Q a system has, the thinner the bass will sound. A Q of .5 will sound very thin for most people, but it will offer the lowest overall cutoff frequency. It will have a higher F3, but due to the VERY shallow slope of the rolloff, the driver will go deeper in it's overall frequency response. It will have lower power handling, but you will have the absolute smoothest response with a minimum of resonant peaks, both output and impedance.

A Q of .707 is what most people call "max-flat". It will offer good power handling with reasonable rolloff and extension. It will do this also with a decent trade off in resonant peaks. It will usually sound pretty good.

A Q of 1.1 is a maximum power handling enclosure, and will sound like CRAP. Their response is VERY boomy, with many high level peaks in output AND impedance. They will not go very deep at all. It usually happens when an enclosure is too small for the driver.

This is what my enclosure is right now (or close to it) but I have equalized many of the peaks and dips out and I am brute forcing it into its desired output curve. This can be (really, it is, there is no "can be" about it) very hard on a driver, as it requires MUCH more power be available (and used) but I have enough to do this. The Eclipe Titanium 12 is an excellent woofer for this approach, but as I said, it DEAMANDS MUCH POWER be available... (and with my DA7232, I think I can say I have the power necessary) I do not usually recommend doing this, but I really did it first as an experiment in my house, and was quite pleased with the results. If you want to try this, I will not be responsible for you popping your Sony Xplod 10 inch "sub" and hooking it to a HiFonics Brutus... Get it? This method requires a VERY high power handling woofer...

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Great explanation of how to use it in speaker designing!  The simple definition of the term is:  "Q" is a measure of the relative damping factor in a loudspeaker system.  Higher Q factor = more speaker dampening.  Speaker dampening = resistance to cone movement.

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I always thought speaker damping was the light application of moisture to the cone.

Steven Kephart

Adire Audio

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Steven Kephart wrote:

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I always thought speaker damping was the light application of moisture to the cone.

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Or when I cry over my spelling errors!  :)

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I thought it could be described at both damping and dampening.  Aren't they pretty much the same thing?  Tyme too git owt thee ole dictunaree.

In other words my intent wasn't to make fun of you for a spelling error, but to just make a joke. 

Steven Kephart

Adire Audio

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From www.dictionary.com:

"damp·ing    ( P )  Pronunciation Key  (dmpng)
n.

The capacity built into a mechanical or electrical device to prevent excessive correction and the resulting instability or oscillatory conditions."

"dampening

2. To depress; to check; to make dull; to lessen."

Hmmm.  I suppose Damping would be the most correct word to use.  But I still think dampening is just fine as well, so you are ok.  That is unless you were talking about something else. 

Steven Kephart

Adire Audio

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 Damping it is and should have been!  And please, feel free to both make jokes, and to make fun of my copious spelling errors.  I'm the first to admit I wish there was a spell checker on this forum....

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if your serious about spelling errors. i run Opera as my main browser, and if im ever concerned about spelling errors (which i rarely am, i just dunn care), i hit preview post, and i am able to copy a word to dictionary.com or encyclopedia.com, both are very handy sites, and i would recommend the browser to anyone, solid piece of software :-).

btw - there is also a plugin for opera which allows you to install a built in spellchecker but my last attempts to get it working failed.

ok, so how do you design a system to the Q of .707, is it mainly the enclosure design? basically all you did was give me a definition, i wanted to know how to design it.

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what!?!?! you want some??

Oh, well you need to know the math, and all of the parameters for the driver. Me, I plug in the numbers to my JBL Speakershop, and hit the button, The software will simultaneously provide me with a .707 alignment (the default) and a custom alignment which I can specify, simply by clicking a button. If you want, provide ALL of the specs you have for your chosen driver, and somebody can help you design the enclosure.

AND if you take a box with X alignment, and add damping (stuffing) it will change that alignment, or if you change the driver, it will change the alignment. And while almost ALL software assumes (or should assume) a perfectly rigid box, as well, and while we all know this DOES NOT EXIST (for all practical purposes) it does underscore the importance of a very rigid cabinet - any flex in the walls will change the Q from the ideal. The less flex in the enclosure, the less drift you will have from the calculated value of Q.

I hate spell checkers, because they allow "your" (the possessive) to be accepted (or excepted) as "you're" (a contraction for you are). I think typing grammar is more abused than spelling. Most people can make out the spelling errors, and see them as such, but how many people can see the grammatical errors. I LOVE OUR PUBLIC SCHOOLS!!!   BWAHAHAHAH (And the ACLU, Sorry DYohn!)

I agree, though. I always thought dampening was a light application of liquid to a surface, and damping was the adding of mass to a mass to lower the resonant capabilities of the original mass... I guess we all learn something new everyday. I never bothered to look it up. Thanks, Steven. Oh, and BTW, I will be in Las Vegas for the CES. See you then!

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Kickerstang,

There are plenty of free sites and software utilities that will help you find an enclosure size with the right Q. Just a warning, many people design car boxes with a higher Q than .707 because .707 can require quite a bit of box volume depending on the woofer.

For example, .8 many times leads to a significant decrease in box size with an acceptable effect on sound. In fact, some people like the slighly peaked sound for car audio.

Anyway, look for software packages that allow you to see the estimated curve and you'll be able to see what effect Q has on the curve as you change box volume.



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New Project: 2003 Pathfinder

A couple things to add.........

First of all, a .707 alignment might offer a maximaly flat response anechoic, but might sound a little bloated on the low end in the car due to the vehicle's transfer function.  You might want to keep that in mind when designing the enclosure.

Also, I see many people worry about being very accurate in their design.  Well I highly doubt anyone could hear the difference between a Q of .6 and .7 in a vehicle, and that offers a pretty large cushion in the enclosure size.  As long as you are close, don't worry about it.  You don't have to take the speaker displacement into account unless your enclosure is less than about .5 cubic feet.  Good luck!

Steven Kephart

Adire Audio

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haemphyst mentioned his JBL speakershop program, there is also WinISD which if you have all the parameters for your sub is a great program as well.

Isn't Q an alien on star trek?

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