subwoofer Qs

[steven]

ive heard about the total Q of a sub determines proper enclosure size??? how does that work exactly? because i have two different subs, one thats .35 and another thats .62 and they sound equally good to me in the same 2.75 ported enclosure. thanks for anyone that might be able to clear this up for me.

[daryl]

Provided Link: Daryl's Speaker Stuff. (http://www.villagephotos.com/pubgallery.asp?id_=144711)


> ive heard about the total Q of a sub
> determines proper enclosure size??? how does
> that work exactly? because i have two
> different subs, one thats .35 and another
> thats .62 and they sound equally good to me
> in the same 2.75 ported enclosure. thanks
> for anyone that might be able to clear this
> up for me.

Yeah I am seeing lately a lot folks seem to be figuring out what size box is necessary to raise the Q of a driver to a given value regardless of Ftc (which is important) and, viola that according to them is a subwoofer.

It's more complicated than that if you ask me.

There are a number of approaches to designing a subwoofer.

Sometimes you wish to implement a certain approach and sometimes you are going to let the specifics of each individual driver steer you toward the approach you wish to use for that driver and in turn help you make your final decision based on the possibilities presented by each prospective driver.

With a low Qts and low Le driver you might just put it in a sealed box that results in a fairly low Qtc which will in turn result in a smooth response easily extended with a simple line level passive or active filter.

Other drivers might have specs which lend themselves to unassisted sealed or ported alignments.

Of course you are going to have some sort of target response in mind and manipulate the enclosure parameters to achieve your goals.

Systems with lower corner frequencies can likely be more damped to compensate room gain and save excursion and enclosure volume.

Qts can be increased to any level desired with the addition of series resistance but you must be aware that Re and Znom will increase as well (Znom is approxamately 1.4 x Re) and sensitivity and efficiency will go down (they will still be exactly what they ought to be for a driver with the new specs so you don't really lose efficiency you just end up with a different driver).

A capacitor can be used in series with drivers in sealed boxes creating a 'third order sealed' system and extending response below Ftc.

This type of system is especially benificial for high Qts drivers since third order sealed systems use the highest Qtc's.

If you have a driver where Re/Le is less than 1500 or so it is a good idea to employ as much series resistance as possible and utilize the third order sealed alignment since it uses the highest Qtc and will allow you to use the most series resistance.

This approach with high Le driver will help you swamp the effects of Le which not only causes the response of such drivers to be a skinny peak which is unlike what most box software predicts but also causes distortion due to non-linear Le wich will be modulated by coil position and current.

I guess what I am saying is that there is more to consider than Qts and Vas.

[Chris Roemer]

> ive heard about the total Q of a sub
> determines proper enclosure size??? how does
> that work exactly? because i have two
> different subs, one thats .35 and another
> thats .62 and they sound equally good to me
> in the same 2.75 ported enclosure. thanks
> for anyone that might be able to clear this
> up for me.

I found 2 drivers in WinISD <A HREF="http://www.linearteam.org">www.linearteam.org</A> that match your criteria. Dayton's "Classic" 10" has a Qts of .35, and a Vas of 3.5. It would "like" a box that size tuned to 27 Hz, but would probably be OK in a box that size tuned to 30 Hz.

The Beyma 6 B30P has a Qts of .62, and a Vas of 0.64 cf. It would like a 2.75 cf box tuned to 33 Hz, but would probably be "OK" if it was tuned to 30 Hz.

The lower Q driver has a much smoother response near the tuning freq. IMHO a driver with a Qts up in the .50's or .60's would be best used in a sealed enclosure.

A box program (like WinISD) basically just looks at Qts. and Vas to determine the proper box size. For the same size box, if the Q goes up, the Vas has to go down.