Different "Q" in sealed boxes

[Moondog55]

OK, this isn't a question about what effects the size of the box has on the overall response of the driver.

Rather what effect when listening is the effect of having two two different "sub-woofers" handling the same pass-band i.e: frequencies below 120Hz, but with different drivers with different "Qtc"

I just finished rebuilding the Kicker box and I want to utilize a big Cerwin Vega woofer i have sitting on the shelf, if I make a box of 120 liters it will be almost critically damped and have a "Qtc" of about 0.57.

I do not have the WAF to built the big TL that this driver deserves so I have to build as small as possible, NO 3 meter towers in the corner.
So I will have the Kicker with a warm "Q" of 0.85 and the Cerwin Vega with "Q" of 0.57

Is this good or bad? or will the room totally over-ride these differences??

[Moondog55]

What???
No opinions from any-one??

Well then; I guess I'll spend a few dollars on chipboard and make a full size test box and listen for a few days.

it is a very small room5M * 4.5M and not the best shape and the Kicker box when EQ'd gives a rich bottom end, one both of us can live with ( which is important ) the main problem that I can see is having the amp clip when driving the CV

[breez]

Originally posted by Moondog55
will the room totally over-ride these differences??

Yes! And this is the reason why sealed box Q factor does not have a great effect on sound quality. Forget talk about sloppy bass, tight bass etc. usually associated with small differences in Q (say ~0.6 vs ~0.9). The room mode Q factors are certainly much much higher.

There are other considerations though. Too small box may roll off the bass too early and may be a problem if you can't equalize it back. And even EQing is problematic because of the reduced efficiency of small box and much higher power requirements.

[Moondog55]

OK thanks, just confirming what my thoughts were.

The 120 litres is a big box for this particular driver

[RobWells]

Don't know anything about the drivers but I do know that the phase / group delay will be different on each driver which won't help..

How about using a big EBS type vented enclosure for 1 driver down low and cross it to a Linkwitz transformed small box for the other one ? Xo around the 30Hz mark. Uses both drivers and when the home theater EBS is kicking out the huge rumbles the LT box will still be unstressed and 'tight'

Rob.

[Moondog55]

Hadn't thought too much about group delay and phase.

From that POV maybe I should use a smaller box for the CV but chip board is cheap enough.

LT is a brute force solution that reqires amplifier power I don't have at the moment but it has been in the back of my mind

[breez]

Regarding phase/group delay, again the room dominates. By having the other subwoofer even a short distance from the other yields much larger difference than between the subs. What we hear is the total response, there is no 'direct sound' at low frequencies.

[Ron E]

Originally posted by Moondog55
Rather what effect when listening is the effect of having two two different "sub-woofers" handling the same pass-band i.e: frequencies below 120Hz, but with different drivers with different "Qtc"

Is this good or bad? or will the room totally over-ride these differences??

I'd say it doesn't matter much as long as they are fairly close together and they are receiving the same signal. If one is "Left" and the other "right" you could have symmetry/imaging issues depending on where they are crossed over.

[RobWells]

What happens if the x-max is different, or there are vast differences in the response at high power levels ? one driver could be distorting or hitting its end stops whilst the other isn't. - What would that do to the other drivers response ?

I've read many times that a drivers parameters will vary with heat on the voice coil. This would put other differences into the equation...

Anyway maybe I should have typed " Personally I'd prefer to run like for like drivers in my system " It was opinions he asked for and you know what they say about those


Cheers,
Rob.

[Baldin]

Totally agree with breez (and glad to see someone with the same rational view point

Any way. I think you should start with determining what you'll use the sub(s) for.

1. It it's for a home theater where it will be connected to the LFE output of a 5.1 set-up, I would defenetly go for a big reflex box.
(haven't tried horns (tapped) but I guess this might also be a good solution). A reflex system will give som much more slam for the buck than a seled system. You need to make it go down to about 35 Hz for a good result, but you don't have to go all the way down to 20 Hz in my perspective/experience.

2. For stereo listening you could make a smaller sealed system. You will probably have to use a Linkwitch transform to make it go deep enough. The smaller the box, and the lower you want it to go, the more power you need (and the more power the sub needs to handle)

As for multiple subs, it's actually a very good idea to minimize room mode influences ... the more the better

Actually the smaller the room the more problems you'll nrmally have with room modes. (the larger the room the more evenly spread the modes will be and will reduce the problem).

As for reflex/closed, the closed box will sound more "dry". But a well constructed reflex system can to my mind sound really good, and will "breathe" more.

I use 2 x 12" JBL's in a old school 2 x 120 l reflex system with 100 W to each. For movies, it's really scarry, and I have never had to play at more than ½ volume!
http://home20.inet.tele.dk/audio/Hom.../Construct.htm
Look at the bottom of the page

For Stereo I just finished my 12" Peerless XLS based sub. It uses 400W, and going down to 20 Hz, it realy need this amount of power to max out. But again you need much higher sound levels for movies than for stereo, so it can easily handle the situation.
http://home20.inet.tele.dk/audio/SubZero/SubZero.htm
I build in a parametric eq to handle the most dominate room mode. It works fine, and can be reccomended, but after I have rebuilt my room, doing a lot to suppres room modes, I don't use it.

And as breez said, the room is what sets the limits for good bass.

Looking forward to hearing/seeing what you ended up with and how it sounds
Best regards Baldin



PS. If you tell us the exact drivers you have, I'll try to do a simulation, and tell you what I would do .... (not all drivers are subwoofer material )