Aperiodic loading to lower qt

[Defo]

I'm planning a design with a pair of Seas CA22RNY and I want a slim closed enclosure with a qt of 0,5 for the best low end extension and transient response. I need over 50 liters to achieve that. The problem is that with the current enclosure dimentions I have a qt of over 0,7 and volume of only 20 liters.

For that reason I wonder if aperiodic loading could be a solution? Maybe make some slits in the back plate and cover them with damping material. Or some finished aperiodic vents?

[planet10]

If you can damp the ports from the inside, this is my favotite (bottom right)



dave

[dantheman]

Defo, I wouldn't worry about transients in the low end. The room will dominate there and the transients in music are higher in frequency.

Dan

[ultrakaz]

Hello, are there any guidelines as to how many, and size of the holes? And what type of material for damping? I believe the Scanspeak vents, are used per cubic foot, but doesn't the type of driver (ie high Q) make a difference?

[planet10]

I use open cel foam to damp the ports. I have a number of densities to play with. I typically use Sd or less as a ref (start with less you can always drill more).

Best way to tune is to measure impedance... you want to reduce the magnitude of the impedance peak. Almost flat is perfect. A click test with a battery can be used doe a sonic test. Hard to calibrate... GM has posted on this one. It can also be done by ear with music.

dave

[dantheman]

Originally Posted by planet10

Best way to tune is to measure impedance... you want to reduce the magnitude of the impedance peak. Almost flat is perfect. A click test with a battery can be used doe a sonic test. Hard to calibrate... GM has posted on this one. It can also be done by ear with music.

dave

What would you listen for Dave?

Thanks,

Dan

[Defo]

Originally Posted by planet10

I use open cel foam to damp the ports. I have a number of densities to play with. I typically use Sd or less as a ref (start with less you can always drill more).

Best way to tune is to measure impedance... you want to reduce the magnitude of the impedance peak. Almost flat is perfect. A click test with a battery can be used doe a sonic test. Hard to calibrate... GM has posted on this one. It can also be done by ear with music.

dave

So the thicker or thinner layer (or higher density?) of damping material behind the holes is the way to experiment?

Can the Dayton woofer tester be used for this?

How do you think the concept presented in the first post looks like? Is it a bad idea with such a slim enclosure?

[planet10]

When faced with listening i pick some well recorded bass and listen for well defined bass with no artificial overhang.

The woofer WT-3 (or better WT-2) will work fine.

the tall box should work well... the aperiodic vents would go at the top. You might want to leave the top removable to get at the posts to adject damping.
I use different densities of foam as well as different thicknesses. Fortunately i get a lot of apple service parts boxes which gives up supplying all the foam i ever need.

I got a big boost from the work done by Bill Perkins on aperiodic damping, and then added experience on top of that. Attached are some pics & diagram of the speaker that culminated Bill's research.

dave

[dantheman]

When faced with listening i pick some well recorded bass and listen for well defined bass with no artificial overhang.

Seems like a daunting task. I've learned that anytime I do something by ear, I screw it up--unless it's tuning an instrument. Measurements always do a better job for me. Can you really get this right in a regular room or do you have an anechoic chamber? Have you done this by ear and then measured it to see how you did?

Thanks again,

Dan

[planet10]

In room. Yes, measure confirms ear (it is a chore to hump a big woofer into my office wher ethe impedance jig is), You can usually close in on optimum faster with the impedance tester at hand.

dave