Lowering Fs.

[tinitus]

Originally Posted by audiomagnate

Had what "been around 20hz?"

new 88db SPL

hey, how about trying them both in the presents box, which sounds like its too small ...isobaric clamshell mounted

[audiomagnate]

Originally Posted by tinitus

new 88db SPL

hey, how about trying them both in the presents box, which sounds like its too small ...isobaric clamshell mounted

The clamshell models very close to a simple sealed design. Since I have two boxes, I think I'll stick with simple sealed systems.

[tinitus]

clamshell would be closed as well....it just means it halfs the box volume
from your describtion I suspect your present closed boxes are too small
relatively speaking, it would make your present boxes twice as big
it should be easy to try with additional attached front baffle

[sreten]

Hi,

The current 3cuft boxes with the original drivers should be vented
to about 40Hz, which will add about 5dB to 40Hz over sealed.

If they are sealed, Q is about 0.6 and they are ideal for adding
bass boost, ideally with a peaking 2nd order high pass.

Adding significant mass means they would need to be sealed.

Doubling mass and 3cuft well stuffed would work quite well.
Q would be about 0.8, less mass you add the lower the Q.

Personally rather than sand and epoxy I'd spray car
underseal onto the cone, masking off the surround.
Use a digital scale to measure the added mass, if
that's possible, or monitor Fs changes for the same.

Tetroseal car plan Black 500ML BLACK UNDERSEAL AEROSOL - LIMITED OFFER | eBay

I'd guess is enough to do both.

rgds, sreten.

Investigate / review spraying techniques if you are not sure.
Something you can spin the driver on can help a lot.

[audiomagnate]

Thanks again streten. The boxes are currently tuned to 35 Hz and I don't like the sound. It's great for rock but other music makes it sound thumpy and resonant. I'll pick up a can of undercoating and give it a shot. My scale is not accurate at those weights so I'll just keep spraying until I get to my desired Fs.

[bjorno]

Originally Posted by audiomagnate

Thanks again streten. The boxes are currently tuned to 35 Hz and I don't like the sound. It's great for rock but other music makes it sound thumpy and resonant. I'll pick up a can of undercoating and give it a shot. My scale is not accurate at those weights so I'll just keep spraying until I get to my desired Fs.

Hi audiomagnate,

Why chase fs..IMO,you should consider other options:

b

[OMNIFEX]

Originally Posted by audiomagnate

I already have a pair of very nice cabinets, 3^ft in size.

Your cabinets are too small to achieve low bass with 15-inch pro drivers. You can either build larger boxes or step down to twelves or tens.

Even if you lower the fs with mass on your 15-inch drivers, your cabinets may raise the fs right back up. If the box was very big, the fs of the driver would be lower in the box than residing in free air.

[audiomagnate]

[QUOTE=OMNIFEX;3342806... If the box was very big, the fs of the driver would be lower in the box than residing in free air.[/QUOTE]
That makes no sense to me at all.

[OMNIFEX]

Originally Posted by audiomagnate

That makes no sense to me at all.

The fs of the loudspeaker in the cabinet usually shifts downwards if the cabinet is optimum sized or larger than the loudspeaker's requirements.

The link below offers the TS Parameters of one of my older Beyma 18-inch drivers.

Beyma Speakers - Beyma 18LX60 speaker - Beyma 18LX60 1200 watt 18" woofer for all bass applications. Beyma 18LX60 and other Beyma 18" speakers here.

This is the measured impedance curve of the loudspeaker in the box.




As you can see, the loudspeaker offers an fs of 27 Hz in free air and, 19.04 Hz in the box. A 3 cubic foot box for a 15-inch pro driver is not going to give you low bass for the limiting factor is the enclosure size.

[tinitus]

I suppose it shows a very low tuned vented box, and what we see is port tuning ?