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Old 25th January 2013, 03:09 PM   #11
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by audiomagnate View Post
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
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Old 25th January 2013, 04:02 PM   #12
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Quote:
Originally Posted by tinitus View Post
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.
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Old 25th January 2013, 06:00 PM   #13
tinitus is offline tinitus  Europe
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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
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Old 25th January 2013, 06:59 PM   #14
sreten is offline sreten  United Kingdom
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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.
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Last edited by sreten; 25th January 2013 at 07:10 PM.
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Old 25th January 2013, 08:34 PM   #15
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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.

Last edited by audiomagnate; 25th January 2013 at 08:36 PM.
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Old 25th January 2013, 09:37 PM   #16
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by audiomagnate View Post
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
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Old 26th January 2013, 10:23 AM   #17
OMNIFEX is offline OMNIFEX  Jamaica
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Quote:
Originally Posted by audiomagnate View Post
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.
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Old 26th January 2013, 12:33 PM   #18
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[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.
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Old 26th January 2013, 04:13 PM   #19
OMNIFEX is offline OMNIFEX  Jamaica
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Quote:
Originally Posted by audiomagnate View Post
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.

Click the image to open in full size.


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.
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Last edited by OMNIFEX; 26th January 2013 at 04:23 PM.
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Old 26th January 2013, 04:19 PM   #20
tinitus is offline tinitus  Europe
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I suppose it shows a very low tuned vented box, and what we see is port tuning ?
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