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Old 9th December 2003, 09:51 PM   #11
Illusus is offline Illusus  Canada
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I have built a test ML TL for a Fostex FE206E with a downfiring port, I extended the cab below the port and used a slanted panel to deflect the port's output toward the back. Works great. Even better is a tractrix contour cone centered underneath the port to diffuse the output, but a lathe is with a large capacity is almost essential, stacking sections and then using a rasp to file the contour is also plausible but some "artistic" skill is necessary to keep the contour accurate.
Using the Baffle thickness as a flare is a good practice I use in all my front firing port cabinets. I use a ring with the inside rounded glued to the port end inside of the cab as a flare. The driver cutout is great stock for making these, cuts down on waste.
Regards,
Bart G.
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Old 10th December 2003, 01:26 AM   #12
Guss is offline Guss  Canada
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Are flared port immune to Helmholtzs ''whistle''?
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Old 10th December 2003, 01:28 AM   #13
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In my experience with subs, flared ports are less likely to whistle, but really, an appropriately sized port won't whistle either way.
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Old 10th December 2003, 01:51 AM   #14
Guss is offline Guss  Canada
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You guys just scared me...and you still! And BTW, sorry for hijacking the thread turning it on my own for a while

Using a single 2x9 port I had a match of 13
Using two 2x20 port gave me a match of 03 which is satisfying. The ratio would then be 1:10 right ? Which is not desirable. In your experience, is it worth destroying a nice responce to fit a port ratio?

65Hz to 200Hz at -1dB (MIGHT be compensated by a significant raise a these freq from the woofer)
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Old 10th December 2003, 03:33 AM   #15
usekgb is offline usekgb  United States
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Quote:
Originally posted by Guss
You guys just scared me...and you still! And BTW, sorry for hijacking the thread turning it on my own for a while

Using a single 2x9 port I had a match of 13
Using two 2x20 port gave me a match of 03 which is satisfying. The ratio would then be 1:10 right ? Which is not desirable. In your experience, is it worth destroying a nice responce to fit a port ratio?

65Hz to 200Hz at -1dB (MIGHT be compensated by a significant raise a these freq from the woofer)
First off, that's Mach, not Match for your ports. The Mach number that WinISD is giving you is, the speed of the air traveling through the port. Generally, a good rule of thumb is to keep the Mach speed under Much .1, although WinISD will still stay green a little higher. As far as your 2x20 port with a Mach speed of 0.03, that will actually be very good. throw that ratio thing out. You don't need it now that your modeling software can tell you the Mach speed of the air in the ports. A Mach speed of 0.03 will ensure that your ports never resonate, as the air speed through the ports will be quite low. In fact, you will barely be able to feel the air coming out of them at that speed.

My current speakers use 2 3"x9" ports, and the Mach number I got was 0.03. I can only feel the air moving through them during VERY loud LF passages. I hope this helps.

Cheers,
Zach
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Old 10th December 2003, 05:03 AM   #16
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Quote:
Originally posted by usekgb
...throw that ratio thing out. You don't need it now that your modeling software can tell you the Mach speed of the air in the ports. A Mach speed of 0.03 will ensure that your ports never resonate, as the air speed through the ports will be quite low. In fact, you will barely be able to feel the air coming out of them at that speed.

Cheers,
Zach
You can through it out the "ratio thing" if you wish, it's my preference and Small's recommendation. The air speed in the port has nearly zero to do with the Helmholtz resonate frequency of the port. The Helmholtz resonance of the port is a factor of the length of the port and to a lessor degree, the diameter.
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Old 10th December 2003, 06:32 AM   #17
usekgb is offline usekgb  United States
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Sorry Rod.....I don't mean to offend. But, with some of the newer sofware models, it isn't really a strict rule anymore. It is a good idea to keep the ratio smaller, but I think Guss's 2 2x20" ports should work just fine. Personally, I would try to use a 3" port as you suggested earlier. 2" ports just make me nervous.

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Zach
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Old 10th December 2003, 06:50 AM   #18
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mOtion if there was a Nobel prize for missinformation you should have it. Y.ou must include the baffle thickness in the length of the tube. If you have a 5" thick baffle you just make a hole. A 4" and you make the tube 1". What counts is the air volume in the tube. Donīt post if you donīt know.
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Old 10th December 2003, 06:58 AM   #19
usekgb is offline usekgb  United States
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Thanks Wcoil. I noticed that earlier, but forgot to say something. I'm glad somebody caught it.

Cheers,
Zach
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Old 10th December 2003, 11:25 AM   #20
Guss is offline Guss  Canada
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Quote:
Originally posted by roddyama

You can through it out the "ratio thing" if you wish, it's my preference and Small's recommendation. The air speed in the port has nearly zero to do with the Helmholtz resonate frequency of the port. The Helmholtz resonance of the port is a factor of the length of the port and to a lessor degree, the diameter.

Yeah actually I know about the winsid match the speed of air and resonance blablabla. When you mentionned Helmholtz I was affraid reproducing it with very long tubes, anyway I'll see... I'll flare both ends

Thanks

Quote:
3" port as you suggested earlier. 2" ports just make me nervous.
Well I'd need a 23''long tube for a single one to get a match ( winsid ) of 6. I had the pipe bought long time ago and I didn't want to waste much money, just another way saving for the drivers.
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