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Old 25th January 2006, 11:35 AM   #1
venki is offline venki  India
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Lightbulb Alternative to flaring of ports

Hello all,

This might be the most weirdest idea. I am in the process of making a 4th order sub. The maximum possible vent dia I could find was 12cm (PVC Pipe). For this also when i increase the volume i can clearly hear the turbulence noise coming through the vent.

I could not find any flare ready made in the market. So i was thinking whether making a diagonal cut at the mouth of the pipe
(say at 45 deg) will do the trick. This is a weird idea that came to my mind no mathematics to back just that a diagonal cut will increase the cross-sectional area and can be approximated for a one side flare.

Any comments are welcome.

Thanks in Advance,

Venki.
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Old 25th January 2006, 11:57 AM   #2
hooha is offline hooha  Canada
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If you have the tooling, you can create a 'flare' out of stacked wood/MDF/plywood - say, 3 pieces of 19mm thickness. You can then mount this flare on the outside of your box and adjust the length of your tube for the difference. If you shape the wood accordingly, the result may even be cosmetically pleasing...

Mark
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Old 25th January 2006, 10:09 PM   #3
Ron E is offline Ron E  United States
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Use a second port?

Make your chamfer and use a rasp to round the edges?

Heat PVC with a blowtorch (carefully) and flare the pipe?

Us a large funnel?

Build up a flare with layers of wood and automotive body filler?

Make a flare with polymer clay and bake it? - mind the shrinkage.

Turn a flare with wood and lay up a fiberglass/resin flare?

Make a prototype profile and thermoform it.
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Old 25th January 2006, 10:42 PM   #4
Collo is offline Collo  Australia
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Hi Venki,

cutting your pipe at an angle does give you a larger exit CSA, but there is no gradual transition to allow the airspeed to drop at a measured rate.

It's a too rapid deceleration of the air as it leaves the port that causes the noise.

I've written up a few options for DIY flares at:
http://www.users.bigpond.com/bcolliso/port-flares.htm

regards
Collo
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Old 25th January 2006, 11:02 PM   #5
owdi is offline owdi  United States
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Can you post the driver parameters, chamber size, and vent size?

Dan
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Old 31st January 2006, 04:26 PM   #6
venki is offline venki  India
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Hello all,

Thanks for all your replys

Sorry for the delay in responding i was out of station for about 1 week. Any way i did try out the diagonal cutting method, it did actually reduce the noise (even though adding the extra pipe changed the resonant frequency. As for the driver the T/S parameters are ( I used a T joint pipe and cut thru the diagonal joint)

fs 30.0 Hz free air resonance frequency
Rdc 5.3 Ohm DC-resistance
Qms 2.95 mechanical Q of the speaker
Qel 0.76 electrical Q of the speaker
Qts 0.60 total Q of the speaker
Mmd 34.95 g mass of driver's cone
Cms 0.80 mm/N compliance of driver's suspension
Vas 46.16 liter compliance volume of the speaker

The front volume is approx 25lt (including a 12cm dia vent about 21.5cm length) rear approx 30lt. I did add some stuffing in the front chamber since initially i considered the cent dia to be 8.5cm.

Thanks in advance,

Venki.
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