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-   -   Flex hose as port in vented cabinet ? (http://www.diyaudio.com/forums/subwoofers/96106-flex-hose-port-vented-cabinet.html)

Jan Dupont 11th February 2007 07:10 AM

Flex hose as port in vented cabinet ?
 
2 Attachment(s)
Does someone out here have any experience with using a flexible hose (e.g. those used in ventilation systems) in your vented woofer cabinet ?

The hose will be firmly attach in both ends, so it keeps the required calculated lenght.

Volenti 11th February 2007 07:37 AM

I don't think it would be stiff enough to support the resonance properly, that and the irregular internal surface would make for a very lossy port.

A harder,stiffer plastic like a vacume cleaner hose would be more suitable.(though larger of course)

Jan Dupont 11th February 2007 07:48 AM

My problem is that I need a port lenght at app. 68 cm = 26.5" so it could be nice to use a flexible hose to make a nice bended port without 90 degree bends.....

The dia. of the port is 10 cm = 2.5", so vacume cleaner hose isn't big enough (not those I've seen)

I was thinking of coating/spraying the hose with some kind of "hardener" after the fitting, so it won't flex.
Could this be an idea ???

infinia 11th February 2007 12:03 PM

Hi
I think you could use corrugated flex hose for a tuned port. But you should be careful to keep maximum air speed velocity in the port lower due to non smooth surface of the hose. IMO target air speed say less than 3% speed of sound max.
Then you would be more likely to see a larger diameter and in turn longer port dimensions than the normal calculation.
You could try the program UniBox if you have MS Excel which charts air speed velocity versus frequency in a vented enclosure as you change port dimentions. As always check final tuning with a measurement of impedance minima. IMO Flexing would most likey be a second order effect for such a large port.
regards,

Original Burnedfingers 11th February 2007 12:06 PM

Jan,

Have you tried PVC pipe? You will be able to make your bends and still be rigid.

Ron E 11th February 2007 12:16 PM

I don't think the flexibility is necessarily a bad thing, but the corrugations mean that your port may make noise. A whistling noise is often made by these sorts of pipes. The flexibility may actually reduce this tendency; but this is just conjecture, I have never used one.

Jan Dupont 11th February 2007 02:56 PM

infinia;
Thanks for the advise :)
However as the 15" driver I'm using got the exact same specs as the one used in the 1000 Watts B&O Penta 5, I had one of the engineers at B&O to calculate the the port and box volume for me ;)

burnedfingers;
I will look for suitable PVC pipe tomorrow, thanks ;)

Ron E;
Thanks for the input ;)

infinia 11th February 2007 10:44 PM

Hi
Thanks Jan, I guess you have Bang&O engineers on the job already.:D Seems B&O would use a custom driver for that design along with heavy EQ. IMO would be concerned with using just one 10 cm tube with a 15' sub. It's too small for such low tuning with a big driver at 1000W, will be supersonic air flow here. Look around and get other advise on this. OR check the design with UniBox.
Regards,

Jan Dupont 12th February 2007 02:26 PM

2 Attachment(s)
infinia;

I didn't say that I would put 1000 Watts into it... Only 400 :D
And I know for fact that this port size works ;)

The reason B&O uses 1000W is that they are using freq. Eq to get it to play straigh down to 20 Hz... I go for 25 Hz.

I have attached a copy of the calc. he did :)

infinia 12th February 2007 03:58 PM

FYI
 
2 Attachment(s)
Port air speed with a single 10cm port in a 2x10" 80l vented design at 440W which is tuned higher than a single 15".

Conclusion I would use at least 2x10cm ports for this design


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