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Old 11th April 2008, 03:52 PM   #1
JakeDN is offline JakeDN  United Kingdom
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Default Ported Enclosure Advice

First post here.

I've built a few kits in the past, but have now decided to start totally from scratch and do everything, all the way through to designing the crossovers.

None of the maths phases me so far, but after running the numbers (using equations from DIYSubwoofer website) for the sub im using, im starting to wonder if i have done something wrong, or am missing something. I think i just didnt expect it to be that big.

Im using a SEAS Prestige L26RFX/P 10" driver. From what i have come up with, the enclosure should be 88 litres (not including port volume) with the port being 12cm in diameter and 15" long.

The port calculations were made from the DIY subwoofer page, minimum diameter came out at 9.6 cm and it said to make it a bit bigger, so i used 12cm, is this ok? The length originally came out 21.6 inches, but after reading around the internet and talking to a couple of well respected builders it seems that it is too long and should be multiplied by 0.7 in order to get a better length. Obviously i will make it longer and play around once the speakers are built.

Some parameters:
Fs: 20Hz
VAS: 171 Litres
QTS: 0.33
QES: 0.39
Xmax: 7mm


Any advice anyone can provide would be greatly appreciated.

Cheers
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Old 11th April 2008, 03:58 PM   #2
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I would get yourself some modelling software like Basta! and check out the response, you can then play with volume and tuning to get the overall performance that you want.

Using software like this you can check power requirements and excursion as well.
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Old 11th April 2008, 04:27 PM   #3
sreten is online now sreten  United Kingdom
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Hi,

Box size is OK but IMO the tuning is not low enough and the port
should not be shortened by 0.7. Vent tuning of ~ 25Hz should be
reduced to ~ 20Hz IMO.

http://www.subwoofer-builder.com/flare-it.htm

/sreten.
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Old 12th April 2008, 10:10 AM   #4
Thawach is offline Thawach  Thailand
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JakeDN please you try to calculus two port. sometime it can work.
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Old 12th April 2008, 10:56 AM   #5
JakeDN is offline JakeDN  United Kingdom
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Cheers for the reply's.

@sreten: From what i have read, a port should not be tuned to the exact Fs of the driver as it can cause problems with the port, noise etc. Is this information not accurate? Tuning the port to 20Hz sounds like a fine idea, as i would really like these woofers to perform as low as they can go, but don't want to sacrifice quality in the process.

@Thawach: Is there a benefit to using two ports instead of one? The enclosure is most likely going to be trapezoid shaped, so the positioning of two ports would have to be 'stacked' vertically instead of horizontally. Could this cause problems?
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Old 12th April 2008, 11:06 AM   #6
Thawach is offline Thawach  Thailand
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JakeDN



i try 89 litre
fb=24.65
f3=27.72
vent dia=9.6 cm
vent length=32.92


regards/
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Old 12th April 2008, 11:56 AM   #7
JakeDN is offline JakeDN  United Kingdom
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Thawach, are those numbers for two ports? The volume is the same as i have been getting, not including the driver, ports and bracing.

The port diameter is the exact same as i have been getting, and reading around it seems making it slightly larger will reduce the chance of port noise. The length however is quite different.
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Old 12th April 2008, 01:15 PM   #8
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by JakeDN
Cheers for the reply's.

@sreten: From what i have read, a port should not be tuned to the exact Fs of the driver as it can cause problems with the port, noise etc. Is this information not accurate? Tuning the port to 20Hz sounds like a fine idea, as i would really like these woofers to perform as low as they can go, but don't want to sacrifice quality in the process.

@Thawach: Is there a benefit to using two ports instead of one? The enclosure is most likely going to be trapezoid shaped, so the positioning of two ports would have to be 'stacked' vertically instead of horizontally. Could this cause problems?
Hi,

The Fs of a driver does not influence the practical choice of the vent
tuning frequency. The driver has a very low Fs, consequently in a
large vented box handling of subsonics below the the port frequency
will be poor, ideally a subsonic filter is needed for high levels.

Multiple ports do not really help, CSA and length ends up near the same.

Flaring does help = smaller CSA = shorter length.
http://www.subwoofer-builder.com/
Has all the info you likely ever need to know for vented subs.

Dropping the port tuning from ~ 25Hz to ~ 20Hz will improve "quality".
The response droops but transient response and phase delay improves.

/sreten.
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Old 12th April 2008, 01:25 PM   #9
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by sreten
Dropping the port tuning from ~ 25Hz to ~ 20Hz will improve "quality".
The response droops but transient response and phase delay improves.
Is this the same as saying "aim for Bessel rather than Butterworth Q?"
If not then please explain.
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Old 12th April 2008, 01:55 PM   #10
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by AndrewT

Is this the same as saying "aim for Bessel rather than Butterworth Q?"
If not then please explain.
Hi,

You do not end up with Bessel but you do get nearer.
With the 90L volume it is a detuned Butterworth.

/sreten.
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