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Old 18th August 2008, 11:31 AM   #1
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Default Question about using 2 ports of unequal length. Why?

I rescued a pair of Pioneer SCS13 2-ways from a footpath (/sidewalk /nature strip).
8" W + 2" T.
You can see in the attached photo that they have two ports of equal diameter, but unequal length.
Intriguing. Why did they do this?

Any ideas?

cheers

Doug
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File Type: jpg pioneerscs13.jpg (46.8 KB, 420 views)
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Old 18th August 2008, 11:39 AM   #2
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It's "supposed" to give two tuning frequencies to offer broader support to the driver, but I've read that it doesn't work that well. It would be fairly easy to tell by some manual visual sweeps and impedance curves.
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Old 18th August 2008, 12:06 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

It does not work "well" at all. Close off the shorter port.

/sreten.
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Old 18th August 2008, 12:12 PM   #4
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Quote:
Originally posted by sreten
Hi,

It does not work "well" at all. Close off the shorter port.

/sreten.
That's easy enough to try. I'll have a go at it this weekend.

Cop ya later!

Doug
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Old 18th August 2008, 05:19 PM   #5
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It doesn't work full stop. The effect of two vents is to just combine the two vent masses into one single mass, and give one tuning frequency.
However if you block off the shorter vent you will change the overall vent tuning frequency. Whether you prefer the result is up to you, but you will have made a change to the sound.

Andrew
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Old 18th August 2008, 05:58 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by AndrewJ


It doesn't work full stop.
The effect of two vents is to just combine the two vent masses into one single mass, and give one tuning frequency.

However if you block off the shorter vent you will change the overall vent tuning frequency.

Whether you prefer the result is up to you, but you will have made a change to the sound.

Andrew
Hi,

a) No. it does not work like that. The short one has more effect.

b) True. The asssumption being the lowered frequency still works.
Blocking off the longer port will not make much difference.

c) True. but b) should go deeper with less boom.

/sreten.
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Old 18th August 2008, 06:55 PM   #7
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I wonder what the effect would be on the BR impedance peaks with two ports of different lengths. Would the traditional two peaks broaden or even separate into more peaks?

Also, what if the 'shorter' port (tuned higher) also was of a slightly different diameter? Could this be used to counteract the tendency to favor that port as far as tuning goes?
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Old 18th August 2008, 09:01 PM   #8
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Quote:
Originally posted by thoriated
I wonder what the effect would be on the BR impedance peaks with two ports of different lengths. Would the traditional two peaks broaden or even separate into more peaks?

Also, what if the 'shorter' port (tuned higher) also was of a slightly different diameter? Could this be used to counteract the tendency to favor that port as far as tuning goes?
Visually they appear to be identical diameter, but I will measure them and report back.

Doug
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Old 18th August 2008, 09:35 PM   #9
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Default Re: Question about using 2 ports of unequal length. Why?

Quote:
Originally posted by Brisso57
two ports of equal diameter, but unequal length.
Intriguing. Why did they do this?

Any ideas?

cheers

Doug
maybe lowering port self resonance?
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Old 20th August 2008, 01:57 PM   #10
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Default Re: Re: Question about using 2 ports of unequal length. Why?

Quote:
Originally posted by crazyhub
maybe lowering port self resonance?
does somebody agree with my statement?
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