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Old 17th January 2013, 03:10 PM   #1
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Default multiple ports all tuned to different Hz

I've been into car audio for around 15 years. I have a fairly good understanding of how things operate concerning car audio. I've been wondering what would a subwoofer eclosure built with 2, 3, 4, 5, 6, 7, or even 8 or more ports, all tuned to different Hz e.g. (1stp-25Hz, 2ndp-30Hz, 3rdp-35Hz, 4thp-40Hz, 5thp 45Hz, etc) sound like. And would it work (function properly).
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Old 17th January 2013, 05:35 PM   #2
JMFahey is offline JMFahey  Argentina
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You mean a single air cavity with various different sized ports in its walls?
It does not work that way.
You basically have a single "capacitor" (the air elasticity inside the box) and many "inductors" (the air mass in the different tubes).
That system will have a *single* resonant frequency, coming from the single "capacitance" and the *single* "inductance" , coming from the combination of all the individual ones.
Quite a rough analogy, but hope it to be a reasonable explanation.
The most you can achieve is with a speaker mounted inside a dividing wall in a cabinet, where each half can be tuned to a different frequency, and that because each half becomes a different "capacitor".
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Old 17th January 2013, 05:42 PM   #3
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very god explanation.. i bet someone will come along and calculators will come out and then after 10,000 words . will come to the same conclusion..
Regards mark
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Old 17th January 2013, 06:31 PM   #4
sreten is offline sreten  United Kingdom
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It doesn't work, as I've explained may times and you haven't searched.

The higher tuned ports "short" out the lower tuned ports, so all they
do its take up cabinet volume without doing anything useful at all.

rgds, sreten.
There is nothing more practical than a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
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Old 19th January 2013, 10:16 AM   #5
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As a car audio competitor, I've tried MANY enclosure variations. The many diff port lengths, it doesn't work quite like you'd think. If your looking for adjustable tuning, the best I can recommend is look into using aero ports. They are the easiest way. Then you can add/remove different port lengths, to achieve the tuning you desire.

Good luck, hope this helps.
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Old 19th January 2013, 10:42 AM   #6
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Say you have a long port and a short port side by side. Cover the short port and dial the frequency down to where the long port is really pumping and consequently the driver cone is barely moving. Uncover the short port and the driver loses it's load and maxes out because at that low frequency the short port acts just like a big leak in the box. At the higher frequency where the short port would work, the long one would appear to be somewhat blocked, the more so the higher the frequency. As mentioned, the best you can do is different sized boxes and ports on the front and back of the driver. Look up 6th order bandpass.
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Last edited by Circlotron; 19th January 2013 at 10:45 AM.
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Old 20th January 2013, 01:52 AM   #7
mat3833 is offline mat3833  United States
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or you can use plugs to plug the ports you arent using. or make an adjustable aero port. my home theater has 3 ports. 1 tuned to 34hz, one tuned to 28 hz and the last is tuned to 20 hz. i keep 2 of the 3 blocked(sometimes block all 3). it lets me have a system that sounds good on music, VHS, and DVD. :-)

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Old 20th January 2013, 09:33 AM   #8
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Just blocking the ports changes the enclosures VB every-time you unblock one and block another due to the different port lengths. I have tested this a few different times. The only way to have a solid predictable outcome, is to change only one variable at a time and test. If your playing with port for tuning, you must keep the internal volume the same, otherwise your just shooting in the dark.

This is why people do like I said above. One box, keep port on outside and change port lengths as you like. We usually use 2... one for daily (much longer) and a shorter one for competition (tuned higher).

Last edited by Deadly Sones; 20th January 2013 at 09:36 AM.
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Old 20th January 2013, 01:45 PM   #9
amc32 is offline amc32  United States
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If your looking for the benefits of extended output using multiple ports@multiple tuning freq. Study and research a series-tuned ported enclosure. Not to be confused with a bandpass varitation enclosure. I have use this type of enclosure in a car audio, though it is for home audio due to its volume requirements.

Basic requirments: Standard Vb for woofer X
Vb is the total of V1+V2
V1 is twice the volume of V2
Tuning Fz@Vb
Calculate single port demensions for Vb
Make 3 identical ports of Vb, install@V1,@V2 and to connect V1 to V2 internally

Effective tuning freq's are an octave apart. Example: Vb tuning frequency is 30hz, enclosure now has 2 tuning freq's 30HZ & 60Hz.....

This is just a general overview of the design
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Old 20th January 2013, 02:15 PM   #10
Illusus is offline Illusus  Canada
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I you are thinking you can build a vented tuned to multiple frequencies for a wideband response the only ways I can think of , other than multiple chambers, is one can extend a port's bandwidth by cutting a Karlson slot in it or use a conical vent. Panasonic(Technics) used conical ports to that effect (I think). I'm not sure about the effectiveness of either technique. In my experience aperiodic (stuffed vent) vents are a good reliable solution to peaky-response bass-reflex enclosures, or a well designed BR system in the first place.
Fighting the program since 1976.
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