Passive radiator use in bass trap? - diyAudio
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Old 19th September 2006, 10:54 PM   #1
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Default Passive radiator use in bass trap?

Hi there

I need an basstrap that is transportable and can be tuned to different fundamental room frequencies. While i was calculating the port lenghts for several fundamental room frequencies and could not find an adjustable port tube to fit the range i wanted my corner bass trap to absorb, i thought of an passive radiator instead of an adjustable port tube.

Is this an crazy idea? Or might it work out ok. I like the idea of mass tuning, instead of tubes between 4 and 30 inches long.

Roland
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Old 20th September 2006, 04:20 AM   #2
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That sounds quite reasonable, in theory.

In practice, you may find that a bass trap based on a port will have a sharper resonance than the passive radiator, and will pick out a single frequency more accurately. That's just a guess- it would have to do with whether the passive radiator's surround is more or less lossy than the air moving in a port tube.

One phenomenon that you may observe is distortion in your bass trap. As the surround reaches the end of its excursion, I think the nonlinearity will cause some harmonics to be produced. Of course, if there's so much bass in the air that the passive radiator is running out of excursion.... you may not care if it starts to sound funny since it will be so loud.
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Old 20th September 2006, 08:26 AM   #3
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Hi Joe

Thanks for the reply. Your post remembered me to make the volume of the Helmholtz enclosure not smaller than 50 times driver vd to minimize distortion caused by the non linearity's of compresed air.

I am, going to build it and will tell if it works ok.

Roland
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Old 20th September 2006, 08:59 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

as far as I'm aware it would be impossible to drive a bass
trap with a PR to anywhere near the PR's excursion limits.

/sreten.
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Old 20th September 2006, 01:50 PM   #5
Joules is offline Joules  United States
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Ive have often thought of using an inexpensive 12 or 15 inch woofer for just that. instead of mass loading a PR you could and and electrical filter to the terminals of the woofer, a resistor just to damp and or an arrangement capcitor and inductor as an easy to ajust notch, high pass or low pass filter - adjustable!
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Old 20th September 2006, 01:58 PM   #6
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Cool idea! with the adjustable Q and fs!

I just ordered some cheap dayton 10 inch Passive radiotors for the basstrap.

Thanks for the advice.
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Old 20th September 2006, 04:12 PM   #7
Ron E is offline Ron E  United States
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A more typical way to make tunable resonators is to use hardboard with different hole patterns in it. You could just use pegboard and put painters tape over some of the holes to tune it.

You could also just make a big membrane out of hardboard and put varying amounts of mass to it bay adding asphalt shingles or lead sheet or some such ....
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Old 20th September 2006, 04:28 PM   #8
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Hi Ron

I want to use them in this type of bastrap, not in an panel absorber.

http://www.mhsoft.nl/Helmholtzabsorb...zPanelAbsorber

The type called Helmholtz-Resonator.

Groet Roland
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Old 20th September 2006, 04:52 PM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by roland bios
Hi Ron

I want to use them in this type of bastrap, not in an panel absorber.

http://www.mhsoft.nl/Helmholtzabsorb...zPanelAbsorber

The type called Helmholtz-Resonator.

Groet Roland

Quote:
Originally posted by Ron E
A more typical way to make tunable resonators is to use hardboard with different hole patterns in it. You could just use pegboard and put painters tape over some of the holes to tune it.
As RonE states the above is a Helmholtz Resonator trap.
I built a whole series tuned 1/2 an octave apart ranging from 2"
depth all holes open to 8" depth with 1/4 of the holes open.

Area does not affect the tuning but they were 8ft x 2ft each.

/sreten.
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Old 20th September 2006, 09:53 PM   #10
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Hi

something like this:

Click the image to open in full size.

Every Radiator tuned to an different fundamental freq. And 3 separated enclosures inside.

Would it be an good idea to put the radiators on the small side to give them some better "corner loading"?

Groeten Roland
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