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Old 30th January 2008, 08:42 AM   #1
focal7C is offline focal7C  Australia
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Default Port to Passive Radiator conversion

Have you any experience with Passive Radiators in speaker design and/or do you you any good sources I can read?

Decided to investigate the possibility of converting a ported reflex speaker to use a Passive Radiator element instead.

Is feasible? Will the deep bass efficiency be similar? What are the constraints/initiations?

The inside dimensions of the box are 623mm high x 198mm wide x 241mm deep. The inside is lined with lined with 13mm bituminised panels on all surfaces. The current steel port is 65mm wide 80 mm deep.

What are the guidelines for tuning the passive radiator to the cone motion and box?

The selection of locally available Passive radiators seems limited? I have so far only found the Peerless 830800 (8") which may be suitable to front mount with my 7" woofer. It is also reasonably priced.

/Roger
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Old 30th January 2008, 01:25 PM   #2
fpara is offline fpara  Canada
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PR enclosures are slightly more complex to build and calibrate, but can be better performers if done properly.

The bass response can even be improved slightly, and/or the enclosure volume, lessened.

Checkout Seas, they make a few good passives.

A good read, which should answer many of your questions:
http://www.aespeakers.com/phpbb2/vie....php?f=4&t=549
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Old 30th January 2008, 07:39 PM   #3
Svante is offline Svante  Sweden
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This is an attempt to convert a bass-reflex to passive radiator...

http://www.tolvan.com/portmassa.3gp

Apologies for the obscure file format (from my mobile phone).
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Old 30th January 2008, 11:44 PM   #4
Ron E is offline Ron E  United States
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small passives typically have a rather high Fs and low Vas, which is opposite from what you want and results in a PR notch very close to tuning frequency and a sharp rolloff.

attached is a picture of the amplitude response of a Vifa P17WH with a small 8" PR made from a typical coil-less woofer. The Peak in maxSPL is at the tuning frequency, the notch is the free air resonance of the PR.

What I am trying to say, run the numbers in software before buying.
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File Type: gif smallpr.gif (9.8 KB, 94 views)
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