looking - theory

rathek

Member
2004-10-21 4:32 pm
Helo!

Im looking for a "A Bandpass Loudspeaker Enclosure"
by L.R. Fincham [Preprint 1512 presented at the 63rd Convention of the Audio Engineering Society Journal of the Audio Engineering Society (Abstracts), Vol. 27, p. 600 (1979 July/Aug.)]

or some pdf, txt,…about theory of speakers enclosures, equivalent circuits ( bandbass, vented, closed ) from AES.

Thanks.
 
I have it ! I got it from Mr. Fincham himself. But it will take me some time to undig it. There was one a speaker-builder article abput those equivalent circuits. I wrote a Pascal Program to simulate those years back. But nowadays there are many CONVENIENT (mine wasn't) programs around to simulate all kind of bandpass enclosures.

Regards

Charles
 
I have it ! I got it from Mr. Fincham himself. But it will take me some time to undig it. There was one a speaker-builder article abput those equivalent circuits. I wrote a Pascal Program to simulate those years back. But nowadays there are many CONVENIENT (mine wasn't) programs around to simulate all kind of bandpass enclosures.

Regards

Charles
Hi Charles, did you ever find your copy? If so, do you mind sharing? I tried to PM you but you have too many stored PMs. Thank-you!
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Steve,
I never use Bing, being a Micro$oft product and all. No way to I trust them! The other thing is that I'm useless finding anything on the internet.

I built a system like this in the very early 80's. Amazing bass from an 8" woofer, tight too. Everyone keeps looking for the subwoofer in the room. And these are just the proof of concept prototypes that I built first. The group got the real deal that used Peerless drivers. I'm using less good Philips drivers and they are still going strong. I hear everyone is still using the speakers we made - every single pair.

The one problem I see with the prototypes is the doppler distortion due to the excellent low frequency response.

-Chris
 
Initially I was disappointed as I was hoping the article was about traditional bandpass enclosures (ported). Yet, it was mostly about bandpass enclosures with passive radiators instead of a ports.

However, I read the whole thing and was glad I did!

Quick summary: While bandpass enclosures are often assumed to have good low pass acoustic filter characteristics, it is not often the case as resonances may be audible above the pass band. Thus, a low pass filter is recommend for bandpass enclosures. However, the resonances above the pass band may be also be acoustically treated. Even though the test enclosure was lined with bonded acetate fibre wadding, the measured resonances were horrible and did not match the predicted response (using simplified equivalent circuit). The author loosely filled the front chamber (one with passive radiator) with 300mm discs of 50 glass fibre (fiberglass?). Interestingly, the author measured the filled enclosure twice, via analogue and digital FFT. As the measurements differed, the author was able to deduce the loosely fastened fill as the culprit. Once the fill was secured in the enclosure, the analogue and FFT measurements agreed. Thus, it may be worthwhile to consider adding appropriate fill in a bandpass type enclosure to mitigate out of band resonances which color the sound (although this may only be effective for passive radiators, not ported bandpass - not sure). However, as the author points out, while resolving the out of band resonances, such fill may negate the efficiency advantages of the bandpass.

Also of interest is Figure 1 illustrating the contributions of the drive unit and vent to the total output of a vented bandpass enclosure.
 
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