Silencer Speaker Baffle

[IG81]

Any tips on how to roughly size a boffle for a specific driver? Seems like this one is a fairly decent match for the BG20. Am I correct to think that mid-Qts drivers would be best in such an enclosure?

IG

 

[Joachim Gerhard]

The size is approximately like a comparable reflex box.

 

[bjohng]

Thanks for sharing your experiments and results.

However, It seems to me that the 5/8" thick under carpet felt used by Hartley was a significant component in his testing. This is very different from your fiber board which appears to give the results expected of an aperiodic speaker. If I am wrong then perhaps you could give a us a more detailed description of your fiberboard.

In an optimally designed "Boffle" would the impedance curve be completely flat? I don't think this was ever addressed by Hartley.

 

[Joachim Gerhard]

I think the impedance curve can be made flatter when the exit hole is damped, just like a variovent.

 

[Joachim Gerhard]

My question is : do we want that and how does it sound ?

 

[Joachim Gerhard]

The felt that Hartley used may also damp the impedance peaks but i think they will not go away unless the exit is damped. I can try that.
My "green" material is stiffer and harder then felt, sure.

 

[Joachim Gerhard]

Here is a closed box with and without a variovent :
http://www.troelsgravesen.dk/W1501_95_files/15W_8530_K01_9500_imp_closed_Variovent_D.gif

 

[Joachim Gerhard]

Here Ted Jordan is describing his Axiom cabinet, a kind of variovent i think so the idea is not new :
http://www.ejjordan.co.uk/PDFs/A-Cabinet-of-Reduced-Size-with-Better-Low-Frequency-Performance.pdf

 

[IG81]

Aperiodic can be good with the right driver, but is often a compromised versus simple sealed box, where a small enclosure size is the prime goal. This here boffle clearly has multiple tuning frequencies and lots of damping would make it aperiodic, but I'm not sure either we want that; it would not be a boffle anymore. Hard to say what would be best from this point without hearing it though.

IG

 

[xrk971]

For some reason I think it would sound like a driver mounted in a hole in a wall between two rooms. Like an open baffle but without any rear wall reflection.

 

[Joachim Gerhard]

A speaker mounted that way would only have one fundamental resonance peak, the boffle has two, more like a reflex.

 

[Joachim Gerhard]

The first picture shows the round exit at the back lightly stuffed with foam.
The second picture shows the effect of more stuffing, foam and polyester wool.