A question on membrane tension

[Carl Van Camp]

Hi all-

On the Bev 3 thread it was mentioned the tension of the membrane is very high.  I assume this held true across all the different models.

My question is - why was this done?  What aspects did this improve?  What problems did it avoid?  Is there anyone left who knows?

Thank you.

[Rich Morin]

Arthur or Rick can supply chapter and verse, but I think the simple answer is that the mylar is thicker and heavier than the stuff used in other electrostats (partly because of the aluminum coating). I also think that the higher tension allows the speaker to be louder. Arthur?

-r

[av]

The membrane needs to be critically centered between the stators, else one side (on this type) will travel more one side than the other. To achieve that (as well as proper return to center), the membrane is stretched far more than "normal" ESLs. To sustain such tension, the mylar is thicker than normal ESLs by a factor of 2 to 3, to withstand the stretching forces. The aluminium coating doesn't add too much to the overall thickness.

Interestingly for some, the potential propensity of the mylar to be "discentered" was the late Roger Modjeski's (who worked with Harold Beveridge) main criticism of the transducer, claiming this might/will introduce distortion.

Even when H.B. moved to Model 3 and 5, with half voltage and spaced stators, he kept the same mylar thickness and tension (including the last "pegboard", perforated and not so successful stators).

As to the guy from Chicago, I checked with him and he tells me that he is currently "overwhelmed with helping too many Bev owners", as he puts it, so unfortunately he doesn't take new orders. We'll probably have to wait.

AV.