How to calculate low and high frequency extension of a driver...? (1 Viewer)

[RichardHOS]

I know enclosure design + T/S parameters will indicate low frequency rolloff. I've modeled that in WinISD eval version, so I suppose that covers that end?

But what about high frequency extension? In one or two other threads here, I've seen mention of an electrical T/S parameter that indicates high frequency extension. What exactly is that, and how is it used to determine high frquency extension? Is that influenced heavily by enclosure design, or is it essentially dependant only on the driver?

Are there other factors to consider other than frequency response to choose an appropriate driver for a certain frequency range (e.g., a mid-bass passband from ~80Hz to ~200Hz)? i.e., I know driver size and frequency have some relationship (as in above a certain size for a given frequency, the driver no longer looks like a point source)... how critical is that?

 

[Michael R Price]

Richard,

The inductance (Le) of the voice coil creates a 6db/oct rolloff starting around a certain frequency. I've seen drivers with different inductance specifications at different frequencies, so it's probably a nonlinear effect. Most woofers roll off steeply past a certain point, which is probably higher than the inductance's corner frequency because many drivers have a naturally rising response with increasing frequency, counteracting the inductance. (I think the big peaks before rolloff are breakup modes, but I don't know exactly what that means. It might be that the cone starts to flex and becomes ... un-pistonic.)

I forget the directivity rules for driver size, but I do think an 8" woofer starts to beam around 2KHz, for example.

 

[RichardHOS]

A good start... thanks. So, can anyone explain how to go from Le to finding the -6db high freq. roll-off point of a woofer or mid-woofer? Also, are cone break-up frequencies commonly available for various speakers?

I suppose the size thing is to just keep the driver diameter less than one wavelength at the maximum frequency desired... correct?

 

[RichardHOS]

^^ anyone? ^^

 

[Michael R Price]

Sorry Richard, I don't know much more than that. I don't think you can accurately predict a driver's high end extension just from the inductance, though. The cone breakup characteristics are different for every speaker... though it usually doesn't sound very good (distortion) and that's part of the reason why larger drivers tend to be crossed over lower.

 

[RichardHOS]

Heh, thanks for trying anyway.

Anyone else? I would have thought this was a standard question when choosing drivers appropriate for a certain frequency range. Maybe I should have posted this in the DIY forum instead. :frowning: