Midrange sealed box, Qtc and box spring distortion

[spice house]

Wonderful post TMM!

 

[Grasso789]

You seem to forget that the non-linearity of the air cannot be compensated without active feedback. So your suggestion only adds further non-linearities through the overcompensation instead reducing it.

I may seem to but i do not. My suggestion was not to compensate air distortion but to avoid it by raising air volume. As Q will be lower then, motor distortion will be higher. I suggested to fight this distortion by raising source impedance either by current feedback or a specially designed passive highpass.

Back on topic, air distortion raises with frequency. For direct radiators, excursion raises with the square of the inverse of frequency, so air distortion still raises with the inverse of frequency.

 

[ICG]

I may seem to but i do not. My suggestion was not to compensate air distortion but to avoid it by raising air volume. As Q will be lower then, motor distortion will be higher. I suggested to fight this distortion by raising source impedance either by current feedback or a specially designed passive highpass.

You don't even understand amplifiers, do you? With current feedback you don't increase the source impedance or the other way around, if you increase the source impedance and (over)compensate it via current feedback, you decrease it again because it effectively alters the damping factor.

Back on topic, air distortion raises with frequency. For direct radiators, excursion raises with the square of the inverse of frequency, so air distortion still raises with the inverse of frequency.

Exactly the opposite, because with rising frequency you have more radiating surface on the same driver which equals to higher acoustical impedance and less excursion, which means less air to be compressed, the minimum and maximum air pressure within the back volume are much closer together, therefore not more distortion instead it's less distortion.

Easy to follow that in 'real life': Loudspeakers with huge membrane surfaces usually sound relaxter, more souvereign.

 

[spice house]

For those wondering what box air spring distortion is here is a good thread on it from this site

http://www.diyaudio.com/forums/multi-way/144749-air-spring-non-linearity-causes.html

the equation and thought for that thread originates on linkwitz lab site

Electrical and mechanical limits