While this seems reasonable, the formula comes up with a frequency of nearly 13kHz, which is obviously wrong. There are series resistances in the entire treble control network, and the interactions are interesting to say the least. In fact, the +/- 3dB frequency for the treble control changes with the pot setting. For example, at 80% of rotation, treble boost is +3dB at just over 3.5kHz, with a maximum boost of 6.3dB at 20kHz. This may seem to be a bad thing, having the frequency shifting about as the pot is varied, but in practice it works very well. To obtain the results you want, I suggest that experimentation is in order !
Thanks Nico but I'm a little unclear about which circuit you like. Is it this?
http://www.diyaudio.com/forums/atta...8-aspen-headphone-amp-hpampvolbaldeftone1.gif
or this?
file:///C:/DOCUME~1/Linda/LOCALS~1/Temp/loudness.bmp
Problem with the Baxandal eq. is that it continues boosting the treble and bass to the full frequency extremes. This overdrives the woofer and I also have a room resonance at 40hz.
Yes, exactly as I mentioned before:
Normally a series capacitor would attenuate the low frequency below some chosen point.
The -3dB point is when Xc = 56K, now change the capacitor value to give the roll-off you want