TIM reduction for treble drivers/tweeters
In the old days before T/S parameters - in this particular instance that means 1977, we had a loudspeaker guru here in Denmark with the name of Peter Holm. I don’t exactly know his background, but it was academic with a lot of practical experience. He was somehow connected with the distributor of Goodmans speakers out of the UK.
He designed a TIM reduction stage for treble drivers, because TIM distortion with frequencies above 20 KHz needs somewhere to go, not to distort the area below 20 KHz, and not to be converted into heat in the treble driver voice coil eventually killing it.
It all seems very plausible, and it is actually just another 6 dB ´way´ in a traditional filter, and can be used both in parallel and serial filters, and it only needs 3 components - 4 if you want a visual indicator.
Hopefully the picture is attached.
And here are the formulas:
f the attack frequency of the filter, down 3 dB
R the nominal impedance of the treble driver
C 160,000/(f x R) in uF
L (160 x R)/f in mH
D standard LED (optional)
Example, 8 ohm driver, and 20 KHz:
R = 8 ohm power resistor, probably 5 – 10w will do
C = 160,000/(20,000 x 8) = 1 uF, plastic crossover cap
L = (160 x8)/20,000 = 0.06 mH coil
If you can’t get the coil in the right value just buy the closest one larger, and hook it up to a inductance meter and unwind straighten out and measure until the value is right, then cut the excess wire.
All that said I have also had very good experience in reducing aggressive tendencies in the upper mids (typically 400 – 1200Hz) in HiFi speakers by using a standard treble driver resonance reduction filter – try it!
Best regards
Arthur.
In the old days before T/S parameters - in this particular instance that means 1977, we had a loudspeaker guru here in Denmark with the name of Peter Holm. I don’t exactly know his background, but it was academic with a lot of practical experience. He was somehow connected with the distributor of Goodmans speakers out of the UK.
He designed a TIM reduction stage for treble drivers, because TIM distortion with frequencies above 20 KHz needs somewhere to go, not to distort the area below 20 KHz, and not to be converted into heat in the treble driver voice coil eventually killing it.
It all seems very plausible, and it is actually just another 6 dB ´way´ in a traditional filter, and can be used both in parallel and serial filters, and it only needs 3 components - 4 if you want a visual indicator.
Hopefully the picture is attached.
And here are the formulas:
f the attack frequency of the filter, down 3 dB
R the nominal impedance of the treble driver
C 160,000/(f x R) in uF
L (160 x R)/f in mH
D standard LED (optional)
Example, 8 ohm driver, and 20 KHz:
R = 8 ohm power resistor, probably 5 – 10w will do
C = 160,000/(20,000 x 8) = 1 uF, plastic crossover cap
L = (160 x8)/20,000 = 0.06 mH coil
If you can’t get the coil in the right value just buy the closest one larger, and hook it up to a inductance meter and unwind straighten out and measure until the value is right, then cut the excess wire.
All that said I have also had very good experience in reducing aggressive tendencies in the upper mids (typically 400 – 1200Hz) in HiFi speakers by using a standard treble driver resonance reduction filter – try it!
Best regards
Arthur.
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