I am replacing an 8 ohm tweeter with a 4 ohm. The woofer and mid are 8 ohm.
4 ohm - Tweeter = 91.6dB (2.83V/1m)
8ohm - Bass, Mid = 86dB (2.83V/1m)
5.6dB Difference
How is it best to design the new crossover with an Lpad. I can make the Lpad look like an 8 ohm load impedance or should I just make it a 4 ohm Lpad. I am referring to the impedance the filter and amp sees.
I can’t actually make the Lpad an 8 ohm load impedance as I can’t achieve 5.6dB attenuation, but I can make it say a 5 ohm load impedance.
The tweeter actually measures 3 ohm at 3Khz. That is low and making the Lpad with a higher input impedance may be better. But this will also make the series resistor in the Lpad larger and effect the dampening of the tweeter.
The amp is a Quad 405-II
Tweeter – ScanSpeak illuminator D3004/662000
Mid – KEF B110
Bass – KEF B139
Speakers - Cambridge R50
Please Help 🙂
4 ohm - Tweeter = 91.6dB (2.83V/1m)
8ohm - Bass, Mid = 86dB (2.83V/1m)
5.6dB Difference
How is it best to design the new crossover with an Lpad. I can make the Lpad look like an 8 ohm load impedance or should I just make it a 4 ohm Lpad. I am referring to the impedance the filter and amp sees.
I can’t actually make the Lpad an 8 ohm load impedance as I can’t achieve 5.6dB attenuation, but I can make it say a 5 ohm load impedance.
The tweeter actually measures 3 ohm at 3Khz. That is low and making the Lpad with a higher input impedance may be better. But this will also make the series resistor in the Lpad larger and effect the dampening of the tweeter.
The amp is a Quad 405-II
Tweeter – ScanSpeak illuminator D3004/662000
Mid – KEF B110
Bass – KEF B139
Speakers - Cambridge R50
Please Help 🙂
It might work fine with just a 4 ohm resistor in series with the tweeter which makes it look like an 8 ohm driver to the crossover and pads it down a few dB. I would try that with no other changes and if it still seems a little hot then put an 8 ohm L-pad in front of that to adjust the level down. All this is assuming that the new tweeter is capable of comfortably playing just as low as the old one did..
Agree, the chance of hearing a 0.4dB error is very low. Alternatively you could just use a slightly lower value resistor. 3R3 would give 5.2dB.
BUT... and a big BUT....
Watch the actual impedance of the tweeter across the passband. The resonance will put in a peak in the impedance at resonance (generally 800-1500Hz) that goes up a lot if the tweeter is not highly damped. Peaks in the 20+ Ohm range are normal for many tweeters.
This will mean your attenuation is near zero at resonance resulting in:
- A peak there that sounds annoying - sometimes - depending on the material being played.
- Poor power handling due to excess power below XO
This part of the crossover design needs to be watched....
Look at the tweeter freq response and ALSO the impedance. It is important.
BUT... and a big BUT....
Watch the actual impedance of the tweeter across the passband. The resonance will put in a peak in the impedance at resonance (generally 800-1500Hz) that goes up a lot if the tweeter is not highly damped. Peaks in the 20+ Ohm range are normal for many tweeters.
This will mean your attenuation is near zero at resonance resulting in:
- A peak there that sounds annoying - sometimes - depending on the material being played.
- Poor power handling due to excess power below XO
This part of the crossover design needs to be watched....
Look at the tweeter freq response and ALSO the impedance. It is important.
Thanks Guys
The tweeter is 3.03 ohms at 3Khz (crossover freq). I have accurately measured this and it differs from manufactures spec of 3.9 ohm.
Resonance freq = 500Hz with max impedance of approx. 21 ohm (not measured)
I don’t like the idea of a series resistor as it is greater than that of an Lpad (less dampening).
I can make an Lpad that has an input impedance of 5.2 ohm with 2.47 ohm series, 27.5 ohm parallel.
I think this may be a good compromise, but I worry I am missing something.
Tweeter - http://www.scan-speak.dk/datasheet/pdf/d3004-662000.pdf
The tweeter is 3.03 ohms at 3Khz (crossover freq). I have accurately measured this and it differs from manufactures spec of 3.9 ohm.
Resonance freq = 500Hz with max impedance of approx. 21 ohm (not measured)
I don’t like the idea of a series resistor as it is greater than that of an Lpad (less dampening).
I can make an Lpad that has an input impedance of 5.2 ohm with 2.47 ohm series, 27.5 ohm parallel.
I think this may be a good compromise, but I worry I am missing something.
Tweeter - http://www.scan-speak.dk/datasheet/pdf/d3004-662000.pdf
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