active crossover vs. full range

[Vix]

Hi everybody!
I have built a class A amplifier (zen). It is currently working with 4 inch fullrange TL speakers. I have also built an active, sealed subwoofer using a 12 inch driver to handle the low frequencies(using 100w amp). As a crossover, I am using 24db/octave active crossover (can be found on a Rod Elliot's webpage). However, I am having difficulties with a choice of crossover frequency. At first, I crossed the subwoofer at 80 HZ, and let my fullrange speakers operate at full signal. At low to medium levels, it works fine. However, when it's louder, small fullranges suffer from large cone movements, at low frequencies. To cure that, I tried to let the signal go through high-pass, 80Hz x-over, to prevent the low frequencies overlad the small fullrange drivers. And, they seem to be more relaxed, however, the sound quality degraded. Imaging and clarity at medium levels was not as good... What is the problem? Is it because of opamps in a signal path? I am using TL 072 devices. BTW, some folks say that a subwoofer and main speakers should overlap for one full octave...etc, etc.
Generally, I am confused about a right choice of a crossover frequency. What combination of crossover frequencies would sound best? Any advice is welcome. Thank you very much,
Vix

[sreten]

TL071's and a Zen class A don't sound like a happy combination.

NE3552/4 may be better.

However you could try a simple high pass filter by reducing the
input coupling capacitor value of the Zen, I presume it has one.

24dB/octave sounds too fast a rolloff for the subwoofer.

You could try driving the input of the crossover with a simple
passive 1st order low pass to complement the above and set
the active crossover an octave or so higher.

First set the Zen input capacitor to clean up high levels and
take it from there. I'd set the c/o to 250Hz and then play
with the passive 1st order low pass to match the speakers.

sreten.

[ThorstenL]

Konnichiwa,

Originally posted by Vix
I have built a class A amplifier (zen). It is currently working with 4 inch fullrange TL speakers. I have also built an active, sealed subwoofer using a 12 inch driver to handle the low frequencies(using 100w amp). As a crossover, I am using 24db/octave active crossover (can be found on a Rod Elliot's webpage).

Knowing Mr. Elliots usual design style, this sounds like a surefire way of making sure that the result will be pretty much FUBAR.

Originally posted by Vix
However, I am having difficulties with a choice of crossover frequency. At first, I crossed the subwoofer at 80 HZ, and let my fullrange speakers operate at full signal. At low to medium levels, it works fine. However, when it's louder, small fullranges suffer from large cone movements, at low frequencies.

As they would.

Originally posted by Vix
To cure that, I tried to let the signal go through high-pass, 80Hz x-over, to prevent the low frequencies overlad the small fullrange drivers. And, they seem to be more relaxed, however, the sound quality degraded.

What do you epect with that kidn of X-Over?

I would also expect the integration to be poor as your 4" System will probably already start rolling off around 100Hz..

Originally posted by Vix
Imaging and clarity at medium levels was not as good... What is the problem? Is it because of opamps in a signal path?

What do you think?

Originally posted by Vix
I am using TL 072 devices.

Yuck. Why not go straight for a 741? This way the sound will be even a little worse.

Originally posted by Vix
BTW, some folks say that a subwoofer and main speakers should overlap for one full octave...etc, etc.

If a "textbook" crossover is desired to work - yes.

Originally posted by Vix
Generally, I am confused about a right choice of a crossover frequency. What combination of crossover frequencies would sound best?

Well, your TL Speakers have a rathe runpredicatble response. Have you measured the frequency response? Also, have you suitably equalised the Subwoofer to offer flat response? If not, that would be the first steps to get an idea how this works best.

I personally would likely use the Fullrange driver in a sealed box, which gives the system a very predictable, 2nd order highpass charateristic. Complement this with a suitable bessel 2nd order highpass and you have an acoustic 4th order highpass at exactly the point where the Fullrange system runs out of steam anyway. Then using a textbook 4th order lowpass on the (equalised) subwoofer will make sure everything falls into place.

You can implement a 2nd order highpass by reducing the Zen Amplifiers input and output capacitor in value to a suitable Value to match the fullrange's requirements. This will at the worst leave the sound of the Amplifier untouched but will likely provide you with the opportunity to use better quality components (the smaller value a capacitor the better quality solutions become readily available, affordable and suitably sized), thus actually improving the sound.

Sayonara

[dokter dB]

I think you probably don't really make good use of the acoustic load of the TL if you c/o @80Hz 24 dB, at least it could be shorter/smaller if you don't use it under 80Hz. So it can be a waste of space/length, although I don't know ho big it is now, with the 4" it is probably not that long.
Why not use a coaxial speaker, in that way that the cone can be more optimized (xmax etc.) for the TL, but thats probably against the fostex fullrange-lover rules?

I disagree with textbookfilter not being ok (its just a filter, if adjusted right for the application its just ok). I also disagree with the good old TL072 being not good enough. I think if the filter is configured proper, the TL072 doesn't contibute that much audible side effects as the filter does itself (high pass).
And I wouldn't go for 5532/5534 as they are transistor opamps. Good for the noisefigures, but better for circuits with impedances under 10k. The 5532 transistor-inputs have an impedance of 100k, so distortion is rising outside the filters passband. If you want better performance than TL-072, take one of the burr brown opa's (opa 4132 dual, note that the quad version 4134 only comes in smd package). Or something else with fet inputs and bipolar outputs orso.

Soundwise: I think there is someting else wrong and agree with
sreten that a first order high pass filter can be far much better in your case, and probably sums much nicer with the sub, also because you can overlap without too much problems. but it still depends on a lot of things. Did you measure the filter as being right? is there maybe an allpass network in the highpass section that is changing the mid/high response too much, do you have a link to the filter?

[Vix]

Thanks very much, I will try implementing a first order high pass, thus eliminating opamps from Zen's signal path. For a low bass I assume that a 24db/octave can ramain as it is; probably I may need to experiment with a different x-over freq. (100-110Hz?).
Or, what about this: first order high pass filter for fullrages, and I could build a 12db/octave low pass for a sub? And...does anyone have a suitable schematic for that?
Thanks a lot
Vix