[planet10]

a PLLXO requires smaller component values than speaker level high-pass filters...

The PLLXO is also being loaded by a fixed resistance as opposed to a highly reactive load that, near the bottom of its passband, has dramatic changes in magnitude. A PLLXO can be pretty much text-bookm not the case with a passive XO between speaker & amp.

Also a PLLXO can be implemented with gigh quality parts that cost $10s of dollars (if onw goes to town on parts), similar qualirt parts for a passive XO (if you could get it to work) will be $100s of dollars.

Further, with a SET, you are much less likely to saturate the OPT if you filter out the low frequencies and you put less strain on the power supply.

dave

[doug s.]

in other words, what's being said here is something i have always believed - active x-overs rule!!!   

ymmv,

doug s.

[chadh]

So, is there any difference between (1) an active crossover and (2) an active gain stage (for example, in the pre-amp) that is immediately followed by a PLLXO?  Can an active crossover completely replace one's pre-amp?

Chad

[chrisby]

in other words, what's being said here is something i have always believed - active x-overs rule!!!   

ymmv,

doug s.

Well actually, Doug - I think what Dave is talking about is only passive components (i.e. L, C &  R - depending on function and slope, it can be reduced to only passive 2 parts per filter pole) In many cases either using or altering the input impedance of the amp can reduce it to only 1 part .  That allows lots of budget room for boutique zoot parts, if one is so inclined 

In fact I did exactly this a few years back with a pair of Decware Zen amps driving a pair of Fostex / Heil AMT 2-ways.  For those not familiar with this particular amp, it has 2 pairs of inputs jacks and a selector switch for adjusting bias load on input tube.  By re-purposing these, and fixing the bias setting, it was easy to provide for selection between full-range bypass, or HP filtering for the amp driving the tweeters, which were crossed over somewhere around 3500 IIRC.

While of course there may be some minor insertion loss, we are talking systems that are at least bi-amped, so ....

[FullRangeMan]

Hmmm...I was thinking about a pair of these.  But I don't think I can get them in the same finish as my Omegas.



Chad

WOW,  Looks this is the FOSTEX 32 inches woofer, 2500 dollars at Madisound catalog...
I just wish this cone for a FR OB speaker and stop listen small FR forever, Why Fostex do not made a real FR with this Cone/Basket ?
 and just add a Alnico motor please...
P.S.: This woofer must work fine as OB panel, as VAS is 3200 litres and QTS 0,69.

[doctorcilantro]

So it's essential to  utilize a low-pass on my sub wiring? I have some Omega 3i on the way with sub and Louis suggested hooking up the sub to amp terminals for a better impedance matchup. He said the amp won't even see the sub. The only amp I have on hand is a Sophia Electric Baby which will be fed by a Peachtree Nova with either fixed or variable output, not sure yet.

DC

[chrisby]

So it's essential to  utilize a low-pass on my sub wiring? I have some Omega 3i on the way with sub and Louis suggested hooking up the sub to amp terminals for a better impedance matchup. He said the amp won't even see the sub. The only amp I have on hand is a Sophia Electric Baby which will be fed by a Peachtree Nova with either fixed or variable output, not sure yet.

DC

Yes, if you plan on running your mains full range, use the speaker (high) level inputs of a sub woofer's plate amp - it will track more closely the "sonic signature" of your Sophia. 


For a couple of reasons, you're probably better off to use a separate stereo run of wire from the main amp to the sub:

First, the best sounding or aesthetically most appealing location for the sub might require a much longer series run of wiring through to the mains than it  would in parallel. When compared to impedance fluctuations of even the most well damped full range driver, the attenuation circuit on the speaker level input of the amp is high enough in impedance that it would have negligible effect on the load to the amp.

Second, some plate amps with outputs for return to mains, there may be a cheap high pass filter at a fixed setting.  Even if the nominal XO point an slope "works" for your configuration, the sonic quality of these networks is usually quite poor.

The speaker wire to the sub doesn't need to be anything special.

 

[Telstar]

My 2 cents.

4-5" FR can work in a well designed box. I dont have direct experience with such drivers. i'm pretty sure that the suggestion to highpass it at (least) 100hz is a good one.

I have experience with 8" and 12" in open baffle, where roughly double of the diameter is required to keep distortion at acceptable levels and recreate a nice "live" sound.
I have a 300hz highpass on the FR with a very steep curve (Q=6)(active and digital of course). Any lower and I feel both distortion with loud/complex music and discontinuity with the bass (12" woofers in U-frame).
This in my small room. In a bigger room I would consider to use 2x8-inchers, or a 10", a 12"+ or 12/15" coaxials. I'm actually considering getting a 12" widerange anyway. I think i like "big", "live" sound, those who know the old JBL know what I'm talking about. Less the crossovers.

In a big room I also think that a 4.5" is too small for the job.