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Old 22nd December 2002, 03:14 AM   #41
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Quote:
Originally posted by JoeBob
I'd like to put a passive line-level xover between two tube buffers, would this be a good idea, or should I just build a traditional active xover?
This is exactly how you make an active tube XO.

Active Tube XOs

The heath XO-1 is a good example.

dave
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Old 22nd December 2002, 05:07 AM   #42
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Quote:
Originally posted by bob4
Hi folks,

I wanted to ask if the passive line level crossover would be ok for PA?
Hi Bob,

For compression drivers, definitely no. In this instance if you use a shallow rolloff at the recommended xover frequency, and put a decent amount of power into them, the diaphrams will hit the phase plug, and dent them, or if you use TADs, shatter the beryllium diaphram. The lower the frequency a compression driver has to produce, the more excursion required, and like all drivers, distortion is proportional to about the square of the excursion, so keep it as low as possible. In a domestic situation, you can get away with a lot. My compression drivers are specced for 800W continuous at 400Hz with a 24db HPF at 400Hz. I use 6dB at 400, but seldom see 2W at home, so I'm still not going near the excursion limits.

Cone drivers front hornloaded will flap around madly if you put too much LF into them below the Fc of the flare, and it may not damage them, but could set up FM distortion within their passband and make them sound crappy. At the top end the mass corner of the driver, and it's inductance will eventually form about a 12dB rolloff, but it might not be that much on axis, making pattern control in an array difficult.

Ported boxes, sound best rolled off below the port frequency IMO. At the top end the large cones will start to beam and breakup, interfering with the performance of the units above in the system. Roll them off hard.

So in summary, no, rolloff the individual elements in a PA system out of band. Saves on wasted amplifier power too. The only exception I could think of would be in an installed system that was way over designed for the application, say something that was capable of supporting a loud rock band, and only ever did girl and guitar type performances. In that case it might sound better: might not too, and you want to be sure no one ever booked a thrash band for the room.

I had a chance to play with one of <a href="http://bpgprod.sel.sony.com/Professional/webapp/ModelInfo?m=0&sm=0&p=10&sp=89&id=55637">these</a> for a couple of weeks recently, and it sounded great when used in a PA application as I could dial everything in very well, but annoyed me at home on the Khorns, which sound better passive 6dB on the mid/high, and the bassbin run wide open..

Cheers
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Old 22nd December 2002, 05:21 AM   #43
halojoy is offline halojoy  Sweden
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Quote:
Originally posted by planet10


This is exactly how you make an active tube XO.

Active Tube XOs

The heath XO-1 is a good example.

dave
Another way to make exactly the same:

Use a Dual OP-amp
and put the Crossover between the 2 buffer amplifiers.
As gain is only 1 - the eventual effect on signal quality
would be minimal - you can say the OPamp is transparent,
doesn't effect signal to measurable degree

low cost - mininmal space - no complicated Power supply
even possible to use a couple of batteries.

There are OP amps (CMOS) - Complementary MOSfet output stage= PNP+NPN
that only consumes LESS than 10uA - 0.00001 Ampere
A litium battery would supply such an OPamp
for Years and Years.

CMOS OPamps - shouldn't this be heaven
for all our MOSFET - Loving Fellows

/halojoy wants to know more
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Old 22nd December 2002, 05:32 AM   #44
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Quote:
Originally posted by halojoy

Another way to make exactly the same:

Use a Dual OP-amp
and put the Crossover between the 2 buffer amplifiers.
As gain is only 1 - the eventual effect on signal quality
would be minimal - you can say the OPamp is transparent,
doesn't effect signal to measurable degree
Why go to the trouble of creating a good tube system, and then stuffing everything through a couple of crappy opamps? Very strange and a big WOFTAM.
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Old 22nd December 2002, 09:26 AM   #45
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Just figured out what WOFTAM means....

In my unenlightened days, I utilized a Crown VFX-1 active crossover with my ssssssolid sssssstate amps and thought I was really onto something.

Later on I made the mistake of using it between the drivers of the VOT with two tube amps.

If one ever needs a demonstration of just how horrible inserting solid state devices into the signal path can be, just try doing something like that!!!

Lee
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Old 22nd December 2002, 09:29 AM   #46
bob4 is offline bob4  Germany
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Talking Industry's best kept secret

Frank,

thanks for the answer,
Quote:
Originally posted by fdegrove
Hi Bob,

Pssssst...

Industry's best kept secret...

Bob..Why shouldn't it?

Ciao,
I was just wondering if it would be efficient enough.....

Brett, I will be using it to cross over between my subs and Mid/Hi CAbs at about 300 Hz or so. The tops are 2way, 15" / 1" , so the HF driver won't get in trouble. And I won't be using it forever, just until I can afford something better.

thanks for helping out everybody, I'll build the thing and tell you how I liked it.
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Old 22nd December 2002, 09:44 AM   #47
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Default Re: Industry's best kept secret

Quote:
Originally posted by bob4
Brett, I will be using it to cross over between my subs and Mid/Hi CAbs at about 300 Hz or so. The tops are 2way, 15" / 1" , so the HF driver won't get in trouble.
Bob,
Try the 12dB PLLXO. Probably work fine in your instance.

Cheers
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Old 22nd December 2002, 04:10 PM   #48
bob4 is offline bob4  Germany
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Brett,

I'll do it. Simple enough to build, and as I'm on christmas vacation.....
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Old 22nd December 2002, 04:55 PM   #49
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Whats the driver number? I'll look it up in my Altec book and post it. Typically the HF drivers for Altec/EV/JBL either cross at 500HZ or 800HZ. It is recommended to keep the crossover either 18 or 24db per octave unless you enjoy cleaning the diaphram material out of the gap.

Joe
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Old 22nd December 2002, 05:17 PM   #50
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Quote:
Originally posted by burnedfingers
Whats the driver number? I'll look it up in my Altec book and post it. Typically the HF drivers for Altec/EV/JBL either cross at 500HZ or 800HZ. It is recommended to keep the crossover either 18 or 24db per octave unless you enjoy cleaning the diaphram material out of the gap.

Joe
]
Joe,
My reading of Bob's intention is to use the PLLXO between a sub and a 15" mid at 300Hz.

Cheers
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