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Passive Line Level Compensation Network? [message #44096]

Mon, 01 March 2004 09:01

GarMan
Messages: 960
Registered: May 2009

Illuminati (2nd Degree)

Wayne,

In a bi-amp configuration, what are your thoughts on implementing HF compensation as a passive line level network, rather than at the speaker. My thinking is, if the 10db or so attenuation is done before amplification, I can get away with using an amp with one tenth the power.

If the compensation network is brought to line level, can the high pass filter remain at the speaker, or do the two have to stay together?

thanks,
Gar.

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Re: Passive Line Level Compensation Network? [message #44100 is a reply to message #44096]

Mon, 01 March 2004 16:26

Wayne Parham
Messages: 18677
Registered: January 2001

Illuminati (33rd Degree)

You can certainly install an EQ network in the preamp circuit. That's a great way to do it, actually. But you will benefit a great deal by doing the crossover frequency division ahead of the amplifier as well.

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Re: Passive Line Level Compensation Network? [message #44102 is a reply to message #44100]

Mon, 01 March 2004 19:19

GarMan
Messages: 960
Registered: May 2009

Illuminati (2nd Degree)

I considered the crossover ahead of the amp, but that means I'd have to go active, and that's a much bigger project than a simple passive line level network. Most of the readings I've come across said that passive line level crossovers are great, but only up to second order.

Is this true?

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Re: Passive Line Level Compensation Network? [message #44104 is a reply to message #44102]

Tue, 02 March 2004 01:42

Wayne Parham
Messages: 18677
Registered: January 2001

Illuminati (33rd Degree)

Well, passive line-level crossovers have some similarities with active crossovers. The idea in both philosophies is to put the crossover ahead of the power amps instead of in the high-current circuit. An active crossover has a buffer amplifier and sometimes it forms part of the filter, like in a Sallen Key circuit. But just as often, it is not anything but another stage, and is then almost the same thing as the amp stages prior to and following a passive line level filter. So that sort of blurs the distinction.

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Re: Passive Line Level Compensation Network? [message #44108 is a reply to message #44104]

Tue, 02 March 2004 03:44

Adrian Mack
Messages: 568
Registered: May 2009

Illuminati (1st Degree)

Passive line level filter? Is this getting a normal passive filter but putting it on the line level input to the amplifier instead? (like an active xover). That seems very strange to me :S

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Re: Passive Line Level Compensation Network? [message #44110 is a reply to message #44108]

Tue, 02 March 2004 07:27

GarMan
Messages: 960
Registered: May 2009

Illuminati (2nd Degree)

Hey man, I don't make this stuff up. Just a poor soul trying to make sense of all this.

Here's a couple of links with some info. Interested in hearing your thoughts, Adrian.

http://www.marchandelec.com/xm46.htm
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

(sorry, but don't know how to include multiple links)

Gar.

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Re: Passive Line Level Compensation Network? [message #44111 is a reply to message #44108]

Tue, 02 March 2004 16:23

Wayne Parham
Messages: 18677
Registered: January 2001

Illuminati (33rd Degree)

It's a reactive network, and the only real difference is that the output level filter is designed for a low impedance load whereas the input level filter is designed for a high impedance load. As an example, a filter designed for the output circuit might use a 10�F capacitor, having reactive impedance of 8 ohms at 2kHz. With an 8 ohm speaker load, that's an appropriate value. If the preamp input impedance is the typical 47Kohms, then a similar preamp-level filter might use a 1700pF capacitor instead. But the basic filter is the same, just using different values that are appropriate for the impedance of the circuit.

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Re: Passive Line Level Compensation Network? [message #44112 is a reply to message #44111]

Wed, 03 March 2004 09:55

billfort
Messages: 34
Registered: May 2009

Baron

Ok, I think I understand how to implement a passive line-level (6 or 12db) crossover but how do I add and size components to accomplish horn compensation?

Thanks! Billfort

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Re: Passive Line Level Compensation Network? [message #44115 is a reply to message #44112]

Wed, 03 March 2004 16:29

Wayne Parham
Messages: 18677
Registered: January 2001

Illuminati (33rd Degree)

Use Spice to analyze and model your R1/R2/C1 network to make the response curve shown below. Start off with values for R1, R2 and C1 having reactive impedance that is proportional to values in the low-impedance (speaker output level) crossover, but scale them 1000-times or so to more closely match the impedance of your preamp circuit. Then fine tune the values of R1, R2 and C1 until you obtain the response curve you want.

Top octave compensation response curve