Does anyone know how an amp's damping factor is affected when it is bridged? Since it is related to the impedance of the output section of an amp, depending on the amp design I am guessing it drops. I'm not talking about a parallel bridge mode.

Thanks,
D

I would think it would not be effected enough to make a difference that you could hear. The load impedance that can be attached cannot be as low as would be the case if you were using single channels however - a 4 ohm speaker across a bridged amplifier would likely try to draw more power than the amp can deliver.

[This message has been edited by soundhound (edited January 16, 2004).]

Actually the particular amp (Crown) is capable of driving 2 ohm loads when bridged. I guess what the info I'm after is whether or not I should use this amp (for subwoofer purposes) in bridged mode, or get an amp that is capable of supplying the necessary power per channel, and then just using one of the channels to drive the sub.

I used to use crown amps to drive subs down to 2ohm loads in professional sound reinforcement, they ran hotter, but they never ever quit and always had excellent extension. Of course, these were their professional series, they cost between $1500-$5000 for two channels per amp. We had two of the 10,000W/2Ohm models to drive 8 subs. Great amps.

The fact that it can drive 2 ohms in bridged mode is enough information to suggest that the internal impedance of the amp is low enough to do what you want to do with it. If your subwoofer is 8 ohms (or even 4 ohms), you should not have any problems with current delivery or damping factor from that amp.

I appreciate the info. Although this is not related to Outlaw-specific material, I will be purchasing a 755 to drive my mains, center, and surrounds.
If anyone familiar with Crown amps could enlighten me, I have a particular question:
I currently own a fairly old Microtech 1000.
I could bridge it, and use it for my new SVS sub. It does not,however, have level controls on the front to change the levels if needed, but I may be using an ART351 eq with whatever sub amp I use, so I could adjust the input levels using the ART. OR...
I could purchase a Crown CE2000 for a pretty good price. It can drive the sub using only one channel (@660 watts/channel)and has many newer features like variable fan speed (quieter), front level controls, etc.
Any recommendations?

I have some Crown amps at home: two K1s, a MT600 and a vernerable D60. In particular, the K1s claim something like a damping factor of 10,000 into 8 ohms. The impedance of speaker leads will drastically reduce this high damping factor.

I will generalize here.

Damping factor, in amp. context, is defided as the ratio of the load impedance to the source impedance.

If mfr. says that their amp. has a damping factor (d.f.) of 100 (a reasonably high value) with an 8 ohm speaker (load), that means that the amp's (the source of the signal to the speaker) output impedance is 100 times lower than the 8 ohm impedance of the speaker. The amp has an output impedance of 0.08 ohms (80 milli-ohms). Thus, by this definition, the Crown K1s will have an output impedance of 0.8 mill-ohms.

Damping factor tends to increase as frequency goes up because an amp's source impedance increases as frequency goes up. Most amp. mfrs specify damping factor at low frequencies.

A real-world amp (RA) can be modeled as an ideal amp (IA), which has an output impedance of zero, in series with a resistor (RO) whose impedance is the same as the output impedance of the real-world amp (RA).

A hookup diagram:

RA = (RO + IA) in this case.

A speaker hookup would look like:

S(red lead)......(RO + IA) signal
S(blk lead)......amp return "gnd" connection

Where ...... repesents each speaker lead (which is being ingnored in the calculations of D.F.)

In a non-brided amp connection, one speaker lead is connected to the "hot" (red) output terminal of an amp (this connection is to the amp's output signal) and the other lead is connected to the return (black) teminal of the amp, which is usually at or near ground or circuit common voltage.

In a bridged configurarion, one speaker lead is connected to the output of an amp. The other speaker lead is connected to an output of a second amp whose output has the same magnitude as the amp connected to the red lead but is inverted (opposite polarity).

A hookup diagram:

A speaker hookup would look like:

S(red lead)......(RO + IA) signal
S(blk lead)......(RO + IA) inverted signal

In the above diagram, you can see that the term RO appears once in the red lead path and once in the blk lead path. The impedance of the speaker is the same for bridged amp or non-bridged amp hookup. Also, the speaker is receiving a signal of magnitude twice that of the non-bridged configuration. Again, this is assuming "ideal" amps. Real world amps have real world power supplies in them and thus will be limited by these real world considerations.

So beings D.F. is defined as the ratio of the load impedance to the source impedance, ideally, ignoring speaker lead impedance,

a D.F. for a bridged amp configuration will be half of that for the same speaker in a non-bridged configuration.

This is because the source impedance for the bridged configuration is twice that of the non-bridged configuarion. See that the term RO shows up twice in the bridged configuration diagram and only once in the non-bridged configuration diagram.

On a practical basis, if the D.F. is low enough, it won't matter that the D.F. in a bridged configuration is "only" half that of the D.F. in a non-bridged configuraton. Again, this is ignoring the limits on D.F. imposed by the speaker leads (and internal speaker wiring, etc.), whose impedance is the same for either bridged mode on non-bridged mode operation. The effects of the speaker leads will make the non-bridged D.F. and bridged D.F. both lower and closer together (LESS than a factor of two difference).

Paul

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the 1derful1

[This message has been edited by Paul J. Stiles (edited January 16, 2004).]