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Author Topic: Subwoofer amps - what are we REALLY hearing?  (Read 34396 times)

Silas Pradetto

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #40 on: February 06, 2008, 03:35:36 pm »

Damping factor is the load impedance divided by the output impedance of the amplifier. This means, with an 8 ohm load and a .01 ohm output impedance of the amplifier, you would have a damping factor of 800. Damping factor has quite a bit to do with bass quality. It is related to cone control such that a higher damping factor is more control. If there is more control, the woofer flaps around less and relies less on it's own suspension to return it to the "zero" point in it's travel, making everything sound "punchier." I hope that kind of made sense.
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Andy Peters

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #41 on: February 06, 2008, 03:40:44 pm »

Silas Pradetto wrote on Wed, 06 February 2008 13:35

Damping factor is the load impedance divided by the output impedance of the amplifier. This means, with an 8 ohm load and a .01 ohm output impedance of the amplifier, you would have a damping factor of 800. Damping factor has quite a bit to do with bass quality. It is related to cone control such that a higher damping factor is more control. If there is more control, the woofer flaps around less and relies less on it's own suspension to return it to the "zero" point in it's travel, making everything sound "punchier." I hope that kind of made sense.


You forget the salient point: overall damping factor is severely degraded by the cable between the amp and the driver, as that cable's resistance adds to the amp output impedance.

In fact, the cable resistance essentially sets the damping factor, making amplifier damping factor irrelevant except maybe as a marketing bullet point.

This horse is dead.

Please stop beating it.

-a
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Bennett Prescott

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #42 on: February 06, 2008, 03:43:29 pm »

Oy.

Here's another article that I wrote because of frustration from the last time this came up.

http://www.bennettprescott.com/downloads/dampingfactor.pdf
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Bob Leonard

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #43 on: February 06, 2008, 03:52:02 pm »

Andy Peters wrote on Wed, 06 February 2008 13:08

Bob Leonard wrote on Wed, 06 February 2008 08:02

Yes Tim, I am aware those are all tube circuits, and;

A class C amplifier is biased beyond cutoff. The class C amplifier like the class B amplifier will draw no current with no signal input but a class B will start to draw current as soon as a signal is applied and a class C will only start to draw current when the signal strength is sufficient to go beyond the bias level. The class C amplifier is not linear but is the highest in efficiency.

In all classes of amplifier the linearity of the amplifier is determined by it's class.

The APS-20 radar on an EC-121 Willy Victor used a class "C" amplifier. RTTY, CW are often used with class "C" amplifiers, but they can not be used with SSB.


As The Good Tim says, flat view, anyone? USE THE QUOTE BUTTON.

And how is this relevant to the topic at hand? Other than to get into another mudwrestle with Duffin?

Quote:

I posted these as classic examples, and being as basic as these classes of amplifier are I would think it may be good reading material for people who may want to understand amplifiers and how they operate. Guitar players may find interest in class A/B amplifier circuits especially if they use a Fender amplifier.


And the design goals of a guitar amplifier are at cross purposes with one designed for sound reproduction.

One is a tone generator, one is not.

So the discussion is rather pointless.

-a


Andy,
I don't care about Duffin. He asked for an answer and got it. And since when are class A/B amplifiers not a part of sound reproduction. I seem to remember working with many prior to the use of transistors in amplifier output stages. I don't remember saying anything about preamplifier circuits at all. Maybe that's where your confused. Besides that the above were used as examples of amplifier class in response to someone who doesn't understand the meaning of the word linear. Ever read an RCA tube manual? Regardless of the class most amplifiers can trace their roots back to those simplistic amplifiers of days gone by in some way or another.
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John Roberts {JR}

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #44 on: February 06, 2008, 04:42:16 pm »

Silas Pradetto wrote on Wed, 06 February 2008 14:35

." I hope that kind of made sense.


No... it doesn't.

DF has been well discussed here, again, and again, and again...

JR
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Ted Olausson

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Re: Sound Is Subjective
« Reply #45 on: February 07, 2008, 12:27:05 am »

Quote:


I think the way that amps are used today they do have a "sound".  It is typical to see amps driven into the non linear mode.  In fact I think it has become commonplace.  That makes a smaller system sound "louder".  



http://www.moultonlabs.com/more/power_amps_revisited/

Andy Peters

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Re: Sound Is Subjective
« Reply #46 on: February 07, 2008, 01:24:43 am »

Ted Olausson wrote on Wed, 06 February 2008 22:27

Quote:


I think the way that amps are used today they do have a "sound".  It is typical to see amps driven into the non linear mode.  In fact I think it has become commonplace.  That makes a smaller system sound "louder".  



http://www.moultonlabs.com/more/power_amps_revisited/


Well, he's driving easier loads at lower SPLs than typical for SR use and it's obvious that driving the amps to the edge all night is not a requirement.

But, really, it just sounds like the guy who built the amps conservatively rated them lower than what they can really do. Which is fine, and even laudable, especially considering that he leaves some "marketing watts" on the table.

Note how they measure SPL, but not amplifier output power, which would be the better test.

-a
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Bob Lee (QSC)

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #47 on: February 07, 2008, 01:26:49 pm »

Duncan McLennan wrote on Tue, 05 February 2008 08:22

linear power supplies.


I suppose a battery could be a linear power supply.

An AC-to-DC power supply, whether switch-mode or conventional, is almost always non-linear.
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Bob Lee
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Bob Lee (QSC)

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #48 on: February 07, 2008, 01:29:29 pm »

The RMX5050, 8001, and 10001 all have conventional (mains frequency) power supplies, not linear ones.
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Bob Lee
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Chuck Fry

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #49 on: February 07, 2008, 01:43:01 pm »

I found this "smackdown" thread via a link from a DIYaudio.com thread:

http://srforums.prosoundweb.com/index.php/m/229083/19784/

Now what would explain the lower power output at low frequencies of 3 of the 4 amps tested? The PLX 3402 puts out literally twice the power at 20 KHz that it does at 20 Hz. Even the Crest 9001 has a dip in the power curve at 50 and 200 Hz - in the heart of subwoofer country. The burst test should be pulling the same energy from the power supply irrespective of frequency, shouldn't it?

Answer that question and maybe we'll have a clue what we're really hearing from amps on sub duty.

(BTW this is not intended as bashing any particular amp maker - I happen to own a PLX 3402 and have been happy with it as part of a bass guitar rig.)
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