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shouldn't use my speakers with a tube amp?

markus said:
I dunno :)

I'm always dubious of advice from people who want to sell you something :)

It sure doesn't say anything on their website about "NO TUBE AMPS" :scratch2:

http://www.mordauntshort.com/specifications.php?PID=77&Title=Specifications

Judging by the Speakers spec's, I'm guessing your 15 wpc amp will run out of steam if you *really* push it, but what's you're listening space like ? Are these for nearfield ?
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Right. I would be more concerned with that 88db efficiency than the damping factor.

Dave
 
IIRC, in my limited experience with Mourdant-Short speakers, there may be more than one factor going on here:

1.Bass damping- the woofer/box tuning. Some woofer/box combinations are simply tuned in such a way that there's not enough total damping, if the amp doesn't have a high damping factor.

2. Large swings in impedance- if the speaker has a crossover that is tuned with large impedance swings in the crossover (i.e, going from low to high impedance, at the crossover point, for one example), then an amp with non-negligible output impedance will deliver DIFFERENT voltages to the crossover, proportional to the impedance, at different frequencies! This can upset the tuning of the crossover, leading to peaks or dips in the response!

I've seen this happen- this is why, when I build speakers, I try to keep the impedance curve as 'flat' as possible... even if it takes adding compensation circuits (series RLCs) in parallel with the speaker, to make it a "flatter" load to the amp. It can make a difference, between a speaker that's "amp picky" and one that sounds good on virtually any amp...

Personally, I think all speaker manufacturers should keep this as a high priority... but some do so more than others. If there are great swings in impedance, you could be looking at sound issues, using a tube amp...

Regards,
Gordon.
 
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If I were to look at replacing my speakers or just buying new ones I would look at efficiency as a deal maker. I probably wouldn't lay down any cash for a speaker with lest than 93-95 db efficiency. With that part of the equation in my pocket I could power them with just about anything.
 
I'd recommend listening and deciding for oneself. Generally, vacuum tube amps are far more tolerant of reactive loads than many pieces of solid state equipment. The infamous Polk Audio Cobra Cables (with scads of capacitive reactance) are a classic example of an potentially amp-killing load... as are some (most) electrostatic loudspeakers.

The "damping factor" discussion, in my experience, is - as such - almost entirely specious.
 
Well, it's not quite that bad - the problem is that the numerical value of DF is a horrid oversimplification of any factors that actually have sonic - or performance - consequences. The output impedance of the amp, and the load impedance of the speaker are not constants; they depend on frequency. Thus, an amplifier's DF is not a number, it's a function of frequency. That may be what you hear. But no one gives you data to compare quantitatively; and one cannot assume performance characteristics a priori just because an amplifier uses tubes or transistors.

The other, traditional, problem with DF is that there used to be a tendency to use NFB like ketchup on french fries to reduce amp output impedance and to broaden and flatten frequency response. The cure can be worse than the disease. Thankfully in the last few decades even ss amp designers have gotten more judicious in the application of NFB. There are some fine sounding ss amps... they ain't cheap, and in most cases the quality of their sound, I expect, has little to do with vanishingly low output impedance.
 
mhardy6647 said:
I'd recommend listening and deciding for oneself. Generally, vacuum tube amps are far more tolerant of reactive loads than many pieces of solid state equipment. The infamous Polk Audio Cobra Cables (with scads of capacitive reactance) are a classic example of an potentially amp-killing load... as are some (most) electrostatic loudspeakers.

The "damping factor" discussion, in my experience, is - as such - almost entirely specious.
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Tolerant in terms of survivablity does not equate to Tolerance in terms of being able to control the position of the cone of the woofer. The ability of the tube amp to survive being connected to such loads is actually a perfect example of its inability to supply enough current to control the load and self destruct in the process. Its ouput impedance being the limiting factor.

I do agree however that one should listen and judge for themselves. Some folks may enjoy the sound the tube amp's "loose coupling" effect provides on the bottom end.


Steve
 
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So a bit if sarcasim if you don't mind....... If Damping factor (output impedance) were not a significant issue then we can all toss our 16+ gauge speaker wire in term of space and money saving 22- gauge speaker wire.

Steve
 
brightpav said:
I'm very pleased with the speakers but I mentioned to said dealer that I was looking to upgrade my current tube amp (which only pushes 15WPC) with a more powerful tube amplifier. This guy tells me that "Mourdant Short insists that listeners NOT use a tube amplifier." He claims tube amps "don't account for damping, can't properly control the speaker and that only a solid state amp could make my Mourdant-Shorts sound "like they should."
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Maybe they really mean SET amps. On paper, there doesn't seem to be any reason why you couldn't use a tube amp with these speakers. Did you try them with your 15w tube amp?

jeff
 
Damping factor is a measurable spec, and a very important one IMHO. When I hear newer audio enthusiast say they got some great synergy on a certain speaker amp combo, I chalk it up to them accidentally or otherwise getting the right damping factors working.
 
Jay (or anyone else who's posted to this thread for that matter), please point me to a manufacturer or designer that measures his/her amp's actual output impedance at, say, 10 different frequencies into a pure resistive load and a reactive load and calculates and tabulates the DF for all 20 of those cases. Then I might start to pay some attention to it as a specification.

Most mfgrs don't even specify the reference frequency of their DF specification... and those that do, that I've noticed, have referenced 1000 Hz.

The thing that gets my knickers in a bunch is this notion that the interaction of an amplifier and its load can be expressed in any meaningful way by one number.
Maybe for a sine wave... but I don't listen to them much anymore.
 
mhardy6647 said:
Jay (or anyone else who's posted to this thread for that matter), please point me to a manufacturer or designer that measures his/her amp's actual output impedance at, say, 10 different frequencies into a pure resistive load and a reactive load and calculates and tabulates the DF for all 20 of those cases. Then I might start to pay some attention to it as a specification.

Most mfgrs don't even specify the reference frequency of their DF specification... and those that do, that I've noticed, have referenced 1000 Hz.

The thing that gets my knickers in a bunch is this notion that the interaction of an amplifier and its load can be expressed in any meaningful way by one number.
Maybe for a sine wave... but I don't listen to them much anymore.
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Good points Mark, I think 1k is pretty much the standard for all sorts of measuring; power, distortion, etc......

As a funny aside note, I have the owners manual for my old Urbans and it said they needed solid state amplification due to their need for a high damping factor. I never could find a tube amp that sounded worth a darn on them, and I tried stuff like ST35, ST70, and even some SET. I'll see if I can locate that manual and see what all it says. FWIW, the best amp I found for the Urbans was a little Pioneer SX650 and it was an awesome combo.
 
I gotta say... the only person I know locally with a pair of Urbans (which he picked up last spring at NEARC for $125 if memory serves) is using a homebrew PP EL84 amp with them and loves them. I haven't heard 'em myself yet, though.

The 302 saga gets a little complicated - there were two and three way versions, at least.
Peruse the scans at www.hifilit.com

This one, e.g., is from 1958 - pretty safe to say in 1958 that vacuum tube amps were being used to drive them.

http://www.hifilit.com/hifilit/Bozak/blue-2.jpg
blue-2.jpg

http://www.hifilit.com/hifilit/Bozak/blue-4.jpg
blue-4.jpg
 
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This came from the manual for the 302 Urban;



Each speaker should be powered with at least 20 watts RMS or 40 watts IHF music power of amplification. The amplifier should be able to handle full power with 1/2% or less distortion at every frequency from 20 to 20k Hz. The higher the amplifier damping factor the better. Most Solid State amplifiers are ideal in this respect.


:dunno:
 
mhardy6647 said:
I gotta say... the only person I know locally with a pair of Urbans (which he picked up last spring at NEARC for $125 if memory serves) is using a homebrew PP EL84 amp with them and loves them. I haven't heard 'em myself yet, though.

The 302 saga gets a little complicated - there were two and three way versions, at least.
Peruse the scans at www.hifilit.com

This one, e.g., is from 1958 - pretty safe to say in 1958 that vacuum tube amps were being used to drive them.

http://www.hifilit.com/hifilit/Bozak/blue-2.jpg
blue-2.jpg

http://www.hifilit.com/hifilit/Bozak/blue-4.jpg
blue-4.jpg
Click to expand...

The first gen Bozak woofer had a paper cone, and Rudy did use tubes on them for voicing. After he designed the special "wooly paper" cone that was much heavier was when he started voicing with SS Marantz amps. The first run paper cone woofers are awfully rare, and i would bet your friends are the heavier cones.
 
Next to THD, there may not be a more useless spec than damping factor, in all of audio. I used to hold DF near and dear as an important spec, but I can't tell you how many times I've been proven wrong. When you actually do the math with DF, it quickly becomes clear that anything over some fairly low DF doesn't matter much in the real world.

A while back, in a similar thread, I did some math to show the real world effects.


dnewma04 said:
Let's do some math.

We know that damping factor is a ratio, specifically, it's the load impedance divided by the output impedance of the amplifier. For now, we'll ignore how amplifiers attain low output impedance just for the sake of simplicity.

So, let's say we have an amplifier with a damping factor of 2000 and an impedance of 8 ohms.

DF = Load Impedance / Output Impedance

2000 = 8 / Output Impedance

Output Impedance = .004

All is well in the world, right? We have our staggeringly high damping factor but we've ignored something important.

We forgot to include the series resistance of the speaker wire between the amp and speakers. Let's redo the calculation now.

Again, we know that DF = Load Impedance / Output Impedance, but now we are going to add in the effects of the speaker wire into our equation to figure out what the "real" or "effective" damping factor is of the real world situation. For simplicity sake, we'll err on the side of caution and say that it's very low resistance wire and only presents a .1 ohm load.

DF = 8 ohm / (.004 ohm + .100 ohm)
DF= 8 ohm / .104
DF= 76.9

The advertised damping factor of 2000 is now only 77 at the terminals of the speakers.

Now, let's look at what is going on at the terminals of the woofer in a speaker system with a passive crossover.

It's not unusual to have a series resistance of 1 ohm in a passive crossover, but just for a best case scenario, let's say that it's only .25 ohm.

DF = 8 / (.004 + .100 + .250)
DF = 8 / (.354)
DF = 22.6 at the woofer.

Now, let's say the damping factor of the amp is 20000! Surely that must make a huge difference being an order of magnitude higher than 2000!

Unfortunately, the reality is:

DF = 8 / (.0004 + .25 + .1)
DF = 22.8

It's essentially the same.

Now, let's say that the amplifier in the same scenario is only at 50.

DF = 8 / Output impedance

50 = 8 / Output Impedance

Output Impedance = .16

Now that we have the output impedance of the amp with a DF of 50, let's subsitute into our scenario to see the DF at the woofer:

DF = 8 / (.16 + 1 + .25)
DF = 8 / (.51)
DF = 15.7



Do you see how most people just don't find DF that important? In the real world, the difference between a low DF amp and a ridiculously high DF amp is essentially moot at the woofer.
Click to expand...
 
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