[Freo-1]

 
 
 
I found these links that may help some with discussions about sonic qualties that have come up:
 
http://en.wikipedia.org/wiki/Frequency_domain
 
https://6002x.mitx.mit.edu/wiki/view/TimeDomainVersusFrequencyDomainAnalysis
 
The major thrust of the thread was to discuss the power required to adequately power speakers effectively.  The issues involved:

• Speaker effencicy
• Output RMS power (actual) provided to a speaker over the entire frequency range when playing back music (not test tones)
• Listening environment
• Dynamic range of the source material

The above are independat of the actual amp topology (at least in theory) .

[Tyson]

Due to how SS vs Tubes work, I think the answer to "how much power" can be broken down like this:

SS - A lot.
Tube - A little.

[James Romeyn]

 
 
I found these links that may help some with discussions about sonic qualties that have come up:
 
http://en.wikipedia.org/wiki/Frequency_domain
 
https://6002x.mitx.mit.edu/wiki/view/TimeDomainVersusFrequencyDomainAnalysis
 
The major thrust of the thread was to discuss the power required to adequately power speakers effectively.  The issues involved:

• Speaker effencicy
• Output RMS power (actual) provided to a speaker over the entire frequency range when playing back music (not test tones)
• Listening environment
• Dynamic range of the source material

The above are independat of the actual amp topology.

I'll add listening distance, power response vs. on-axis, and useful power handling of the speaker, which per my post above may be only a very small fraction of continuous power handling.  What good is a 600W source if the load thermally compresses 30 dB with such input?  (Hint: bias ply tires testing lateral G on a high performance automobile.)   

Persons unfamiliar with system suffering no audible thermal compression at any level up to live, and persons highly familiar with live music, may have radically different perspective vs. those lacking such qualifications. 

The funny thing is that live music performers often suffer from hearing loss, another story entirely.

[James Romeyn]

Due to how SS vs Tubes work, I think the answer to "how much power" can be broken down like this:

SS - A lot.
Tube - A little.

Perfect! 

Or...
SS: X
Tube: X/2

[*Scotty*]

Mike, did the Atmoshpere amps have 3 or 4dB of headroom compared to their RMS rating?
Scotty

[Russell Dawkins]

Perfect! 

Or...
SS: X
Tube: X/2

From my experience i would go as far as to say X/4 for the tube amp. In my mind I think of a 60W tube amp as having about the same useable power as a SS amp honestly rated at 240W.

Speaking generally in response to the original question of how much power is needed, it is difficult not to sound glib but I would say "much more than you might think". To expand, I would add to the more technically inclined "work out your loudest desired average (or rms) SPL required and how much power than requires with your speakers, then add 20dB. Or, add 10dB to what you think are your peak needs. Further to all the above, but in the same vein, much more power handling than is usually suspected is needed on the speaker side of the equation.

So really, the question might be "How much dynamic range do I need?"  I say "lots".

[James Romeyn]

IIRC Duke LeJeune showed the OTL's rising power with impedance + rising impedance below woofer resonance could and sometimes does result in lower bass cutoff (OTL vs. SS).

IIRC at one show Ralph Karsten strongly emphasized that woofers need voltage more than current.  I wonder if he refers to the fact that there is at least one impedance peak in the bass range (the natural resonance peak) and a second peak for reflex systems (port tuning), and these peaks benefit tubes which increase voltage at higher impedance while SS voltage and current both decrease with rising voltage.  Conversely, this may be the prime reason we usually see SS power stats, which tend toward 1 Ohm loads in the treble, sometimes lower.  Stats have low sensitivity, but their rate of decrease per distance is only 1/2 a mono pole.  The stat's ultra low load impedance in the treble may be the most significant spec when searching for a coupling amp.

Not to stray too far OT, but what is general Ncore consensus driving stats?     

[James Romeyn]

From my experience i would go as far as to say X/4 for the tube amp. In my mind I think of a 60W tube amp as having about the same useable power as a SS amp honestly rated at 240W.

Speaking generally in response to the original question of how much power is needed, it is difficult not to sound glib but I would say "much more than you might think". To expand, I would add to the more technically inclined "work out your loudest desired average (or rms) SPL required and how much power than requires with your speakers, then add 20dB. Or, add 10dB to what you think are your peak needs. Further to all the above, but in the same vein, much more power handling than is usually suspected is needed on the speaker side of the equation.

So really, the question might be "How much dynamic range do I need?"  I say "lots".

Read every post.  This gem has best clarity and least "inclusions," to stretch the metaphor.   

[mgalusha]

Mike, did the Atmoshpere amps have 3 or 4dB of headroom compared to their RMS rating?
Scotty

For power (Watts) it would be 105/60 = 1.75, Log(1.75) * 10 = 2.43dB, in terms of voltage it's double, 4.86dB, Log(1.75) * 20. That was very short term but unless the music is horribly compressed the peaks are short term and I can't tolerate highly compressed music at high levels, makes me grimace.

[medium jim]

From my experience i would go as far as to say X/4 for the tube amp. In my mind I think of a 60W tube amp as having about the same useable power as a SS amp honestly rated at 240W.

Speaking generally in response to the original question of how much power is needed, it is difficult not to sound glib but I would say "much more than you might think". To expand, I would add to the more technically inclined "work out your loudest desired average (or rms) SPL required and how much power than requires with your speakers, then add 20dB. Or, add 10dB to what you think are your peak needs. Further to all the above, but in the same vein, much more power handling than is usually suspected is needed on the speaker side of the equation.

So really, the question might be "How much dynamic range do I need?"  I say "lots".

Mike:

The x/4 would apply to tube amps with lots of beef in the power supply.   I've had a few Tube amps that didn't, but more that did.  My current Tube Amp is a Audio Research VS110 that while stated to be 100 per side, is closer to 110 and possibly more.  It has no problem driving a pair of Magnepan 2.5's....in fact, as easily as my SS amp that in 4 ohm is around 425, so I would concur...the VS110 has 332 joules of Power Supply Energy Storage to aide with dynamic peaks.   The 2.5's are 86db.   

I agree that if you have a SS amp to have plenty of Watts as it truly is ugly when they do clip....the first thing to go is the tweeters, if not your hearing from the clipped squared off sine wave.....

Jim

[*Scotty*]

Thanks for the reply Mike.
I think it should be firmly borne in mind that if the tube does put out 3X or 4X it RMS rated power on music peaks the frequency extremes, 20Hz and 20Khz, will be compromised due output transformer core saturation and inter-winding capacitance effects.
Both of these graphs are best case representations of what the amp can do. They do not portray what the amplifiers full rated power bandwidth looks like. Also not shown is what happens to the distortion versus frequency relationship at full rated power levels. If such graphs were included in the measurements most mfgrs. of tube amplifiers would cry foul and pull advertising from the magazine. Graphs below from Stereophile magazine.

Fig.1 Octave Audio RE 290, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (1dB/vertical div.).

Fig.7 Octave Audio RE 290, THD+N (%) vs frequency at 2.83V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (left gray).


The graph below is the kind of graph that is missing from tube amplifier reviews. This is the solid state Musical Fidelity AMS 100 power amplifier's distortion versus frequency response behavior at 50watts output into an 8ohm load.

Fig.8 Musical Fidelity AMS100, THD+N (%) vs frequency at 20V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green).
 The effects transformer core saturation and inter-winding capacitance at higher powers are grim and contribute markedly to the perception of the tube amplifier's performance when asked to produce more than a couple of watts.
This is a fact of life and in no way accounts for anyone's preference for transformer coupled tube amps.
Scotty

[Freo-1]

OK, What about McIntosh SS amps with autoformers?  One would think that similar issues would exist.

[*Scotty*]

Bingo!

Scotty

[*Scotty*]

Here are a couple of graphs from Stereophile. The Audio Research Reference 110 and the Audio Research Reference 150.

Fig.8 Audio Research Reference 110, 8 ohm tap, THD+N (%) vs frequency at 2.83V into (from bottom to top): 16, 8, 4, 2 ohms (right channel dashed).

Fig.7 Audio Research Reference 150, 4 ohm tap, THD+N (%) vs frequency at 4V into: 16 ohms (left channel green), 8 ohms (left blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (left gray).
Fig.7 plots the THD+noise percentage from the 4 ohm tap into loads ranging from 2 to 16 ohms at a level, 4V, where the actual distortion rises above the noise floor. The THD increases at low frequencies due to the onset of saturation in the output transformer, and in the top octave due to the decreasing open-loop gain margin in this region reducing the effectiveness of the negative feedback. But over most of the audioband, and when the load impedance is very much higher than the transformer-tap value, the Ref150 offers low distortion. The picture from the 8 and 16 ohm taps was similar (not shown), but with higher levels of distortion overall.
Remember, we are seeing increasing distortion due the effects of transformer saturation at only 2.83Volts into 8ohms at 1watt of output, contrast this with the performance of the Musical Fidelity AMS 100 at 50 watts into a 8ohm load in my previous post.
Scotty

[James Romeyn]

On a related matter, especially for frequency extremes, i.e. bass below 80 Hz, a question for science minds (not used as an epithet, I envy their understanding) like Scotty and Mike:

Please quantify the distortion in the bass for systems not employing Distributed Array, when, for instance, a bass note continues bouncing between walls long after the note on the recording stopped, and the new bass note appears...presume, as is almost always the case in reality as anyone who plays an instrument knows, the two bass notes are discordant in the extreme and a-musical in the extreme.

How do you quantify such "distortion" common to any system employing two full range single column speakers?  Tens of percent?  Hundreds?  Thousands?  I am really curious.  I presume it is in the hundreds or higher.  Yes, it may be brief, but it is extremely high and extremely audible and extremely damaging to performance.  Bass is the base, the foundation of music.  No orchestra plays faster nor with more competence than the bass section.     

Personally, I find the ignoring of such distortion quite laughable in any context related to audio.  Also, the existence of this distortion makes any conversation about bass performance relative to any (properly functioning) certain speaker purely a myth: you do not describe or perceive the speaker performance but rather describe the physical interaction between the listener, two speakers, and the boundaries, an infinite array of potentials vs. the speaker with its fixed anechoic specs.     

The other interesting item I'm now keenly aware of, and this is not intuitive, is that bass seems to strangely hover around or inside the physical volume of the box of full range single column speakers, whereas Distributed Array bass tends to exist in a free standing space, changing from software to software.

[DS-21]

OK, What about McIntosh SS amps with autoformers?  One would think that similar issues would exist.

"One would think..."

Why spew idle conjecture when there are readily available data to answer the question definitively?

Google "mcintosh autoformer stereophile" as I just did, and you might learn something, as I just did. Confirmed by two different reviews that both popped up in the first page of search hits.

(Spoiler alert: the answer is no, similar issues don't seem to exist.)

[Freo-1]

Note the rather large differences with a 150 WPC Solid State Unit:
 

Fig.4 Pass Labs INT-150, THD+N (%) vs frequency at 10V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green).



 
 

[DS-21]

Unfortunately, this situation has become the norm in the so-called "high end" of audio.  Many of the people designing this stuff don't have a clue WTF they're doing, but they really know how to do the marketing thing.  It's sad, really, because so many people not only fall for it, but actually think that people who do not fall for it are in the wrong.

Yep. I'm convinced that "audiophile" is really an acronym for "technically illiterate, not-very-critical listener, highly gullible" in some obscure language.

The problem is that the prevalence of such types starts to either crowd out the good guys. So people buy fetish amps and run boutique wires on special little audiophool wire holders, but drive loudspeakers with midrange mushroom polar patterns and midbass peaks like bad 1980s car stereos.

[*Scotty*]

Jim it depends on ones priorities I guess. It would appear that most mfgrs. side step the issue and simply do not address it. You don't want to tell your prospective buyer of a MEGABUCK speaker system the they are purchasing a problem that can only be solved by the purchase a separate bass SUB system consisting of multiple sub-woofers.
People don't appreciate the complexities associated full range music reproduction and don't want the problems related to it pointed out to them either.
Here is the missing text explanation for the Pass Labs INT-150 graph from the Stereophile review of same.
 Fig.3 Pass Labs INT-150, distortion (%) vs 1kHz continuous output power into (from bottom to top at 10W): 8, 4, 2 ohms.

The shape of the traces in fig.3 reveals that the THD+noise percentage is dominated by noise below 8W or so. I therefore measured how the distortion changed with frequency at a level of 10V, equivalent to 12.5W into 8 ohms (fig.4, blue and red traces), 25W into 4 ohms (cyan, magenta), and 50W into 2 ohms (green). The right channel is not quite as linear as the left, but the INT-150 still offers uniformly low distortion below 1kHz into all loads. The THD rises in the top octaves, due to the usual reduction in open-loop gain margin at high frequencies, and the amplifier is starting to be stressed a little above 10kHz into 2 ohms.
It is not uncommon for the feedback loop to loose its effectiveness at higher frequency in many amplifiers.
My own amplifier has .002 THD at full power up to 10kHz and at 20kHz it has doubled to .004 THD.
These kind THD numbers by themselves do not guarantee that the amplifier will sound good, but by the same token amplifiers that have several percent THD at the frequency extremes at higher power levels than 1 watt that might be required in the normal course of reproducing music in the home are not amplifiers that I would choose for myself.
Scotty
midrange mushroom polar patterns
DS-21,consider your ax ground.

[medium jim]

Here are a couple of graphs from Stereophile. The Audio Research Reference 110 and the Audio Research Reference 150.

Fig.8 Audio Research Reference 110, 8 ohm tap, THD+N (%) vs frequency at 2.83V into (from bottom to top): 16, 8, 4, 2 ohms (right channel dashed).

Fig.7 Audio Research Reference 150, 4 ohm tap, THD+N (%) vs frequency at 4V into: 16 ohms (left channel green), 8 ohms (left blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (left gray).
Fig.7 plots the THD+noise percentage from the 4 ohm tap into loads ranging from 2 to 16 ohms at a level, 4V, where the actual distortion rises above the noise floor. The THD increases at low frequencies due to the onset of saturation in the output transformer, and in the top octave due to the decreasing open-loop gain margin in this region reducing the effectiveness of the negative feedback. But over most of the audioband, and when the load impedance is very much higher than the transformer-tap value, the Ref150 offers low distortion. The picture from the 8 and 16 ohm taps was similar (not shown), but with higher levels of distortion overall.
Remember, we are seeing increasing distortion due the effects of transformer saturation at only 2.83Volts into 8ohms at 1watt of output, contrast this with the performance of the Musical Fidelity AMS 100 at 50 watts into a 8ohm load in my previous post.
Scotty

Scotty:

And here's the associated Reviews that tell the real story:

Ref 110:

http://www.stereophile.com/tubepoweramps/807ar

and the Ref 150:

http://www.stereophile.com/content/audio-research-reference-150-power-amplifier

Yes Scotty, it all depends on priorities...There is no doubt that SS will look prettier on a graph or have better numbers on paper, but we don't listen on paper!

Jim