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High power amplifiers for Heritage speakers


KeyOfGee

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I'm pretty sure PWK always referred to RMS values. After all he was an electrical engineer before he invented the KHorn. All this "peak music power" and "peak power" is a bunch of fluff.

 

 

I also said I worked from the premise that he would use RMS power output; however, it still doesn't reconcile the implied inconsistency between your table and his table regarding the availability of power to handle peaks in music. I haven't figured it out, which is why I did a type of "brain storm" of thoughts to see if anyone else can help reconcile the two tables (hopefully) using plain English.

Edited by Fjd
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Fjd,

 All I was trying to say is if you play your KHorns at 2 watts (loud) and you want to be able to handle 10dB peaks over this(very loud) you need 20 watts.

 

And that would be 20 watts of unadulterated, unclipped RMS power.

Edited by babadono
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What'd i get wrong?

 

 

It is no secret that PWK thought that all the world needed was a good 7 watt amplifier, but high powered amplifiers really started gaining a foot hold in the late 70's.

 

PWK through in the K-43 into MWM's and Pro La Scalas for more power handling for people who couldn't seem to understand low watt efficiency.

 

Even with this knowledge, to think or state that head room doesn't matter, is a bunch of fluff, or that PWK might have not addressed it or the like is ridiculous and assumes a lot about his intelligence or lack there of that he might not have addressed it just because one hasn't seen it addressed.

 

Roger

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Fjd,

 All I was trying to say is if you play your KHorns at 2 watts (loud) and you want to be able to handle 10dB peaks over this(very loud) you need 20 watts.

 

 

 

I understand your calculation.  In trying to determine why PWK indicated 2 watts instead of 20, I was trying to reconcile the two numbers.  For example, one thought that I was wondering about is if PWK may have been looking at the voltage gain factor (e.g., 3.16 multiplier for a 10dB voltage gain) required to handle peaks, which would be a sound pressure ratio using an amplitude multiplier rather than the sound power gain factor measuring sound intensity outlined in your calculations.

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I for one think PWK chart is hogwash... PWK is one of my all time hero's but that chart IMHO is way off. 3000 cubic foot room is a large room... no way could one speaker fill a room of that size to those levels with that kind of power let alone be able to reach 10 db peaks... Think about it a Khorn can and does hit 104db 3 feet away with one watt....now start backing away from that speaker in a 3000 cubic foot room, that 104 db is going to drop dramatically and fast. 

 

Look at the chart he has 20 watts to get 110db but to get just 5 db more takes 43 more watts...  

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I just figured that there must be a precise method in how PWK defined a "peak" or did his analysis to recommend that a 2 watt amplifier had sufficient head room for music with 10dB peaks. I just haven't been able to "back" into it.

 

Essentially, there are three different "measurements" in relation to sound; (1) power (sound intensity level - calculated), (2) Amplitude (sound pressure level - measured), and (3) Loudness (psycho acoustic - sensed).  The common mistake that I see is that people will relate the three different measurements all to the psycho acoustic or sensed loudness.

 

Basically, if all three were measures of psycho acoustic 'sensed' loudness, think about it this way. If you consider the typical frequency response of +/- 3dB (Khorn, Belle & La Scala +/- 4dB in literature but often more in measurements) would result in an overall swing of a 6 dB swing meaning that music could have swings of 4 times (3 dB double loudness; therefore, 6 dB would be quadruple loudness) increase in the loudness or 4 times decrease in loudness that would not be attributed to the dynamics in the music itself. 

 

Note that the term “perceived” sound volume and the term “loudness” are both subjective terms trying to describe the strength of the ear's perception of a sound.   Essentially, loudness is only a subjective feeling that is commonly confused with objective SPL measurements in decibels.

 

When you consider the works of psycho-acoustic researchers such as Stanley Smith Stevens and Richard M. Warren; a more accurate rule of thumb would be that a doubling of the sensed volume (loudness) is equivalent to a level change approximately between 6 dB and 10 dB.

 

Think of it this way in that you have three different situations. There are two objective measurements, power and amplitude; and one subjective measurement, loudness.

 

 

_ Cause-Effect-Perception.jpg

 

 

Here is a nice sound level comparison chart showing the various ratios the respective ratios of subjective volume (loudness), objective sound pressure (voltage), and sound intensity (acoustic power).

 

 

_ CHART for loudness volume doubling sound level change factor of perceived loudness.jpg

 

 

 

From the chart above:

 

 

Power (sound intensity level - calculated):

Sound power ratio 2 (two times the intensity) changes the sound power level by 3.01 dB

 

Amplitude (sound pressure level - measured):

Sound pressure ratio 2 (two times the pressure) changes the sound pressure level by 6.02 dB

 

Loudness (psycho acoustic - sensed):

Loudness ratio 2 (two times (twice) the loudness) changes the sound loudness level by 10 dB

 

 

From the chart above:

20 dB gain change should give about the ratio of 4 (four times) for sensed volume and loudness

20 dB gain change gives the ratio of 10 for measured voltage and sound pressure

20 dB gain change gives the ratio of 100 for calculated sound power and acoustic intensity

 

 

Here are a few of the resources that I've considered:

 

http://scitation.aip....1121/1.1912298

 

http://trace.wisc.ed.../2004-About-dB/

 

http://www.campanell...#basic_loudness

 

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Does the chart take compression into account?  You can add power and the volume increases accordingly, but every speaker has a limit, beyond which it will not play any louder, no matter how much power you send to it.

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Does the chart take compression into account?  You can add power and the volume increases accordingly, but every speaker has a limit, beyond which it will not play any louder, no matter how much power you send to it.

 

 

 

Basically, in babadono's calculation, he outlines that 10 db = 10X the power and 1 Watt + 10dB = 10 Watts and most of us are aware of that  logarithmic relationship.  This logarithmic relationship appears to be the same ratio in PWK's table where he outlines 2 watts to drive "average" SPL of 100dB; and 20 watts to drive "average" SPL of 110dB maintaining the logarithmic 10x ratio. 

 

However, I asked how people believed the ratio applied to how PWK determined that a Klipschorn (104dB sensitivity) driven with a 2 watt amplifier to an "average" SPL of 100dB SPL would also be enough power to allow peaks of 10dB above the "average" SPL to pass without clipping the amplifier?   I outlined the different ways that sound is measured to see if I could back into PWK's data in the chart.

 

If an amplifier is measured using the root mean squared (RMS) method, it is often capable of short bursts of more power output (power supply capacitors maybe?) to handle peaks where this power output will occur for very small fractions of a second but cannot be maintained as a continuous output measured as RMS, but how do you translate that power over RMS output into handling peaks in music (e.g., how did PWK determine the 2 watts RMS was sufficient for the 10dB peaks in the music as opposed to the view that many hold that 20 watts RMS would be required)?

 

 

 

AMPLIFIER RATINGS TO DRIVE KLIPSCH SYSTEMS_table Page_2.jpg

Edited by Fjd
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I'm no expert, but here's what I have heard:

 

I have read that whether an amplifier will "pass" a peak without clipping depends on the duration of the peak.  Briefer peaks will pass easier.   I have read that the peaks being considered when writing amplifier specifications are 200 milliseconds to 2 milliseconds in duration.

 

I don't think "peaks" in a steady tone (the top of a sine wave) are like peaks in music.  I think that RMS is 0.707 times the height of the sine wave of the steady tone.  The leading edge of a musical peak can be much more powerful.  Someone posted here (maybe 7 or 8 years ago?) that the intensity of a rim shot close up would beyond the capacity of any amp/speaker combination, if it were not for the brevity of the leading edge of the peak.

 

I would think that separate amps would have beefier power supply sections, and should be able to produce more instantaneous power above their rated power than would receivers. 

 

My dealer measured one of my power amps at 171 watts per channel at the point where the top of the sine wave would just begin to flatten.  The manufacturer (NAD) rated them at 150 w.p.c..  If the 0.707 thing is correct, they would be (0.707x171) about 120 wts RMS. 

 

I think that doubling the distance in an anechoic environment, or outside at the top of a flagpole, causes a 6 dB loss, BUT doubling the distance in a room causes only about a 3 dB loss.  In music, for just an instant, I can get 110 dB through 1 Khorn quite easily in my 4,000+ cu.ft. room @ 16 feet (no, I don't subject my ears to that for more than and instant ... the loud passages in the orchestral music I play average about 90 dB).  My room is 1/3 larger than the one PWK was using for the chart.  The 110 dB figure is right at the top of the needle swing ("C," "Fast").  Since this is a needle meter, the true, instantaneous peaks may be 13 dB higher than the meter reads, at more like 123 dB (according to PWK in another paper).  According to the Klipsch chart, 123 dB (120 dB +3 dB, doubling the power needed) may take about 400 watts (or more, because my room is bigger), just for a split second, but I only have 171watts to "spend."  I am familiar with what clipping sounds like, and I hear no clipping.  But then I have a separate amp with a good sized power supply.

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I think what everybody is ignoring is that he is even mentioning a room into the chart. Why did he not just give the db and wattage alone? What would your resulting calculations say when considering 1/8 space corner gain in a sealed 14.42' cube? (or of a 20'x20'x8' ceiling room with closed doors...)

 

One other note. He doesn't say the measurements are an average of the db of the room. 1 meter away? In the far corner? In fact, he doesn't mention where in the room the measurements would happen.

 

Also, he says a single system, which doesn't really mean a single speaker. It means mono. I don't really see this as pertinent, but it is something that seems odd to mention IMO.

 

Edit: With 1/8 space +12db just in corner loading and a mic at 1/2 meter, wouldn't a single watt drive an LS at substantially higher than 104db. In fact, wouldn't .1 watts?

Edited by mustang guy
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I'm no expert, but here's what I have heard:

 

I have read that whether an amplifier will "pass" a peak without clipping depends on the duration of the peak.  Briefer peaks will pass easier.   I have read that the peaks being considered when writing amplifier specifications are 200 milliseconds to 2 milliseconds in duration.

 

I don't think "peaks" in a steady tone (the top of a sine wave) are like peaks in music.  I think that RMS is 0.707 times the height of the sine wave of the steady tone.  The leading edge of a musical peak can be much more powerful.  Someone posted here (maybe 7 or 8 years ago?) that the intensity of a rim shot close up would beyond the capacity of any amp/speaker combination, if it were not for the brevity of the leading edge of the peak.

 

I would think that separate amps would have beefier power supply sections, and should be able to produce more instantaneous power above their rated power than would receivers. 

 

My dealer measured one of my power amps at 171 watts per channel at the point where the top of the sine wave would just begin to flatten.  The manufacturer (NAD) rated them at 150 w.p.c..  If the 0.707 thing is correct, they would be (0.707x171) about 120 wts RMS. 

 

I think that doubling the distance in an anechoic environment, or outside at the top of a flagpole, causes a 6 dB loss, BUT doubling the distance in a room causes only about a 3 dB loss.  In music, for just an instant, I can get 110 dB through 1 Khorn quite easily in my 4,000+ cu.ft. room @ 16 feet (no, I don't subject my ears to that for more than and instant ... the loud passages in the orchestral music I play average about 90 dB).  My room is 1/3 larger than the one PWK was using for the chart.  The 110 dB figure is right at the top of the needle swing ("C," "Fast").  Since this is a needle meter, the true, instantaneous peaks may be 13 dB higher than the meter reads, at more like 123 dB (according to PWK in another paper).  According to the Klipsch chart, 123 dB (120 dB +3 dB, doubling the power needed) may take about 400 watts (or more, because my room is bigger), just for a split second, but I only have 171watts to "spend."  I am familiar with what clipping sounds like, and I hear no clipping.  But then I have a separate amp with a good sized power supply.

 

 

 The .707 RMS is factored in before arriving at the max power of an amplifier (at least it should be). So if they measured 171 watts then that is what your amplifier made. Many manufacturers under rated the max power of amplifiers so they can boast better distortion numbers at full rated power.

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I'm no expert, but here's what I have heard:

 

I have read that whether an amplifier will "pass" a peak without clipping depends on the duration of the peak.  Briefer peaks will pass easier.   I have read that the peaks being considered when writing amplifier specifications are 200 milliseconds to 2 milliseconds in duration.

 

I don't think "peaks" in a steady tone (the top of a sine wave) are like peaks in music.  I think that RMS is 0.707 times the height of the sine wave of the steady tone.  The leading edge of a musical peak can be much more powerful.  Someone posted here (maybe 7 or 8 years ago?) that the intensity of a rim shot close up would beyond the capacity of any amp/speaker combination, if it were not for the brevity of the leading edge of the peak.

 

I would think that separate amps would have beefier power supply sections, and should be able to produce more instantaneous power above their rated power than would receivers. 

 

My dealer measured one of my power amps at 171 watts per channel at the point where the top of the sine wave would just begin to flatten.  The manufacturer (NAD) rated them at 150 w.p.c..  If the 0.707 thing is correct, they would be (0.707x171) about 120 wts RMS. 

 

I think that doubling the distance in an anechoic environment, or outside at the top of a flagpole, causes a 6 dB loss, BUT doubling the distance in a room causes only about a 3 dB loss.  In music, for just an instant, I can get 110 dB through 1 Khorn quite easily in my 4,000+ cu.ft. room @ 16 feet (no, I don't subject my ears to that for more than and instant ... the loud passages in the orchestral music I play average about 90 dB).  My room is 1/3 larger than the one PWK was using for the chart.  The 110 dB figure is right at the top of the needle swing ("C," "Fast").  Since this is a needle meter, the true, instantaneous peaks may be 13 dB higher than the meter reads, at more like 123 dB (according to PWK in another paper).  According to the Klipsch chart, 123 dB (120 dB +3 dB, doubling the power needed) may take about 400 watts (or more, because my room is bigger), just for a split second, but I only have 171watts to "spend."  I am familiar with what clipping sounds like, and I hear no clipping.  But then I have a separate amp with a good sized power supply.

 

 

 The .707 RMS is factored in before arriving at the max power of an amplifier (at least it should be). So if they measured 171 watts then that is what your amplifier made. Many manufacturers under rated the max power of amplifiers so they can boast better distortion numbers at full rated power.

 

 

 

I've read that Nakamichi PA-7 amplifiers that are rated at 200 watt RMS actually can put out 370 watts per channel, but have never measured them.

 

Roger

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Yes, the upperend AVR would drive the system and sound fine, but separate power amps would almost certainly sound better, and the better the speakers, the easier it is to hear the difference.

This is what I don't understand--If a power amp delivers enough current to drive the speakers efficiently and within the speaker's specs how can it or the listener change/differentiate the sound at a certain SPL that is also below clipping?    

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The perfect 3,000 cu ft listening room would look like this. Note the 10' ceilings, which in PWK's day weren't all that uncommon. If you have lower ceilings than that, you can't have an ideal 3kcf listening room. Even 9' would be too low to satisfy RH Bolt's criteria for smoothest LF frequencies in a rectangular "listening room" (Note on Normal Frequency Statistics for Rectangular Rooms R. H. Bolt, 1946). Simply putting the mic at the critical distance of 2.23' would amplify the reading by 20db or more  (1).

 

DTpg593.png

 

(1Critical Loudspeaker / Listener Distance "Critical Distance - Critical distance is finding that balance between the direct sound from our sources and the reflections from our room boundary surfaces. Where a person sits or stands within the room can make a large difference. There are paces within the room where the room sound or reverberate field would be 20dB or greater above the threshold of the direct sound. The area within the room where the two sound fields are equal is termed the critical distance."

Edited by mustang guy
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