From the thread "Wanting to start a DIY tube amp"...
http://www.diyaudio.com/forums/showthread.php?t=148106
If you want to measure power at normal listening levels, you don't need the synthisizer, just play whatever you like to listen to at your normal settings.
Then measure the peak and average voltage levels at your amp speaker terminals with your oscilloscope and asume your nominal speaker impedance to calculate power (we used different equiptment, but a scope should be good enough). If your scope can't do average, etc, you will just have to guess where average level is.
Since these are rough measurements you can leave you speaker hooked up and not switch to a resistive load which would give better lab numbers. (The resistor is easier to compare results since the speaker impedance varies with frequency and someone with different speakers will get different results, but that is the whole point. We expect to get different numbers.).
What you listen to has an impact on level, especially peak values. I think we were listening to Freddy Hubbard, but I can't find what I thought was the album on the web (Sky Dive?).
Please post your results along with the amp you are using and your speaker type and efficency.
Steven
http://www.diyaudio.com/forums/showthread.php?t=148106
I will.. tell me how
I've a scope, and a synthesizer (lets call it a "signal generator"). Obviously a multimeter, too, but for ac it only measures hundreds of volts. If there's a way to do it w/out lugging the synth up here, all the better. (Its a giant modular synth I built)
If you want to measure power at normal listening levels, you don't need the synthisizer, just play whatever you like to listen to at your normal settings.
Then measure the peak and average voltage levels at your amp speaker terminals with your oscilloscope and asume your nominal speaker impedance to calculate power (we used different equiptment, but a scope should be good enough). If your scope can't do average, etc, you will just have to guess where average level is.
Since these are rough measurements you can leave you speaker hooked up and not switch to a resistive load which would give better lab numbers. (The resistor is easier to compare results since the speaker impedance varies with frequency and someone with different speakers will get different results, but that is the whole point. We expect to get different numbers.).
What you listen to has an impact on level, especially peak values. I think we were listening to Freddy Hubbard, but I can't find what I thought was the album on the web (Sky Dive?).
Please post your results along with the amp you are using and your speaker type and efficency.
Steven
Last edited:
Ok, Ive taken my measurements, and what is the math? Just ohms law? so voltage/resistance?
-edit-I think my scope is in bad need of calibration, so just ignore the rest of the message!! but let me know if Im on the right track. I'll go calibrate my scope.
so, 1 volt is loud.. .5 volts is about average (I'll take some better measurements later)
so, lets do 1... 1/.8 = 1.25, so 1.25 watts is loud? and thats my computer speakers which are tiny 3" ff85k fostex @ 88db sens.
thats from a st-35 clone (one of the diytube PCB's)
- ok, I dont know why I used .8 for the ohms, I guess that should be 8! so that's .625 watts?
I'll get some measurements off my set and 96db sens. fostex speakers later.
So, is that correct for the math, or is there more to it?
-edit-I think my scope is in bad need of calibration, so just ignore the rest of the message!! but let me know if Im on the right track. I'll go calibrate my scope.
so, 1 volt is loud.. .5 volts is about average (I'll take some better measurements later)
so, lets do 1... 1/.8 = 1.25, so 1.25 watts is loud? and thats my computer speakers which are tiny 3" ff85k fostex @ 88db sens.
thats from a st-35 clone (one of the diytube PCB's)
- ok, I dont know why I used .8 for the ohms, I guess that should be 8! so that's .625 watts?
I'll get some measurements off my set and 96db sens. fostex speakers later.
So, is that correct for the math, or is there more to it?
Last edited:
Well you got the right answer but with the wrong equation.
Power = V^2 / R.
Fortunately for you the answer is 0.625W.
But this is pretty inaccurate. The speakers will be more like 6ohms at DC with big humps in the mid band and trying to guess the average level of music is next to impossible.
I would say you're within a factor of 2 (somewhere between 0.3 and 1.2W)
Power = V^2 / R.
Fortunately for you the answer is 0.625W.
But this is pretty inaccurate. The speakers will be more like 6ohms at DC with big humps in the mid band and trying to guess the average level of music is next to impossible.
I would say you're within a factor of 2 (somewhere between 0.3 and 1.2W)
I got pretty much the same results when I measured power on my speakers, just few hundred milliwatts, with peaks somewhere up to one watt for normal listening.
I used oscilloscope too.
I use 5-7 watts tube amps for midrange and 40-70 watts solid state for bass.
Now things get pretty crazy once you start turning the volume up.
It's easy to clip the solid state amp! In one of my systems the solid state amp is AKAI with nice and fast fluorescence display measuring the power. I can hit the red (100 watts) with dynamic music (very loud).
But again at normal listening levels the power stays below 1 watt and I have to switch x100 on the display to see it.
I used oscilloscope too.
I use 5-7 watts tube amps for midrange and 40-70 watts solid state for bass.
Now things get pretty crazy once you start turning the volume up.
It's easy to clip the solid state amp! In one of my systems the solid state amp is AKAI with nice and fast fluorescence display measuring the power. I can hit the red (100 watts) with dynamic music (very loud).
But again at normal listening levels the power stays below 1 watt and I have to switch x100 on the display to see it.
Hi,
the average level for listening is around 60 to 90dB.
Let's settle for 70dB, about equal to a conversation.
If the speakers are 85dB/W/m, then a pair are ~80dB/W @ 2.5m
Input ~100mW to the speaker and the SPL ~70dB.
So about 100mW into 85dB/W/m speakers results in an average level roughly equivalent to a conversation.
Now look at the dynamic range of the music you are listening to. It could be 60dB from peak to quiet. Most recordings will have a peak to average of <20dB, that leaves the quiet at >40dB below the average level or about <=30dB SPL.
That +20dB figure is ten times the signal voltage.
Yes, your 900mV average signal can go as high as 9Vpk when listening to dynamic sources at conversation level.
Now turn up the volume to loud domestic, about 80dB. That results in peak voltage levels of ~30Vpk
Turn up the volume to party levels approaching 90dB. That requires a peak signal capability of ~90Vpk That is 500W into 8ohms.
Yes, we listen to average levels of 100mW to 1W but the amplifier and 85dB speakers are required to handle 500W in a domestic listening environment.
95dB/W/m speakers will require one tenth of the quoted power levels for the same SPL conditions, i.e. 50W from a chipamp driving 95dB 8ohm speakers is good for most domestic listening conditions
the average level for listening is around 60 to 90dB.
Let's settle for 70dB, about equal to a conversation.
If the speakers are 85dB/W/m, then a pair are ~80dB/W @ 2.5m
Input ~100mW to the speaker and the SPL ~70dB.
So about 100mW into 85dB/W/m speakers results in an average level roughly equivalent to a conversation.
Now look at the dynamic range of the music you are listening to. It could be 60dB from peak to quiet. Most recordings will have a peak to average of <20dB, that leaves the quiet at >40dB below the average level or about <=30dB SPL.
That +20dB figure is ten times the signal voltage.
Yes, your 900mV average signal can go as high as 9Vpk when listening to dynamic sources at conversation level.
Now turn up the volume to loud domestic, about 80dB. That results in peak voltage levels of ~30Vpk
Turn up the volume to party levels approaching 90dB. That requires a peak signal capability of ~90Vpk That is 500W into 8ohms.
Yes, we listen to average levels of 100mW to 1W but the amplifier and 85dB speakers are required to handle 500W in a domestic listening environment.
95dB/W/m speakers will require one tenth of the quoted power levels for the same SPL conditions, i.e. 50W from a chipamp driving 95dB 8ohm speakers is good for most domestic listening conditions
-and basically what im trying to say, is I can't believe anyone would ever need 500 watts for a home, or even 100! My most powerful amp is an old 100w per channel sansui, w/ some early 80's consumer speakers (no idea on the specs) but I never turned that thin up past 3 or 4 on the dial.. and thats the amp I was using in the mid 90's in my wilder louder days.
I can't imagine an adult every needing more than 10 watts!
I guess it's the difference these high efficiency speakers make.. why hasn't the commercial market focused on high eff. speakers?
I can't imagine an adult every needing more than 10 watts!
I guess it's the difference these high efficiency speakers make.. why hasn't the commercial market focused on high eff. speakers?
Some of the market has. Look at Klipsch, the K-Horns (3 horn sections) is rated at 105dB/W-M and have been built from the late 30s on.
Drive them with a 1W amp and it better be clean or you will hear every defect in it.
Dissadvantage - Very expensive, very large, require moderate large room for proper setup, require corners with unobstructed walls as speaker extensions for proper loading of the horns.
On the other hand LaScala (Three horn sections 105dB/W-M)works well in corners without being as sensative as K-Horns. Still quite a bit of ka-ching.
Cornwals (Base Reflex with horn loaded mid and high 102dB/W-M) were (to me) too obtrusive, although better sounding than the Herasey (96dB/W-M, Heresy III is 99db/W-M but I'm not about to buy new ones).
I havn't looked at the speaker market in 30 years, but I am willing to bet the average efficency has crept up a bit, but you still have to pay for efficency and quality.
I'm sure there are other companies making speakers as good or better, and possibly at lower cost.
The Heresy never had the greatest specs as far as frequecy response went, but they sounded good to me when I got them in 77, and they still do sound good.
Drive them with a 1W amp and it better be clean or you will hear every defect in it.
Dissadvantage - Very expensive, very large, require moderate large room for proper setup, require corners with unobstructed walls as speaker extensions for proper loading of the horns.
On the other hand LaScala (Three horn sections 105dB/W-M)works well in corners without being as sensative as K-Horns. Still quite a bit of ka-ching.
Cornwals (Base Reflex with horn loaded mid and high 102dB/W-M) were (to me) too obtrusive, although better sounding than the Herasey (96dB/W-M, Heresy III is 99db/W-M but I'm not about to buy new ones).
I havn't looked at the speaker market in 30 years, but I am willing to bet the average efficency has crept up a bit, but you still have to pay for efficency and quality.
I'm sure there are other companies making speakers as good or better, and possibly at lower cost.
The Heresy never had the greatest specs as far as frequecy response went, but they sounded good to me when I got them in 77, and they still do sound good.
a few more factors....
An amplifier rated 100W is usually several percent THD at that power. If you want clean, low distortion peaks then you need a 500W amplifier to deliver a clean 100W.
Also, if you have exotic speakers/crossovers with wild impedance curves then you need more spare power to control the complex load.
BTW, nice synopsis AndrewT!
An amplifier rated 100W is usually several percent THD at that power. If you want clean, low distortion peaks then you need a 500W amplifier to deliver a clean 100W.
Also, if you have exotic speakers/crossovers with wild impedance curves then you need more spare power to control the complex load.
BTW, nice synopsis AndrewT!
I hope the specified maximum power is quoted @ <=0.1%distortion @1kHz and preferably <=0.2% from 20Hz to 10kHz.
I expect a 500W amplifier to sound clean on all transients within it's voltage and current capability.
Hi,
I think it is more or less standard to define output power as the point where distortion is 1% at 1kHz. For most solid state amplifiers or tube amplifiers with moderate to high amounts of feedback the distortion will rise very quickly when you have reached the 1% point as it will involve some form of clipping. Stereophile use the 1% criteria for solid state amplifiers and 3% at 1kHz for tube amplifiers as many SETs will give very low output power at 1%.
Many amplifiers giving 1% at 1kHz will have much higher distortion at the frequency extremes, in many cases so much that it would be of no useful purpose to measure at these points at maximum output power. This behavior is typical for solid state or other amplifiers that use feedback as a distortion control tool but with low open loop bandwidth.
I think it is more or less standard to define output power as the point where distortion is 1% at 1kHz. For most solid state amplifiers or tube amplifiers with moderate to high amounts of feedback the distortion will rise very quickly when you have reached the 1% point as it will involve some form of clipping. Stereophile use the 1% criteria for solid state amplifiers and 3% at 1kHz for tube amplifiers as many SETs will give very low output power at 1%.
Many amplifiers giving 1% at 1kHz will have much higher distortion at the frequency extremes, in many cases so much that it would be of no useful purpose to measure at these points at maximum output power. This behavior is typical for solid state or other amplifiers that use feedback as a distortion control tool but with low open loop bandwidth.
More measurements.. Last was my PC system, so I'm right in front of the speakers, and that was the 31mw level. I measured my living room system, 300b w/ 96db fostex speakers. I listen to that one up near 500mw to fill the room w/ sound.
I'm not sure if I'm reading my voltage correctly from the scope, though. Not exactly sure how to explain this.. But I have the scope show the signal fairly dense, and there's a section in the middle where most of the sound is.. then from there all the little percussion spikes and other peaks pop up about 2x higher than the bulk of the sound. Well, I'm reading the voltage off the top of that dense middle section.
-also, my comment yesterday about adults not needing more than 10 watts.. I understand why someone would WANT more than that. But was talking more about the mid grade consumer market.. A little 12-20 watt chip amp and high eff. speakers can sound quite good, and probably costs less than a 100watt normal consumer grade system. But, marketing starts to come in to play I guess, and selling less watts could be tough.
I'm not sure if I'm reading my voltage correctly from the scope, though. Not exactly sure how to explain this.. But I have the scope show the signal fairly dense, and there's a section in the middle where most of the sound is.. then from there all the little percussion spikes and other peaks pop up about 2x higher than the bulk of the sound. Well, I'm reading the voltage off the top of that dense middle section.
-also, my comment yesterday about adults not needing more than 10 watts.. I understand why someone would WANT more than that. But was talking more about the mid grade consumer market.. A little 12-20 watt chip amp and high eff. speakers can sound quite good, and probably costs less than a 100watt normal consumer grade system. But, marketing starts to come in to play I guess, and selling less watts could be tough.
You're quite right wicked1. With benign-impedance, efficient speakers and sane listening levels, a genuine, clean 10W amp is all you need.
I think the trend though, as the cost of a watt goes down, is to sacrifice speaker efficiency to get more bandwidth, more excursion and less distortion. This isn't necessarily a bad thing.
<edit> and yes, you are reading your scope correctly, these readings are in line with my experience.
I think the trend though, as the cost of a watt goes down, is to sacrifice speaker efficiency to get more bandwidth, more excursion and less distortion. This isn't necessarily a bad thing.
<edit> and yes, you are reading your scope correctly, these readings are in line with my experience.
A friend has a terrible 80s portable stereo with a logarithmic level indicator, with power marked in watts. We were using it while woodworking & drinking beer, leading to a relatively high apparent listening level. The meter was hovering around slightly less than one watt in most cases. I did cut LF on the EQ since the speakers were bad. Surprised me since we had it loud to get over the chopsaw.
Since I haven't seen it mentioned here, it is worth pointing out that perceived loudness in hearing (like most human senses) is logarithmic in nature. Roughly speaking, each 10dB increase in power is perceived as sounding "twice as loud". If your friend has a 1W amp any you want something that sounds twice as loud you need a 10W amp. Similarly a 100W amp sounds twice as loud as a 10W amp. This is also why volume knobs have a logarithmic resistance.
Since most consumers perception to value is linear, they will assume a 100W amp must be considerably better than a lowly 10W amp. In truth, if they never turn the volume knob beyond half way, they are really listening to a 10W amp that they paid too much for (and probably sounds worse than a well designed 10W amp).
If you are interested in deciding what power is needed on an amplifier, I guess it would be better to look for the highest peak during playback and use that as an indicator of amplifier power.
And don't forget that power means RMS power: P = (V_RMS)^2/R (for resistive loads). For a purely sinusoidal signal, you would take the peak voltage amplitude and divide by root(2) to get V_RMS. This isn't exactly accurate for transients, but it still gives a better estimate than just taking the peak voltage.
So in fact a 1V amplitude sine wave into an 8 ohm resistive load is really only 1/16th of a Watt.
Oops' you'll better modify that statement. For a given o/p tranny size and B+
I'm quite content with the thd performance of my 100W amp.
See graph.
richy
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.