Understanding Amplifier Measurements (Video)

[amirm]

Continuing the series on learning measurements, I recorded one last night on power amplifiers. Alas, my external microphone got disconnected and internal one to the camera was used. So the sound quality is rather poor.

A personal note: as you may know, I don't allow advertising in my videos, nor do I pester people to subscribe, give likes, etc.. Alas, it seems some out there are keeping score on popularity of my content as proof point of whether their audio videos are more correct than mine. So let's even the playground and subscribe to my channel if you have not before. Click on this link to go to my youtube channel (youtube.com/@audiosciencereview) and do that. Appreciate it in advance.

 

[SmackDaddies]

some out there are keeping score

name and shame, name and shame

 

[SmackDaddies]

I mean, I don't agree with everything you put out there, but you are hands down the most informed and dedicated person I know in this field.

 

[SmackDaddies]

Headroom question - does someone have a link for me to understand this issue? Does headroom matter if I am at a desk and never roll the power more than 50%? Thanks!

 

[amirm]

Headroom question - does someone have a link for me to understand this issue? Does headroom matter if I am at a desk and never roll the power more than 50%? Thanks!

In that case, no. Headroom just means a bit of extra power for free. If you don't need the full power you have all the time, then the headroom is not needed either.

 

[estuardo4]

Waiting for Pavel to critique...

Thank you again Amir. I don't need an Electronic or Audio degree to understand what you say. I almost feel like an intelligent being... Almost.

 

[AdamG]

In that case, no. Headroom just means a bit of extra power for free. If you don't need the full power you have all the time, then the headroom is not needed either.

Dude, I want some of what you’re taking ! Your spitting out high quality/value hour long Videos like a Peds Dispenser.

 

[AdamG]

Headroom question - does someone have a link for me to understand this issue? Does headroom matter if I am at a desk and never roll the power more than 50%? Thanks!

This is a good read and will take you into the parallel topic of headroom:

Clipping 101

Amplifier clipping has been cited as the cause of audible distortion, destruction of speakers (especially tweeters), and total annihilation of the known universe. More or less. In fact, clipping does cause distortion that adds significant high-frequency content not in the original signal, and...

www.audiosciencereview.com

Class D FAQ

unfortunately the science of evaluating amplifiers strictly from measurements and what my ears tell me are often two different things. many things come into play by the time an amplified audio signal reaches one's ears, not the least of which is the electrical interaction with the loudspeaker's...

www.audiosciencereview.com

How Much | Crown Audio - Professional Power Amplifiers | English

www.crownaudio.com

 

[_thelaughingman]

Dude, I want some of what you’re taking ! Your spitting out high quality/value hour long Videos like a Peds Dispenser.

Bruh is spitting facts!!

 

[amper42]

Is ASR running low on product to review?

 

[johnp98]

Amazing videos that you have been releasing recently!

If we can't reliably trust the manufacturers reported power output for amps nor can we trust the manufacturers reported speaker sensitivity (let alone impedance) is there a rough rule of thumb now much reported "power" to look for in an amp?

I am thinking about a general livingroom or home theater where listening distances would be 8-10ft and wanting reasonable levels / headroom for dynamic range.

I found this: https://www.crownaudio.com/en-US/tools/calculators#amp_power_required
but don't know if people have other suggestions or rules of thumb.

Thanks again for the amazing videos!

 

[IAtaman]

I am sad we do not have PMPO anymore. It was possible to get a 2000W amp for $150 before. Now for $150 you can get max 100-150W. Thanks science!

 

[BuddyJ]

This was excellent. Please do one on Phono Preamps.

 

[Oristo]

other suggestions or rules of thumb

Look at power input plate; safety regulations enforce accuracy of those.
While class D amplifiers may be more efficient, others are mostly less than 2/3;
100W output requires 150W power supply.

 

[juliangst]

I think mentioning phase response of amps would also have been useful.
Some ‚audiophiles‘ always criticize hypex or class d amps because of their phase shift or some other bs reason.

Phase shifts of electronics obviously are not audible

 

[DonH56]

Headroom question - does someone have a link for me to understand this issue? Does headroom matter if I am at a desk and never roll the power more than 50%? Thanks!

Others have provided links. Here is my standard answer:

Power Needs:

For many years I have used 17 dB peak-to-average power based on an old AES article I can no longer find. Anecdotally various audio fora report 20 dB or more for movies. IME most people use much less average power than they think, but require more peak power. An online calculator can help you estimate your average power; note 80 dB is very loud to me (YMMV). Here is one:

Peak SPL Calculator

Most people think of volume in dB and most modern AVR/AVP/etc. units list dB on the volume knob. Power in dB goes as 10log10(Power_ratio) so the change in power is 10^(dB/10). Here are some reference numbers in dB and power:

1 dB is barely noticeable and requires 1.26x the power
3 dB is what most people hear as "a little louder" and requires 2x the power
6 dB is significantly louder and requires 4x the power
10 dB sounds twice as loud and requires 10x the power
17 dB is the headroom for music and requires 50x the average power
20 dB for movies requires 100x the power

If you listen at around 1 W average, then you need 50~100 W to avoid clipping on most source material. You can figure out your estimated average power from the calculator knowing your speaker's sensitivity and distance from them. Note music may be more compressed and thus require less headroom, and the loudest sounds in movies tend to be things like gun shots and explosions where a little clipping is likely unnoticeable.

HTH - Don

 

[JimWeir]

Headroom question - does someone have a link for me to understand this issue? Does headroom matter if I am at a desk and never roll the power more than 50%? Thanks!

Playing music you will rarely produce a power (voltage x current) over a few watts which is measured as an RMS quantity. The peak to RMS ratio is called the crest factor.
The music signal voltage corresponding to peak sound pressure might be 10x (20dB) higher. This is because music is not like the sine waves used in testing which have a 1.4 x crest factor.

You might enjoy this.

 

[Vini darko]

Quality video thanks Amir.

 

[Barrelhouse Solly]

Playing music you will rarely produce a power (voltage x current) over a few watts which is measured as an RMS quantity. The peak to RMS ratio is called the crest factor.
The music signal voltage corresponding to peak sound pressure might be 10x (20dB) higher. This is because music is not like the sine waves used in testing which have a 1.4 x crest factor.

You might enjoy this.

I always enjoy mention of the square root of 2. <g>

 

[JimWeir]

I always enjoy mention of the square root of 2. <g>

3dB. Voltage or pressure.