How much power do you use? A Test

[Panomaniac]

OK, I promised a power test in another thread, here it is. It's easy to do, all you need is an AC voltmeter with a low voltage scale. Anything in the 5-20V range should do. If your meter has only high voltage AC scales (200V-1000V) it won't be accurate enough for this.
How to proceed:

1. Download this 120Hz file. Test Signals
2. Unzip it and burn it to a CD or put it in whatever digital playback gadget you use.
3. Select and play back a few music tracks as loud as you ever do (like after a few beers.) Take note of your volume settings - you probably know where they will be already.
4. Use the highest setting you found when playing back music really loud. Leave the volume control there for the following measurement.
5. Playback the test tone and measure the voltage at your speaker terminals. Measure at the amp or at the speaker, either is fine.
6. Make a note of this voltage
7. Take the square of the voltage* you measured from the test tone (multiply it by itself). You now have the minimum power rating of amp you need. Easy!

The file is a mono 120Hz sine wave in MP3 format. The MP3 is inside a zip file. Just unzip it and burn it to a CD or put it on whatever digital playback device you use.

Lets take an example:

• You play a few tunes nice and loud.
• You find the highest setting of the volume knob during your loud playback.
• You play the 120Hz tone at that volume setting and measure 3.5 volts AC at the speaker terminals.
• 3.5 squared is 12.25 (3.5x3.5=12.25)
• You need an amp that can supply at least 12.25 watts RMS into your speakers. With that much, the amp won't clip, even on your loudest music.

You may be surprised how low the power is. In fact, that's the rating in RMS watts of an amp that will allow you to play your loudest music and not clip. Normally, you probably use a fraction of this power. My max is about 6W with my A5s, in my small room.

If you have questions about this test, please don't hesitate to ask, I'll do my best to explain. The 120Hz and -12dB point were chosen for several reasons, one being to make the math easy.

*assuming an 8 ohm load.

[Altec Best]

I don't think I'm understanding this. Is this just to find the minimum your speakers need for a amplifier ? If you have an amp with lots of power then you won't need to know this correct ? I guess this is really for small tube amps right ?

[Panomaniac]

Yes, it's to give you an idea of how much power you really need for your speakers and room. If you have an amp with lots of power, you may still be interested to know how much power you are using. With Altecs, you might be surprised how little you need.

If you are interested in how much average power you actually use, then just take the voltage you measured, square it and divide by the nominal speaker impedance. That will be a good estimate of the average power you are using during loud sections at that volume setting. For example: You measure 3V at your normal listening volume and you have an 8 ohm system. 3x3/8=1.125W. That would be the average power you use. Peak power will be much higher, maybe eight or ten times more.

The reason for using the 120Hz tone is that just about any AC volt meter (with the right scale) can measure it accurately. Music signals are much harder to measure accurately.

[Nipper]

Very nice work Pano! Excellent!

THANK YOU!

Somewhere along the line in the 70's someone started the myth that you need all the watts you can afford because your amp will have more headroom. Because of that most people think more is better and that statement was and still is widely accepted.
To the average person 1000 watts looks better than 40.

The problem is nobody mentioned or took into consideration the quality of the amp or the efficiency of the speakers. You just had to have 100 watts to have a good amp and if you had more, it was even better.

Most of us know that with highly efficient speakers you don't need much more than 10 watts if that. When you have a set of VOTT's your money is better spent pursuing a high quality amp and not necessarily one with a lot of watts. You can get amps with 500+ watts cheap now but that will not make them sound good.

The problem I encountered most was a lot of people do not understand what speaker efficiency means. I could have use a tool like this many times. The only way I could demonstrate this before was to connect an Altec speaker to an amp and note the volume knob position at a certain dB level and then connect something like a Bose 901 and note the volume knob position to achieve the same dB level. The Altecs at 2 were producing the same level as the Bose were at 8.

People would understand efficiency then.

Then Sansui made a few amps that had watt meters. That made it easy to show people how few watts they really needed with efficient speakers. Most amps have VU meters which help in keeping the signal clear. Personally I think having both would be great.

On the subject of watts, it was not until the 70's (IIRC) that everyone started using the RMS rating. Before that there were a few different audio governing authorities like the IHF (Institute of High Fidelity) and the AAHEA (Academy for the Advancement of High End Audio) that used different methods for extrapolating this power information.

If someone here could take the time to explain the different methods they used and add it to this thread this would make an excellent sticky for an Altec forum.

Altec VOTT's don't require a ton of watts. They are extremely amp sensitive and your money is best spent on a high quality amp vs. a high power amp. Of course you can have both but the extra power is not necessary.
Some speakers do need a higher wattage amp to perform satisfactorily. Altecs dont.

Around here, It used to be that high efficiency speakers were referred to as "loudspeakers" and less efficient were referred to as "high fidelity speakers". Something I could never agree with. It made it sound like a loudspeaker had no range.

Altecs are extremely efficient and that is the first thing one should understand when choosing an amp.

Just my .02 dB

[Altec Best]

Yes, it's to give you an idea of how much power you really need for your speakers and room. If you have an amp with lots of power, you may still be interested to know how much power you are using. With Altecs, you might be surprised how little you need.

If you are interested in how much average power you actually use, then just take the voltage you measured, square it and divide by the nominal speaker impedance. That will be a good estimate of the average power you are using during loud sections at that volume setting. For example: You measure 3V at your normal listening volume and you have an 8 ohm system. 3x3/8=1.125W. That would be the average power you use. Peak power will be much higher, maybe eight or ten times more.

The reason for using the 120Hz tone is that just about any AC volt meter (with the right scale) can measure it accurately. Music signals are much harder to measure accurately.

Thanks Pano for the explanation my Friend ! I seem to understand your explanations a lot easier for some unknown reason !

[bowtie427ss]

Efficiency vs. sensitivity.................

Handy calculator if you like to see different expressions for the same number/value: Efficiency and sensitivity conversion - loudspeaker percent and dB per watt and meter loudspeaker efficiency versus sensitivity vs - sengpielaudio Sengpiel Berlin

Interesting note, GPA, and a few other high quality speaker manufacturers do indeed give an efficiency rating for many of their drivers.

[Panomaniac]

You're welcome!
Just as a point of reference; with my speakers a 1 volt (rms) signal gives me ~85dB at the listening position. That's nice and loud as an average level. That would put the peaks in the 100-105 region.

OK, anyone actually going to measure? I'd love to see what you guys get. Those with bigger spaces will be using more power. My room is small to medium at about 3000 cubic feet. (84 cubic meters)

[Nipper]

I got 1.8 (small system in a sun room) so 3.2 watts is plenty out there. No dB meter handy but it was way louder than I would normally go in there. Speakers were 3 way Cerwin Vegas.

This test might not interest the pros here but I have friends that are learning and thats a effective demonstration. The usual comment when someone sees the Altecs is "How big of an amp do you need to run those monsters?".

It helps to show them.

Thanks! Appreciated.

[Altec Best]

You're welcome!
OK, anyone actually going to measure? I'd love to see what you guys get.

OK I will be.But I first have to get my project done that is priority now.

Before I was real busy with work,now that work has slowed considerably my unheated detached garage is too friggin cold. I'm in the process of hooking up some heat though (propane) which gags you with fumes.

I'm working on the ports again. Trying to install a grill cloth over the PVC pipe ends that are exposed on the outside of the cabs.

[Panomaniac]

Great, thanks Nipper! You're in a similar power range to me.
AB, looking forward to your results when you can.