• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

How to properly judge wattage.

Y

Yerp!

Member
Hi. I need info.

How does one properly judge wattage?

I just bought a Pioneer SX-626. I've been looking at the manual and the specs say several different things when it comes to wattage:

Music Power Output (IHF)
Continuous Power Output (each channel driven)
Continuous Power Output (both channels driven)
Power Output (20Hz-20kHz)

I'd like to pick the biggest number and be done with it, but what's the truth?

Thanks!
 
Register to hide this ad
They're all the truth. Just different ways of stating it.

The most commonly-accepted "truth" however, at least in the USA, is continuous average power, 20Hz to 20kHz.
 
Explaining only what you gave (no experience of the mentioned equipment):

Firstly: Maximum power output is a function of the power supply voltage. This can decrease somewhat under load, thus maximum power available under full load (say heavy organ music) will be lower than e.g. a string trio playing. Further, a characteristic of typical music is that the 'on-off' ratio is low, i.e. between signal peaks a longer period of low amplitude signal occurs. While average music energy content varies all over the show, one can say that when peaks go to e.g. 50W, the average value might be <12W. This places a lower demand on the power supply. Therefore peaks of 50W might be 'available', while when 'full' music is reproduced, a drawn-down power supply might reduce peak power available to say 30W.

When that is understood, the meanings of the terms are:

Music Power Output: This is normally the peak available power output when playing normal music with low average/peak value, e.g. 50W.

Continuous Power Output per channel: This value will be available with full signal load, such as a sine wave, which will place greater demand on the power supply, for one channel at a time. It is often rated as say 25W r.m.s. (although 'r.m.s.' is an erroneous term, pertaining to signal amplitude only, not power - another subject).

.... both channels driven: As above but with both channels now drawing against the power supply. It will be a still lower value, say 20W per above example.

Power Output (20Hz - 20kHz) The above maximum figures are normally not available at band extremes. The maximum 'maintainable' output will be available only say 40Hz - 12 kHz.

I hope this makes sense to you.

P.S: Regarding small differences in power ratings: It needs to be kept in mind that the ear hears logarithmically. A factor 2 in wattage value might appear high, but it is barely audible.
 
Last edited:
Take a look at the back of the unit and finds the watts figure on the power rating tag. Divide that nuber in half. The halve it again. If the unit says 100 watts, it roughly be about 25 wpc. The hz figures probably won't be correct until the unit has been properly serviced. Same for the wpc (although a properly serviced unit will slighty exceed your initial wpc estimate...if the unit is capable, as the pioneer should). Of course there's variances to my simple formula (proton or carver amps for instance), but it's a good rule of thumb to figure our the wpc of an amp.
 
Your unit is from before Nov 1974 when the US Federal Trade Commission required all home stereo amplifier products to be tested the same way. This lead to the lower numbers because of the test methodology.

The FTC required a 30 minute, 1/3 power preconditioning and some amps got hot and shut down then came back on when they cooled, not a fail I guess.

The results of the test required:
State the power in RMS watts
State the Frequency Response of the test (some lower units were tested 40Hz to 20kHz)
State the Impedance
State THD, total harmonic distortion maximum
State how many channels were operated.

This is what changes your SX-626 from a 110 (IHF) watt monster into a 20 WPC, 20-20kHz, 8Ω, 1%THD, both channels driven machine.

But we don't listen to wpc rms we listen more to IHF watts which are really peak performance and that is what the loud peaks in music are.

But with the FTC numbers everything could be compared on equal terms.
 
Last edited:
Continuous power output, both channels driven will put you as close as you're likely to get to a figure comparable to the 1974 FTC spec. No specification of frequency range, though, so the number they state may be at, e.g., 1000 Hz. The 20 to 20 kHz continuous may also be fairly comparable to the "modern" (1974!) method of rating (in the US). That said, unless the harmonic distortion level is stated, it's probably the power output at 1% or even 10% (the classically-accepted level of audible clipping, believe it or not).

EDIT: Yeah, 20 wpc into 8 ohms 20 to 20 kHz at 1% THD according to the brochure at http://www.hifiengine.com/manual_library/pioneer/sx-626.shtml
Not "technically" the FTC 1974 spec, because the latter specified the (very stringent) 1 hour preconditioning... but probably close enough.. for Government work :-)
 
Last edited:
Thanks everyone. I have a pair of big RTR speakers and have been told that I need a powerful amp (100+ watts) to push 'em. My Pioneer SX-626 obviously isn't that, but I'm experimenting with different speakers and receiver/amps. Is the there any possibility of damaging anything by mismatching or reading these numbers wrong?
 
There is almost always the possibility to damage something in almost any pairing if you are not paying attention to the signs and symptoms the system is telling you.

If it sounds good it probably is good. If something sounds harsh, or shrill, or sounds flat/non-dynamic, or the speakers are making popping or clunking noises, those are all good signs to turn it down.

Bear in mind the system doesn't damage itself, damage is caused by the operator of the system.
 
all of the above is good advice, but I'd add this "prequel" quantum of advice -- just resist the temptation to turn it up crazy loud in the first place... and you should be fine.
 
There is a direct relationship between the power you need, the volume at which you want to be able to listen (without overt distortion), and the sensitivity of your speakers. Sensitivity is a measurement of the loudness (the sound pressure level, or SPL, stated in decibels, or dB) a speaker will produce at 1 meter with one watt of input.

It takes a doubling (or halving) of wattage to make a 3dB change in loudness, and 3dB is considered the smallest change to be distinctly noticeable. And, you can assume a 6dB drop in volume for each doubling of distance from the speakers. So, if a speaker produces 90dB at 1 meter with 1 watt, it will produce approximately 84dB at 2 meters (actually, somewhat more due to room reinforcement of the sound waves).

Generally, you need enough power to achieve the loudness at which you might want to listen, plus another 10-12db to accommodate transient peaks in the music without too much clipping distortion.

Your RTR speakers probably have a sensitivity of around 90dB. Add 3dB (for second speaker), then subtract 8-9dB for 10 foot listening distance. That puts you at approximately 85dB with one watt. Most people would consider this moderately, but not very, loud.

Allowing enough "headroom" for peaks of 12dB, your Pioneer amp will be pretty much tapped out somewhere around 88dB. For many people, this is loud enough to meet their needs.

Hope this helps...and in any case, pay particular attention to posts 8 and 9, above.
 
Very useful info! I also have a modern Pioneer VSX model (240 Watts Total Stereo Power - 120 watts x 2 (20 Hz - 20kHz .2 THD @ 8 Ohm). It tempts me to break quantum post 9!!! I'm a sinner.

How do I find out the sensitivity of a speaker? How does a speakers Ohm rating come into play?
 
The sensitivity ratings of most speakers are widely available. The manufacturer usually publishes them. A speakers Ohm rating is not directly related to its sensitivity. As for posts #8 and #9, it's really quite simple. If you hear signs of strain turn the volume down. The impression of strain can be from the amplifier, speakers or both. Just pay attention!
 
Sensitivity is often a listed specification. What speakers? Maybe (??) "we" can help.

All things being equal (and, again, painting in very broad strokes) a lower impedance load (loudspeaker) will make any given amplifier work harder. At extremes, this can be detrimental to amp and even possibly loudspeaker (depending on what the amp does).
 
Yerp! said:
Very useful info! I also have a modern Pioneer VSX model (240 Watts Total Stereo Power - 120 watts x 2 (20 Hz - 20kHz .2 THD @ 8 Ohm). It tempts me to break quantum post 9!!! I'm a sinner.

How do I find out the sensitivity of a speaker? How does a speakers Ohm rating come into play?
Click to expand...

A local acquaintance has some RTR speakers, and told me that at least in his series (which I think consisted of 6 models), sensitivity of all was 90-91dB, and rated impedance was 4 ohms for some, 6 ohms for others.

Sensitivity and nominal impedance are often printed on the backplate of the speaker.

As noted above, lower resistance = higher current demand on the amp. A 4 ohm speaker pulls, nominally, twice as much current as an 8 ohm speaker. Since very few amps are equipped to double the current they can deliver as impedance drops, their maximum power capability at 4 ohms is less than at 8 ohms (for example). In fact, some amps are not rated to accommodate 4 ohm loads (or lower, of course). Bottom line, with the same amp, you will have less headroom when running lower impedance speakers.
 
I have RTR 280DRs (and ESR-15 electrostatics, not hooked up yet).

Here's what I know about my RTRs:

System: 4-Way / 7-Driver, Acoustic Suspension with 'Down Firing' 'Sub' Woofer
Frequency Response: 22-25,000Hz +/- 3dB
Nominal Impedance: 8Ω
Cross-over frequencies: 2500Hz & 7500Hz
Recommended Power Amplifier: 25-100 watts

- Quad (4X) 10" Woofers featuring vented dust caps and non-deteriorating Butyl rubber surrounds, and AlNiCo magnets (1 front, 1 each side and 1 down firing)
- 5X 2.5" Mid-Tweeters utilizing AlNiCo magnets
- Front firing Piezo 'Super Tweeter' horn
- "Real" internal cross-over.
- Dual 'Hi' and 'Mid' frequency attenuators, using resistors.
- Speaker Protection Circuit Breaker
- 10" 'Down Firing' woofer for extended low end into the 'sub' region
- 5-Way Banana / Binding Post connectors

I don't listen to music to loudly (85 db is good for album length bursts of sound). Plus, these RTRs are no wimps, so I'm not afraid of pushing to hard. I'm afraid of underpowering! Is there such a thing? The recommendations are 25-100 watts. Is 20wpc too weak? Using the wisdom of posts 8, 9 and 10 I'd use caution not to strain the amp, but can little 7 watt, 12 watt, 17 watt amps be used, or is that a no-no?

How about the opposite? little speaker giant amp combinations. Is that ok in moderation or stupid?
 
A good recording has peaks at least 10-12 dB above the average level of the signal. This difference is known as the crest factor.

As an example, if it takes 1 watt to amplify a signal so that you get an average of 85dB at your listening position and you have a crest factor of 12dB, then your amp must be capable of delivering 16 watts to reproduce these peaks without distortion (that is, without clipping them off). Remember that each 3dB requires double the power.

Now, lets say that you turn up the volume a bit...to 88dB. Now you need 32 watts to avoid clipping distortion. Minor clipping is not a big deal, but keep in mind that some recordings have a crest factor of 15dB or even higher. At 88dB with a crest factor of 15dB, you would need 64 watts to avoid clipping.

No matter how much power your speakers can take, the amp must be able to deliver a clean signal at the volume you want. It cannot exceed its maximum voltage capability. The more you try to do so, the greater becomes the portion of the signal that is clipped/distorted. And keep in mind that an amp in heavy clipping can trigger other problems...in both the amp and the speakers.

Bottom line, you can use a very low powered amp to power speakers of any sensitivity. But the lower the sensitivity, the less volume you can achieve before clipping begins.

You can also use a very high powered amp on speakers of any sensitivity. But in this case, the higher the sensitivity, the more careful you must be with the volume control to avoid overpowering the speakers and damaging them. The upside to this approach is that the chances of clipping are minimized.

Generally, there is no such thing as an amp that is too strong or too weak. It all comes down to how loud you want to listen and how much power it takes to achieve that loudness with a given set of speakers (that is, with a given speaker sensitivity). The other closely related variable is the power-handling capability of the speakers, but these specs are usually vague and not particularly reliable. Better to use your ears (refer to posts 8 and 9, again).
 
Last edited:
A clean amp..

A "clean amp"... will do all of the above stated..

Back when.. how did we define "clean"... Well some believed dual power supply-direct coupled, others hi power out-low distortion (THD), still others.. clean (preamp) signal, through-n-through, and a boss power amp to boot!

But I agree with one prior post... never "up your amp" to prove your speakers work well as the point of no return.. only has to be reached once :yes:.

I'm thinking.. :scratch2:...if you look at the speaker system specs.. this is a pretty good "definer of the range and power handling"... it will/can survive.
 
Yerp! said:
I have RTR 280DRs (and ESR-15 electrostatics, not hooked up yet).


I don't listen to music to loudly (85 db is good for album length bursts of sound). Plus, these RTRs are no wimps, so I'm not afraid of pushing to hard. I'm afraid of underpowering! Is there such a thing? The recommendations are 25-100 watts. Is 20wpc too weak? Using the wisdom of posts 8, 9 and 10 I'd use caution not to strain the amp, but can little 7 watt, 12 watt, 17 watt amps be used, or is that a no-no?

How about the opposite? little speaker giant amp combinations. Is that ok in moderation or stupid?
Click to expand...

Under powering is only bad if you clip your amp, or if you are unsatisfied with the sound level when the amp is not clipping. As others have said, if it sounds bad, turn it down. I've used 12 watt tube amps on my Magneplanars, which are usually recommended for use with a minimum of 100 watts. They sounded great, and went plenty loud (for me).

Overpowering is OK in moderation. Meaning don't expect bad sound to clue you in to danger. I'm using a 100 watt amp on my Quads, which can't take more than 30 or so. Yes, I'm careful. More than careful - I just don't do loud, with those rare, fragile gems.

Speaking of gems, ESR-15s look amazing! Would love to hear them - hope you get them going and tell us how they sound.

:music:
 
IHF power is bogus. A typical musical peak will last more than a few cycles of 120 Hz power and it only takes a few cycles to pull the filter capacitors down to a long term steady state voltage for the duration of the musical peak.
 
You must log in or register to reply here.
Back
Top Bottom