Speaker Power Issues

[derrickdj1]

I have a fairly simple question with a
more complex answer. How many watts of power am I using when I
listen to my system at -30 db or at reference level? I keep
hearing that the Klipsch speakers are so effiecient and it does not
require as much power to drive them. I see a lot of members
use power amps to increase the headroom for their systems. I
recently seen on the forum where a member damaged a RF 83 rated 250W
RMS/ 1000W Peak. He had the speaker attached to a power amp and
fried the voice coil or caused physical damage from playing the
speaker to loud. Those are much better speakers than I have and
my speakers get very loud. My speakers are not even close to the
rated power handeling load of the RF 83's.I have ran across post
where some people are saying they are only using 20-40 watts of power
for normal listening with there speakers. I know in general
larger speakers are more efficient and lounder at a given avr setting
than a smaller speaker. I would like to hear some other members
take on this issue. I am a newbie to the forum and consider
this as part of my learning process. Let's not consider the
Heritage line of speaker in this discussion; they seem to be in a
separate category when discussing power issues.

[mustang guy]

Here is some oversimplified math that might amaze you.

To make a speaker sound twice as loud, you need 9 to 10 times more watts. In other words, to be twice as loud as 40 watts, in human perception, you need almost 400 watts.

The LaScala has an efficiency of 104 db at 1 watt. At 10 watts is will be roughly twice as loud to your ear. At 100 watts, it's RMS, it will double its loudness again. To get twice a loud as that, you would need to pump 1,000 watts into the speaker which would damage it.

[Ski Bum]

Take a look at this:

http://myhometheater.homestead.com/splcalculator.html

If you have an spl meter, you can use your listening position spl readings and plug in different watt values to figure out, at least ballpark, how many watts you're actually using.

Most of the time, you're using only a few watts. Using the above method, I'm using 2-3 watts to get to 95db at my chair.

It doesn't matter if your discussing Heritage, Reference, any other line. The important thing is sensitivity. A speaker that produces 100db/w/m requires only one-tenth the amp power as a speaker that produces 90db/w/m to achieve the same volume.

[Quiet_Hollow]

How many watts of power am I using when I

listen to my system at -30 db or at reference level?

AC power is not easy to determine in reactive loads, especially when multiple frequencies are involved. To determine this empirically, you're going to need the tools of the trade. A multi meter, an SPL meter, and a calibrated input signal. With out those, at a minimum, it's anyone's guess.

A "complex" answer indeed.

[psg]

I have a fairly simple question with a
more complex answer. How many watts of power am I using when I
listen to my system at -30 db or at reference level?

If your receiver is the kind that does not reset 0 dB, then typically 0 dB is the maximum possible output if the input signal is also maxed out. -30 dB from that one thousanth of the max power output, so 0.1W for a 100W receiver or 0.05W for a 50W receiver. A 10 dB increase is a ten-fold increase in power, 20 dB is hundred and 30 dB is one thousand, and so on.

I typically listen to jazz trios much below -30 dB, so use a small fraction of a Watt.

[derrickdj1]

l Thanks for the link on SPL Calculations. The temporary threshold shift I think most of us have experienced this firsthand. A key point to draw from that article is respect your hearing and consider what is an appropiate levels of loudness. This will protect your hearing and your equipment. I think, I will take this adivce, so that I don't have to keep getting louder systems; I just cannot afford the Palladium Series, lol.

[russ69]

Some simple rules for operating a HI-FI. If you want to play loud, you will need some serious power, more than a 100 wpc receiver can deliver. If you try to find the limits, you will (something will break). Listen at a volume that is comfortable for you, don't try to impress the neighbors.

[garyrc]

The SPL calculator mentioned in this thread is very good, but there are a few parts of the text in the "O.K., so what does this mean for my hearing?" section that I disagree with.

• Repeated exposure to SPLs of considerably over 85 dB are not a problem if we're talking about fairly brief passages in the music. Long lasting exposure to a steady SPL of 85 dB could conceivably be a problem, but notice that 85 dB doesn't even make the OSHA chart listing maximum exposure levels for up to 8 hours! Loud passages in classical/orchestral/film music will often be well above 85 dB, but they don't last long. In live music, bass drum beats from a few rows back in the audience can range from 100 to 110 dB ("fast" setting, "C" weighting), and as Paul Klipsch pointed out, to reproduce the "blood stirring" levels of a full orchestra, you will need 115 dB at your ears ..... but not for long. Later researchers, with better, peak reading, meters found a brief peak figure more like 125 dB. All of these brief peaks and longer surges occur within loud passages that may themselves average 80dB to 95dB.
• Rock, electronic, and other loud music that is more steadily loud can be more of a problem.
• The estimate of dialogue SPL if you are running a movie with very loud sound effects or music -- and you are running it pretty loudly -- is way too high. And, even if bursts of dialogue were that high, they are bursts ... not the steady roar of machines that OSHA is concerned about. Brief sounds are a concern when they are much louder than what we're talking about ... gunfire, for instance, can damage hearing. Modern movies with extremely high dynamic range and the volume set so that the loudest effects and music are very nearly overwhelming (i.e., 90 to 115 dB) will have dialogue that is about 70 to 80 dB, going higher very rarely. They master the dialogue that much lower so that they can have their big effects. Excluding screaming, an 80 dB conversation is very loud indeed (I
  measured the SPL in a crowded office, with much laughter and voice
  raising, and got about 80 dB), and dialogue turned up higher would sound
  unatural and would usually be turned down by the operator.

[Ski Bum]

Derrrickdj1, here's another link with a more complete complex answer:

http://knol.google.com/k/secrets-of-amplifier-and-speaker-power-requirements-revealed

Garyc, good points. Music is far different than industrial noise which the OSHA limits are based on.

[StephenM]

Here is some oversimplified math that might amaze you.

To make a speaker sound twice as loud, you need 9 to 10 times more watts. In other words, to be twice as loud as 40 watts, in human perception, you need almost 400 watts.

To clarify a bit, perceptually, a jump of 10dB is considered to be twice as loud, and requires 10x more power. Therefore, listening at 0dB on your receiver versus -30dB requires 1000x the power.

In a calibrated THX receiver/processor, 0dB is supposed to equate to THX Reference Level, which calls for 85dB average levels and 105dB peaks on your satellite channels, and peaks of up to 115dB on the LFE channel. -30dB will consequently call for 55dB average levels and 75dB peaks on your satellite channels, and peaks of up to 85dB on the LFE channel. All of these numbers are of course at the listening position.

As mentioned, calculating the actual power used is tricky: you may be familiar with your speaker's voltage sensitivity, 96dB at 1 meter with a 2.83 volt input. Because your speaker's impedance varies by frequency, this could equate to 1 watt (8 ohms), 2 watts (4 ohms), 0.5 watt (16 ohms), etc, depending on the frequency. Of course, the 96dB figure is a nominal specification arrived at (as is my understanding at least) by taking the average voltage sensitivity in Klipsch's anechoic chamber and adding 4dB for room gain. As such, ACTUAL power is rather difficult to determine. However, you can make some conservative guesses to try and get a ballpark figure.

For example, using the previously linked calculator, plug in the distance as normal, and instead of 96dB for the speaker sensitivity, try 90dB (3dB to account for dips down to 4 ohms, 3dB as a fudge factor). For speaker placement, choose "away from walls", and number of speakers, choose 1. Unless you happen to sit very far from your speakers, you should find that you need a fraction of a watt on your mains to produce even peaks at -30dB from reference. At 0dB, you will need a fair amount of wattage.

[derrickdj1]

This has been a very informative discussion and I would like to give thanks to everyone who participated, for the their comments and shared information. This type of discussionis is a must read for other newcomers to HT and 2 Channel Audio. This knowledge is invaluable for making upgrades and purchasing decisions on speaker, audio equipment and home theater construction. I now have a better understanding of the role of power amps, speaker selection and the limitation of a given system.

Now I understand how the RF 83 mentioned in my original post was damaged, even though it has a great power handeling capacity, RMS 250W/1200W peak. The damaged was caused by over excrusion of the drive/cone or heat. It may have been a combination of both of these factors and a expensive lesson to learn regarding power management. Here is a little clip from the above link in one of the post.

Secrets of Amplifier and Speaker Power
Requirements Revealed

But things begin to change, and rather
dramatically. Let's push the M80ti's to what we might experience from
a solo grand piano, 109 dB. We're at 96 dB with 10 watts per channel.
Let's go to 106 dB. So that requires 10 x 10, or 100 watts. Close,
but not quite there yet. Just 3 dB more. Remember, we have to double
the power for a 3-dB increase in sound level. So 100 watts becomes
200 watts. Yikes! Our receiver has only 110 watts maximum output!
We've run out of amplifier power! And what about the rock concert?
Let's lower our expectations and aim for 119 dB. Going from 109 dB
SPL, which needs 200 watts per channel, to 119 dB SPL (get out your
ear plugs) is another 10-dB jump and--you do the math--that requires
10 x 200, or 2,000 watts per channel!

[Y]

[mustang guy]

These are some of the facts the receiver and amp manufacturers don't want you to know. How many times have you been in the store looking at two receivers, and paid an extra $100 for the one that is the same except 10 more watts per channel. Funny, isn't it? The normal human cannot discernt the difference in 100 and 110 watts. It is a fraction of a decibel!

[garyrc]

So that requires 10 x 10, or 100 watts. Close,
but not quite there yet. Just 3 dB more. Remember, we have to double
the power for a 3-dB increase in sound level. So 100 watts becomes
200 watts. Yikes! Our receiver has only 110 watts maximum output!

When you do run out of power, the receiver may clip and send out tweeter destroying distortion. If you have two amps side by side, feeding two identical speakers (these probably don't exist) and measure the same very loud SPL from each set-up, the low power amp (say, 100 watts) may clip and fry your tweeters, while the high power amp (say, the McIntosh 2,000 wt per channel set-up) probably won't clip just yet, and your tweeters may survive. So there are at least two ways to destroy a speaker: 1) sending too much power through it, period, & 2) using an amp that is not powerful enough to avoid damaging clipping.

Of course, with a speaker like a Klipschorn, which when in a trihedral corner measures at least 103 dB @1 Watt @ 1 meter, it takes only 100 watts (the power limit) to produce the SPL that a typical speaker (90 dB @ 1 Watt @ 1 meter) would take more than 1,600 Watts to produce.