# how can a 1W speaker produce 105dB?

Discussion in 'General Electronics Chat' started by strantor, Aug 13, 2012.

1. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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My uncle was showing me his new vintage Klipsch speakers which he says produce 105dB with only one watt of power. This sounds completely out to lunch to me, as my audio knowledge is limited to rusty peewee league car audio. I'm used to seeing a price tag of several hundred watts for that much sound. I looked it up and found the newer version of the same speaker here. Massive things.

He says it's because the speakers are 'horn loaded', meaning the sound is bounced around inside a horn cone before coming out, which amplifies it; passive amplification instead of power amplification. Sounds like overunity to me. I see cone shapes common in megaphones, victrolas, etc. but I thought the purpose was to directionalize the sound, not amplify it. I guess I was wrong about that. How can the horn shape amplify sound? Is it dependent on the size of the horn? If I made a horn the size of a jumbo jet an put a headphone earpiece in the little end, could I get earth shaking sound out of it?

2. ### takao21203 Distinguished Member

Apr 28, 2012
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I guess the 105dB is limited to a relatively small spot, and high frequency as well.

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3. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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they were pretty loud, throughout the room, and at all frequencies. I am a believer in their performance, but I have trouble believing that they only use one watt to accomplish it.

EDIT:
I went back and looked at the detailed specs in the link and I see this:
So you were right, at a certain spot (1m) and probably at a certain frequency, it can produce 105dB @ 1W. But any other time, it is probably running much higher than 1W (up to 400W). I assume it's a high frequency it can do @ 1W @ 105dB.

I wonder if I should tell my uncle, or just let him be happy with his speakers. I'm 90% sure he believes that they don't ever go above 1W, or at least he intentionally described it wrong to make it sound more impressive.

Last edited: Aug 13, 2012
4. ### ramancini8 Member

Jul 18, 2012
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Sometimes ignorance is bliss until he tries to impress an audiophile at a party and gets embarrased.

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5. ### #12 Expert

Nov 30, 2010
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Lacking the fervor of an audiophile, I will try to explain this within the laws of physics.

The purpose of the horn, or any other good cabinet design, is to couple the speaker to the air in the room. The cabinet doesn't amplify except that a bass reflex design can invert the backside (of the speaker) wave in the lowest frequencies and present that to the audience, too. My Cerwin Vega H15's can do 103 db with the first watt and the response is flat within 3 db from somewhere to somewhere else, and those somewhere's contain most or all of the audio frequencies.

Another way to put it is, I have to stuff towels under the closet door to stop it from rattling if I turn my 50 watt per channel amplifier up to the highest clean power level.

ps, 1 watt at 1 meter is the standard for measuring speakers.

Last edited: Aug 13, 2012
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6. ### crutschow Expert

Mar 14, 2008
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It likely uses a few watts for a good room volume.

Efficient speakers were needed in the old tube days when a 25W amplifier was high power. Understand that modern speakers are very inefficient (≈1%) at converting electrical energy to sound. That's the penalty for generating large sound levels from relatively small speakers. Horn type speakers are significantly more efficient which is why they are often used in theater applications. Here's a discussion of that.

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7. ### bretm Member

Feb 6, 2012
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Some of the testing methodology seems pretty weak for some claims that I've read. A common technique seems to be to use a 2.83V signal (square root of 8) which would be 1W for an 8ohm load, but not all speakers are 8 ohms and even 8 ohm speakers have impedence that varies by frequency.

8. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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Ah I see. I didn't realize that the speakers I'm used to are so grossly inefficient. 1% efficiency sucks, and the article said it could be as low as .5%. Considering the subwoofer enclosures I was building were not based on any real science or understanding of how sound works, it's quite possible that I was achieving even less than that. Which explains my preconceived notion that 100+ dB costs hundreds of watts. If his speakers are 25% efficient, that's probably 50X more efficient than mine, or more.

Thanks guys

9. ### #12 Expert

Nov 30, 2010
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As usual, you can read all kinds of misinformation on the internet (bret). The fact that idiots and nutcases abound does not preclude some people from doing good science, like having the sense to change the amplitude for 4 ohm or 16 ohm speakers.

Geeze guys, educate yourselves, and I don't mean by looking up "oxygen free copper" speaker wire. There are valid testing laboratories and standardized specifications, and there have been for decades. Look up the Thiele-Heil equasions. Read books like, Sound System Engineering by Don and Carolyn Davis. Even Radio Shack had some valid books like, Building Speaker Enclosures by David Weems and Speaker Enclosures by Badmaieff and Davis.

When you get done with those you will understand that every loudness specification must be at some named distance. If sound didn't diminish with distance, you wouldn't need a telephone to talk to your grandmother in Wisconsin.

and while I'm at it, Radio Shack used to sell speakers that boasted 78db for the first watt. Compare that to a Cerwin Vega at 103 db or a Klipsch Horn at 105 db and you'll see why Crown makes bridgable 1000 watt amplifiers.

Honorable mention: Altec-Lansing "Voice of the Theater" folded horns.
and Bose thinks they can do the same with a 4 inch speaker and a convoluted tube. I'd rather stick ice picks in my ears!

Last edited: Aug 13, 2012
10. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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you mean to tell me that bose isn't the best thing since toilet paper? I have had my worldly perception rocked twice in this thread!

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11. ### #12 Expert

Nov 30, 2010
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I ALWAYS click a "Thanks" for an LOL!

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12. ### strantor Thread Starter AAC Fanatic!

Oct 3, 2010
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I'm not a big audiophile or even close. I dabbled in car audio in high school and thought I was badass. I wasn't. Now I don't have much interest. I am content enough with the sound that comes out of my 25% blown, dry-rotted dash speakers in my car, if that tells you anything. My taste in sound is much like my taste in food, alcohol, cigars, cars, and clothes. The cheaper the better. I have no class.

My uncle on the other hand gets a big stiffy over these vintage audio things. He won't have anything but a tube amp, turntable, and vintage speakers. He has them positioned strategically in the room and sits a specific spot to listen to them. He balks at the quality of digital music. He had me sit in his chair and listen to his music and I could see a look in his eye which reminded me of when my daughter brings me her latest craft paper creation. I pretended to be uber impressed but in truth it didn't sound any different (to me) than the sound that comes out of my 20y/o TV.

I was just interested in the technical aspect of those speakers, and I am very impressed now that I know the truth.

Thank you for enlightening me.

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13. ### #12 Expert

Nov 30, 2010
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Some people have an ear and some don't. When I heard Ventura Highway on the original 24 track master tape, the hair on the back of my neck stood up. After spending years working with bands in Los Angeles, I think MP3's are pathetic. So much detail is missing, and I'm not the best! I have a friend that can tell you what year a certain guitar was made because he can tell the difference in the sound of maple wood and ash wood. When I want an audio design tested, I send it to him.

If you have, "The Ear" and you've been there in person, a low bit-rate MP3 is less impressive than a cat in heat howling on the back fence. At least the cat has harmonics.

Last edited: Aug 14, 2012
14. ### bountyhunter Well-Known Member

Sep 7, 2009
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One W of continuous average power will make a relatively efficient speaker produce a very loud level. When playing music, peak power levels are much higher.

15. ### bountyhunter Well-Known Member

Sep 7, 2009
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Don't get freaked out about power. It's a game they use to sell hardware. many quality tube amps had power outputs of 50W or less. The point is that playing music with an average power level of 1W (will actually be pretty loud) but will probably have power peaks up to 20W or a more. Very few stereos need as much power as they have on tap: my brother had Infinity Column speakers circa 1980 which were absolutely huge (like six woofers stacked and separate mid/tweeter set) and he liked to play classical music at "live" volume levels. I hooked a power meter to his amp and he rarely went above 100W peak but did clip a 150W level one time. very few typical stereos get near that.

16. ### bountyhunter Well-Known Member

Sep 7, 2009
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To make it even more confusing:

they could be rated in RMS signal power or ACOUSTIC POWER which is an entirely different way to spec it.

17. ### t_n_k AAC Fanatic!

Mar 6, 2009
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Thanks for the interesting thread.

For my own interest I thought I would try to make some physical sense of the numbers.

Speaker sensitivity seems to be expressed as dB SPL [Sound Power Level] where the reference level is 20 micro Pascal [rms] at 1kHz. A speaker test would apparently involve injecting pink noise at 1 W electrical into the speaker in an anechoic chamber and measuring the sound pressure level in Pa [rms] a distance of 1 meter from the speaker.

As a performance index, the sensitivity would be found from

$20log{$$\frac{SPL[P_a]}{20E-6}$$}$

So if the speaker has a sensitivity of 105dB the measured SPL would be 3.557Pa [rms]. This would also correspond to a power density of 0.0316 Watts per square meter at the 1 meter distance in the chamber test. It seems 20uPa is the same as 10^-12 W/m^2.

Have I got this right?

18. ### vk6zgo Active Member

Jul 21, 2012
677
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But then aqain,there is no such thing as RMS power.

You can have RMS voltage,& RMS current,but not RMS power.

RMS voltage is 0.7071*Pk

RMS current is 0.7071 *Pk.

P=VI,but
0.7071*0.7071=0.5Pk watts.

19. ### Audioguru New Member

Dec 20, 2007
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Look up Bose Bashing in Google where they talk about the very expensive cheap little 4" speaker as a sub-woofer but producing no deep bass.
Also their very expensive cheap little tweeters don't tweet high frequencies.

20. ### #12 Expert

Nov 30, 2010
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(Agreeing with bountyhunter) Most music contains peaks of about 10x the average level. When your stereo is making music that is undistorted, you can usually assume you are running at about a tenth of its power rating...like, in the 5% to 20% range.

for vk6...The usual method is measure the RMS voltage and use the speakers' rated impedance to calculate RMS watts.

Just a note on Fender brand musical instrument amplifiers. The last time I figured one out, they were using 3 stacked lies to arrive at their power rating. Still, (4) 6L6 tubes driving (4) 12 inch speakers produces some pretty good results. It just isn't what the label says it is. (Other Mfg's probably use the same kind of math.)