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Thread: How do I find out RMS for a speaker?

  1. #1
    Who am I? HiJackZX1's Avatar
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    How do I find out RMS for a speaker?

    I decided to buy speakers from a company called Volfenhag. There where a lot of mixed reviews about them and in the end I went for them. Problem is that I get the speakers and they only have peak power. How do I find out what the RMS is so I can buy the appropriate AMP for them. I tried calling the company and it didnt seem like he had any type of clue. Plus his heavy accent didnt help either. 80% of what he said, I couldnt understand. The only thing listed on the box is:

    This is for the 3 1/2" speakers
    300w Peak Per Pair
    Freq. Resp: 100Hz - 20KHz
    Sensitivity 90dB @ 1W/1M
    4 OHM Impedance

    This is for the 6 1/2" speakers
    450w Peak Per Pair
    Freq. Resp: 65 - 20kHz
    Sensitivity: 91 dB
    4 OHM Impedance

    Would it be safe to say the 6 1/2 do about 50 RMS? The small ones about 25 RMS?
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  2. #2
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    Since peak is such a relative term, and varies GREATLY company to company, there really isn't any way to find out RMS unless the manufacturer tells you so. If he didn't know what you were talking about, perhaps they're not the best company to buy audio equipment from? :/. You could always try 50WRMS, and see if it blows the speakers :-D
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  3. #3
    Who am I? HiJackZX1's Avatar
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    Here is what sonicelectronics has:

    6-1/2" 2-way Speakers

    Power Handling:
    Peak: 900 watts per pair / 450 watts each
    RMS: 300 watts per pair / 150 watts each

    3-1/2" 2-Way Car Speakers

    Power Handling:
    Peak: 300 watts
    RMS: 150 watts

    Im just wondering where they got their numbers from!
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    Variable Bitrate chris350's Avatar
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    for safety reasons... half the peak power is close to RMS power....
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  5. #5
    MySQL Error soundman98's Avatar
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    rms used to be half of the peak, so they probably just halved the peak value. now with so many companies faking the specs, that is proving to be a unreliable method..

    i think a 50w rms/channel amp would be fine..

  6. #6
    Who am I? HiJackZX1's Avatar
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    Quote Originally Posted by chris350 View Post
    for safety reasons... half the peak power is close to RMS power....
    OK, but they claim 450 watts per peak per speaker. 225 RMS doesnt sound right.

    Quote Originally Posted by soundman98 View Post
    rms used to be half of the peak, so they probably just halved the peak value. now with so many companies faking the specs, that is proving to be a unreliable method..

    i think a 50w rms/channel amp would be fine..
    You think 75 rms is pushing it?

    Also have another question. Not sure if you know, but my setup uses a soundcard for music etc. Then there is a second soundcard only for phone. The two small speakers are going to be center, but I would also like to use those same speakers for the phone. Is that possible and or wise? If not, I may buy another speaker then.
    Last edited by HiJackZX1; 11-30-2011 at 10:53 PM.
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  7. #7
    Raw Wave
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    It's 450W peak per PAIR, hence 225W peak each.

    Using traditional music peak, that means 112.5W RMS.

    Using a common bullsh "peak vs rms" of 3, 225/3 = 75W RMS.

    I'd assume 75W RMS as a max, and if there are 75W RMS speakers out there, that's probably it (unless ~112.5W is).


    But maybe it's a 1:9 rms to peak, hence 25W RMS each.

  8. #8
    Who am I? HiJackZX1's Avatar
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    Nothing seems to be easy when it comes to my car pc, lol. Once again Soundman98 and OldSpark, your help is greatly appreciated. You also Chris350. Thanx!
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  9. #9
    Who am I? HiJackZX1's Avatar
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    How do I determine what AMP to go for? It seems different brands list all their info different. I'm trying to get a decent amp that is $100 and under. I want one that hit 66 - 75 rms per channel. Any recommendations?
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  10. #10
    Constant Bitrate
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    Watt RMS is a nonsense term. Still everyone keeps using it. The manufacturers keep using it because the man on the street is used to it. A much better term is continuous power. It makes not the slightest sense to square power in Watt, average it and then compute the square root. Volt RMS is another story. Volt RMS squared divided by resistance gives average power, which is useful.

    When a vendor states peak power, they certainly don't mean by it that a sinusoidal voltage wave will twice per period cause a momentary power that is twice the average. What they mean instead is that with dynamic music, for a short but unspecified time, the speaker can withstand a power much higher than the continuous power. Peak power can be specified at the whims of whatever who writes the marketing propaganda. It's essentially meaningless.

    A sub 100 dollar amp will not provide the specified power I guarantee it. Look at the fuse and multiply it by 8, that is the power you may hope to get out of it at 2 Ohms load. At 4 Ohms, you may get two thirds of that.

    Need I remind that the power delivered to the speakers depends on the listening volume and on the music recording.

    Therefore, it makes not the slightest sense to trying to match the phony peak power rating of a speaker to the just as phony Watt RMS rating of a sub 100 dollar amp.

    I have expensive amp and speakers, totaling about nearly 4000 dollars. I've never even begun to try matching amp and speaker power. Instead, I adjust the subwoofer level and the front system to match, so that when my girlfriend maxes out the volume, nothing clips and nothing gets fried.
    Last edited by JuniorGeezer; 12-01-2011 at 04:53 PM.

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