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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
    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
    "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
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    • #3
      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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      • #4
        for safety reasons... half the peak power is close to RMS power....
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        • #5
          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..
          My OLD 2001 Mitsubishi Eclipse GT:
          "The Project That Never Ended, until it did"


          next project? subaru brz
          carpc undecided

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          • #6
            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.

            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, 10:53 PM.
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            • #7
              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.

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              • #8
                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
                  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?
                  Nirwana Project, the Android/Win 7 hybrid system!

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                  • #10
                    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, 04:53 PM.

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                    • #11
                      Well I am not in the mood to take my time with audio. I want to do it cheaply and fast. Ive spent so much on the PC system itself, that I just want to get audio done.
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                      • #12
                        Fair enough, as an example list of amps sorted by price see:
                        http://www.onlinecarstereo.com/produ...&ShowAll=True&

                        From this list, I'd avoid anything having "2000 W" printed in bold print on the enclosure. The first amp that I would consider would be the JBL GT5-A604, it's one of the first ones specifying power in Watt RMS. Ironically, having a Watt RMS rating seems to be a certain criterion for quality even though it's a misnomer.

                        As for the speakers, you seem to have yours, but the next guy could do a lot worse than to conduct a comparative listen, preferably with a few known music tracks, in the nearest store's demo wall.
                        Last edited by JuniorGeezer; 12-01-2011, 09:36 PM.

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                        • #13
                          hijack, in reference to getting the dash speakers to do more then one thing-- the easiest thing to try is to use a rca y-adapter, and try to feed the amp with both of the required signals. it doesn't always work, sometimes adding some odd noises to the audio, but sometimes does.

                          the other option is a switch/relay that would allow you to select which audio source is playing through those speakers-- not automatic, and if one is active the other can't be heard..

                          Originally posted by JuniorGeezer View Post
                          From this list, I'd avoid anything having "2000 W" printed in bold print on the enclosure. The first amp that I would consider would be the JBL GT5-A604, it's one of the first ones specifying power in Watt RMS. Ironically, having a Watt RMSrating seems to be a certain criterion for quality even though it's a misnomer.
                          there was some discussion about this in a recent thread about the dwindling amount of optical-input car audio amps on the market-- the end concept that was guessed is that even though the consumer electronics industry is getting flooded with new tech all the time, car audio is not getting much of the new tech, partly because of the lack of education of the car audio shops(i always make a point to tell them i run full active audio processing with a carpc just to watch their eyes glaze over), but it was also brought up that if car audio was to go past the analog-realm and use things like optical cables, that things like ground loop isolators would no longer have a market, so the makers don't want to shoot themselves in the foot..


                          so basically, stick to name-brand gear, and it should be alright.
                          My OLD 2001 Mitsubishi Eclipse GT:
                          "The Project That Never Ended, until it did"


                          next project? subaru brz
                          carpc undecided

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                          • #14
                            Just for grins, I had a peek into the manual of that amp JBL GT5-A604. It's fused for 40 A, multiply by 8 and you get predicted 320 Watts, that's 4 x 80 Watt at 2 Ohms. And the specs of the thing match exactly, 4x 80 W. Man, I'm good :-).

                            But if the original poster wants a digital in amp, I hadn't noticed that up until now.
                            Last edited by JuniorGeezer; 12-01-2011, 10:43 PM.

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                            • #15
                              no, he doesn't, that was just in reference to your remarks about the reliability of amp-manufactures wattage ratings.
                              My OLD 2001 Mitsubishi Eclipse GT:
                              "The Project That Never Ended, until it did"


                              next project? subaru brz
                              carpc undecided

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