Trying to figure out right amp to speaker watts and ohms...

Discussion in 'Amp Central Station' started by Mahinavai, Dec 7, 2018.

  1. Mahinavai

    Mahinavai NEW MEMBER!

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    I need help with this... I'm looking at an amp that is 135 watts with 6 ohms resistance. The speakers have a nominal resistance of 4-8 ohms and can handle up to 140 watts (rms) of power. I've calculated that it is 202 watts at 4 ohms and 101 watts at 8 ohms, but I'm not sure what that means. Is the amp ok for the speakers or will it blow them out? Thanks if you can help with this. Yes, newbie here...
     
  2. Phrygian77

    Phrygian77 Tele-Afflicted

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    Your post is lacking information. What is the amp? What are the speakers? Your speakers should be about twice the RMS power level of the amp if you're going to crank/overdrive the amp regularly. At 135 watts, I'm guessing not, so you can probably get away with a lesser power rating on the speakers, closer to the RMS rating.
     
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  3. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    Yeah, you said the speakers have a resistance of 4-8 ohms. Usually resistance is stated as a single number, not a range; either 4 ohms or 8 ohms is typical. A hundred watts is a lot, for most speakers. Some amps are rated by peak power, some are rated by RMS power, which is somewhere around 70% of peak power. I'm just guessing; it sounds like this is a 100 WRMS amp. The make and model of the amp and speakers would help answer your question.

    If the speakers are rated 140 W RMS, that's around 200 watts peak. You said speakers. Are there 2 of them? It sounds like 2 140WRMS speakers could handle this amp, but a single speaker may blow if you crank it.

    It would also be loud enough to peel paint.
     
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  4. soulman969

    soulman969 Telefied Ad Free Member

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    In your analysis also include that the power output is divided by the number of speakers.

    If an amp puts out 100w into 2 speakers each will see 50w and if into 4 speakers each will see 25w. So an amp producing 135w will have roughly 70w going to each speaker. Therefore speakers that can handle 140w peak should be fine.
     
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  5. Tonetele

    Tonetele Poster Extraordinaire

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    The "old" rule of thumb was to double the RMS rating and then some.
    MusicMan amps. of the late 70s were 65/130 watts ( switchable)- I'd check out the specks on the speakers they used- they were great amps.
     
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  6. robt57

    robt57 Telefied Ad Free Member

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  7. Mahinavai

    Mahinavai NEW MEMBER!

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    I'm sorry, I went through the replies--and I'm so glad you took the time to write--but I understand about half of it and yes, I left out important information because I'm really over my head with this. It is an audio system for a small planetarium that my father is putting up. I'm trying to help him with it, but I really don't know enough... The speakers are Pure Acoustics Slim Dream series, basically used for home cinema; there's one active subwoofer, and then a couple of passive tweeters and woofers. The tech specs actually say nominal range 4-8 ohms, so yeah, weird that it's not a specific number. The woofers can handle 170 watt power, while the tweeters can handle 130. All have a 89dB sensitivity. The amp is actually part of a receiver: Onkyo TX-SR373 with a 210 watt operational capacity and 135 watt amp output power. I live in Chile and that's a pretty good medium range amp/receiver that we can afford, but I'm not sure it would work with the speakers...
     

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    Last edited: Dec 7, 2018
  8. Blue Bill

    Blue Bill Poster Extraordinaire Ad Free Member

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    It looks like it will work fine. I would say, avoid cranking it all the way up. 2/3 or maybe 3/4 volume is as hard as I would push it. Turning an amp like that past 3/4 can result in clipping distortion, which can damage speakers, even if it's less than the speaker's rated power.

    Speakers for a guitar amp need to be rated at double the amp output because electric guitars use all kinds of distortion as part of the sound, also various squeals, pops, and buzz, which are tough on a speaker. If you are using the system as a PA, with a microphone, the speakers maybe in danger; with recorded music playback, it should be OK.
     
    Last edited: Dec 7, 2018
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