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Speaker watts input vs. amp output power ratings

Discussion in 'Home Theater Projects' started by Dan Miller, Feb 26, 2004.

  1. Dan Miller

    Dan Miller Extra

    Feb 26, 2004
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    I am considering building a 5.1 speaker system. My idea is to use the Audax AT170MO which is a 6 1/2" speaker. The input rating shows 50 watts RMS / 70 w max. This speaker will be use in conjunction with the Audax tweeter AW025M1 which can take about 70 watts. I will mount one of each, in a sealed 1 cu. ft. box with some sort of simple crossover, somewhere around 3000hz. Obviously I will run my center channel in a vertical rather the horizontal stance.

    Here is my confusion. The majority of A/V receivers that I am looking at show output ratings of around 75 - 90 watts. The AT170MO shows as mentioned above. I do not worry too much about the tweeter surviving but the rating of the 6 1/2" makes me ask ..... can my speakers take average HT listen loads as put out by 75 - 90 advertised watts per channel amps?

    I am an oldie and understand vacuum tube amps but solid state ( and the cloudy printed representations of specifications, as published by manufacturers ) sort of make me wonder.

    I read many postings, in forums like this, that mention lots of receivers are much over rated, by the makers, when it comes to output audio power. Also, these manufactures must all be using their own made up variable scale of said numbers. The examples I read show amps advertised at 90 watts output actually delivering about 40 - 45 or so.

    Any fudge factor numbers you can toss back my way would help.

    By the way, I think I have a good lock on my subwoofer. It will be a Titanic MK 2, with a PE 250w amp, in a sealed 54 litre box.

    How does my overall setup sound on paper to you guys? I just want to make a better than store bought average sound system for my HT listening. I have just recently started to look into HT and see a lot of premade, overpriced, poorly performing garbage out there.


    Dan Miller
  2. AndersP

    AndersP Stunt Coordinator

    May 17, 2002
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    I wouldn´t be to concerned about the input power ratings on the 6 1/2".

    I agree on most of your conclusions regarding the HT market. To me, HiFi buffs are generally more competent in science of sound than the typical HT afficionado. We are also older.[​IMG] Compared to serious HiFi there seem to be a considerable inflation in the output ratings of receivers. The measurements are typically taken one channel driven and "dynamic" ( a couple of milliseconds ).

    On the other hand you get a lot of amplification per buck. These products are not expensive. I think that for a HT receiver to be comparable with a stereo integrated the receiver should be twice the cost of the integrated as every HT receiver contains at least 5 power amps, sometimes more.

    My experience says that modern dynamic drivers can withstand obscene amounts of clean power and you can hear the typical compression when you are driving them to hard. I had a pair of JBL L40,s in the 80,s driving them with a PA amp rated 350W @ 8 Ohms, with no problems taking the amp into "red". You´d probably be better off with an amp twice the size/power of what you mentioned.

    Also; In a HT setup you will define those speakers as "small", meaning that they will typically be rolled off with a HP filter at 80 Hz, leaving the two basement octaves to the sub. The process is called "bass management" in the HT world and is integrated in every HT receiver/processor/preamp.

    One interesting setup for you could be a HT processor/preamp hooked up to a bunch of tube power amps keeping the subwoofer amp solid state. That would be a pretty cool rig in my book.[​IMG]

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