How much RMS do I need for the RB-51 Bookshelf System?

[slammy77]

The RC-52 can handle 125 watts RMS. The RB51s and RS42s can handle 75 watts RMS. I have an old Sony 5.1 receiver that's 100 watts per channel. Will I be okay downstepping to a 75 watts per channel Onkyo or Denon? I don't want to need an amp.

[ricktate]

Whats wrong with the sony???.Rick

[slammy77]

I don't have a problem with Sony. It's an old receiver and I'm looking to get a new HDMI receiver to modernize my HT a bit. At first I was looking for receivers that are at least 100 watts per channel, but I'm tempted to go with a 75 watt per channel receiver if that's enough juice for my new bookshelf speaker system.

[WMcD]

The power specifications on the amp end or the speaker end are not really as exact as people are invited to believe.

For the most part, the amp and the speaker is going to be dealing with 10 watts on peaks in normal home settings and reasonable volume levels.

There is a lot more behind what I'm saying and I cring at generalizations. However, it is not a matter that amp and speaker ratings have to match like feet and shoe sizes. Note, please, that the amp manufacturers don't say you have to have speakers of X power and the speaker manufacturers don't say you have to have an amp of X power. You'd think that such is implied, but it really is not true.

In my view, the peak ratings are conditions which are thrashing both the amps and speakers to the edge of their acceptable limits. So they are near train wrecks in the making. If you are getting even close to those, you're in big trouble, and need to take a good look at the system as a whole. But again, with reasonable use, you're not.

The good news is that the smaller Sony will do just fine.

Gil

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[DrWho]

The difference in acoustic output between 75W and 100W is 1.2dB. Classically, 1dB is considered the smallest perceivable difference, and 6dB is perceived as a doubling of loudness.

Like Gil said....the power ratings are just the maximum power ratings. Most of the time, you're probably going to find yourself only using about 1W of power.

All that to say, you will be just fine with a 75W receiver. Instead of looking at the power ratings for the receivers, I would try narrowing them down by the feature set you're looking for. You might try checking out Denon, Harman Kardon, and Yamaha since they all have many models to chosoe from and generally sound good with Klipsch products.

[WMcD]

I'm in agreement with Dr. Who, as usual. Except that I recall that 10 dB is doubling of perceived loudness above 40 phons. 40 phons is fairly quiet.

There are a lot of issues about power handling and ratings. The most fundamental is that music has many peaks. This can be okay with speakers the sense of power handling before distruction because the little wires in the voice coil can take short term peaks before burning out. Distortion is a separate issue, though.

I see that the RB-51s have a rating of 75 watts. So you might feel better about the Sony based on that. Also, its rating of 92 dB at one watt is fairly, ummm, low as Klipsch speakers go. But they will serve you well.

Again, the amp power ratings really don't tell you much about the power output you are typically listening to. The 10 dB for perceived doubling of level lead to some interesting math. Those 10 dB require 10 times more amp power. in each step. If you are at 100 watts, you need 1000 watts to get it twice as loud. Of course that is a big danger to speakers.

There is some good news. Consider, just how much power is being produced as you turn up the volume knob to make things louder.

Probably you're into much lower numbers even though they have the same progression. Speaker efficency has a lot to do with the ultimate result but still, let's look at some numbers

0.001 watts (our start)

0.010 watts (twice as loud)

0.100 watts (three times as loud)

1.00 watts (four times as loud) (this is 92 dB with your speaker which is very loud).

and 10.00 watts. (five times as loud- which is pretty dang loud from where we started, again depending on the efficency rating of the speaker - but even 92 dB output at one watt is not half bad in the world of small speakers).

The major point is that generally speaking, your amp is generally working at well below max rating. As Dr. Who points out the 25 extra watts at the top doesn't get you much more and you shouldn't even get there unless there is a wild party.

Gil

[WMcD]

I looked at W. Marshall Leach's book on this. And maybe I'm a little incorrect.

He does report that above 40 phons, it does take 10 times power for perceived doubling of loudness.

What is not quite clear is whether we should say that the additional doubling of loudness is 2, to 4 to 8 for every 10, 100, 1000 of power.

That might be the case instead of my 1,2,3 progression.

My main point is that at low levels starting at 1 milliwatt or less, it is not too difficult for the amp to keep up with the logarithmic function of our ears.

There is also a cautionary tale, built in. Our logarithmic ears do very well until we flirt with man made sound levels which do not occur in nature. It is my thought that OSHA levels said to safe are not really that safe. Also, in the big city, we have el-trains, subway trains, sirenes on fire trucks, rock concerts, etc. which are more harmful than is appreciated.

Gil

[Ryan6796]

Regarding your new reciever choice, You should definitly consider getting a reciever with HDMI 1.3 which will decode Dolby TrueHD and DTS-HD Master. I'm not a big fan of Onkyo, but the Pioneer Elite VSX-92THX, Denon AVR-2808 and AVR-3808, as well as the new Yamaha RX-V1800BL which as four HDMI inputs are all great choices, and all have over 100 watts per channel. Ive heard all of them with the RB-51's and RS42's and they all sound great. The Pioneer Elite and Yamaha both seem to push out a little more power. The VSX-92 is my top choice