# PCB Heaven

## General Category => Analog discussion => Topic started by: colombo on September 15, 2008, 22:10:08 PM

Title: Watt and RMS of speaker
Post by: colombo on September 15, 2008, 22:10:08 PM
Am i really bombing your forum with questions  ::) ::) ::)

As i told you, i like it because of the range you cover. And looking around, i always come to a new question in my mind that was bothering me. And i happen to be a very-bothered boy  ;D

So, here i go. I had a discussion once about my car speakers. I was talking about the watt that they provide, and the other dude insist that watt have nothing to do with output power, only RMS does. First of all, what is this damn RMS? He did not know to tell me but insist that my 250 watt speakers provide 150 RMS. I could not make any sense. Maybe not you.

Title: Re: Watt and RMS of speaker
Post by: Johnny2Bad on October 16, 2010, 16:39:54 PM
This is an old post, but it's a common enough question that I will try to answer for the benefit of others who may search the topic.

" ... I had a discussion once about my car speakers. I was talking about the watt that they provide, and the other dude insist that watt have nothing to do with output power, only RMS does. First of all, what is this damn RMS? He did not know to tell me but insist that my 250 watt speakers provide 150 RMS. ..."

These are car speakers. Good, that is helpful to provide the answer.

" ... watt have nothing to do with output power, only RMS does ..."

Neither is correct, really.
First of all, "RMS" is a reference to how the value "Watts" is specified. So, you can have "Watts RMS" or "Watts Peak" or "Watts Peak to Peak" (as a few examples).
They are all mathematically related, so if you know the value of one, you can calculate the other two.
The relationship is thus:
RMS = .707 x Peak; and Peak is 1/2 Peak to Peak.
As you can see, without the full specification, the value is not meaningful ... is it 70 Watts RMS, 100 Watts Peak, or 200 Watts Peak to Peak? These are all exactly the same electrically, but represented differently.
Since your speakers do not specify which specification is used, it's essentially meaningless. You may as well ignore it, for all practical purposes.