I am a little confused about the RMS rating of a speaker. Let me explain my confusion by giving this example. Say, I have Polk MOMO 6900 3 way coaxial speakers rated at 100 RMS. Now when I am selecting a two channel amp to power these speakers, should I buy an amp that is rated 50Wx2 RMS or 100Wx2 RMS?
Thanks
100Wx2 - The speakers are rated individually (each speaker handles 100W) and the amp is rated by individual channels.
The exceptions to this are:
Subwoofers - Typically rated for the whole sub, but sometimes by the voice coil (i.e. 400W RMS DVC, each VC handles 200W RMS)
Component speakers - Rating applies to both speakers together (100W components take a 100W amp for both the woofer and tweeter).
Aftermarket tweeters - (35W tweeters normally mean 35W to both them and the woofer in parallel with them).
Hope This Helps!!!!!
2002 Ford Focus Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs
Hi Tiger - thank you so much.
I have following follow up question
1. When you say that for component speakers rating apply to both speakers together, you are talking only about the woofer and the tweeter. If the components are rated at 100 RMS I will still need a two channle amp that can produce 100W per channel? Am I correct?
2. How much RMS has to do with the frequency at which the speaker is tuned. For example, my components may have a rating of 100 RMS, but if I have tuned them to be playing at 200 Hz and above, will they still need that power. I am asking this because I have my Polk Momo 650 components and a P450.2 RF amp . I had to reduce the gain to less than 25% otherwise my speakers will start jarring (I mean they will not produce clean sound). Any idea why>
Thanks again. I really appreciate your help.
akbaree:1. When you say that for component speakers rating apply to both speakers together, you are talking only about the woofer and the tweeter. If the components are rated at 100 RMS I will still need a two channle amp that can produce 100W per channel? Am I correct?
Correct - 100W components should mean the tweeter and woofer as a system take 100W and you need a two channel 100Wx2 amp to power a pair of them.
Carolinasp3 is a lot better at this, but a couple of things I can think of:
1) RF typically underrates their amplifiers, so while the specs are 100Wx2, the actual amp could well be putting out 150 or 175Wx2.
2) Neither impedance nor wattage are totally constant with frequency, so as you go to higher frequency, perhaps the wattage requirements are less.
If it sounds fine at 25% gain, I wouldn't worry about it, but maybe someone else can explain it more thoroughly.
TigerHeli: Carolinasp3 is a lot better at this, but a couple of things I can think of: 2) Neither impedance nor wattage are totally constant with frequency, so as you go to higher frequency, perhaps the wattage requirements are less. If it sounds fine at 25% gain, I wouldn't worry about it, but maybe someone else can explain it more thoroughly.
Thanks Tiger.
I will wait for Carolinasp3's response on this though.
Tiger is absolutely correct. Higher frequencies are produced by a lighter, faster moving cone, which ideally would utilize an amp with a high control factor, but doesn't require large quantities of power. There are exceptions to this as some speakers are deliberately designed to be very tight for better control and accuracy with a high end amp. These are not very efficient and require more power. Bass frequencies, on the other hand, require gobs of power to produce with any accuracy, because they require a larger cone movement to produce (a longer "throw") as well as the cone is bigger, thus heavier. The rule of thumb I was taught was to plan on a subwoofer amp that is ten times as powerful as your main amp if you want tight bass that will still go loud. Keeping this in mind, if you are not producing low frequencies that will use the extra power, you are going to be pushing more power than is required by the speaker, so yes, you could be overdriving the speakers even though the specs say you shouldn't be.
As for the question about RF products, I love their amps, and have two of the 25 to Life amps in my own vehicle. I can't say anything with regards to their subs, because I haven't heard one in over ten years. Their rep used to be that they had decent if unremarkable sound quality but could go low and loud. From what I have seen on other forums that appears to still be the case. You might want to check RF's site for size recommendations: remember, smaller end of the chart equals tighter bass with less volume and not quite as much extreme lower end. This is going to sound crazy, but wrap a brick in plastic wrap to control the dust and set it in the box. By doing this, you are taking up interior space, effectively making the box a little smaller. If it sounds tighter, add another one. At some point you will no longer get any improvement. Take the last brick out and test it again. DO NOT DRIVE THE CAR. This is only an experiment. If it works, then glue and screw some pieces of MDF inside the box to do the same thing without worrying about bashing the back of your sub with flying bricks.
akbaree:Your explanation is so lucid. Thanks so much.
Agreed, Carolina does a really good job of coming up with word pictures to explain this!!!!
TigerHeli:It's better than "pedantic" which I was referred to as on another forum, but it fit, so I couldn't complain too much.
I don't know, I think of you as didactic, rather than pedantic. Hey, look at all that glass in front of me: I'm gonna just drop this rock on the floor... (walks away, whistling, looking around innocently)
I wish I could find the pedantic forum thread, but I can't remember where it was anymore. It was one of the forums I was not especially active on, and I made a reply similar to what I'll say on here sometimes when someone says "So I should just set the amp for a 2-ohm load" and I'll reply "You should wire the subs so that they present a 2-ohm load to the amp, yes" (Not meaning to pick on any one member with that comment, I've said similar things to many members on here). If I remember correctly the thread went downhill from there, I replied with "You can argue semantics all you want" and the other member came back with "You can be as pedantic as you want", which I thought was applicable.
For those who don't want to google Dictionary.com:
Pedantic:
adj. Characterized by a narrow, often ostentatious concern for book learning and formal rules: a pedantic attention to details.
Synonyms: These adjectives mean marked by a narrow, often tiresome focus on or display of learning and especially its trivial aspects: a pedantic writing style; an academic insistence on precision; a bookish vocabulary; donnish refinement of speech; scholastic and excessively subtle reasoning.
Didactic (another word I had to look up):
carolinasp3:You're welcome. "Lucid"? I know the word, but you just don't see an enhanced vocabulary in forums for the general public very often. Bravo!
Carolina, I may just have below average vocabulary. Thanks for the compliment though.