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Old 22nd February 2008, 12:36 PM   #1
Flyin11 is offline Flyin11  United States
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Default Subwoofer RMS ratings?

I have a quick question as I'm kind of confused on what you look for in RMS ratings when you match up a amp to the sub...They say you are suppose to try match the RMS wattage of the amp to the RMS wattage of the sub(s)....So let's say that a site shows the sub as 220w RMS and that's all it says...Does this mean that's 220w RMS minimum power handling that it can handle and you need a amp that puts out atleast 220w or does this mean max RMS power and you would need a amp that rates no more than 220w?

I get confused on some of the ratings on certain sites when they just say one wattage spec....
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Old 22nd February 2008, 01:06 PM   #2
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It usually refers to the thermal capacity of the voicecoil, so what it will take before it overheats and breaks. However there more factors to consider that actually influence how much power a sub will take, the box design is important.

Don't get too hung up on power ratings. You might only need a 100W amp in the right box. And it's not dangerous par se to have more amp power than you need.
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Old 22nd February 2008, 02:45 PM   #3
Flyin11 is offline Flyin11  United States
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Yeah...I understand all that but the question still remains. I just see a sub that's rated for like 400rms but I don't know if that's a minimu rating or a maximum rating. Like on Crutchfield they will say one will be rated like 50-200rms but then you see a apage on Ebay or somewhere and they just say 350rms or something. Not sure what that rating means...
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Old 22nd February 2008, 05:21 PM   #4
jol50 is offline jol50  United States
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Default I try to hit some points for you

If it says 50-200rms then 200 should be the max and it should work ok on 50 up to 200 amp. Ratings other than RMS are really b* and usually just double RMS, though some amps do not double RMS for peak output. If a sub says 200RMS that should be 200RMS max, should not use over a 200wrms amp....however a larger amp can play cleaner and maybe have more control depending on quality of it, so that is why it can be better to use a larger amp (often done in SQ setups). Then again, if you max out the larger amp likely it will blow the sub at some point but it really depends on use. If you play it really loud it can blow, if you play bass tracks that max out the sub system it will put more stress on it. If you play loud for extended time it will get the VC hotter and may eventually blow it when you are exceeding or on edge of ratings. Note that clipping any amp might cause something like double the RMS to be put into the sub as explained on Perry's site.

The enclosure has a lot to do with what sub will handle. A sealed box supports the cone more so it does not hit xmax so you can usually run max rated power, or thermal rating (the rating you see on it). If you use a ported box sub it will get out of control below port frequency, you need a subsonic if you lay the power to it. IB install (free air) has no support from a box, so often you figure half the rated wattage as max...your 200wrms sub will take 100wrms before it hits xmax and runs out of physical travel. That is guess, you would have to inspect them in use to know exactly. A large ported box might hit physical max before thermal also.

Another issue is efficiency, the SPL db. Often a higher power sub has a lower efficiency because the cone/VC wire/etc is bigger and does not work as well. Think of a light econo car and a heavy truck. Truck takes more power/gas to go 60mph and gets there a little slower....but it can haul a big load that would crush the car. What happens is if you take a 100w amp (econo car size motor) and put it on a 1,000w sub (loaded truck) it does not go very loud (can't get to 60mph). If you put a 100w sub (econo car body) that is more efficient on it, it will go loud but may blow up if you clip it or really beat on it. Note that more expensive subs might be more efficient and still take a lot of power. This efficiency is why it is generally better to match your power up sub to amp depending on how you will use/care for it instead of getting a sub with way more power handling than you need. Unless you plan on a larger amp soon of course.

One last gray area is the ratings themselves. Subs might be rated above or below what they actually can take in a variety of situations...and amps are as well. Depending on brand and so on, it is not a precise thing even if they are good ratings because of all the variables just in musical signals themselves...how they are mastered...even instruments used. You can get a great idea with a sine wave, but that is not music. Then toss in the enclosure and it is a pretty murky area. But the ratings are supposed to give you an idea and they do.

If you don't see RMS on the rating, it is usually MAX that is double or more than real RMS. With amps they even rate RMS at 14.4v or at 1khz so it is not even a true rating then as you often will never see constant 14.4v in a car and is usually easier for an amp to make 1khz tone than 20hz-20,000hz entire span of human hearing as is the real standard. But if two amps are rated the same way then you should be able to compare them. With subs they may take a peak of much more than RMS before the VC heats up enough to melt. Thus 300wrms and 1200w peak. Amps often don't make over double RMS for peak due to electronic reasons. Either way peak is not listening to music so it's still really only a marketing ploy to put a larger watts number on the box.
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Old 22nd February 2008, 06:07 PM   #5
Flyin11 is offline Flyin11  United States
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Thanks...What I was kind of figuring that it meant max rms but wasn't sure. Just trying to keep my eyes open as I might look into the possibility of getting different subs or another amp for my situation. I sent the custom enclosure place money for the enclosure today and he is going to start building it for me in the next couple days and he said it'll take about 4-5 days to build (He's pretty busy as well). So I should hopefully have it in about 1-2 weeks and we'll see how it sounds then. If it doesn't agree with me then I have a choice this summer of getting new subs or a bit more higher wattage amp. Also when looking for subs I'm looking at the sensitivity rating...The higher the rating, the more sensitive it is to the wattage coming for your amp...meaning it will push and bump more than one with a lesser rating, giving you more bass. Why I have my eyes on some Boston Acoustics that have a rating of 94 when my JL's are 86....
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Old 22nd February 2008, 06:26 PM   #6
jol50 is offline jol50  United States
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Yes, sensitive will go louder. But...they don't always rate that the same way either. They can just lie, or there is a difference in 1v and one watt I forget offhand but generally are two ways of doing it. I usually search that brand and try to find postings about their ratings....more expensive/well known tend to be better in general than mass produced ones, as usual. I want to try some cheap old pyramids that are rated high 90s and 250wrms I think....pyramid ratings...lol...but they worked well back in the day on smaller amps. Hard to say, I just have to decide if I want to spend $17 per 12" sub plus shipping to find out. That kind of sub can work well for the IB setup with lots (4 12s) of drivers I run. Subs often have higher quality sound at lower travel and you can't put big power into IB subs anyway. Right now it shakes the car at 100wrms each...don't really need much more power for my use so I may as well try more efficient/cheaper/lower wattage/and lighter weight subs right? These infinity work good but are heavy when x4 in my little car. I could hardly manage the baffle loaded, and I'm not a little guy. I certainly could not get it set right in the trunk on my own and screw it in at same time. A big heavy box, that was what I was trying to get away from.
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Old 22nd February 2008, 08:16 PM   #7
Flyin11 is offline Flyin11  United States
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Quote:
Originally posted by jol50
I just have to decide if I want to spend $17 per 12" sub plus shipping to find out.
You can do better than Pyramid I would think even Sony's are better than that

Then again, listen to me saying that, $17 is a lot cheaper than $110 or $119 per sub
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Old 23rd February 2008, 02:52 AM   #8
jol50 is offline jol50  United States
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Everyone likes to say that, but I used to run the snot out of the 10s back in the day. At that power level and for IB, they were great. Now they have been changed so not sure how they would work. No they will not do what some high power sub will, but that is not what I am using them for. Also they would wear out in about 2-3years of running at xmax every day...lol.

I was not sure if this IB would work, I bought all the infinity used for around $30 each.

Lol, $86 for 4 pyramid 12s to my door! 10s are only 12.99 each. http://www.teptronics.com/wx125.html They have more HD ones but the efficiency is much lower. I don't know, all I know is for IB at moderate power they used to work really well. I used better subs at the time and they could barely out do them. I had pyles (huge back then and expensive) and they would, until I put 4 pyramids in that car and then my car was better....I paid 15 each for them back then in maybe very early 90s. Subs now are made for boxes, to handle a lot of watts with a box holding them still....kind of contradictory, but that gives you a louder small box. I used to run about 75wrms to each 10 back then depending on the amp, and they would move a lot.

Now a box, that is a different story. These only worked well in large ported boxes, 2cf for each 10 was nice and would get 30Hz if you pushed them.
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Old 24th February 2008, 12:52 PM   #9
Clipped is offline Clipped  Thailand
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JBL has a white paper on power handling for speakers....look it up.

i coud tell you what they say, but you wouldnt believe me.
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