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Old 9th November 2004, 03:22 AM   #1
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Default what makes a good 6by9

I want to know what RMS is when looking at speakers. I have an idea but not exactly sure. please let me know.
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Old 9th November 2004, 07:18 AM   #2
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Power handling is no indication of how loud a speaker will go nor how good it is.
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Old 9th November 2004, 09:04 AM   #3
muhy3 is offline muhy3  Australia
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richie00boy you weren't very helpful mate.

lilduff88 rms stands for 'root mean square' and is generally used in relation to speakers representing the amount of power they can either handle or reproduce (pmpo). pmpo is peak musical power output or something along those lines and is vague and misleading as company's dont follow standards of measurement so you see cheap speakers that claim thousands of watts.

to explain what rms in relation to how loud a speaker will go depends on many factors, primarily the sensitivity which is generally measured at 1 watt per 1 metre in decibels (dB).

If you were to have a speaker with 89dB sensitivity 1W/1M and the said driver can handle 15W then you could work out vaguely what kind of spl (sound pressure level) you can achieve. For ever 3dB gained you also double the power requirements, in this case 92dB requires 2W, 95dB requires 4W, 98dB requires 8W and 101dB requires 11W and so on...

To work out the "RMS" or power handling of a driver to which you don't have specification sheets is near impossible and at best you can only approximate by testing the driver. Expensive equipment and a lot of electromagnetics/mechanics/acoustics knowledge is required to find out the power handling. Hope this has helped!
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Old 9th November 2004, 09:25 AM   #4
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My apologies. I misread the post to be asking what RMS he should be looking for when checking out speakers.

Your explanation is quite right with the exception that in your example you need 16W not 11W for 101dB

To add to your comments, the power rating refers to the voicecoil thermal rating only and takes no account of whether the cone can actually withstand the excursion that running the full power at low frequencies demands -- thus it could quite conceivably be limited to only 1/3 of the rated power once any real bass gets to it.

The problem with most car speakers is that they do not come with any tech specs that actually mean anything useful or facilitate modelling. The best thing to do is listen to a few models and choose that way.
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Old 9th November 2004, 08:20 PM   #5
busman2 is offline busman2  United States
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I always look at the sensitivity rating when buying car audio because you want the most efficient speaker to use smaller amounts of power to drive them.
A speaker with a 92db rating will be louder at a lower volume number on your stereo than a speaker with a rating of 88db.
Frequency response is also a very big determinig factor.
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Old 9th November 2004, 09:01 PM   #6
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You are right about sensitivity, but bass response is traded for sensitivity, so buying the most sensitive speaker you can may not give you the most bass.
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Old 9th November 2004, 09:21 PM   #7
busman2 is offline busman2  United States
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You are correct and that is when subwoofers come into the mix. At least that is the way I look at it.
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Old 10th November 2004, 02:38 AM   #8
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There is no "end all be all" parameter to look for with any given speaker.

Sensitivity is a good measure for how loud a speaker will be with a given amount of power. It is very important that you realise that loud is not the same as good. Remember, that it's relatively easy to just add more power!

Frequency response is more important. It should cover the majority of what you want to hear.

Crossover design is heavily overlooked, but it is very important, IMO. Most coax speakers (And most 6X9s are coax) have a very simple crossover, consisting of a single capacitor to block low frequencies from the tweeter. The woofer cone is fed a full range signal, depending on the low efficiency of the woofer cone at those frequencies to prevent it from interfering with the tweeter. This invariably ends up with a muddy crossover point, and nearly always leaves the resonant spike still present with the tweeter. This will leave a harsh quality to the sound, though it is more pronounces with some than others. Good 6X9s will use a capacitor to the tweeter, and a coil to the woofer, which makes a simple 2 way 1st order crossover. This is somewhat better. A very select few will incorporate an external 2nd order (12dB/octave) crossover, and these are about the only ones that I would give serious consideration to.

Cone material is something to pay attention to. While paper cones are generally superior for dry, climate controlled indoor use, in a car, polypropylene is generally the rule. The cone needs to be as light ans stiff as possible. If you get a chance to feel the cone material on both sides of the basket, check for thickness. A good cone will be very thin and very rigid. Many tweeters are titanium dome, which can be made very thin and still be rigid. I personally like silk dome tweeters myself, although the ones in the car are titanium.

Mostly though, what makes a good speaker is good sound. Go into the stores and listen. This will tell you more about the sound quality (And that's what it's all about, right?) than anything that we can tell you here.

To quote an oldie: There's a new band in town but you can't get the sound from a story in a magazine...
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