Jon Moeller

I ordered a set of MB Quart RKC 116 speakers for the rear of my car, and I'm wondering if I can run them with my current head unit. The speakers are rated for 60-115 watts (rms), but my head unit only delivers 40 watts rms. I plan to get a 4 way amp to power everything in the car, but I'm wondering if I'll be killing the speakers by underdriving for the time being.

Can anyone tell me if I can get away with this configuration? I won't be cranking the volume on these, if that makes any difference. I'm just hoping that I can install the speakers, now, rather than waiting until everything is in place. Yes, I lack patience.
-J

bart1

Your head unit doesn't provide 40w RMS. Unless I am out of touch with the little power supplies they put in there 20-25w RMS is all you are gonna get. They will be okay to run like that, but be aware that you are more likely to damage them from distortion with low power than some good clean high power. I would suggest looking at an amp with 25w to 50w per channel. Don't get a cheapo. A good Rockford or Soundstream will put out more than many lesser brands. I like the two mentioned, Orion, PPI, Alpine is okay, Blaupunkt has some neat digital amps. There are some others and I have been out of the stereo scene for a while. The last amp I bought was a Soundstream Lil Wonder. It has been a trooper. The Rockford I had before that did very well for 4-5 years.

-Bart

johne

dude, what model is your head unit. I really doubt it is putting out 40x4 rms. It's probably 40x4 peak with about 20x4 rms.

And you should be fine just don't turn your volume up past 75-80% and you won't hurt your speakers. Past that volume and your crappy head unit amp will start clipping. It is this act of clipping that usually destroys speakers because the sharp cut in the signal forces the speaker to move at a very high speed to try and instantly reverse direction. And don't be insulted, all head unit amps are crappy.

Have fun,
John

johne

Bart, you just beat me on the reply.

John

Skitch

I agree, over-driving the head unit, not under-driving the speakers is what is going to do damage. You might want to put a capacitor on the speakers to roll off the low end since the head unit is sending them a full range signal. You should be able to pick up a cap from a local stereo shop for less than $5. Just an insurance policy to keep from blowing them before you get an amp. As far as amps go I really like Xtant and PPI personally, but I think I am about 10 years behind.

my .02

Jon Moeller

Thanks guys. I'll look into the capacitor and keep the volume down. I greatly appreciate the knowledge.

On the amp front, I'm planning to purchase the JL Audio 300/4. Please feel free to comment at will. You guys were right on the head unit. I've got an Alpine cda-9807, which is rated at 23 watts continuous, and 50 watts peak. For some reason, I had a brain fart on that one.

-J

xsboost90

i have had plenty of radios that put out 45x4!!! You only need a capacitor if you run too much power to an amp, or it draws too much that is, unless you are referring to some 47microfaric caps, which will cut the low end. GO ahead and hook em up to the radio, they will distort when the power is not enough, but they will work.

bart1

xsboost - Car radios do not put out 45x4 rms unless they are some super duper new tech. The vastly overrated 45x4 stamped on your head unit in no measure comes close to a decent amp as small as 25x4. A stiffening capacitor like you are referring to is not what was being discussed here. They are talking about cutting out low frequncies - bass blockers. 47 microfarad is a potential one, but I don't know what frequency that filters at on a 4 ohm speaker.

www.crutchfield.com has these "bass blockers" and very good customer service to help you figure out what you need. I think JL makes a very good amp. Thier subs are excellent.

944Play

I'm not a guru, but the only time I've ever destroyed car speakers was when I attempted to use an Alpine Flex4 amp, bridged, to drive two 5.25" front speakers. I burned out two sets of speakers (including some JBL GT's with paper tweeter cones that I REALLY liked!) with that setup.

Manning

Do you have to use special pulleys to underdrive speakers?

AlexE

That is a wonderfull amp..... one of the best out there.

I have one.

Jon Moeller

Mike,
I'm quite sure that underdriving the speakers is worth at least 50 hp. After I do the install, I'll make a full report to the board. On a turbo these gains may be even greater.

Thanks, again.
-Jon

Skitch

xsboost90

Yes, I wasn't talking about a Cap on the amp, just a small one on each speaker that will roll off the low frequencys. Just in case.

Charlotte944

What fries the speakers is the straight DC voltage applied to the speaker voice coil by the clipped portion of the input wave form.

The voice coil is designed for an alternating wave form, such that the resultant inductive reactance or X-sub- L limits current flow. X-sub-L is directly proportional to the applied frequency. As the applied signal approaches O hz, X-sub-L approaches O ohms. X-sub-L = (2 x Pi x Frequency x Coil Inductance in Henrys)

With the actual coil resistance being near 0 ohms, and X-sub-L being at or near 0 ohms, you get maximum current, maximum smoke, and minumum output.

Legoland951

To end Charlotte 944's statement...... and 100 percent THD

If you figure 40x4 root min square (rms), that is 160 watts in a 12 volt system, comes out to 13.3 amps continuously. What size fuse do you have in your head unit? The amp section of the head unit will require probably three times the power input to produce that output and that would put it at around 40 amps assuming the rest of the head unit requires no power to run. Don't believe everything you read because I have never seen a 40 amp fuse for a head unit. Get an external amp. Charlotte944 is right and if you ever see the square wave of a clipped amp in an oscilloscope, you will know this is what not to do to your speakers. I rather have too much power from the amp and turn the volume **** down to not blow the speakers. Consider it dynamic headroom. What happens from the speakers I had to repair, people bottom out their voice coils to the magnet by clipping (under powering and cranking volume too high) their amp or over powering their speakers (too much power and cranking volume too high. The voice coil gets damaged and smashed at the bottom and scratching the post the voice coil goes around (paper thin tolerance) making horrific noises. What I had to do is recoil and rebuild the speakers, which is no fun but back then those nakamichi sp1010 subs cost around $250 a piece so it was worth fixing. Use what you have in the head unit but don't crank it to the point where it distorts (clipping). Get high quality amps like soundstream that has a little higher rating than the speaker in terms of rms and make sure not to crank it too high where it distorts (over powering and bottoming out voice coils) is how I would set it up.