I have installed polk 651s 65watts 4ohms in the kicks. I have a cadence 1502 two channel amp 75 watts x 2 at 4ohms. My head unit is a sony with 4x50watt 4 ohms(19 watts /channel min continous average power for 4ohms/4 channels). This unit also has a d bass button with 1-2-3 settings. I planned only the two polks in the kicks . Should I install two rear 50 watt speakers with good bass response off the head unit to take advantage of the head unit amp? Or just use the 2 polks and the amp only . DB ??? Any stereo guys

 

Definately put in a pair in the back, I would go bigger than 50 watt speakers tho, get them rated at least 200, you don't have to use all of it.

 

gbags, you don't need rear speakers if the front ones are big enough to handle the music at the volume you want and a 6.5" speaker in the front running off a good amp should give you PLENTY of sound.
The correct use of rear speakers in any vehicle should be for a low level of rear fill only, basically to try to duplicate what you would hear at a live performance and the only sound that you get during that is echo's and reverbration bouncing off the rear walls of the venue where the performance is being held. Unless you stand or sit at a concert with your back to the stage all the music is coming from the front of you.
In a corvette the interior is so small it doesn't take much to fill it up with sound and with 6.5" speakers and a decent amp you are going to get lots of sound and by eliminating rear speakers you will keep the soundstage up front where it belongs. The only speaker i'd recommend in the back, IF you feel you need it, would be a small subwoofer run off it's own seperate amp.
forget the built in amp of the radio, I don't care how good the radio is the built in amp sections are crap and low power and I wouldn't run any speaker off them.

Sixfooter, sorry to disagree but the power ratings of a speaker basically are meaningless. A 200 watt speaker does make it any better than a speaker rated for 50 watts. Most of those numbers are peak power handling anyway and listed only for impressive marketing on the box.
One of the factory demo systems I built when I was in the car audio industry used all Phase Linear speakers. They were rated for a continious power handling of 50 watts. I drove them off very hi-end amps putting out almost 1000 watts/channel. When I was building the vehicle they accidently shipped me double the speakers I needed so as a test of the speakers and what they would REALLY handle in power I threw all 1000 watts to each midrange/tweeter set, set all the gains on the amp and radio to max, set the gains on the parametics EQ's to max, and to abuse them even more cranked the bass levels on the radio to max to really torture them. I actually TRIED to blow the speakers and they wouldn't fail.
The point is simple, speakers tend to usually fail because of distortion, which the most common cause is underpowering them. Give speakers a good, clean, undistorted signal from a good quality amp and they will survive most things regardless of what their power rating is.
Also, a common misunderstanding is that the speakers power rating has NOTHING to do with the amount of volume a speaker will . A 200 watt rated speaker does not necessarily give a higher output of volume over a 50 watt rated speaker. In fact MANY 50 watt rated speakers will play louder than many 200 watt rated ones. The power handling capability and the speakers efficiency (what the speaker will reproduce in db levels with an input of 1 watt) are not related at all actually.

 

If you want something for the back put a small subwoffer. The 6.5" in the kick are a great start but there just is not enough room behind them to reproduce any really good "pounding" bass. My suggestion would be to use the stereo's internal amp to run the 6.5s, "bridge" your amp to run as a mono amp (probably would put out in the neighborhood of 150 watts....your amp's manual should tell you about how to bridge...its very easy), then get or have a subwoffer made for the back. I have a JL 75x4 amp that I'm going to use to do run my system. I'll use two of the four channels to run speakers in the kick pannels then bridge the other two channels to run a sub in the back of my 75 vert. Good luck with the project!!

Tom

 

I must say that with just the speakers in the kicks isnt enough.. Atleast not for me anyway.. I like to be able to hear my music. I had just the kick playing and want able to geta good sound out of them. then after i turned on the 10 in sub in the rear it just mad a world of difference. .. The best mod I have done to the car so far..=)
I have an alpine with ipod controller, 6.5 infinity in the kick and a 10 in mb quartz sub being pushed with a cadence 300 wt amp 4 chnl. 75 per.
And I still ahve room for my tops...... Thanks again Matt(DB) for the help...

 

BarryK is 100% correct in his description of proper sound stage and the best way to acheive that in a mobile system. The rear speakers should be used to produce fill only, particularly in a two-seater. Their power handling has little to nothing to do with their sound quality, and typically speakers with higher power handling ratings have lower efficiency levels. This means that you actually have to run more power to get the same volume levels compared to a speaker with higher efficiency eevn if rated lower for power handling.

The biggest hole that you will have is in low frequency sound reproduction with the 6.5" speakers. Their ability to produce lower frequencies will be somewhat limited compared to larger drivers or dedicated subwoofers that only have to reproduce lower frequencies rather than the entire frequency spectrum. If you power them correctly and keep the distortion levels down they should sound great.

The other big upgrade you should make if you haven't yet is to make use of the incredible variety of dampening materials that are available now. If you can keep outside sound outside, you won't have to work nearly as hard to overcome the that exterior noise.

If you do choose to put in a sub, make sure you limit the frequencies to them as well as to the kick panel speakers (mids and highs to the kicks, bass to the sub).