Matching amp to speakers

[l1ttle_d3vil]

I'm completely new to this sort of stuff, so some pointers would be appreciated.

Currently running JVC speakers:

2 way component speakers (running off the headunit).
45w RMS @ 4 Ohms.

Going to add some 6x9's which will be
80w RMS @ 4 Ohms.

Ideally would run both sets of speakers through an amp, but what sort of amp would be best? I know you need to match the amp to the power rating of the speakers without overpowering them too much, but since the speaker ratings are so different is this possible?

For example, JVC have an amp which will do 60w RMS x4 @ 4 Ohms. Will this be overpowering the components, and underpowering the 6x9's too much?

Is it better to run 2 different amps for the front and back speakers? Or what other options are there?

Any advice, in simple english would be awesome

Cheers
-Matt

[sergei]

There is no such thing as underpowering speakers.

You can have 1000W speakers powered by 1W amp and it will perform almost like 1W speakers of same sensitivity/efficiency (discarding the whole spectrum range).

Guess what happens when you put volume down? You reduce power output of the amp. Most of the time you are not using all power, in fact most of the time you are using small fraction (1/10). So, for example your 60W JVC outputs 6W when you are listening normally.

On top of that you cannot compare watts between speakers without looking at things like frequency response graph, sensitivity, THD etc.

For example 1" speaker can handle 100W @ 10kHz, while same 1" speaker can only handle 10W @ 1kHz at same THD.

You will find that most speakers are rated convenient frequency of 1kHz. This frequency is where (near) the human hearing most sensitive. It says nothing about what its handling ability at 100Hz (bass) or 10kHz (treble).

Most importantly 60W RMS amp does not equal same 60W RMS on speakers.

TL;DR having more powerful speakers will not harm, while having underpowered speakers could cause speaker failure, but we are talking doubling or tripling power, thus running 40W speakers on 60W amp most likely will not cause any harm either except some distortion.

[l1ttle_d3vil]

There is no such thing as underpowering speakers.
...
...
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TL;DR having more powerful speakers will not harm, while having underpowered speakers could cause speaker failure, but we are talking doubling or tripling power, thus running 40W speakers on 60W amp most likely will not cause any harm either except some distortion.

These are the only parts I really understood... and they seem to contradict each other

Most importantly 60W RMS amp does not equal same 60W RMS on speakers.

Aah, that's handy to know - I read on a few websites to make sure you compare RMS to RMS when matching amps and speakers

[holden_fan2005]

Always better to get a slightly over powered amp and reduce the levels rather than an underpowered amp and maxing everything out.

http://www.nzicemag.co.nz/forum/ - Check it out

[alimac]

There is no such thing as underpowering speakers.

Not entirely true. The main issues are that higher powered speakers, particularly in sound quality situations, tend to be less efficient than lower powered ones. As a result they need more power to make the same volume. This means the amp needs to produce more power, and if it is too small when it gets turned up it will start to clip. This produces square waves instead of sine waves, which will ultimately destroy speakers, particularly tweeters.

[RUKI]

Can't pass the subject as my university degree was in Ultrasound Engineering and while at the uni I've designed and built (using Acoustic theory, available professional measuring equipment and best components) several Hi-Fi speaker systems for home.
When it comes to car speakers/amplifiers bullet points here in simple terms are:
- Mission almost impossible to built high quality system that would sound equally good in the car as at home or display room. Simply because there is not enough space in the car -> not enough for the speaker enclosure and too small with heaps of reflective surfaces - not good for listening pleasure. For that reason bear in mind - what you hear in store - will sound differently in your car!!!
- Don't worry about power ratings. The worst you can do is to damage the speakers (they are cheap anyway) if throwing a party from your car to entire neighborhood. Amplifiers nowadays should have protection from the short-cuts hence should be no danger for the amplifier. Just avoid to put too many speakers in parallel (that will reduce resistance and amplifier may not be designed for that load)
- Volume for the woofer enclosure matters the most - to give you richness of the sound. Say for 12" woofer - something like 150 liters of the box volume would do (closed type or bass-reflex type - with the properly designed box and "hole in it", thick, non vibrating walls and special material inside to absorb sound waves). Mid-range requires pan size enclosure, twitter requires almost nothing.
That's why car manufacturers put woofers in the doors where isolated volume is relatively big. For the same reason [volume for the woofer] - stereo system with the speakers on the rear panel using the boot as enclosure may sound much better than a system with a woofer sitting in a small box and making nothing but noise.

When somebody sells you 20" woofer (bass speaker) in a box which is little bit bigger than the speaker itself - they have no idea about sound engineering.... Improved materials (cone, magnets) in speakers manufacturing did not change the fundamentals of acoustics - volume of bass enclosure affects sound quality.

Just revisited latest publications in CAR speaker Design (from Moscow sources) on Monday - it is what I though - special adjustment formulas are put into speaker design software to cater for CAR interior in the low (Bass) range .. Saved it - will use to build something in the new car.