70w RMS Speakers powered via Head Unit?

Question

Simple enough question... Can I moderately effectively power some MB Quart Premium speakers that are rated at 70w RMS via a head unit (that typically deliver ~20wRMS)? I know ideally you would want to use a separate amp but it simply is not feasible (due in large part to size constraints) in this install in a Miata.

I know pumping less watts to the speakers can be dangerous if the gain on the amp gets turned too high (clipping), but how viable would this be overall. I am not looking for max db or even quality but I am simply trying to figure out a decent solution to the absolutely horrid Bose system that was in the car initially.

Please don't reply with get an amp. I have a very nice Eclipse amp that was initially paired with these speakers, but it and most others are simply too big/heavy for this application. I know there are smaller amps, but most smaller ones are still too large for the application.

So... How bad will it sound if I use these 70wRMS speakers off a 20wRMS HU?

Answer 1

A speaker's RMS rating tells you its maximum power-handling capacity, but it doesn't really give you a clue to the minimum power requirement.  (ie, a 100-watt speaker doesn't necessarily require more power than a 50-watt speaker).   If you're comparing speakers, the spec you'll want to look at is "sensitivity".  This is a measurement of the speaker's output with a given amount of power input.  At low power levels, a speaker with a 90 sensitivity should sound noticeably louder than a speaker rated at 85.

A look at MB Quart's current Premium speaker line shows a sensitivity of 87 in their 6.5" model.  That's about average for an after-market speaker.  

Other factors to consider will be speaker location, and the level of background noise in your car (ie, how loud do you need to play it to hear it clearly?).   If you have a convertible Miata, then your background noise level will be pretty high.

You won't hurt anything by trying it out with the head unit power; if you hear audible distortion, just turn it down.  You won't be endangering your speakers by connecting them to the head unit and giving it a try.  I suspect, however, that you're going to find you need an amp to play them as loudly as you want (especially if you put the top down).

Answer 2

it will still sound better,mb quart makes awesome speaker sand i cant imagine them sounding bad under any circumstances. as long as you don't blast them they should sound nice.i know you don't want to hear it but why cant you throw the amp in the trunk?.they wont sound "bad"