lew -
You’re partially correct is assuming that the amp will give you ‘lots of headroom’ - if you mean capability of handling sound levels, but a high output amp cranked down to low volume will miss out on the high end especially - these frequencies are always lower in level than low end sound, so you would be missing out on the full spectrum of sound. For my money (though it ain’t mine!) I would say you’d be a lot better off with something like a 50w per channel amp (max), when you could crank the volume up a bit and enjoy the full spectrum better. I currently have an Aiwa home system, giving 25w per channel (stereo) and I have never cranked it up more than 2/3 - it would blow me out the room! The rooom is about 13 foot square, so gives you some relative idea of sound level v’s space - in comparison to a car. In comparison to that, I also have an old Goodmans amp, which coupled with Wharfedale speakers, has a max output of 10w per channel - but that’s RMS rated, which means it produces almost as much sound as the Aiwa running at 25w ‘peak to peak’
If I’m not teaching you how to suck eggs, most sound systems sold to the public are ‘peak to peak’ where commercial systems are RMS rated. RMS = root mean square, which is equal to a higher rated domestic amp. RMS means the average of the power produced - not the maximum. ‘Peak to Peak’ means the power developed across the highest peaks (full bass for instance)which is periodic, so the RMS system is pumping out more power on average per watt than a peak to peak amp. E.G. - a 10w commercial amp would equal a 15 to 20w domestic one.
The company I used to work for had a theatre sound division, and I was shocked when I discovered that cinemas running huge horn assemblies were working off a 10w amplifier - this was in the days when 35mm films were all the rage. The difference? high efficiency speakers! What we buy in shops is crap in comparison. You pay for power rating - not efficiency.
You are right on the 1F capacitor, but bear in mind that while this will take care of the power surge for a full bass hit, if you are one of the ‘gimee bass’ fans, then those full bass hits are arriving in rhythm, and if that’s fast, then the battery/alternator are working hard to keep the capacitor charged. You can slow down the capacitor charge by sticking in a series resistor, but then it won’t cope with a fast beat anyway. Lets assume your amp produces about 800w RMS - then it’s drawing 66 amps off the battery to do it! - The battery is normally 32AH which means it can throw out 1 amp for 32 hours, or 32 amps for 1 hour, and the alternator (if I remember correctly) is 45 amp max. See what I mean about power requirements? If you want to check, get hold of a 100amp D.C. meter, and stick it inline between the battery and the amplifier supply (live) - I have no idea what current it will draw at low output levels, but it’s got to be as much, if not more than the battery can cope with. My son had a good system in his Pug - but the supply cable for the amp was 6mm if I remember right, and the fuses were 100amp - - - - - The main battery cable ain’t much more than 6mm! His battery was a 45AH one. The amp size - can’t remember exactly, but it wasn’t much more than 250w (more than enough)
Going further with this - bear in mind the MX-5 has little to no sound deadening material, unlike most passenger cars. If the alternator and battery could handle your 1300W amp at full power, then the effect will be as much panel vibration as bass, and you will be amazed how much material you will need to stuff into every cavity to try and reduce that. You will then need forced induction to overcome the weight problem - - - - -
So - motto - lower is better! I hope that helps?
