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A few basic questions answered whilst I'm not busy.
When installing amps;
1, How do I know what size power cable to run?
The answer in basic terms is;
Add up the on board fuses on each amp you are going to use, say your mono amp (for the sub/subs), is fused with 2x 40amp fuses,(80amps in total), and your second amp,(for the fronts or fronts & rears), is fused with 2x 30amps,(60amps in total), then you can work on the assumption your maximum current draw is going to be 80+60=140amps, so with this set up you would require 0awg power & earth cable.
2, How do I know what size fuses I require?
The answer is;
The actual cable rating denotes the required fuse rating, you must remember you are fusing the cable and not the amp, as an example;
If running a 0awg power cable from the battery to the boot then the required fuse should be higher than the load,(current draw from the amps etc), but lower than the cables rating.
So with a max current draw of 140amps, and a cable rating of 250amps, you would use a fuse of 200amps. This fuse should be mounted as close to the battery as possible.
3, Why do i get engine whine through my speakers?
The main cause of alternator whine is poor earthing, you should always select a good earthing point, I recommend the boot floor, be careful when drilling to avoid the fuel lines/tank, electrics & brake pipes, clean the area back to bare metal and use a nut & bolt. You should avoid using, seat belt anchor points, rear light cluster earthing points, rear seat hinge bolts.
4, Where can i mount my amplifier?
When mounting your amp/amps I would recommend you avoid placing them in direct line with your sub, a sub firing directly into an amp will eventually cause damage due to excess vibration. You should also avoid mounting amps on the outer faces of the sub enclosure, this will also expose the amp to excess vibration.
You should also avoid mounting the amp upside down or at any angle beyond the vertical,(on rear seat backs for example), this is because of the heatsink. The amps heatsink is designed so that when it heats up, the warmed air rises and draws in cooler air from the ends, this cooler air then cools the heatsink, becomes warmer air and rises away and so the cycle continues, however if the amp is mounted incorrectly the warmed air rises into the amps internals and can't escape, because it can't escape it can't pull any cooler air in, and so the amp runs hot, and can cause the amp to trip into thermal protection.
5, When installing multi amps can I daisy chain the remote switch on lead.
If using two amps then this shouldn't be a problem, if however you require your remote lead to operate on say, two amps, a sound processor, dvd unit, etc etc, then I would recommend the use of a relay, using the remote lead as the switching supply.
6, Fed up with amps now so lets move onto headunits and distortion;
1, The average head unit is fused at 10amps, these 10amps at any one time are supplying;
cd drive motor
cd laser carriage
flashy graphic display panel
and eventually the internal amplifier
When playing a full range signal the internal amplifier will require more power than it would if it were say playing a signal high passed at 100hz, so to translate this into basic terms, the more bass you ask your head unit to play, the more likely it is to distort,(this is due to voltage drop within the head unit, not poor speakers).
A simple test;
Play a dynamic cd, gently increase the volume until you can hear distortion, now lower the bass settings on your head unit and the distortion will stop, now increase the volume again, it should play at an increased volume without distortion.
A speaker can only reproduce what it receives, if it receives a good strong signal, it will reproduce a clean clear sound, if it receives a weak signal thats ragged it will reproduce poor ragged sound,(distortion). The higher excursion that is required for lower frequencies demands a stronger signal, (which is why sub amps have higher rms ratings), and unfortunately head units just don't have that kind of power.
When selecting a new head unit you should take into consideration exactly what you require from it. In most cases if you are fitting a head unit and using it to drive stock speakers you will notice an improvement in sound quality and output level, however if you decide to upgrade the speakers at the same time you may find its not as loud or warm, (bassy).
Most people when they detect distortion in the stock audio system run down the local audio outlet and purchase uprated speakers, then discover that it still doesn't sound any better, so they then assume the problem is that the head unit is still too powerful for the new speakers, when in truth the opposite is correct, the head unit is not powerfull enough.
Pointers on speaker selection;
Speakers being driven by a headunit without a sub installed
These should be rated at around 20watts rms, either component or coaxial, capable of playing down to around 45hz with a sensitivity of 93db+.
Speakers being driven by a headunit with a sub installed
These should be rated at around 30watts rms, preferably components, capable of playing down to around 70hz with a sensitivity of around 91db+.
Speakers being driven by an external amp without a sub installed
These should be rated at around 70watts rms, definitely components, capable of playing down to around 45hz with a sensitivity of 90db+
Speakers being driven by an external amp with a sub installed
These should be rated at around 90watts rms, definitely components, capable of playing down to 70hz with a sensitivity of at least 89db+
To supply rearfill, for those that want it, should be done using small coaxial speakers.
Now to the dreaded 6x9 debate.
These should be used where the fitting of a sub is not desired or possible. They should not be fitted in parcel shelves with their cones sharing the same air as a sub or subs. If you decide you want 6x9's in the back they should be fitted so that you can enclose their baskets to afford them protection from the sub/s.
As previously stated a speaker reproduces sound according to a signal it receives, to reproduce that sound correctly the speakers cone needs to react naturally to the signal, but when you have a sub firing massive shock waves through the boot it reacts to those shock waves causing poor sound reproduction. You can actually see this happen if you have 6x9's mounted in a shelf above a sub, all you do is disconnect the negative speaker wire off each 6x9 speaker, shut the hatch and play your music, watch the 6x9's cone, it will pulse with the beat, the louder you go the further it will move. This movement affects sound reproduction, causes the voice coils to work harder, which causes heat build up, which in turn promotes premature speaker failure.
When fitting 6x9's into a car, if they are fitted correctly, and driven by an external amp they are a decent alternative to a sub, but when driven with a headunit they sound crass and harsh.
7, Sound deadening on the cheap
When fitting a sub into your car I would recommend sound deadening the following;
1, boot floor
2, rear quarter panels
3, rear hatch panel
4, boot sides
The difference between a car thats deadened and a car thats not is truly amazing, it seems so much warmer and louder, all the sound thats lost through thin panels is held in the car, thin panels no longer ressonate and so it sounds cleaner.
When doing budget jobs I always use,"wickses high tack flashing tape", its not as good as dynamat or similar but it certainly makes a difference at a fraction of the price.
I would also recommend doing the front doors, its easy to do this when fitting new speakers, just cut tape into small strips and apply it to the outer panel through the holes in the inner panel. When you are satisfied with the outer panel you can then do the inner panel taking care not to foul any levers or operating rods, (for best results you should cover all the access holes, effectively sealing the door cavity).
When installing speakers always try to use mdf baffles, and where the baffles join the mounting surface seal it with grip fill or similar.
Hope you have found the above useful, if not i hope you found it interesting lol.
8, The art of speaker & amplifier matching
Firstly i should point out that when selecting speakers or amplifiers you should ignore max output figures, they are misleading and rarely accurate. You should however take note of the rated figures,(commonly noted as RMS figures).
The RMS figures refer to the average output that the unit can output continuously.
Secondly, I should point out that recording levels vary from source to source, so for example a 50hz test tone recorded at 0db,(the highest possible level), will play extremely loud, where as the same test tone recorded at -3db will play at around half the volume. This sliding scale can become extremely confusing so I'm not going to go there lol.
So in effect a 50watt rms amp will deliver 50watts rms when playing a test tone recorded at 0db, but will deliver much less if playing a test tone recorded at -3db.
If you were to represent a test tones rms output on paper, it could be shown as a straight horizontal line.
If you were to represent music in the same manner it would be a series of peaks and dips, now because the maximum recording level is 0db, the peaks would be recorded at 0db, everything else would be recorded at a lower level, giving a much lower average output, (or rms output). So, because of this, when selecting equipment you should bear in mind what you will be playing.
So I always take note of the speakers rms figures, then select an amp that is rated at least 25% higher, so if I was selecting a mono amp to drive a sub, I would check the subs rms figure, say its 300watts rms, I would then look for an amp capable of delivering at least 375watts rms into the correct impedance, the same applies to all amps and speakers. This is referred to as,"headroom".