Watt Acoustic

Categorized | Guitar Parts & Accessories

Posted on 02 October 2009. Tags: 15-watt, 200 watt acoustic amp, acoustic, acoustic 100 watt bass amp, amplifier, at108, audio, soul watt acoustic, watt acoustic

Watt Acoustic

can a 400 watts and another 400 watts subs over power an 800 watts amplifier?

i have a 400 rms watts audiobahn 12 inches sub in my car and an 800 watts power acoustic amp. i'm planning to add another 400 rms watts audiobahn sub which is also 12 inches. Will my amp over heat or get damage??

Your question is phrased incorrectly.

First some basics about speaker watt sizing.

A 400 watt speaker can be over driven by an 800 watt amplifier if someone is not gentle with the volume knob. This will cause distortion, over heating, and possible tearing of the cone and surround and burning of the coil. However it is not a bad practice to have the ability to overdrive your speakers, as this will prevent the distortion that can be caused by an amplifier nearing its rails or maximum output. As a rule of thumb, I tend to undersized my speakers by 20%. So an 800 watt amplifier would be driving a 640 watt speaker. Watts are a relatively minor consideration when mating speakers and amplifiers. Even so there are still questions to resolve about the amplifiers real power capability.

Firstly is the 800W amplifier rating the total power output of a multi channel amplifier? If yes, then you have considerably less than 800 watts to work with for your sub(s). You will have to do some checking to to find out how much power you have available for the one channel you are concerned with. If the amplifier is a single channel amp, or you already know that the channel you are using is capable of 800 watts, then your good to move on to step two.

Step 2: impedance matching.

Your amplifier was designed to power a specific size or size range of load. A load in electrical terms is measured in Ohms. Most amplifiers for cars are designed to power a 4 Ohm load on each channel quite well. And most car speakers are rated at 4 Ohms. You will have to check to see what range of impedance your amplifier is designed to handle. With out changing your amp, or adding transformers, this is the real limiter for speaker choice. If you are below this rating in Ohms with your speakers, your amplifier will over current the output FETs, unless fuse protected, and over heat. If you are above this range, the output voltage levels will rise to the rails or maximum level at a relatively low volume. This will destroy a sub very quickly, because the output wave form will become a square wave with a flat DC top and bottom. After you know your impedance (Ohms) for the load, and you know the Ohms of your speaker(s), we can do some playing around with simple math.

For the purpose of simplicity I will not use the actual equations as we will most likely be using a pair of 4, 6, or 8 Ohm speakers.

Lest say we know the load your amplifier can drive, and we are trying to connect 2 speakers to it. There are two primary ways to connect speakers to an amplifier. Series or Parallel. There are permutations for more than 2 speakers, but you are just talking about 2.

Series... When wired in series, the + lead from the amplifier connects to the + terminal on the first speaker. The - terminal of the first speaker connects to the + terminal of the second speaker. The - lead of the amplifier connects to the - terminal of the second speaker. Connected in this fashion, the resistance of the two speakers is added together like this:

4 Ohm + 4 Ohm = 8 Ohm load
6 Ohm + 6 Ohm = 12 Ohm load
8 Ohm + 8 Ohm = 16 Ohm load

Wattage adds as well. 400 watt + 400 watt = 800 watt.

Parallel... When wired in parallel, the + lead from the amplifier connects to the + terminal on speaker one and speaker two. The - lead from the amplifier connects to the - terminal on speaker one and speaker two. Connected in this fashion the resistance is divided by 2 like this. ( the division by 2 only works if both speakers are of the same value resistance. Other wise the formula is R=1/((1/Ra)+(1/Rb)) where Ra is the resistance of speaker 1, and Rb is the resistance of speaker 2, and R is the effective resistance of the circuit. )

4 Ohm ][ 4 Ohm = 2 Ohm
6 Ohm ][ 6 Ohm = 3 Ohm
8 Ohm ][ 8 Ohm = 4 Ohm

Wattage adds again. 400 watt + 400 watt = 800 watt.

So if your amp is rated for 8 Ohm loads, two 4 Ohm speakers in series will work. Or if your amp is rated fro 4 Ohm loads, two 8 Ohm speakers in parallel will work.

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