First we've got to understand the signal we are trying to amplify. These signals can come from a guitar string picked up by the "pickup", a micorphone, or even just our mp3/cd player. Do people actually still use cd players? Anyway. So, we have a small vibration of sound that is evenutally turned into an electrical signals. (transduction will be covered later). These electric signals can be differect strengths, but we're not covering that today either. We just want to talk about what our amplifier and speakers are doing with that signal.
So lets start at the speaker and work backwards to the amp. Speakers have two ratings. Watts and Ohms. The speaker can producs X number of watts at X number of ohms. It is typaclliy labeld like 100 watts @ 4 ohms. So most of us know what watts is, its the loudness. If your a guitar player your number one goal is to have the most watts EVER! but ohms, what is ohms? Ohms is a measure of resistance. You don't think of it, but substances conduct or resist electricity on a scale. Rubber isn't very conducive, copper is. This is why some premium cable are made out of gold- gold & other expensive materials - they conduct electricity better than others. When the electricity passes into the speaker, some of it is resisted. The ohms rating of the speaker is a measure by how much electricity is resisted by the speaker, and an indication of how much energy it takes to drive it - the higher the ohms rating, the more difficult it is to drive.
An amplifier amplifies the electrical signal, causing the speaker to vibrate with greater force, otherwise the impulse would be barely audible (think of the size of a microphone vs. the size of a speaker). How much the amp drives the speaker is measured in watts. So again, when an amp manufacturer gives it's wattage rating, it's always at a specific Ohm resistance. "100 watts @ 4 ohms," for example. When the resistance is 4 ohms, this amp will produce 100 watts. If that resistance changes, the amp will produce a different amount of watts
This is the core concept to understand. We're used to things that have a strength independent of their surroundings. A flashlight produces light independent of how bright or dark it is. Since electricity usually travels in a loop, from a negative terminal to a positive one (which is why you have to hook up both halves of a battery) the elements in the loop affect the output.
Real word practice:
If you connect your amp to one speaker, the ohms rating is equal to that speaker's ohms rating. An 8 ohms speaker would have a rating of 8 ohms.
If you wire two or more speakers in series, you add the ohms rating together to get the total ohms. I know what series & parallel wiring is from grade school science. It's hard to describe without diagrams, so I'll keep my description minimal.
An easy example is christmas lights. When you wire the lights in series, you connect the + terminal of one light to the - terminal of the next light. The electricity flows through one light, and then on to the next. If any of the lights goes out, or any of the connections breaks, all of the lights go out. The connection is broken.
This increases the total resistance, reducing the total acoustical output. That is, because the electricity has to flow through each speaker one at a time, each speaker adds it's resistance to the whole. The formula is as follows:
Speaker A + Speaker B = Total Ohms Rating
8 Ohms + 8 Ohms = 16 Ohms
Two 8 Ohms speakers wired in series will have a total rating of 16 ohms.
This reduces the total resistance increasing the total output. That is, because electricity flows through all of the speakers simultaneously, each speaker added reduces the resistance of the chain. If you visualize all of the negative electrons on one side trying to get to the other, they'll have an easier time because there are so many possible paths for them to go by.
Resistance = (Speaker A x Speaker B) / (Speaker A + Speaker B)
Resistance = (8 Ohms x 8 Ohms) / (8 Ohms + 8 Ohms)
Resistance = 64 / 16
Resistance = 4 Ohms
Follow so far? Good. So, now the Amp.
The calculation for figuring out how much is fairly straightforward, and pretty much what you would expect it to be. Since ohms measure resistance, the more ohms, the less output from the amplifier. Conversely, the less ohms, the more output from the amplifier.
Since the amp is rated at a specific amount of ohms (i.e. 100 watts @ 4 ohms), a different amount of ohms will produce a different output. Two 8 ohms speakers wire in series (16 ohms total) would cause the amp to produce 25 watts to each speaker.
Amplifier Output = Amplifier Watts x (Amplifier Rated at Ohms / Speaker Chain Ohms)
Amplifier Output = 100 watts x (4 ohms / 16 ohms)
Amplifier Output = 100 watts x 1/4
Amplifier Output = 25 watts
An amplifier designed to put out 100 watts into 8 ohms will put out 200 watts into 4 ohms. Two 8 ohms speakers wired in parallel (4 ohms total) would cause the amplifier to produce 200 watts.
200 watts = 100 watts x (8 ohms / 4 ohms)
The amp produces 100 watts at 4 ohms. When the resistance is increased to 16 ohms, four times what it was rated, the amplifier produces one fourth as many watts.
You must be careful when wiring multiple speakers together in a series or parallel chain because the amplifier may have trouble dealing with certain Ohms chain ratings, especially below 4 and above 16, and you must be sure that your speakers are capable of handling the wattage that they're receiving. Be sure to check the manual for all of your equipment before doing any of this.
The limiting factor is the power supply. If the power supply isn't designed to handle a 2 Ohm load, you may fry your amp. In fact, it takes a very special amp to work below 4 Ohms. Again, check the manual, call the manufacturer, don't just start wiring things into a 1 Ohm load hoping to get 4 times the power out of your amp.
No comments:
Post a Comment