Thought I'd put this together since I see a lot of people who are just starting out asking the same questions. This is by no means meant to be an all encompassing list. It is also intentionally kept basic because, well, the tech talk can go on forever and IMHO only serves to confuse people who are just learning.
Ohms (also called Impedance) - Ohms are a measurement of resistance to the flow of electricity and electrical signals through things. The higher the ohms, the more resistance. Why is this important and why do you hear people talk about matching ohms? It's because audio components, like nearly everything else, have their limits as well as the area in which they operate at their best. If you start mismatching components that were designed to operate in different areas you can run into problems. Particularly because when it comes to audio stuff everyone usually wants to push things to the max. For example, you add a component to the system that creates too much resistance for another one. That resistance will build heat...somewhere. For an example that's bike relevant let's take a look at the stock Harley radio. It is rated at 2 ohms. Now you change out your speakers to a set rated at 4 ohms. You've essentially doubled the resistance to the signal your radio is trying to push out. It can't get that power out but it keeps on trying. Something has to give and it will most often be the internal amplifier in your radio. While this should demonstrate why increasing ohms or impedance is bad, there is also a risk with lowering impedance. This risk however is very slight when talking about the speakers you would generally put in a bike. It is most applicable to subwoofers. The quick explanation is that the amp becomes free to pump out more power even faster and the amp heats up. Like I said though this is a very slight risk especially since in this scenario you'd turn the radio down...hopefully before things get blown.
RMS - For the record means Root Mean Square and refers to the mathematical equation used to determine the average amount of power an amp or speaker were designed to operate at. This number is very important though. What it represents is the number of watts, or amount of power, your speakers or amp were designed to operate at for prolonged periods of time without doing damage to them. DON'T fall in love with the max wattage rating for speakers! First, it is almost always exaggerated for real life applications since you don't likely have the equipment to provide the perfectly clean signal the manufacturer did to reach that number. Second, if you run your awesome new speakers at the max rated wattage for an extended period of time they WILL fail. Keep in mind that the RMS ratings are also occasionally exaggerated. Why? Well, it sells speakers. Sometimes, however, you will find speakers where the manufacturer underrated the RMS for their speakers. I'm not 100% sure why they would do this but finding out which ones are underrated isn't usually that difficult. You will have heard people positively discussing how much more power they could handle as compared to what they were listed at.
Gain - This is a term you will see used regularly when talking about installing an amp. "Once you have everything connected you'll need to set your gains." While a lot of people think that the gain adjustment is what controls the power the amp produces, and subsequently the volume, this isn't its purpose or what it's actually doing...exactly. While it does have some effect on volume the purpose of the gain adjustment is, in the simplest of terms, to match the volts at the amps input to the volts being produced by the source's output. Say for example your HU without an amplifier starts to cause distortion to the speakers at 80% of max volume. Then you hook up your amp and the distortion now starts at 40% of your maximum volume. Your gain is set too high. On the other side of the coin, you hook up the amp and there is still no distortion right at the same level as without the amp. In this case your gain is set too low.
Headroom - You'll hear this term used too when talking about amplifiers. What it is referring to is the extra amount of power, in this case watts, your amp has to give. Ideally you would like an amp that can provide 50% more watts than what you're going to need to power your speakers at their RMS rating. If you have an amp that is rated for 100w per channel and you put in speakers rated at an RMS of 90 your amp is working really hard. If you were to use those same speakers and an amp rated at 150 watts per channel it isn't working as hard, will run cooler, produce a cleaner signal, and has some extra power to give when that favorite song comes on.
Marine Grade - Marine grade DOES NOT mean waterproof. Marine grade simply means that the component was built to better resist corrosion. Are they more water resistant? Yes, but not waterproof. There are waterproof components like speakers available but plan on paying a premium price for them.
Wiring Configurations – When considering any of the below please remember to make sure your source, be it a HU or an amp, has the capability to provide enough watts to drive the number of speakers your planning on connecting. If it doesn’t you will never be satisfied with how your system sounds. As a result, you may be inclined to push your amp too far trying to make it sound the way you think it should and could damage it. This is another instance where an amps headroom comes into play.
Parallel – Parallel wiring two speakers together is done to reduce the load (resistance) the amplifier sees. This is accomplished by connecting the positive terminals of two speakers and the negative terminals of those same two speakers to a single channel on the amplifier as seen below. So two 8 ohm speakers become a 4 ohm load, two 4 ohm speakers become a 2 ohm load.
By wiring the speakers this way it allows you to connect two speakers where the impedance wouldn’t otherwise match the power/signal source you’re using. Again using the stock Harley head unit as an example. The HU is a 2 ohm source. Then you went out and purchased two sets of 4 ohm speakers to replace the stock ones and fill the rear pods you picked up. To keep from possibly doing harm to your HU, specifically the internal amplifier, you are going to need to wire them in parallel. Now if your bike has fade control you run into another problem. The 2 speakers on the right and two on the left are connected to a single output and your ability to fade the front and rears independently is gone. Starting to see why matching the impedance values can be important? A last note on wiring speakers in parallel. By decreasing the resistance to the signal it is capable of flowing more freely through the speakers voice coil. This will increase the volume of the speakers and is why it is often done in motorcycle application.
Series – Wiring your speakers in series has the opposite effect of wiring in parallel. It will increase the load seen by your source. This is done by connecting the positive terminal of one speaker to one of the positive output posts/wires on your source. Then connect the negative terminal of that speaker to the positive terminal of the next speaker and finally connect the negative terminal of the second speaker to the same channel's negative post on the source. Think of it as creating a loop as shown below.
Why would this need to be done? Say you bought an amp that was not 2 ohm stable and only rated for a 4 ohm load but you just couldn’t pass up the deal on a pair of speakers that you later discover are rated at 2 ohms. By wiring them in series you will increase the impedance to match the source. Two 2 ohm speakers wired in series become a 4 ohm load. Two 4 ohm speakers, an 8 ohm load..etc. While wiring in parallel and reducing resistance increased volume, wiring is series increases resistance and will lower the volume since the signal can't flow as freely.
Bridging An Amplifier – When you bridge an amp you are wiring it in such a way that you combine two channels into one. Essentially doubling the amount of power (watts) it produces. This is most often done when powering a single speaker like a subwoofer. There are a couple of things to pay attention to when bridging an amp. The first is whether the amp is designed to safely produce and handle the additional power from being bridged. If it is or not can be found in the spec sheet and those that are will often be marketed as bridgeable. Unlike the above wiring options, when bridging an amp you’re not looking to make sure your amp has enough power to drive your speakers but that it won’t produce so much power that you blow the speaker. Remember, in this configuration you’re DOUBLING the power being sent to the speaker. Again, this is done by combining two channels. Picture outputs of a 2 channel amp, almost always they will be next to each other. You have a left and a right channel and each one has its own positive and negative. It’ll be configured as some combination of + - - + or maybe + - + -. As can be seen below the positive side of one channel is connected to the positive terminal of the speaker and the negative terminal of that speaker is connected to the negative post of the other channel. Also shown in the picture is how this causes the impedance of the speaker to be cut in half as far as the amplifier is concerned.
One last thing. We enjoy helping with these things in any way we can and there are a bunch of very knowledgeable people here that share that knowledge freely. It is a great help to everyone if, when you post your question, you list what year and model of bike you have, a ballpark on what your budget is if any, what your short/long term audio goals are, and if you want to keep your FM reception.
Last edited by Little Mike; 01-31-2015 at 09:59 PM.
I thought about including a section about bridging and wiring in parallel but wanted to keep it basic for those just starting out. But, if enough people think it would be advantageous to have them in there I can certainly edit it and add those. What are everyone's thoughts?
I thought about including a section about bridging and wiring in parallel but wanted to keep it basic for those just starting out. But, if enough people think it would be advantageous to have them in there I can certainly edit it and add those. What are everyone's thoughts?
May as well have it all together in one spot. If they get lost in thought it's there for them to start over.
01-30-2015, 11:27 PM
Audio System FAQ's
