All the audio that comes out of your speaker system is what we call analogue audio, and analogue audio is simply an electrical signal. The intensity (voltage) of this electrical signal is what we call the Audio Level. But not all devices can work with all Audio Levels, and mixing them up can cause big problems, putting your hardware at risk and degrading your sound quality.
There are three main Audio Levels that are worth knowing about:
The determining factor here is the voltage which runs them. Speaking into a microphone only produces a few thousandths of a volt, but loudspeakers need a whole bunch of volts to make their big magnets move.
Mic Level is measured in millivolts, and usually comes in around the 1mV to 100mV range, depending largely on whether you're speaking at a wedding or screaming at a rock concert. As you can imagine, this isn't a whole lot of power, and so microphones need to be fed into Pre-Amps or Amplifiers with special Microphone inputs which boost it up to another Audio Level.
Turntables and instrument pickups which don't have built-in amplifiers usually fall into the same voltage range as microphones, and also require preamps or dedicated inputs to amplify the signal.
Line Level is measured in volts, usually hitting between 0.5V and 1V. Home Theatres abound with Line Level connections; a 2RCA stereo connection between your DVD Player and Receiver is Line Level. The 3.5mm cable between your iPod and the Aux input on your speaker system is also line level. Same goes for Media Centres, PCs, Tablets, CD Players - you name it!
Earbuds and headphones cleverly use Line Level power to drive very small speakers. They sound loud because they're placed right up next to your ears, but sending that level of power directly to a desktop or home theatre speaker won't give it enough juice to move their much larger magnets.
Speaker Level is also measured in volts, typically using over 10V. The physical size and power handling of the speaker, combined with the volume set by the output, can push this number up to 100V or more. Big speakers have large, stiff components that need a lot of juice to move.
Because of the higher voltage and wattage used by speakers, we connect them up using heavy-gauge, bare-wire speaker cable. This allows for more power to go through cleanly without overheating the wire.
At Cable Chick, we're often asked for a solution that allows the joining of bare-wire or banana plugs to RCA sockets (or vice-versa). The problem is that if you're feeding high voltage Speaker Level audio into a device that is expecting Line Level (eg: a powered speaker with its own amplifier) you're running the risk of overloading the device and causing permanent, irreperable damage to your equipment. Additionally, even if the receiving device can handle the power, the sound quality is likely to suffer dramatically as the amp is overloaded.
This also applies in situations that don't use bare-wire! If you're feeding Line Level into a microphone Pre-Amp, or connecting a Line Level RCA into a socket on a receiver designed for turntables - things are not going to go well.
You'll also run into trouble if you try connecting a Line Level input to the microphone jack on a PC or an iPod, etc. At best, you get very bad audio, and at worst you can fry a circuit board component.
Conversely, connecting Line Level RCA to bare-wire speakers can lead to bad audio, low volume and overheated speaker components, as some large speakers need the airflow from cone movement to keep themselves cool. Prolonged use under these conditions is bad for the speaker.
As much as possible, always try to join components together in a manner that keeps Line Level outputs connected to Line Level inputs, mics to Mic Level inputs and bare-wire speaker outputs to speakers that use bare-wire connections.
This isn't always possible if you're working with a variety of unmatched components, so in the cases where you don't have the right gear for the job, you may need to look at slotting in a Pre-Amp or an Attenuator, or bypassing the issue altogether (see below).
Pre-Amps take a lower voltage and boost it up to another level. A pre-amp on a P.A. speaker system may step Mic Level straight up to Speaker Level for a direct connection, but a Pre-Amp for a turntable may just bump it up to Line Level so a home theatre receiver can do its thing. dB Gain is a whole different topic, though, so we won't go into it here.
Attenuators, usually in the form of a DI Unit, does the opposite - taking a Line Level signal and reducing the voltage to suit a Mic Level input. You typically see these used in recording studios or for electric instruments feeding into mixing decks. There's little call for them in a Home Theatre, but if you need to get a Line Level signal into a device that only accepts Microphone Level input, an attenuator will be the device to look for.
This common problem is usually the result of upgrading just one component of your home theatre without checking for its compatibility with the remaining devices. It happens a lot, and the fix can be tricky depending on the source device. Basically, you have to go back to a point before the amplifier to avoid the Speaker Level output. In both of the examples below, you'll end up with two volume controls - one on the speakers, and another on the amp.
The easy solution is when your source device has 2RCA or Stereo Audio Jack output at Line Level. You simply use a pair of RCA splitters before the Amp, sending the Line Level RCA signals to both the Speakers and the Amp simultaneously:
The more difficult solution is when your source device only has SPDIF Digital output. In that case, you will need to convert back to Analogue with a Digital to Analogue Converter before splitting the signal with RCA as before:
Alternatively, this solution can be adapted to use a TOSLINK splitter instead of RCA splitters.
If you're still not sure about how to hook up your home theatre and would like some help, please contact us.