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AUDIO FAQ's
Q: How do I wire a mixer with a balanced (3 pin) XLR output on it to my amplifier which only has unbalanced (phono or jack) inputs on it?
A: There's two ways of doing this, but we'll keep it simple and tell you the method which is the most reliable. First, make sure the wire you're going to use is the screened type (metal braiding wrapped around an inner signal wire). Next, solder the unbalanced phono or jack plug onto one end - the screen goes to the outer or larger terminal. Solder the other end of the screen to pin 1 on the XLR connector. Next, solder the centre signal wire to pin 2 on the XLR. Thirdly and last, solder a small (1/4 watt will do) 47 kilohm resistor between pins 1 & 3 on the XLR. You can sometimes get away with not doing this, but for reliability & sound quality's sake, it's worth it. Note: The colour code for the resistor is yellow violet orange + either gold or silver.
Q: Can I wire a mixer with only phono ouputs on it into an amplifier which only has balanced XLR sockets on it?
A: Yes - quite easily. All you need to do is first wire your phono plug onto one end of your signal cable (see above for description of this). Next, connect the screen at the other end to pins 1 & 3 of the XLR which will go into the amp. Finally, connect the cantre signal wire to pin 2. This isn't a technically perfect method of doing things, but it will work fine!
Q: You've been going on about balanced XLR's... Both my amplifier and mixer have these connectors on. Is there any advantage in using them? The cables seem more expensive - am I just wasting money or is it worth the extra?
A: Yes, there are advantages in using balanced connectors to link your equipment together. The main one is less likelihood of interference or hum, especially when using longer cables. Also, signal levels are slightly higher within balanced systems, which can help with driving a professional power amplifier properly. Thirdly, the cables themselves are usually physically stronger, so less likely to break internally. A reasonable quality XLR male to XLR female cable of about 3 metres should cost about £10.00. We can make you any audio cable you need - including XLR's, using various makes of connectors and cable, depending on your requirements. Give us a call!
Q: Can I run more than one amplifier from my mixer at the same time?
A: Yes. There's two or three methods of doing this one. If your mixer has more than one pair of outputs on it, you can run an amplifier from each pair. If one pair is balanced and the other isn't, you'll need to refer to the notes above on wiring non-balanced and balanced connectors together. Another method is to 'daisy chain' the amplifiers. Run the output from the mixer (either balanced or unbalanced) into one amplifier. Then, use the parallel inputs on the first amplifier to run into the second one. There's usually two inputs / link outs on a power amplifier per channel. You can link from balanced to unbalanced, but again, you'll need to refer to the advice above on this. Thirdly, the most unattractive method of doing it! Make up a splitter cable or box, which basically splits the output from the mixer into two. One pair of cables feeds one amplifier and the other pair feeds the second amp. Doesn't look very pretty, but works. One note about this - NEVER feed the input of an amplifier from the speaker output of another amp. This will result in two dead amplifiers (one at the very least) and can be expensive!
Q: What's a crossover and how would I go about using one?
A: There's two different types of crossover, active and passive. PASSIVE crossovers are usually built into speaker cabinets and consist of a load of components on a board, or sometimes a simple capacitor on cheaper cabs. Active crossovers are pieces of kit which are mains powered and are usually rack mounted. Both do basically the same job, but in different ways. All crossovers are filters. They direct the parts of the sound to the speakers which reproduce them the best; bass to the bass speakers, mid to the mid speakers, etc. No speaker can do all frequencies well - this is why we use crossovers. In your average speaker cabinet, consisting of, say, a 15" bass driver and a tweeter, the crossover is of the two-way type. It directs the lower frequencies to the bass driver and the higher stuff to the tweeter. This allows the bass driver to get on with producing bass without having to worry about the treble side of things, giving better sound. On some multi - box systems, each cab will have it's own passive crossover in, so if you feed a full range signal into a bass bin, you only get bass out - the rest of the signal is filtered out by the crossover. Same with the mid/top cabs - the bass is all filtered out, so you just get mid/top out of them. when used as a full system, the results from these can be very good.
ACTIVE crossovers do the same thing as passive crossovers, but they sit in the low level signal path between the mixer and the amplifiers instead of being in the speakers. Basically, the mixer feeds a full range signal in to the crossover and the crossover then sends the various selected frequencies to different amplifiers, so one amp does the bass, one does the mid, etc etc. Active crossovers are sometimes only two way (bass & mid/top) but are equally likely to be more complicated types, with variable crossover frequencies and more outputs. This is great if you want to 'tweak' a system for maximum sound output & quality, as you can fine tune the crossover to send the exact frequencies you want to each set of speakers. A more expensive way of doing things, but the way to go for serious sound. One of our bigger rigs uses a six way crossover system, using both active and passive filters.
Q: Can I run more than two speakers off my amplifier? It's only got two speaker outputs.
A: Yes and no. Look on the back of the amplifier and see what the minimum speaker impedance ('Ohmage') is. It's usually 4 Ohms on modern amplifiers. If this is the case, you can run two 8 Ohm speakers off each side of the amplifier, as two 8 Ohms speakers in parallel makes 4 Ohms. You can either run four speaker cables from the back of the amplifier or link the speakers by running a cable from the back of one cabinet into a second one. This is electrically the same method. Doubling the number of speakers to two per channel has it's advantages... If your amplifier is 500 watts per channel into 4 Ohms, if you've only got one 8 Ohms speaker on each channel, you're not getting the full power from your amplifier. Adding another similar speaker allows the amp to run at full power and also gives you better sound dispersal. Without going into dB's etc here, add two speakers and you'll probably notice a difference in sound level as well.
Q: I've seen loads of different types of connector used for speakers, mixers etc. Which pins do what?
A: Right - we'll start with jack plugs. On a mono jack (one black ring) the tip and the small connector inside are [+] and the sleeve and the big connector are [-]. On Stereo Jacks (two black rings) the tip is [+], the sleeve is Earth and the Ring (between the two black rings) is [-] signal. These are sometimes also known as T.R.S. plugs. On XLR's, Pin 1 is Earth, Pin 2 is [+] Signal and Pin 3 is [-] Signal (Usually, some equipment can be different, but is usually marked if it is!) Phono Connectors are the same as mono jacks. Speakon connectors (4 pole type) has four connectors. There are two [-] and two [+] terminal, which are numbered. If the equipment is only using two pins, it'll be 1[+] and 1[-]. Four pins are usually used when a single cabinet has two inputs - one for the bass amp and one for the mid/top amp. (See Crossover Section). These will probably be the only types of connector you'll come across on modern sound equipment.
Q: Can I run an extra CD player into the spare 'phono' input on my mixer?
A: No - not without an adaptor. The phono channels are much more sensitive than the CD or line channels and putting the high output from a CD player, tape deck or other similar equipment into one of these inputs leads to severe distortion and a possible risk of damage. You can buy a unit which will let you do this however. if you can't get one locally, call us - we stock them.
Q: My amplifier has 'peak' lights on it. Often when I'm playing, these lights flash. Is this good or bad? What do the lights mean exactly?
A: If the lights flash every now and then, this is acceptable. If, however, they flash on and off most of the time, you're driving the amp too hard and risk damaging your speakers. Turn the input level down slightly. This can also happen if the amp isn't loaded enough - i.e. if the amplifier is capable of 4 Ohm working but is only loaded down to 8 Ohms. Either add another pair of 8 Ohm speakers or use 4 Ohm cabinets. See above bit on speakers for more info.
Q: I keep hearing different stories about the wattage of speakers and amplifiers. How should I match speakers to an amplifier? Do they need to be rated higher than the amp? How do I know if I'm risking damaging either?
A: For simplicity, if an amplifier is rated at 500 Watts RMS, you should try to match your speakers as near as you can to 500 Watts RMS. A bit of 'headroom' on an amplifier doesn't go amiss though - a few extra watts lets the amp run easier and cooler. Ideally, if your amplifier's rated power is around a third greater RMS than your speakers, this is about right. Make sure that you're in control of the gain controls though! Note the use of RMS - ignore any other ratings such as music power, peak music power, PMPO etc. These are all misleading and have almost no real value. Do remember that if your amp is rated at, say, 500 Watts at 4 ohms, you will get about half that power from an 8 ohm speaker. Don't think that this will be half as loud - it won't. You'll probably notice little diffence between 8 Ohm and 4 ohm speakers, except your amp won't run as hot and will probably last longer as a result. Also, did you know it's possible to damage a speaker by using too small an amplifier? Running a 500 watt speaker off a 100 watt amplifier makes the amp struggle. This causes the amp to put out signals which can damage your speakers. It's possible to damage a 500 watt speaker with a 100 watt amplifier!! Remember - to double the perceived volume of a system, you need to increase the wattage by a factor of ten. So, if you have a 100 watt system and you want to double the volume, you'll need about 1000 watts to do it! Also, when looking at speakers, remember we're aiming to move air here - so the bigger the cone area the better, especially for bass applications. Also, look at the dB/W/M rating - this is the efficiency of the speaker. Some speakers will push out as much volume at 50 watts as some others do at 250. Think of those little car speakers you see rated at 600 watts... Great - you push 600 watts into them and hardly anything comes out! They're inefficient and just waste the power going in as heat, which, of course, you can't hear! So, buy speakers which match the rated output power of your amplifier, are efficient and have a nice big bass driver and you won't go far wrong!
Q: My system works great when I'm using it on it's own, but when I plug into the system which is installed in a local pub I regularly play, there's a background hum. How do I get around this?
A: This is what's known as a 'hum loop' and it can happen when you link pieces of equipment together which have their own earth connections. Never be tempted to remove a safety earth connection from any equipment - this is very dangerous and can kill should a fault develop. What you need to do is look for 'ground lift' switches on either your, or the pub's equipment. switching these on or off will usually help, by isolating the signal ground. If all else fails, try removing the earth from the signal wire which links your gear to the pubs system. Ideally, you can use a stereo DI box, which usually uses transformers to maintain the signal, but which has the 'ground lift' option built in.
Q: I have a pair of bass bins which are 4 Ohms. I also have a pair of mid/tops which are 4 Ohms. The bass bins have a passive crossover in them to run the tops from. I've been told that as the bass bins are 4 Ohms and the tops are running via the internal crossover on the bins, the amplifier will still 'see' 4 Ohms - is this right? Am I safe to use a 4 Ohm capable amplifier?
A: This myth that if you run a pair of 4 Ohm tops via a passive crossover in a pair of 4 Ohm bins you still get 4 Ohms at the amp is WRONG!!!!!
Where this comes from is that if you hook this combination up and stick a multimeter across the input, it still reads 4 Ohms whether the tops are connected or not.
This is because the internal crossovers in the bins have a capacitor (or two!) to feed the top cabs with just the higher frequencies, allowing the bins to do the bass side of things.
Now...
When you check a circuit with a multimeter, it uses DC to do the test, via a battery.
But, with speakers systems we're not USING DC so the readings given by the multimeter are irrelevant as the capacitors in the crossover don't pass DC - only AC as present in the audio signal!
We're talking impedance here, which is the AC equivalent of DC (DC is given as resistance and is what can be measured by the multimeter).
So - you hook your top cabs up to your bins and the meter says 4 Ohms. All well and good. Not so.
At certain frequencies, the load presented to the amplifer will indeed be 4 Ohms. But at other frequencies, the load with this combination can drop momentarily to 1 Ohm OR LESS.
Even with a standard speaker setup using one 8 Ohm speaker, the impedance can drop below 4 Ohms with certain programme material so as you can see, using a 4 Ohm top cab and a 4 Ohm bin leaves you with absolutely NO safety margin, even using an amplifier which is 2 Ohm capable, which few truly are.
With this speaker combination, the way to go would be two amplifier matched to the speakers and an active crossover to drive them. More power, better sound and greater reliability.
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CORPORATE FUNCTIONS, WEDDINGS, DISCO, BIRTHDAY PARTIES, CELEBRATIONS,
CORPORATE FUNCTIONS, WEDDINGS, DISCO, BIRTHDAY, CELEBRATIONS
