My initial choice of speaker for my combo, the Celestion G10D-25 turned out to be fairly disappointing. They were great for the quieter clean tones, and were fine when the amp was turned up beyond 8, but were very farty and flappy in the zone in between. Unfortunately this coincided with reasonable home practice volume with just the slight crunch I was after. After a search for alternatives and advice on Twitter from Steve Busby of BBZGuitars I settled on a pair of Eminence Legend 105’s. These are an American made 75 watt, 10″ speaker that would fit right in as replacements.
After a bit of searching round I found that the best price available was from Blue Aran. If you are looking for speaker or PA hardware then I’d recommend that you check them out. They have a great range of products and, certainly for the items I investigated, about the best value available in the UK. As promised these fitted straight into the combo without a hitch.
I was going to use a length of fairly high spec hi-fi speaker cable that I had available. With two speakers you have two potential wiring options; either in series or parallel.
To calculate the resulting overall impedance you use the following formulae:
- When wired in series,
OverallImpedance = ImpedanceOfSpeaker1 + ImpedanceOfSpeaker2; - When wired in parallel,
OverallImpedance = 1/((1/ImpedanceOfSpeaker1)+(1/ImpedanceOfSpeaker2));
The amp has 8 ohm and 16 ohm outputs. The speakers are each 8 ohm and were replacing the two Celestion G10D-25 speakers which were 16 ohm each. Two 16 ohm speakers were wired in parallel and were therefore 8 ohm when combined. The two new 8 ohm speakers would need to be wired in series to give 16 ohm.
I didn’t have any examples of series wiring to follow and nor could I find any advice on the internet. I found plenty of schematics, but no suggestion for the neatest way to actually wire them up, so I put a little thought into it myself and this is what I came up with.
click to enlarge
The cores of the cable run side-by-side together from the jack plug. As they pass the first speaker, one of the cables is cut and the end nearest the jack plug is soldered to the negative terminal. Thother side of the cut is soldered to the +ve terminal. Then on to the second speaker, where the cable from the +ve terminal of the first speaker is soldered to the -ve terminal of the second speaker. The uncut side of the cable is soldered to the +ve terminal of the second speaker and runs straight back to the jack plug. This creates the circuit with the speakers wired in series, with a minimal length of cable.
Note: The polarity of the whole thing is not relevant. The main thing to make sure is that the connection between the speakers goes from the +ve of one to the -ve of the other. If you don’t then the speakers will be wired out of phase (i.e. one will be moving forward at the same time as the other is moving back) which will result in a very thin sound, because the speakers are trying to cancel each other out.
Dave Mac's Window on the World 