2

OK, so I always experiment in my studio. Six amps, multiple speaker cabs, but I have a new question and need help. Most of my amps are 8 Ω output, but some have ext speaker jack in which they convert to 16 ohm when you plug in the ext.

For example, with my Black Magick, I'll often blend the stock speaker with a 57 (highly inefficient) Jensen 10" 8 Ω. It gives me a blend of the clear "sparkle" of the stock speaker and a very satisfying saturated speaker OD on the 10.

Recently- I found 4 of these 8 Ω cletron 6X9, 8 Ω speakers wired in parallel in a case from a 67 B-3 type organ in series, so I think that's 32 Ω impedence. I've heard from other guitarists that these speakers are superb for recording to get the early Joe Walsh/James Gang OD. How would I rewire these speakers to experiment w/o hurting any of my 8 Ω amps?


OK guys, Gator here. I took the diagram that Tetsujin used in his answer. I wired the speakers accordingly (each pair of speakers wired in series, then wired the two pairs in parallel). I tested the 2 output wires for resistance/impedence before I hooked them to a jack-- the meter showed almost exactly 8.1 ohms. I plugged and played with several 8 ohm amps and they sound great. And now I'm not worried about hurting an amp. I was surprised how much air they moved. There was no indication of the max output anywhere on these speakers, but they are really clear with more bass response than I would have expected. In addition, around 7-8 on a 25 watt amp, they sound fantastic with just the right amount of breakup. Thanks, for all the help from you guys. -- Gator

  • 1
    There's only usually a problem when the speaker/s have an impedance lower than the output impedance of an amp. The overall volume may well be sapped, but it won't harm the amp to feed into more Ohms. – Tim Aug 3 at 14:26
  • Tim, that's what I've read. But I've also read that 8 ohm into 32 is a bit much and can burn up your power tubes quicker. But that may be my only choice. – Gator Aug 3 at 14:37
  • 1
    From memory, pairs in parallel, then series the two pairs, brings it down to 8 Ohms. It's been a long time... – Tim Aug 3 at 14:40
  • 2
    A 32 ohm load on an amplifier that is expecting 8 can't burn up your power tubes quicker. This is BS. All you're losing is efficiency. Other way round might do it. – user207421 Aug 4 at 9:48
  • 2
    Four 8-ohm speakers in parallel is 2 ohms! – Jim L. Aug 4 at 18:32
8

What you have described is inaccurate. Four 8 ohm speakers wired in parallel would result in a 2 Ohm load not 32 Ohms. To achieve an ideal load for you amp, you'll need to wire 2 of the speakers in series, then wire the other two in series, and then wire the two pairs in parallel to give you a perfect match of 8 Ohms for your amplifier.

  • OP probably meant series. Wouldn't have thought mid/late '60s amps went below 4 Ohms output generally. – Tim Aug 3 at 14:57
  • I mean to say series. But, yes I get your idea which is what Tim suggested. Now, I guess I need to draw up a "routing map" to make sure I do this correctly. – Gator Aug 3 at 15:04
  • @Tim-As usual, you're probably correct. The only tube amps that I've ever repaired that had a 2 Ohm tap were commercial sound amps for factories and grocery stores. some of them had multiple taps for matching different loads. – skinny peacock Aug 3 at 15:04
  • 2
    @Tim If he meant series he shouldn't have said parallel. This is not something to be guessing about, or second-guessing. – user207421 Aug 4 at 9:49
  • 1
    @Tim I can say from experience thata multimeter is no good for measuring speaker impedances. All it can do is measure the DC resistance, which often differs significantly from the nameplate impedance (actual impedance varies massively with frequency anyway.) In addition, test leads can have a resistance of 2 ohms or more, which is a lot when measuring a 4 ohm speaker (though with a bit of arithmetic you can subtract this out.) – Level River St Aug 5 at 0:15
1

Wire two paralleled pairs in series and you arrive back at 8Ohms. It sounds like you did and measured 8.1 Ohms of DC resistance which is a bit high (I'd expect about 6 Ohms DC resistance for 8 Ohms of impedance) but nothing to worry about as long as all speakers show a reaction (if one is dead, the resulting impedance would be 12 Ohms which I would consider more likely to measure as 8 Ohms DC).

Just make sure that all speakers go in the same direction (you can use an 1.5V battery for checking) or you'll have an acoustic shortcircuit. Given the low efficiency of typical speakers, a mistake here will likely harm the resulting sound more than it will backfire on your equipment, but no need to be worse than necessary.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.