Series or parallel speakers?

[Tractorfan]

Hi,
I often do the sound system for a quiz night organised by local ex-pats and, up until now, I've used a Leak Delta 30 stereo amp which works fine.
However, this time I've decided to use a transistorised mono guitar/PA amp which has an 8 ohm output, according to the rear panel.
I want to connect two 8 ohm speaker cabinets and I'm wondering what would be the preferred method of connection; series or parallel?
It has two speaker jacks in parallel, but I have fitted a pair of 2 amp BS 546 sockets as well for my convenience (I have more 2 amp plugs than 1/4" jacks!)
However, I'm assuming that it would be happier with a 16 ohms load, rather than 4 ohms, or does it not make much practical difference? apart from less volume?
Cheers, Pete.

[Nuvistor]

I would go for the 16ohm, speakers in phase, you could be in trouble if the amp gives up when reading out the answers.

[Tractorfan]

Hi,
Thank you, Frank. I was thinking along the same lines and was curious to canvass opinion among our learned members. I don't think it'll make a lot of practical difference to the output.
If it's going to pack up, it's guaranteed to happen during the music round, or the answers, as you say. So, series it is!
Cheers, Pete.

[Lucien Nunes]

Transistor amps will work happily into a load impedance greater than their optimum, albeit with reduced maximum output power before clipping. Connecting a lower impedance can overload the output stage well below clipping level, and potentially cause damage depending on how sophisticated the protection is.

Valve amps are more tolerant of incorrect load impedance and unlikely to be damaged under any normal conditions (except open-circuit, which can cause flashovers.) The maximum available power will usually be reduced due to the mismatch and the distortion will change in some way, although exactly what occurs will depend on whether the OP TX ratio and operating point were intended to produce maximum power or minimum distortion in the first place.

[Backtoreality]

As a mobile disco DJ in the late 1970's I had two 2 x 12 speaker cabinets which had two Fane 16 ohm Disco 60 speakers in each. They were wired in series to give 32 ohms impedance. The power output may have been reduced but the volume was always more than adequate, even in some really big venues, and the 2N3773 output transistors on the FAL Stereo amplifier never got more than warm to the touch.
David

[Skywave]

Originally Posted by Tractorfan

. . . . I've decided to use a transistorised mono guitar/PA amp which has an 8 ohm output, according to the rear panel.

Just for reference: that amp. does not have an "8 Ω output". What the rear panel statement should say - or is trying to tell you - is that the amp. requires a 'speaker of 8 Ω impedance. The actual O/P impedance of the amp. will be a lot less than 8 Ω.

Al.