4 speakers on one amp channel

Hello all, Sorry for all the silly questions lately, this may be my last one. I have an amp (GTD 750) 1500 watts @ 4 ohms per channel. (not sure if i belive it, but its working good for me). Right now i run 2 mth 30's a side and turn it to about 3/4 power. Plenty loud (too much sometime) and it treats the drivers well.
My problem is i need to run a pair of 18's and i dont have the funds for a new amp.

My question is: Can i run four cabs in series- parallell on one side? Or would i get better respnse from running 2 parallell and leaving two home. From what i understand the latter would be right. Any help or a smack to the head would be helpful.
Mike

First question, Would all you speakers be 8 ohms each and if you used 4 speakers would they have the same signal running through them?

Tony- I would like to run the 2 18s on one channel (8 ohm each whichmakes 4). And the four mth30 (8 ohm each) on the other channel. If I wire the 4 mth is series parallel, will I get more output than running two parallel?
Thanks
Mike

Four 8 ohm speakers in series parallel will end up at 8 ohms, two speakers will end up at 4. If your amp is stable at 2 ohms then you could chance running four cabs, although the combination will dip below 2 ohms on occasion.

Thanks sir! Does running in series parallel put the speakers out of phase or anything like that?

No, everything will be in phase.

Tony,
Could you simply explain why it may sometimes drop below 2 ohms (not an electrical expert), and what are the dangers/consequences involved with running two ohms? Burning out drivers? amps?
Thanks,
Mike

MAutopsy wrote: Tony,
Could you simply explain why it may sometimes drop below 2 ohms (not an electrical expert), and what are the dangers/consequences involved with running two ohms? Burning out drivers? amps?
Thanks,
Mike

if u use 2ohms we called fully loaded to amp it is not burning your speaker but over heat your amp. if you use it more than 3 hours sometime your amp burn then try to reduce heat using external extra cooling fan. if you use 4 8ohms speaker in parallel mode you can load 2ohms if use 3/4 volume ur 8ohms speaker minimum handling watt may be 600w if is not ur speaker burning percentage may be increasing

GTDaudio GTD-750 Power Amp Review.
Specs
◆ 1500 Watts RMS @ 8 Ohm Bridged Mono
◆ 2 X 2250 Watts RMS @ 2 Ohms
◆ 2 X 1250 Watts RMS @ 4 Ohms
◆ 2 X 750 Watts RMS @ 8 Ohms

MAutopsy wrote: Tony,
Could you simply explain why it may sometimes drop below 2 ohms (not an electrical expert), and what are the dangers/consequences involved with running two ohms? Burning out drivers? amps?
Thanks,
Mike

If you look at an impedance curve, The speaker gets its measured figure from the results. This is one reason why it's called nominal Impedance. With an 8 ohm speaker you will notice that the curve may drop to 7.5 ohms, so as you can see 4 of these together will not be 2 ohms. This is why it can be touch and go with some amps with this configuration. Only good strong amps will survive this. That's how I have always seen it anyway.
One other thing I have just thought of. This low impedance will only occur at the tuned frequency, and as you know, impedance goes up with frequency, so the amp is only in the danger zone at a given frequency.

With the added resistance of the cables and plenty of cold air I should be safe then?