two cabs 8ohm and 4 ohms

[tkelly150]

okay i have a eden highwayman head and i have a 8 ohms cab and a 4 ohms cab can i hook both cabs up at the same time?   

[chris_b]

Only if the amp can handle 2.67 ohms or 2 ohms. Otherwise, no.

[tkelly150]

its a stereo head can I one side 8 and the other 4 ?

[tkelly150]

I've alway just used 1 /4/10 cab got the 8 ohms one for free or just get another head?

 

[paul_5]

You could use the separate left and right speaker outs - one for each speaker, but as Chris has already said, running them in parallel (two speakers from the same output) isn't safe to do. 

 

You'll notice that your 4Ω cab is MUCH louder than the 8Ω, as it allows the full 250W to be delivered to the cab, but it's possible.

 

Another way to do it would be to run it in Bridged mode (8Ω minimum) with the cabs wired in series (giving you a 12Ω load), but you'd need a specialist cable to do that as it would need to run:

 

Amp hot ->8Ω speaker hot, 8Ω speaker ground -> 4Ω speaker hot, 4Ω speaker ground -> Amp ground.

Edited May 19, 2023 by paul_5

[paul_5]

2 minutes ago, tkelly150 said:

its a stereo head can I one side 8 and the other 4 ?

If it's stereo then yes - I run a stereo PA amp with separate 8Ω and 4Ω cabs.

[tkelly150]

Thank you I'll give it a try. 

[itu]

50 minutes ago, paul_5 said:

You'll notice that your 4Ω cab is MUCH louder than the 8Ω, as it allows the full 250W to be delivered to the cab, but it's possible.

Really... we are talking about few decibels... if the 4 ohm version is much more sensitive, I'd buy that. Otherwise not.

 

Sometimes an 8 ohm impedance speaker may be louder than a 4 ohm counterpart.

[paul_5]

15 minutes ago, itu said:

Really... we are talking about few decibels... if the 4 ohm version is much more sensitive, I'd buy that. Otherwise not.

 

Sometimes an 8 ohm impedance speaker may be louder than a 4 ohm counterpart.

Fair point, it’s just my experience with my cabs. The 4ohm cab IS more sensitive though.

[Bill Fitzmaurice]

2 minutes ago, itu said:

Sometimes an 8 ohm impedance speaker may be louder than a 4 ohm counterpart.

Quite right. Impedance alone doesn't define how loud a cab will go. It has nothing to do with power. The reason a 4 ohm speaker will go louder than an identical 8 ohm speaker is excursion. An amp at the same settings will deliver the same voltage into both, but the excursion of the 4 ohm speaker will be longer, so it will be louder. The fly in the ointment is if the speakers are identical other than impedance. They almost never are. If you compare the T/S specs on the Eminence Kappa 15A and 15C, one of the very few drivers made in 4 and 8 ohm versions, the rest of the specs aren't the same. Even the DCR isn't doubled from the 4 ohm to 8 ohm versions, they're 3.68 and 5.22 ohms respectively. Most significantly, the xmax of the 4 ohm is 2.44mm, that of the 8ohm version 4mm. That being the case the 8 ohm can go significantly louder than the 4 ohm.

[Downunderwonder]

Without going to check myself, be absolutely sure it's two amplifiers in one head. I have seen a lot of people think two speakons at the back = stereo. They might even have dual preamp channels that switch and blend but only one volume knob = mono amp.

[BassmanPaul]

A thought that struck me was are the two cabinets working with the same polarity. If one is 'pushing' whilst the other is 'pulling' they are going to fight each other all night long, and that's not a cue for a song!

[Bill Fitzmaurice]

They should be the same polarity, the standard is for the + input connector to be wired to the + driver lugs, but it's not guaranteed. Once upon a time, for reasons unknown, JBL had the black lug positive, the red lug negative, the opposite of convention.

[BassmanPaul]

I remember that from my JBL days. I still love the brand though I don't use them to play through any more.

[Baloney Balderdash]

On 19/05/2023 at 19:22, paul_5 said:

You could use the separate left and right speaker outs - one for each speaker, but as Chris has already said, running them in parallel (two speakers from the same output) isn't safe to do. 

 

You'll notice that your 4Ω cab is MUCH louder than the 8Ω, as it allows the full 250W to be delivered to the cab, but it's possible.

 

Another way to do it would be to run it in Bridged mode (8Ω minimum) with the cabs wired in series (giving you a 12Ω load), but you'd need a specialist cable to do that as it would need to run:

 

Amp hot ->8Ω speaker hot, 8Ω speaker ground -> 4Ω speaker hot, 4Ω speaker ground -> Amp ground.

You can get a small box especially made for combining speaker in either series or parallel to one amp  speaker/cab output, like this one, the Palmer CAB M Merger :

Doesn't cost much either, a mere 26£ : https://www.thomann.de/gb/palmer_cab_m_merger.htm

 

Edited May 30, 2023 by Baloney Balderdash

[BassmanPaul]

IMO those little boxes are not safe to use with a high power amplifier. The 1/4" phone sockets are simply not up to the current/voltage needed. They were originally designed for telephone switchboards operating at 48V DC and a couple of hundred milliamps. That's far below what a typical bass amp puts out.

 

if they had used SpeakOns I would have no objections.