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Speakers swap 8 ohm or 4 ohm ?

mercuryman

mercuryman

Dec 4, 2017
7
0
#1
I have a vented 2 15 cab and i wonder about buying 2 8 ohm speaker who give 4 ohm total or buying 2 4 ohm speakers who give a 8 ohm cab .

I know the 4 ohm cab is easier to drive but witch one will sound better ?

I can choose Eminence or Celestion in 4 or 8 ohm .

Thank's
 
#3
mercuryman said:
I have a vented 2 15 cab and i wonder about buying 2 8 ohm speaker who give 4 ohm total or buying 2 4 ohm speakers who give a 8 ohm cab .

I know the 4 ohm cab is easier to drive but witch one will sound better ?

I can choose Eminence or Celestion in 4 or 8 ohm .

Thank's
Click to expand...
I think you are taking an overly simplistic view of this project.

Impedance alone has no bearing on how a cab will sound.
Nor does brand name.

There is a lot more to all of this than just picking a couple of speakers and bolting them into a box.
Are you familiar with Theile/Small speaker parameters?

What do you mean "the 4 ohm cab is easier to drive"?
An amp has to work harder to drive a 4 Ohm cab, at least a solid state amp does.
 
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#5
mercuryman said:
I am using a GK as pre amp and QSC MX1500a as power amp .

Need less power to drive in 4 ohm . Am i right ?
Click to expand...
No.
The speaker (Impedance) in use determines how much power the amp will deliver.
Think of the job of a speaker to be to convince the amp how hard it will work.
A 4 Ohm speaker will cause the amp to deliver more power than an 8 Ohm.

When you discuss how a speaker might need less power to drive it, you are looking at the efficiency of the speaker.
One of the parameters to consider is the speaker's SPL rating. (Sound Pressure Level).
But the impedance (Ohms) by itself is not a determining factor in how easy it is to drive a speaker.
 
#6
mercuryman said:
Need less power to drive in 4 ohm . Am i right ?
Click to expand...
It takes less voltage swing for the same output with 4 ohm, but it also takes more current. More current puts more demand on the amp, not less. You don't see it referred to with bass cabs, but some home stereo speakers are called difficult to drive, and it's because they are low impedance.
There is a lot more to all of this than just picking a couple of speakers and bolting them into a box.
Click to expand...
+1.
 
#7
For power matching with that amp, I would be looking at an 8 ohm cabinet. Iirc, that amp does 1500 watts RMS at 4 ohms bridged and about 900 watts at 8 ohms bridged. 900 watts is a safer and better match imo.

There were 2 versions of that amp, the earlier one may not have been rated for 4 ohms bridged. Also, there are parts that are no longer available for that amp (rail commutator pens) that often fail catastrophicly. Be very careful with your experiments.
 
#9
mercuryman said:
I have a vented 2 15 cab and i wonder about buying 2 8 ohm speaker who give 4 ohm total or buying 2 4 ohm speakers who give a 8 ohm cab .

I know the 4 ohm cab is easier to drive but witch one will sound better ?

I can choose Eminence or Celestion in 4 or 8 ohm .

Thank's
Click to expand...

What’s wrong with the drivers that are already in the cabinet?
 
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#11
mercuryman said:
They are finish and i dont want to recone . I was playing and they start to smell electric burn .....
Click to expand...
agedhorse said:
For power matching with that amp, I would be looking at an 8 ohm cabinet. Iirc, that amp does 1500 watts RMS at 4 ohms bridged and about 900 watts at 8 ohms bridged. 900 watts is a safer and better match imo.

There were 2 versions of that amp, the earlier one may not have been rated for 4 ohms bridged. Also, there are parts that are no longer available for that amp (rail commutator pens) that often fail catastrophicly. Be very careful with your experiments.
Click to expand...

All the more reason to keep your cab at 8, or even go to 16 Ohms.
If the speakers are smelling of an electrical burning smell, you are running too much power.
The smell would be the insulation of the voice coil wires burning.
You have exceeded the thermal power limits of those speakers.
They likely are compromised now.

Having two 15" speakers with a total load of 8 ohms will put a max of 450 watts on each one.
That's assuming clean audio. If you are driving into distortion, you can put even more power to the speakers.
As it is, 450 watts seems to me to be lot to ask of a single 15" driver.
And there is the question of what the speakers are actually rated to handle and is that rating in peak or RMS or what? If it's peak, for instance then they won't handle nearly as much power on a continual basis as you might think they will. Hence the burning smell.
 
#13
agedhorse said:
What does "finish" mean?

Why not recone? What's wrong with that?
Click to expand...
I think he has an issue with the country of origin. :woot:

On a serious note. If he has burned the coils, is a re-cone a good idea or just throwing good money after bad?
I really don't have a good handle on how bad the smell of burning speakers is for the future usability. Can they recover from something like that?
It seems like a pretty bad thing to me.
 

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