going from 8 ohms to 4 ohms without an extension cab..

[Bob Lee (QSC)]

Just because you would in theory double your power to the cab with another 8 ohm load in parallel to the existing one, that existing 8 ohm load is going to perform just the same as if you'd done nothing at all.

Actually, the power to the cab would not double, either in practice or in theory.

 

[bumperbass]

More speakers trump more watts any day, all other factors equal. Get another cab.

 

[Relsom]

It would if the dummy load were placed inside the cab

 

[Wasnex]

The Epifani D.I.S.T line can switch between 4 and 8 ohms.

As the guys are saying the difference won't give you more usable volume or better tone.

Adding a second cab would do both.

The D.I.S.T cabs achieve multiple impedance by using dual voice coil drivers. If the coils have equal efficiency (unlikely), switching from 8 to 4 ohms should yield 3db, but only if voltage is held constant (unlikely) (see post #7 and #18). I would expect some tonal changes due to the different loading of the output. Whether the changes are good or bad is subjective.

 

[gumtown]

Use a 8 ohm resistor in parallel with the speaker and sit a cup of coffee on it to keep your coffee hot during your live set.

options are:
a) add an extra 8 ohm cabinet
b) replace the 8 ohm speaker with a 4 ohm one
c) replace the amp with a higher powered one
d) use a 4:8 ohm impedance matching transformer (most wasteful of your $$$)

 

[Old Garage-Bander]

It would if the dummy load were placed inside the cab

Dummy in a cab. Isn't that like a self driving car?

 

[Relsom]

Dummy in a cab. Isn't that like a self driving car?
View attachment 2956910

I guess so, lol. I was only trying to make a point that adding an additional load in parallel isn't going to make that existing speaker sound any different, even though the amp will be driving twice as hard.

 

[MDBass]

I dont think it's that strange (and whatever happened to the "there is no such thing as a dumb question"). You can connect two 8 ohm speakers and end up with a 4 ohm load right?

I would think that in theory if you had a single 8 ohm speaker, there could be something that could be connected to that speaker in some manner to make a 4 ohm load (and no Im not talking about adding another speaker).

Just because you would in theory double your power to the cab with another 8 ohm load in parallel to the existing one, that existing 8 ohm load is going to perform just the same as if you'd done nothing at all.

This ^

The one cab you do have will still be getting the same amount of power, and the dummy load getting the other: your amp will simply be working harder for no reason.

 

[Ric5]

Is it possible?

If I have an 8 ohm cab, is there something I can put between the amp and the cabinet to make the amp think its actually on a 4 ohm load?

change the speaker or speakers

 

[InhumanResource]

Is it possible?

If I have an 8 ohm cab, is there something I can put between the amp and the cabinet to make the amp think its actually on a 4 ohm load?

Why?

 

[physics]

If you're trying to extract the maximum power(500 watts) from the amp, I would recommend going with a single 4 ohm cab that can handle the power or two 8 ohm cabs in parallel, each capable of handling at least 250 watts. Assuming that the amp's power section is designed to handle a reactive speaker+cabinet load, I would be concerned with the effect on the tone if you were to add a large resistance to the total output impedance.

Either way, I would estimate that you're only going to get about a 1.5 db gain in volume. That's not much of a difference and I would question whether it would be worth it.

 

[BogeyBass]

I think its been well covered

In a single driver application even very expensive drivers can hardly handle that much power. Even at 8ohms your amplifier exceeds the actual low frequency capability of the single driver.

Getting " more watts" doesnt always equal " more louder" or more sound pressure.

Eventually it comes down to you just need to increase the sensitivity of the system to get more sound pressure. Which is simply moving more air with more speakers.

Most efficient way of doing this is to simply add 2x or 4x 6x 8x etc etc of the same exact driver. Basically double up.

If your using a single 1x15 then add another matching 1x15

Single 2x10 add another matching 2x10

4x10 add another 4x10

Everytime you double the effective speaker area you add 3dB of sensitivity

Likewise as far as power or watts you have to double the power to gain 3dB

So its much more effective to gain sound pressure with more speaker.

Likewise speaker ratings are very misleading and mainly based on thermal capabilitys not actual power handling before distortion or fart out as we call it.

Say you have a mystical magical "400watt" cabinet. Doesnt mean 400 watts before distortion. At frequencies below 100hz the power rating could be half that even 30% of that 400watts when it reaches distortion

 

[Timpanogos Slim]

Tube (and very early "transistorized") amps have separate outputs for different cabinet impedances because they have transformer coupled outputs - and because with transformer coupled outputs the impedance of the load has a direct and meaningful impact on the behavior of the output stage.

Modern (since the 70's) solid state amps just dump power directly through the jacks with no transformer coupling. The impact that the load impedance has is more about whether the output devices can service the load. A lot of transistor amps can't handle a 4-ohm load gracefully. The vast majority of them can't handle a 2-ohm load at all. But given a 16-ohm load, for example, they behave just like they would with an 8-ohm load.

If you have two 8-ohm cabinets and a 4-ohm compatible amp, hook the cabinets up in parallel and see if you like it.

If you are chasing some sort of distortion characteristic where the amp makes a desired kind of distortion when loaded with 4 ohms and you only have an 8 ohm cabinet, you could hook up an 8 ohm dummy load in parallel with the cabinet for a 4 ohm load but it won't be louder, you'll just be making more heat and the amp will be acting like it does with a 4 ohm load. Be aware that power ratings for dummy loads are "right before bursting into flames" ratings. If you seek to dump 50 watts continuous into a dummy load, use a 100w rated dummy load.

 

[theculprit]

This ^

The one cab you do have will still be getting the same amount of power, and the dummy load getting the other: your amp will simply be working harder for no reason.

What about a situation where you have a bridgeable stereo power amp? Here is a hypothetical.... 8ohm cab rated at 1,000 watts with a power amp rated at 500w per channel at 8 ohm.... 1500w bridged at 8 0hm... or 2000w bridged at 4 ohms. Ignoring the debate about under or overpowering speakers, is this a situation a dummy load would allow the best use of the bridged amp? Could you not show the bridged amp a 4 ohm load, and 1/2 the power (1000w) would go to the 1000w cab, and the other half goes somewhere (dummy load land)?

 

[Downunderwonder]

If elephants could be taught to dance in high heels would they look graceful?

 

[theculprit]

If elephants could be taught to dance in high heels would they look graceful?

Ha! Point taken. But extracting the proper wattage from a bridgeable power amp which is capable, sounds a hell of a lot more graceful than a fancy dancing elephant.... Assuming the cost or weight of the device needed to make it happen isn't illogical.

 

[Downunderwonder]

Ha! Point taken. But extracting the proper wattage from a bridgeable power amp which is capable, sounds a hell of a lot more graceful than a fancy dancing elephant.... Assuming the cost or weight of the device needed to make it happen isn't illogical.

your hypothetical is illogical since the bridged output drives the cab into the afterlife.

 

[theculprit]

your hypothetical is illogical since the bridged output drives the cab into the afterlife.

How so? 2000 watts. 1000 watts go to the 1000 watt 8 ohm cab, and the other 1000 watts go to the hypothetical 8 ohm dummy load (if there is such a thing that can do this).

 

[gumtown]

1000 watt dummy load would be expensive and hard to find. It would also have to dissapate 1000 watts of heat, sitting next to your cabinet, might start a fire.
Burning watts to gain watts doesnt make sense.

 

[Kevin1960]

The device, which would be a very large resistance of some kind, capable of handing half the power of your amp is called, in more than one electronic dicipline one, a dummy load. I deal with dummy loads often in my work.

Here is what happens. I'll use a well known popular amp in my example. The Rumble 500.
This amp is rated at 350 watts with an 8 Ohm load, and 500 watts with a 4 Ohm load.
To keep using your 8 Ohm cab and get 500 watts would require a special resistance of 8 Ohms wired in parallel with your cab, just as you would wire two 8 Ohm cabs.

When you wire two 8s in parallel, half the amp's power goes to each. So your dummy load has to handle half of the 500 watts, or 250 watts and your cab gets the other half.

So instead of getting 350 watts delivered to one 8 Ohm cab, without the dummy load, you now only get 250 watts into the one cab. The other half of your 500 watts just gets turn into heat by the dummy load.

So if you're going for a power reduction then this is a way to do it.

BTW, the resistance you use needs to be rather special. You need a non inductive resistor and to handle 250 watts in a practical manner, you need to double the power handling capacity of the resistor.

So Google yourself up a 500 watt, 8 ohm, non- inductive resistor, and there ya go.

Be aware that in addition to the loss of power, there are other more dynamic reasons that a resistor will not act like a speaker.

This is reality. Ohms law will not change unless you are in an alternate reality.