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4 ohm amp into 8 ohm cab- will I blow the speaker?

#21
Never crank any amp - it'll distort and do things that can damage speakers, whatever their rating.

8 ohm cab is perfectly safe (no less so than a 4 ohm cab...), but won't be as loud as a 4 ohm cab probably on the same amp.

Simple answer, skipping the details. Hopefully that's a helpful summary :-)
 
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#23
Jordy4strings said:
I have a 4 ohm amp 500 watts and a 8 ohm cab 300 watts. If I crank the amp will I blow the speaker or does the difference in impedance mean I will only get half of the wattage going from amp to speaker, thus making it impossible to ruin the cab?

Thanks in advance for any help you can give me. Have a great day.
Jordy
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Assuming the amp is solid state. Assuming the minimum load for the amp is 4 ohms. Most likely the amp will deliver about 350 watts into an 8 ohm load, not the 250 watts that theory says. (I say this based on power ratings of real amps rather than a strict application of P=IE).

So 350 watts of power being pushed into a speaker rated to handle 300? If you don't crank it and don't boost the lows you would probably be fine. If you really are trying to get every last ounce of power out of the amp and/or you decide that you need to crank the lows then all bets are off.
 
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#25
mmbongo said:
Thus the importance of specifying the exact amp you're using...which you still have not done :)

Saying you have a '4 ohm amp' is the confusing part, as that only matters if you have a tube amp.
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(Unless someones using some speaker combination that's less than the "4 ohms".)


OP, if your amp is 500 watts @ 4 ohms, you should have zero issues running an 8 Ohm 300 watt cabinet. :bassist:

Now, you haven't stated which cab it is, so I will say (as always) use caution and your ears. If you find that you have to crank your volume way up to be heard, then you should get a 2nd "matching" 8 ohm cabinet to achieve more volume.

As was stated, its easier for the gang to help if you post exactly what your equipment is that you are asking for advice on. :thumbsup:

T$
 
#27
Jordy4strings said:
I have a 4 ohm amp 500 watts and a 8 ohm cab 300 watts. If I crank the amp will I blow the speaker or does the difference in impedance mean I will only get half of the wattage going from amp to speaker, thus making it impossible to ruin the cab?

Thanks in advance for any help you can give me. Have a great day.
Jordy
Click to expand...

Your amp will produce a little over half it’s rated power at 8ohms.

The wattage rating on a cab is thermal, meaning how many watts it can take before components literally start to melt and burn.

You can still damage a cab via mechanical over excursion (too much speaker cone movement due to lots of low frequencies) with a “safe” amp rating.

Your suggested paring is fine for reasonable volume usage, but if you’re trying to get loud you’ll more than likely need to add a second cab.
 
#30
mmbongo said:
Since you say you have a '4 ohm amp' I'm assuming it's a large tube amp? Yeah you cannot use an 8 ohm cab if your amp is on the 4 ohm setting. Your cab must match the transformer setting on your amp.

And yes, a 500 watt tube amp will shred right through a 300 watt speaker cabinet if you get crazy with the volume.
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Who has a 500 watt @ 8 ohm all tube amp? I think I saw something like once that was a home-brew from Jamaica. Just wondering.
 
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#37
Jordy4strings said:
I have a 4 ohm amp 500 watts and a 8 ohm cab 300 watts. If I crank the amp will I blow the speaker or does the difference in impedance mean I will only get half of the wattage going from amp to speaker, thus making it impossible to ruin the cab?

Thanks in advance for any help you can give me. Have a great day.
Jordy
Click to expand...

It's never impossible to ruin the cab and cranking an amp is a great way to do it, whatever the wattage is.

If you're picking stuff to buy it would be helpful to know how you want to use it (loud rock band?) etc. If this is about a cab you already have, the safest bet is to get another cab when you need more volume. More wattage will just help you fry stuff most of the time.

Welcome aboard :)
 
#38
4 Ohms is the minimum impedance the amp will typically be happy with. Running at 8 ohms won't hurt the amp. Now, the other way....when you run an amp at 8 ohms, you typically get a bit more than half the power you do at 4, so if the thing is rated 500 watts into 4 Ohms, then a little more than 250 into 8. So, less than the rating of the speaker - probably.

Still, common sense should be used - just because the wattage numbers say you're safe, doesn't mean that you can't blow the speaker if you push it hard, especially at lower frequencies.

Use good judgement, listen for signs of stress - you'll likely be OK with that combination.
 

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