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are 4 ohm cabs technically "better" than 8 ohm cabs?

#61
It's about the amp head to me.
I've read whole articles about tube heads where "x output transformer pairs best with y speaker load for z type of music".
That's fine, but I'm not the type who can get the tone I want when the amp isn't even up past 9 o'clock. I bought it for how it sounds on bake or broil, not preheat.
8 ohm load gives you more options and more control in a number of situations. You can always add another cab if you need to move more air.
 
#65
How do I know if my amp can handle a 2 ohm load, is this a shot in the dark? Also, is pairing cabs the only way, and not using 3 cabs? Is it unusual to use 3 separate cabs?

Rip Van Dan said:
True! Twice the wattage usually means a 3db gain in sound levels.


Nope. Increasing your wattage by 100% increases your sound level by 3db, which is technically twice as loud. However, the human ear hears a 10db increase as twice as loud. Another way to look at it is if it takes 500 watts to drive you cab to 120db, it will take 1000-watts to drive it to 123db. Since doubling your speaker area will also raise it 3db, it's usually cheaper to add on speaker cabs than to upgrade amps.

If you are only planning on using 1 cab, then a 4 ohm cab will get the most out of your amp. If you need to get more sound out, a common thing is to add a second cab. If your amp will handle a 2 ohm load, then you can add another 4 ohm cab and you'll be fine. However if your amp has a 4 ohm minimum load rating, you can either use just that one 4 ohm cab, or two 8 ohm cabs (8 ohm + 8 ohm=4 ohm load with industry standard parallel connections). Most people who are expecting to run two cabs, buy both of them as 8 ohm cabs because almost all of the amps out there can handle a 4 ohm load whereas not a lot can handle a 2 ohm load.
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#66
Before getting too deep into this discussion, when a program power rating for a speaker is provided, it's generally accepted that it's 2x the "RMS" rating and when a peak rating is generally 4x the "RMS" rating.

When matching an amp to a speaker rated this way, I would caution no more amplifier power than the program rating and recommend much closer to the "RMS" rating of the speaker (when the amp is specified using "RMS" units).

This is a common cause of misunderstanding, and damaged speakers. unfortunately, there are manufacturers that are not clear how their products are rated or what units are used, often resulting in overly optimistic numbers, which means that such mistakes are even easier to make.
 
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#70
bushy said:
What if the cab is 800 watts, 1600 watts peak 8 ohm? Using a 500 watt amp?
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The ability of the cabinet to handle a specific wattage is completely irrelevant and unrelated to how much wattage the amp produces. The Wattage produced by the amp is function solely of the amp, the signal it is amplifying, and the load it is driving, measured in Ohms.

The amp is what "makes" Wattage; it generates a voltage that pushes current into the cab; the speakers in the cab then turn that signal into sound. It helps to know Wattage is a measure of power, which has a very specific meaning in physics and engineering. P = VI -- power = voltage x current. If you measure the voltage in Volts and the current in Amperes, the power will be in Watts.

The cabinet is just a sink for that Wattage. It is a passive electro-mechanical component. If the amp pushes more Wattage into a cabinet than the cab can stand (more than it is rated for) then the cabinet's components will be damaged or destroyed by heat from all the excess power that could not be handled properly. If the amplifier puts out fewer Watts than the cabinet is rated for then you will be safe from a thermal failure. Some here are quick to point out you could still experience a mechanical failure due to over-excursion of the speakers, but a failure like that usually provides a sonic warning in the form of speaker farting.

So the lower the rated load, in Ohms, the more Wattage an amp will produce. Notice how amps have a minimum safe load, usually either 4 Ohms or 2 Ohms. Anything below that load will allow the amp to produce too much Wattage for it to safely handle. The amp itself is not perfectly efficient, so as the Wattage it is putting out goes up, so does the excess power lost inside the amp, which expresses as heat. The amp can only handle disposing of so much heat. The heat sinks and fans and such all help, but below the minimum safe load the amp will eventually suffer a thermal casualty of some sort, or some component will have to carry more current than it is rated for and it will fail.

In a way, a very crude analogy, thinking that the power handling capacity of the cabinet would affect how much power the amp puts out is like thinking the size of the bucket will somehow determine the flow rate of a hose. Only the nozzle, spigot, dimensions of the hose, and the water pressure determine the flow rate of water coming from a hose. The size of the bucket the water is going into has no effect at all. It does affect how quickly the bucket will fill up for a given flow rate, but will not affect the flow rate. Note that this analogy is imperfect! But it should help give an idea as to why the thermal rating of the cabinet has no effect on a given amp's output power.
 
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#77
JeezyMcNuggles said:
Yeah, they all do. But the cabinet doesn't take it.
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Not true. Amps without output impedance matching will deliver different power with different impedance.

JeezyMcNuggles said:
16 of course. With tubes. Makes the amp work harder. When tubes are cookin, everyone's lookin
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Not true. With tube amps, output impedance matching matches the load impedance (2/4/8/16 ohms) to the output tubes by changing the matching transformer's ratio taps. The plate load remains constant due to these different ratios.
 
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