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

#101
Downunderwonder said:
Subway might be the exception but I am pretty sure most of the rest of the micro bass amps don't have such good power supplies if that's what's up.
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Not the exception. Amps such as the Bergantino and the Darkglass and others using the same power amp/power supply module follow this as well.

Going back almost 15 years, the Shuttle 3.0 uses the same type of power supply, so it's not something brand new.
 
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#102
agedhorse said:
A solid state amp (of all classes) acts more like a solid voltage source and behaves in accordance with ohm's law with no source impedance. A tube amp's source impedance acts less like zero ohms source impedance even when well matched.
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So, when running different impedances, it raises or lowers the actual voltage of the power supply?
 
#103
agedhorse said:
Not true. In fact the class D amp in the Subway (for example) delivers exactly double the 8 ohm rating at 4 ohms.

It has nothing to do with the amplifier class, it has to do with the power supply being regulated.

Line frequency (lead sled) supplies almost always deliver less than double the power into half the load impedance irregardless of class, because they are not regulated.
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Tangentially related but as opportunities go, this seems as good as any: whenever the max power delivered at 4 ohms (let's assume 4 is the minimum acceptable load for the amp) is less than double the rating at 8 ohms, should we expect the 16-ohm rating to be exactly half the 8-ohm one, or are the two in the same proportion as the rating @ 8Ω vs. @ 4Ω, or similar?
 
#106
Downunderwonder said:
Subway might be the exception but I am pretty sure most of the rest of the micro bass amps don't have such good power supplies if that's what's up.
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I don't see that.

Say you have an amp, a BeeGee1000, any class you like, and the ratings are honest:

600 Watts RMS @8 Ohm, .1% THD
1000 Watts RMS @4 Ohm, .1% THD

So the power supply allows it to hit 1000 WRMS before it runs out of supply and you're hitting the rails. Sounds adequate to me.

What if it's a dirty amp or unspecified THD, like:

A DirtyBoy1000
600 Watts RMS @8 Ohm, 10% THD
1000 Watts RMS @4 Ohm, 10% THD

Still honest and adequate. It just needs to sound good breaking up, regardless of why it has 10% distortion and regardless of how the yummy tone is accomplished. One of the reasons some amps sound better to some people and other amps sound better to other people.

or

The Uncertain1000
600 Watts RMS @8 Ohm
1000 Watts RMS @ 4 Ohm

Same as above amps, but not stated how much distortion. This one had better sound good if it distorts, or it will be called dishonest or just a bad amp.

Of course there is always the BWord10000, just speced:

10000 watts

This is the one to beware of. Weak power supply. It only does 100 WRMS, downhill with the wind at it's tail.

:laugh::roflmao::laugh:

The Subway is not the only one to breakup nicely. I'd expect the same from GB and Genzler amps. Others may have gone and designed similar circuits.

Perhaps you perceive a difference with class D because we're generally dealing with more power out and there are plenty of very simple (cheap) class D examples where the sections probably are pretty borderline. I don't see as a power supply weakness in any class unless the amp is falsely rated. Enjoy your extra 100 Watts :thumbsup:
 
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#107
5thsand4ths said:
If you have a 4 ohm amp does it make any difference if you run one 4 ohm cab or 2 8ohm cabs?
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If the cabs are identical except for the ohms, 2 x 8 ohms will be louder. No difference to the amp itself.

If the 4 ohm is very different cab than the two 8's, there are other factors to consider.

If the two 8's are very different from each other, all bets are off. That doesn't mean it won't work and work well.
 
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#108
agedhorse said:
Not the exception. Amps such as the Bergantino and the Darkglass and others using the same power amp/power supply module follow this as well.

Going back almost 15 years, the Shuttle 3.0 uses the same type of power supply, so it's not something brand new.
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I was wondering how far back that went. I didn't see your post as I was clubbing away at the keyboard. The SL came out before the shuttle, right? Was the SL the first commercially available bass amp with (useful/meaningful) power management?

I wonder what Peavey has done with power management. Or other larger scale manufacturers, Ampeg et. al.
 
#109
JeezyMcNuggles said:
So, when running different impedances, it raises or lowers the actual voltage of the power supply?
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No, on a typical solid state amplifier, the voltage remains fixed while the current changes.

On a typical tube amp, the output voltage (not the power supply voltage) changes and the current remains constant through the use of a variable ratio step-down transformer on the power amp's output.

HaphAsSard said:
Tangentially related but as opportunities go, this seems as good as any: whenever the max power delivered at 4 ohms (let's assume 4 is the minimum acceptable load for the amp) is less than double the rating at 8 ohms, should we expect the 16-ohm rating to be exactly half the 8-ohm one, or are the two in the same proportion as the rating @ 8Ω vs. @ 4Ω, or similar?
Click to expand...

Generally in proportion for amps without regulated power supplies, because the power supply losses are roughly proportional, but for regulated supplies, there is no proportional losses because the those are corrected for by the regulation circuitry and you tend to see exact halvings or doublings when the impedance is halved or doubled.

BadExample said:
I was wondering how far back that went. I didn't see your post as I was clubbing away at the keyboard. The SL came out before the shuttle, right? Was the SL the first commercially available bass amp with (useful/meaningful) power management?
Click to expand...

I was using output power management techniques going back about 20 years (I checked and it looks like 1998 was the first time I applied this). The Shuttles came out before the Streamliners, they all used different types of power output management, along with power supply management. The NeoPak was the first SMPS that I designed which also included VI emulation of a line frequency (lead sled) supply, but there are better techniques available now that were not possible (in practice) back then.
 
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#111
bushy said:
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?
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1. The manual for the amp will tell you what the minimum ohms load is and it should also be printed on the back of the amp itself. If in doubt do NOT run it with a 2 ohm load because it can melt the amp if your protection circuits don't turn it off in time.

I can get into specifics on Eden amps if you like. Marshall decided to change the ohm ratings in 2012 without any changes to the amp itself because they weren't "comfortable" with the ohms rating that low, even though some of these amps had a 7-year+ history of that capability. Outside of that, you'll need to check the manual and/or look at the back of the amp for the minimum ohms rating.

2. Three cabs is a bit unusual but you sometimes see it. If all three cabs are 8 ohm cabs, you will be running a 2.67 ohm load. You will also be running a 2.67 ohm load if you run one 8 ohm cab with one 4 ohm cab. You can NOT run three 4 ohm cabs together. To do so would drop your ohms load to 1.34 ohms and to my knowledge there is no amp that can run that ohms load safely.
 
#112
Rip Van Dan said:
...To do so would drop your ohms load to 1.34 ohms and to my knowledge there is no amp that can run that ohms load safely.
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Behold ~8000W into 0.5R.

MA10000.jpg



They made a few ludicrous amps back in the 90s. This one is my favourite but I am also partial to the Crest 10001. Each channel was over 5kW into 1R iirc.
 

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#116
For me, 4ohm is better. Bad back. I use light gear and cabs. My amp doesn't bridge. Instead, each channel pumps out the right wattage out each (of 2) channel to match my cabs.

It's easier and better for me because I can take one cab or two and not have to fiddle with anything or change my setup. Extra cab just means I need an extra cable (and backup).

But overall, no. It won't sound any different. Had an 8ohm Eden 410xlt and loved it for years. But it's 98lbs. No go. That's why I changed. Impedance had nothing to do with it.
 
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