Any tonal difference between 4 or 8 ohm cabs?

[BawanaRik]

I bet this will be interesting.

I hope someone has actually done a study so we can get facts.

 

[B-string]

Apparently facts have little audience.

 

[Downunderwonder]

BFM never had any trouble swatting Ric down. Older but not wiser.

Fact is this thread was all explained until Ric chucked a spanner in it.

Fact remains an identical enough sounding 4ohm driver has same volume potential as its 8ohm cousin given the same wattage. Nothing Ric says is actually related to that fact. It's all noise.

 

[GMC]

All things being equal ...

Then ...

fewer ohms = more watts ... that is a fact

and ...

more watts = more volume ...this is also a fact

and yes of course if you run through a substandard speaker it may not be able to produce the additional volume.

Otherwise a 15 watt bass amp would be as good as a 500 watt bass amp.

Yes I know that output numbers are not always accurate.

From the amp point of view...yes, but we also have to consider that most drivers loose efficiency as wattage increases. So 500w into a single 15" driver might not do much extra than say 250w. Many cabs max out in their SPL at surprisingly low wattage compared to their RMS power handling. Plus we have to take into account the cab's box dynamics...I've seen some cabs max out at only 150w even though they are rated at 450w RMS. We are trying to move as much air for our wattage...so spreading the load across multiple cabs is usually a better option than maxing out a single cab. Given the driver limitations and that we are assuming a powerful head. This is easiest with a pair of 8ohm cabs. Otherwise, we'd need 4 cabs and some complicated parallel wiring to get the same load.

 

[sratas]

The max volume difference is negligible between a 4-ohm & 8-ohm cab. Most ss/hybrid amps put out ~ 60% to 2/3 the 4-ohm output @ 8-ohms. A doubling of wattage increases volume by 3dB, the smallest increment discernible by the human ear. To double volume, you need 10X the wattage.

I'd never buy a 4-ohm box because of the nominal volume difference, because another 8-ohm can be added, & because 8-ohm cabs are lots easier to unload when it comes time.

Agree on everything but do not think about the logaritmic scale ad if it was linear, so + 3 db is a very noticeable difference.
I'm a sound engineer, perform a true studio work, I'm able, as well as the vast majority of people I guess, to distinguish increments of volume of very few decimals of a db, this is the studio editing cornerstone as far as volume goes, lowering the volume by 3 db always is a vaste change. This maybe applies less in non controlled situations, but the concept maintains its value.

Better to add to your many valid points that when an amp puts out maximum wattage, there will probably happen power compression from speakers, and when they heat up under high wattage, things can get worse and you could find that your rig sounds weaker after some time of continuous playing.
This adds to the concept that having more wattage not always brings a grin, but having more speakers always does

 

[dincz]

At most, a 3dB change will sound like this:

http://static.talkbass.com/data/att.../1307235_997e5431239d8fe52e387d06ef08569a.mp3

 

[bebass]

Reading this thread, seems like Ohm's law has changed. Why is it you fellows didn't let me know when this happened?

 

[Rick James]

4 will be louder

4 will be louder with the amp settings the same, but not louder in maximum output, because maximum output is limited by the speaker excursion . The tone will be different because a 4 ohm and 8 ohm voice coil won't have the same inductance and capacitance. But it won't be a big difference.

 

[Nephilymbass]

I think it depends on the amp used with the cab. What cab in question is also a big part of it. The speakers in a ampeg 810e which is a 4 ohm cab are the same speakers in a 410he which is an 8 ohms cab. The cabs have a different rating but the speakers do not

 

[DavC]

NO ...

get an 8 ohm cab so you can another one later ... you/we know it will happen .. !! ha

 

[MJ_Sotti]

So using a 410he alone w a svtcl will work, just not be as loud?

 

[b-b-b-bass]

4-ohm is better for Metal.
HTH...

 

[cfsporn]

Only with amps that do not use an output transformer and then the sound output to extra watt input is extremely disproportionate. In amps with an output transformer (most all tube output) the wattage output is essentially the same at 4 ohms and 8 ohms impedance.

Sound output difference from 350 to 500 watts with the same cab is very small and more waste heat than sound. Speakers are only 5% to 10% efficient at converting electrical power (watts) into usable sound.

There are limitations to amplifier design and some that even derate to a lower output power under 4 ohms load impedance.

But with an output transformer that has 8Ω, 4Ω, and 2Ω outputs, wouldn't the 8Ω speaker be getting more power in it's voice coil thanks to Ohm's Law?

Off topic, but something that has been puzzling me.

 

[BbbyBld]

According to transducer engineers I've talked to, 8 ohm impedance is typically the sweet spot for speakers themselves. Cabinets with multiple speakers are a different story unless all the speakers are 8 ohm impedance. With an 8 ohm speaker, the reactance, DCR, and parasitics balance out in sort of an ideal way.

 

[Yorin]

According to transducer engineers I've talked to, 8 ohm impedance is typically the sweet spot for speakers themselves. Cabinets with multiple speakers are a different story unless all the speakers are 8 ohm impedance. With an 8 ohm speaker, the reactance, DCR, and parasitics balance out in sort of an ideal way.

Uhm why?

 

[BbbyBld]

To put it another way, a perfect speaker would have a constant impedance across the audio frequency spectrum, so it would have a frequency response that would cover the entire audio spectrum at equal volume. Perfect speakers do not exist. There are different classifications of speakers for specific purposes, like subwoofers, mid range, tweeters. If you HAVE to use one speaker to perform as ideally as possible, 8 ohm impedance is the way to go, combined with the right cone and magnet.

 

[Rick James]

To put it another way, a perfect speaker would have a constant impedance across the audio frequency spectrum, so it would have a frequency response that would cover the entire audio spectrum at equal volume. .

Constant impedance would give constant current and power delivery, but that doesn't affect frequency response. If you look at an impedance sweep and a response chart you'll see that the impedance swings don't match up with response swings.

 

[walterw]

So using a 410he alone w a svtcl will work, just not be as loud?

you don't want to do that, SVT heads want 4 or 2 ohm loads only.

 

[Downunderwonder]

But with an output transformer that has 8Ω, 4Ω, and 2Ω outputs, wouldn't the 8Ω speaker be getting more power in it's voice coil thanks to Ohm's Law?

Off topic, but something that has been puzzling me.

The output side of the transformer is ( approximately ) paired to the expected load. The total forms an appropriate back loading to the front side of the transformer to get the rated power. Something like that, I think, one of the real tube guys may shoot me.

 

[walterw]

My 350 watt Ampeg head IS louder than my 200 watt Ampeg head, and my 200 watt Ampeg head is not as loud running 8 ohms as it is running 4 ohms.

I know that is is not a linear relationship but there is a relationship. Otherwise we would all be playing through 15 watt amps.

this seems perfectly reasonable to me, don't know why there's any fighting about it.

as for the OP, he's probably asking with the idea of "one cab to get all the watts". the answer to his likely actual question is, "if it's a big cab that you'd never need two of, make it 4Ω; if it's a small cab make it 8Ω so you can get another one and stack 'em."