Louder-- 4 ohms or 8 ohms?


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Jerry.thewise
05-29-2010, 12:02 AM
So I have an amp that can output both a 4 ohm signal and an 8 ohm, and have multiple 8 ohm speakers.
1-Would two 8 ohms in parallel (=4 ohm) be significantly louder than one out?
2-In theory, would one single 4 ohm speaker be louder than an 8 ohm?

In context, this is a 6 channel mixer that will be running 2 mics and a bass with two other guitar rigs and a drummer.

18th_Angel
05-29-2010, 12:20 AM
Try it and see?

jof1029
05-29-2010, 12:20 AM
1 - no
2 - no

Jerry.thewise
05-29-2010, 12:44 AM
alright, gonna need to find a different rig then. Thanks guys

Vinson
05-29-2010, 01:05 AM
If it's a solid state amp, getting down to a 4ohm load will give you the most power.
a 4ohm speaker isn't going to be louder than 2 8ohm speakers run parallel...your still ending up with 4 ohms.
If it has a switch to change from 4 ohms to 8 ohms, you won't gain anything by running 4 ohms.

My Randall "Ninja v2" was 280w @ 8ohms, 400w @ 4ohms, and 480w@ 2 ohms.
My Bugera 6262 is 120w at 4/8/16 ohms (tube amp, and has a switch to match impedance)

boardsofcanada
05-29-2010, 01:51 AM
there might be something to gain in an SS amp where there is no transformer and you arent matching impedences but can lower the load resistance and allow more output...but it isnt going to make a quiet amp loud or vice versa.

Phil Starr
05-29-2010, 02:38 AM
Oh dear the advice hasn't been completely accurate. The loudness depends upon a whole collection of factors. Wattage (which is dependant upon impedance for a SS amp), speaker efficiency, cone area.

Basically giving an SS amp a lower ohms will increase the power until the mains transformer runs out of oomph. Halving the impedance for most amps will double the power and increase the volume by 3dB.

Doubling the cone area will increase the efficiency of the speaker and straight in front of the speaker will give you an extra 3dB, Equivalent to doubling the amp power, but not twice as loud.

So far this is all just physics. Adding an extra identical speaker will give you up to an extra 6dB depending upon the power transformer being up to the job.

There's another effect. Most speakers are designed as 8ohm units and the 4's and 16's are an afterthought so the 8's are usually better than the 4's or 16's anther reason why 2x8's will give more volume than a 4. If the speakers are different models all bets are off as speakers can vary in efficiency by more than 10dB

Read this for more detail http://www.ultimate-guitar.com/columns/gear_maintenance/making_it_loud.html

cheers

Vinson
05-29-2010, 03:31 AM
Reading that article, I should be good for a solid 130dB SWEET!!!
(didn't take into effect cone surface area before)

Hmmm that Randall might have been good for up to 135dB! 138dB with a full stack!!!

NOTE: the 16ohm version of the Eminence Wizard is 103.6db vs, the 8 ohm version at 103. Usually, the 8s are better, not always.

jof1029
05-29-2010, 10:57 AM
Oh dear the advice hasn't been completely accurate. The loudness depends upon a whole collection of factors. Wattage (which is dependant upon impedance for a SS amp), speaker efficiency, cone area.

Basically giving an SS amp a lower ohms will increase the power until the mains transformer runs out of oomph. Halving the impedance for most amps will double the power and increase the volume by 3dB.

Doubling the cone area will increase the efficiency of the speaker and straight in front of the speaker will give you an extra 3dB, Equivalent to doubling the amp power, but not twice as loud.

So far this is all just physics. Adding an extra identical speaker will give you up to an extra 6dB depending upon the power transformer being up to the job.

There's another effect. Most speakers are designed as 8ohm units and the 4's and 16's are an afterthought so the 8's are usually better than the 4's or 16's anther reason why 2x8's will give more volume than a 4. If the speakers are different models all bets are off as speakers can vary in efficiency by more than 10dB

Read this for more detail http://www.ultimate-guitar.com/columns/gear_maintenance/making_it_loud.html

cheers
when you double the cone size by adding an extra speaker, you also cut the power going to each speaker in half. with a SS power amp being able to output twice the power now based on seeing half the load impedance, you should be seeing a total increase of 3dB.

now, if i remember correctly, around 3dB of a volume increase is where humans can actually percieve a volume difference. so the whole thing would be noticably louder, but not significantly.

i also took the second question to mean using one 4 ohm speaker instead of two 8 ohm speakers in parallel. one sees a volume boost from using 2 speakers, the other from running the speaker at a higher power level. in theory, both should be putting out approximately the same ammount of volume.

Phil Starr
06-02-2010, 04:55 AM
when you double the cone size by adding an extra speaker, you also cut the power going to each speaker in half. with a SS power amp being able to output twice the power now based on seeing half the load impedance, you should be seeing a total increase of 3dB.

now, if i remember correctly, around 3dB of a volume increase is where humans can actually percieve a volume difference. so the whole thing would be noticably louder, but not significantly.

i also took the second question to mean using one 4 ohm speaker instead of two 8 ohm speakers in parallel. one sees a volume boost from using 2 speakers, the other from running the speaker at a higher power level. in theory, both should be putting out approximately the same amount of volume.

Sorry you haven't quite got this. Adding an extra (identical) speaker will halve the impedance. the amp if SS will pump out the same voltage and so will deliver twice the current, and therefore power if the power supply is up to it.

the minimum increase in sound we can reliably hear is 1dB 3dB is very noticeable though not a doubling in volume just in power.

Trust me I am a science teacher.

Phil Starr
06-02-2010, 05:02 AM
Reading that article, I should be good for a solid 130dB SWEET!!!
(didn't take into effect cone surface area before)

Hmmm that Randall might have been good for up to 135dB! 138dB with a full stack!!!

NOTE: the 16ohm version of the Eminence Wizard is 103.6db vs, the 8 ohm version at 103. Usually, the 8s are better, not always.
OK, I confess to wording the 8/4 ohm thing carefully but not fully.

They usually make 4 ohm coils by making them short and 16's by making them long. They ought to use different thickness wires and more/fewer layers to maintain the sonic characteristics they carefully design in for the 8 ohm versions.

The long 16 ohm coil means most of the coil is outside the magnet and so the power in this bit is wasted hence lower efficiency.

The short 4 ohm coil means there is more coil in the gap so greater efficiency at low sound levels but at higher levels the coil moves out of the gap and the maximum sound level is restricted. Look at Xmax on the charts and you can see what I mean. The figures they quote are at 2.83V which is1W into 8 ohms.

littlephil
06-02-2010, 05:09 AM
the minimum increase in sound we can reliably hear is 1dB 3dB is very noticeable though not a doubling in volume just in power.
Somewhat irrelevant, but 3dB is a 50% increase in volume (theoretically, so its probably going to be slightly less in the real world)

Vinson
06-02-2010, 12:04 PM
So, to be clear.
If we have a combo amp running at 100dB, and add a second identical combo amp running at 100dB. What is your total dB. 110dB? This is double speakers, and double power.
if your wearing 30dB earplugs (lets just pretend they are 30dB across the range) and then put on 30dB ear muffs your total cut would be 40dB?

Everything else I have ever read would suggest the amps would be at 103dB, or 106dB, not 110dB and the ear protection be at 33dB.
What I had been told previously is that while sound doubles, our perception of sound does not double, hence the reason we say 10dB SOUNDS double.

NOT arguing!!! Honestly asking for clarification

`digitaL.braVo
06-02-2010, 03:13 PM
So, to be clear.
If we have a combo amp running at 100dB, and add a second identical combo amp running at 100dB. What is your total dB. 110dB? This is double speakers, and double power.
if your wearing 30dB earplugs (lets just pretend they are 30dB across the range) and then put on 30dB ear muffs your total cut would be 40dB?

Everything else I have ever read would suggest the amps would be at 103dB, and the ear protection be at 33dB.
What I had been told previously is that while sound doubles, our perception of sound does not double, hence the reason we say 10dB SOUNDS double.

NOT arguing!!! Honestly asking for clarification

The Decibel system is also a measurement of sound pressure, so standing 6" away from the amp sounds significantly different than being 6' or 12' away from the amp. This thread is awfully bonk in that regard.

jof1029
06-02-2010, 06:46 PM
Sorry you haven't quite got this. Adding an extra (identical) speaker will halve the impedance. the amp if SS will pump out the same voltage and so will deliver twice the current, and therefore power if the power supply is up to it.

the minimum increase in sound we can reliably hear is 1dB 3dB is very noticeable though not a doubling in volume just in power.

Trust me I am a science teacher.
you missed the fact that i also completely contradicted myself in my post. eh, thats what i get for posting while cooking :shrug: i guess in the first half i was thinking more with tube amps, then half crossed into SS territory. my bad.

also, if you are delivering twice the current at your rated output, i will 100% gaurentee that you will not be putting out the same voltage. voltage will drop. maybe only a small ammount since we arent talking a ton of power here, but it will go down.


anyway, based on the original question, just adding a couple speaker (even if you are double the power) isnt going to actually add enough volume to make a huge difference. maybe in theory, but not in practice. especially not when we are talking about a bass.

Phil Starr
06-03-2010, 07:15 AM
So, to be clear.
If we have a combo amp running at 100dB, and add a second identical combo amp running at 100dB. What is your total dB. 110dB? This is double speakers, and double power.
if your wearing 30dB earplugs (lets just pretend they are 30dB across the range) and then put on 30dB ear muffs your total cut would be 40dB?

Everything else I have ever read would suggest the amps would be at 103dB, or 106dB, not 110dB and the ear protection be at 33dB.
What I had been told previously is that while sound doubles, our perception of sound does not double, hence the reason we say 10dB SOUNDS double.

NOT arguing!!! Honestly asking for clarification

These are two great questions but they kind of expose the true complexity of all this. Mr braVo is right the decibel is a measure of the sound pressure. This is all in my article which is in itself a simplification. The sound pressure drops by 6dB every time you double the distance from its source. Doubling the sound pressure by standing the same distance from two identical sources will actually give you a 6dB increase but standing closer to one source will mean that this one will dominate what you hear. To further complicate matters at least three other things are going on:

Speakers are directional especially at high frequencies so the level depends upon what notes you are playing and exactly where you stand.

The sound pressure from two sources depends upon phase (where in the cycle the speaker and sound waves have got to) If the two speakers are moving exactly together then the sound adds. if one is moving forwards and one back then they will cancel and there will be no sound. If the distance from the speakers are different then the waves will arrive at different times and you get cancellation or reinforcement depending upon the exact conditions. Add in reflected sound off walls and floors and you find that there are hot spots and null spots all over the stage. For the musician this explains why sometimes you can hear yourself on stage and sometimes not and also why mic feedback is so unpredictable.

Sound level should be measured in Phons not decibels and is as much to do with how the brain and ears work as with pressure levels. We are much more able to detect changes in sound volumes at low levels than high and at mid frequencies more than extreme lows and highs. Saying 1dB is the minimum change we notice and that 10dB is twice as loud is just a rule of thumb to keep life simple.

So the basic answer is that two combo's will give a maximum increase of 6dB but only if you point them straight at yourself and they are equal distances away. Ignoring all the pressure stuff (which involves algebra and log calculations) that is 3dB for the extra power and 3dB for the double speaker cones.

Now you get to know how geeky I really am, I'm going to do the experiment. I don't know exactly what will happen if you wear plugs and defenders. I suspect that the sound that gets through one will also bypass the other (air leaks and bone transmission). If they are perfect you should get 30+30= 60dB so I'll guess that you'll get something like 45dB with both.