Ohm calculation & comparison

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Charles Jenkinson
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Ohm calculation & comparison

#1 Post by Charles Jenkinson » Sun Aug 28, 2016 3:58 pm

I need a sanity check on a few numbers please.

If one has a 4x12 cab which is a 16ohm load then that can only have 16ohm drivers in it configured as 2 pairs in series and then those pairs in parallel...?

Now, if one used two of those 16ohm drivers to make an 8ohm 2x12 cab, for the same voltage (knob position) on the amp, the 2 driver cab would be the same loudness as the 4 driver cab...? I've run this on sengelpie audio calculator and the wattage definitely doubles for the same voltage when you half the impedance, ...fairly obvious, so unless someone is running at insane SPL they will be able to achieve the same loudness without needing more of something; by swapping from 4 drivers to 2, if the impedance drops by half anyway.
2xJ12L (3012HO) switchable/melded (http://billfitzmaurice.info/forum/viewt ... 30&t=18773)
2xT30 : http://billfitzmaurice.info/forum/viewt ... 30&t=20386

No sound is better than bad sound.

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Radian
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Re: Ohm calculation & comparison

#2 Post by Radian » Sun Aug 28, 2016 4:40 pm

For starters.....what's the real question here?
Charles Jenkinson wrote:If one has a 4x12 cab which is a 16ohm load then that can only have 16ohm drivers in it configured as 2 pairs in series and then those pairs in parallel...?
or four [4 ohm speakers] in series
Charles Jenkinson wrote:Now, if one used two of those 16ohm drivers to make an 8ohm 2x12 cab, for the same voltage (knob position) on the amp, the 2 driver cab would be the same loudness as the 4 driver cab...?
All fine until you introduced "loudness" into the fold. Loudness can have a relationship to power, but it is not discrete. There's much more to it than that.

Especially where instrument sound is concerned, and particularly guitar cabs.
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Bruce Weldy
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Re: Ohm calculation & comparison

#3 Post by Bruce Weldy » Sun Aug 28, 2016 7:51 pm

Radian wrote:
Especially where instrument sound is concerned, and particularly guitar cabs.
It's a scientific fact that if the cab looks bigger and has more speakers it will be louder....regardless of any other factors.

From "The Guitarist's Guide to Physics"

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Charles Jenkinson
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Re: Ohm calculation & comparison

#4 Post by Charles Jenkinson » Sun Aug 28, 2016 8:45 pm

Radian wrote:For starters.....what's the real question here?
Charles Jenkinson wrote:If one has a 4x12 cab which is a 16ohm load then that can only have 16ohm drivers in it configured as 2 pairs in series and then those pairs in parallel...?
or four [4 ohm speakers] in series
Charles Jenkinson wrote:Now, if one used two of those 16ohm drivers to make an 8ohm 2x12 cab, for the same voltage (knob position) on the amp, the 2 driver cab would be the same loudness as the 4 driver cab...?
All fine until you introduced "loudness" into the fold. Loudness can have a relationship to power, but it is not discrete. There's much more to it than that.

Especially where instrument sound is concerned, and particularly guitar cabs.
I forgot about 4ohm speakers. :fruit:

Ok, I should have not used the term loudness. What I mean is 'is the approximate 6dB loss from halving the numbers of speakers accommodated by halving the impedance?'

Radian, I know you're one of the best there is at this sort of thing. :ugeek:
2xJ12L (3012HO) switchable/melded (http://billfitzmaurice.info/forum/viewt ... 30&t=18773)
2xT30 : http://billfitzmaurice.info/forum/viewt ... 30&t=20386

No sound is better than bad sound.

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Charles Jenkinson
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Re: Ohm calculation & comparison

#5 Post by Charles Jenkinson » Sun Aug 28, 2016 8:47 pm

Bruce Weldy wrote:
Radian wrote:
Especially where instrument sound is concerned, and particularly guitar cabs.
It's a scientific fact that if the cab looks bigger and has more speakers it will be louder....regardless of any other factors.

From "The Guitarist's Guide to Physics"
I'd better get a copy of that. Could be handy.
2xJ12L (3012HO) switchable/melded (http://billfitzmaurice.info/forum/viewt ... 30&t=18773)
2xT30 : http://billfitzmaurice.info/forum/viewt ... 30&t=20386

No sound is better than bad sound.

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Bill Fitzmaurice
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Re: Ohm calculation & comparison

#6 Post by Bill Fitzmaurice » Sun Aug 28, 2016 9:48 pm

The 16 ohm cab will have the same sensitivity as the 8 ohm cab. It's able to go 6dB louder than the 2x12 because it has twice the cone displacement, but it will take four times the power to realize that 6dB.

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Radian
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Re: Ohm calculation & comparison

#7 Post by Radian » Sun Aug 28, 2016 11:05 pm

Charles Jenkinson wrote:Radian, I know you're one of the best there is at this sort of thing. :ugeek:
You won't find me designing my own speakers anytime soon. :wink:
Good food, good people, good times.

NukePooch
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Re: Ohm calculation & comparison

#8 Post by NukePooch » Mon Aug 29, 2016 6:52 am

Bruce Weldy wrote:
Radian wrote:
Especially where instrument sound is concerned, and particularly guitar cabs.
It's a scientific fact that if the cab looks bigger and has more speakers it will be louder....regardless of any other factors.

From "The Guitarist's Guide to Physics"

Wow. I didn't know that. Is it like hot rodding cars where you can add horsepower with the addition of chrome engine components and speed parts stickers? I wonder how many chrome air cleaners you'd need to add to a guitar cabinet to add 6dB?
4 Jack 112L- 3012HO, melded array
2 Jack 112 (bought), straight array
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6 Wedgehorn W6 w/ Panel Mount Piezos
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Charles Jenkinson
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Re: Ohm calculation & comparison

#9 Post by Charles Jenkinson » Mon Aug 29, 2016 7:23 am

Bill Fitzmaurice wrote:The 16 ohm cab will have the same sensitivity as the 8 ohm cab. It's able to go 6dB louder than the 2x12 because it has twice the cone displacement, but it will take four times the power to realize that 6dB.
Thanks Bill
2xJ12L (3012HO) switchable/melded (http://billfitzmaurice.info/forum/viewt ... 30&t=18773)
2xT30 : http://billfitzmaurice.info/forum/viewt ... 30&t=20386

No sound is better than bad sound.

Bruce Weldy
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Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: Ohm calculation & comparison

#10 Post by Bruce Weldy » Mon Aug 29, 2016 11:11 am

Charles Jenkinson wrote:
Bill Fitzmaurice wrote:The 16 ohm cab will have the same sensitivity as the 8 ohm cab. It's able to go 6dB louder than the 2x12 because it has twice the cone displacement, but it will take four times the power to realize that 6dB.
Thanks Bill

Of course, the reality is that using a 4x12 or even a 2x12 is really overkill 90% of the time.

I ran sound for 4 bands last weekend ...... the loudest guitar player was running through a Fender Blues Junior w/18 watts and a single 12.....and he was still too loud. This wasn't a small place and we were thumping it pretty danged good.

The old days of high powered heads and big guitar cabs is gone - especially with PA support.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Bill Fitzmaurice
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Re: Ohm calculation & comparison

#11 Post by Bill Fitzmaurice » Mon Aug 29, 2016 11:24 am

Bruce Weldy wrote: The old days of high powered heads and big guitar cabs is gone - especially with PA support.
+1. I saw Brian Wilson last night, 8000 seat amphitheater, there wasn't anything on stage larger than a 2x12.

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