Double Cabs are Louder ..or are they.

[Chienmortbb]

It is often said on here that if you have two cabs rather than one it is louder. Is that really the case and if so is it always the case? I am not trying put over a point here it is just that in some ways that statement makes no sense and in some ways it does.

Take for instance a Valve/Tube amp running into one cabinet at 8 ohms it is a 100 watt amp running at 100watts. Add second cabinet and switch the impedance switch to 4 ohms and at each cabinet will recieve 50 watts is all else is equal. Added to gether we have twice the speaker size in both driver ans cabinet but the same power, so no extra acoustic output, the SPL is the same. The only difference is that the new cabinet is closer to the player's ear so it will sound louder and have more mids and highs.

So that would suggest that only the player will hear a difference.

If we do the same trick with a well specified solid state amp it is different. If the SS amp has a meaty power supply, the two speakers would each get 100 watts and there would be a 3dB lift in power and presumably SPL. However in this case we have upped the power as well as adding a speaker cabinet. Be aware that many amps skimp on the power supply and the giveaway is if the 4 ohm output in only a few tens of watts higher than the 8 ohm output rather than double.

It may be that speakers get less efficient as you drive them harder ( a stretched surround is harder to pus that a relaxed one) or it could be a reduction in power/thermal compression, some form of maybe the combined size of the two baffles helps with bass response.

So my question is are people talking about the second case where there is a corresponding increase in power or is there some acoustical magic that happens when two identical cabinets are used instead of one, even if the power feeding then is the same?

Edited August 13, 2014 by Chienmortbb

[Dad3353]

The experts and pundits will rip into this, I don't doubt, but, for my tuppence-worth, I think it's the impedance change that gives the extra watts (and so volume...). It will only be really applicable to ss amps, as you intimate; valve amps won't give more power per se, but the better dispersion will give a better 'spread' of the spl generated. An ss amp rated at 200w into 8 ohm, and 350w into 4 ohm will be able to get louder with 2 x 8 ohm cabs (and so 350w...) compared to with only one (with only 200w available...). The difference will only be a couple of db, though.

Edited August 5, 2014 by Dad3353

[chrismuzz]

Something to do with "moving more air", there are plenty of people on here who know the science behind it! Bigger rigs certainly LOOK louder

[HowieBass]

I think it's because SPL does not follow a linear relationship with power; in other words the speaker is more efficient in the lower power handling range than when it reaches its upper power handing range, so two cabs driving more air at a lower power per speaker has a higher SPL than one cab running at higher power.

[Bill Fitzmaurice]

[quote name='Chienmortbb' timestamp='1407251484' post='2518791']
It is often said on here that if you have two cabs rather than one it is louder. Is that really the case and if so is it always the case?
[/quote]The number of cabs doesn't matter, the number of drivers does. Maximum output is limited by the total driver displacement, T/S spec Vd. The displacement of two drivers is double that of one, the resulting increase in maximum output by doubling the driver count is 6dB. It doesn't matter if the two drivers are in one cab or in two cabs with the same net internal volume.
By the same token when you plug a second identical cab into your amp the voltage swing into each cab remains constant, the total driver displacement doubles, and you get a 6dB increase in output. But you can only do so if the halving of the impedance load doesn't go below what your amp can deliver.

[0175westwood29]

I'd say it's just a fact of more speakers which create the jump in volume,

[xgsjx]

[quote name='Dad3353' timestamp='1407252852' post='2518815']
The experts and pundits will rip into this, I don't doubt, but, for my tuppence-worth, I think it's the impedance change that gives the extra watts (and so volume...). It will only be really applicable to ss amps, as you intimate; valve amps won't give more power per se, but the better dispersion will give a better 'spread' of the spl generated. An ss amp rated at 200w into 8 ohm, and 350w into 4 ohm will be able to get louder with 2 x 8 ohm cabs (and so 350w...) compared to with only one (with only 200w available...). The difference will only be a couple of db, though.
[/quote]

This would be right if you're using identical cabs. But if not, then it can vary greatly.
An efficient single 8Ω cab (e.g. my Markbass 2x10) could be very much louder than two not very efficient cabs (e.g. my 2 old Marshall 1x15s at 4Ω).
Having 1 efficient cab has many benefits. Having 2 gives you even more db if needed.
It's not so much about how many watts there are, but what a cab can do with the signal provided.

[stingrayPete1977]

[quote name='Chienmortbb' timestamp='1407251484' post='2518791']
It is often said on here that if you have two cabs rather than one it is louder. Is that really the case and if so is it always the case? I am not trying put over a point here it is just that in some ways that statement makes no sense and in some ways it does.

Take for instance a Valve/Tube amp running into one cabinet at 8 ohms it is a 100 watt amp running at 100watts. Add second cabinet and switch the impedance switch to 4 ohms and at each cabinet will recieve 50 watts is all else is equal. Added to gether we have twice the speaker size in both driver ans cabinet but the same power, so no extra acoustic output, the SPL is the same. The only difference is that the new cabinet is closer to the player's ear so it will sound louder and have more mids and highs.

So that would suggest that only the player will here a difference.

If we do the same trick with a well specified solid state amp it is different. If the SS amp has a meaty power supply, the two speakers would each get 100 watts and there would be a 3dB lift in power and presumably SPL. However in this case we have upped the power as well as adding a speaker cabinet. Be aware that many amps skimp on the power supply and the giveaway is if the 4 ohm output in only a few tens of watts higher than the 8 ohm output rather than double.

It may be that speakers get less efficient as you drive them harder ( a stretched surround is harder to pus that a relaxed one) or it could be a reduction in power/thermal compression, some form of maybe the combined size of the two baffles helps with bass response.

So my question is are people talking about the second case where there is a corresponding increase in power or is there some acoustical magic that happens when two identical cabinets are used instead of one, even if the power feeding then is the same?
[/quote]
Im no expert but as I see it in laymans terms the problem with your calculation is that you are working on the 100 watt amp running flat out, constantly, I suppose if you did that your theory might work until the amp or speakers died but in real world terms how much wattage is an amp putting out during a gig?

[Lozz196]

I`ve no idea re the science but I know that when I add in my 112 ext cab to my 112 combo the sound is much bigger. Don`t know about louder, but a much fuller sound, with more depth to it.

[LukeFRC]

I just go by what bill says

[Ghost_Bass]

I think you're going hipotetical on this, from your post i got the impression that you'tre trying to know the difference between (example):

1- 100W feeding a 4ohm cab
2- 100W feeding two 8ohm cabs (assuming identical cabs and each cab is identical to the 4ohm one except for the impedance)

I don't understand the phisics of this but my guess is that doubling the number of speakers you'll double the cone area so you get more air being pushed out. This will definetly get more "volume" out even with the same power being fed to both systems.

I think that Bill explained the theory part very well.

[51m0n]

[quote name='Bill Fitzmaurice' timestamp='1407255491' post='2518853']
The number of cabs doesn't matter, the number of drivers does. Maximum output is limited by the total driver displacement, T/S spec Vd. The displacement of two drivers is double that of one, the resulting increase in maximum output by doubling the driver count is 6dB. It doesn't matter if the two drivers are in one cab or in two cabs with the same net internal volume.
By the same token when you plug a second identical cab into your amp the voltage swing into each cab remains constant, the total driver displacement doubles, and you get a 6dB increase in output. But you can only do so if the halving of the impedance load doesn't go below what your amp can deliver.
[/quote]

This.

Every time.

[Count Bassy]

[quote name='Ghost_Bass' timestamp='1407324533' post='2519411']
I don't understand the phisics of this
[/quote]

or, it seems, the spelling.
(With apologies)

Edited August 6, 2014 by Count Bassy

[Count Bassy]

Surely there are two different things here.

Obviously if you put two drivers in parallel then, as bill says, they each seems the same voltage so so you'd shift twice the air. Providing that the amplifier can drive twice the current. And I suspect that this is where most of the "two drivers is better than one" thing comes from.

However, as ghost says, if you have one 4 ohm driver, or two 8 ohm drivers being driven by the same amp at the same settings, then the total electrical power delivered would be the same. I guess, as someone else said, the cone gets harder to move as the excursion increases due to the spring effect of the surround, so the two 8 ohm drivers might actually be more efficient (less energy loss in the surround), but by how much?

Ignoring this, if the one 4 ohm speaker cone taking 100 watts moves twice as far as each of the 50 Watt 8 ohm speakers then surely the total air shifted is the same?

A solid state amp has two limiting factors: The max voltage swing (mostly determined by the DC rail voltages), which determines how much current it could drive into a specific load, and the current limit (determined by both the output devices/heat management, and the power supply)

....... Or not??

[gadgie]

[quote name='chrismuzz' timestamp='1407253120' post='2518820']
Bigger rigs certainly LOOK louder
[/quote]

Post of the week for me lol!

[grenadilla]

With two cabinets (getting the same number of watts, say 300 watts to two 410s ) you have a "wider piston of air" to push the air in the room with your playing. With the same 300 watts and one 410 it is a more narrow piston of air. It is like knocking on a door with two knuckles and using four knuckles.

[Count Bassy]

[quote name='grenadilla' timestamp='1407327598' post='2519444']
With two cabinets (getting the same number of watts, say 300 watts to two 410s ) you have a "wider piston of air" to push the air in the room with your playing. With the same 300 watts and one 410 it is a more narrow piston of air. It is like knocking on a door with two knuckles and using four knuckles.
[/quote]

But surely, although the piston is smaller, for the same watts (and all other things being equal) then the cones in the single 4 x 10 would be moving that much further, so total displacement wouldn't be that much different?

[grenadilla]

That single 410 will be pushed harder but it won't drive the air in the room as well as two 410s.

[Bill Fitzmaurice]

[quote name='Count Bassy' timestamp='1407327376' post='2519440']
Obviously if you put two drivers in parallel then, as bill says, they each seems the same voltage so so you'd shift twice the air. Providing that the amplifier can drive twice the current. And I suspect that this is where most of the "two drivers is better than one" thing comes from.
However, as ghost says, if you have one 4 ohm driver, or two 8 ohm drivers being driven by the same amp at the same settings, then the total electrical power delivered would be the same. I guess, as someone else said, the cone gets harder to move as the excursion increases due to the spring effect of the surround, so the two 8 ohm drivers might actually be more efficient (less energy loss in the surround), but by how much?
Ignoring this, if the one 4 ohm speaker cone taking 100 watts moves twice as far as each of the 50 Watt 8 ohm speakers then surely the total air shifted is the same?
[/quote]This points out why power alone is meaningless. Driver output is determined by cone excursion, cone excursion is determined by voltage swing. One can no more anticpate the output level in decibels based on watts than one can the output of a lightbulb in lumens based on watts. If engineers ruled the roost you wouldn't see watts used at all, but we don't. Watts are the darlings of marketing departments.

[Ghost_Bass]

[quote name='Count Bassy' timestamp='1407326342' post='2519431']
or, it seems, the spelling.
(With apologies)
[/quote]

It's true, i need more practise, but it's easier for you to read my bad english than my good portuguese, hehehe

[Count Bassy]

[quote name='Ghost_Bass' timestamp='1407332673' post='2519517']
It's true, i need more practise, but it's easier for you to read my bad english than my good portuguese, hehehe
[/quote]
My apologies Ghost - I hadn't realised you weren't a native English speaker. And you're correct about my Portuguese !!

I feel really bad now. [size=4] [/size]

[Count Bassy]

[quote name='grenadilla' timestamp='1407329148' post='2519466']
That single 410 will be pushed harder but it won't drive the air in the room as well as two 410s.
[/quote]

Because ?? (Not being facetious, it's a genuine question).

[Ghost_Bass]

[quote name='Count Bassy' timestamp='1407335995' post='2519557']
My apologies Ghost - I hadn't realised you weren't a native English speaker. And you're correct about my Portuguese !!

I feel really bad now.
[/quote]

LOL

No need for feeling bad, it's absolutely fine, i'm the first to admit that sometimes i need to google some words that i can't spell and i'm fully aware that my grammar is very poor. On another side i'm feeling a bit more confident knowing that my english spelling isn't so bad that it would immediately tell that i'm not a native speaker (writer).

Cheers

Edited August 6, 2014 by Ghost_Bass

[Ghost_Bass]

[quote name='Count Bassy' timestamp='1407336131' post='2519560']
Because ?? (Not being facetious, it's a genuine question).
[/quote]

I think that this must have something to do with sound wave propagation or air movement. I can understand that, just talking about free air movement, two speakers might cause more turbulence and shift more air than a single speaker with twice the travel. Maybe it won't reach as far but it will spread more.

I'll wait for the gurus with charts and equations to explain the sound wave propagation thing.

[xgsjx]

[quote name='Ghost_Bass' timestamp='1407337039' post='2519573']
...two speakers might cause more turbulence and shift more air than a single speaker with twice the travel. Maybe it won't reach as far but it will spread more.
[/quote]

Sounds political to me.