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Add another cab or increase wattage?

R

RiseOfTheWooten

Jan 4, 2006
755
4
Australia
#1
Take for example your amp is 500watts @ 4ohms, but at the moment you've only got an 8ohm 4x10 cab. So you're only getting 300watts out of the amp and cab.

We all know if you add another 8ohm 4x10 cab to your rig, you have a louder sound because you're "pushing more air".

But is that mainly due to having more speakers 'pushing more air' or mainly due to the increase in wattage?

How much louder would your rig be, if you simply replaced the 8ohm 4x10 cab with a 4ohm 4x10?
 
#2
Bear in mind that, all else being equal, in order to be "twice as loud" as a 100 watt amp, you would need a 1000 watt amp.

That being the case, logic would suggest that the majority of the advantage gained by adding a cab to get the full "juice" out of your amp is down to the fact that there are extra drivers involved and you are pushing more air.

Hope this makes some sense and that I'm not talking technical nonsense. I'm sure someone will correct me if I am.:D :D
 
#6
How much louder would your rig be, if you simply replaced the 8ohm 4x10 cab with a 4ohm 4x10?
Click to expand...
Plus 3dB. Maybe. Most speakers won't go beyond 1/2 power before power compression limits their output anyway.
alexclaber said:
if you added another matching cab you would really notice the extra bottom and loudness.
Click to expand...
Plus 6dB to be exact, although the response curve would remain the same. It would only seem to have more bottom due to its being louder.
 
#7
billfitzmaurice said:
Plus 3dB. Maybe. Most speakers won't go beyond 1/2 power before power compression limits their output anyway.

Plus 6dB to be exact, although the response curve would remain the same. It would only seem to have more bottom due to its being louder.
Click to expand...


What do you mean 1/2 power before power compression? Half the advertised power of the cab?
 
#8
billfitzmaurice said:
Plus 6dB to be exact, although the response curve would remain the same. It would only seem to have more bottom due to its being louder.
Click to expand...

On the other hand doesn't the rather low Xmax of most bass cab drivers cause LF compression at anything above moderate volumes so therefore adding an extra cab (and thus halving the required excursion for equal volume) will reduce Xmax limitations and therefore increase the bottom?

Alex
 
#9
alexclaber said:
On the other hand doesn't the rather low Xmax of most bass cab drivers cause LF compression at anything above moderate volumes so therefore adding an extra cab (and thus halving the required excursion for equal volume) will reduce Xmax limitations and therefore increase the bottom?

Alex
Click to expand...

That totally went over my head.
 
#10
Wow now I am really confused.

I have an amps with 2 channels of 130w each. I can't bridge my amp but I can connect two speakers to each channel.

I currently have 2 speakers but only use them at home. When I go to rehearsal I bring only one.

At home: Would I get better sound with 2 speakers on the same channel or 1 on each? Would I get louder sound with 2 on same or 1 on each?

I think my speakers are 4ohms, not sure. I have no idea what my amp can do for ohms but I guess worst case if the breakers trips. It's a PA.
 
#11
RiseOfTheWooten said:
That totally went over my head.
Click to expand...

Most bass speakers can't move all that far before the motor pushing them (the coil and magnet behind the cone) starts to run out of push. Very few bass cabs can take anywhere near full power without this happening - even 20% of full power on a low E could cause this non-linearity.

Double the number of speaker cones and they only need move half as far to produce the same quantity of bass. Which means they can remain in their linear region.

Alex
 
#12
alexclaber said:
Most bass speakers can't move all that far before the motor pushing them (the coil and magnet behind the cone) starts to run out of push. Very few bass cabs can take anywhere near full power without this happening - even 20% of full power on a low E could cause this non-linearity.

Double the number of speaker cones and they only need move half as far to produce the same quantity of bass. Which means they can remain in their linear region.

Alex
Click to expand...

In that case, I've often seen recommendations on TB that getting a cab that is rated lower than your amp is ok as long as you listen for distortion and keep it below that threshold. Does this mean that it is always better to have a higher rating cab than your amp, since using 20% of full power would already cause problems?
 
#13
RiseOfTheWooten said:
What do you mean 1/2 power before power compression? Half the advertised power of the cab?
Click to expand...
Yes. The output of a speaker is not linear with respect to input power. All speakers suffer from power compression, and very few will put out any more sound at their full power rating than they will at half that. The rest is burned off as heat in the voice coil. The power rating of a speaker is not how much power it will accept before it stops giving additional output, it's how much power it will take before the voice coil burns up.
On the other hand doesn't the rather low Xmax of most bass cab drivers cause LF compression at anything above moderate volumes so therefore adding an extra cab (and thus halving the required excursion for equal volume) will reduce Xmax limitations and therefore increase the bottom?
Click to expand...
It would increase the bottom if you were driving the single cabinet beyond xmax at low frequencies, yes. But that doesn't change the frequency response of the system per se, it just allows the system to run at 6dB higher output before xmax is exceeded again.
At home: Would I get better sound with 2 speakers on the same channel or 1 on each? Would I get louder sound with 2 on same or 1 on each?
Click to expand...
Can you lift more weight using one arm or two?
 
#14
RiseOfTheWooten said:
Take for example your amp is 500watts @ 4ohms, but at the moment you've only got an 8ohm 4x10 cab. So you're only getting 300watts out of the amp and cab.

We all know if you add another 8ohm 4x10 cab to your rig, you have a louder sound because you're "pushing more air".

But is that mainly due to having more speakers 'pushing more air' or mainly due to the increase in wattage?

How much louder would your rig be, if you simply replaced the 8ohm 4x10 cab with a 4ohm 4x10?
Click to expand...
Not much, 300 to 500 watts is less than 3db and I don't think it would be worth the trouble. Adding another 8 ohm 4x10 cab which would give you 8x10's at 500 watts. If that isn't loud enough :eyebrow: Tell everybody else to TURN DOWN
 
#15
billfitzmaurice said:
Yes. The output of a speaker is not linear with respect to input power. All speakers suffer from power compression, and very few will put out any more sound at their full power rating than they will at half that. The rest is burned off as heat in the voice coil. The power rating of a speaker is not how much power it will accept before it stops giving additional output, it's how much power it will take before the voice coil burns up.

It would increase the bottom if you were driving the single cabinet beyond xmax at low frequencies, yes. But that doesn't change the frequency response of the system per se, it just allows the system to run at 6dB higher output before xmax is exceeded again.

Can you lift more weight using one arm or two?
Click to expand...

Great analogy but are the arms the amps channels or the speakers? I probably get better and/ou louder sound with two speakers. But which is best, two on same channel or two on different channels?
 
#16
billfitzmaurice said:
Yes. The output of a speaker is not linear with respect to input power. All speakers suffer from power compression, and very few will put out any more sound at their full power rating than they will at half that. The rest is burned off as heat in the voice coil. The power rating of a speaker is not how much power it will accept before it stops giving additional output, it's how much power it will take before the voice coil burns up.
Click to expand...

Power compression is undeniably an important issue but it's also important to bear in mind that bass guitar signals tend to be very dynamic and consequently the peak power is vastly higher than the average power. This means that although you may be running your 500W amp at full volume your cabs may receive less than 100W of average power (although the peaks could be as much as 800W) which is unlikely to cause serious power compression in an cab that is rated for more than three times this power.

If you run heavy compression and/or overdrive/distortion the peak to average power ratio will be much less, whilst bassists that are very much into slap and don't use compression will have a much larger peak to average power ratio.

Alex
 
#17
i dunno the math, but you deff wanan get another cab. have you ever seen those cabs with like 24 speakers with 3'' drivers? pb something? there crazy expensive. but besides from pushing more air, you get constructive interfearence on the sound wave. theres some 11th grade physics for ya :-)
 
#18
Fastfwd said:
Great analogy but are the arms the amps channels or the speakers? I probably get better and/ou louder sound with two speakers. But which is best, two on same channel or two on different channels?
Click to expand...
Use both channels, other wise you have one doing all the work and the other doing nothing.
 

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