Are low impedance cabinets inferior?

[ryla]

Bob Gallien (in norm stock tons bass book) claims he doesn't like 4ohm cabinets or low impedance cabinets in general.he claims you lose power in the speaker cord and connectors and lose control of the cone? I drive a 4 ohm 4x10 with a Gk 400rb. Anyone care to shine a light?

[cjj]

Hmmm, interesting thought...

When you get down to it, watts are watts so as long as everything is set up for the impedance, you shouldn't lose anything.

Now, one equation for calculating watts is:

P = I^2 * R

Where 'I' is current and "^2" means "squared. So, for a given Power value (watts) the lower the R (resistance/impedance), the higher the current has to be. So, for 200 Watts, we get the following:

8 ohms, current is 5 amps
4 ohms, current is 7.07 amps

So what? Well, losses in electronic systems are directly related to the current, since everything that electrons travel through has some resistance.

That's where the "everything is set up correctly" part comes in. In order to handle the extra current, you need bigger (fatter) wires. The same goes back to whatever is providing the current (output transistors or whatever). They will lose more power unless the design is done to account for that.

I'm not really familiar with the specifics of the design of modern amps that handle different impedance speakers, but most will put out more power into lower impedance speakers. This suggests to me that they are operating off of a constant voltage rail. So with lower speaker impedance they put out more current:

I = V/R (Ohm's Law)

So lower resistance means more current, which equates to more power delivered.

So, what does all of this mean? Well, you'll need fatter wires for lower impedance speakers, otherwise you'll get more loss. The output transistors will also have higher "loss" with a low impedance speaker, meaning they will run hotter.

So yeah, you will be "losing" more power with a low impedance speaker, but you'll likely have more available to lose, which will probably more than make up for the loss. Unless you have too thin of wires. Then you could lose a lot there too...

[ryla]

Excellent, thanks for that cjj I think I'll use the speakon socket instead of the jack socket on my cab and get a good cable, is ther really a big difference in cable quality ?

[john]

Hmmm, interesting thought...

When you get down to it, watts are watts so as long as everything is set up for the impedance, you shouldn't lose anything.

Now, one equation for calculating watts is:

P = I^2 * R

Where 'I' is current and "^2" means "squared. So, for a given Power value (watts) the lower the R (resistance/impedance), the higher the current has to be. So, for 200 Watts, we get the following:

8 ohms, current is 5 amps
4 ohms, current is 7.07 amps

So what? Well, losses in electronic systems are directly related to the current, since everything that electrons travel through has some resistance.

That's where the "everything is set up correctly" part comes in. In order to handle the extra current, you need bigger (fatter) wires. The same goes back to whatever is providing the current (output transistors or whatever). They will lose more power unless the design is done to account for that.

I'm not really familiar with the specifics of the design of modern amps that handle different impedance speakers, but most will put out more power into lower impedance speakers. This suggests to me that they are operating off of a constant voltage rail. So with lower speaker impedance they put out more current:

I = V/R (Ohm's Law)

So lower resistance means more current, which equates to more power delivered.

So, what does all of this mean? Well, you'll need fatter wires for lower impedance speakers, otherwise you'll get more loss. The output transistors will also have higher "loss" with a low impedance speaker, meaning they will run hotter.

So yeah, you will be "losing" more power with a low impedance speaker, but you'll likely have more available to lose, which will probably more than make up for the loss. Unless you have too thin of wires. Then you could lose a lot there too...

So when using two 8 ohm cabs to get 4 ohms, there could be a case for using two parallel speaker outputs from the amp, as opposed to linking the speakers together through there parallel plugs? Unless of course you have real thick cable

[Bill Fitzmaurice]

Bob Gallien (in norm stock tons bass book) claims he doesn't like 4ohm cabinets or low impedance cabinets in general.he claims you lose power in the speaker cord and connectors and lose control of the cone?

That's simply not true. You will suffer some signal loss if you're using a 4 ohm cab with a 50 foot long 18 gauge cable. That's easily cured, you just use a 14 gauge cable:
http://www.bcae1.com/images/swfs/speake ... istant.swf

With the cable lengths that bass rigs use even 18 gauge cables aren't a problem with signal loss, though you usually use a larger gauge for adequate current capacity.

[David]

Where 'I' is current and "^2" means "squared. So, for a given Power value (watts) the lower the R (resistance/impedance), the higher the current has to be. So, for 200 Watts, we get the following:

8 ohms, current is 5 amps
4 ohms, current is 7.07 amps

Except a GK400RB will be 125 watts with a single 8 ohm cab so current would be 3.95 amps?

[David]

Excellent, thanks for that cjj I think I'll use the speakon socket instead of the jack socket on my cab and get a good cable, is ther really a big difference in cable quality ?

I think speakon sockets prevent shorting so worth using 1/4" to speakon cable with a 400RB as its safer at the cab end at least

[martyforrer]

There's another factor at play here.... speaker and cabinet efficiency. An 8 ohm cabinet with a 99db efficiency is going to be louder than a 4 ohm cabinet of 93db efficiency, despite the amp giving the 4 ohm cabinet more power. You would have to compare apples to apples to get the true picture. Your setup of 4 ohm 4x10 with a 400RB is fine. I doubt you'll hear any real world difference using heavier speaker cables unless you get up to 600 watts+. Having said all that, you will probably get more volume and more "grunt" by using 2 8ohm cabinets because you would be pushing twice as much air physically, plus acoustic coupling will likely give better bass response too.
New outfits such as Bill Fitzmaurice (Harley here on the forum is an agent), Phil Jones Bass and Greenboy are in the process of refining speaker and cabinet design to a point where the traditional big heavy 4x10s, 1x15s, 8x10s, 2x15s etc are now largely outdated and virtually obsolete, although they will always have their adherents. Example.... A Greenboy Fearless 112 has 1x12, 1x6 and a 1" compression driver, weighs a lot less than a conventional cab, and is rated at 900 watts RMS. I forget the effiency, but it's up there. Phil Jones Bass (my rig) uses multiple 5" Neodymium drivers that are very light and will handle around a 100 watts each.

[monster]

...(a) cabinet with a 99db efficiency is going to be louder than a... cabinet of 93db efficiency...
...you will probably get more volume and more "grunt" by using 2 8ohm cabinets because you would be pushing twice as much air physically, plus acoustic coupling will likely give better bass response too.

All good stuff, I think.
Adding a 2nd identical cabinet should result in a +3dB increase, however you need to use the correct impedence settings on a valve amp (usually 4, 8 or 16 ohms) or take note to stay at or above the minimum impedance of a solid state amp.

New outfits such as Bill Fitzmaurice (Harley here on the forum is an agent), Phil Jones Bass and Greenboy are in the process of refining speaker and cabinet design to a point where the traditional big heavy 4x10s, 1x15s, 8x10s, 2x15s etc are now largely outdated and virtually obsolete, although they will always have their adherents. Example.... A Greenboy Fearless 112 has 1x12, 1x6 and a 1" compression driver, weighs a lot less than a conventional cab, and is rated at 900 watts RMS. I forget the effiency, but it's up there. Phil Jones Bass (my rig) uses multiple 5" Neodymium drivers that are very light and will handle around a 100 watts each.

The 'new stuff' is certainly very interesting and the designs are clever; no excuse for hit-and-miss any more!

I'll confess to being an adherent to some old stuff - I really like my pair of TL-606 cabs loaded with Eminence 3015HO drivers.
These drivers claim to have an efficiency of 101dB and I don't find the cabs too heavy or large at this stage.
They seem to work well with my old-school amps too

[martyforrer]

The drivers are unlikely to be reaching that efficiency in those cabs though.

[pins]

All I know is my 4 ohm ( low impedance ? ) 1000 watt Genz Benz 4x10 Uber bass cab is freaking loud !!!! inferior or not I don't know or care !!!!!

and if was was lucky enough to own 2 such cabs I could run them both from my 2 ohm capable Sunn 1200s (1200w@2ohms) amp and create complete and utter devastation.....

oh and cheers for the nuts and bolts cjj

[blues.bass]

All I know is my 4 ohm ( low impedance ? ) 1000 watt Genz Benz 4x10 Uber bass cab is freaking loud !!!! inferior or not I don't know or care !!!!!

EXACTLY!
If it sounds good (to you) - who gives a crap.

[cjj]

All I know is my 4 ohm ( low impedance ? ) 1000 watt Genz Benz 4x10 Uber bass cab is freaking loud !!!! inferior or not I don't know or care !!!!!

EXACTLY!
If it sounds good (to you) - who gives a crap.

And that, right there, sums it up perfectly...

[martyforrer]

Hey Pins.... tell my f****d back again just how heavy is it?

[pins]

bah ! ....a mere paltry 72 inferior lbs marty....no worries for a young fella like me