Discussion in 'Amps [BG]' started by shanabit, Nov 4, 2012.
Im looking at that cab. Should I get the 8 Ohm or 4 Ohm version? Havent decided on the head yet
Get the 8 ohm version, so you can double up later. The difference in volume between the 2 will be minimal, (4 ohm vs 8 ohm), but the pair will be considereable, (8 ohm + 8 ohm).
Thanks man, appreciate it. This will be my first bass cabinet
Thats what I was thinking too, get another Neo212 when I need it and if I do
Got to figure out the amp head next
The decision depends on the driver impedance being used in the cabinet and how the drivers are wired as Series or Parallel.
For example, Eminence makes both 4 and 8 ohm versions of several driver models.
For a given unit of power, they are virtually identical in output.
A 4-ohm driver is not "louder" than the 8-ohm version. It just gets there at a lower voltage level.
Amplifiers are voltage devices, and the Volume knob is the general indicator of some voltage level.
If you leave the knob unchanged, the 4 ohm cab will be louder than the 8 ohm cab, because it draws more power.
For example, 2.83 volts into 8 ohms is 1 watt.
2.83 volts 4 ohms is two watts.
The knob setting is unchanged, but the lower impedance draws 2x more power.
Here is where it gets ugly under the surface:
The 8-ohm version of a 2x12 can be either two 4-ohm in series, or two 16-ohm in parallel.
More than likely, the 2x12 is a pair of 4-ohm in series.
For a series pair, sensitivity decreases by -3dB because each driver only sees half the voltage.
The doubling of the cone area increases sensitivity by +3dB over a single speaker.
A parallel wired pair gains +3dB sensitivity from the doubled power handling.
It also gains another +3dB boost from the doubling of the cone area.
A parallel wired 2x is +6dB higher sensitivity than a 1x of the same driver.
An arbitrary example of one 12" driver at 95 SPL at 2.83 volts.
1x = 95
2x series = 95 +3 -3 = 95
2x parallel = 95 +3 +3 = 101
The ideal solution is having all your drivers, and all your cabs wired in parallel.
This means a head capable of sustained 2 ohm operation, or a two channel power amp.
I run all PLX which are two channel, and 2-ohm capable.
A 4-ohm load in each channel is a safe and effortless load for the PLX.
Heads can be less tolerant of low impedance loads.
In the situation where you require two cabs, a simple series-wired box lets you run a pair of 4 ohm cabs as an 8-ohm load.
For normal conditions, you run a single 4-ohm cab which makes more noise for a given volume knob setting.
G-K only uses parallel wiring in their speaker cabs.
Most 212 cabs are 4ohms, so you would probably really be limiting your brand choices. Most use the same drivers that they use in their j112's, which are typically 8ohm, resulting in 4ohm impedance when using two in one box.
If you know you are only going to use one cab, and/or have a moderate power or less amp (i.e., 500 watts into 4ohms or less), a 4ohm version will give you a bit more volume and typically (assuming it is a decent one) a more open, less compressed tone, since you are less likely to hit power amp limiting.
If you have a higher power amp that puts out good power at 8ohms, or think you might want a second one eventually, 8ohms is the way to go if you can find one.
G-K Neo and MBE 212 cabs are 8 ohm cabs. Wired parallel 16 ohm drivers.
+1 There 8ohms are out there. Of my four favorite 212's, three are 4ohms only (Genz Neox212 or Uber212, Bergantino AE212 or HD212, Audiokinesis TC212), and one has an 8ohm/4ohm option (Aguilar DB212)
Whoa... I suggest that you re-check your math here, I think you failed to account for the different driver inpedances in parallel versus series as well as a squared factor.
An 8 ohm cabinet with 2 x 4 ohm drivers in series is identical with respect to power, power handling, and sensitivities (assuming the raw drivers have indentical power sensitivities) to an 8 ohm cabinet using 2 x 16 ohm drivers in parallel.
the easiest way to see this is with the total power equation, and that power can not be gained or lost but must be completely represented through a seires or parallel circuit.
(for a series pair, using total power into 8 ohms as 100W, or 3.5 amps)
P1=Itotal squared x 4 = 49 watts
(for a parallel pair, using total power into 8 ohms as 100W, or 3.5 amps)
Ptotal=P1+P2, P2=P1 (parallel branch eq.)
Itotal=I1+I2, I1=I2 (parallel branch eq.)
P1=I1squared x 16 = 1.75**2 x 16 = 49 watts
The individual driver power as well as the total power will be identical in both configurations.
As far as acoustic coupling goes, they will be identical as well.
Yall went deep quick. Let me clear this up a bit. Im looking for a 2x12 cabinet to hook up a head to here. I just saw that the G & K had a 8 and 4 Ohm version and wanted to know the preference. Im NOT a bass guy per say so this is all new to me. I dont know if Ill want another 2x12 to go with it or not, probably wont need that to be honest.
Ill add the head once I figure out which cabinet, 4 or 8 Ohm if you will.
Love the information so far and much appreciated. Remember, Im a keyboard guy so we think differently. Patches, MIDI controller numbers, etc.
The 4 Ohm, 8 Ohm diff and regards to power/watts and all that is quite new to me.
Be easy on me.. I have figured out I like the sound of the 12 verses the 10 or 15
Simply, this is what you will need to make an informed decision:
1. if you plan on adding another cabinet in the future and the amp's minimum rated load is 4 ohms than you must get the 8 ohm version
2. If you do not plan on adding another cabinet, and the cabinet's power handling is adequate for the amp's rated 4 ohm power than the 4 ohm version will get you the most performance out of that single cabinet.
3. If the amp is capable of significantly more power at 4 ohms than the cabinet can SAFELY handle then it may be better to get the 8 ohm version... or you can hope that you have good judgement when it comes to driving the cabinet out on a gig so that you do not damage it.
Short story.....8 ohm cab.
As Rickenboogie posted, get the 8-ohm. You'll get very little increase in output if you get the 4-ohm, and you'll end up driving your head harder than it needs to be driven for little gain (especially if you're running things loud). If you do eventually want more output, you run a second 8-ohm in parallel and you move twice as much air at a 50% power increase. THAT will make a difference.
If it means anything to you, I have a GK 212 Neo paired with a GK 700RB-II and it's a great rig for what I need and like. So, try out a few setups to be sure you're getting what you like.
There is no simple answer regarding the best thing to get. If you are really confused, get the 8ohm... it will never do you any harm. If you want to really sit down, read the impedance stickies on this site, and do a little more homework, you will find out that if you are sure you will only use a single cab, a 4ohm version of a high quality 212 can make more of a difference than you think.
Those who say 'always get the 4ohm' or 'always get the 8ohm', IMO don't really understand the issue.
Again, no harm in not really wanting to deal with all of this. If you are confused, the 8ohm will allow you the most 'error range'.
If you are concerned with moving twice as much air, solve the displacement equation and the increased power of a 4 ohm cabinet will do exactly this./
Assuming the cabinet is adequately rated for the amp's power. Otherwise, power compression will rob you of much of this gain. Adding speakers will improve performance (less power compression if that was a limiting factor) and low frequency extension some due to coupling however, which (assuming transportation allows) might justify choosing 2 x 8 ohm cabinets over a single 4 ohm cabinet.
Agreed. There is really no "best" solution for everybody, it's not a black and white decision.
I do recommend that he review the stickies and learn, knowledge is always a good thing.
+1 It all depends... cabinet efficiency, absolute power of the head, mechanical specs of the cab, etc., etc., etc.
I have 8ohm cabs that totally scream with limited power at 8ohms. I have cabs that go way deep, and can use ever drop of power you can give them at 4ohms.
Yes there is no one correct, best answer if you have the understanding of all variables.
IMHO the answer I offered was just the safest/best for this OP
I"ll +1 that
You should buy mine!
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