Not to hijack, but this really struck a chord in me. I intended to get a matching MB210-II for the one I already have to use the full 500W power rating. Do I understand correctly, that I may overpower one of my two amps?
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Ohms - How do they work?
- Thread starter jmattbassplaya
- Start date
amps or cabs? GK have powered extension cabs for some models so I don't know what you are operating or intending.
I presently use a 210 combo. I want to chain it up with another one of the same kind, as the MBE is no more.
I don't know what your chaining options would be but it's not uncommon. Just don't take extension cab out to amp in. That will kill both amps instantly.
You might find an extension cab that sounds good enough.
As a calculator-less "rule of thumb" for parallel loads/speakers, the total impedance will be lower than the speaker with the lowest impedance.
e.g: 8 Ohm in parallel with 4 Ohm will result in an impedance lower than 4 Ohm. Even if one of the speakers is 500 Ohm, when in parallel with a 4 Ohm, it'll be lower than 4 Ohm. (actually approximately 4 Ohm, since the other load is so high it can be "somewhat" ignored, but those are technicalities
To be precise, 8 // 4 = 2.666(6) Ohm
And also, 500 // 4 = 3.968 Ohm
In series, that would be 12 Ohm and 504 Ohm respectively. But since usually cabs are connected in parallel, use rule above I've seen folks using the average formula to calculate this, and it's oh so wrong. 8 // 4 is not definitely 6.
But the current flowing through the cabs won't be the same, doesn't this affect the volume? Imagining that we can rewire the same cab for 8 and 4 Ohm, the speaker configuration would change, and so the current flowing. I'm trying not to confuse dissipated power with volume, although if the volume is the same for less power dissipated, it would become a more efficient system
Great thread!
e.g: 8 Ohm in parallel with 4 Ohm will result in an impedance lower than 4 Ohm. Even if one of the speakers is 500 Ohm, when in parallel with a 4 Ohm, it'll be lower than 4 Ohm. (actually approximately 4 Ohm, since the other load is so high it can be "somewhat" ignored, but those are technicalities
To be precise, 8 // 4 = 2.666(6) Ohm
And also, 500 // 4 = 3.968 Ohm
In series, that would be 12 Ohm and 504 Ohm respectively. But since usually cabs are connected in parallel, use rule above
I've seen folks using the average formula to calculate this, and it's oh so wrong. 8 // 4 is not definitely 6.But the current flowing through the cabs won't be the same, doesn't this affect the volume? Imagining that we can rewire the same cab for 8 and 4 Ohm, the speaker configuration would change, and so the current flowing. I'm trying not to confuse dissipated power with volume, although if the volume is the same for less power dissipated, it would become a more efficient system
Great thread!
I never really gave this matter much thought when younger i just accepted that you matched the appropriate size cab to the amp.
The one thing i was told was that the lower the ohms the better the set up worked for bass, it got a better response drawing less power, so was going to be more stable in output, and more reliable.
The ideal set up for bass was 2 ohms, then 4ohms, then 8ohms, then 16 ohms, though 16 ohm setups are rare these day.
Peavy used to make 4 ohm cabs, with bins/cabs with 15" speakers that could take 2 ohms i believe, one of, if not the only, companies to do so that i knew of.
Like i said this was what i was told by an engineer, is there any truth to these statements, or are they just rules of thumb?
The one thing i was told was that the lower the ohms the better the set up worked for bass, it got a better response drawing less power, so was going to be more stable in output, and more reliable.
The ideal set up for bass was 2 ohms, then 4ohms, then 8ohms, then 16 ohms, though 16 ohm setups are rare these day.
Peavy used to make 4 ohm cabs, with bins/cabs with 15" speakers that could take 2 ohms i believe, one of, if not the only, companies to do so that i knew of.
Like i said this was what i was told by an engineer, is there any truth to these statements, or are they just rules of thumb?
Totally the opposite of the truth..
The cabinet impedance (or resistance/ohms as some call it) has very little effect on the response, or 'suitability for bass'.
Too low impedance for an solid state amp will make it unstable, and make the amp work harder to provide more power.
the ideal setup is to have the cabinet impedance match the amp's rating.
Did you mean amps which could run at minimum 2 ohm load?, there are many which are 2 ohm rated.
I have a Marshall MB450H amp which is rated to run at 2 ohms = 450 watts, 4 ohms = 300 watts output, but with 2 ohms cabs (2 x 4ohms) it has run into thermal shutdown on me twice.
Either the Engineer got it wrong, or you may have mis-heard.
Nice explanation except the last line is incorrect. A speaker with higher impedance can be connected to an amp rated for lower impedance (8 ohm to a amp rated for 4 ohm) but not visa versa.
I saw this a long time ago.......
with all the answers already posted it might help
with all the answers already posted it might help
Ric5
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- Jan 29, 2008
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Like i said a long time ago and he did build Valve Amps, so i do not know if that has a bearing on it.
Obviosly you match the cab to the Amps rating, or have duel impeadence amps and cabs.
His point was that bass amps worked better on a low ompeadence rather than a hight one, 4ohm being ideal that can rate to 2ohm, again this was about the amps working, not volume.
Loke i said i really take no interest in how these matter work, i just make sure the cabs and amp match, or are compatable, i run a 4 ohm rig of two 1x12 cabs rated at 8 to give me a 4ohm load.
8 and 4 ohm cabs seem to be popular with Manufacturers, so maybe there is something in lower impedence for bass gear...maybe technology is making it easier today?
Yes being young i may have mis-heard him, but it was over 40 years ago...maybe i am mis-remembering LOL..
Ohms themselves have no impact on volume. They are more a measure of how a given amp and a given cab will play together. A 4 ohm cabinet receiving a signal from an amp that puts out 500 watts (into a 4 ohm load) should be indiscernible (volume wise at least) from an 8 ohm cabinet receiving a signal from an amp that puts out 500 watts (into an 8 ohm load). The difference is that (generally) the amp that can put out 500 watts into 8 ohms can probably put out 800-900 watts when connected to a 4 ohm load. So for a single cabinet a 4 ohm load will seem louder as it can get more signal from the amplifier. But, if you connect two 8 ohm cabinets in parallel then you are getting the higher wattage output (2 8 ohm cabs in parallel = 4 ohm load) AND you have more speakers to move air, so that setup will sound even louder (assuming all the cabinets are equivalent of course).
Confused yet?
Confused yet?
the sensitivity of a driver has to do with mechanical and electrical properties. and would not be completely based on the impedance. so some 4ohm drivers could be "louder" and some could be less. but it's not all based on the impedance.
and yes some guys just don't get it
a amp is only as powerful as it's power supply. and the power supply doesn't magically grow with a lower impedance. a lower impedance draws more current....more current
and yes some guys just don't get it
a amp is only as powerful as it's power supply. and the power supply doesn't magically grow with a lower impedance. a lower impedance draws more current....more current
To a point - The output stage must be able to flow enough current without burning out too.
Thanks for the explanationthis part I actually do already understand. I guess my main question is regarding the question of loudness between a 4 and 8ohm cab.
They don't directly tell you any measurement of volume/loudness. An ohm is a measurement of load or resistance on a circuit. You can use this measurement to understand how many watts are going to go through the circuit to whatever devices you are powering (in our case speakers) but again, they don't really give a direct measurement of how loud something is. For that you need to know how efficient the speakers are, their frequency sensitivity and how much "air" they push. Very sensitive speakers will move a lot with less energy (watts) and give you more volume than a less efficient speaker would. An 8 ohm cabinet isn't necessarily quieter than a 4 ohm cabinet, although powered by the same amplifier you know that the 4 ohm would get more juice. What defines how loud they go is the speakers that are being powered + how much juice they get. If the 4 ohm cab has inefficient speakers, it might be the same as or quieter than the 8 ohm. It all depends on what gear you are using. These things are more about the system of components you are using than any 1 individual rating.
There's lots of good information in this thread but please remember you are asking about 1 small piece of an equation that adds up to your sound, which includes volume, tone and everything else you want to have control over. Some other things to keep in mind:
- Two 8 ohm cabinets net a 4 ohm load. Two 4 ohm cabinets net a 2 ohm load. Mixed ohm (ie, 4 and 2) are messy and not really a clean solution for 1 setup unless you have a more sophisticated amp designed to do this.
- Most bass amps can be safely run at 4 or 8 ohms. Some can run at 2, but you want to make sure of the capabilities of what you have.
- If you have an 8 ohm cabinet and later decide you need more speaker, you can usually add another 8 ohm cabinet to get a 4ohm yield and probably be safe (depending on what your amplifier can handle, see above). If you try the same thing with a 4 ohm cabinet and decide you need more, you better well make sure your amp is 2 ohm stable or you risk breaking things (expensive!).
- Speaker sensitivity is important. Speakers are also the quickest path to loud, not necessarily watts. High efficiency speakers and MORE speakers or surface area get you more mileage towards volume than wattage does. Dumping more wattage into something can be a good path towards blown speakers, though. It all depends on the specifics of each piece of the system (amp, cabs, speakers) you decide to use.
- Use common sense. You can use an amp that is capable of making more juice than your cabinets are rated for (say, 600 watt amp into a cabinet rated for 400 watts) and not break things, as long as you don't crank the volume up and pummel your poor speakers. Use your ears - your speakers will give you clues that you are punishing them a bit too much. If it sounds unhealthy, it probably is.
Actually it is the right question. Nothing about the impedance of two cab tells you which is louder.
If you amp is rated for 4ohm and you run an 8ohm cab the amp is not working harder or hotter. Is actually working less hard and cooler. Less ohms means more current more heat more power. Amps are rated for a minimum load usually 4ohms . If you run higher ohms you'll just never get the full power rating . But in reality your never using the full power rating anyway unless you're running wide open on 11 .
