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-   -   250w at 8 ohm = 500w at 4 ohm? (http://www.talkbass.com/forum/f15/250w-8-ohm-%3D-500w-4-ohm-1016811/)

 bloodshot sun 09-20-2013 09:56 AM

250w at 8 ohm = 500w at 4 ohm?

Would i lose any volume if i played 250w @ 8 ohms rather than 500w at 4 ohms? and also on the amps that can do both 4 ohms and 8 ohms do you change it manually?

 HolmeBass 09-20-2013 10:02 AM

You will lose a bit of volume going from 500w to 250w, all else being equal, but perhaps less than you might expect. Only about 3dB, which is clearly audible, but still not a lot. If your master isn't maxed out, you can make it up by turning the master up. If you are also changing the number/type of speaker cabinets you are using, you will probably experience more of a change in volume, especially if you are losing / using fewer speaker cabinets.

As for the 2nd question, it really depends on your amp. On an amp with a solid state power section, no need to switch, just plug in the different load. On a tube amp (tube power section) you should use the provided switch, or on some amps, the correct "tap" - the output marked for the load you're connecting.

 xabicho 09-20-2013 10:03 AM

No you do not flip anything this is related to how you connect the speakers to your amp and impedance. Here is some info that can be useful for you.
Impedance is a measure of resistance. When electricity flows to a load some of the electricity is resisted, or impeded. Impedance is measured in ohms (denoted with the Greek letter omega &mdash; &Omega;). Most bass cabinets have an impedance of 4 ohms or 8 ohms.

More ohms (higher number) means more resistance. The more resistance there is, the less power will flow to the speaker.

Bass amp heads specify how much power is sent to a load (a cabinet or group of cabinets) of a certain impedance (the amount of resistance measured in ohms). For example, you may see an amp rated &ldquo;400 Watts @ 4 ohms&rdquo;.

Let&rsquo;s look at an example so you better understand all of this. A particular amp head might send 200 Watts into an 8-ohm load. That same amp might send 350 Watts into 4 ohms. More power will flow from an amp as the ohm rating (resistance) decreases. If you went down to 2 ohms, that same amp might send 600 Watts to the load.

All of this is important because amps are designed to work with a certain resistance in mind. If there is not enough resistance, the amp will put out more juice than the amp can handle, and it will overheat and burn up! You don&rsquo;t want your precious bass amp catching fire no matter how cool it looks on stage.

 karl_em_all 09-20-2013 10:46 AM

The answer is yes. You will lose volume. Most amps don't have impedance switches. If yours doesn't just plug in and play with either of the following combinations:

You can run a single 8ohm cab (you won't be using the amp's full power),
2 x 8ohm cabs (amp runs on 4ohm delivering full power),
or a single 4ohm cab (amp delivering full power).

Note: never pair a 4ohm cab with an 8ohm cab.

And: an impedance switch on an amp will allow you to switch your amp between 8ohm and 4 ohm. This allows for the amp to deliver full power with the single 8ohm cab scenario (purpose is to allow a for smaller but powerful rig set up).

For the other 2 scenarios switch it to 4ohm.

 SactoBass 09-20-2013 10:56 AM

Quote:
 Originally Posted by karl_em_all (Post 14893353) Note: never pair a 4ohm cab with an 8ohm cab.
...unless your amp can handle a 2.67 ohm load, then it's perfectly okay. Some amps can handle a 2 ohm load, but make sure it can, because many amps cannot handle a 2 ohm load.

 CL400Peavey 09-20-2013 11:07 AM

Quote:
 Originally Posted by karl_em_all (Post 14893353) Note: never pair a 4ohm cab with an 8ohm cab.
Um not quite.

Quote:
 Originally Posted by SactoBass (Post 14893394) ...unless your amp can handle a 2.67 ohm load, then it's perfectly okay. Some amps can handle a 2 ohm load, but make sure it can, because many amps cannot handle a 2 ohm load.
+1

In fact there are cases when you *should* run a 4 Ohm cab with an 8 Ohm cab.

i.e. a four Ohm 410 with an eight Ohm 210. This only works if your amp is 2 Ohm stable.

 karl_em_all 09-20-2013 11:09 AM

Good point SactoBass. I was making an assumption in my last post. Let's investigate!

@bloodshot sun: what amp are you using?

 Remus_Redbone 09-20-2013 11:14 AM

Quote:
 Originally Posted by bloodshot sun (Post 14893113) Would i lose any volume if i played 250w @ 8 ohms rather than 500w at 4 ohms? and also on the amps that can do both 4 ohms and 8 ohms do you change it manually?
The answer to the first question can only be "maybe" without the other variables considered.

One scenario where the answer would be "no" is if the 8 ohm speaker had a sensitivity rating of 100db and the 4 ohm speaker had a sensitivity rating of 92db. There are many other variables that can toggle the answer to your question between "yes" & "no". "Watts" are only one of the many factors in determining "volume".

The answer to the second part about changing the impedance of the amp output is also variable. Lots of tube amps have an impedance selector. Few, if any, SS amps in production have an impedance selector switch.

 BassmanPaul 09-20-2013 11:40 AM

Several SS amps have impedance switches. The Carvin BX500 is one and IIRC so is the Orange Bass Terror. It allows the user to run into a 4Ω minimum at the 4Ω position and a 2Ω minimum at the 2Ω position.

 karl_em_all 09-20-2013 11:42 AM

Quote:
 Originally Posted by BassmanPaul (Post 14893604) Several SS amps have impedance switches. The Carvin BX500 is one and IIRC so is the Orange Bass Terror. It allows the user to run into a 4Ω minimum at the 4Ω position and a 2Ω minimum at the 2Ω position.

I don't know about the other ones but the Orange TB500 (Terror Bass) switches from 8ohm to 4ohm.

 Remus_Redbone 09-20-2013 12:01 PM

Quote:
 Originally Posted by BassmanPaul (Post 14893604) Several SS amps have impedance switches. The Carvin BX500 is one and IIRC so is the Orange Bass Terror. It allows the user to run into a 4Ω minimum at the 4Ω position and a 2Ω minimum at the 2Ω position.
Quote:
 The answer to the second part about changing the impedance of the amp output is also variable. Lots of tube amps have an impedance selector. Few, if any, SS amps in production have an impedance selector switch.
Sounds like "few" was an accurate description. A few more than I was aware of, but still "few".

Do you know if those amps have a transformer coupled output?

 bloodshot sun 09-20-2013 03:20 PM

I don't yet :p just asking to see what cabs i should buy with the aguilar tone hammer 500 ... whether i should go with 2 of their 8 ohm 250w sl112s or go cheap since i don't have much of a budget and get a fender rumble 410 500w rms at 4 ohm and just call it a day ...would cost around 30% of the 2 sl112s

 two fingers 09-20-2013 03:29 PM

.

 bloodshot sun 09-20-2013 03:38 PM

two fingers you have the exact same bass as mine dude ...high-five !

 Downunderwonder 09-20-2013 03:49 PM

Quote:
 Originally Posted by bloodshot sun (Post 14893113) Would i lose any volume if i played 250w @ 8 ohms rather than 500w at 4 ohms? and also on the amps that can do both 4 ohms and 8 ohms do you change it manually?
It depends on which implied assumptions one takes up.

If you're talking about the difference between one cab and two cabs, around 6db advantage to using two cabs.

Substituting a 4ohm for an 8ohm could make no difference, some difference, or even lose headroom, depending on the cabs.

 Major Softie 09-20-2013 04:08 PM

Quote:
 Originally Posted by bloodshot sun (Post 14894705) I don't yet :p just asking to see what cabs i should buy with the aguilar tone hammer 500 ... whether i should go with 2 of their 8 ohm 250w sl112s or go cheap since i don't have much of a budget and get a fender rumble 410 500w rms at 4 ohm and just call it a day ...would cost around 30% of the 2 sl112s
The 2 Aguilars will give you a lot more flexibility, as well as being much more easy to transport. The sound will also be significantly different, but what sounds better is up to you (although I imagine the majority here would probably prefer the 2 Ags).

As far as volume, It depends on the sensitivity, but it's really hard to know for sure since Fender chooses not to give that spec on the cabinet (something that steers me away from it right there). The 4 ohm 410 will probably be a lot louder than just one of the 8 ohm Aguilar 12's, but it's hard to know how it will compare to two of them - probably pretty close, but who knows? The two 12's may even be significantly louder than the 410.

 will33 09-20-2013 04:11 PM

Quote:
 Originally Posted by two fingers (Post 14894773) .
+1

 bloodshot sun 09-20-2013 04:27 PM

Quote:
 Originally Posted by Major Softie (Post 14894969) The 2 Aguilars will give you a lot more flexibility, as well as being much more easy to transport. The sound will also be significantly different, but what sounds better is up to you (although I imagine the majority here would probably prefer the 2 Ags).

of course i would prefer the ags myself too but there's a mountain of a price difference and much more subtle tone difference..if i had the budget definitely ag but i don't want to put myself in a tight spot

 karl_em_all 09-20-2013 06:55 PM

Quote:
 Originally Posted by bloodshot sun (Post 14895033) of course i would prefer the ags myself too but there's a mountain of a price difference and much more subtle tone difference..if i had the budget definitely ag but i don't want to put myself in a tight spot
That Fender cab will get the job done and be easy on the wallet too. Besides, you have the rest of your life for upgrading :D

 SactoBass 09-20-2013 07:03 PM

Quote:
 Originally Posted by karl_em_all (Post 14893474) Good point SactoBass. I was making an assumption in my last post. Let's investigate! @bloodshot sun: what amp are you using?
Well, it turns out you were right with your assumption if he is going with a TH 500. Min 4-ohm load with that puppy!

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