Ohms and extensions - Answers needed!

MattyH · #1 02-01-2011, 06:52 AM

Hey all. I just have some basic questions that I can't find a direct answer on, so what better place to go then Talkbass?

I'm currently running a Hartke LH1000 through a 4ohm Ampeg 410HLF and it sounds great. Clean, powerful, and all around a great match. I know adding another 4ohm cab (say a 1x15 extension, or another 4x10) will bump me down to 2ohm. Does anyone know if the Hartke LH1000 can handle this? I'm not rushing to get one, I just want to know for future reference. What if I added another cab at 8ohm? Where would that leave me?

Thanks guys, cheers

perogato02 · #2 02-01-2011, 06:55 AM

AMPS FAQ!! Info on OHMS, Allsize RIGS-OverUnderPowerCabs DIY TechTalk-Links

very useful for all your questions concerning Ohms - watts and extension cabs

perogato02 · #3 02-01-2011, 06:57 AM

But to answer your questions:
no the Hartke LH1000 can't handle 2 Ohm
Adding a cab with 8 ohm will leave you (very roughly) at 5 ohm ... but the power distribution will awkward.

MattyH · #4 02-01-2011, 07:06 AM

Cool guys thanks. I don't want to get rid of my 4x10, so I guess I'll just have to pick up a 6 or 8x10 cab instead of extensions!

xring · #5 02-01-2011, 07:59 AM

4 ohms + 8 ohms = 2.67 ohms.

ezstep · #6 02-01-2011, 08:13 AM

Quote:

Originally Posted by perogato02

Adding a cab with 8 ohm will leave you (very roughly) at 5 ohm ....

NONONONONONO!!!!

8+4 = 2.67 and a burnt amp.

As far as the distribution... electrically, it will follow the formula, but sonically (what you hear) will also depend on the sensitivity of each speaker. Might sound wonderful. I know a guy running 2x12 @ 4 ohm with 4x10@8 ohm and says the sound is "perfect" to him. Just get a head that can handle 2 ohms and experiment with it.

MattyH · #7 02-01-2011, 08:24 AM

Quote:

Originally Posted by ezstep

NONONONONONO!!!!

8+4 = 2.67 and a burnt amp.

As far as the distribution... electrically, it will follow the formula, but sonically (what you hear) will also depend on the sensitivity of each speaker. Might sound wonderful. I know a guy running 2x12 @ 4 ohm with 4x10@8 ohm and says the sound is "perfect" to him. Just get a head that can handle 2 ohms and experiment with it.

Yea it might be perfect until he smells a burning coming from his head haha. Would pairing it all with a power amp help?

Also, my head is BRAND new, so I'm not going to be buying another one anytime soon(and I LOVE it). So instead of buying a new head, and extension cabs, I can just add an 8x10 for larger shows (even though I haven't needed it, and probably wont any time soon. It would just be cool). Probably the same as lugging around a 410hlf and a 1x15 haha.

I play every single weekend in a wedding band, and also with 2 bar bands, so I'm far from a noob. The ohm section is just what always got me confused. You guys made it very clear though, thanks a lot.

Wes Whitmore · #8 02-01-2011, 08:38 AM

MattyH,
You pretty much got it nailed. You have a great one cab solution, and are getting the most out of your amp now. Switch to a bigger cab if you want a little more, but your sound does change when you switch cabs. If that works for you, then awesome. If you decide you want more of what the 410HLF does, just louder, then get another HLF and a cheap poweramp to run it, sized somewhat close to what the hartke can do. Not spending your money, but I wouldn't put too much money in a power amp. If it got close to the price of a used LH1000, I would just get another LH1000 for preamp reduncancy. You play often enough. It also allows you to split your rig if you need to for some reason.
Wes

perogato02 · #9 02-01-2011, 09:17 AM

Quote:

Originally Posted by xring

4 ohms + 8 ohms = 2.67 ohms.

right, sorry about that, I forgot to inverse it (or how does it get called in English :s)

I stand corrected

Jaco who? · #10 02-01-2011, 10:32 AM

Uhm, the LH1000 is pretty much two LH500s in the same box, meaning you can run both sides together bridged, or each side into it's own cab. You might want to download the manual.

kosmicwizard · #11 02-01-2011, 10:48 AM

Quote:

Originally Posted by perogato02

But to answer your questions:
no the Hartke LH1000 can't handle 2 Ohm
Adding a cab with 8 ohm will leave you (very roughly) at 5 ohm ... but the power distribution will awkward.

This is the first time I have ever heard of a 4 and an 8 Ohm load equaling 5 Ohms ... I have alway heard it is 2.67 Ohms which you can't do with that head because it is only 4 Ohm minimum stable. Cheers.

kosmicwizard · #12 02-01-2011, 10:54 AM

In stereo mode (read not mono-bridged) you can send 375 watts to two different 4 Ohm cabs. Get another 410HLF and run one off each side, if you get an Ampeg 8x10 it is going to have a VERY different tonal character than the ported HLF. If you like your head you should try the Ampeg B4r if you ever get the chance. Cheers.

ezstep · #13 02-02-2011, 09:18 AM

Nearly 100% of the time someone burns an amp, it was because they needed [TIM ALLEN] MORE POWER!!! [/TIM ALLEN] and they hooked up yet another speaker to the chain. It is by far best to carry one - that way you won't be tempted to daisy chain a dozen cabs....

I have been "mentoring" a new bassist, and the first thing I told him to learn and gave him homework about was memorizing cab combinations and overall ohms.

8+8=4
4+4=2
8+8+8=2.67
8+4=2.67
etc.

It saves time, money, and tears in the long run.

It is often humorous to read questions here where a guy has, say, a 2x15 cab @ 8 ohms running, say, a head 400 wts @ 8 ohms, 800@ 4 ohms. They want to know how to get the "full 800 watts" out of their amp. In reality, doubling the power makes the overall volume just a touch (3 db) louder...barely noticeable. And, in reality, if they were running the full 400 wts @ 8 ohms, it would be so loud that there would be no reason to add more volume.

Stay safe, and keep your equipment safe.

50000 Repairs · #14 02-02-2011, 10:09 AM

Basic stuff:Amps impress a voltage (electrical pressure) upon the cab, which represents the load to the amp. The lower the impedance of the cab, the greater the load it is to the amp. In other words 4-ohms is a greater load than 8-ohms. Fortunately, properly designed amps put out more power when the load increases. An amp designed to 'put-out' 150 watts into 8-ohms should almost double its power output to 300 watts into a 4-ohm load. Limiting factors are then the current capability of the speaker and the stability of the amp when driving a larger load (smaller ohms number.)

50000 Repairs · #15 02-02-2011, 10:10 AM

Oh, by the way. If you want your rig to sound twice as loud, 10X power is needed! OMG

50000 Repairs · #16 02-02-2011, 10:17 AM

DC resistance (R1 x R2) divided by (R1 plus R2) is not exactly the same as AC impedance. That is a different formula that is frequency dependent. Far more complicated for the layman to figure.

billfitzmaurice · #17 02-02-2011, 11:52 AM

Quote:

Originally Posted by 50000 Repairs

DC resistance (R1 x R2) divided by (R1 plus R2) is not exactly the same as AC impedance. That is a different formula that is frequency dependent. Far more complicated for the layman to figure.

The formula is exactly the same. Impedance does vary with frequency, but where considering amps, speakers and impedance loads the nominal speaker impedance is used, calculated as if it was resistance.

kosmicwizard · #18 02-02-2011, 12:31 PM

Quote:

Originally Posted by 50000 Repairs

Fortunately, properly designed amps put out more power when the load increases. An amp designed to 'put-out' 150 watts into 8-ohms should almost double its power output to 300 watts into a 4-ohm load.

PROPERLY designed amps are all-tube and do not care if you are running at 4 or 2 Ohms they still give you 300 Watts RMS. Cheers.

tlaubs · #19 02-02-2011, 02:46 PM

I have a similar situation and could use some advice. I have a SWR 350 (red face) and a goliath III jr 2x10 which is 4 ohms.

Found a nice deal on a Ampeg BSE115 8 ohm cab. My amp can run at 2 ohms, and I was hoping the 15 would take some of the bite of the goliath.

In this situation can I add the 15 or is this a bad idea to run at 2.67 ohms? Also, I noticed a reference to akward power distribution earlier in the thread; is this something I need to be concerned about?

Bass_Pounder · #20 02-02-2011, 03:04 PM

Quote:

Originally Posted by tlaubs

I have a similar situation and could use some advice. I have a SWR 350 (red face) and a goliath III jr 2x10 which is 4 ohms.

Found a nice deal on a Ampeg BSE115 8 ohm cab. My amp can run at 2 ohms, and I was hoping the 15 would take some of the bite of the goliath.

In this situation can I add the 15 or is this a bad idea to run at 2.67 ohms? Also, I noticed a reference to akward power distribution earlier in the thread; is this something I need to be concerned about?

Running at 2.67 is not an issue for your amp........

However, the power split is - your 2X10 will get 2/3 of your output, while the 1X15 gets 1/3