8 ohm speakers on a 4 ohm amp?

[rcpmac]

My son's Peavey twin speaker 4 ohm stereo guitar amp has a bad speaker.

I am wondering about changing both speakers with a different model speaker however most 12" guitar speakers are 8 ohm. I have been told the result of using an 8 instead of a 4 will result in a reduction of volume, (as a father and resident of the house, this could be a good thing :)).


Coincidently, we still have his old Peavey amp that has the identical speaker in the 8 ohm version. I patched the speaker cable from the bad speaker over to the 8 ohm version. My observation is that the volume levels are the same between the two speakers playing together.


Thoughts?

[Alex Lancaster]

For some reason, most musical instrument amps are rated at 4ohms; If you have 2 8ohm speakers in paralell, You´ve got 4 ohms.

I got my son an amp for bass, and built a cabinet with an 8 ohm speaker, theoretically You should get a 3dB reduction in output, but it is loud enough.

Alex.

[rcpmac]

Originally posted by Alex Lancaster
For some reason, most musical instrument amps are rated at 4ohms; If you have 2 8ohm speakers in paralell, You´ve got 4 ohms.

I got my son an amp for bass, and built a cabinet with an 8 ohm speaker, theoretically You should get a 3dB reduction in output, but it is loud enough.

Alex.

I don't believe you are correct about "most amps" being "4 ohms". Of all the 12" fender speakers listed on their site, only one is 4 ohms and it only has one application, an amp that is out of production for 4 years now.

Similar stats over at Peavey.


Eminence, which makes the lion's share of OEM and aftermarket guitar speakers, has no 12" 4 ohm speakers,- 1 15" 4ohm, and 1 or 2 6"and 8" classic replacement speakers for little 15w tube amps..

Tha Amp as I mentioned, is stereo and thus 4 ohms per channel. Putting the speakers in series or parallel isn't an option.

[scott fitlin]

If the amp has a transformer coupled output like a McIntosh it will drive any speaker! Just that with a 4 ohm coil it will sound the best because they optimized the amp to do so.

If the amp delivers more power as the impedance drops, it will still drive any speaker 4 ohms or up, just as the impedance of the driver increases, the power output of the amp decreases!

Most musical instument amps are rated 4 ohms because they like to use 4 ohm drivers or two 8 ohm drivers in parallel to get the higher output! look on the back of an old Marshall amp and its marked 4 ohms! 4 ohms can also be the minimum impedance rating of the amp. Many manufacturers mark the minimum rated load impedance on the back panel of the amp as well as stating it in the manual.

The amps outputs see whatever the impedance of the drivers they power. Its not carved into stone that the amp outputs are 4 ohm impedance!

But 4 ohm guitar woofers are available, and if thats what it originally had, get another 4 ohm speaker. eminence does in fact make certain models with 4 ohm coils. They dont make all drivers available with 4 ohm coils though.

BTW, whether you use two 8 ohm drivers in parallel or 1 four ohm driver, 4 ohms is 4 ohms!

Of course, you could contact peavey, and find out if they have replacement drivers for your amp!

[rcpmac]

I've reviewed the eminence line of guitar speakers. There aren't any 4 ohm 12" drivers available.

I will likely replace the driver with a Peavey. This exploration was to determine my options.

Point of interest. Peavey makes these speakers in such a manner that one can unbolt the magnet and core, remove it and buy a basket assembly which includes the cast aluminum frame and pre mounted cone/voicecoil. The process is to clean the slot out with double stick tape and carefully slip the magnet into place and bolt it up. The basket assembly is cheap at $52.00.

[Mr. Widget]

That repair option is interesting, and if your son is happy with the original sound of the amp, that sounds like the way to go.

As far as impedance is concerned, if the amp is a 4 ohm design, then you want 8 ohm speakers as two 8 ohm speakers in parallel is a 4 ohm load as Alex pointed out.

[GordonW]

Sounds like a Scorpion or Black Widow. IIWM, I would just get the replacement Peavey basket and do the rebuild. Saves the problem of any potential change in the sound of the amp due to the change in speaker, change in amp loading, etc...

I wish more pro manufacturers would make things as easy as Peavey, Hell, with the prices JBL charges for cone kits, you'd expect a new, loaded basket from them as well!! :p

Regards,
Gordon.

[scott fitlin]

Originally posted by rcpmac
I've reviewed the eminence line of guitar speakers. There aren't any 4 ohm 12" drivers available.

I will likely replace the driver with a Peavey. This exploration was to determine my options.

Point of interest. Peavey makes these speakers in such a manner that one can unbolt the magnet and core, remove it and buy a basket assembly which includes the cast aluminum frame and pre mounted cone/voicecoil. The process is to clean the slot out with double stick tape and carefully slip the magnet into place and bolt it up. The basket assembly is cheap at $52.00. This is called " field replaceable " and is a good thing! cheaper than reconing, and if you have the part on hand, virtually no downtime!

Peavey is very much in buisiness, they sell alot of stuff and are quite popular, and in my opinion, peavey replacement parts are the only real option.

[rcpmac]

Yea...replacing the the peavey is the practiclal thing to do...but so boring! I've had two people in the business advise me to get rid of them and use Jensen or Eminence. I've even found someone who will buy the old Peavey speakers (1 good 1 bad) for $75. Hmmmmm.

[scott fitlin]

first of all, did you like the sound of the Peavey amp when it worked properly? If you did, you replace the parts with original manufacturers specified parts!

now if you go with another 12in driver, are you sure you know how its gonna sound? Theres alot of MI drivers and each has its own unique sonic flavor! And each musician likes a particular one for whatever reason. Good chance that if you use something other than what was originally in the cabinet it wont sound the same way!

Something to think about.

[rcpmac]

Scott,
No, I don't like the sound of the Peavey Scorpion. Listening to other speakers in this amp is going to be difficult as you can imagine.
Two different guitar amp gurus have recommended replacing the scorpions with almost anything. Although Jensens are mentioned. As thjey do have a 100W 4 ohm 12" guitar speaker, I am inclined to follow that route.

Now get this. As we discussed, the mafnet assm. is easly removed from the basket/cone/voice coil assembly. My son and I pot an ohm meter on the terminals of the bad unit, and it indicated an open circuit. We pulled the magnet assm. exposing the VC and immediately noticed that the lead to the voice coil from the terminals is soldered at the top edge of the VC. A few probed with the ohm meter quickly revealed the solder joint had failed!
Out comes the iron. touch up the joint, test at the terminals indicates 3.8 ohms. Bolt on the magnet and stick in back in the cabinet. Total time including removing the front screen, removing the speaker diagnosis repair and replacement and then playing a few riffs was 65 minutes.

So what's next? I sold the scorpions for $100 to a guy who has the same amp and I am placing an order for the jensen c12k 4 ohm guitar speakers from DIYproaudio.com for $63 ea. Dirt cheap! Most places get $99 for that one.

Thanks again for all of the discussion.
I will post when the Jensens go in. (:fingers crossed:)

[jackrhein]

Almost all modern guitar amps are 4 ohm amplifiers. This requires (2) 8 ohm speakers wired parallel. the peavey speakers are horrible but if you replace them with high quality speakers the sound will be louder and much more aggressive and penetrating. I would replace the blown peavey with an 8 ohm jensen speaker and it will sound fine.

[grumpy]

dude, this thread is like four years old...