OHM gonna blow up my amp!

gavinmurph

I have a homemade 2x12 cab with 2 8 ohm speakers in it but have an opportunity to get a 16 ohm vintage 30, is it possible to run them in the same cab ? If so, what impedance should i plug it into on my amp head?
Will i blow it up or blow valves ? :eek:

Thanks in advance for your opinions.

CianRyan

Well i really don't know much about this subject but i always presumed you set your amp(if possible) to what ever your speakers run at. After all the rest of the cab is just wires and wood right?

As i said, i don't know much about this, so wait for thee others to pop in before making any moves.:p

Seziertisch

gavinmurph wrote: »

I have a homemade 2x12 cab with 2 8 ohm speakers in it but have an opportunity to get a 16 ohm vintage 30, is it possible to run them in the same cab ? If so, what impedance should i plug it into on my amp head?
Will i blow it up or blow valves ? :eek:

Thanks in advance for your opinions.

If the cab is wired in series at the moment it is rated at 16 Ohms (8 + 8 = 16), if it is wired in parallel it is (8 x 8) = 64 = 4 Ohms
..................................... ..................................................................................................... (8 + 8).....16

Your amp probably has 4, 8 and 16 Ohm settings. Do the math, if you replace one of the speakers with a 16 Ohm speaker you are not going to get any of those numbers. That said, replacing as is is probably not going to immediately damage your output transformer. I so know though that an impedance mismatch with the speaker the lower of the two is just asking for trouble i.e. connecting a 4 Ohm speaker load to an amp with an 8 Ohm output.

In the case of going the opposite direction, I am not so sure i.e. connecting a 24 Ohm (8 and 16 wired in series) load to a 16 Ohm output, or an approx 5.3 Ohm (8 and 16 wired parallel) load to a 4 Ohm output. Such a difference would probably affect the tone of your amp (potentially quite significantly), although you may or may not like the change, I don't know. I have never heard of such a mismatch damaging an amp as such, and in the case of a load difference of just one of two ohms with the speaker the higher of the two ratings (as in the case of an 8 and a 16 Ohm speaker wired in parallel), I don't think it should alter the sound of your amp that significantly.

That said, I personally have never experimented so I can't say for sure. There are others on here who are more knowledgeable than I am on the subject, and I am sure they could probably tell you more.

Paolo_M

gavinmurph wrote: »

I have a homemade 2x12 cab with 2 8 ohm speakers in it but have an opportunity to get a 16 ohm vintage 30, is it possible to run them in the same cab ? If so, what impedance should i plug it into on my amp head?
Will i blow it up or blow valves ? :eek:

Thanks in advance for your opinions.

You need to tell us what amp you are using.
Also, are you getting a pair of V30s or just the one?
How is your cab currently wired, series or parallel?
What speaker types are currently in there?

If it's just the one V30 (and it seems it is) the impedance mismatch with the amp wont be the problem. Seziertisch mentioned the frequency responce may skew slightly. I've done a lot of eperimenting here and a 100% mismatch does produce a noticable skew, but this can easily be dialed out with the amps EQ. A 50% mismatch will be even less noticable.
If you currently have two 8s wired in series then the amp sees 16 ohms. With an 8 and 16 in series the amp will see 24 which isn't a significant mismatch for most transformers, we do need to know the amp though, some amps use less equal transformers than others!!. :pac:

Your problem will be that the lower impedance speaker, ie the existing 8 ohm, will draw most of the power.
This poses two problems; a. the 8 ohm speaker will need to be capable of dissipating most of the amps power or it will blow eventually and b. most of the sound will come from the 8 ohm and the V30 will get swamped.

Mixing speakers in a 2 X 12 is cool, you can really blend the best aspects of mutiple speakers, I run a V30 and G12H combo myself. To get the best tone and ensure that your speakers stay healthy, it's best to have the speakers matched impedance wise.
You'll notice that the power handling for the G12H is 30 Watts whereas the V30 is 60 Watts. That's perfectly fine as long as you remember that your 2 x 12 cab can only handle double the power handling ability of the lesser speaker, in my case it's 60 Watts.

gavinmurph

Sorry i should have been clearer , i want to put an 8 ohm celestion wolverine & a 16 ohm vintage 30 into a cab together using a blackstar ht 5 head.

jimmy99

gavinmurph wrote: »

Sorry i should have been clearer , i want to put an 8 ohm celestion wolverine & a 16 ohm vintage 30 into a cab together using a blackstar ht 5 head.

Using a 8 ohm & 16 ohm together with a tube is not possible.It will give a total load of either 12 ohm or 6 ohm which is not compatible with the output transformer in your blackstar.

Paolo_M

gavinmurph wrote: »

Sorry i should have been clearer , i want to put an 8 ohm celestion wolverine & a 16 ohm vintage 30 into a cab together using a blackstar ht 5 head.

In that case, the ohm mismatch will be fine but and you probably wont have and speaker problems because, AFAIK, the HT5 is a 5 watter so it can push out enough power to do any damage.
I don't think it will sound go though, as the wolverine will drown out the V30. Some people would probably say that's a good thing!!

Paolo_M

gavinmurph wrote: »

Sorry i should have been clearer , i want to put an 8 ohm celestion wolverine & a 16 ohm vintage 30 into a cab together using a blackstar ht 5 head.

In that case, the ohm mismatch will be fine but and you wont have and speaker blowing problems because, AFAIK, the HT5 is a 5 watter so it can't push out enough power to do any damage to either speaker.
I don't think it will sound good though, as the wolverine will drown out the V30. Some people would probably say that's a good thing though!!
I actually quite like the V30 once it settles down, for the record.