ohmage question and suggestions

sandman72202 · April 1st, 2008, 05:13 PM

i picked up a jbl d130 15 in speaker to match my li'l dawg 15 inch. was gonna get jim to build a cab for me but i don't think jim is building his cabs anymore.
i have a sealed closed back 16 ohm speaker cab with 2 OEM eminence V12 thirty watt speakers. i think they are suppose to be eminence knockoffs of greenbacks.
for the sake of economy i'm thinking of just rewireing the 16 ohm cab to make it a 4 ohm cab and using it. the amp is built to see a 4 ohm load. the main 15 inch speaker is an 8 ohm load so i know i'm not getting the full volume out of the 15. as i understand it if i combine the 4 ohm cab with the 8 ohm main speaker it will give me something like a 5. something ohms the amp will see. i'm guessing i will get more sound out of the cab then than the main 15 but the overall load to the amp will be closer to what its looking for. is a mismatch such as this too much ?.....5 1/2 ohms is closer than the 8 ohms its seeing now.
thinking of doing it but was looking for input.
if anyone has a suggestion on some speakers....the speaker in the amp is a jenson p15N. alnico. would like to get alnicos to match but thats not a must.
and please don't start suggesting $100-200 speakers....i'm thinking of this because its a less expensive alternative. i can change the wiring for next to nothing.

Dacious · April 2nd, 2008, 03:15 AM

Not quite sure of what you're asking. If it's a 16 ohm cabinet, must be two 32 ohms speakers wired parallel or two 8 ohm speakers wired serial. If the latter, you can rewire to a 4ohm cabinet by putting two 8 ohm in parallel.

Running an 8 ohm speaker will in parallel will give you 2.66666 ohms.

Impedance = 2.6666666

1/3 rd power will go to each speaker, but it depends on the relative efficiency of the speakers as to which is louder. Teh cabinet will have more speaker area. The sonics could work out good, they could work out bad. As the 15" will get only as much power as the 12s , it'll may tend not to be very good at bass. Alternatively, they may not be real flash at bass so it might work out OK.

If this is a solidstate amp with a min 4ohm impedance, I would not do this. It's runing close to a dead short. A tube amp like most Fenders might be OK, not a Marshall or Vox IMO.

sandman72202 · April 2nd, 2008, 05:07 AM

my mistake for not explaining properly. the cab is a 16 ohm cab with 2 8 ohm speakers wired serial. if i wire them in parallel i will have a 4 ohm cab. coupled with the 8 ohm 15 in in the amp i'm thinking 2x12 4 ohm cab + 8ohm speaker will give an impedance somewhere between 5 -6. the amp is a 5E3 looking for a 4 ohm load. with the 8 ohm 15 inch speaker in it i figure its being held back a bit on power.
my question is i guess is whether theres a problem mismatching speaker ohmage if the total impedance is close to what the amp is set for.
another question is if the 4 ohm cab being more efficient will be louder than the 8 ohm 15. making the cab dominant soundwise. if that makes any sense.
i know i could just try to sell the jbl speaker plus the two speakers in the cab and try to get two 16 ohm speakers and wire them parallel to make an 8 ohm cab to create a 4 ohm load which is optimal.
not really meaning to make this confusing.

hers what i have
5E3 tweed with an ohm 15in speaker P15N

have a weber rebuilt JBL 130 15in 8 ohm speaker

have a 16 ohm cab with two 12 in eminence 8 ohm greenback knockoffs OEM

wanting an extension cab to go with the tweed and rewireing the cab to make it 4 ohms seems like the cheapest way to go. but not sure if its safe or whether mixing ohmages can be a problem

Dacious · April 2nd, 2008, 05:32 AM

In effect you'll have 3 8 ohm speakers in parallel - the amp doesn't care what cabinets they are in.

1
_
1/8+1/8+1/8

=2.66666667 ohm

I'd stick with the 2 x 12.

The JBL is about 98db efficient but biased to the bass response side. So it might be predominant in bass registers. Speaker impedance is not consistent - outisde of it's optimum range it will be higher, so above 2khz teh 12s will probably dominate.

Steve G · April 2nd, 2008, 09:53 AM

Dacious, im so glad there are people out there who really 'get' this stuff!

sandman72202 · April 2nd, 2008, 07:23 PM

Quote:

Originally Posted by Dacious

In effect you'll have 3 8 ohm speakers in parallel - the amp doesn't care what cabinets they are in.

1
_
1/8+1/8+1/8

=2.66666667 ohm

I'd stick with the 2 x 12.

The JBL is about 98db efficient but biased to the bass response side. So it might be predominant in bass registers. Speaker impedance is not consistent - outisde of it's optimum range it will be higher, so above 2khz teh 12s will probably dominate.

ok, soo sorry for the continued confusion, but this is different than i understood it.

the cabinet is a 16 ohm cab, 2 8 ohms in series to make a 16 ohm load.
if i wire it in parallel i can make it a 4 ohm cab.

the amp does not see it as a 4 ohm load combined with the 8 ohm speaker in the cab ?

i thought mixing the 4 ohm cab.....with the 8 ohm speaker would put closer to what the amp was requiring which is 4 ohms.

if
1
_
1/8+1/8+1/8

=2.66666667 ohm
wouldn't that be harmful to my amp ?

living in a state of confusion here

sandman72202 · April 2nd, 2008, 07:39 PM

nevermind...i understand now......i would be creating almost a short situation by changing the cab to a 4 ohm cab.

as it is the 16 ohm cab with the 8 ohm speaker is yielding about 5.33 ohms which is what i was seeking. i thought i would be getting a considerable amount of volume increase when i dropped the load to the amp.

and thnx for the reply dacious.....i'm thick headed but with a bit of steady pounding it eventually gets through

April 1st, 2008, 05:13 PM	#1 (permalink)
sandman72202 Tele-Meister Join Date: Jun 2005 Location: Arkansas, currently on walkabout Posts: 476	ohmage question and suggestions i picked up a jbl d130 15 in speaker to match my li'l dawg 15 inch. was gonna get jim to build a cab for me but i don't think jim is building his cabs anymore. i have a sealed closed back 16 ohm speaker cab with 2 OEM eminence V12 thirty watt speakers. i think they are suppose to be eminence knockoffs of greenbacks. for the sake of economy i'm thinking of just rewireing the 16 ohm cab to make it a 4 ohm cab and using it. the amp is built to see a 4 ohm load. the main 15 inch speaker is an 8 ohm load so i know i'm not getting the full volume out of the 15. as i understand it if i combine the 4 ohm cab with the 8 ohm main speaker it will give me something like a 5. something ohms the amp will see. i'm guessing i will get more sound out of the cab then than the main 15 but the overall load to the amp will be closer to what its looking for. is a mismatch such as this too much ?.....5 1/2 ohms is closer than the 8 ohms its seeing now. thinking of doing it but was looking for input. if anyone has a suggestion on some speakers....the speaker in the amp is a jenson p15N. alnico. would like to get alnicos to match but thats not a must. and please don't start suggesting $100-200 speakers....i'm thinking of this because its a less expensive alternative. i can change the wiring for next to nothing. Last edited by sandman72202; April 1st, 2008 at 05:50 PM.

April 2nd, 2008, 03:15 AM	#2 (permalink)
Dacious Friend of Leo's Join Date: Mar 2003 Location: Godzone Posts: 2,623 35 Photos	Not quite sure of what you're asking. If it's a 16 ohm cabinet, must be two 32 ohms speakers wired parallel or two 8 ohm speakers wired serial. If the latter, you can rewire to a 4ohm cabinet by putting two 8 ohm in parallel. Running an 8 ohm speaker will in parallel will give you 2.66666 ohms. Impedance = 2.6666666 1/3 rd power will go to each speaker, but it depends on the relative efficiency of the speakers as to which is louder. Teh cabinet will have more speaker area. The sonics could work out good, they could work out bad. As the 15" will get only as much power as the 12s , it'll may tend not to be very good at bass. Alternatively, they may not be real flash at bass so it might work out OK. If this is a solidstate amp with a min 4ohm impedance, I would not do this. It's runing close to a dead short. A tube amp like most Fenders might be OK, not a Marshall or Vox IMO. __________________ My other Telecaster is a Thinline The Tele Bible, Ch 1, v 10 Love thy Telecaster, covet not thy neighbour's Strat!

April 2nd, 2008, 05:32 AM	#4 (permalink)
Dacious Friend of Leo's Join Date: Mar 2003 Location: Godzone Posts: 2,623 35 Photos	In effect you'll have 3 8 ohm speakers in parallel - the amp doesn't care what cabinets they are in. 1 _ 1/8+1/8+1/8 =2.66666667 ohm I'd stick with the 2 x 12. The JBL is about 98db efficient but biased to the bass response side. So it might be predominant in bass registers. Speaker impedance is not consistent - outisde of it's optimum range it will be higher, so above 2khz teh 12s will probably dominate. __________________ My other Telecaster is a Thinline The Tele Bible, Ch 1, v 10 Love thy Telecaster, covet not thy neighbour's Strat!

April 2nd, 2008, 09:53 AM	#5 (permalink)
Steve G Tele-Afflicted Join Date: Nov 2005 Location: LeeK (England) Posts: 1,854 64 Photos	Dacious, im so glad there are people out there who really 'get' this stuff! __________________ "He was a drinkin' man with a guitar problem..." http://www.myspace.com/stevegiddings http://www.myspace.com/hiandlonesome

April 2nd, 2008, 05:07 AM	#3 (permalink)
sandman72202 Tele-Meister Join Date: Jun 2005 Location: Arkansas, currently on walkabout Posts: 476	my mistake for not explaining properly. the cab is a 16 ohm cab with 2 8 ohm speakers wired serial. if i wire them in parallel i will have a 4 ohm cab. coupled with the 8 ohm 15 in in the amp i'm thinking 2x12 4 ohm cab + 8ohm speaker will give an impedance somewhere between 5 -6. the amp is a 5E3 looking for a 4 ohm load. with the 8 ohm 15 inch speaker in it i figure its being held back a bit on power. my question is i guess is whether theres a problem mismatching speaker ohmage if the total impedance is close to what the amp is set for. another question is if the 4 ohm cab being more efficient will be louder than the 8 ohm 15. making the cab dominant soundwise. if that makes any sense. i know i could just try to sell the jbl speaker plus the two speakers in the cab and try to get two 16 ohm speakers and wire them parallel to make an 8 ohm cab to create a 4 ohm load which is optimal. not really meaning to make this confusing. hers what i have 5E3 tweed with an ohm 15in speaker P15N have a weber rebuilt JBL 130 15in 8 ohm speaker have a 16 ohm cab with two 12 in eminence 8 ohm greenback knockoffs OEM wanting an extension cab to go with the tweed and rewireing the cab to make it 4 ohms seems like the cheapest way to go. but not sure if its safe or whether mixing ohmages can be a problem

April 2nd, 2008, 07:39 PM	#7 (permalink)
sandman72202 Tele-Meister Join Date: Jun 2005 Location: Arkansas, currently on walkabout Posts: 476	nevermind...i understand now......i would be creating almost a short situation by changing the cab to a 4 ohm cab. as it is the 16 ohm cab with the 8 ohm speaker is yielding about 5.33 ohms which is what i was seeking. i thought i would be getting a considerable amount of volume increase when i dropped the load to the amp. and thnx for the reply dacious.....i'm thick headed but with a bit of steady pounding it eventually gets through