Speakers.....4 ohms to 8

[JD Cardella]

I have (3) JBL 225H 15" speakers, (1) is 8 ohms and thr other
(2) are 4 ohms.....
Can the 4 ohm speaks be made to run @ 8 ohms...?
i.e. rewiring or having reconed.....?

Thanks, Jeff

[Thomas Bishop]

"JD Cardella" > wrote in message
> I have (3) JBL 225H 15" speakers, (1) is 8 ohms and thr other
> (2) are 4 ohms.....
> Can the 4 ohm speaks be made to run @ 8 ohms...?
> i.e. rewiring or having reconed.....?

Connect the two 4 ohms in series. You now have 8 ohms. Each speaker is
still 4 ohms, but together they create an 8 ohm load. You may not want to
do this for several reasons, but you didn't provide any other information
and my solution solves the given problem.

[Geoff Wood]

"JD Cardella" > wrote in message
...
> I have (3) JBL 225H 15" speakers, (1) is 8 ohms and thr other
> (2) are 4 ohms.....
> Can the 4 ohm speaks be made to run @ 8 ohms...?
> i.e. rewiring or having reconed.....?

Reconing with 8 Ohm voice-coils, and rebuilding the crossover with different
value components, ie not worth the excersize.

geoff

[Scott Dorsey]

JD Cardella > wrote:
>I have (3) JBL 225H 15" speakers, (1) is 8 ohms and thr other
>(2) are 4 ohms.....
>Can the 4 ohm speaks be made to run @ 8 ohms...?
>i.e. rewiring or having reconed.....?

You could probably replace the voice coils, but it would be cheaper just to
buy new speakers, I suspect.

Why is it important?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[JD Cardella]

> Why is it important?
> --scott

Well im trying to get our P.A. back up and running, I baught two speaker
Cabs. JBL 225H"s 1 Cab has 1 15" and a horn and is rated @ 8
ohms..... The other Cab. has 2 15" s and a horn and is rated @ 4
ohms....... I dont want to miss match the ohms and blow someting like my
power-amp......! So, Im lookin for a way to run them both w/o having
to buy another Cab to match one of the other's.....HELP...!!! lol
Thxs, Jeff








"Scott Dorsey" > wrote in message
...
> JD Cardella > wrote:
> >I have (3) JBL 225H 15" speakers, (1) is 8 ohms and thr other
> >(2) are 4 ohms.....
> >Can the 4 ohm speaks be made to run @ 8 ohms...?
> >i.e. rewiring or having reconed.....?
>
> You could probably replace the voice coils, but it would be cheaper just
to
> buy new speakers, I suspect.
>
> Why is it important?
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

[Peter Larsen]

JD Cardella wrote:

> > Why is it important?
> > --scott

> Well im trying to get our P.A. back up and running, I baught two speaker
> Cabs. JBL 225H"s 1 Cab has 1 15" and a horn and is rated @ 8
> ohms..... The other Cab. has 2 15" s and a horn and is rated @ 4
> ohms....... I dont want to miss match the ohms and blow someting like my
> power-amp......! So, Im lookin for a way to run them both w/o having
> to buy another Cab to match one of the other's.....HELP...!!! lol

One box on each amplifier(channel). What you can not do is to have both
boxes on one amplifier channel. Also all you 15" loudspeakers appear to
be 8 Ohm speakers, so it could be a matter of the woodworking required
to clone the dual 15" loudspeaker cabinet and getting an extra 15" and a
suitable electronic cross-over or long term get an extra of each
cabinet.

ymmv & you may want to get local technical assistance.

> Thxs, Jeff


Kind regards

Peter Larsen

--
************************************************** ***********
* My site is at: http://www.muyiovatki.dk *
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[Samuel Groner]

> Well im trying to get our P.A. back up and running, I baught two speaker
> Cabs. JBL 225H"s 1 Cab has 1 15" and a horn and is rated @ 8
> ohms..... The other Cab. has 2 15" s and a horn and is rated @ 4
> ohms....... I dont want to miss match the ohms and blow someting like my
> power-amp......! So, Im lookin for a way to run them both w/o having
> to buy another Cab to match one of the other's.....HELP...!!! lol

If you have an amp thats rated for 2 Ohm you can just wire them in
parallel (gives about 3 Ohm). But I guess it's not a clever idea to
use two different cabs in this way because they may have quite
different levels. Next time ask bevor you buy...
Samuel

[Scott Dorsey]

JD Cardella > wrote:
>
>> Why is it important?
>
>Well im trying to get our P.A. back up and running, I baught two speaker
>Cabs. JBL 225H"s 1 Cab has 1 15" and a horn and is rated @ 8
>ohms..... The other Cab. has 2 15" s and a horn and is rated @ 4
>ohms....... I dont want to miss match the ohms and blow someting like my
>power-amp......! So, Im lookin for a way to run them both w/o having
>to buy another Cab to match one of the other's.....HELP...!!! lol

The impedance is the LAST of your worries here. You really do not want to
run a pair of totally mismatched systems.

And no, you can't just swap the drivers out without also changing the
crossover, since the crossovers are designed aroound the driver impedances.
What crossovers do you have and what are they designed for?

Probably the reason the one with two drivers is rated for 4 ohms is because
it has two 8-ohm drivers in parallel. Does it have the right crossover for
that configuration?
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Thomas Bishop]

> JD Cardella > wrote:
> >Well im trying to get our P.A. back up and running, I baught two
speaker
> >Cabs. JBL 225H"s 1 Cab has 1 15" and a horn and is rated @ 8
> >ohms..... The other Cab. has 2 15" s and a horn and is rated @ 4
> >ohms....... I dont want to miss match the ohms and blow someting like
my
> >power-amp......! So, Im lookin for a way to run them both w/o
having
> >to buy another Cab to match one of the other's.....HELP...!!! lol

Why don't you sell one and buy a matching cabinet for the remaining? You
can run your amp in stereo with each cabinet on its own side. It will sound
odd, though. As Scott said, you've got two mismatched systems that require
different EQ, have different dispersion patterns, frequency ranges, etc.

[[email protected]]

Scott Dorsey > wrote:
> JD Cardella > wrote:

>>Well im trying to get our P.A. back up and running, I baught two speaker
>>Cabs. JBL 225H"s 1 Cab has 1 15" and a horn and is rated @ 8
>>ohms..... The other Cab. has 2 15" s and a horn and is rated @ 4
>>ohms....... I dont want to miss match the ohms and blow someting like my
>>power-amp......! So, Im lookin for a way to run them both w/o having
>>to buy another Cab to match one of the other's.....HELP...!!! lol

Scott is pontificating again and I agree with almost NOTHING
he has said!

> The impedance is the LAST of your worries here. You really do not want to
> run a pair of totally mismatched systems.

Absolutely a TOTALLY false and erroneous statement! Impedance is NOT
the "LAST of your worries"!!! If you just happily connect these
two cabs in parallel you'll end up with 2.66 Ohms total. Now assume
you've got a typical PA amp that has a minimum load limit of 4 Ohms.
Can you say "smoke, heat, and melted parts"? I knew that you could.
Scott may call that the least of your worries, but *I* wouldn't!

Futhermore, your systems aren't really all that mismatched. They both
are basically single horns with woofers which is close enough. The
problem is that the woofers are of different impedances which means
that 4 Ohm pair will draw more power than the 8 ohm single. That will
unbalance the bass. But before Scott starts to feel justified,
let me point out that this won't be serious on the deep lows
because Lows are more or les non-directional. So the higher output
from one cab won't be so noticable. But it WILL be noticed in the
mids! So if you simply Swap out the dual 15" 8 Ohm drivers with
two 16 Ohmers in parallel or two 4 Ohm ones in series, you'll
have balanced cabs that will work fine. (assuming you've bought
new drivers that match the efficency of the single driver cab!)
It should be more than balanced enough for almost all things! But
there is an even cheaper way to go! (see below).

> And no, you can't just swap the drivers out without also changing the
> crossover, since the crossovers are designed aroound the driver impedances.
> What crossovers do you have and what are they designed for?

Pooh! Geek-talk! Yes, you CAN just swap out the 15" drivers
and no, the crossovers will hardly notice! Yes, Theoretically,
you'd like the crossovers to be designed for the Ohms in question,
but since you really aren't changing horns, in the practical case
it won't matter a bit! At most if there is a problem (which I VERY
much doubt) the most you'd have to do is cut the value of the
capacitor(s) to raise the crossover frequency to keep some of the
lows out of the horns. It would manefest as sort of horn "overload"
at very loud levels IF there is a problem at all. EASY to test with
a signal generator!

> Probably the reason the one with two drivers is rated for 4 ohms is because
> it has two 8-ohm drivers in parallel. Does it have the right crossover for
> that configuration?

Now I do agree with Scott on this and IF it's true, what I'd do
if it were my problem is to first, check to make sure
the 2-15" speakers are indeed a pair of 8 Ohm drivers in
parallel. IF that's the case, I'd take ONE of them out
of the dual cab and move it to the single cab. Then I'd
cut a round circle of 3/4 plywood to fit the hole where
you took the speaker out.

Now, you've got TWO cabs. BOTH with identical 15" 8 Ohm drivers.
Sure, one cab is larger, but that won't matter much at all
except visually. Because the enclosure was designed for two
drivers it may be a bit out of tune with one, but since you are
going from two drivers to one, I doubt the detuning will give
rise to any serious bass problems. And anyway, remember bass
is non-directional. You may have to balance the horn levels.
Easy if the louder horn has a pad. If not just install one.

This should be quick, dirty, let you use BOTH cabs on a
Standard PA amp without fears of blowing it up as
well as produce a reasonably balanced PA sound.

Scott is cool, but sometimes he just gets too caught up in
theoretical details.

Benj

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[Mike Rivers]

In article > writes:

> Absolutely a TOTALLY false and erroneous statement! Impedance is NOT
> the "LAST of your worries"!!! If you just happily connect these
> two cabs in parallel you'll end up with 2.66 Ohms total.

No problem with that, as long as you don't exceed the maximum power
that the amplifier can put out. The reality is that you won't get as
much power from the amplifier at an impedance that's lower than what
the manufacturer recommends, but you'll only blow stuff up if you
crank the system too far. You can do that with a propler load, too.

> Futhermore, your systems aren't really all that mismatched. They both
> are basically single horns with woofers which is close enough.

Right, but they'll be getting different amounts of power delivered to
the speakers. While the mechanical end might not be all that badly
mismatched, the SPL from each cabinet in parallel won't be the same.
That will mismatch the sound in the room.


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