| Author |
Message |
Mark
Guest
|
 Posted:
Mon Nov 22, 2004 6:05 pm Post subject:
Amp power/bridging |
|
|
Hi,
I want to get as much power as I can out of my small P.A. system for a rock
gig.
Here is what I have:
1 - Citronix PPX-450 amp, 225 watts per channel RMS, 4ohms.
2 - 1 mono 350 watt amp
3 - 1 mono 250 watt amp (intended for monitors at the mo)
4 - 2 JBL SF15's, 250 watts per channel, 1000 watts peak
5 - 4 generic 2 x 12 + horn speakers (not sure of make/etc.) - using 2 of
these for monitors
Firstly, when the citronic says its 4 ohms, does that mean per channel ?
Secondly, how realistic is the 1000 watts peak rating given by JBL ?
Basically, if I bridge the PPX-450 amp and run a mono rig, does this mean I
can use both JBL speakers in parallel and effectively run them from the amp
in mono mode up to 450 watts per speaker ? That would sacrifice stereo but
I'd get double the power, right ?
If the JBL speakers are only 8ohms, if I had another set that are also
8ohms, could I then run yet another 2 in parallel ? I.e. run 4 speakers off
the one bridged amp ?
If I DON'T bridge the amp, could I run 2 8ohm speakers per channel then ?
Would that add up and give me effectively 450 watts per channel ? (225w per
speaker).
My last alternative is to bridge the amp and make it a mono 450 watt amp,
use ANOTHER mono 350 watt amp I have, and run 2 speakers with one amp, and 2
speakers with another. That way I have more power in the amps than the
speakers are rated at as recommended.
Oh, finally, is it fairly unlikely that the 2 x 12's are 8ohms ? If its 2
12" drivers, its likely to be 4ohms is it not ?
Sorry I know this is a bit vague, but any advice regarding all of this, or
more specifically what definately NOT to do would really be much
appreciated. I'm basically trying to get as much FOH volume as I can
without blowing things up. I'm used to having more power available !
Cheers,
Mark.
--
|
|
| Back to top |
|
 |
Hubert Barth
Guest
|
| Posted:
Mon Nov 22, 2004 6:05 pm Post subject:
Re: Amp power/bridging |
|
|
"Mark" <marks@nospamhere.net> wrote:
| Quote: | Basically, if I bridge the PPX-450 amp and run a mono rig, does this mean I
can use both JBL speakers in parallel and effectively run them from the amp
in mono mode up to 450 watts per speaker ? That would sacrifice stereo but
I'd get double the power, right ?
|
YouŽd probably run into problems because the bridged amp wants to see
8 ohms minimum and you let it drive 4 Ohms. It may work for a while
until the amp shuts down reaching its temperature limit.
| Quote: | If the JBL speakers are only 8ohms, if I had another set that are also
8ohms, could I then run yet another 2 in parallel ? I.e. run 4 speakers off
the one bridged amp ?
|
No, the total load would drop to 2 Ohms, the amp would either go into
protect mode or blow up.
| Quote: | If I DON'T bridge the amp, could I run 2 8ohm speakers per channel then ?
Would that add up and give me effectively 450 watts per channel ? (225w per
speaker).
|
Yes, still leaving you seriously underpowered.
| Quote: | My last alternative is to bridge the amp and make it a mono 450 watt amp,
use ANOTHER mono 350 watt amp I have, and run 2 speakers with one amp, and 2
speakers with another. That way I have more power in the amps than the
speakers are rated at as recommended.
|
*Might* work, but is a umm... unelegant solution.
YouŽd better rent an amp that can deliver around 500W @ 8 Ohm per
channel to power your JBLs.
| Quote: | Oh, finally, is it fairly unlikely that the 2 x 12's are 8ohms ? If its 2
12" drivers, its likely to be 4ohms is it not ?
|
There is no rule, could be two 4 ohm drivers in series. If you find no
info youŽll have to open Žem up to read the labels or measure them.
regards
--
Hubert Barth
Cologne/Germany
http://www.bigbands.de |
|
| Back to top |
|
|
Pooh Bear
Guest
|
| Posted:
Tue Nov 23, 2004 2:05 am Post subject:
Re: Amp power/bridging |
|
|
Mark wrote:
| Quote: | Thanks all, point taken ;-)
Mark.
|
YW !
Hope I didn't sound *too* harsh !
So many ppl get the wrong ideas about gear from hearsay and stuff. Bridged
giving *more power* is a classic.
Hang around and listen to the stuff here. You'll get some good tips.
Cheers, Graham |
|
| Back to top |
|
|
Pooh Bear
Guest
|
| Posted:
Tue Nov 23, 2004 2:05 am Post subject:
Re: Amp power/bridging |
|
|
Mark wrote:
| Quote: | Hi,
I want to get as much power as I can out of my small P.A. system for a rock
gig.
Here is what I have:
1 - Citronix PPX-450 amp, 225 watts per channel RMS, 4ohms.
2 - 1 mono 350 watt amp
3 - 1 mono 250 watt amp (intended for monitors at the mo)
4 - 2 JBL SF15's, 250 watts per channel, 1000 watts peak
5 - 4 generic 2 x 12 + horn speakers (not sure of make/etc.) - using 2 of
these for monitors
|
It would be ever so helpful if you could give the impedances of cabs 4 and 5.
| Quote: |
Firstly, when the citronic says its 4 ohms, does that mean per channel ?
|
Yes, I believe so ( without looking up the spec for you ).
| Quote: | Secondly, how realistic is the 1000 watts peak rating given by JBL ?
|
It's a joke number put there by marketing ppl. It may be technically accurate
with respect to an instantaneous peak - but has no relationship to anything
useful in the real world.
A bit like car stereo power ratings !
| Quote: | Basically, if I bridge the PPX-450 amp and run a mono rig, does this mean I
can use both JBL speakers in parallel and effectively run them from the amp
in mono mode up to 450 watts per speaker ? That would sacrifice stereo but
I'd get double the power, right ?
|
No !
Bridging doesn't give *double the power* when it's already running at its
minimum load impedance.
There's way too much crap talked about bridging.
You get the same power from both channels operating into the designed load
impedance as you do in bridged mode ( operating into the designed load impedance
).
Bridged *does not* equal more power.
I do not recomment that line of action with a Citronic amp.
| Quote: | If the JBL speakers are only 8ohms, if I had another set that are also
8ohms, could I then run yet another 2 in parallel ? I.e. run 4 speakers off
the one bridged amp ?
|
That would be 2 ohms load total. Equivalent to 1 ohm per channel. Astonishingly
stupid.
< snip >
Suggest you re-evaluate your requirements and consider replacing equipment with
what you require.
Graham |
|
| Back to top |
|
|
Mark
Guest
|
| Posted:
Tue Nov 23, 2004 2:05 am Post subject:
Re: Amp power/bridging |
|
|
Thanks all, point taken ;-)
Mark.
"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:41A265BD.F4EDF489@hotmail.com...
| Quote: |
Mark wrote:
Hi,
I want to get as much power as I can out of my small P.A. system for a
rock
gig.
Here is what I have:
1 - Citronix PPX-450 amp, 225 watts per channel RMS, 4ohms.
2 - 1 mono 350 watt amp
3 - 1 mono 250 watt amp (intended for monitors at the mo)
4 - 2 JBL SF15's, 250 watts per channel, 1000 watts peak
5 - 4 generic 2 x 12 + horn speakers (not sure of make/etc.) - using 2 of
these for monitors
It would be ever so helpful if you could give the impedances of cabs 4 and
5.
Firstly, when the citronic says its 4 ohms, does that mean per channel ?
Yes, I believe so ( without looking up the spec for you ).
Secondly, how realistic is the 1000 watts peak rating given by JBL ?
It's a joke number put there by marketing ppl. It may be technically
accurate
with respect to an instantaneous peak - but has no relationship to
anything
useful in the real world.
A bit like car stereo power ratings !
Basically, if I bridge the PPX-450 amp and run a mono rig, does this mean
I
can use both JBL speakers in parallel and effectively run them from the
amp
in mono mode up to 450 watts per speaker ? That would sacrifice stereo
but
I'd get double the power, right ?
No !
Bridging doesn't give *double the power* when it's already running at its
minimum load impedance.
There's way too much crap talked about bridging.
You get the same power from both channels operating into the designed load
impedance as you do in bridged mode ( operating into the designed load
impedance
).
Bridged *does not* equal more power.
I do not recomment that line of action with a Citronic amp.
If the JBL speakers are only 8ohms, if I had another set that are also
8ohms, could I then run yet another 2 in parallel ? I.e. run 4 speakers
off
the one bridged amp ?
That would be 2 ohms load total. Equivalent to 1 ohm per channel.
Astonishingly
stupid.
snip
Suggest you re-evaluate your requirements and consider replacing equipment
with
what you require.
Graham
|
|
|
| Back to top |
|
|
Jason Lavoie
Guest
|
| Posted:
Tue Nov 23, 2004 6:06 am Post subject:
Re: Amp power/bridging |
|
|
On Tue, 23 Nov 2004 01:33:19 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: |
Mark wrote:
Thanks all, point taken ;-)
Mark.
YW !
Hope I didn't sound *too* harsh !
So many ppl get the wrong ideas about gear from hearsay and stuff. Bridged
giving *more power* is a classic.
|
that comes from a fixed impedance speaker. bridged gives more power
than one channel alone.
it's still not right though.
Jason |
|
| Back to top |
|
|
Ian McKeown
Guest
|
| Posted:
Tue Nov 23, 2004 6:08 pm Post subject:
Re: Amp power/bridging |
|
|
The Citronic amp is a bit underpowered for running the JBL speakers. I think
Hubert Barth hit the nail on the head when he said to rent a bigger amp to
power the JBLs. Even at that don't expect a huge sound with chest thumping
bass.
If you need a lot of power for a rock gig rent a larger rig, preferably with
an operator. |
|
| Back to top |
|
|
Mark
Guest
|
| Posted:
Thu Nov 25, 2004 2:23 pm Post subject:
Re: Amp power/bridging |
|
|
I'm thinking of hiring a Crown 900 watt amp or a Carver PM 1.5 kw, so
that might help.
Cheers for your comments all, appreciated.
Mark.
--
Ian McKeown wrote:
| Quote: | The Citronic amp is a bit underpowered for running the JBL speakers. I think
Hubert Barth hit the nail on the head when he said to rent a bigger amp to
power the JBLs. Even at that don't expect a huge sound with chest thumping
bass.
If you need a lot of power for a rock gig rent a larger rig, preferably with
an operator.
|
|
|
| Back to top |
|
|
Pooh Bear
Guest
|
| Posted:
Thu Nov 25, 2004 10:14 pm Post subject:
Re: Amp power/bridging |
|
|
Jason Lavoie wrote:
| Quote: | On Tue, 23 Nov 2004 01:33:19 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
Mark wrote:
Thanks all, point taken ;-)
Mark.
YW !
Hope I didn't sound *too* harsh !
So many ppl get the wrong ideas about gear from hearsay and stuff. Bridged
giving *more power* is a classic.
that comes from a fixed impedance speaker. bridged gives more power
than one channel alone.
it's still not right though.
|
You might be surprised how widespread the bridged = more power myth is.
One system I occasionally service / maintain was reported as 'sounding wrong'.
The stereo amp driving the LF cabs had been selected to 'bridged' by some clown
who thought it would make things louder.
Just put the 2 LF cabs out of phase though ( and drivien by the left channel )
- since nothing else had been done other than pressing the switch !
I suspect a DJ was responsible.
Graham |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in