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From: Leon on 23 Oct 2009 18:48

Right now we have 2 - 18" subs each driven by a 1450 amp in bridge mode. The
spks are 8 ohm so its a pretty good match.

We played a cafeteria that was a very bad room, it was all cement and had huge
glass doors and windows down both sides, and the upstairs of the building had
also rows of huge glass windows looking in. To try to fix the reverb, huge
acoustic blankets were installed hanging from the ceiling on the support beams.

The stage was an after thought, a large fat "T" shaped platform on one end. I
guess 30 or 40 feet across the room, over 100' long to the far wall. This is
usually a cafeteria room for the school, very very modern.

The cafeteria tables were all piled up in the space afforded by the "T" shaped
stage, in the corners. Not really nice looking!

We put the subs center in front of the stage, top of stage equal to top of subs
maybe 30". We put the 450's off to the side on stage.

Sound was quite good compared to other DJs that have been unlucky enough to get
booked, but with a xover of 150 - 180hz there seemed to be a weird spatial
effect with the bass coming from the middle and everything else from the sides.

OK... question 1

If we put the subs in the corners behind the stage (have to clear the dam
tables) would we be able to drive the room better and lose the center/sides
effects? There is actually floor space from the corners on out because of the
"T"shape. We can't put the subs at the edge of the stage because the doors are
there.

Question 2

If we get 2 more subs, and run them with the 1450's in stereo mode, can we get
better sound? In other words, will the grouping of the spks compensate for the
loss of power going from bridged to stereo mode?

Present system = (1450 amp 800 watts 1 spk) x 2

New system = ((1450 amp 230 watts x2) 2 spk) x 2

Hope I describe this right! We go from 2 to 4 subs with the same amps.

The reason for going this route is because we can work this room a few times a
year, and I'd like to group 2 subs on each side, maybe in the comers.

The present PA in the room has 4 speakers in the ceiling facing down, each near
a corner... not really useful, we ignore it.

Thanks!

From: Rupert on 23 Oct 2009 21:12
On Oct 23, 3:48 pm, L...(a)nospam.com wrote:
> Right now we have 2 - 18" subs each driven by a 1450 amp in bridge mode. The
> spks are 8 ohm so its a pretty good match.
>
> We played a cafeteria that was a very bad room, it was all cement and had huge
> glass doors and windows down both sides, and the upstairs of the building had
> also rows of huge glass windows looking in. To try to fix the reverb, huge
> acoustic blankets were installed hanging from the ceiling on the support beams.
>
> The stage was an after thought, a large fat "T" shaped platform on one end. I
> guess 30 or 40 feet across the room, over 100' long to the far wall. This is
> usually a cafeteria room for the school, very very modern.
>
> The cafeteria tables were all piled up in the space afforded by the "T" shaped
> stage, in the corners. Not really nice looking!
>
> We put the subs center in front of the stage, top of stage equal to top of subs
> maybe 30". We put the 450's off to the side on stage.
>
> Sound was quite good compared to other DJs that have been unlucky enough to get
> booked, but with a xover of 150 - 180hz there seemed to be a weird spatial
> effect with the bass coming from the middle and everything else from the sides.

Why are you running such a high crossover point? I wouldn't run any
higher than 120Hz but more likely around 100Hz using a L/R 24dB/octave
slope.

>
> OK... question 1
>
> If we put the subs in the corners behind the stage (have to clear the dam
> tables) would we be able to drive the room better and lose the center/sides
> effects? There is actually floor space from the corners on out because of the
> "T"shape. We can't put the subs at the edge of the stage because the doors are
> there.

Lowering the crossover point will help with the boxy, directional
sound from the subs. Corner loading the subs will definitely increase
their apparent output compared to an open floor. In theory if they're
placed against a corner you should see a 6dB increase in output.

> Question 2
>
> If we get 2 more subs, and run them with the 1450's in stereo mode, can we get
> better sound? In other words, will the grouping of the spks compensate for the
> loss of power going from bridged to stereo mode?

With coupling effects of the paired subs but with the decrease in amp
power, it's going to be close to a wash in terms of output. FWIW, the
QSC RMX1450 (I assume this is the amp you have) is rated for 4 ohms in
bridge mode. You should be able to just daisy chain another sub with
the setup as is and increase the output of your subs by 6dB. Yes, the
maximum output of the amp per speaker will drop to 700 watts due to
current limiting, but the overall output will be increased by 6dB. I
can't speak to the reliablity of the RMX1450 in 4 ohm bridge operation
though. It may not hold up well under heavy use. But a lot of people
seem to like the RMX amps. I believe the 1850HD was designed for
better cooling than the 1450 for running 4 ohm bridged loads, hence
the HD designation.

>
> Present system = (1450 amp 800 watts 1 spk)  x   2
>
> New system = ((1450 amp 230 watts x2) 2 spk)  x  2
>
> Hope I describe this right!  We go from 2 to 4 subs with the same amps.
>
> The reason for going this route is because we can work this room a few times a
> year, and I'd like to group 2 subs on each side, maybe in the comers.
>
> The present PA in the room has 4 speakers in the ceiling facing down, each near
> a corner... not really useful, we ignore it.
>
> Thanks!

Rupert
From: Michael Dobony on 23 Oct 2009 21:30
On Fri, 23 Oct 2009 18:48:14 -0400, Leon(a)nospam.com wrote:

> Right now we have 2 - 18" subs each driven by a 1450 amp in bridge mode. The
> spks are 8 ohm so its a pretty good match.
>
> We played a cafeteria that was a very bad room, it was all cement and had huge
> glass doors and windows down both sides, and the upstairs of the building had
> also rows of huge glass windows looking in. To try to fix the reverb, huge
> acoustic blankets were installed hanging from the ceiling on the support beams.
>
> The stage was an after thought, a large fat "T" shaped platform on one end. I
> guess 30 or 40 feet across the room, over 100' long to the far wall. This is
> usually a cafeteria room for the school, very very modern.
>
> The cafeteria tables were all piled up in the space afforded by the "T" shaped
> stage, in the corners. Not really nice looking!
>
> We put the subs center in front of the stage, top of stage equal to top of subs
> maybe 30". We put the 450's off to the side on stage.
>
> Sound was quite good compared to other DJs that have been unlucky enough to get
> booked, but with a xover of 150 - 180hz there seemed to be a weird spatial
> effect with the bass coming from the middle and everything else from the sides.
>

You got what you set up. You said DJ so assuming recorded music, correct?
How are the subs wired, one per channel so both stereo channels are coming
from the middle?

> OK... question 1
>
> If we put the subs in the corners behind the stage (have to clear the dam
> tables) would we be able to drive the room better and lose the center/sides
> effects? There is actually floor space from the corners on out because of the
> "T"shape. We can't put the subs at the edge of the stage because the doors are
> there.
>
To do this you will also need to add a delay to the side speakers to match
the subs behind the mains. Best to keep subs and tops together in your
situation, like the subs on the bottom and the tops on sticks.

> Question 2
>
> If we get 2 more subs, and run them with the 1450's in stereo mode, can we get
> better sound? In other words, will the grouping of the spks compensate for the
> loss of power going from bridged to stereo mode?
>
> Present system = (1450 amp 800 watts 1 spk) x 2
>
> New system = ((1450 amp 230 watts x2) 2 spk) x 2
>
> Hope I describe this right! We go from 2 to 4 subs with the same amps.
>
> The reason for going this route is because we can work this room a few times a
> year, and I'd like to group 2 subs on each side, maybe in the comers.
>
> The present PA in the room has 4 speakers in the ceiling facing down, each near
> a corner... not really useful, we ignore it.
>
> Thanks!
From: Leon on 24 Oct 2009 00:30
On Fri, 23 Oct 2009 18:12:37 -0700 (PDT), Rupert <foodsteaks(a)linkline.com>
wrote:

>On Oct 23, 3:48�pm, L...(a)nospam.com wrote:
>> Right now we have 2 - 18" subs each driven by a 1450 amp in bridge mode. The
>> spks are 8 ohm so its a pretty good match.
>>
>> We played a cafeteria that was a very bad room, it was all cement and had huge
>> glass doors and windows down both sides, and the upstairs of the building had
>> also rows of huge glass windows looking in. To try to fix the reverb, huge
>> acoustic blankets were installed hanging from the ceiling on the support beams.
>>
>> The stage was an after thought, a large fat "T" shaped platform on one end. I
>> guess 30 or 40 feet across the room, over 100' long to the far wall. This is
>> usually a cafeteria room for the school, very very modern.
>>
>> The cafeteria tables were all piled up in the space afforded by the "T" shaped
>> stage, in the corners. Not really nice looking!
>>
>> We put the subs center in front of the stage, top of stage equal to top of subs
>> maybe 30". We put the 450's off to the side on stage.
>>
>> Sound was quite good compared to other DJs that have been unlucky enough to get
>> booked, but with a xover of 150 - 180hz there seemed to be a weird spatial
>> effect with the bass coming from the middle and everything else from the sides.
>
>Why are you running such a high crossover point? I wouldn't run any
>higher than 120Hz but more likely around 100Hz using a L/R 24dB/octave
>slope.

I guess we could lower the point...

>>
>> OK... question 1
>>
>> If we put the subs in the corners behind the stage (have to clear the dam
>> tables) would we be able to drive the room better and lose the center/sides
>> effects? There is actually floor space from the corners on out because of the
>> "T"shape. We can't put the subs at the edge of the stage because the doors are
>> there.
>
>Lowering the crossover point will help with the boxy, directional
>sound from the subs. Corner loading the subs will definitely increase
>their apparent output compared to an open floor. In theory if they're
>placed against a corner you should see a 6dB increase in output.
>
>> Question 2
>>
>> If we get 2 more subs, and run them with the 1450's in stereo mode, can we get
>> better sound? In other words, will the grouping of the spks compensate for the
>> loss of power going from bridged to stereo mode?
>
>With coupling effects of the paired subs but with the decrease in amp
>power, it's going to be close to a wash in terms of output. FWIW, the
>QSC RMX1450 (I assume this is the amp you have) is rated for 4 ohms in
>bridge mode. You should be able to just daisy chain another sub with
>the setup as is and increase the output of your subs by 6dB. Yes, the
>maximum output of the amp per speaker will drop to 700 watts due to
>current limiting, but the overall output will be increased by 6dB. I
>can't speak to the reliablity of the RMX1450 in 4 ohm bridge operation
>though. It may not hold up well under heavy use. But a lot of people
>seem to like the RMX amps. I believe the 1850HD was designed for
>better cooling than the 1450 for running 4 ohm bridged loads, hence
>the HD designation.

I wouldn't trust the 1450 to run bridge at 4 ohms, regardless of what the
manufacturer may say, that means a 19 ampere load per channel with only 6 output
transistors of limited capability... The 1850HD has more output devices, else
seems to be about the same circuit.

>> Present system = (1450 amp 800 watts 1 spk) �x � 2
>>
>> New system = ((1450 amp 230 watts x2) 2 spk) �x �2
>>
>> Hope I describe this right! �We go from 2 to 4 subs with the same amps.
>>
>> The reason for going this route is because we can work this room a few times a
>> year, and I'd like to group 2 subs on each side, maybe in the comers.
>>
>> The present PA in the room has 4 speakers in the ceiling facing down, each near
>> a corner... not really useful, we ignore it.
>>
>> Thanks!
>
>Rupert

From: Leon on 24 Oct 2009 00:46
On Fri, 23 Oct 2009 20:30:48 -0500, Michael Dobony <survey(a)stopassaultnow.net>
wrote:

>On Fri, 23 Oct 2009 18:48:14 -0400, Leon(a)nospam.com wrote:
>
>> Right now we have 2 - 18" subs each driven by a 1450 amp in bridge mode. The
>> spks are 8 ohm so its a pretty good match.
>>
>> We played a cafeteria that was a very bad room, it was all cement and had huge
>> glass doors and windows down both sides, and the upstairs of the building had
>> also rows of huge glass windows looking in. To try to fix the reverb, huge
>> acoustic blankets were installed hanging from the ceiling on the support beams.
>>
>> The stage was an after thought, a large fat "T" shaped platform on one end. I
>> guess 30 or 40 feet across the room, over 100' long to the far wall. This is
>> usually a cafeteria room for the school, very very modern.
>>
>> The cafeteria tables were all piled up in the space afforded by the "T" shaped
>> stage, in the corners. Not really nice looking!
>>
>> We put the subs center in front of the stage, top of stage equal to top of subs
>> maybe 30". We put the 450's off to the side on stage.
>>
>> Sound was quite good compared to other DJs that have been unlucky enough to get
>> booked, but with a xover of 150 - 180hz there seemed to be a weird spatial
>> effect with the bass coming from the middle and everything else from the sides.
>>
>
>You got what you set up. You said DJ so assuming recorded music, correct?
>How are the subs wired, one per channel so both stereo channels are coming
>from the middle?

Yes, not sure iif he's set to mono or stereo, I'm not the DJ, but essentialy,
yes.

>> OK... question 1
>>
>> If we put the subs in the corners behind the stage (have to clear the dam
>> tables) would we be able to drive the room better and lose the center/sides
>> effects? There is actually floor space from the corners on out because of the
>> "T"shape. We can't put the subs at the edge of the stage because the doors are
>> there.
>>
>To do this you will also need to add a delay to the side speakers to match
>the subs behind the mains. Best to keep subs and tops together in your
>situation, like the subs on the bottom and the tops on sticks.

Unfortunatly, cant do it... Moving the subs towards the sides of the stage on
the floor puts them at the doors. They would have to go on top of the stage at
the sides, which is NOT near the wall, and we lose the coupling effect... so
need more speakers!

Other DJs have set up that way and can't drive the room from there, some kind of
node point I guess. So far we're the only company to get good bass in that room,
but we're clipping the amps.

Like I said it's a bad room, and being a school cafeteria most of the time we
can't get "play" time.

What if we put all the speakers into the corners? That adds maybe 20' to the
450s throw...

>> Question 2
>>
>> If we get 2 more subs, and run them with the 1450's in stereo mode, can we get
>> better sound? In other words, will the grouping of the spks compensate for the
>> loss of power going from bridged to stereo mode?
>>
>> Present system = (1450 amp 800 watts 1 spk) x 2
>>
>> New system = ((1450 amp 230 watts x2) 2 spk) x 2
>>
>> Hope I describe this right! We go from 2 to 4 subs with the same amps.
>>
>> The reason for going this route is because we can work this room a few times a
>> year, and I'd like to group 2 subs on each side, maybe in the comers.
>>
>> The present PA in the room has 4 speakers in the ceiling facing down, each near
>> a corner... not really useful, we ignore it.
>>
>> Thanks!

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