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[Doug Bishop]

I am in charge of Audio/visual in a medium sized church holding services in a 250 seat sanctuary AND a gym that gets setup/torn down weekly seating 500 in 2 contemporary services.

I am looking for advice concerning what I and a couple of my more experienced team members feel is an unclean sound from our subwoofers.

Our current configuration is:

Allen & Heath GL2400-432 mixer
dbx DriveRack-260
4 ea Yamaha CW115 main speakers paired up as inner and outer.
Each set powered by a Crown CE2000 in bridge mono.

2 ea Yamah CW118 Sub woofers powered by a single Crown XS1200 in bridge mono.

Hearback system
4 ea Yamah SM15VCA Wedge monitors. running from another CE2000.

Power supplied via 1 Furman PS8RII and 1 Furman PS-ProII sequencers.
_________________________

We had a recent problem regarding over compression on the Bass (see the following thread)
http://churchsound.prosoundweb.com/index.php/t/14544/77a3fdd 8d3250c7fa19074e0c8be3b6d/

This caused us to start scrutinizing the sub woofers.  What we are hearing when the main speakers are muted is a kind of "dirty" or "fuzzy" sound with what sounds like more mid frequencies bleeding into the subs.

The crossover is currently set at 96.4 on the drive rack.  It does not seem to be related to a grounding issue as there is no sound when the system is powered on but no signal being fed from a cd track or instrument.

Any thoughts?

Thanks

[Rob Warren]

Is this something that is suddenly happened and the system
was fine all along until recently?  Or is this a system fairly new
and it never has been fine?  

First thought is your system is way under powered so maybe they were pushed too hard and now they are in need of repair.  
Especially if it's the case where they system was fine all along and now it's not.

[Doug Bishop]

Not really certain.  It's just that we are not liking what we hear from the sub when we mute the main speakers via the DriveRack 260.  When we un-mute the mains and either play a track or if the full band is playing it seems to be ok.  What we are thinking is that possibly the condition has always been there (at least with this configuration) and went undetected until we had the issue with the bass player and started scrutinizing stuff.  We had one sub malfunction about a year ago.  It just went dead.  That one was repaired under warranty.  About a month ago the other one went bad...not sure of the problem but it just sounded like crap.  That's also a warranty deal which I am picking up today.  Both times we used the sub from our youth room (same model) as a stand in for the #2 sub.

The sound is the same from both speakers and just not quite right.  This is an evolving system.

Originally just 2 Yamaha CW115's on a Crown CE2000 using a DriveRack-PA

Phase 2 was to add 2 more 115's and the pair of 118 subs along with 2 more CE2000's.  All of this was always run in bridge mono.

During this phase we had still not begun to use any compression/limiting other that what was available in the DriveRack-PA.

Phase 3 was to donate the DriveRack-PA and one CE2000 to other areas of the building replacing the Sub amp with the Crown XS1200 and upgrading to a DriveRack-260.

I also purchased a PreSonus ACP-88 to utilize compression on the drum kit predominantly.

I am not entirely satisfied that we have set up the driverack correctly to match our amps/speakers.  I shouldn't think that we are underpowered but if we are not set up properly perhaps we are short changing our system.

Maybe I need to get some expert advice on setup and try reprogramming the driverack.

[Brad Weber]

Doug Bishop wrote on Wed, 13 August 2008 23:12

4 ea Yamaha CW115 main speakers paired up as inner and outer. Each set powered by a Crown CE2000 in bridge mono. 2 ea Yamah CW118 Sub woofers powered by a single Crown XS1200 in bridge mono.

Rob Warren wrote on Thu, 14 August 2008 00:13

First thought is your system is way under powered so maybe they were pushed too hard and now they are in need of repair.

Way underpowered?  Power is application dependent and there is no reason to assume something is underpowered unless there is some indication that the user is trying to get more out of the system than it can provide.

Besides that, the mains, which I assume are actually Yamaha C115 boxes and not CW115 subs although both have the same power ratings, are 8 Ohms with a 250W continuous/1,000W peak rating, for a 4 Ohm, 500W continuous/2,000W peak rating for the pair.  A bridged CE2000 is rated at 1,950W into 4 Ohms and I don't see being 0.11dB down from peak as being way underpowered.  However, the issue was really the subwoofers, so let's look at those.  The CW118 subs are rated at 8 Ohms, 300W cont/1,200W peak per sub. The Xs1200 is rated at 3,000W (4 Ohms, bridge mono) and is driving two of the subs.  If anything, I would be worried about the system, especially the subs, being run too hard for too long with the amount of power available, but it seems the system is definitely not underpowered.

Doug Bishop wrote on Wed, 13 August 2008 23:12

This caused us to start scrutinizing the sub woofers.  What we are hearing when the main speakers are muted is a kind of "dirty" or "fuzzy" sound with what sounds like more mid frequencies bleeding into the subs. The crossover is currently set at 96.4 on the drive rack.  It does not seem to be related to a grounding issue as there is no sound when the system is powered on but no signal being fed from a cd track or instrument.

Crossovers are not a brick wall, they have a slope.  Yamaha recommends as 90Hz, 12dB/octave crossover for the sub which means that you probably can hear some low/mid frequency content in the subs, just at a much lower level.

You might tell more if you listened to a sine sweep, you should be able to find several sine sweep audio files or software generators online for free.  That way you can actually better hear what is happening at different frequencies, which might add some insights.  I'd also make sure you are not clipping the Drive Rack input or anything like that.

I would suggest getting a qualified Consultant or Contractor to help with the system tuning and gain structure.  Especially if you always set up the system in exactly the same way, someone with all the proper tools and knowledge could probably really help with the system gain structure and tuning and you could probably learn a lot for future use from watching and asking questions.

[Tim Padrick]

Most subs sound pretty funky if you mute the tops - lots of resonances and overtones.

I'll compress the kick drum if the drummer has an inconsistent foot.  I'll sometimes compress the snare so when the drummer wails on it and it gets loud in the room, it does not also get loud in the PA.  Otherwise I never comp the kit.

I find that 99% of kits need a gate on the kick and each of the toms.  .5% of kits don't needs gates because they are as dead as cardboard boxes.  That leaves .5% that are tuned well.

[Gary Creely]

Tim Padrick wrote on Sun, 17 August 2008 02:07

Most subs sound pretty funky if you mute the tops

That would depend on whether you know what you are listening for. To me hearing the subs alone reveals what they are really up to. It is certainly a different listening experience, but a lot of subs are really messy and it is when the tops are removed that is sticks out.

As related to this particular circumstance I would say my experience with Yamaha subs is not the greatest. If it is set up correctly the weak link in this chain IMO is the Yamahas.

An other thing that happens when folks listen to subs alone is they will push them up much louder than they would with the tops on. So you crank it up and the subs are breaking up and it doesn't seem that loud, but if the tops where on at that level they would be breaking up to.

[Rob Warren]

Quote:

Way underpowered? Power is application dependent and there is no reason to assume something is underpowered unless there is some indication that the user is trying to get more out of the system than it can provide.

I am not a big fan of running amps in bridge mono mode.  I don't think they perform as good.
Not to mention it's a lot more demanding on the amp.  
So by that, I think there rig is way under powered.  I realize that power is partly application dependent, but Not totally.  Application for volume reasons may only dictate lower watts but I like a lot more cleanliness and headroom in my stuff that will drive the power need up a bit more.  But I like to stay at a 8 or 4 ohm load in stereo mode, NOT bridged.  
the other thing I've think I saw is the damping factor on these amps are like 200.  which is terrible especially for subs.

I could very well be off here, but I am wondering if the amp really is happy being bridged and driven hard.  On a Macro tech maybe but the XLS??

the other thing could be this.  You might be trying to get more low end than a couple subs will produce in your room.  so then your driving the daylights out of the 2 subs you have.  In this case since you are sending a lot power to them you could just be plain going past what they can handle.  In this situation it's possibly a case of NOT enough speakers.  Are the cones moving a lot when being driven?  If they are moving too much they actually move past there excursion limit and they are toast.  

[David Sumrall]

Hey Rob!

I think you are on to something here with the bridge mono part and these particular amps and box combination.

There is definitely more to it then just saying there are x many watts coming out and this box can handle this many watts.

One amp that putts out 500 watts might not be able to do it as well as another or sound as good.  

And one box rated at 500 watts may work better then another box rated the same 500 watts. Efficiency and spl output ratings can help tell the difference.

We've got Crown CE, XLS, K2, Macro techs etc in various sizes in different venues.

They are all very different beasts and all respond differently depending on how they are setup and the use.

The macro techs take a lickn and keep on tickn pretty much through everything.

The CE's and K2's have been around for a while.

Both seem slow to me for sub applications.  

My experience with the CE's is that they don't like being pushed that much and most of the time you have to push them to get something loud especially with inefficient boxes.  They are not very forgiving when you starting hitting the peak lights. Setting up limiters correctly in your dsp could go a long way to keep you from peaking the amps and getting more out of them.

The CE's for us did not like bridge mode as much for subs or trying to run at 2 amps.

My favorite application for the K2 is beach gigs since they are sealed:O)

The xs is newer and faster and better then the CE and K2 but not the monster that the Macro techs are. It was replaced with the xls.

We've tried a few different configs on subs with this. Yep bridge can have some output, but it is not as punchy to me as dual mono or parallel.

That's not to say you can't do decently with what you have.

Rob may be on to something with the pushing of the system as well.

Maybe even try the whole rig as stereo?

Remember the ratings for these boxes have high peaks and that is not really where you want to sit in my opinion with these boxes especially without some really tight dsp settings. The average is about a half to a third 3rd of that and probably closer to where they will sound good.  I would probably run these in dual mono or maybe parallel off one amp channel in this application.  

You could try running both subs off one mono channel from the amp in parallel and see how they do.

Ditto on the comments of running some tone through the subs to see if they are actually ok. Typically i will do this with a minirator right into the amp right to the box. No dsp no console etc. start at a low volume and be careful. Do a sine wave sweep from the low freq to the highs.

Ditto on the comments about the sub frequencies. Most people are not used to hearing the audio split up into its various components. That may be part of your issue.

Are your amps peaking? some? all the time? none?

You could also try lowering your crossover frequency a bit to maybe around 80 to get some of that higher freq bleed out as you described. Then your sub amps would be working a little less as well.

Another idea would be to add another crossover or use the driverack PA to drive the subs off an aux. If implemented and run correctly that could cleanup a ton of low end issues. In short your gain structure should be exactly the same. You would just be able to assign what needs to go to the subs and what does not.

A lot of this is very subjective and hard to pin point over the internet since we cant be there to see and hear what exactly is going on.

I hope that helps a bit.

Good luck!

David

[Gary Creely]

Rob Warren wrote on Sun, 17 August 2008 21:07

I could very well be off here, but I am wondering if the amp really is happy being bridged and driven hard.  On a Macro tech maybe but the XLS??

You are a little off here, because the amp in question is an XS not an XLS. The XS is a better amp than the XLS, and a XS1200 is 3000 watts bridged at 4 ohms.

I don't think the amp or its power are the issue.

[Brad Weber]

Rob Warren wrote on Sun, 17 August 2008 21:07

I am not a big fan of running amps in bridge mono mode.  I don't think they perform as good. Not to mention it's a lot more demanding on the amp.   So by that, I think there rig is way under powered.

So are you saying that you would run the rig differently and if configured your way the subs would be underpowered?  If run within rated limits, which seems to be the case here, what are the specific problems with running an amplifier in bridge mode and how is that inherently more demanding?  Going from one speaker per channel in stereo mode to two speakers in parallel off the same amp in mono bridge mode actually involves two separate issues, the amplifier operating mode and the load, and I do think there may be some apparently attributing the resulting combination to being solely a factor of the amplifier operating mode.

Quote:

I realize that power is partly application dependent, but Not totally.  Application for volume reasons may only dictate lower watts but I like a lot more cleanliness and headroom in my stuff that will drive the power need up a bit more.

Isn't the desired headroom an integral part of the application dependency?  But the point is really that regardless of the equipment, we don't seem to know enough about the situation to judge that the system is underpowered.  Maybe I'm misunderstanding the situation, but I don't recall any comments indicating problems getting sufficient output or any mention of clipping, etc.  Perhaps these were just not mentioned but all the comments seem to relate to the content of the output and not the level.

Quote:

the other thing I've think I saw is the damping factor on these amps are like 200.  which is terrible especially for subs

I used to put great import in the amplifier damping factor as well but eventually learned better.  In practical applications the cable and load impedance have much more bearing on the resulting damping factor, which in most installed systems is much lower than 200, than does the amplifier damping factor and in the real world the amp damping factor is rarely actually a factor.  You might want to study a little more about damping factor, for example http://www.prosoundweb.com/ee/images/uploads/df.pdf.

Quote:

the other thing could be this.  You might be trying to get more low end than a couple subs will produce in your room.  so then your driving the daylights out of the 2 subs you have.  In this case since you are sending a lot power to them you could just be plain going past what they can handle.

Maybe I'm missing something but this seems to directly contradict the previous assertion that they are underpowered.

Quote:

In this situation it's possibly a case of NOT enough speakers.

More speakers is not always a good or even desirable solution, in fact this segues into a somewhat off topic issue I noted in the system description.  It was mentioned that they are using two of the 90 degree Yamaha mains per side and I am curious as to what the space is like as unless the listening area is very wide and the speakers are properly splayed, using two speakers per side might be less than optimal.

Quote:

Are the cones moving a lot when being driven?  If they are moving too much they actually move past there excursion limit and they are toast.

Isn't cone excursion a factor of the actual driver and box design with many speakers intentionally using high excursion drivers, thus making "moving a lot" and "moving too much" very relative?  Overexcursion tends to be a catastrophic failure and readily apparent, but given the power and loads involved there could be long term thermal problems that may not be as immediately noticeable.


Doug, have you tried listening to the subwoofer output of the DriveRack using a headphone amp and headphones or anything like that?  That might let you identify whether what you are hearing is in the processing and signal or from the actual sub itself.  The more you can do to narrow down where any problems are caused, the better.

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