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Author Topic: Which 4 dual 18 reflex cabinets?  (Read 4284 times)

Mark J Snyder

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Re: Which 4 dual 18 reflex cabinets?
« Reply #20 on: December 20, 2012, 09:04:03 pm »

Agreed.  When somebody make a comment like that, I ask for more SPECIFICS.  What can HE do that others can't?  WHAT is he going to adjust?  And that statement is based on WHAT?

Sounds like a lot of "fluff"and over confidence (typical of most of the Full Sail graduates I have met) if you ask me-and he is con the OP.

In my opinion, getting a better tool would be a better approach, rather than listening to somebody who says "whatever you get I can make sound better".  Better than what it is capable of?

I think we all are still waiting for an explanation about what is so special about a dual 18" sub.  And nothing else is considered.

Ya I'm starting to see through what all he's been telling me as far as that type of stuff is concerned.  The other thing he told me like that and I questioned immediatly was his suggestion to use 2 PRX635's for each side.  He pointed out there trap boxes and said they could be arrayed as such and I think JBL also says this somewhere maybe.  But ya he said the comb filtering wouldn't be a big problem and that your going to encounter comb filtering somewhere in almost every system which sure but from different points not within 1 single stack.  I've never put two 90deg boxes beside eachother to see what exactly it would do.  I know my LA325's can be touchy with arrangement and must be pointed straight out.  When I first got them someone tried angling them inwards and before I got out front to hear it myself one stage hand with no experience or knowlege of sound what so ever said that sounds funny like that. 

Why reflex cabinet's?  Mostly because they can be combined with other cabinets avaliable for rent around here.  Why 18's?  I have no particular preference over a 21" driver other than I see big company's with huge stages sticking with 18's.  Also I see them sticking with reflex cabinets so I figure theres a reason for that.  Ya I'm not going to have anything near that size but maybe 12 cabinets is not so far away depending on how things go.
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Ivan Beaver

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Re: Which 4 dual 18 reflex cabinets?
« Reply #21 on: December 20, 2012, 09:39:33 pm »

Ya I'm starting to see through what all he's been telling me as far as that type of stuff is concerned.  The other thing he told me like that and I questioned immediatly was his suggestion to use 2 PRX635's for each side.  He pointed out there trap boxes and said they could be arrayed as such and I think JBL also says this somewhere maybe.  But ya he said the comb filtering wouldn't be a big problem and that your going to encounter comb filtering somewhere in almost every system which sure but from different points not within 1 single stack.  I've never put two 90deg boxes beside eachother to see what exactly it would do.  I know my LA325's can be touchy with arrangement and must be pointed straight out.  When I first got them someone tried angling them inwards and before I got out front to hear it myself one stage hand with no experience or knowlege of sound what so ever said that sounds funny like that. 

Why reflex cabinet's?  Mostly because they can be combined with other cabinets avaliable for rent around here.  Why 18's?  I have no particular preference over a 21" driver other than I see big company's with huge stages sticking with 18's.  Also I see them sticking with reflex cabinets so I figure theres a reason for that.  Ya I'm not going to have anything near that size but maybe 12 cabinets is not so far away depending on how things go.
A real easy test to see if any cabinet is arrayable is to put them in the array position and run some pink noise through them.  You can get a pink noise file from many places or on the output of an RTA.

 Then walk from one side to the other. Paying special attention to the area in the middle of the cabinets.

You can also do the same thing with a line array.  Put pink noise through it and walk from front to back.

The swooshi swooshi sound you hear is combfiltering.

Yes it most often happens within a single cluster-but you can also get combfiltering between different clusters.  The result is the same.

Even if you use front loaded ported cabinets together, that are different brands-with different tunings- you will end up with cancellations due to the different tunings.  It does not matter if they use 18" drivers or not.

Even if it is the same 18" model number (not the same cabinet model), the tunings may be different as different manufacturers have a different idea of what is the best compromise. 

How bad will it be?  Not as bad as most make it out to be-but it will still be not as good as using all of the same model number.
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Ivan Beaver
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Mark J Snyder

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Re: Which 4 dual 18 reflex cabinets?
« Reply #22 on: December 20, 2012, 10:21:40 pm »

A real easy test to see if any cabinet is arrayable is to put them in the array position and run some pink noise through them.  You can get a pink noise file from many places or on the output of an RTA.

 Then walk from one side to the other. Paying special attention to the area in the middle of the cabinets.

You can also do the same thing with a line array.  Put pink noise through it and walk from front to back.

The swooshi swooshi sound you hear is combfiltering.

Yes it most often happens within a single cluster-but you can also get combfiltering between different clusters.  The result is the same.

Even if you use front loaded ported cabinets together, that are different brands-with different tunings- you will end up with cancellations due to the different tunings.  It does not matter if they use 18" drivers or not.

Even if it is the same 18" model number (not the same cabinet model), the tunings may be different as different manufacturers have a different idea of what is the best compromise. 

How bad will it be?  Not as bad as most make it out to be-but it will still be not as good as using all of the same model number.

Ya I use Smaart and took the seminar when I got it.  I run pink everytime I setup if I can.  I know enough about comb filtering to know that's what it was when I heard that swooshi but not 100% sure how it affected the music as I couldn't hear any difference.  The only places I've gotten comb filtering is between stacks when they are close and my 460s get it off axis where they trap together.  The only thing I can notice is a drop in volume some where the boxes overlap.  Maybe not very significant comb filtering?  I'm giving myself homework tonight read through the chapters on comb filtering!

The gigs where I may need to add sub cabinets the sound quality isn't as much of a concern as spl is so it's an acceptable option.
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Randall Hyde

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Re: Which 4 dual 18 reflex cabinets?
« Reply #23 on: December 21, 2012, 12:35:06 am »

The other thing he told me like that and I questioned immediatly was his suggestion to use 2 PRX635's for each side.  He pointed out there trap boxes and said they could be arrayed as such and I think JBL also says this somewhere maybe.  But ya he said the comb filtering wouldn't be a big problem and that your going to encounter comb filtering somewhere in almost every system which sure but from different points not within 1 single stack.  I've never put two 90deg boxes beside eachother to see what exactly it would do.
I'm actually running two PRX 625 cabinets side-by-side, per side, at a show I'm doing right now. Comb filtering isn't a problem (as a result of running four cabinets, versus two) as I run vocals through one cabinet and backline through the other (on each side).

That said, PRX series cabinets don't have the oomph for outdoor gigs in my opinion. My current gig is outdoors and the only thing saving my butt is the building that is about 100' in front of the stage (providing a reasonable reverberant field to get the volume up). I get 105 db at about 50' with no problem, but I'm not a big fan of the sound quality when I push it much beyond that.

I've tried to use the PRX 625 cabinets (which are about 4 dB louder than the PRX 635 cabs, according to the specs) in a free field, they don't work very well. Good indoor speakers, not my first choice for outdoors.
Cheers,
Randy Hyde
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Ivan Beaver

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Re: Which 4 dual 18 reflex cabinets?
« Reply #24 on: December 21, 2012, 09:19:19 am »

Ya I use Smaart and took the seminar when I got it.  I run pink everytime I setup if I can.  I know enough about comb filtering to know that's what it was when I heard that swooshi but not 100% sure how it affected the music as I couldn't hear any difference.  The only places I've gotten comb filtering is between stacks when they are close and my 460s get it off axis where they trap together.  The only thing I can notice is a drop in volume some where the boxes overlap.  Maybe not very significant comb filtering?  I'm giving myself homework tonight read through the chapters on comb filtering!

The gigs where I may need to add sub cabinets the sound quality isn't as much of a concern as spl is so it's an acceptable option.
Regarding the issue of how bad is combfiltering-it really depends on the person listening.

To some people a little bit is quite annoying-while to others they might mot hear ) or recognize it.

Kind of like the flavor of food or wine or how a car handles etc.

And to the people that aren't picky-it is not an issue.  But to the more professional-it is a real problem that they are constantly looking to make it better.

And yes it can be subtle. And while the average person may not say it is bad or an issue-if a system that did not have combfiltering was then played-they would recognize the new system as being clearer sounding.

Not that the combfilter system was bad-just that the one without is clearer.

Is that a big deal?  depends on who is listening.

And if it is there-you WILL hear it-you may not recognize it as such.  You won't hear the swooshi swooshi sound-but you will notice that the vocal lack clarity/openness, the timbre of the instruments is not as it should be, the attack of the percussive instruments is not a bright (due to the different arrival times which causes the issue in the first place) and so forth.

It comes down to your personal reference. 

So to sum it up, people often talk about combfiltering.  Is it this horrible thing that makes a system unusable?  NO.  But a system that doesn't have it sounds better. 

The fewer number of speakers that can be used-the better it will sound-no matter how well the manufacturer say they array.
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Ivan Beaver
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Chris Van Duker

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Re: Which 4 dual 18 reflex cabinets?
« Reply #25 on: December 21, 2012, 10:41:12 pm »

The thing which can bite you worst when combining subs, even if they're nominally the same type (e.g. ported 18's) is that the phase response can vary quite a bit -- at certain frequencies, the two subs may be working against each other rather than with.

For kicks, I modeled two sub designs which wouldn't be outside the mainstream of what's out there. One uses an Eminence Omega Pro 18 in a small 4.5 ft^3 cab tuned to 48Hz (barely a subwoofer), and the other uses an RCF LF18X400 in an 8 ft^3 cab tuned to 35Hz. I've attached a chart with the calculated phase responses for each. Notice that at 45Hz, there are about 8 lines separating the two, which comes out to an 80 degree phase response difference. They're barely helping each other -- past 90 they're considered out of phase (that is, fighting each other). They're probably also aiming the bass off in some weird direction rather than where you want it.

It can be very hard to get different subs to play nicely together. Heck, sometimes it's hard to get things right with only one kind on hand. I think you'd be doing yourself a disservice by planning to mix-and-match. If you're planning to rely on augmenting yours with someone else's, your best bet is to buy what they've already got if it's a good choice, or start from scratch if it's not.

-Chris
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duane massey

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Re: Which 4 dual 18 reflex cabinets?
« Reply #26 on: December 22, 2012, 02:32:53 am »

Comb-filtering is a major issue with systems that are used for more "stationary" audiences, and Ivan pretty much nailed it. I (possibly foolishly) don't worry too much about comb filtering in a dance-type situation, as much as I concentrate on focusing the sound on the dance floor, and some (if not most) club owners are in love with the "four corner" approach.
Since this is a live sound forum, I'd stick with the expertise of Ivan and the other guys here with extensive experience.
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Duane Massey
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David Morison

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Re: Which 4 dual 18 reflex cabinets?
« Reply #27 on: December 22, 2012, 04:46:52 am »

I know enough about comb filtering to know that's what it was when I heard that swooshi but not 100% sure how it affected the music as I couldn't hear any difference. 

Here's an example which may help illustrate it.
I once was helping a friend who had a rig with two mid-high speakers per side, each with a nominal 60O HF horn, but the boxes were tight packed so only had about 25-30O splay between them.
If you moved even half a metre to one side or the other, certain parts of the sound changed significantly - for example, the attack of the snare drum was noticeably reduced at some locations compared with others.
Now if you happened to be mixing (or EQing the rig) from one of the nulls, then you might end up trying to boost those frequencies to get the snare to sound right (which wouldn't be particularly successful even for that location anyway). But for other locations away from the nulls, that EQ would over-exaggerate the snare, making it obnoxiosly loud for everyone else.

In our case, we ended up living with the combing as the lesser of two evils (increasing the splay between boxes on each side would have significantly increased reflections from side walls), but we had to bear the combing in mind when EQing/mixing, and take care not to get caught out by it.
HTH,
David.
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Ivan Beaver

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Re: Which 4 dual 18 reflex cabinets?
« Reply #28 on: December 22, 2012, 08:14:30 am »

Here is an example of a moment "when the light turned on" for me-regarding combfiltering.

There is a local venue (2500 seats) that I provided sound for all the time.  I would take out a "4 stack a side" system.  This was back in the pre line array days.

We got a call to do a wedding and the budget was small-and they only wanted to cover the dance floor.

So we took out 1 stack a side.  Both my help and me noticed right away-when we played our "standard" setup songs-how much clearer the system sounded.  It wasn't as loud-but sure did sound better.

Same venue-same physical setup-same speakers-just less of them.

From that point on-I used a few loudspeakers as I could to do the job.

Very rarely do you "pickup" on combfiltering as a specific "sound".  But when you hear the sound without it-you QUICKLY realize how big a deal it can be.

You can easily play with this effect on the sound quality with a digital console.  Just patch (or physically Y) a mic to 2 channels.  bypass all compressors-eq etc. Set the input trim the same as well as the channel level.

Apply some input delay to one channel only.   Start with 0ms delay and start increasing it.  While listening to the sound, you can hear how it starts to "degrade" and become not as clear.

You can mute and unmute 1 channel (it doesn't matter which one) and hear the back and forth differences.

Yes the level will drop-but it is the sound quality you are interested in hearing.
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Ivan Beaver
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