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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: Eric_John on February 06, 2011, 09:01:31 am

Title: Proprietary Boxes
Post by: Eric_John on February 06, 2011, 09:01:31 am
I did this one-off show with a touring band that I have worked with before (their FOH guys had something come up) and since they had played this particular venue before, I didn't bother advancing the technical side of the show. I get to the venue and I got a little concerned. It was a long room with stage on one end, 2 Dual 18 SRX subs on the floor, and what their guy said were JBL hung horizontally over the stage. The first thing I noticed was that the pitch of each boxes was different and that they were homemade mdf with foam covering the components. The foh position was way off to the side in the DJ booth and it consisted of an AH2400 with some mismatched eq's. some DBX combo's and a pair of midiverbs. a DRPA was at the stage.

I got the system fairly flat but couldn't get the sound right. I just couldn't put my finger on it but moving just a few feet around the room gave me a really different sound. I shined my flashlight into the grill foam and saw what I think was the problem. The 12" drivers were on each end of the box and the horn was in the middle. I couldn't tell if the horn was in the right position or not but it didn't sound like it was.

All things considered and with respect to the patched together rig, it all seemed to be working, I think the odd sound I was getting was A) because SR box was angled down towards floor and SL box was angled a bit more "correctly" and B) the drivers in the top boxes needed to be closer together instead of seperated by the horn. Am I right?

I understand a little about coupling and to me this was part of the issue.

Anyway, I did get a few compliments on how the band sounded so I guess it could have been worse.

Title: Re: Proprietary Boxes
Post by: Art Welter on February 06, 2011, 01:49:46 pm
The 12" drivers were on each end of the box and the horn was in the middle. I couldn't tell if the horn was in the right position or not but it didn't sound like it was.

The wide horizontal spacing of the 12" speakers will cause a deep off axis null below the crossover region that can not be corrected with eq.
Depending on the spacing of the cones and HF horn, the range of the null is fairly wide, but would  be in the low to mid vocal range, fairly easy to hear.

For that type of arrangement to work decently off axis, one of the cones (usually the outside cone) should be rolled off an octave or two lower than the other.

This still leaves the off axis suckout between the mid driver and the HF driver, a compromise one has to accept when using non-coaxial sources when vertical height is the primary concern.
Title: Re: Proprietary Boxes
Post by: Jay Barracato on February 06, 2011, 06:42:03 pm
I did this one-off show with a touring band that I have worked with before (their FOH guys had something come up) and since they had played this particular venue before, I didn't bother advancing the technical side of the show. I get to the venue and I got a little concerned. It was a long room with stage on one end, 2 Dual 18 SRX subs on the floor, and what their guy said were JBL hung horizontally over the stage. The first thing I noticed was that the pitch of each boxes was different and that they were homemade mdf with foam covering the components. The foh position was way off to the side in the DJ booth and it consisted of an AH2400 with some mismatched eq's. some DBX combo's and a pair of midiverbs. a DRPA was at the stage.

I got the system fairly flat but couldn't get the sound right. I just couldn't put my finger on it but moving just a few feet around the room gave me a really different sound. I shined my flashlight into the grill foam and saw what I think was the problem. The 12" drivers were on each end of the box and the horn was in the middle. I couldn't tell if the horn was in the right position or not but it didn't sound like it was.

All things considered and with respect to the patched together rig, it all seemed to be working, I think the odd sound I was getting was A) because SR box was angled down towards floor and SL box was angled a bit more "correctly" and B) the drivers in the top boxes needed to be closer together instead of seperated by the horn. Am I right?

I understand a little about coupling and to me this was part of the issue.

Anyway, I did get a few compliments on how the band sounded so I guess it could have been worse.

E

if you were in northern va, I know the room. if not than I know one that is exactly the same as you described. Part of the problem is not only the orientation of the boxes, but also their position in relationship to the side walls. The first reflection also causes significant cancellation. If I remember, walking across the room about 15 feet in front of the booth had three regions where there was a big change in the vocal range. In addition, the sound you hear at the booth wasn't representative of most of the room. I don't remember any separate processing for the different speakers in each box. It really comes down to damage control, but eq is just going to move the frequency of the problem around in different locations in the room.
Title: Re: Proprietary Boxes
Post by: Marsellus Fariss on February 07, 2011, 02:55:45 am
"The foh position was way off to the side in the DJ booth"


Well there ya go.


This kinda thing happens all the time. Problem is a.) you can't make good money running a venue unless your in a big market. And b.) Good audio gear is very expensive.

So more often then not you get whatever gear the place can get by on for the least amount of money because quite honestly half the time (or more) you don't make anything off the door, you just make money off booze. So why spend $30k on a D&B rig? You should probably build a second bar instead.  :-\  At the end of the day customers either liked seeing the show in the venue or they didn't. And I've heard way more bitching about the big room in town with a Midas and an Adamson/Meyer rig they I've heard about the room I work in that has broke down old JBL shit (we're replacing.) I know it's screwed up but there it is. And us engineers get stuck dealing with it.

What can ya do?

On the other hand I've been in a couple rooms where somebody affiliated with the business knew how to build a DIY box and the rig sounded really good. It's rare but it happens. And I love it when it does.

I have a friend close to town here that builds his own boxes and recones old drivers to load them that he buys used and his rigs sound really good! I'd just get him to build our new boxes but there's the whole rider issue. Although I guess we could write some three letter company name on the front in nail polish.  ;D
Title: Re: Proprietary Boxes
Post by: Bennett Prescott on February 07, 2011, 10:51:03 am
I got the system fairly flat but couldn't get the sound right. I just couldn't put my finger on it but moving just a few feet around the room gave me a really different sound. I shined my flashlight into the grill foam and saw what I think was the problem. The 12" drivers were on each end of the box and the horn was in the middle. I couldn't tell if the horn was in the right position or not but it didn't sound like it was.
A few questions...
What do you mean by flat?
What's wrong with having the horn in the middle (http://en.wikipedia.org/wiki/Joseph_D'Appolito)?
What about the sound indicated that the horn was in the wrong position?
Title: Re: Proprietary Boxes
Post by: Art Welter on February 07, 2011, 11:56:04 am
What's wrong with having the horn in the middle (http://en.wikipedia.org/wiki/Joseph_D'Appolito)?
What about the sound indicated that the horn was in the wrong position?
The D'Appolito MTM (mid tweet mid) arrangement works OK when in the vertical orientation, where the lobes are directed ostensibly to where the listeners are not.

In the horizontal, it is not good unless small enough drivers are used so the spacing does not cause large dips within the coverage area.

12" and a "normal" size horn are too large to work well in a horizontal D'Appolito configuration unless the coverage area is quite narrow.

You use  simulation programs, put in a pair of sources about 24" apart, about the minimum of a MTM using 12" speakers and horn. You will see it looks (and sounds) quite ugly at a variety of mid frequencies off axis, while in the vertical it looks just fine.


Title: Re: Proprietary Boxes
Post by: Eric_John on February 07, 2011, 02:30:32 pm
Well, I wasn't trying to bash the clubs rig, I was just wondering if I was right in my logic as to why (to me) it just didn't sound right except for a couple of very small spots in the room.

BP: I sent some pink noise through the rig and used my ivie to flatten the EQ with the mic, where I thought center should be. I really didn't know if the horn was mounted wrong, it just seemed like the highs would diminish just by moving a few feet to either side of the cab. I don't know if the horn being in the middle was the problem either. What I DID know was that they were homemade boxes and weren't flown with anything other than convenience in mind.

Bottom line was, the club was happy and the band was happy.  8)
Title: Re: Proprietary Boxes
Post by: drew gandy on February 07, 2011, 06:38:52 pm

12" and a "normal" size horn are too large to work well in a horizontal D'Appolito configuration unless the coverage area is quite narrow.


As you lower the crossover frequency the useful coverage area that is free of nulls widens.  But agreed, most horns can't play low enough for this to make sense.  Have a look at the Bag End Crystal polar response for instance.
(http://www.bagend.com/bagend/images/crystal-i_sm.jpg)

 It uses 2 - 12" woofers with a horn in between with a crossover point @ 1.9khz.  Look at the 1khz and 500hz polars in particular. 
 
Title: Re: Proprietary Boxes
Post by: MARK PAVLETICH on February 16, 2011, 02:10:28 am
Yorkville U215's have the horn in the middle and they are a darn fine sounding box IMHO.
Title: Re: Proprietary Boxes
Post by: Ivan Beaver on February 16, 2011, 07:45:16 am
Yorkville U215's have the horn in the middle and they are a darn fine sounding box IMHO.

The thing you have to consider is not just whether or not the horn is in the middle, but ALSO the freq reanges involved-think in terms of wavelength and 1/4 wave length. 

In the U215 the crossover between the horn and the woofers is MUCH MUCH lower than a typical small cabinet that basically goes between a tweeter and the woofers.

So how well the different boxes "work" in terms of this arrangement is very different.

I would guess in the case of the U215 the woofers are spaced so as to reduce the vertical pattern (reducing the energy off of the floor and ceiling).

In the case of smaller boxes this doesn't work because the drivers are not far enough apart to accomplish that, and yet are often to large to get close enough to the HF driver for proper summation.

Let's say the crossover is 2000 Hz,  A wavelength of around 7".  Now divide that by 4 ( for 1/4 wavelength) and you have 1.75".  So the driver center to center spacing needs to be less than 2" for a crossover of 2K.

Granted these are not "stop" numbers, but rather a grey scale to be used as a guid line.

Just something to think about.