Boundary Loading Question (Wall length of corner)

Combining subs, tops and all the rest of your kit.
Post Reply
Message
Author
AcousticScience
Posts: 106
Joined: Tue Jan 20, 2015 4:37 pm

Boundary Loading Question (Wall length of corner)

#1 Post by AcousticScience » Sat Nov 02, 2019 1:58 pm

Here's a picture of the setup I did for my 30th a few months ago. I didn't have time to program exact times into the DSP and the bass sounded a little sloppy (mostly due to room acoustics) but how long do the walls have to be to be considered a decent corner for corner loading? Is it about a quarter wavelength on each side?
30th.jpg
The subwoofers were in the right hand corner under the purple curtain (yes those pictures are screwed to the wall top and bottom!).
Also there is a window hatch I'm curious about how much output is lost, although the shutters were down later so the disco lights had a darker room.
Next time I'm in that hall I'm curious to try wall loading with the back stage wall and time delaying the tops to match the phase with the subwoofers.

Aside: How do you guys deal with slap echo? I mean I could bring a huge load of old duvets to line the back wall but that would be a hassle to load in and out.
I could also only play music at 110 or 220 bpm so that the slap echo keeps in time.
I used down angle on the mid/highs and put them up as high as possible without the top of the stage curtain getting in the way (the poles didn't tighten well so they gradually slipped down a bit as the night went on). You may or may not be able to make out my makeshift down angle device but I may be upgrading it soon to increase its durability and to prevent the tops from being able to swing over forwards if the front of the cab is pulled on.
A few more friends would be a plus to absorb the sound on the floor.

CoronaOperator
Posts: 1648
Joined: Wed Mar 25, 2009 7:07 pm
Location: Medicine Hat, Alberta, Canada

Re: Boundary Loading Question (Wall length of corner)

#2 Post by CoronaOperator » Sat Nov 02, 2019 2:56 pm

AcousticScience wrote:
Sat Nov 02, 2019 1:58 pm
Here's a picture of the setup I did for my 30th a few months ago. I didn't have time to program exact times into the DSP and the bass sounded a little sloppy (mostly due to room acoustics) but how long do the walls have to be to be considered a decent corner for corner loading? Is it about a quarter wavelength on each side?
30th.jpg
You would start to get some gain at 1/4 wavelength, probably not too much though with full gain closer to 1 wavelength, That open hatch would lose a lot of loading. I've corner loaded before where there was a window and opening and closing it made a world of difference.
AcousticScience wrote:
Sat Nov 02, 2019 1:58 pm
Next time I'm in that hall I'm curious to try wall loading with the back stage wall and time delaying the tops to match the phase with the subwoofers.
That may or may not help you as the gain you get by loading against the back wall might be lost by the time it gets to the dancefloor just due to the further distance. In new rooms, I usually bring a dolly to put the subs on to easily move the subs around to try out all the locations before committing to a spot. Usually there will be a spot where the subs just come alive. Have the subs playing as you move them around. If you can't get a good spot that fills the whole room then concentrate on the dance floor.
AcousticScience wrote:
Sat Nov 02, 2019 1:58 pm
Aside: How do you guys deal with slap echo? I mean I could bring a huge load of old duvets to line the back wall but that would be a hassle to load in and out.
That is a harder one to deal with, keep the sound off the back wall as much as possible. Get the tops up high, point them down into the crowd toe them in drastically so most spill hits the side walls rather than the back wall. Get lots of people to show up and tell them it's a fuzzy sweater themed party. Pipe and drape the back wall. Most cities have rental shops for that where you can rent wedding/reception stuff, get the heaviest velour that they have or use your duvets behind the fabric. Keep the fabric about a foot away from the wall as it is more effective there than right against the wall.
AcousticScience wrote:
Sat Nov 02, 2019 1:58 pm
I could also only play music at 110 or 220 bpm so that the slap echo keeps in time.
That's a tough one, 110 is about 10 bpm's too slow for a dance party and 220 is well .. going to have an interesting effect on the crowd, lol.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

AcousticScience
Posts: 106
Joined: Tue Jan 20, 2015 4:37 pm

Re: Boundary Loading Question (Wall length of corner)

#3 Post by AcousticScience » Sun Nov 03, 2019 10:42 am

Well here's what the back of the hall looks like so you can see why there is an echo problem....
Handstand.jpg
I think it's about 16 metres by 8 metres though haven't measured it, just going by how many roughly 2m doors would fit across it. As the speed of sound is 343m/s that corresponds to about 1/10 of a second, but because the stage is about 3-4m extra and the back of the bar (locked) probably about the same, all I remember is it kept time to Eye Of The Tiger quite well.

The woman who rented me the hall wanted me to setup on stage (to prevent people tripping over speaker stands and wires) so using the back wall and firing into a drawn stage curtain is out. (Also it looks good on stage but according to Bill Fitzmaurice and the off centre Simplexx arrangement, what looks good doesn't always sound good). I could still draw the curtain anyway next time I'm likely to use the hall as it would soak up a bit more sound. Some venues the ceiling tiles are quite absorptive, but this is not one of them. I could do with a few of those crash mats the martial arts club uses when they rent the hall!

As for the subs, they weigh about 35 lbs each but are an awkward carry at 18" x 18" x 22" with no handles so a dolly would be useful. Just 2 simple reflex boxes with a Kappalite 3012LF driver each but it gets the job done where vehicle space is at a premium 96dB 1w/1m and 300w/45-50V max per box. I got them out of the back of a Citroen C2 and straight onto the stage and down into the corner. There are corners at the back of the stage but they are a bit out of the way behind further curtains and is beyond the time delay capabilities of the DBX driverack. I think I had 6dB of bass headroom at the loudest I ran it (my mum asked me to turn it down) but a really noisy EDM disco in that room would need them all out in the corner. I don't know how much output I lose in the "traditional" one under each top arrangement but didn't bother trying as I knew it would probably be worse.
Last edited by AcousticScience on Sun Nov 03, 2019 11:45 am, edited 1 time in total.

Bruce Weldy
Posts: 6807
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: Boundary Loading Question (Wall length of corner)

#4 Post by Bruce Weldy » Sun Nov 03, 2019 11:39 am

On thing I've done with pretty good success is to crossfire the speakers. Aim each one directly at the opposite corner of the back of the room. That will cut down on some of the direct reflections that come right back at you and give 'em a chance to die out.

The more you can deaden the room the better. If there are curtains - pull 'em! And I can pretty much guarantee you that there is going to be a build up of mud around 100-250hz in a room like that. Don't know what you are using for room EQ, but start pulling some of those frequencies until you find the right one....or two....

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

AcousticScience
Posts: 106
Joined: Tue Jan 20, 2015 4:37 pm

Re: Boundary Loading Question (Wall length of corner)

#5 Post by AcousticScience » Sun Nov 03, 2019 2:49 pm

As I recall I think the speakers were set up so they were pointing dead on at the opposite bottom corner of the room. Although I've discussed this elsewhere on the forum I think the piezo tweeter option has better pattern control at not spraying the highs up and down. The wooden DIY compression horns I recall Bill saying are about a 60 x 90 pattern whereas piezo (crossfire array) ends up at about 20 x 120. What that room really needs is something like the Danley SBH20LF or even the Shark Fin (or maybe the TLAH Pro as a BF option) hung on the wall either side of the stage with a down tilt. And yes plenty of acoustic treatment. As far as portable acoustic treatment goes ideally I would have a huge wall of open cell foam on the back but that's not always feasible. It would be nice if that room actually had a curtain divider about 10 feet from the back wall as it would also help mute the sound when people want to talk at the tables in the back. I actually know of another hall that does have this.

CoronaOperator
Posts: 1648
Joined: Wed Mar 25, 2009 7:07 pm
Location: Medicine Hat, Alberta, Canada

Re: Boundary Loading Question (Wall length of corner)

#6 Post by CoronaOperator » Sun Nov 03, 2019 4:20 pm

AcousticScience wrote:
Sun Nov 03, 2019 2:49 pm
I actually know of another hall that does have this.
What's the rent like? :wink:
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

Grant Bunter
Posts: 6159
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia
Contact:

Re: Boundary Loading Question (Wall length of corner)

#7 Post by Grant Bunter » Mon Nov 04, 2019 2:08 am

AcousticScience wrote:
Sun Nov 03, 2019 2:49 pm
The wooden DIY compression horns I recall Bill saying are about a 60 x 90 pattern whereas piezo (crossfire array) ends up at about 20 x 120.

CD horn around 60 x 100 degrees with one I think. Start stacking them, and by 4 cabs high it's still 100 horizontally, but something like 15-20 vertically.
Melded Piezo is, IIRC, much the same, but 120 degrees horizontal instead of 100, and 15-20 with 4 stacked.
Built:
DR 250: x 2 (melded array) with March 2012 plans. 2 more under way with CD horn
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

AcousticScience
Posts: 106
Joined: Tue Jan 20, 2015 4:37 pm

Re: Boundary Loading Question (Wall length of corner)

#8 Post by AcousticScience » Fri Nov 15, 2019 10:02 am

Booked two hours in the hall to play around.
I tested back wall of the stage with the subwoofers and the maximum 10ms delay on tops. (I tested phase alignment with one top on one sub and it was pretty even at 0ms give or take). It did sound quite good and punchy. As I suspected, due to distances, the ratio of bass to top increased as I moved to the back of the room, and also the back of the room wall boundary reinforced the bass if I was right by it.
Compared to the corner, (and no delay), less total output and reached the limit on the subs more quickly. The corner did amplify the upper bass more than the lower bass due to the short wall length. The kitchen hatch did rattle a bit but was drowned out with the mids/highs on. The corner was the best SPL position - superior to the stage back wall and also put less bass on stage which would matter more in a live band scenario at war volume.

Testing slap echo with a range of down tilt it didn't change much. The pattern control of these tops especially in the mids isn't that tight, but then there could be floor bounce in the empty room. The room had a 2-3 second reverb time with loud sounds. I tested with just my voice/clapping what the echo would be if set up on the other side of the room opposite the stage, and it was less, but still significant even with the curtain drawn. I don't know how that room sounds when it's full of people but couldn't be bothered with getting lots of chairs out to see what empty padding covered chairs would do, would probably help a bit. I could get quite a good clear sound at the front of the hall that was progressively less clear towards the back.

I also tested the "traditional" placement of one subwoofer directly under each top. The "power alley" wasn't as pronounced as I thought but I did need to turn the subwoofers up a lot more to provide the same level of bass. I also tested two of them together on the front of the stage, which was slightly louder and more even. It seems like the corner is the best for SPL and less bass on stage, and back wall is best for sound quality.

Post Reply