New to Bose Forum today, but a Bose user for a couple of years. Running MIDI tracks with guitars and two vocal mics. I have 2 L1 Model II systems with 2 B1 Bass units on each tower. Over the 4th, we had a job outside where we used both towers about 17 feet apart. Sounded great, except right down the middle of the venue, about 5’ wide, there was complete cancellation of audio. Very little volume, no fullness at all. I didn’t have a cable long enough to try to get the towers farther apart, but I tried different aim angles, from aimed apart 90 degrees to X/Y, and the cancellation stayed in exactly the same position. Very strange. I am running dual-mono used a T1. I also came across an old posting on Forum referring to needing at least 20’-50’ spacing between towers, but this was using the original L1 model. I called Bose yesterday and the guy I talked with had never heard of such a thing. 
I’m really disappointed in this quirk, and am interested in hearing if anybody else has had this problem and any success they’ve had fixing it. Thanks for any help!
Hi The Double D,
Thank you for joining the Forum.
There IS a documented recommendation from the Bose Engineers - that when you have one source coming out of two L1®s, you want the L1®s to be at least 20 feet apart. This is applicable to the Classic/Model I and the Model II (and the Compact). Reference: Multiple Source Interference
In the specific situation you described, you might have been able to make things better if you had moved the B1s around. I can’t give you a specific suggestion about where you might have moved them or how much, but a few feet in any direction would probably have shifted the the position/orientation of the cancellation to someplace less troubling.
Here are some notes about Dual Mono (that includes the references to phase cancellation).
And here’s another link with related information: Stereo / Mono / Distributed systems
Something you could consider is getting longer B1 cables so that you can put the B1s together in the middle of the stage. That should eliminate the problem with respect to the B1s. Source for cables: Longer B1 Cables
Another idea (I highly recommmend) is to get another T1® and make sure that NOTHING is coming out of both L1®s. This is because at best you might get 3dB SPL running the same signal through two L1®s in close proximity, but you also run the risk of what you experienced with Multiple Source Interference.
It’s a little harder to do… but you can route your signals so that each source goes to either AUX output or Master. Then you could send the Master output to one L1® (using the ToneMatch cable - the normal way) and the Aux output to the other L1® using a ¼ inch jack cable. You can read up on how you can route things to the Aux output here: T1 ToneMatch® Audio Engine Aux Output
I don’t know if you actually have enough inputs to do that though but you could experiment with it.
Does that help?
Hi The Double D,
The effect that you describe sounds just exactly like what happens if one of the two channels gets inverted somehow, usually by using a cable with one end wired up “backwards”. Then the sound between the speakers cancels instead of adding up. Is there any way you could have inverted the polarity on one channel? I’m not aware of any way to flip the polarity of a channel of the T1 or on the L1 Model II either, so I’m guessing that it’s a cable issue. Was there anything different about your wiring on the 4th?
You can definitely diagnose this at home by setting up in stereo outdoors. (It’s a lot more subtle indoors.) If it IS a polarity problem, you will hear it no matter what the distance between the speakers and at any volume. If you do have the problem, try swapping out cables for replacement cables and see if you can make the problem go away. When it’s gone, there will be no doubt; the cancellation will disappear. The most likely culprit in my experience is a home-made cable with a 1/4 inch plug. It is too easy to reverse tip and ring connections when soldering those up.
Hope that helps,
Chris
Hey Chris,
Great to see you here. Thanks for the whack on the side of the head.
All cables check out fine, and hadn’t changed at all. That said, ALL sources were affected by the cancellation.
All good ideas. I thought about running the aux out as you described to the second tower. For areas that I cannot separate towers 20’ apart, but where the extra 6db headroom/volume is desirable, would it be feasible to use MIDI playback on main output to one tower, then vocal mics (2) and guitar aux out to the second tower, but place towers close together? Like RIGHT together with 4 basses in between? Small stages…
Hey DD,
Okay, the fact that all sources were affected (along with the symptom of full-range cancellation in the middle) supports the idea that polarity somehow got inverted between the T1 and one L1. But how? My next theory is that one of the four 1/4" plugs was perhaps not fully inserted, so that its tip (plus signal) only contacted the jack’s ring (minus input or output). Whether you were using balanced 1/4" cables or unbalanced, either way, you’d get an inversion. But you sound like you know your way around audio gear, so you probably checked that on the 4th and ruled that out.
If so, could the source material possibly have the two channels out of phase? To rule that out, if you put the two source channels into channels 1 and 2 of the T1 and feed the output to a single L1, do you get good signal or cancellation?
Also, is the problem repeatable now with your regular setup, or has it gone as mysteriously as it came? If it’s gone, that raises the probability of some kind of 1/4" insertion issue.
In any case, I’m sorry you had such a bad experience and I’m sure the forum can help you get it cleaned out of your rig once and for all. The folks here are second to none in digging to the bottom of problems, including helping Bose on a number of very tough cases.
Chris
Chris - thanks again for your help! - I joined the forum because I’m certain I’ll find resolution to the problem, and feel we’re on the right track. So… 1) I ran unbalanced between the two L1 systems, and I’m sure they were plugged in all the way, as I tried other cables, then want back to the original. Possible, but not likely. 2) 2 channels out of phase - when I turned one L1 off, the phase cancellation went away. I tried this with BOTH sides and they worked independently as they should. Cancellation was only with 2 systems running. 3) Repeatable - I haven’t tried it yet. My backyard is impossibly small and my basement won’t be big enough to try it. I won’t be in a situation again for a while to try to duplicate it - just small stages for the next month. What about (for small stages) running 2 towers right next to each other, 4 subs in the middle, MIDI playback in one, guitar and vocals in the other tower via AUX T1 output? This might work for smaller situations (stages) needing the extra 6db headroom or output…
Hi Double D,
While theoretically possible if you could get the two L1®s close enough together (you can’t), so you can’t really get 6dB gain from the L1®s running them dual mono.
quote:Originally posted by The Double
All good ideas. I thought about running the aux out as you described to the second tower. For areas that I cannot separate towers 20’ apart, but where the extra 6db headroom/volume is desirable, would it be feasible to use MIDI playback on main output to one tower, then vocal mics (2) and guitar aux out to the second tower, but place towers close together? Like RIGHT together with 4 basses in between? Small stages…
quote:Originally posted by Ken-at-Bose:
…
When two sources are uncorrelated the only thing you can count on is that the total amount of acoustic power going into the room will be doubled. Doubling the power is 3 dB.
Source: Two L1®s in Mono (this is a subsection of the previously referenced Stereo / Mono / Distributed systems)
quote:Originally posted by Double
For areas that I cannot separate towers 20’ apart, but where the extra 6db headroom/volume is desirable, would it be feasible to use MIDI playback on main output to one tower, then vocal mics (2) and guitar aux out to the second tower, but place towers close together?
The gain of 3dB would be the result of identical sound coming from both L1®s. If you split the signals (not a bad idea anyway) then the 3dB is not going to happen.
And unless you are actually running full out, you can get 3db by turning up the Master Volume on the T1®.
I can’t turn up the T1 anymore, since I’m at the compression point of the power amplifier in some instances. Really, my goal here is to get more headroom. Perhaps splitting the signal (MIDI tracks in one tower and vocal tracks in the other) will let each tower work more efficiently, dividing the work load, thereby adding headroom?