I think I read somewhere in this message board that the PAS has no integrated feedback detection and suppession circuitry.

However, after I plug everything in and power up, I usually get a feedback howl when I open up the gain. This initially freaks me out because the level is low, and I'm afraid I won't be able to get a sufficient volume level for the venue. But then, sometimes as we are playing, I find that I can increase the gain until I have sufficient levels, and the feedback problem disappears.

So, my question is: Is there some sort of dynamic adjustment that the PAS makes automatically to reduce feedback? I'm hard pressed to explain this behavior otherwise.

--Rick
Original Post
Hi rikart,
No dynamic feedback compression installed in the system.

I have a couple questions for you. What mic are you using? Also, have you set your TRIM control properly on the PS1? Having the TRIM set improperly can sometimes lead to some anomalys things. It's nice knowing that the TRIM is set properly for a couple reasons:
1) You can ALWAYS set the TRIM back to the same position if you're using the same mic (or instrument) and player.
2) All the control has transfered to the front at the remote, no more crawing around back at the PS1. Set and forget the rear panel and take charge from up front.

Let us know what you find. Good luck. Smile
Thanks, Kyle. I'm thinking that I simply have something too hot in my mix when I open the gain on the Bose system (I usually use a mixer, and at the moment we have only one L1/B1 system). Then, as I tweak in all of the signals, I get the sound I'm looking for without feedback.

We're typically using Shure SM-58 mics (typically only 2 or 3). I begin with the master down on the Bose system, setting the trim just below peaking on the loudest inputs. Then, I do indeed leave the trim settings alone and control levels from the remote. But I think the feedback often comes from one of the acoustic instruments with on-board piezo pickups. At any one time, we might have a mandolin, a dobro, a dreadnaught guitar, a nylon-string guitar, a fiddle, an upright bass, a banjo, or a Portuguese guitar in the mix.

I'm using this system with three different acoustic-style bands at the moment, so repeatablity is a bit of an issue :-)

Thursday night one of the groups (http://www.eklectica-band.com) played an outdoor concert from a gazebo stage in a park. Because the structure seemed to be trapping the sound, I opted to put the PAS out in front of us -- outside the gazebo, actually. Then, we introduced floor monitors to let us hear what was going on. There were no individual instrument amplifiers, but we had degenerated to a house-and-band-monitors setup. It worked okay, and the crowd really liked the sound, but from a player's perspective I don't think I'll take that approach again. If I had another tower in the same circumstances, I'd try having one on either side of us near the railing and, if feedback became a problem, put them outside the gazebo and just use the sound coming from the back of the tower as monitor.

Those floor monitors -- what can I say? -- they suck. And, since I'm mixing from the stage, it was disconcerting not to be hearing exactly what the audience heard. I guest this means I'm a firm convert to the Bose Way!
rikart,
The output level from the mixer could be causing some problems, mainly in terms of gain staging. What mixer are you using? What output from that mixer (balanced or unbalanced, 1/4" or XLR)? What input are you using on the PS1 power stand? I can make some recommedations based on your answers.
> The output level from the mixer could be
> causing some problems, mainly in terms of
> gain staging. What mixer are you using? What
> output from that mixer (balanced or
> unbalanced, 1/4" or XLR)? What input are
> you using on the PS1 power stand?

Behringer Eurorack UB1222FX-PRO, running Left output thru XLR to PS1 Channel 1, preset 00. I have set gain pots on the mixer to near 0 db and adjusted channel trims for desired sound pressure level. The PS1 Channel 1 and Master settings typically don't need to be higher than 12 o'clock to get the volumes I need.
> Does the Behringer have a switch to drop
> its output down to mic level? If not, you
> may be overloading the PAS input.

The ouptus are not switchable. Mains out is +4 dBu. Level and impedance match doesn't seem to be a problem, though. I don't get distortion or overload (as monitored by the trim LED) on the PAS input.

What I do get is a fair amount of hiss coming out of the mixer, even though I seem to have the gain structure set up correctly. The effects loop on the mixer is especially noisy.
The PAS inputs are mic level. Do a search on the term "pad" and you'll find a lot written on the use of either direct boxes or 20 dB inline pads for optimizing the level between mic and line level. (I'd use the inline pads since you've already got XLR outs.)

I think that'll give you better results.
Hi Rikart,

One suggestion, make sure the mixer and anything else connected to it are running on the same circuit as the PAS, preferably off of the same powerstrip. I have the same mixer as you do and its usually very quiet. Sometimes you can't get rid of the noise, though, so I always carry a couple of ground-lifting direct box and that usually stops it. I try to get my levels out of the mixer as low as possible, with the sliders near 0 dB and the trims on the mixer as low as possible. I set the trims on the PAS as high as possible without clipping. I've thought about getting some 20 dB pads for the outputs, but haven't gotten it done yet.

Larry
Thanks for the tips, guys. I'll try the XLR inline pad to see if it reduces the noise -- which is not too objectionable as it is, actually.

I'm hearing Johnson noise, which is to say a white-noise hiss, rather than the 60-cycle hum associated with grounding issues. And, I always plug the mixer and the PAS into the same circuit.
quote:
Originally posted by gitarzan:
Hi Rikart,

I try to get my levels out of the mixer as low as possible, with the sliders near 0 dB and the trims on the mixer as low as possible. I set the trims on the PAS as high as possible without clipping. I've thought about getting some 20 dB pads for the outputs, but haven't gotten it done yet.

Larry

Hmmm....now this is exactly the OPPOSITE of what Bose told me to do! I was told to make the signal out of my mixer as HOT as possible, and NOT use the PAS to boost up the signal.

WHICH IS IT & WHY??
One achieves the best signal to noise ratio by keeping one's level at unity gain throughout until the final output stage.

When using a mixer:

• I set my keyboard output at 85-90% (so that there's a bit extra available for a solo)
• trim the mixer input so that I'm solidly in the green, maybe just touching red on the peaks
• set the faders (both channel and master) at 0 dB (unity gain)

Were I to be using XLR outs on a mixer ahead of the PAS mic inputs, I would do all of the above, making sure my output was set to mic level, prior to adjusting the trim on the Bose. Use 20 dB pads if your mixer is line level only.

I hope that makes sense.
OK, the pots are my mixer are rotary and do have the 12:00 detents, so that clears that part up for me. As to the trims, I will now try setting those to the right levels, with the channel & master set at 0db.

Now, my outs are line not xlr, so should I use di boxes for each line? Do I need one for the channel that will only be carrying line level sources (md/synth module), too?

And any idea about where I would either expect, or would be optimal, for the trims on Ch. 1 & 2, to be set?
Ch. 1 is for mics (Beta 87, 58, 57, ATM35), ususally 3, sometimes 4, and Ch.2 is for md player/synth module.....
Saxman7

It won't hurt to try 2 conductor, 1/4" jacks for short runs (10 or 12 feet) it has worked fine for me that way.

PS1 input trims should be At or Near Zero on channels one and two.

Anything that comes through the mixer should hit the PS1 at a level that makes it unneccessary for the PS1 preamp to do anything at all.

Use remote Channel and Master volume controls as neccessary to get proper system SPL.

You can think of the PS1 as a power amp. Like a conventional setup, the Presets and the EQ controls on the remote become system EQ between the mixer and amp.

Hope this helps, Oldghm
Thanks, I'll try it like that.
When we gigged last, it seemed like I had to boost the trims on 1 & 2, as it wasn't getting loud enough. And turning up my mixer was getting distortion.
But I'll try and set the mixer channels & main at Odb, then work with each trim to get the max signal before peak.

Hopefully this will help....
saxman, I know this is a confusing area. By the time people are talking about the "sliders" on their mixer, they're talking about the VOLUME of the overall signal that they are sending to the PAS. There are gain stages prior to that, as Alan has pointed out, that are critical. I've been using a mixer with 3 PAS' for a year with excellent results. If it may be of any help, here's how I go about setting my mixer gains.

Plug the mic or instrument into the mixer. Turn all the output faders (sliders/knobs) all the way down - on the individual channels as well as the subgroups and masters. Set all the eq knobs to center default, and turn all "extra" aux knobs, etc all the way down - any effects should be turned off. (Concern yourself with getting a good strong clean basic signal first, and then you can add stuff to it later, after you're certain you've got a strong "foundation"). Look for a "solo" button on the channel strip that you're plugged into. This will give you a visual representaion of your signal strength, using the LED's on your mixer. My Soundcraft has two rows of LED's (left & right out) that run from green to amber to red. This is pretty common on most current mixers.

Usually the very top knob on your channel strip is the "gain" or "trim" or "attenuation" knob. Different manufacturers call it different things, but it always does the same job, and it's CRITICALLY important. For our purposes, we'll call it "trim" since that's the most commonly used term. You need to sing or play your instrument at the loudest typical volume that you perform at, and watch the LED's. Adjust that "trim" knob until you are, as Alan said, solidly in the green, with the loudest spikes into amber - even an occassional red is ok as long as it's just a spike, and not constant. This trim knob is tailoring the preamp's sensitivity on THAT channel to YOUR instrument being played at YOUR typical volume. Some people just set their trims to "unity", which is okay, but it is rarely maximizing your signal-to-noise ratio. Although unity is a safe general setting, I've rarely come across a mic or instrument that was "optimized" at unity gain - many mics are optimal as high as +30db above unity.

Once the trim is optimized for that channel, do the same thing for every channel that's being used on the mixer. Be sure to use the actual instrument and/or mic and the actual person's voice or playing that goes with it. Remember, you are tailoring the channel to that specific person / instrument as well as their playing style.

Now that your trims or "gains" are optimized, you can push the individual sliders/knobs on the active channels, as well as the subs and mains up to "unity" or 0 db. You'll want to keep the main output section (subgroups and mains) at or close to unity, and use the individual channel faders to adjust individual VOLUME levels for your mix. You really don't want to mess with the trims once they're set, but some people DO tend to give you a weaker signal at sound check, and will turn up as the night goes on, which could cause clipping. You can periodically check each channel by hitting the "solo" button to watch the LED's to make sure they are not in the red. If they are, just back off the trim knob on their channel until it's back in the green - turning the slider down will NOT fix the clipping, it will just turn down the VOLUME of the clipped signal... it's important to remember that "gain" and "volume" are two separate issues.

Now the "mixer" part of the equation has optimized gain staging on each individual channel, and a good strong global output signal. Next we need to feed that to the PAS, and we'll have to adjust the input sensitivities on the Bose channels. If you're running your mixer to channels 3 or 4, you unfortunately have only your ears to go by to set the gain. All you can do is turn the remote's channels and master volume up to performance levels and listen for clipping, adjusting the trim on the PS1 powerstand as best you can. If we've done the first part correctly, you KNOW you've got a clean signal coming into the PAS, so any clipping that's happening is at the PAS' "Trim". I've found that a good general rule of thumb is to start with the trim in the 12 o'clock to 3 o'clock range. Just about everything I've plugged in to ch 3 or 4 has had a gain in that range (assuming the incoming signal has been properly optimized).

If running your mixer to ch 1 or 2, you have the benefit of the LED's to guide you. Using these channels, you can turn the remote's master and channel volumes all the way down (save your ears) and play at your normal volume while you turn up the trim on the Bose. Again, watch the lights and make sure you're strongly into the green, with hints of amber or red. As Alan and Oldghm pointed out, with a "line level" mixer output, you will find that the trims on the Bose need to be all the way down, or nearly there, to keep out of the red. That's okay, it'll still work fine. If you have -20db pads on the output, your trims will be set more like ch 3 or 4 - somewhere in the 12 - 3 o'clock range, most likely. In my particular situation, I have 1/4" balanced (trs) lines out of my mixer. I use 1/4" trs to xlr cables (to keep the lines balanced - plugging any 1/4", even a trs into ch 1 or 2 will be unbalanced) and I plug those into ch 1 of each PAS. The trims are turned all the down, and we use various presets, depending on what's being panned to that particular PAS.

This has worked great for us. We get a LOT of good clean volume out of our systems, with little or no noise (room/electrical dependant), never any clipping and VERY rarely any feedback at all - with 9 mics, sometimes all running open at once. We also get the benefit of the presets, which really are very well done. I hope this helps more than it confuses the issue.
One thing I forgot to mention is that you may have gain stages BEFORE the mixer input, and they'll need to be adjusted first. Most wireless units have trims of their own, and from my experience typically tend to run pretty hot. With these types of units, starting them at unity is a good idea. The key is to find the very first trim pot that your signal hits and start there, trying to maintain a good strong clean signal at every consecutive trim pot throughout the entire signal path. Good luck.
I agree - great explanation g-j. I'd like to add that different mixers can vary greatly in their actual output at "unity". My Mackie mixers (1202 & 1604 VLZ's) typically sound good with ch 3/4 levels set between 11 and 1 o'clock. My little Samson MD 1064 is much hotter, and I usually set it at about 9 o'clock. The Behringer "baby mixers" (some of which don't really have unity markings) seem to require much more gain on the PAS - up to 3 o'clock.

So much for standards!
Yes, use the Remote. Master Volume.

Once you've got everything that is connected to the PS1 set, use the Master Volume to control the overall volume for the System.

Use the Channel Volumes to control the relative loudness of the inputs you've run into Channels 1 and 2.

For overall control of the loudness use the Master.
Hi Saxman7 - I'll typically make small "mix" changes at the mixer from the individual channels. Large global volume changes I make from the PAS remote. Using the method and equipment that I described, my band can typically run our remote's channel volumes and masters in the 2 -3 o'clock area...which is pretty loud.

And Saxhound makes an excellent point about the "standards". There have been ongoing debates for years about "unity" and the huge degree of fluctuation from one manufacturer to the next. The situation that I described is what works best for me using my particular equipment...but the basic method of setting gain staging should work for most situations.

Although I've run many sound systems over the years, and I'm familiar with many mixers, since switching to the PAS, I've only used a couple of different mixers with the Bose system - so my firsthand experience with specific details of how various brands may react in relation to this system is limited.
Good stuff, everyone. I've ordered a couple of 20 db pads for the XLR line outs of my mixer, and will also pay more careful attention to my trim settings on the PAS.

Now I have another issue: I recently played a venue that had a high-ceilinged atrium in the center. We set up as usual with the PAS behind us, but we were outside of the atrium area -- performing just in front of it, actually, while the audience was in in the atrium area. The ceiling where we were playing was about 8 ft high; the ceiling of the atrium was 20-25 ft. We could hear ourselves fine, the people on either side of us could hear fine, but the audience in the atrium and beyond said that they couldn't hear us well at all.

In my mind I can see the cylindrical sound wave shooting out of the low ceilinged area and difracting into the high-ceilinged space, dispersing into unintelligiblity. Is this what's happening.

Would be better off with the PAS beside or in front of us, catching our monitor sound from the back or side of the tower? We are a low-volume acoustic group, so hearing ourselves hasn't been an issue.

--Rick
Hi featcovers,

quote:
Originally posted by featcovers:
I seem to remember reading somewhere (here, I think) that because of the way the Bose L1 projects the sound they aren't as easy to use with a mixer - not simply a matter of panning everything to the centre or slightly left or right. Am I dreaming? (haven't been here for a long time, band prsonnel changes, new mixer bought)

4 piece band (3xvox, elec gtr, kbds, bass, Roland Electronic Kit with Yamaha MG166 mixer and 2x Bose L1 towers with 2x bass modules per side)


I have posted a reply to your question over here in

5? Piece band - featcovers

Please follow the link and join me in that discussion.

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