I run a jazz band and use the PA for vocals as well as having static microphones that the trumpet and trombone play into.
The mixer/amp is Yamaha 512SC. When I use it with Mackie C200 passive speakers I get howl and feedback, even at fairly low volume. These speakers are rated at 8ohm and placed in front of all microphones.
When I use Celestion SR3’s, also rated at 8ohm with the same mixer/amp, the sound is crystal clear with no feedback or howl. In fact, I can place them behind the band and microphones, still no feedback or howl.
The Mackie speakers were purchased brand new, and also acted in the same way when used in conjunction with a Mackie mixer/amp.
Any idea what the problem could be?
Thank you
Kevin
The mixer/amp is Yamaha 512SC. When I use it with Mackie C200 passive speakers I get howl and feedback, even at fairly low volume. These speakers are rated at 8ohm and placed in front of all microphones.
When I use Celestion SR3’s, also rated at 8ohm with the same mixer/amp, the sound is crystal clear with no feedback or howl. In fact, I can place them behind the band and microphones, still no feedback or howl.
The Mackie speakers were purchased brand new, and also acted in the same way when used in conjunction with a Mackie mixer/amp.
Any idea what the problem could be?
Thank you
Kevin
The Mackie speakers are billed as ultra-wide dispersion according to their web site, so that could be the cause. Have you tried pointing them out a bit? A speaker with narrow dispersion would push more of the sound forward away from the microphones allowing more gain without feedback. The Celections look like a single driver which would be quite directional at the frequencies where feedback can occur
Brian
Brian
Feedback is a function of how much gain is being applied in the loop:
- Mic picks up sound according to its polar pattern and position
- Mixing desk and power amps amplify the signal
- Speakers convert the signal into loud sound, according to the polar pattern of the speakers
- Mic picks up that sound according to its polar pattern and position.
That's happening at all times. Even if the system isn't ringing, the mics are always picking up a little bit of what the speakers are doing.
If the gain around the loop is more than 1, you get howling feedback that rises in volume. If it's 0.999997x, you'll find everything rings a little before dying down.
I can imagine that the Mackie speakers are a little more sensitive than the Celestions, and that's enough to push the loop gain from below 1 to above, resulting in feedback.
The solution there is simple - pull the master fader down a touch.
It might well be the case, though, that the plastic cabinet of the Mackie speaker is throwing a lot of lower-midrange sideways, straight into the mics. In that case, opening them up and adding bracing might help.
If swapping out the speakers (and changing nothing else) produces a problem, then the problem is with the speakers.
Chris
PS - if you're near Sheffield, feel free to get in touch and I can take a look in person. It's much easier to troubleshoot things that way.
- Mic picks up sound according to its polar pattern and position
- Mixing desk and power amps amplify the signal
- Speakers convert the signal into loud sound, according to the polar pattern of the speakers
- Mic picks up that sound according to its polar pattern and position.
That's happening at all times. Even if the system isn't ringing, the mics are always picking up a little bit of what the speakers are doing.
If the gain around the loop is more than 1, you get howling feedback that rises in volume. If it's 0.999997x, you'll find everything rings a little before dying down.
I can imagine that the Mackie speakers are a little more sensitive than the Celestions, and that's enough to push the loop gain from below 1 to above, resulting in feedback.
The solution there is simple - pull the master fader down a touch.
It might well be the case, though, that the plastic cabinet of the Mackie speaker is throwing a lot of lower-midrange sideways, straight into the mics. In that case, opening them up and adding bracing might help.
If swapping out the speakers (and changing nothing else) produces a problem, then the problem is with the speakers.
Chris
PS - if you're near Sheffield, feel free to get in touch and I can take a look in person. It's much easier to troubleshoot things that way.
The Mackie C200 is a 10+1 two way speaker system while the Celestion SR3 has just an 8" fullrange driver. The Celestion is going to have a response that falls off at the extreme high and low range which is ideal for vocal reproduction, if you want the same results from the Mackies the highs and low have to be rolled off with the EQ on the mixer.
Those Mackie C200 horns look like they are actually wider than 180 degree dispersion, not what you want on stage at all - the polar diagrams show a definite spike straight back across a wide range of high frequencies. The C200Z variant doesn't have that spike as the horn flare is conventionally shaped.
The preamp difference could be related to eq and delay/phase differences, but I'm sure the speakers are given many dB more backwards to the microphones - the directionality implies there's scope for aiming the speakers differently, but the polar response is basically problematic.
The preamp difference could be related to eq and delay/phase differences, but I'm sure the speakers are given many dB more backwards to the microphones - the directionality implies there's scope for aiming the speakers differently, but the polar response is basically problematic.
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