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Author Topic: Frequency Drop Off  (Read 1098 times)

Aaron Baxter

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Frequency Drop Off
« on: April 02, 2021, 12:26:45 am »

I'm trying to isolate a strange problem in our sound system.  First off, the equipment is roughly 10 years old, Yamaha MG166cx board, Sennheiser mics (bout $100 range IIRC), Mackie Thump 15 mains.  We are getting frequency drop off around 1K and up.  It's there but at about 1K the output drops about 5DB on those frequencies and up with a slow downward taper.  What's driving me mad is it doesn't always do it (about 70% of the time) and every time I go to tinker with it it doesn't want to do it lol.  If I use the EQs in the thumps to gain the mids and highs it helps, but the singers still sound muffled.  I'm not sure if it's a fault in the board or the mics or something else.  I replaced the tweeters in the thumps because one wasn't working and the other, well why not keep them the same just like finals in an amp.  Also, sometimes (without adjustment) the singers will be way louder than the instruments or vice versa but it's usually pretty "normal" volume wise which is making me lean toward the board but I without knowing where it is I couldn't begin to repair it.  It's not like electrolytic cap pop or heat fade off in transistors.

I thought I'd get a few opinions on what to try first or if anyone might know what the issue likely is before I start throwing thousands in hardware at it.
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Chris Grimshaw

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Re: Frequency Drop Off
« Reply #1 on: April 02, 2021, 04:43:31 am »

Sounds like some methodical troubleshooting will be required.

First up, find another way of getting signal directly into the speakers (FWIW, having worked with them, I'd advise replacing them asap anyway). Phone/laptop is usually a good place to start. Verify whether or not the speakers themselves are working properly without the mixing desk.

If they're working fine, on to step 2: the mixing desk. If I had to bet, I'd say it's the likely culprit. I don't know what the storage conditions have been, but it sounds to me like dust/moisture in the pots and faders could be the cause of your problems. Play music from the phone/laptop/whatever into the problematic channel(s). Figure out if it's just some of the channels, or all of them. Try the headphone output as well as the main outputs feeding into the Mackies (which you've verified are working fine).

The mics may be the issue. I've heard of saliva build-up seriously degrading a mic's performance, which makes sense: if the internal foam becomes saturated, the HF performance will be very different. You can check easily enough by taking the grille off and poking a finger inside to see how the foam's holding up.
To fix that in the future, external foams swapped out occasionally would likely help.

Let us know how you get on.

Chris
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Steve-White

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Re: Frequency Drop Off
« Reply #2 on: April 02, 2021, 06:42:52 am »

Do some testing.  Run some pink noise through the system and some program music.  You need to determine where it's manifesting from rather than shogtunning all over the place.
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Kevin Maxwell

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Re: Frequency Drop Off
« Reply #3 on: April 02, 2021, 09:04:39 am »

I assume these are powered speakers. It sounds like you have an intermittent section of the internal power amp(s) that feeds the high end of the speakers.
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Jay Marr

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Re: Frequency Drop Off
« Reply #4 on: April 02, 2021, 09:20:04 am »

I assume these are powered speakers. It sounds like you have an intermittent section of the internal power amp(s) that feeds the high end of the speakers.

I had a similar issue with some JBL PRX512s.  I had 4 of them and they all had different amounts of output from the tweeter (so some sounded darker, etc).
They were under warranty....brought them in, and they replaced the amps.  No issues after that.

Different box I know, but just sharing that experience in case it's helpful.
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Mike Caldwell

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Re: Frequency Drop Off
« Reply #5 on: April 02, 2021, 12:08:20 pm »

It sounds like a speaker issue but yet odd they both are doing the same thing, when it does start working do both speakers start working properly at the exact same time?
Are the speakers each directly connected to the mixer or jumping from one speaker to the other.

Don't just start throwing money at a problem that you have not isolated what the cause really is.
Call in someone who knows what they're doing to help go through your system and sort out
the issues.
Where are you located, someone here may be close by.
« Last Edit: April 03, 2021, 05:21:08 pm by Mike Caldwell »
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Steve-White

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Re: Frequency Drop Off
« Reply #6 on: April 02, 2021, 01:29:47 pm »

^^^  Yeah Mike for sure.  First thing that came to mind was horn compression driver diaphragms.  They were replaced.  Could be almost anything or a combination of issues up to and including Operator Error.

Time to systematically sift through the chain to find the squeak.
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Nathan Vanderslice

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Re: Frequency Drop Off
« Reply #7 on: April 03, 2021, 03:44:42 pm »

I'm trying to isolate a strange problem in our sound system.  First off, the equipment is roughly 10 years old, Yamaha MG166cx board, Sennheiser mics (bout $100 range IIRC), Mackie Thump 15 mains.  We are getting frequency drop off around 1K and up.  It's there but at about 1K the output drops about 5DB on those frequencies and up with a slow downward taper.  What's driving me mad is it doesn't always do it (about 70% of the time) and every time I go to tinker with it it doesn't want to do it lol.  If I use the EQs in the thumps to gain the mids and highs it helps, but the singers still sound muffled.  I'm not sure if it's a fault in the board or the mics or something else.  I replaced the tweeters in the thumps because one wasn't working and the other, well why not keep them the same just like finals in an amp.  Also, sometimes (without adjustment) the singers will be way louder than the instruments or vice versa but it's usually pretty "normal" volume wise which is making me lean toward the board but I without knowing where it is I couldn't begin to repair it.  It's not like electrolytic cap pop or heat fade off in transistors.

I thought I'd get a few opinions on what to try first or if anyone might know what the issue likely is before I start throwing thousands in hardware at it.
  The one thing I haven't heard yet here is what about connections? I don't know anything about these speakers, but what about problems with various connectors that may be in the boxes? Push ons or screw held connections that are loose. Is it possible that the trouble is coming from connections that are just loose enough that they are making a partial connection that is affecting the performance of the speaker?  Could this include some solder connections?
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Tim McCulloch

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Re: Frequency Drop Off
« Reply #8 on: April 03, 2021, 07:01:20 pm »

If it's the Thuds« that are lacking HF, it's their way of telling you it's long past time to buy better speakers.

No, I'm not kidding.  The "Thud"« is the satisfying sound they make (the only one) when they hit the bottom of the dumpster.

Ask for more if you want to know how I really feel.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Steve-White

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Re: Frequency Drop Off
« Reply #9 on: April 03, 2021, 09:33:03 pm »

^^^ ROFL - I tend to feed the recycle bin much sooner in the "turd polishing" cycle these days as well.
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ProSoundWeb Community

Re: Frequency Drop Off
┬ź Reply #9 on: April 03, 2021, 09:33:03 pm ┬╗


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