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Speaker buzz question


VLH

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Can someone here familiar with sound reinforcement explain to me what causes a speaker to buzz at certain frequencies?

 

Lately I've been trying out a few different powered speaker units as I prepare to upgrade. On one, brand new, I noticed a marked buzz from the F above middle C to the Bb. (This unit was a Roland SA300.) The buzz seemed to emanate from the 6.5 inch speakers in that unit.

 

Today I tried a different kind of unit--a mildly used Fishman Soloamp, and found that the Bb a seventh above middle C on both my piano and my vibraphone caused a marked buzz at all but soft volumes, and even as I adjusted other parameters. Both instruments produced the buzz. I'd hoped this unit would work well for the vibes, and it did with the exception of that note. The soloamp is a line array with 6, 4-inch full range speakers and a tweeter. The fact that both instruments caused the buzz indicates that it is something in the soloamp rather than in my equipment. (I haven't returned the soloamp yet and can still try other adjustments if anyone has ideas.)

 

Meanwhile, my older Gallien Krueger MK2OO, which has a 12-inch speaker, does not break up at any pitches.

 

Overall, this trend is making me think that a larger speaker may simply be better.

 

By the way, if there is a better forum for me to ask this kind of question in, let me know. I've not experimented with a lot of sound solutions and with the number of variables and the mix of ideas out there, it gets a wee bit confusing.

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1. You have a partially torn speaker cone

2. You have a partially fried voice coil

3. You have a loose speaker

4. You have something else loose in the cabinet

Moe

---

"I keep wanting to like it's sound, but every demo seems to demonstrate that it has the earth-shaking punch and peerless sonics of the Roland Gaia. " - Tusker

http://www.hotrodmotm.com

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1. You have a partially torn speaker cone

2. You have a partially fried voice coil

3. You have a loose speaker

4. You have something else loose in the cabinet

Thanks.

I can manually see the cones, and they look "whole."

What is a voice coil? What causes it to fry?

Other things could be checked.

Why the buzz on only one pitch?

 

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are you sure that the noise is coming from the speaker itself? The description can cover a wide range of things, but most often if it is acoustical it is something loose buzzing as a function of resonation to a certain frequency...a nut, a wire, a handle, grille cloth....

"I believe that entertainment can aspire to be art, and can become art, but if you set out to make art you're an idiot."

 

Steve Martin

 

Show business: we're all here because we're not all there.

 

 

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You could also just be simply reaching the excursion limits for those speakers. Every speaker has a maximum amount the cone can travel, and on mids and tweeters, this is a very small amount - you typically won't see it. Lower frequencies require greater excursions to produce any kind of volume. Each speaker is crossed over so that it only gets a range of frequencies. You could be hitting the low end of what that particular speaker is receiving, and just giving it more than it can handle.

 

Yes, bigger speakers will not suffer as much from this. They do not have to travel as much to move the same amount of air. Sound volume is just a matter of how much air the speaker can move. A larger speaker is going to move more air. If it also has a long excursion, that further increases it's max output. Of course, efficiency has a huge impact on this, but that's another story.

 

It's possible also that these buzzes can be leaks in the box or loose materials vibrating. But most likely, the sounds you are playing have some frequency that is just over driving the speaker.

Dan

 

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.

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One of my speakers was buzzing, I found that the wires that went from the terminal into the cone were laying against the cone. A little electrical tape, problem solved. If it's going from speaker to speaker, but on different notes, then I'd look for the vibration things mentioned above- screws, grill covers, etc. The clasps that hold the covers on my rack will buzz at certain frequencies.

Live: Korg Kronos 2 88, Nord Electro 5d Nord Lead A1

Toys: Roland FA08, Novation Ultranova, Moog LP, Roland SP-404SX, Roland JX10,Emu MK6

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I found that the wires that went from the terminal into the cone were laying against the cone. A little electrical tape, problem solved.

 

Careful, any interference with those can cause them to break prematurely. I had this happen once and after resoldering, it kept breaking, even after adding additional wire. They have to be able to move freely. Maybe gluing a little foam to the cone where the wire contacts it to dampen it might be a better solution.

Dan

 

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.

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I made sure there was plenty of slack and they could move freely.

Live: Korg Kronos 2 88, Nord Electro 5d Nord Lead A1

Toys: Roland FA08, Novation Ultranova, Moog LP, Roland SP-404SX, Roland JX10,Emu MK6

www.bksband.com

www.echoesrocks.com

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You could also just be simply reaching the excursion limits for those speakers. Every speaker has a maximum amount the cone can travel, and on mids and tweeters, this is a very small amount - you typically won't see it. Lower frequencies require greater excursions to produce any kind of volume. Each speaker is crossed over so that it only gets a range of frequencies. You could be hitting the low end of what that particular speaker is receiving, and just giving it more than it can handle [....]

It's possible also that these buzzes can be leaks in the box or loose materials vibrating. But most likely, the sounds you are playing have some frequency that is just over driving the speaker.

 

Well, the interesting thing is that it is just one particular pitch--Bb a 7th above mid C--and it creates the buzz regardless of which instrument I play through the unit. Higher Bbs and lower ones do not cause the issue. There are 6 speakers and one tweeter in this unit. I can turn the tweeter off and have and still get the buzz, which eliminates the tweeter as the cuse. So, regarding the concept of excursion limit, does the fact that it's only one specific pitch and that lower and higher notes do not create the buzz indicate that the cause is more likely a resonance with something loose in the box or within the design of the box itself?

 

BTW--thanks to all for you input.

 

 

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I suspect you're right that resonance is a big factor, though it may not be the ultimate cause. I also think that rules out simply exceeding the excursion range, unless you're really pelting the speakers -- does it happen at reasonable volumes?

 

What's a reasonable volume? A simpler and almost equivalent measure is a reasonable wattage -- make sure you're well within the speaker's max continuous wattage range. Something to be aware of: speakers made for playing music (e.g., PA speakers) are rated assuming you're playing a full mix through them. You can easily exceed their capacity playing a synth at far lower wattages.

 

So, do you hear the buzz at about 1/10 the rated wattage (which would be about half the rated volume)?

 

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Here's how I pinpoint speaker buzz. Set one of your synths to a sine wave, and play a chromatic scale until you hear it buzz the loudest. So you don't blow your ears out, back off the level to the point that the buzz is still audible, place something on the key to hold it down, and then carefully listen to the cabinet. In that Fishman array, are all six speakers buzzing, or just one? Or is it coming from a speaker at all? These are often loose hardware issues but small speakers in particular can have voice coils that get misaligned in the gap and rub at certain frequencies.
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