KRK 10S2 - Rattling Noise Below 40 Hz

N

new123

Audiophyte
Hey.

Just got myself a new KRK 10S2 recently and there's this rattling noise that's coming out of it when it goes below 40 Hz.

So the video starts at the middle of a sine wave sweep. It loops back to 50 Hz and drops to 40 Hz where you can start to hear this noise sustaining down to somewhere around 20 Hz where it loops back again. And of course it gets louder the higher the volume.

I've never had any experience with subwoofers before and I still got a lot to learn about audio equipment and audio in general. So my question is is this how it supposed to behave or should I be concerned and send it to service?
 
lovinthehd

lovinthehd

Audioholic Jedi
Well, my laptop is lousy at listening to videos of subs (and when I tried in a somewhat noisy room couldn't hear anything anyways), but don't see this sub on the KRK site although I find a manual without specs for 8S/10S/12S subs. Likely 20hz is asking too much of this type of sub. What is your application....home theater? music? what is the system it is in, how is it hooked up, what are the details of you set it up, etc. ? A sub shouldn't make bad noises at reasonable volume, tho altho some ported/vented subs can make port noises at higher volumes if not well designed.
 
j_garcia

j_garcia

Audioholic Jedi
Looks like the sub list 28Hz as its lowest, but it does sound like you're bottoming it out or at the very least, stressing it. Not sure why exactly that would happen at 40Hz, but it could be that sending it 20Hz tones at an elevated level could have damaged the driver.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Hey.

Just got myself a new KRK 10S2 recently and there's this rattling noise that's coming out of it when it goes below 40 Hz.

So the video starts at the middle of a sine wave sweep. It loops back to 50 Hz and drops to 40 Hz where you can start to hear this noise sustaining down to somewhere around 20 Hz where it loops back again. And of course it gets louder the higher the volume.

I've never had any experience with subwoofers before and I still got a lot to learn about audio equipment and audio in general. So my question is is this how it supposed to behave or should I be concerned and send it to service?
Obviously the driver is damaged and or totally inadequate, most likely both are true.

That unit presents the appearance of absolutely supreme junk and to be rigorously avoided.
 
N

new123

Audiophyte
Home studio use is the original intended application. It's connected to a pair of KRK RP5s (G2) via RCA cables and goes directly to my laptop (haven't got an audio interface yet). Though I also tested it on its own, without the monitors and used 2 different RCA to 3.5 mm Jack cables.

Of course before even thinking about what sub should I get the first thing I did was some research on how you should and should not treat this whole audio system thing, my first time after all. The first thing I did after hooking it up was to run a sine wave through and see how it sounds, I didn't even dare to put the volume on max, I was a bit too scared. Also I am aware that the sub is not designed to play frequencies anywhere below 28 Hz, the point of the video demonstration was just to show where the rattle occurs.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Home studio use is the original intended application. It's connected to a pair of KRK RP5s (G2) via RCA cables and goes directly to my laptop (haven't got an audio interface yet). Though I also tested it on its own, without the monitors and used 2 different RCA to 3.5 mm Jack cables.

Of course before even thinking about what sub should I get the first thing I did was some research on how you should and should not treat this whole audio system thing, my first time after all. The first thing I did after hooking it up was to run a sine wave through and see how it sounds, I didn't even dare to put the volume on max, I was a bit too scared. Also I am aware that the sub is not designed to play frequencies anywhere below 28 Hz, the point of the video demonstration was just to show where the rattle occurs.
Therein lies your problem. There is a significant difference of the stress test of sine waves and music program. I would not think that a unit like that would perform well with sine waves, However for music program at modest volume it probably would not rattle.

It seems to me that unit is way oversold deigned to garner way over optimistic expectations. Studio use is a highly demanding application. That unit by virtue of size, and size of driver looks totally unfit for that purpose to me. I would expect, and predict, it would behave in the manner you describe.

You can try a return, but I would expect similar behaviour from its replacement.

I guess my best advice is to turn up your BS alarms to much higher sensitivity level, when dealing with advertising copy. One more tip. If you see specs like those where the spec. says it plays to 30 Hz, and there is no db level quoted in the spec, then run and do NOT press the buy button. The reason is that you don't know how many db down it is at 28 Hz. The ethical way to quote the spec, is to quote it at the -3db point. The way the spec, is written it could be 24 db down for all you know.

The point at which a sub is 3db down is important as it will roll off at 24db per octave below that point if it is ported and 12 db below that point if sealed. Although the sealed sub will have an innate f3 quite high and have its output extended by equalization, which requires a much more expensive driver with a missive motor system and suspension, driven by a powerful amp.

A ported sub can not be equalized. A driver in a ported sub rapidly decouples from the box loading below f3. If driver below f3 it will rattle as you describe, and if continued severe driver damage rapidly ensues. So it seems to me you have driven it with sine waves below f3. Manufacturers often, and should provide a high pass filter just below f3 to prevent driver bottoming and damage. However if you drive it with sine waves, you can drive it though the high pass filter and still cause damage.

I would surmise that sub spec, should actually be f3 40 Hz or 40 Hz -3db. It sounds to me that you drove with sine waves at frequencies where the driver has decoupled from the box. In which case it is not a sub and should have been described as a bass module.
 
S

sterling shoote

Audioholic Field Marshall
Hey.

Just got myself a new KRK 10S2 recently and there's this rattling noise that's coming out of it when it goes below 40 Hz.

So the video starts at the middle of a sine wave sweep. It loops back to 50 Hz and drops to 40 Hz where you can start to hear this noise sustaining down to somewhere around 20 Hz where it loops back again. And of course it gets louder the higher the volume.

I've never had any experience with subwoofers before and I still got a lot to learn about audio equipment and audio in general. So my question is is this how it supposed to behave or should I be concerned and send it to service?
Don't take to heart TLS Guy's gloom and doom appraisal. First, there's likely ZERO damage. Second likely, there's not enough power to drive the sub at what you believe is the proper sub volume; thus, this is causing clipping. Really bad clipping sounds like a sledge hammer hitting a steel pylon. At any rate, adjust sub gain to a full frequency test tone to match main speakers for about 6o db average, not by ear, but by sound pressure level meter. A meter downloaded to your cell phone will do. Then repeat the test you have described and you may find the sub is not damaged at all. The bottom line here is when the sub is properly adjusted you will not sense its presence for music other than electronic, unless you are enjoying cello or double bass, like Celloopa from https://music.apple.com/us/album/uncharted-deluxe-edition/1153830640
 
Last edited:
lovinthehd

lovinthehd

Audioholic Jedi
Home studio use is the original intended application. It's connected to a pair of KRK RP5s (G2) via RCA cables and goes directly to my laptop (haven't got an audio interface yet). Though I also tested it on its own, without the monitors and used 2 different RCA to 3.5 mm Jack cables.

Of course before even thinking about what sub should I get the first thing I did was some research on how you should and should not treat this whole audio system thing, my first time after all. The first thing I did after hooking it up was to run a sine wave through and see how it sounds, I didn't even dare to put the volume on max, I was a bit too scared. Also I am aware that the sub is not designed to play frequencies anywhere below 28 Hz, the point of the video demonstration was just to show where the rattle occurs.
Well, running sine waves at max definitely not a good idea with any speaker. I usually start with music myself altho I do have measuring gear and could also start that way. Do you want to play lower frequencies or is this more for music without lower bass? How does it sound with typical music you want to play and what kind of music is that?
 
j_garcia

j_garcia

Audioholic Jedi
I can't say from the description if the driver is damaged, but as I mentioned, it is likely bottoming out. It could simply be port chuffing as well, because the "noise" that it makes isn't clearly defined, but in any case, it is exceeding its capabilities.
 
N

new123

Audiophyte
What exactly do you guys mean by stress testing? It wasn't that I put a sine wave on max level and just left it to run for hours or something, no not at all. What I did was to just hear what a clean sine wave sounds like on a subwoofer, in the room conditions, on one of the lowest volume settings. Because I only worked with sub frequencies on headphones before.

I did gradually try to put it on max while listening to some of the loudest electronic tracks and did hit the threshold where it started to clip a bit and a quickly turned it down, so I know what clipping sounds like and it's definitely not what I hear below 40 Hz.

It does sound ok & great tho be it just a sine wave or a full music program. Like you can hear the sub frequencies clearly and feel them regardless of the genre. That noise, you can only hear it clear if you listen to it while being really close to the sub and at the right angle.

It might be just port chuffing as well yeah. I just put my hand in the port to hear how the air flow will sound and you know what, I can't really tell if it was the same noise. but it got louder.

I don't know.
 
N

new123

Audiophyte

My phone doesn't seem to record low frequencies.. but they're there.
 
lovinthehd

lovinthehd

Audioholic Jedi
What spl are you playing tones at? At what spl is it making the noises?
 
TLS Guy

TLS Guy

Seriously, I have no life.

My phone doesn't seem to record low frequencies.. but they're there.
I played that video on my big rig. I can hear it. That sort of fluttering sound is what you get if you play a ported speaker, below the frequency where the air pressure in the box controls cone motion. The point is reached suddenly with reflex tuning.

I have attached a file of the model of a 12" speaker, with a performance probably similar to yours.

Take a look at the frequency response curve. Also look at the power handling and output curves. The impedance curve shows the tuning frequency at the low point of impedance. Now look at the cone displacement curve. Note how around tuning and prior to response falling, the cone displacement is well controlled by the box.
Now note what happens below tuning and where the response falls off, the cone displacement shoots up vertically, but the output falls precipitously. If you drive the speaker with a sine wave in this region, you get a fluttering sound, just like you are getting from your speaker. This is how all ported speakers behave.
 

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