Woofer noise, VC rubbing or something else?

[yepimonfire]

Just purchased a pair of rp 160ms. One of the speakers makes a barely audible noise with very low noise, so inaudible, that I didn’t hear it until I was playing sine waves through it. Pressing on center of the cone doesn’t produce any scraping sounds, so I’m wondering if it could be noise from something else. Bout to pull the woofer out and have a look.

What do you guys think?

 

[TLS Guy]

Just purchased a pair of rp 160ms. One of the speakers makes a barely audible noise with very low noise, so inaudible, that I didn’t hear it until I was playing sine waves through it. Pressing on center of the cone doesn’t produce any scraping sounds, so I’m wondering if it could be noise from something else. Bout to pull the woofer out and have a look.

What do you guys think?

It sounds as if you are playing sound waves of a frequency well below the F3 of the speaker and may be also below Fs of the driver. That has great potential to damage speakers.

So either the driver was faulty, or you have damaged it by driving it improperly. It sounds as if there is cone VC separation starting or a problem developing with the suspension.

It is very risky to feed sine waves in the tweeters range and below a woofer's pass band, at least in speakers with cheap drivers like that.

 

[yepimonfire]

It sounds as if you are playing sound waves of a frequency well below the F3 of the speaker and may be also below Fs of the driver. That has great potential to damage speakers.

So either the driver was faulty, or you have damaged it by driving it improperly. It sounds as if there is cone VC separation starting or a problem developing with the suspension.

It is very risky to feed sine waves in the tweeters range and below a woofer's pass band, at least in speakers with cheap drivers like that.

Took the driver out of the box and hooked it up. Still makes the noise, sounds like it’s coming from the pole piece, not the woofer, suspension, or surround. Manually pushing the driver while observing the coil/gap shows that there is no rubbing or misalignment.

The noise is me moving my phone around, not the speaker.

Could some sort of debris be inside the vc gap? It sound perfectly fine with music/movies. Klipsch is sending me a new woofer, just curious where the noise is coming from.

 

[TLS Guy]

Took the driver out of the box and hooked it up. Still makes the noise, sounds like it’s coming from the pole piece, not the woofer, suspension, or surround. Manually pushing the driver while observing the coil/gap shows that there is no rubbing or misalignment.

The noise is me moving my phone around, not the speaker.

Could some sort of debris be inside the vc gap? It sound perfectly fine with music/movies. Klipsch is sending me a new woofer, just curious where the noise is coming from.

One thing I notice is that the VC is not deeply embedded in the gap. Myself I prefer underslung drivers, where the coil is deeply embedded in the gap. I suspect though you have cone VC separation.

First I would remove the other driver and see how much of the VC coil is showing. That might tell you if the VC is not deep enough in the pole pieces.

If there is a lot of coil showing then those are just junk Far Eastern drivers. I would expect that from Audiovox. Drivers built like what I see in your picture have poor linear excursion and are not high quality reproducers.

 

[shadyJ]

Are you able to run impedance tests? If the values of one speaker or driver are way off the other, then you might have a flawed unit. Or you can just make it easy on yourself and ask Klipsch to send you a replacement driver.

 

[yepimonfire]

Are you able to run impedance tests? If the values of one speaker or driver are way off the other, then you might have a flawed unit. Or you can just make it easy on yourself and ask Klipsch to send you a replacement driver.

No unfortunately. As I previously said, it sounds just fine with real music or movies, frequency response and volume is identical to the one that doesn’t vibrate. Klipsch is sending a driver, just want to know why it’s doing that when there is no coil rub when pressing the woofer.

The noise sounds louder in the video because of the iPhones bias towards voice, it’s much quieter than the test tone in person.

 

[yepimonfire]

One thing I notice is that the VC is not deeply embedded in the gap. Myself I prefer underslung drivers, where the coil is deeply embedded in the gap. I suspect though you have cone VC separation.

First I would remove the other driver and see how much of the VC coil is showing. That might tell you if the VC is not deep enough in the pole pieces.

If there is a lot of coil showing then those are just junk Far Eastern drivers. I would expect that from Audiovox. Drivers built like what I see in your picture have poor linear excursion and are not high quality reproducers.

A majority of VC are overhung in most consumer, and lots of pro gear. You seem to make a lot of assumptions on the woofers based off of a crappy phone video that doesn’t provide any objective data.

If the drivers had poor linear excursion, there’s no way the 5.25” driver in the smaller speakers could reproduce 100dB at 50hz with 3.6% distortion at a distance of 11’.

 

[shadyJ]

A majority of VC are overhung in most consumer, and lots of pro gear. You seem to make a lot of assumptions on the woofers based off of a crappy phone video that doesn’t provide any objective data.

If the drivers had poor linear excursion, there’s no way the 5.25” driver in the smaller speakers could reproduce 100dB at 50hz with 3.6% distortion at a distance of 11’.

In-room measurements of distortion in low frequencies are not very meaningful. Pressure vessel gain can boost fundamental frequencies way up with respect to distortion product frequencies. For that matter, in room loudness measurements are not very telling either. Who knows what boundary gain could be doing at that frequency?

Although I do agree that overhung design doesn't mean anything qualitatively. It certainly isn't a sign that the driver is somehow inferior.

 

[Steve81]

In-room measurements of distortion in low frequencies are not very meaningful. Pressure vessel gain can boost fundamental frequencies way up with respect to distortion product frequencies. For that matter, in room loudness measurements are not very telling either. Who knows what boundary gain could be doing at that frequency?

The speakers in question were measured at S&V, and while there are no distortion numbers, the RP-150M's arent really doing a whole heck of a lot by 50Hz (-6dB point of 57Hz):

https://www.soundandvision.com/content/klipsch-reference-premiere-rp-150m-speaker-system-review-test-bench

Given that, and the reality that below tune, distortion tends to rise dramatically in a vented speaker, I'd suggest that there is quite a bit of room related gain in his case.

 

[everettT]

In-room measurements of distortion in low frequencies are not very meaningful. Pressure vessel gain can boost fundamental frequencies way up with respect to distortion product frequencies. For that matter, in room loudness measurements are not very telling either. Who knows what boundary gain could be doing at that frequency?

Although I do agree that overhung design doesn't mean anything qualitatively. It certainly isn't a sign that the driver is somehow inferior.

I'm waiting for numbers to somehow make this irrelevant

 

[KEW]

Could some sort of debris be inside the vc gap? It sound perfectly fine with music/movies. Klipsch is sending me a new woofer, just curious where the noise is coming from.

Don't know what the problem is, but kudos to Klipsch for sending you a new one without extended debate!

 

[yepimonfire]

@shadyJ I simply don’t see the purpose of popping in this thread to debate the quality of a driver from photos and videos alone (which tell almost nothing about the design or performance of a driver without t/s parameters and actual measurements).

The thread is about why one woofer makes a noise while the other does not at low frequencies. Doesn’t matter if the driver in question is a top shelf scanspeak or the tiny plastic speakers in my flat screen tv.

 

[yepimonfire]

Don't know what the problem is, but kudos to Klipsch for sending you a new one without extended debate!

They’re pretty good about that from what I’ve heard. Didn’t even hassle me about trying to go through the retailer first, which is great. I hate sending things back, waiting a week to send and another week to receive, especially when the speakers are pretty much usable as is.

Listened to music yesterday for about 3 hours and then watched a 2hr movie with the volume knob at 0dB (it was a Christmas comedy, so not exactly “torture test” material) with no audible problems.

 

[yepimonfire]

The speakers in question were measured at S&V, and while there are no distortion numbers, the RP-150M's arent really doing a whole heck of a lot by 50Hz (-6dB point of 57Hz):

https://www.soundandvision.com/content/klipsch-reference-premiere-rp-150m-speaker-system-review-test-bench

Given that, and the reality that below tune, distortion tends to rise dramatically in a vented speaker, I'd suggest that there is quite a bit of room related gain in his case.

I don’t know if the S&V measurement is 100% correct. I have to wonder if they somehow didn’t capture all of the ports contribution.

I’ve occasionally seen some strange measurements that don’t make sense pop up in their reviews, for example, giving the tiny 4” Polk OWM speaker an 89dB 1w/1m sensitivity rating. I haven’t measured it myself, but as someone who owns one, I call BS. If we assume their 1w1m rating for the Klipsch 150m is correct (89dB), when placing the two speakers side by side, they should be about equal in level, and they are not, the Klipsch is about 4dB louder.

It’s hard to determine the tuning frequency just by looking at the port because of its shape (tractrix on both ends with a rounded slot), but the woofer on the 150m seems to reach minimum motion at about 55hz. I actually have a graph that shows rapidly increasing distortion below the f3. To be far, I should really measure these full space outdoors. I have no doubt that room gain is helping me achieve higher output at lower distortion.

Considering the knee point where THD begins to rise rapidly, I’d say my 55hz guess isn’t too far off.

 

[everettT]

@shadyJ I simply don’t see the purpose of popping in this thread to debate the quality of a driver from photos and videos alone (which tell almost nothing about the design or performance of a driver without t/s parameters and actual measurements).

The thread is about why one woofer makes a noise while the other does not at low frequencies. Doesn’t matter if the driver in question is a top shelf scanspeak or the tiny plastic speakers in my flat screen tv.

Thread title :
Woofer noise, VC rubbing or something else?

 

[everettT]

I don’t know if the S&V measurement is 100% correct. It’s hard to determine the tuning frequency just by looking at the port because of its shape (tractrix on both ends with a rounded slot), but the woofer on the 150m seems to reach minimum motion at about 55hz. I actually have a graph that shows rapidly increasing distortion below the f3. To be far, I should really measure these full space outdoors.

Considering the knee point where THD begins to rise rapidly, I’d say my 55hz guess isn’t too far off.

Not sure if their measurements are correct either. I would say they (with their methodology) have been doing measurements for a while with quality equipment and would assume they know more about this side of the hobby then most consumers, not saying they know more than you though.

 

[yepimonfire]

Not sure if their measurements are correct either. I would say they (with their methodology) have been doing measurements for a while with quality equipment and would assume they know more about this side of the hobby then most consumers, not saying they know more than you though.

Oh I’m sure they do know more than me, but that doesn’t mean a single measurement on one or two reviews is without error. A deep notch in THD at 55hz with a huge increase thereafter would indicate there’s a good chance the speaker is tuned at ~55hz. I don’t have the equipment to do an impedance sweep, and S&V doesn’t give one, but that would show the tuning via a spike in impedance.

I have seen the same measurements with the Klipsch R-15m. Since the port is a standard round port, it’s easy to measure and find the box tuning is 63hz. Again, this is the minimum motion point for the woofer, and a notch is seen in THD @63hz with a rapid increase thereafter. I also get about 50hz in room -3dB with these, but that is entirely due to room gain. Even with identical woofer diameter, the R-15m measured in the same manner as the 150m @50hz shows 27% THD at 90dB, didn’t even bother going to 100dB because it obviously wasn’t happy at 90 lol.

It’s worth noting when I was measuring the 150m 100dB was the absolute maximum at 50hz. An increase of even 2dB cause the VC to exceed xmax resulting in non linear behavior and a major increase in distortion, that was not only measurable, but clearly audible. More than likely, I’d lose anywhere from 3dB-6dB off that measurement outdoors.

Still, I’ve personally seen tower fail to achieve the same output in my room. My brother brought a pair of towers over with dual 6.5” drivers in a box tuned to 45hz, and an in room f3 of 38hz. They crapped out above 95dB on all bass below 80hz. Didn’t measure THD because we were just goofing off play low bass notes and using an spl meter, but the distortion was audible above 95dB.

 

[TheWarrior]

Oh I’m sure they do know more than me, but that doesn’t mean a single measurement on one or two reviews is without error. A deep notch in THD at 55hz with a huge increase thereafter would indicate there’s a good chance the speaker is tuned at ~55hz. I don’t have the equipment to do an impedance sweep, and S&V doesn’t give one, but that would show the tuning via a spike in impedance.

I have seen the same measurements with the Klipsch R-15m. Since the port is a standard round port, it’s easy to measure and find the box tuning is 63hz. Again, this is the minimum motion point for the woofer, and a notch is seen in THD @63hz with a rapid increase thereafter. I also get about 50hz in room -3dB with these, but that is entirely due to room gain. Even with identical woofer diameter, the R-15m measured in the same manner as the 150m @50hz shows 27% THD at 90dB, didn’t even bother going to 100dB because it obviously wasn’t happy at 90 lol.

It’s worth noting when I was measuring the 150m 100dB was the absolute maximum at 50hz. An increase of even 2dB cause the VC to exceed xmax resulting in non linear behavior and a major increase in distortion, that was not only measurable, but clearly audible. More than likely, I’d lose anywhere from 3dB-6dB off that measurement outdoors.

Still, I’ve personally seen tower fail to achieve the same output in my room. My brother brought a pair of towers over with dual 6.5” drivers in a box tuned to 45hz, and an in room f3 of 38hz. They crapped out above 95dB on all bass below 80hz. Didn’t measure THD because we were just goofing off play low bass notes and using an spl meter, but the distortion was audible above 95dB.

Ported boxes are 'tuned' to the fs of the woofer. If a 6.5" driver has an fs of 45 hz, the shipping probably cost more than the driver - unless of course, you're wrong about the box tuning... (you claimed to interpret the impedance peaks, but then replied to Shady stating you cannot check the impedance)

No unfortunately. As I previously said, it sounds just fine with real music or movies, frequency response and volume is identical to the one that doesn’t vibrate. Klipsch is sending a driver, just want to know why it’s doing that when there is no coil rub when pressing the woofer.

The noise sounds louder in the video because of the iPhones bias towards voice, it’s much quieter than the test tone in person.

The VC usually needs to be warm/hot facilitating thermal expansion which causes the rubbing on older well used speakers where a lifetime of use has warped the VC. Pressing on the cone shouldn't be able to replicate this problem - unless the driver has already destroyed itself. I think TLS Guy was spot on with his opinion that you are asking the driver to play frequencies at amplitudes it is not capable of, and that is the most likely cause of the rubbing.

 

[Steve81]

I don’t know if the S&V measurement is 100% correct. I have to wonder if they somehow didn’t capture all of the ports contribution.

Oh I’m sure they do know more than me, but that doesn’t mean a single measurement on one or two reviews is without error.

I won't claim that the folks at S&V are infallible by any means. OTOH, Klipsch would certainly have been privy to the test results prior to publishing, and if the measurements were significantly off from what they should have been, they would have made some noise/sent replacements/etc.

Re: Port contributions, if they weren't being captured properly, you'd expect it to show up on the FR graph, like this one:

I’ve occasionally seen some strange measurements that don’t make sense pop up in their reviews, for example, giving the tiny 4” Polk OWM speaker an 89dB 1w/1m sensitivity rating.

Different tester and from the look of the test bench page, quite possibly methodology, may account for that.

 

[shadyJ]

Different tester and from the look of the test bench page, quite possibly methodology, may account for that.

+1 this. Sensitivity measurements can vary wildly depending on methodology. There isn't any widely used standardized way of taking this measurement, so it can go all over the map, even for the same speaker. I look at it as a relative measurement; I would only really use one tester's data against that tester's other results.