Subwoofer & Room acoustics - Day vs Night variance

[whazzup]

I noticed that my previously equalized subwoofer (equalized in daytime) had some squiggles in the frequency response at night. So I made more measurements to compare.

It would appear that my room ambient noise has a slightly different profile in the day vs at night. In both instances my room aircon is off. In the day (noon), the peak shifts to 40hz while the peak is at 37hz at night. This change affects my eq at the 35-40hz region.

You can download the REW file here (EQ1 was made during the day, EQ2 at night):
https://app.box.com/s/xj8u0wl2n2llexsszcgqelqngxnch0vh

Mic position is at my seat, ear height, subwoofer inches from me below the desk. Since measurements were taken at different times of the day, the mic position is slightly different. I did a lot more measurements than what I've uploaded, but those are deleted because the measurements have been consistent.

If your room is a typical living space with considerable ambient noise, and 'sound treating the room' means closing your doors / windows, you might wanna take the above into account...

 

[Hipper]

This could be associated with vehicle traffic?

I live on a busy High Street and I found the following using REW:

I took measurements using the REW signal at 1500 hrs on a weekday (with heavy traffic outside) and 2200 hrs on a Sunday (with very little traffic):

Green is weekday, blue Sunday evening. You can see a hump at 42Hz on the weekday which I assume is heavy vehicles.

The Spectograms confirm the traffic issues nicely:

This weekday image shows noise in the 40Hz region already happening before the REW signal at 0ms begins:

On Sunday there is no heavy traffic and no pre signal noise, therefore the extension of the 42Hz signal to about 550ms must be in room resonances.

 

[whazzup]

This could be associated with vehicle traffic?

I live on a busy High Street and I found the following using REW:

I took measurements using the REW signal at 1500 hrs on a weekday (with heavy traffic outside) and 2200 hrs on a Sunday (with very little traffic):

View attachment 77269

Green is weekday, blue Sunday evening. You can see a hump at 42Hz on the weekday which I assume is heavy vehicles.

The Spectograms confirm the traffic issues nicely:

View attachment 77270

This weekday image shows noise in the 40Hz region already happening before the REW signal at 0ms begins:

View attachment 77271

On Sunday there is no heavy traffic and no pre signal noise, therefore the extension of the 42Hz signal to about 550ms must be in room resonances.

Mine's different from yours in that the peak 'moves' between 37-40hz. Could be traffic like you mentioned, although I do try to make sure there's no audible traffic (with my poor human ears) before I record the ambient noise. Or my computer. Or the fact that there's slight position variations between each measurement at different timings.

It started when I noticed that applying eq to push down a peak in that area results in deeper drops at the frequencies right beside the original peak. Even when very high Q values were used. So between 35-40hz, I ended up applying eq to each frequency just to see what happens.

And now I realised that this peak is not 'stationary', making the eq 'unstable' in that region as well. So I'm just recording ambient noise at different times of the day to see if there's any pattern. I'll get a notebook to run REW so that I can switch off my main computer and see whether it's a contributing factor.

Maybe the lesson for me eventually is that I need a more general filter for 35-40hz, rather than very granular filters.

 

[Speedskater]

How careful were you to not move anything (loudspeakers, microphone, furniture) between test?

 

[whazzup]

How careful were you to not move anything (loudspeakers, microphone, furniture) between test?

Furniture and speakers have not been moved at all. But yes to mic, because I have it at my seat. But so far I've done enough rounds of measuring to get a sense of the variance of measurements around my head.

Still testing. Using a notebook to test so as to eliminate the source of noise from my main PC.... And Windows had to pick this time to update... Now need to wait for updating to finish so that the fans will wind down...

 

[Hipper]

Although the measurements I posted were using the REW signal, you can measure ambient noise by turning off the signal at your source's volume control, so all the microphone hears is the ambient sound. I reduced some of this noise by adding a third piece of glazing to my double glazed windows:

Red is without the glazing, green with the glazing, 1/12 smoothing.

You can see that, firstly, at 44Hz there is a large peak and the glazing makes no difference to that.

The addition of glazing does seem to knock the 100 - 1000Hz section down by around 6dB. Indeed the glazing makes the room sound much quieter and I hardly notice the noise except some heavy vehicles and occasional motorbike or boy racer.

Another way of testing the low frequencies in areas of the frequency response where you can't trust measurements because of external noise is to use test tones and listen for yourself. Your brain can probably filter out the external noise. You could use these tones:

https://realtraps.com/test-cd.htm

I use a laptop for measurements but I keep it offline!

 

[Wayne A. Pflughaupt]

Speakers and mics are transducers, and as such their electrical properties can be affected by changes in temperature and humidity. I’m sure you can’t hear a “night and day” difference (pun intended), so it’s nothing to worry about. People really obsess too much over their graphs and worry about things that make no audible difference.

Hat tip: Try making some REW measurements 6 months apart, especially between summer and winter. You’ll see they look slightly different even though nothing has audibly changed.

Regards,
Wayne A. Pflughaupt

 

[whazzup]

Speakers and mics are transducers, and as such their electrical properties can be affected by changes in temperature and humidity. I’m sure you can’t hear a “night and day” difference (pun intended), so it’s nothing to worry about. People really obsess too much over their graphs and worry about things that make no audible difference.

Hat tip: Try making some REW measurements 6 months apart, especially between summer and winter. You’ll see they look slightly different even though nothing has audibly changed.

Regards,
Wayne A. Pflughaupt

Thanks for the heads up on temps and humidity! Will keep that in mind as well. In my case though, what's happening is that I have pretty specific eq to drop the peaks on one frequency (I think 37hz), while adding gain to the adjacent frequencies (to get a flat response). Only to find that at a different time of day, the ambient noise peak has shifted, causing the eq filters to affect the response in an undesirable way, as seen in my attached image where that region has a 5-10db bump / null. So now trying to get a handle on how the ambient noise in my listening position changes over time.

 

[Wayne A. Pflughaupt]

You’re only talking about a couple dB difference between the night and day. Personally I’ve never found anything like that to be audible in a sub, so unless this is something you are actually able to hear, it's not worth stressing over.

On top of that, it’s bad form anyway to use boosted and cut filters a few Hz apart. I’ll bet you could bypass those filters and not hear any difference at all.

Here’s something to think about (2nd paragraph):
https://www.audiosciencereview.com/...asurements-eq-equalizerapo.15067/#post-473615

It also might be beneficial to wade through the first part of this:
https://www.hometheatershack.com/th...levels-and-a-hard-knee-house-curve-long.6818/

Regards,
Wayne A. Pflughaupt

 

[Hipper]

There was a thread on this subject recently:

Crazy? or Temperature, Humidity, and Speaker Sound Matter

 

[whazzup]

You’re only talking about a couple dB difference between the night and day. Personally I’ve never found anything like that to be audible in a sub, so unless this is something you are actually able to hear, it's not worth stressing over.

On top of that, it’s bad form anyway to use boosted and cut filters a few Hz apart. I’ll bet you could bypass those filters and not hear any difference at all.

Here’s something to think about (2nd paragraph):
https://www.audiosciencereview.com/...asurements-eq-equalizerapo.15067/#post-473615

It also might be beneficial to wade through the first part of this:
https://www.hometheatershack.com/th...levels-and-a-hard-knee-house-curve-long.6818/

Regards,
Wayne A. Pflughaupt

Thanks for the links! And double thanks for your link too!

Oh, fixing it is easy, I think. And I'm aware of the too many filters problem. But as long as it doesn't blow up my sub or speakers, it's cool to try and see what happens (and whether there're audible changes I can detect).

And mostly I'm interested in the WHY. Why does the peak move to 37hz at night and goes up a couple points in the day? If it's additional machinery in the day, there shouldn't just be 1 peak, there should be one at 37hz and another one at maybe 38 or 39hz. And it's so precisely captured by the mic that it shouldn't be an issue with the equipment. Temperature / humidity could be factors, so right now I'm consciously testing with the airconditioning on to reduce that variable. And the additional noise from the aircon doesn't change the recorded values that much, so it's fine.

And it's technically not about the subwoofer eq at this point, haha....

Anyway, before this I thought eq is a fire and forget process, but now I'm not so sure. I might not find an answer eventually, but it's still something interesting to figure out.

 

[whazzup]

There was a thread on this subject recently:

Crazy? or Temperature, Humidity, and Speaker Sound Matter

Yup, I actually saw and read that thread shortly after I saw the Dave Rat demo with the fire heating up the air and affecting the sound. Which makes sense given the dependence of sound waves on air molecules.

 

[Worth Davis]

Mics have to be placed in 3D to .1 inch or they are gonna measure different. use a tape measure to get the exact distance from 2 speakers and keep height constant is a good practice

 

[whazzup]

Mics have to be placed in 3D to .1 inch or they are gonna measure different. use a tape measure to get the exact distance from 2 speakers and keep height constant is a good practice

Thanks. What I have found though, is that my room ambient noise has a particular frequency peak at my seated position, some sort of standing waves, if I'm using the term correctly. And this peak shifts and widens depending on time of day. The significance of this is that it affects how I eq my subwoofer. Still collecting data when I'm free.