no audible sound at location (multiples of 60 hz)

[pwn87]

i'm using some pretty big speakers in my small room, on my desk. but i have huge dips at 60 hz, 120 hz, 180 hz ...
i suspect this is because of how soundwaves travel?
like in my graphic, the amplitude on my location would always remain 0... am i right?

(when i go 1 meter back, the frequencies i was missing are extremely pronounced)

 

[RayDunzl]

i'm using some pretty big speakers in my small room, on my desk. but i have huge dips at 60 hz, 120 hz, 180 hz ...
i suspect this is because of how soundwaves travel?

Reflection of the wave off the walls creates cancellations at specific points in the room.

See "Standing Waves".

 

[RayDunzl]

In my case, I have a hole at the listening position around 48Hz, and a much narrower hole around 210Hz, the speakers are dipole above 180Hz.

Experiment:

Play a 1000Hz tone.

Walk around and listen.

Now, plug one ear with a finger and repeat the walkaround.

You will probably find many areas, only inches apart, that are loud and silent.

 

[pwn87]

so the waves travel like this?
i'm confused because i thought when i was having bad reflections, the frequencies wouldn't be so dependand on my position

 

[RayDunzl]

so the waves travel like this?

Maybe like this:

Think speaker on the left, wall on the right.

But in air, it is compression/rarefaction waves - the above video would be representative of pressure, not movement.



Sound in air "moves" more like this:

 

[pwn87]

so it actually is like my first graphic

maybe i'm somehow missing fitting reflections that would add additional waves of the problematic frequencies which might hit my location better.

thank you for the videos, it was really hard to find something on that subject

 

[pozz]

maybe i'm somehow missing fitting reflections that would add additional waves of the problematic frequencies which might hit my location better.

Low frequencies are location-based. Think about them in terms of creating an invisible soundfield full of various pressures throughout your room. It's like a phantom landscape of hills and valleys.

 

[alex-z]

https://amcoustics.com/tools/amroc

Great tool for visualizing room modes. Above 100Hz, you can generally treat room modes with absorption panels if they are thick enough. A 4" mineral wool panel spaced 4" off a wall should have roughly .5 absorption co-efficient around 100Hz. Below 100Hz, you need to stategically position multiple subwoofers to cancel out the standing waves.

http://www.acousticmodelling.com/porous.php

https://www.harman.com/documents/multsubs_0.pdf

Also avoid sitting in locations which are highly prone to room modes, such as right against the rear wall of directly in the middle. One third or two thirds of the length is often best.

Room EQ Wizard has a slightly more advanced room sim tool which allows you to adjust the listening window and speaker positioning.

 

[pwn87]

https://phet.colorado.edu/sims/html/wave-on-a-string/latest/wave-on-a-string_en.html
i guess a standing wave is not always the default outcome if we assume there are no reflections?

since most of my problem is around 60 hz i currently tend to get a subwoofer and some smaller speakers

 

[Rip City Dave]

i'm using some pretty big speakers in my small room, on my desk. but i have huge dips at 60 hz, 120 hz, 180 hz ...
i suspect this is because of how soundwaves travel?
like in my graphic, the amplitude on my location would always remain 0... am i right?

(when i go 1 meter back, the frequencies i was missing are extremely pronounced)

Are you near-field listening? Sitting at your desk? Where are the side walls.

Reflections off of your desktop could be a major contributor to your room modes, among other things.

Or maybe you just need Audioquest cables................................

 

[shawnsingh]

https://phet.colorado.edu/sims/html/wave-on-a-string/latest/wave-on-a-string_en.html
i guess a standing wave is not always the default outcome if we assume there are no reflections?

since most of my problem is around 60 hz i currently tend to get a subwoofer and some smaller speakers

Before you buy, please be aware that a subwoofer may not solve your problem! Because you are experiencing major lack of 60 Hz, 120 Hz, etc, and then if you move to a different position in the room those frequencies have huge bumps, this really is a textbook example of destructive and constructive interference of sound waves (i.e. "peaks and nulls"). But keep in mind that these interference patterns will also happen at other frequencies, too, and the pattern of peaks and nulls will be different for other frequencies. Adding a subwoofer may change the location of where those peaks and nulls are located in your room, so maybe it will help you for 60 Hz at your listening position. But then you will almost certainly be getting other peaks and nulls from other frequencies in that listening position.

If you are adding a subwoofer because you feel it can get louder to compensate for missing 60 Hz, that will also cause problems in other frequencies where your listening position may have peaks, because those frequencies will also become proportionally louder, too. These constructive and destructive interference patterns will depend only on position and frequency - it does not depend on the amplitude (i.e. the loudness) of the sound waves.

I have limited experience with actually solving these issues, but my understanding is that there are three tools to help, just the same as what other people already replied to you =) (1) adjust speakers and listening position to minimize the peaks and nulls of most bass frequencies, (2) use acoustic absorbers to reduce how large the peaks and nulls will be, (3) multiple subwoofers. I think all three of these would ideally be done with measurements to see the improvements.

Cheers!