Acoustics and the Effects of Space and Location on Sound

By Ria Harjani

Background Research

How does sound vary in different spaces?

Sound, in particular its perception, is heavily impacted by the space in which it is produced and heard. Sound waves are reflected off of everything in a room or space. This includes all kinds of furniture, the walls, flooring, etc. In the same way, in spaces that have less objects, such as outdoors or larger spaces, sound waves don’t reflect off of as many things. This results in less reverberation.

Reverberation

Reverberation is typically the build up of sound waves in a space. Reverberation time is the amount of time it takes for the sound to dissipate, where the amplitude end up at zero. When there are more reflections on surfaces, particularly flat surfaces, reverberation time is usually longer. Similarly, where there are less objects and surfaces, such as outdoors, reverb time is usually less.

As a result, when designing musical spaces, or even spaces in which any important communication is to take place, the reverberation time is often taken into account. Too much reverb in a space can result in language that is difficult to hear and comprehend. It may sound muddled and unclear. Furthermore, too little reverb can result in sounds that lack warmth or don’t seem real to us, as we are typically used to sounds that have some reverb.

When designing spaces like large concert halls or auditoriums, there is usually a preference for high reverb, as well as creating uniformity of sound for the audience. Places, like conference rooms, that place heavy focus on having clear speech, design for low reverb. Recording studios also typically have lower reverb because the sound recorded sounds more “pure,” making it easier to edit and work with.

Small Rooms vs. Large Rooms

Because of this sort of reflection, the size of room also plays a role. In smaller rooms, sound waves bounce off of all surfaces in the space. Some of the energy is absorbed and turned into heat, while other parts are reflected back into the air.

In larger rooms, there is generally more space for the sound waves to travel through, meaning less reverberation. This is because more energy is lost and transferred in the larger space.

Experiment

To assess this affect and the presence of echos and reverberations in different spaces, I conducted a small experiment of my own.

I selected four locations: bedroom, bathroom stall, living room and balcony (outside).

In each of these locations, I produced and recorded a clap and a hum noise. To obtain consistent and reliable data, I tried to keep all factors, other than location, the same. These include my physical distance from my laptop (the device which I used to record), limiting background noise (other than in the outdoor variant) and the note I hummed (middle C). Then, I assessed the time and spectrum graphs of each recorded sound. I chose to produce both a hum and a clap (short sound pulse) so that I could see the effect on different types of sound.

These four locations were selected for a variety, due to convenience and that external factors could be fairly consistent. The bedroom acts as a relatively small space/room while the living room is larger, with hallways and more open space. The bathroom stall is an extremely small space, whereas the balcony is effectively outdoors and therefore, a very large space.

Why these two sounds?

I chose to record a clap because a clap, or any short pulse sound, and its time graph, recorded in any space will show the echoes and reverberations that occur when sound is produced in that space. This would, in turn, have an effect on any other sounds generated, such as a hum, in the space. The short pulse sound effectively is just to display and inform us about the presence of echoes and reverb.

Figure 1: Bedroom (Clap)

Bedroom

In Figure 1, we can see a few repeated peaks in the time graph, suggesting the presence of some echo/reverb.

In Figure 3, there is a clear first peak just before 300 Hz.

The second peak at about 580Hz is particularly distinct and slightly higher than this peak in the other locations

Figure 2: Bedroom (Hum)

Figure 3: Bedroom (Hum) Spectrum Graph

Figure 4: Bathroom (Clap)

Bathroom

Figure 4 shows more echoes/reverb, likely because the bathroom stall is a small space with walls packed closely together.
It is clear from Figure 6 that this recording didn't produce as many significant, smaller peaks as the the recordings in the other locations.

Figure 5: Bathroom (Hum)

Figure 6: Bathroom (Hum) Spectrum Graph

Living room

Figure 7: Living Room (Clap)

The time graph for the clap (Figure 7) shows some reverberations/echoes but none that are extremely significant. This may be because the living room space is relatively large with surfaces further apart.

Figure 9 has quite a few smaller, but still distinct peaks

Figure 8: Living Room (Hum)

Figure 9: Living Room (Hum) Spectrum Graph

Figure 10: Balcony (Clap)

Balcony (outside)

When recording outside, I could immediately hear the background noise of the wind, which undoubtedly was captured in the recordings.
Figure 10 shows seemingly a lot of reverb/echo from the shape of the time graph. However, this is somewhat unexpected given that this was recorded in an open, outdoor space. Maybe the winds or balcony door behind me when I recorded could have influenced it.

In comparison with the previous spectrum graphs, this one (Figure 12) has more distinct peaks at about 2300Hz and 3100Hz, in addition to the common first peak just before 300Hz.
The amplitude of this sound was slightly higher than the others, probably because of the background noise of the wind.

Figure 11: Balcony (Hum)

Figure 12: Balcony (Hum) Spectrum Graph

Overall Comparisons

The shape of the clap spectrum graphs seem to be a lot more varied than those of the hum spectrum graphs. This could be because it is more difficult to produce extremely consistent claps than to hum a single note.
The most striking difference I found between the humming spectrum graphs at the different locations is that the bathroom one didn't produce as many smaller peaks. This may be because of the sheer size of space.
The harmonics present in the spectrum graphs are generally pretty consistent, which was expected given that I tried to produce the same tone (middle C).

References

Betancourt, Lina Maria Villa. “Analyzing the effects of room acoustics in different music recordings.” Universitat Pompeu Fabra, 2011, http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.353.1981&rep=rep1&type=pdf/.

Hansen, Colin. FUNDAMENTALS of ACOUSTICS. www.who.int/occupational_health/publications/noise1.pdf.

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“How Does Reverberation Affect the Architectural Acoustics of Different Environments? — Sound Zero.” Sound Zero, 21 Apr. 2021, sound-zero.com/how-reverberation-affects-architectural-acoustics/.

“Reverberation | Reverberation Time | Reverb Effect | Acoustical Surfaces.” Acoustical Surfaces, 2020, www.acousticalsurfaces.com/acoustic_IOI/reverberation.htm#:~:text=Reverberation%20is%20the%20accumulation%20of,direct%20sound%20can%20get%20lost..

‌Shinn-Cunningham, Barbara. “Acoustics and Perception of Sound in Everyday Environments.” 3rd Int. Workshop on Spatial Media, Japan, 6-7 Mar. 2003, http://cns.bu.edu/~shinn/resources/pdfs/2003/2003Aizu_Shinn.pdf.

“The Acoustics of Large vs Small Rooms.” Kiss Your Ears, 2020, www.kissyourears.com/pages/the-acoustics-of-large-vs-small-rooms.

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