AUD175 Project 3

Introduction

For this project we were tasked with applying our knowledge of sound and acoustics to make modifications to physical spaces to meet appropriate standards of sound quality and transmission. However the modifications can not be permanent and they must be a budget solution to the problem. The room I choose for this task was my home office as it is the space where I work on audio/visual projects. To conclude if the treatment has made a positive effect on the room I will be recording the RT60 of each of the different room configurations and comparing the time difference between the each of them to the initial calculated time.

OFFICE

Room Dimensions:

Predictions:

"Reverberation time (RT) is a measure of the rate of decay of sound. It is defined as the time in seconds required for sound intensity in a room to drop 60 dB from its original level." Everest, F., & Pohlmann, K. (2009). Before I can treat the room I need to calculate and predict RT60 of the space in question.

Using two online tools amcoustics.com and csgnetwork.com I was able to calculate the schroeder frequency to be 335hz and the RT60 to be around 0.39 seconds.

To measure the RT60 of the different room configurations I placed the Sonarworks XREF 20 (2021) on a microphone stand in the listening position of the room and using REAPER (2021) I simultaneously played and recorded three clap samples through the Eris (2021) monitors. After analyzing the three claps and combining the individual time of each clap I am able measure the RT60 of the room.

https://amcoustics.com/tools/amroc?l=297&w=298&h=242&r60=0.6

http://www.csgnetwork.com/acousticreverbdelaycalc.html

Semi Treated Room

This is the original layout of the room before I started this project. Two desks in an L shape in one corner an armchair in the other and cube storage along a wall with a glass window. I also had four sheets of acoustic pinboard from Bunnings with two sheets cut in half to make four more smaller sheets. One large sheet was placed as a kickboard behind the main desk and the other was leaning against a wall unused along with one of the small ones. Three of the four small sheets were placed on top of the desk as seen in the images above.

To calculate the RT60 I take the total time of the three individual claps and divide by three to get the average length of the clap in seconds:

1.016s / 3 = 339ms

Once I had recorded the Clap test I Decided to record some other test to help with the comparison of the different room configurations. The first test was music where keeping the microphone in the same position I simultaneously played and recorded a song though the monitors. Next I removed the microphone and held it in my hand and did a voice test both at a normal recording distance and at an arm's length to help with recording the echo of the room. Next I simultaneously played and recorded a tone generator that was set to the rooms schroeder frequency of 335hz. I then moved the microphone from being in the listening position to the right side, then the left side, then behind the listening position and to the right of that position near the doorway.

Clap test:

02-Clap semi treated-211215_1046.wav

Music test:

09-Music semi treated-211215_1105.wav

Voice test:

12-Voice semi treated-211215_1111.wav

Tone test:

05-Tone semi treated-211215_1108-01.wav

Untreated Room

For the untreated test we removed most of the furniture leaving only the desk and small cube storage remaining in the room. It was at this point I had decided to move the desk to be centered with the wall as previously it was slightly off center due to the second desk being in the way. For this test there was no acoustic treatment.

To calculate the RT60 I take the total time of the three individual claps and divide by three to get the average length of the claps in seconds:

1.106s / 3 = 369ms

Once I had recorded the Clap test I did the same 3 additional recordings as I did for the the semi treated room. All three tests were conducted in the same way including the tone which was done in the same pattern.

I forgot to take photos of the room untreated hence why I created the 3d models to show how the room was laid out.

Clap test:

03-Clap untreaed -211215_1203.wav

Music test:

10-Music untreated-211215_1204.wav

Voice test:

13-Voice untreated-211215_1211.wav

Tone test:

06-Tone untreated-211215_1208.wav

Treated Room

Now that I have tested the room untreated and with some minor treatment I now know the base RT60 that I have to beat for the solution to be effective. Since the room is basically a square due to the cupboard It meant from the beginning it was going to be difficult to fix the room acoustically due to the nature of square rooms and there room nodes. I also had no budget at the time at all I due to financial issues so I decided to use what I had in the house that was available to me.

I chose to use the most acoustically absorbent materials i had at hand which were one double mattress the 2 large and 4 small Bunnings acoustic pinboards a blanket and 3 large cushions and an assortment of pillows. I placed the mattress against the wall opposite the glass window along with placing 2 of the small pinboards in the window frame. The three cushions were stacked ontop of eachother on an angle in the doorway alcove and the blanket was held against the cupboard wall with two polls at an angle. The two large pinboards were placed in the corners next to the desk with pillows stuffed behind them (not illustrated) and 2 small pinboards were placed on the desk behind two of the computer monitors.

To calculate the RT60 I take the total time of the three individual claps and divide by three to get the average length of the clap in seconds:

0.898s / 3 = 299ms

I forgot to take photos of the room untreated hence why I created the 3d models to show how the room was laid out.

Clap test:

04-Clap treated-211215_1236.wav

Music test:

11-Music treated-211215_1237.wav

Voice test:

14-Voice treated-211215_1245.wav

Tone test:

07-Tone treated-211215_1243.wav

Comparison:

Once I had recorded all the testes and collected the data I decided to create some short videos containing the recorded sounds and a frequency spectrogram to help aid in the comparisons below.

Claps

Claps.mp4

The RT60 of the three rooms were untreated: 369ms | semi treated: 339ms | treated: 299ms

Meaning the difference between the untreated and the treated room was 369ms - 299ms = 70ms. This is not much of an improvement but its enough to mean that the treatment was working along with the room untreated was unusable but even with this slight improvement it is very usable.

Song

Music.mp4

This test was to see how the different room configurations effected sound the listening experience of sound being played through the monitors. The song chosen was Red Hot Chili Peppers - Can't Stop. I chose this song due to the vocal and percussion nature track allowing for the rooms effect on the sound be more pronounced.

There is a large difference in sound quality between the untreated and treated room. The untreated room has a large mount of room echo making the music sound distant and the treated room sounds much clearer and has far less room echo making for a more natural true sound. And the semit treated room is mixture of both in the middle better then the untreated but worse then the treated.

Voice

Voice.mp4

This test was to see how the different room configurations effect vocal recording. The untreated recording has a large amount of audible echo compared to the semi and fully treated room which is most present in the arms length test. The treated room at normal recording distance sounds warmer and more full compared to the semi and untreated rooms.

Tone

For this test I played a 335hz tone through the monitors and moved the microphone to different positions in the room to attempt to hear the room nodes. Throughout the three tests I moved the microphone in the same pattern and kept the volumes the same. Visually you can see that by adding some treatment is enough to drastically lower the volume of the room nodes however it is not linear and the more you add wont meant lower the nodes volumes.

Since I forgot to take photos of the room while it was empty and when it was treated I decided to use my 3d knowledge to create a model of the space in blender instead. Doing so allowed me to show different angles of what the room looked like for instance the top down view. I believe it to be a good visual representation of the different room layouts.

Conclusion

I had been wanting to fix my office for along time but never had the materials/ time to do so. This project was great in letting me identify what was needed and to see what kind of results I can look forward too. However since the time of this project was around christmas it meant I had no money to spend on acoustic treatment. Initially I was going to prepose the idea of using four blackout curtains on rods to turn the room into a theater like room but that was two expensive and impractical for the rental I live in. My next solution was to buy insulation and wood and create DIY acoustic panels but that two was also too expensive and impractical at the time. So I was left with only using what i had at hand which was not ideal but it was able to get the job done and was definitely an improvement over the semi and untreated rooms.

Reflection on DATA, Process and Feedback

We used the same techniques for both rooms however I only had one mattress in my room compared to the 2 plus an air mattress in Alex's room which had a huge transformation in the acoustics compared to mine. Both rooms still had flutter in the ceiling as we were unable to place treatment that high on the walls but for speech Alex's sounded great while mine was usable but not ideal.

In the process of treating my room I removed the second desk and moved the main desk to be centred with the wall. I also swapped the left and right speakers so all the connections were at one end closer to each other. I made sure to reverse the left and right on the interface so it was still the correct stereo image. In doing so I noticed that the left speaker which was the right speaker now sounds much brighter than the original left speaker. I'm not sure what the cause of this is but I do have a couple of ideas that could be creating this difference. For the past 8 months my desk has been in the same position slightly left of centre on the wall. I believe that due to not being exactly centre I have grown accustom to hearing the slight delay in the sound bouncing off the walls and my brain has adjusted to centre the sound based off of that. And now that everything is centred my brain may need to re adjust to hearing no delay in the sound bouncing off the walls.

After finishing the recordings I had to revert my office to almost its untreated sate as I couldn't leave my mattress against the wall as its my only mattress. I'm also selling my other desk and have decided to save and buy 3 foam double mattresses and place them either side of the desk and one on the cupboard as I believe that this for me will the the best price to performance.

References

Adobe. (2021). Adobe Audition Audio recording and editing software. Adobe. Retrieved 8 November 2021, from https://www.adobe.com/au/products/audition.html.

Adobe. (2021). Adobe Audition Spectral Frequency Display. Adobe. retrieved 8 November 2021, from https://helpx.adobe.com/au/audition/how-to/audition-spectral-frequency-display-cc.html

Adobe. (2021). Adobe Photoshop Official Adobe Photoshop. Adobe. Retrieved 8 November 2021, from https://www.adobe.com/au/products/photoshop.html.

Adobe. (2021). Adobe Premiere Pro Professional video editing software. Adobe. Retrieved 8 November 2021, from https://www.adobe.com/au/products/premiere.html.

Blender. (2022). blender.org - Free and Open 3D Creation Software. blender.org. Retrieved 8 November 2021, from https://www.blender.org/.

Eris. (2021). Presonus Eris E3.5. Storedj.com. Retrieved 8 November 2021, https://www.storedj.com.au/presonus-eris-e3-5-high-def-3-5-studio-monitors-pair

Everest, F., & Pohlmann, K. (2009). The master handbook of acoustics (5th ed.). McGraw-Hill.

REAPER. (2021). Audio Production Without Limits. Reaper.fm. Retrieved 8 November 2021, from https://www.reaper.fm.

Rode. (2021). Ai-1 Audio Interface. Rode. Retrieved 9 November 2021, from https://www.rode.com/interfaces/ai1.

Sonarworks. (2021). Sonarworks XREF20 Measurement Microphone. Storedj.com. Retrieved 8 November 2021, https://www.storedj.com.au/sonarworks-xref20-measurement-microphone-w-sound-id-reference-5-trial.

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