Sean De León

Miranda Martin

John Wharton

Dr. Hawley

PHY 2010.02: Physics for AET

27 April 2015

Studio Setup and Room Measurements

1. ABSTRACT

Belmont’s physics department recently purchased various equipment for an audio workspace in WAC 4078, but needed a group of students to set it up. This paper outlines how our group set up a workspace with surround and stereo speakers in lab 4078 of the Wedgewood Academic Center, the measurements we took in the space, the issues we encountered, and what additional equipment is needed to make it a fully functioning mini studio.

It is our goal that the work we have done will be improved on by future physics and audio engineering students.

2. INTRODUCTION

For this project, we were supplied a Genelec 5.1 surround system, two stereo Tannoy monitor speakers with various connections, and a rack full of analog outboard hardware. The goal was to make the area suitable for future students to use as a workspace for physics projects. This could include mixing, recording, taking measurements, etc. In our attempt to create a good workspace, we encountered many issues. These issues include connectivity between the devices, the subwoofer not working due to a variety of reasons, and missing equipment.

3. METHODOLOGY

To send audio signals to the Genelecs, we used XLR multipin output cables from the Orion 32 Channel AD/DA converter. The input came from a laptop via USB. To take measurements, we used a RTA microphone plugged into a Focusrite 2i2 audio interface for sine sweeps, pink noise, snare hits in different locations around the room and random impulses. The snare hit measurements were taken at the desk where the system is, at the desk next to it, and behind the curtain.

4. 5.1 SURROUND

In the audio world, surround sound is used in theatres, certain musical venues, professional audio studios, and even in the living room. The most common is a 5.1 surround sound system, which has six speakers in total that surround the listener. It is made up of five speakers that all send full bandwidth information with a subwoofer that accentuates the low end and rolls off the highs (White, Robjohns, 2001). The speakers within this type of system are front left, front right, center, left surround, right surround, and subwoofer.

Figure 1 shows a 5.1 ideal surround sound system placement, omitting the subwoofer [1]

The design of a 5.1 system is so that the listener can hear sounds in movies or video games and have an idea where they are located. For example, take a movie with a car driving down a highway from behind the listener that eventually turns left. The sound would initially be directed from the surround left and right speakers, travelling forward until it reaches the center and front left speaker. For video games, professional players rely on surround sound so they can anticipate when enemies are about to attack from behind.

5. SUBWOOFER

In the case of our project, the Genelec system was intended to be 5.1, but we weren’t able to get the subwoofer to cooperate. Our first problem was that our digital audio workstation wouldn’t send any signal to our Orion 32. We tried sending an identical signal within Logic Pro X from channels 3 and 5 directly to channel 6, but it wouldn’t playback sound. We also attempted sending the thru signal from our center Genelec directly into the subwoofer with an XLR cable, but no signal would appear. We repeated our process of trying to send different signals from the various surround speakers and different channels within Logic Pro X, but nothing would work.

Figure 2 shows Logic unable to send signal to subwoofer on right [2]

We tried the subwoofer’s test signal to make sure the sub itself wasn’t the problem, and the test signal showed that the sub worked. After realizing we didn’t know how to properly get signal to the subwoofer, and running out of time to continue to try new ways to set it up, we researched possible approaches we should have attempted.

Genelec’s website actually posted a way to hook up their subs to a surround sound system. According to their site, we would need to run each of the five main channels to the sub via XLR cables. Using the female end of the XLRs, we should have run signal to the sub from the channels by connecting them to the IN connectors on the sub. The next step, according to Genelec, would have been to connect the XLR cables from the OUT male XLR connectors to the input connectors of each of the speakers. This is one way that should have made it possible to get signal to the speaker from our five main channels.

Figure 3 on the left shows a picture from Genelec’s website on how to connect the speakers to the sub. [3]

We didn’t find this page of their site in time to attempt to set it up according to their recommendations, but this would be something worth attempting. You would, however, need to make sure you had enough XLR cables to run into and out of the subwoofer so all the low frequencies are sent to it. Since Genelec made all the 5.1 surround sound speakers and the sub, they should work together easily once they’re properly connected.

6. RESULTS

To take reverb time measurements in our room, we tried a variety of approaches. The first attempt was using logarithmic and linear sine sweeps, but found that the results from using SHAART gave us reverb times upwards of five seconds that were not possible. Instead, we tried using pink noise, but found that in order to get a proper reverb measurement, we needed to record the decay of the noise instead of recording a 15 second duration. We tried using clicks and high frequency impulses, but realized that it lacked too much low frequency content. to properly excite a room, the sound source must be broadband (Everest & Pohlmann, 2009). Finally, we rested on using a snare and hitting it in actual workspace, the booth to the right, and behind a large red curtain about 7 feet behind the workspace.

For our measurements, we kept the RT60 from the booth to the right and behind the curtain. We measured at 125, 250, 1000, and 2000 Hz and averaged the decays of the snare with SHAART. The determined RT60 in WAC 4078 is 0.374 seconds. Considering the amount of absorption added with the curtains, carpet, and all the booths around the room, this was a reasonable result.

Figure 4 shows RT60 for 125 Hz in booth.

[4]

Figure 5 shows RT60 for 125 Hz behind curtain. [5]

Figure 6 shows RT60 for 250 Hz in booth. [6]

Figure 7 shows RT60 for 250 Hz behind curtain. [7]

Figure 8 shows RT60 for 1000 Hz in booth. [8]

Figure 9 shows RT60 for 1000 Hz behind curtain.[9]

Figure 10 shows RT60 for 2000 Hz in booth. [10]

.

Figure 11 shows RT60 for 2000 Hz behind curtain. [11]

We noticed that the RT60 increased from the booth to curtain by about 0.02 seconds in each instance. This was expected because of the increase in distance.

7. CONCLUSIONS

Based on the process of setting up the mixing area in the lab, there are several pieces of equipment that we reasonably conclude would be beneficial for the physics department to purchase for the advancement of this course’s curriculum.

Two female XLR to male TRS speaker cables are needed to connect two outputs of the Orion interface to the inputs of the Samson amplifier so that the Tannoy monitors can be used in the mix station.

A rack space of multi-channel preamps is also recommended to utilize inputs of the Orion interface. While the lab has 32 inputs to a DAW via the Orion, it does not have enough preamplifiers to support 32 inputs. The Yamaha MLA8 is suggested, as it is one of the more affordable multi-channel preamps and offers 8 channels, which should be enough to suit the needs of the lab. If the MLA8 is chosen, a new DB25 to male XLR snake could be purchased (included in the shopping list), or, alternatively, the department could make use of one of the other snakes currently connected to the Orion, since not all 32 channels are needed. The FocusRites currently in the lab provide some preamps, but not enough for recording nearly as many channels as the Orion provides for.

A link to an API channel strip is also provided. An API preamp is most likely unnecessary for the kinds of recording to be done in lab, but for musical recordings several brands (Neve, API, etc) of preamps are desired for their tone.

The department might also consider coordinating with the audio department in acquiring preamps if at all possible-- the studio maintenance class (AET 3260) builds preamps as part of the curriculum, so it may be possible to acquire preamps that students don’t wish to keep or that they are willing to sell for a more reasonable price than a factory made preamplifier. Examples of such preamps can be found in REM Studios.

It is also very possible to use the FocusRites, the MLA8, and the custom preamps in conjunction to cover all input channels of the Orion. It is also recommended that more acoustical treatment be added to the lab space. While the recently added curtains help add absorption to the room, there is little isolation between adjacent booths in the lab.

Below are links to specific products from sweetwater.

MLA8: http://www.sweetwater.com/store/detail/MLA8

XLR to ¼”: http://www.sweetwater.com/store/detail/STX102F

DB25 to XLR snake: http://www.sweetwater.com/store/detail/DTM803

API Channel Strip: http://www.sweetwater.com/store/detail/APIChanStr

8. REFERENCES & IMAGE SOURCES

Everest, F., & Pohlmann, K. (2009). Reverberation. In Master Handbook of Acoustics (5th ed.,

pp. 158-160). New York, New York: McGraw-Hill.

How do I connect the 7050B subwoofer to my 8020B's in a 5.1 surround system? (n.d.).

Retrieved April 27, 2015, from http://www.genelec.com/faq/multichannel/92-how-do-i-connect-the-7050b-subwoofer-to-my-8020bs-in-a-51-surround-system/

"Welcome to Sweetwater.com." Sweetwater. N.p., n.d. Web. 27 Apr. 2015.

White, P., & Robjohns, H. (2001, January 1). Surround Sound Mixing. Retrieved April 27,

2015, from http://www.soundonsound.com/sos/jan01/articles/surround.htm

"10 Best Mic Preamps." Gearslutz.com. N.p., 21 Feb. 2010. Web. 27 Apr. 2015.

[1] Image from White and Robjohns

[2] Image from Logic Pro X session when sending surround sound. (Screenshot)

[3] Image from Genelec site

[4] Image generated from SHAART (Screenshot)

[5] Image generated from SHAART (Screenshot)

[6] Image generated from SHAART (Screenshot)

[7] Image generated from SHAART (Screenshot)

[8] Image generated from SHAART (Screenshot)

[9] Image generated from SHAART (Screenshot)

[10] Image generated from SHAART (Screenshot)

[11] Image generated from SHAART (Screenshot)