Room Survey 36 – Messiah College

by Pat Brown

Our recent Sound System Design seminar was held at Messiah College in Mechanicsburg, PA. The beautiful campus has a number of performance spaces, and we had the privilege of visiting two of them for a tour and room measurement session. High Foundation Recital Hall and Parmer Hall both have variable acoustics, and we were able to collect some room impulse responses that clearly demonstrate the benefits. The data included in this article provides some valuable insights into both room acoustics and acoustic measurements, including room measurements that can be opened by any mainstream measurement program.

The Process

The room measurements were made using a dodec source plus subwoofer, allowing full-range, high level excitation of both spaces. The sweeps were recorded using a Sennheiser Ambeo™ VR microphone onto a Tascam DR-701D. The recorder was setup to save directly to B-Format, eliminating the need for a separate post-processing step.

The loudspeaker system was an Outline GSR™ radiator complemented by a Yamaha DXS12 sub. The GlobeSource was driven by a Bose PM8500™ in I-Share mode, necessary due to the very low impedance of the load (< 4 Ω x 4), and the low crest factor of the stimulus. It is important that the drive voltage not sag during the 14 second sweep. I’ve tested each 3 source section of the GSR to 30 Vrms, which the PM8500 can easily source into a 4 ohm load, even for a continuous sine wave.

The sweep processing was done in GratisVolver Pro™, and the resultant RIRs were evaluated using ReflPhinder™, which was also used to produce and export the omni and XYStereo RIRs below. A major strength of a B-Format RIR is that it serves as a Master that can be used to produce other formats.

Photo 1 – Recording hardware

High Foundation Recital Hall

High Foundation Recital Hall is located on the ground floor of High Center. The Department of Music hosts small concerts and events in this space, as well as student recitals. We only had 30 minutes in the space due to an event, so time was of the essence. This is where the GratisVolver sweep method really shines. The dodec/sub were placed center stage. Two test positions were selected. Test position 2 is shown in the photo below.

Photos 2 and 3 – Source and receiver positions for Recital Hall.

Figure 1 – Room data for “live” acoustics (ReflPhinder)

Figure 2 – Room data for “deadened” acoustics (ReflPhinder)

Location File File File
Recital Hall Live

Play XYStereo RIR

Play Male Voice

Play String Hit
Recital Hall Deadened

Play XYStereo RIR

Play Male Voice

Play Strings Hit

Parmer Hall

Parmer Hall, located in the Calvin and Janet High Center for Worship and Performing Arts, is an expanded performing arts venue with seating for 825, along with choir loft seating for 140-160. It is used for concerts, public lectures and special events. – Messiah College website

Two test positions were chosen. This article includes the data from Test Position 1, shown in the photo below. The room can be deadened by extending curtains over sections of the side walls. You can see one sectioned that is covered in the photo below.

Photos 4 and 5 – Source and receiver positions for Parmer Hall

Photo 6 – Parmer Hall showing approximate coverage of curtains.

 

Figure 3 – Room data for “live” hall (ReflPhinder)

Figure 4 – Room data for “deadened” hall (ReflPhinder)

 

Location File File File
Parmer Hall Live

Play XYStereo RIR

Play Male Voice

Play String Hit
Parmer Hall Deadened

Play XYStereo RIR

Play Male Voice

Play Strings Hit

Download Room Measurements

You can select the RIR files WAV files you want from these matrices. The Omni and XYStereo files can be opened in any mainstream measurement program for analysis. The B-Format files can be opened, analyzed, and processed in ReflPhinder. I have included some balloon pops for comparison. While useful for simple measures like reverberation time, a balloon pop is not the RIR, since it already has a spectrum “cooked into” it, determined by the specific characteristics of the balloon. The RIR is an FIR filter, and like any filter the spectral content of the output depends on the spectral content of the input. This makes the RIR suitable for convolution with anechoic program material.

 

Location File
Recital Hall Live Balloon Pop Omni
Parmer Hall Live Balloon Pop Omni

 

 

Location File File File
Recital Hall Live
B-Format Omni XYStereo
Recital Hall Dead
B-Format Omni XYStereo
Parmer Hall Live
B-Format Omni XYStereo
Parmer Hall Dead
B-Format Omni XYStereo

 

 

 

Conclusion

The B-Format RIR is information-rich with regard to documenting the sound of a space. Not only can it provide acoustic measures using multiple microphone patterns, it can also allow the space to be listened to via convolution. All of this can be accomplished in a fraction of the site time required by other methods. This article contains a fraction of the data collected in two short recording sessions. There is no better way to do a room survey, either before or after renovations to the room or sound system.

We would like to extend a very special thank you to Derek Mauldin of Messiah College. He is responsible for the hosting of our event. Derek also conducted the site surveys and shared some of his valuable experiences with the group.  pb