by Pat Brown
Our spring 2019 Sound System Design seminar was held at Crossroads Fellowship in Raleigh, NC. The massive building is a converted power tool distribution warehouse, gutted and redesigned as an assembly space for Crossroads Fellowship church. It houses multiple large meeting spaces, and we had the opportunity to perform acoustic testing on three of them during the seminar.
This space is especially interesting since it has extensive acoustical treatment throughout. The sound systems are excellent, but the HVAC noise is high.
Photo 1 – The Worship Center at Crossroads Fellowship
The following equipment was used for the collection of room impulse responses using log sine sweeps.
Microphone: Sennheiser Ambeo
Recorder: Tascam DR-701D
Software: GratisVolver Pro
In each venue the Sound Source was placed near the front of the room. The measurement positions were selected based on the following criteria.
1. Farthest position of interest (DF)
2. DF / 2
3. DF / 4 (depending on room size)
This produces a series of log-spaced test positions in a line normal to the sound source.
Figure 1 – Test positions for each room.
Our training seminar was held in the Great Room, a large, flat-ceiling meeting space with acoustical tile ceiling and carpet. The parallel walls are covered with large paintings, some of which have significant absorption. Here are the measures collected 40 ft from an omni source (TP2) post-processed to XYStereo. Have a listen and then review the measures.
Figure 2 – Some key ISO-3382 measures from the Great Room (ReflPhinder).
Photo 2- The Great Room at Crossroads Fellowship
The Chapel is a smaller space with high ceiling and classical design. It is intentionally acoustically “live” with a mid-band reverberation time of about 1.5 sec. Here are the measures collected 40 ft from an omni source.
Figure 3 – Some key ISO-3382 measures from the Chapel (ReflPhinder).
Photo 3 – The Chapel at Crossroads Fellowship
This large shoebox has open-plan seating. A contemporary band occupies much of the large stage. A proposed drop tile ceiling was never installed, so the lighting and HVAC are exposed and painted black. The HVAC is very noisy. Acoustic testing would be nearly impossible if not for the 14-second log sweep method used by GratisVolver. Here are the measures collected 34 ft from an omni source.
Figure 4 – Some key ISO-3382 measures from the Worship Center (from ReflPhinder).
Reflection Finding in the Great Room
Since the RIRs were collected using a B-Format process, they contain directional information that is useful for troubleshooting acoustical anomalies, such as flutter echoes. The Great Room has some audible flutter. ReflPhinder is a software that reads a B-Format RIR and provides some post-processing functions. The following video demonstrates one method for determining the path of a flutter echo.