Meeting Topic: I Have to Mix It in HERE??? | Affordable Acoustical Measurements
Moderator Name: Dan Mortensen
Speaker Name: JJ Johnston - PNW AES Section; Bob Smith - PNW AES Section
Meeting Location: Shoreline Community College, Rm 818 (music bldg), Shoreline, WA
For January 2017 the PNW Section had two of their own talk about and demonstrate how to make poor acoustic mixing spaces better. Since most of us are forced to use mixing rooms never designed as such, this meeting showed simple, low-cost methods to figure out what to do and then treat that. James "JJ" Johnston (retired) and Bob Smith (almost retired) spoke to an audience of 62 (27 AES members) at Shoreline Community College Music room 818.
JJ began the evening, assuming one is given a room to mix in that may be pretty poor acoustically - hard walls, odd shapes, and poor sound. First, he emphasized that any acoustic material MUST be ASTM International (formerly American Society for Testing and Materials) rated for flammability. No egg crates, packing foam, blankets, etc. Bob Smith reiterated that a fire marshal can legally shut you down immediately if you can't show the rating for any material you use.
A demo speaker and measurement mic had been set up next to a hard wall/whiteboard. A swept sine tone was played and the ETC (Energy Time Curve) calculated and displayed, showing early reflections off the wall and floor. They demonstrated calculating the distance of reflections and using a piece of string stretched between the speaker and mic to pinpoint the reflections and thus, where to apply acoustic treatment.
JJ suggested trying to set up the speakers symmetrically, and to try clapping your hands to listen for obvious acoustic flaws (fluttering, echoes) and work on these first. These flaws really affect the sound. Framed acoustic foam panels right on the wall work for medium/high frequencies because of the wavelengths involved. For lower frequency absorption, panels have to be set away from the wall. 9 inches or so will work down to about 282Hz.
Ceilings are hard to work on cheaply and temporarily. And never paint acoustic materials, like tiles - this covers their acoustic structure and they won't work right any more.
After a break, door prizes were given to:
-Belden CAT cable prep tool (courtesy Steve Lampen/Belden) - Lincoln Sin
-Fluke Link Runner tester (courtesy Rick Rodriguez/Fluke) - Rick Chinn
-Syn-Aud-Con mug (courtesy Steve Macatee) - Rick Rodriguez
-Binary Clock (Steve Macatee) - Drew Cady
-Blu-Ray/Cadillac Records (courtesy Rick Chinn) - Howard Grim
Bob Smith continued the evening with demonstrations of analysis software, hardware, and technique.
He suggested using the monitor speakers you'll use (instead of a random test speaker); an ordinary audio interface; a low-cost measurement mic (i.e. Parts Express); measurement/analysis software; and a tape measure and string. A Parts Express mic works fine for $50.
He described various steps for analysis depending on the software chosen. Different software has different analysis features. On some, you may have to use auxiliary software or calculations. Three analysis programs were tried (Room EQ Wizard (REW), ARTA & Holm Impulse), all giving the same answers. Different excitation signals were described. In the end, you still want to find the distances for reflections in order to treat them.