As many who follow this forum know, I am in the process of changing out the woofers in my home theater. The L/R channels are L200 cabinets (2 port) that contain D130s reconed by OCS using 130A cones. These will be replaced by 2205’s reconed as 2235’s.
My center channel cabinet contains three chambers. The two outer chambers are each 4 cu ft and have two 4” dia. 9.5” long ports. One port leads out the baffle board while the other leads to a center 2 cu ft chamber. This center chamber also has a 9.5” port that leads out the baffle board. This cabinet included two “real” 130As; one for the center channel and the other used as a quote/unquote "sub.” (I also use a Sunfire Signature that was turned off for the test.) The 130A used as the center channel will also be replaced with a 2205 reconed as a 2235. The 130A used as a "sub" speaker will truly become a "SUB" when the speaker is replaced by a W15GTI (with the dust cap painted black).
Monitoring was performed using a Quest Technologies Model 2900 Type 2 Integrating/logging Sound Level Meter. The unit meets the American National Standards Institute (ANSI) Standard S1.4-1983 for Type 2, International Electrotechnical Commission (IEC) Standard 651 - 1979 for Type 2, and IEC Standard 651 - 1979 for Type 2 sound level meters. The unit was calibrated using a Quest Technologies QC-10 calibrator prior to the first set of readings. The accuracy of the equipment is maintained through a program established through the manufacturer and is traceable to the National Bureau of Standards. The calibration unit meets the requirements of ANSI Standard S1.4-1984 and IEC Standard 942: 1988 for Class 1 equipment.
The tip of the microphone was placed 39” from the speaker grill cloth and 23” above the carpet. The reading were taken as sound pressure level (SPL) in decibels linear weighted (dBL) (no weighting). The noise floor of the room was 48-50 dBL. The meter goes down to 20 dBL.
A Bell and Howell function generator was used to produce a sine wave. Initially, I wanted to start at 200 Hz and sweep down, but the generator became unstable above 180 Hz in the x10 range. As such, the frequency was set to 180 Hz and the volume was brought up to 80 dBL. All other values are then referenced to this level. The generator is marked off in 20 Hz intervals and 10 and 5 Hz intervals (e.g., 90 Hz, 25 Hz) were eyed from the “hash” marks and could vary by a couple Hz.
The included table shows my initial measurements. Obviously, at some frequencies, the effects of the room come into play. I’ll update it when the new woofers are installed.
Frequency (Hz) / L200 Cabinet (SPL dBL) / Center Cabinet (SPL dBL)
180 80.0 80.0
160 75.7 75.7
140 75.3 73.2
120 74.8 77.9
100 75.9 73.7
90 70.0 76.0
80 74.5 75.8
70 83.8 73.6
60 80.5 73.6
50 74.9 69.3
45 71.6 67.3
40 61.4 61.4
35 54.3 56.9
30 56.4 55.8
25 55.0 55.9
20 58.0 53.2