Documenting Enhancements in Bass Performance

[toddalin]

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

[toddalin]

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

D-oh!

Last night while watching a movie, it occured to me that the eq was set for 6 dBA of boost at 70 Hz causing the L200 cabinet to show improved response in that range. This was not the case with the center sub channel that was run directly by plugging the signal generator into the amp input. I will turn off the eq and retest the cabinet prior to installing the new woofers. I think that this next test will show that my center cabinet is really a good match for the L200 cabinets.

The results of the test clearly show that the D130 and 130A have little bass response. When I set my Yamaha RX-Z9 to autoeq the room, it reports these speakers as "small." OTOH, it reports my front and rear surrounds (Cerwin Vega 10" 3-ways) as "large."

[Zilch]

For what it's worth, I do LF measurements "near field," i.e., about 6" out from the center of the woofer cone. The LF response is actually a combination of direct radiation and port radiation.

At 1M out, you may get first reflection effects off the floor.

I don't have the D'Appolito book yet; perhaps someone who does can tell us the preferred LF measurement methodology....

[toddalin]

Same procedures but this time with bass and room eq turned off.

Frequency (Hz) / L200 Cabinet (SPL dBL) / Center Cabinet (SPL dBL)

180 80.0 80.0
160 76.7 75.7
140 75.6 73.2
120 75.8 77.9
100 77.6 73.7
90 74.0 76.0
80 74.6 75.8
70 74.6 73.6
60 71.0 73.6
50 67.0 69.3
45 63.4 67.3
40 57.6 61.4
35 57.9 56.9
30 55.5 55.8
25 54.3 55.9
20 53.1 53.2

[duaneage]

How flat is your microphone from 20 to 100 hz?

If you reposition the micorphone how much of a difference does it make in the curves?

If you try drivers one at a time what do the curves look like?

It could be possible that drivers are cancelling out one another at low frequencies. AT 150 - 200 hz phase cancellation across the room is less pronounced.

[toddalin]

How flat is your microphone from 20 to 100 hz?

If you reposition the micorphone how much of a difference does it make in the curves?

If you try drivers one at a time what do the curves look like?

It could be possible that drivers are cancelling out one another at low frequencies. AT 150 - 200 hz phase cancellation across the room is less pronounced.

I the frequency response included with my annual calibration curves show the microphone is flat to 20 Hz. I purposely left the wind sock off (though the documentation shows how to account for it). Recognize that this is a professional $2,500 SLM and when I had the mic element replaced it alone cost me about $300.

Certainly repositioning the mic has an effect as room reflections come into play. I am open to a better position that would give a more representative interpretation. Any ideas?

Tests were only conducted using one driver at a time.

[edgewound]

Todd...

You're tests are probably a pretty good indicator of your speakers in-room response....and that's what counts. You might experiment by moving the speakers slightly forward or backward...moving the mike around to the different listening positions...and then feeding pink noise through the whole system at once and taking a reading at the different listening/seating positions. Speaker placement can/will a have a remarkable effect on how they sound in the room....but you already know that

[toddalin]

Todd...

You're tests are probably a pretty good indicator of your speakers in-room response....and that's what counts. You might experiment by moving the speakers slightly forward or backward...moving the mike around to the different listening positions...and then feeding pink noise through the whole system at once and taking a reading at the different listening/seating positions. Speaker placement can/will a have a remarkable effect on how they sound in the room....but you already know that

Thanks Edge, I appreciate it. However, I think you are missing the point. I'm not trying to tune the speakers to room, I'm trying to document improvements in bass response between the 130A/2235/W15GTI when used in the same cabinet. As such, I'm trying to minimize the effects of the room in the measurement while still allowing the sum total of the bass (i.e., cone and port) to be represented.

I suppose that I could experiment with the placement of the mic and try to find a placement that gives the greatest bass response at a given frequency, but another placement could give greater bass at a different frequency.

Speaker measurements are typically reported at 1 meter (39 inches) and so that is what I used. I was trying to determine if anyone knew of another distance that is used in testing bass (as opposed to overall) response.

I don't think that anyone on this forum has documented the response of the W15GTI in a home environment either and I thought this could be of use.