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toddalin
12-19-2005, 04:09 PM
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.

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/speaker2.jpg


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).

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/speaker4.jpg

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
12-20-2005, 09:21 AM
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.

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/speaker2.jpg


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).

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/speaker4.jpg

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


:blink: 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.:bouncy:

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
12-20-2005, 09:33 AM
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
12-20-2005, 10:59 AM
Same procedures but this time with bass and room eq turned off.http://audioheritage.org/vbulletin/images/smilies/redface.gif

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
12-20-2005, 11:26 AM
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
12-20-2005, 11:36 AM
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
12-20-2005, 12:33 PM
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
12-20-2005, 01:02 PM
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.

Mr. Widget
12-20-2005, 01:15 PM
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. If you want to have measurements that are meaningful, you need to go outdoors, mount the box(es) into a large baffle with the driver pointing up to the sky and take your readings with your mic up in the air out over the center of this baffle. Getting meaningful low frequency measurements without a very large anechoic chamber is really tough... even those published in Stereophile by using the close miked technique are only approximate.

You might want to get this book: http://www.audioxpress.com/bksprods/books/bkaa45.htm

or take a look at these:

http://stereophile.com/features/99/

http://stereophile.com/features/100/

http://stereophile.com/features/103/

Widget

toddalin
12-20-2005, 01:41 PM
or take a look at these:

http://stereophile.com/features/99/

http://stereophile.com/features/100/

http://stereophile.com/features/103/

Widget


Thanks.

Interesting that they discuss taking separate cone and port measurements in the near field, but nowhere can I find the actual distance used.

Obviously, there is no way that I can sum cone and port amplitudes with respect to phase. Perhaps a reasonable compromise might be something like 6 or 12 inches from the baffleboard midway between the cone and port.

edgewound
12-20-2005, 01:45 PM
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.



You're welcome, Todd.

But my point is...actually....you can't take the room out of the equation, unless you're taking the speakers out of the room. All the improvements in the world to anechoic bass response will be a exercise in futility if it doesn't work right in your room. More and bigger doesn't always translate into better unless it works right in the room they're intended to be used in...that's all.

Mr. Widget
12-20-2005, 02:06 PM
Interesting that they discuss taking separate cone and port measurements in the near field, but nowhere can I find the actual distance used.I use about 1/4" from the cone and I place the mic right into the face of the port. You are supposed to balance the port output's SPL based on a ratio of it's radiating area to that of the cone. It is explained in detail in Dr. D'Appolito's book. John Atkinson at Stereophile is using this technique. It is sorta, kinda right... but really you need an anechoic chamber... Bass is impossible to measure accurately otherwise.

One issue with in room measurements is that they are accurate for that point in space, but we don't hear that way. It is better to generate a point cloud of measurements, but this is very difficult to do with repeatability if you are comparing multiple designs, or in this case different woofers.

Mr. Edge, I believe these measurements are for our benefit as much as his... they are to give us some inkling of the different levels of bass performance offered by these different drivers.


Widget

edgewound
12-20-2005, 02:38 PM
Mr. Edge, I believe these measurements are for our benefit as much as his... they are to give us some inkling of the different levels of bass performance offered by these different drivers.


Widget

I get the hint, fellas. Sorry I said anything. Merry
Christmas.

Zilch
12-20-2005, 02:58 PM
D.B. Keele Jr., "Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement," J. Aud. Eng. Soc. Vol.22, p.154 (1974 March), reprinted in Loudspeakers Vol.I, pp.330-338, edited by R.E. Cooke (Audio Engineering Society, 1978).

Robh3606
12-20-2005, 03:33 PM
Hello Toddalin

Measure where you sit. By default it is one of the best places in the room to hear changes and also has the smoothest overall response. This makes it one of the best places to run measurements from. You can't get the room out of your measurements so don't waste your time trying. For qualitative measurements it will work but not for absolute measurements. I find the box programs do a very good job of predicting what you will get and it's real easy to see in the program what the differences are without the room. As a source signal I would use warble tones or pink noise to avoid exciting room resonances.Quess it depends on how fast the sweep is. I also reference all measurements from my prime listening spot. It's really what counts. It may look awfull measuring a meter in front and great where you sit. If your unlucky turn that arround. You not going to be 39" out and 23" off the floor when you listen. You may able to see and document the changes but franky who cares what going on there???? This may sound nuts but I can get repeatable relative measurements by keeping the unit under test and the measuring device in the same locations. Down low it gets real hard with the RTA bouncing a bit but you can at the very least see a trend.


Rob:)

Zilch
12-20-2005, 07:02 PM
In the cited reference, Keele says mic on axis at the center of the dust dome, distance less than 0.11 cone radius. Vent measurement is in the center of the vent flush with the enclosure's outside surface.

Driver response nulls at fB, and the vent response must be added after correction for area as described.

So, Mr. Widget uses the method described by Keele, also a convenient means of determining actual box tuning.... :thmbsup:

Measuring just the driver without summing the vent may get you what you want, provided the box tuning does not change due to different driver displacements, and the mic distance to the dome is precisely replicated.