Dave's Speaker Pages

Measurements

              


Measurement Conditions

General Conditions

One of my long-term interests has been that of raw drivers. In an effort to better evaluate them, I started taking measurements on a somewhat large baffle. The problems associated with baffle and nearby driver diffraction led me to the use of a larger one for mounting individual drivers. My first truly large baffle was 4' x 7', but over time I realized that I could extend it to 2m x 2m, the current size and the largest possible in my test room.

I take all measurements at a distance of 0.5m. This provided two benefits, a decrease in the noise floor due to proximity to the driver and a slightly better low frequency extension due to the longer time interval between the direct signal and the first reflection arrivals at the mic.

If you download any of them, be sure to subtract 6db to set them to the standard reference of 2.83v @1m.

Test Baffle Modification, 2 October 2003

I added some extensions to each side to result in a full 2m x 2m size. This will yield true quasi-anechoic response down to 235Hz. If I include the edge diffraction but window out the floor/ceiling reflections I get down to about 185Hz. The sharp angle of this and the distance have a small influence, but it is there. I will be windowing out the diffraction, though, for the posted measurements. I won't be making new measurements to replace the ones when the baffle was 4'x7' right away. I expect that at some time I will. Until all are replaced, the old ones will have a "*" beside the model number for each graph.

I have pages for woofers, mid-woofers, midranges and tweeters. Drivers are affected by baffles too much to make measurements made on specific baffles very useful for other than the baffle on which they were made, in my opinion. These new measurements of typical samples as purchased will allow the use of tools such as the Frequency Response Combiner and the Baffle Diffraction Simulator, both available from the FRD Consortium.

Conditions Prior to October 2003

I made a major change in my tweeter testing and planned to change for midranges and woofers later. I call it a "quasi-IEC" baffle. It's nothing more than a large (1m x 1.2m) baffle on which I can mount and measure drivers to get extended low frequency response without baffle diffraction artifacts and gives a quasi-anechoic response down to about 400hz.

In the center is a 12" x 24" cutout for baffle inserts, allowing me to test most drivers I may acquire. It's sufficient for the normal tweeter bandwidth. I no longer list any averaged measurements, only the on-axis response.

Test System Hardware and Software

The drivers were all flush-mounted and located equi-distant from each side of both dimensions (centered). The distance in all cases is measured to the baffle surface. The start time marker was set to the same value for allmeasurements, set so that it was placed near the earliest noticeable signal input from the microphone (not the impulse peak nor just prior to it), since this has an effect on the high frequency result in the FFT (too close to the impulse peak and there is some false upper end rolloff/non-linearity). This was done so that all measurements have the same amount of excess-phase in relation to the baffle surface and thus each driver's front plate.

The system used to measure includes:

  • Software - Liberty Audiosuite (LAUD)
  • Fiji Sound Card
  • Calibrated Panasonic microphone (from Kim Girardin) in a custom wand
  • Camera tripod used as a microphone stand
  • Baffle dimensions either 2m by 2m or 4' by 7' (older measurements)
  • Baffle constructed with MDF 3/4" thick with a 12" by 24" baffle insert (braced)

Software settings:

  • 4,096 point MLS
  • 16,384 point FFT
  • Square Window or Half Blackman-Harris Window - Midranges and Woofers
  • Half Blackman-Harris Window - Tweeters

No smoothing was applied to these curves. Keep in mind that the driver position on a regular baffle will have an impact on the response, since for all drivers there will be baffle step and and for tweeters there will likely be significant diffraction effects.

              

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