Progress – results

 

The end result

 

      

 

Measurements

 

 

 

1). Output level and acoustic phase 200-20.000Hz – horizontal division 5dB. Smooth response within +/- 2dB, the drop towards the lower end is due to the measurement being done in free-air (so no boundary re-enforcement) – typical in room response is down to about 30Hz. The phase plot is smooth and shows no irregularities. The roll-off above 15kHz is the upper limit of my measuring equipment and not the speaker.

2). Step response – time window 5,0ms. As can be seen from this plot, the tweeter has a fast rise well within 0,2ms it is followed by the midrange driver (connected with reverse polarity), at about 0,4ms – then the midwoofer follows at about 0,8ms.

 

 

 

3). Horizontal response 1-20kHz – division 5dB on axis (red) and off-axis 15° (brown) off-axis 30° (purple) off-axis 45° (black) and off-axis 60° (green). The roll-off above 15kHz is the upper limit of my measuring equipment and not the speaker.

4). Impedance curve 20-20.000Hz – horizontal division 1 ohm, scale 0-24 ohms. Electrical phase plot (grey) horizontal division +/- 90°. This looks like an amplifier friendly load.

 

 

 

5). Waterfall plot 400-20.000Hz, time window 3,0ms. Very fast decay of the tweeter.

6). Waterfall plot 800-20.000Hz, time window 1,0ms (zoomed-in on the upper range).

 

Listening impressions

This must have been one of the most time consuming and expensive loudspeakers I’ve built, so was it worth all the effort? Well, it produces some of the best midrange and treble I have heard, so open and detailed. Imaging is very good with a well-proportioned depth and width. The speakers are much less critical to placement close to a rear wall than I expected, of course (like with any speaker) imaging is best when there is at least 70cm between the back of the speaker cabinet and the wall, but they can also be placed at only half that distance. The soundstage is a little on the high side (a slightly less tall bass cabinet would have been better) but very realistic in producing the difference between a vocalist sitting and standing. Treble is smooth, detailed and with a transparency leaning towards an electrostatic. Midrange is seamless from top to bottom even though there is a large overlap between the 7” and 4” drivers. The open baffle mid has speed and certain ease to it. The bass is deep, very well controlled but modest. The bass is tuned this way so that it matches the speed and dynamics of the midrange. More bass can be created by changing the series inductor to 10mH or even 8,2mH – but I preferred the 12mH inductor – a definite quality / quantity issue. It would have been nice to give the L26RFX/P more volume to play in but overall cabinet size and looks were an issue here.

 

Final cabinet drawing –coming soon!

 

 

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NOTE: This design is strictly for the home DIY enthusiast and not to be used professionally without my permission!

 

Tony Gee

The Netherlands

February 2004