Measurements from MTM with tweeter waveguide - diyAudio
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Old 10th January 2007, 06:43 PM   #1
Few is offline Few  United States
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Default Measurements from MTM with tweeter waveguide

Here are a couple sets of measurements I obtained using SoundQueasy to measure the response of my latest speaker project. It's really an extensive overhaul of a previous design, using the same drivers but modifying the cabinets and adding an MCM waveguide to the tweeter. The drivers are oldies but goodies: ScanSpeak d2900-9300 textile tweeter, and two Vifa 5.5" P13WH-00-08 woofers. These are the same drivers Olson used in his original Ariel speaker design some of you may remember. For historical reasons my two woofers are rather widely spaced (sorry, I have no photo with me as I write this). Given the recent interest in waveguide-terminated tweeters I thought the measurements might be of interest to someone anyway.

The top set shows the total SPL, the woofers with their crossover in place, and the tweeter with its crossover in place. The slight downward tilt in the response was done on purpose because I didn't want an overly bright response. These graphs do not include any nearfield woofer measurements to extend the results to lower frequencies, so ignore the low frequency rolloff. (In case the scales are hard to read: there are 5 dB between neighboring pairs of horizontal grid lines.)

The lower set of measurements is from on axis (0 degrees) and then increasingly off axis in 15 degree increments (15, 30, and 45 degrees). All measurements were taken at about 1 meter, and at the height of the tweeter.

The glitch in the high frequency response around 10 KHz is a bit smaller in the other speaker, but otherwise the responses of the two speakers are nearly identical. Comparing waveguides I think I might have made one waveguide VERY slightly deeper than the other. I've verified by adding pieces of tape to the waveguide that little tiny changes in the tweeter's immediate environment induce significant changes in that 10 KHz range.

In spite of the glitch I was pleased by the controlled off-axis rolloff since that was one of my main design goals. Now I'll just have to learn how to make better use of SE's crossover optimization tools. I came up with these crossovers the old fashioned way: tweak-measure-tweak-measure...

Few

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Old 11th January 2007, 04:20 PM   #2
Few is offline Few  United States
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Here are a couple of photos of one of the speakers. The second is a close-up of the tweeter-waveguide interface (and the dusty tweeter!).

Few

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Old 12th January 2007, 09:04 PM   #3
Few is offline Few  United States
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Can anyone who has worked with tweeter waveguides tell me whether they've seen similar high frequency response glitches? Any sense of whether I've left the hole in the waveguide too large or too small when mating it to the tweeter? I'd like to apply this waveguide idea to another set of speakers but I want to be sure not to repeat any errors I may have made on my first application.

Few
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