My Pseudo-Anechoic Shop of Horrors

I have the typical assortment of equipment on my bench. A couple of home made power supplies (low current 0-25V bipolar and high current 0-15V) a home made function generator, and a couple of DMMs (Fluke 76 and Sabtronics 2035A).

For audio work, I recommend a DMM that (in addition to the usual volts, ohms, and current readings) also measures low ohms, capacitance, and frequency, such as the Fluke 76. Another thing to look closely at before buying is the frequency range over which ac voltage measurements are accurate - 20Hz to 20kHz is ideal, but you can't always get this (the Fluke rolls off before 20kHz unfortunately). RMS is always nice, but not mandatory. Also nice is a dB readout option.

In addition I have a list of the equipment I have been using to develop the LX5 mod and my sub, as well as any future speakers:

• RS analog SPL meter, modified for external mic and flat bass response. I used to use this as a mic preamp into my soundcard. Nice to be able to monitor the level at this point.

  

  Here is a veiw of the external input jack I added to it.

• Preamplifier (home made). I'm using a preamp of my own design instead of the RS SPL meter now.

  

  Here is a picture of it. See the page I have describing the construction of it if you are interested in building one. Lots cheaper than the Mitey Mike, and easier to build, too.

• Panasonic mic cartridge on a wand (home made). This plugs into the SPL meter above, and is on the end of a couple of meters of coax.

  

  The wand is made from plastic plumbing tube that feeds sinks and toilets, and is about 300mm long. A nylon bushing crazy glued into the other end acts as a strain relief.

  

  Here is a picture of the mic in action. It's the gray rod sticking out of the pink foam pieces in the foreground.

• Three variable inductors (home made). I hand-wound some multi-tapped inductors on the ferrite cores I salvaged from the LX5 xovers. One has twelve 1/3 octave taps (0.1mH to 1.28mH) while the other two have twelve 1/6 octave taps (0.2mH to 0.71mH and 0.4mH to 1.43mH). These cover the ranges of inductance most commonly found in two-way designs.

  

  Here is a view of one of them from the outside and inside.

• Three variable capacitors (home made). The two smaller of these were made entirely from those cheesy Radio Shack non-polar caps. Each cap is switchable in and out of circuit (in parallel). Five caps were used with the values of 1uF, 2.2uF, 4.7uF, 10uF, and 22uF. So you can make the following (nominal) values with it: 1, 2.2, 3.2, 4.7, 5.7, 6.9, 7.9, 10, 11, 12.2, 13.2, 14.7, 15.7, 16.9, 17.9, 22, 23, 24.2, 25.2, 26.7, 27.7, 28.9, 29.9, 32, 33, 34.2 35.2, 36.7, 37.7, 38.9, 39.9. Not bad for ~$10 down at the shack!

  

  This is the outside of the capacitance substitution box, along with a view of the guts.

  The third variable capacitance box uses 1uF steps and employs Solen poly caps for the step values up to 16uF, a Solen poly and Solen non-polar electrolytic for the 32uF step position, and a Solen non-polar electrolytic for the 64uF step position (so it goes from 1uF to 127uF in 1uF steps). Got these from Madisound.

• An "L" pad. I use this for tweeter level matching, as well as Zobel fine tuning. Bought this from RS, but they don't sell them anymore (seems customers were toasting them and returning them faster than they could make them).

• Lots of aligator test leads from RS. (Just call me Mr. RS :)

• Speaker Workshop from Audua (free alpha 0.89 release). I can't say enough good about this piece of software. Really useful once you figure it out and make a proper test jig for it. It will also measure caps, coils, and resistors.

• Velleman PCS64i oscilloscope. I was quite fearful of sinking any money at all into a home o'scope, sure that I would be ripped off. This scope has lived up to all of my expectations of a PC-based scope and then some. Very useful, all types of output supported (*.bmp, comma delimited data export) and the FFT is nice too. The somewhat low sampling rate is the only thing that keeps me from using it for just about everything.

  

• Test jig (home made) to measure inductance, capacitance, do calibrations, and hook the test speaker and mic preamp to, via the soundcard I/O. Measurements are so much easier when you put some extra effort into making them convenient. This is my second design.

  

  Here is a picture of it. See my Audio page for construction details.

• My beloved workbench / desk.

  

  Here is a picture of my workbench/desk with a crossover setup using the home made substitution boxes discussed above. You can see the external mic mod I did to the meter (the RCA plug that jacks into the place where the microphone screen was). I'm also using a preamp of my own design instead of the RS SPL meter now (see above).