A very small “bookshelf” using the RS100S-8 and ND20 tweeter. Designed around the Hammond 1590E project box to keep the package as small as possible. This is intended to work with a sub, such as the up-firing RS265HO I have. As such, this is a sealed design with a fairly high F3.

Both the 8ohm and 4ohm RS100 exhibit some broad peaking in response when measured in-room, in-box – with the RS100S-8 it’s not a particular problem, but with the RS100-4 it’s quite an issue. You can see it in the response graphs for the optimized RS100-4 variants below.

For the RS100-4 I have two variants posted – there is a lower parts count version, though I’m still a little wary of the power handling implications on the tweeter here since this pushes the crossover point to 3kHz – a bit lower than perhaps ideal. I also have a version (TM and MTM both) that’s optimized – it’s almost perfect LR4 tracking with a 5kHz crossover point – but the parts count goes up quite a bit (12 parts including a pretty big cap.) It may be worth it in the end if you’re set on the RS100-4.

I will probably be revisiting the RS100-8 design since the shielded version I used is no longer available. I may also try out a couple other tweeters since this was originally a $5 tweeter and is now in range of some other superb (and more flexible) options – not to mention some other interesting options if I use the 5kHz target.

Box design

As noted, the main box is a Hammond 1590E project box measuring ~7.4″ x 4.75″ where the baffle attaches. I have epoxied in bracing of 1/4″ ply (with one 1/2″ ply brace used to allow adequate room to mount the crossover with screws.)

RS100S-8 + ND20, Full BSC

Bill of Materials

  • (1) RS100S-8
  • (1) Dayton ND20
  • (1) 2.5μF capacitor
  • (1) 3μF capacitor
  • (1) 18ga .50mH inductor
  • (1) 18ga 1.0mH inductor
  • (1) 2Ω resistor (10W+)
  • (1) 8Ω resistor (10W+)

RS100S-8 + ND20, On-wall variant

Bill of Materials

  • (1) RS100S-8
  • (1) Dayton ND20
  • (2) 3μF capacitor
  • (1) 18ga .50mH inductor
  • (1) 18ga .56mH inductor
  • (1) 2Ω resistor (10W+)
  • (1) 8Ω resistor (10W+)

RS100-4 + ND20

This should work well unless you push it, though I haven’t verified just how much the tweeter can take with a 3kHz crossover. Some contouring of the response is being done with the zobel here – that’s the key to dealing with the peaking in the RS100 response. Unfortunately, that peak also forces the crossover point.

Bill of Materials

  • (1) RS100-4
  • (1) Dayton ND20
  • (1) 5.2μF capacitor
  • (2) 16μF capacitor
  • (1) 20ga .25mH inductor
  • (1) 20ga .5mH inductor
  • (1) 5Ω resistor (10W+)
  • (2) 8Ω resistor (10W+)

RS100-4 + ND20 – optimized response, high(er) parts count

This is a near perfect LR4 example, using a combination of tweaks to reach this. The parts count is up, but the result should be worth it. This is a 5kHz crossover point to the tweeter.

Bill of Materials

  • (1) RS100-4
  • (1) Dayton ND20
  • (1) 2.5μF capacitor
  • (1) 8μF capacitor
  • (1) 10μF capacitor
  • (1) 25μF capacitor
  • (1) 20ga .1mH inductor
  • (2) 20ga .25mH inductor
  • (1) 20ga 1mH inductor
  • (2) 4Ω resistor (10W+)
  • (1) 8Ω resistor (10W+)
  • (1) 12Ω resistor (10W+)

RS100-4 + ND20

This has NOT been built and is based on measured data from the TM. It features the 3kHz tweeter crossover point and may have power handling issues as a result. Build at your own risk.

Bill of Materials

  • (2) RS100-4
  • (1) Dayton ND20
  • (1) 5.2μF capacitor
  • (1) 8μF capacitor
  • (1) 10μF capacitor
  • (2) 20ga .25mH inductor
  • (1) 20ga 1mH inductor
  • (2) 8Ω resistor (10W+)
  • (1) 12Ω resistor (10W+)

RS100-4 + ND20 – optimized response, high(er) parts count

This again is a near perfect LR4 example but at the cost of more parts. Same 5kHz crossover as the TM. Also tentative based on the TM data, but should be good.

Bill of Materials

  • (2) RS100-4
  • (1) Dayton ND20
  • (1) 2.5μF capacitor
  • (2) 4.2μF capacitor
  • (1) 25μF capacitor
  • (1) 20ga .2mH inductor
  • (2) 20ga .25mH inductor
  • (1) 20ga .7mH inductor
  • (1) 6.5Ω resistor (10W+)
  • (1) 8Ω resistor (10W+)
  • (1) 10Ω resistor (10W+)
  • (1) 12Ω resistor (10W+)