Notes
10 May 2003: Made a slight adjustment to the crossover to add about 0.5dB more
baffle-step compensation.
Intro
There is definitely a shortage of shielded DIY speakers. This design was
intended to give people another option.
For this design I chose the Seas P17RE/TV (aka H690), the shielded brother of the well regarded P17REX. The tweeter is the Seas 27TDFC/TV (aka H1210), which I found superior to the other Seas tweeter I tried, the 27TDC/TV. I the Morel DMS-20 will provide some marginal improvement, but until I can get my hands on one, I won't know for sure. The DMS-20 is not currently imported into the US.
I am also working on a center channel and MTM version of this speaker. Hopefully they will be finished in the next two weeks.
For this design I chose the Seas P17RE/TV (aka H690), the shielded brother of the well regarded P17REX. The tweeter is the Seas 27TDFC/TV (aka H1210), which I found superior to the other Seas tweeter I tried, the 27TDC/TV. I the Morel DMS-20 will provide some marginal improvement, but until I can get my hands on one, I won't know for sure. The DMS-20 is not currently imported into the US.
I am also working on a center channel and MTM version of this speaker. Hopefully they will be finished in the next two weeks.
Box Design
As is my custom, I chose a sealed box design. This is especially important for
speakers intended for use in home theater, as most receivers and pre/pro's are designed for a main
speaker with a Butterworth response at 80Hz - in fact this is the THX standard.
This can only be obtained in a sealed box.
The box is 8"x12"x11" (WxHxD). If you don't want to build your own box, or don't have the required tools, check my boxes page to see if I currently have any pre-made boxes available.
The tweeter is mounted 2 3/8" from the top of the box and is offset from the centerline by 5/8". The woofer is mounted 8 1/8" from the top of the box and is centered.
The box is 8"x12"x11" (WxHxD). If you don't want to build your own box, or don't have the required tools, check my boxes page to see if I currently have any pre-made boxes available.
The tweeter is mounted 2 3/8" from the top of the box and is offset from the centerline by 5/8". The woofer is mounted 8 1/8" from the top of the box and is centered.
Crossover Design
Once again, the standard 4th order Linkwitz-Riley is employed. There is about 5dB
of baffle step compensation on the woofer. The design is intended to use 18ga
inductors. If you want to use thicker inductors, you can do so, but
there will be minimal gain in sound quality. The resistor in series with the inductors is the
DC resistance of the inductor, and is used by the crossover similator.
You don't need to concern yourself with these, as the circuit is fairly
indifferent the the DCR of the inductors.
First, the low-pass (woofer) circuit.
The high-pass (tweeter) circuit is the standard topology attached to most tweeters in a 4th-order LR.
If this speaker sounds too "bright" to you, decrease the 30 Ohm resistor to 20 Ohm. Likewise, if you think it sounds too dull, increase it to 40 Ohm, 50 Ohm, or leave it out altogether. If you can't find an 0.05mH inductor, buy a 0.1mH inductor and unwind about half the coils. As long as you get between 0.05mH and 0.075mH, you should be OK.
First, the low-pass (woofer) circuit.
The high-pass (tweeter) circuit is the standard topology attached to most tweeters in a 4th-order LR.
If this speaker sounds too "bright" to you, decrease the 30 Ohm resistor to 20 Ohm. Likewise, if you think it sounds too dull, increase it to 40 Ohm, 50 Ohm, or leave it out altogether. If you can't find an 0.05mH inductor, buy a 0.1mH inductor and unwind about half the coils. As long as you get between 0.05mH and 0.075mH, you should be OK.
Final Results
Given the restricted availablility of shielded drivers, this speaker turned out fairly well. The P17REX is noted for its smooth midrange, and the P17RE/TV is good in this regard as well.
Depending in component selection, this speaker should cost about $225 to build, including everything but the veneer.
