2-way MT: Dayton RS180S-8 and SEAS 27TDFC

Design Goals

This design employs two cost-effective, low-distortion drive units, Dayton RS180S-8 and Seas 27TDFC (H1189), which have been popular and tested favorably by several well-known DIY'ers. The goal of this designing attempt was to develop a relatively simple crossover network that exploits the potential of the drivers in a 2-way.

Crossover

LR4 crossover at 1.6 kHz

For this design, to suppress the high frequency breakup nodes of the metal cone driver, a bottomless LC notch filter, which is made of C2 and L3 in the above schematic, is used. This not only suppresses breakups but also contributes to low pass filtering of the woofer. In fact, a notch filter alone is not very effective in suppressing breakup nodes when applied to the RS180 since the woofer's breakup has two main peaks at 6 and 9 kHz. In this design, a low crossover frequency (1.6 kHz) through a large shunt capacitor (C2) and a notch filter centered in the middle of two breakups provide a good result.

Predicted system response and individual driver rolloffs

Plots of filter transfer functions and system impedance curve are attached below.

Enclosure

Net internal volume:
For a vented option, 14 to 21 liters with 35 to 45 Hz port tuning.
For example, Dayton 0.5 cu ft cabinet with PE 260-476 tube with no cutting;
or Dayton 0.75 cu ft cabinet with 2" ID Precision Port cut to total 7".

For a sealed option, 8 to 11 liters. Requires a subwoofer or two for full range reproduction.

Baffle size:
8" to 10" wide. Baffle height does not matter though it will somewhat affect midrange tonal balance.

Driver layout on baffle:
Tweeter's center is 3" from the baffle's top edge with 0.75" horizontal offset (L/R mirror image).
Midwoofer's center is 5.75" below the horizontal line at which the tweeter's center is located.
Drivers should be mounted flush with the baffle in recessed cutouts.

Options

Non-BSC, in-wall mount version is here (post yet to be added).

Listening Impressions

These are decent sounding speakers; way better than any commercial offerings under $500/pr I recently auditioned (mostly from Internet Direct loudspeaker companies). Voicing is near-perfect to my ear. The SEAS tweeter is really an excellent performer; it handles the design's low crossover requirement with aplomb. No wonder it's so popular. After trying various filter topologies, I really don't think this driver combination needs a more complex crossover.

See another review here.

Attached Files

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