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Driver Selection

While working as the Product Manager for the Parts-Express house brands i would often explore the capabilities of drivers being developed through example designs and experiments, so the primary factor in deciding these drivers was the overlap of the GRS1.R Ribbon tweeter and the SIG180 Woofer. The SIG180 offered fantastic low-end output, with enough upper fidelity for my intended goals in an enclosure that wouldn't be too overbearing, and the RT1.R was a well-priced ribbon package. Originally it was going to be a 2-way to see how far i could push the drivers, but eventually i just wanted a working speaker that i could enjoy, so i added the RS52FN in the mix to keep the ribbon from burning out. You can find out more of the specifics on each driver in the "Component Details" tab.

Enclosure Modeling and Design

Since I had finally decided to use the RS52FN in the design, the only driver that needed enclosure modelling was the SIG180 so I entered the T/S parameters into VituixCAD (Sorry WinISD, i'm a sucker for extensive toolsets) and ended up with something that would be a good compromise considering some real-world limitations. This is the 6-pack view of the enclosure (enclosure design file included in the snapshot)

Looking at the Data Entry section, Qa and Ql are defined to reflect an enclosure with lined walls and minor leaks, and the signal power is set at 40w (Half of the rated power, but 10W over the limit set by the RT1.R 30W power handling). A single 4" vent with dual flared ends keeps vent noise to a minimum while extending the low-frequency output to meet my intended goal (or close enough...).

At this power level, there is clearly over-excursion around 60Hz that could cause problems, but i figured that i wouldn't necessarily be hitting these levels consistently enough during normal listening. 103dB SPL is good enough for my living room sessions, and is a fair performance considering the VD of a 6.5" Driver. Accepting these compromises, i moved on to the Auxiliary window in VituixCAD to get some rough dimensions based on the target volume and ran into some resonance issues to watch for.

This neat little tool will carry over the target volume and the vent information from the enclosure modelling window and lets you rough in some enclosure dimensions and the relevant resonances for those lengths. I wanted the width of the cabinet to contain the SIG180 without leaving much space on the sides, and the depth to be the same as the width. The SIG180 has a diameter of

180mm, so eyeballing with a measuring tape i ended up with these dimensions (220mm x 749mm x 220mm). After reviewing the resonance frequencies, i noticed there were a few modes that were close enough to interact with each other, particularly around 200Hz, and the first port resonance at around 1kHz (close enough to some higher order modes of the cabinet).

I set the listening position to the height of the tweeter and 2M in distance, added the baffle dimensions, and placed the SIG180 in a position determined by subtracting the diameter of the RT1.R, the RS52FN, 20mm from the top, with 5mm between each driver, AND the radius of the SIG180.

X mm = 749mm - (30mm + 130mm + 110mm + 90mm)

Looking at the transfer function, i decide that a good upper limit for the SIG180 is around 500-800Hz (which avoids the first vent resonance and sits within the acceptable frequency range of the RS52FN) as it keeps BSC for the woofer at an acceptable 6dB shelf.