3-way WWMTM speakers with horizontal MTM layout

Rohit Balkishan Dubla

Introduction

These latest speakers were created because of a furniture overhaul and the WMTMWs did not match the decor. Also the subwoofer had to go for the same reason. Therefore, to compromise between small size and good sound, I decided to go for a WWMTM speaker. Since I wanted the really clear mid-range of the older MTM configuration, I decided to go with a horizontal MTM section. Following are the construction photos...

I wanted a flush appearance for the drivers when fitted to the front panel, and since I did not have the required jig to cut circles smaller than 10" dia, I chose to work with two thinner panels (for easy cutting) - one to mount the drivers and one for the facade. Since the panels are thin, they are strengthened with a woofer frame (the inner frame) to take the woofer's mounting screws. The mids and tweeter are light enough to mount to the panels without needing any strengthening. The driver & facade cut-outs were done by hand as can be seen and are not perfect, but the end result looks quite good nevertheless. The facade is glued to the driver panel and required braces added to attach the side & top panels.

This shows the side & top panels attached to the front. The MTM section is horizontal with the drivers arranged in a triangle rather than a straight line to minimize horizontal dispersion errors. The result is that the horizontal directivity is well controlled and at the same time wide enough so as to not hamper imaging.

These are the almost completed left and right speakers with drivers mounted.

Driver details

The following are the T/S parameters as measured by me for the drivers I chose for woofer and mid-range duty.

Woofers

Make: Local manufacturer

Dia: 20 cm (16 cm effective)

R_e: 4.5 ohms

F_s: 73 Hz

Q_ts: 0.64

V_as: 15 litres

Box: Approx. 50 litres sealed with 2 drivers in series. The achieved box Q & F3 are ~0.74 and 83 Hz, respectively, and equalised for a target F3 of 35 Hz and Q of 1.2 using Linkwitz transform.

Mid-range

Make: Pioneer TS-G1312R

Dia: 13 cm (10.5 cm effective)

R_e: 3.5 ohms

F_s: 110 Hz

Q_ts: 1.036

V_as: 3.71 litres

Box: Approx. 31.5 litres sealed with two drivers in series, with loose stuffing.

Listening impressions

The sound is uncoloured and mids are very well articulated (thanks to the larger drivers used for the mid-range), except for the bass which is only till about 80 Hz. Upon active equalisation with Linkwitz transform, the bottom end is solid and authoritative, almost like large floor-standers, and even at low volume levels, there is almost no loss of bass.