RBH Sound SX-12 Introduction

RBH Sound is a privately held loudspeaker company, in operation for 35 years now, that manufactures and designs its own products from the ground up. The company was founded in 1976 and initially was an OEM manufacturer with which some rather famous audio companies contracted work and consultation from. In 1986 RBH decided to relocate to Utah and strike out in a new direction to establish the brand as an audio manufacturer of finished products in its own right. 25 years later RBH is still going strong and has an extensive line up of products. Today we will take an in depth look at a powered subwoofer model from their Signature SX series, the SX-12 which is a 350 watt bass reflex design based around a 12” driver.

Check out the full video review (including the complete text transcript)

Unpacking and Initial Thoughts

The SX-12 arrived via FedEx and upon arriving home and seeing the condition of the box I noted that it was a little worse for wear. After fully unpacking the SX-12, which was a quick, easy exercise, I noted that two of the mounting tabs were broken off on the right side of the grill and that the back of the enclosure had sustained a dent in the back corner corresponding with some damage to the outer box. This sub was obviously shipped around a lot before I received it, most recently to the Audioholics HD video production studio for a video review shoot. It appeared that at some point the SX-12 had been dropped on the edge of the box. At least that would be my guess as to what happened. At that point I quickly examined the amplifier and woofer and noted that all seemed ok with them and that there seemed to be no structural damage to the enclosure. A couple of snapped off grill inserts and a ding on the enclosure seemed to be the extent of the damage. At that point I plugged the SX-12 in to determine that it was still in working order. It was. I made report of the subs arrival condition and decided that despite the minor cosmetic issues the sub was still in plenty good working condition to continue with the review. Despite the damage to the SX-12 the packaging seemed to be pretty standard and would usually be adequate. The SX-12 is what I would consider as a moderate or average size for a powered subwoofer and weighs in at 53lbs so it isn’t in need of overkill packaging measures. It has the usual thick foam top and bottom protections, a bag for the subwoofer and the cardboard boxing around all of that which is fairly standard for a sub of this size and weight. Contained in the package is the SX-12, the grill and power cord.

With all of that out of the way, the SX-12 looks pretty good in the provided black oak finish with the aluminum driver cone giving it some flash. The graceful curve to the side panels adds a lot to the RBH’s good looks and is also claimed to help reduce internal standing waves. It is funny how something so simple could make such a big difference, but the gentle curve of the side panels on the SX-12 easily take it up an extra notch or two in the looks department differentiating it from just another black cube.

Design Overview

The SX-12 utilizes a nominally 12” driver forward firing in a vented or bass reflex alignment. The vent in this case is a 4” down firing port which is heavily flared at both inlet and outlet and also has a dimpled texture molded into the port flares. This is similar to the surface of a golf ball. This type of surface is said to maintain laminar air flow at higher speeds and offer less surface friction to air flow than a conventional smooth surface. The port is allowed to breathe and held roughly 2” off of the floor by extra tall rubber feet on the enclosure bottom. In addition this close coupling to the floor surface in front of the port can help to slightly lower the tuning of the system by adding to the effective air mass of the port.

The driver utilized in the SX-12 features an aluminum cone, a rubber half roll surround and what appears to be a nominally 2” diameter, single voice coil, centered with a single moderate diameter spider. The single ferrite magnet in the motor is about 6” in outside diameter and 1” thick. The back plate is bumped to provide clearance from bottoming and has a small pole vent with a screen to prevent debris from entering the motor. The assembly is held together by a nice cast aluminum frame. This is not a massive, heavy duty subwoofer driver by the standards of today. This driver appears to be more in the vein of a high fidelity woofer than the high excursion, sub bass air pumps which have become more common in the last decade. RBH does offer a driver and amplifier upgrade as part of their Signature Reference line, but a test unit wasn’t available at the time we reviewed this unit. The driver used in the SX-12/R is much heavier duty and said to offer twice the excursion of the stock unit. The amplifier is also increased to 500 watts. It would be interesting to review the upgraded SX-12R in the future.  

The amplifier utilized in the SX-12 is rated at 350 watts and is labeled as a DSA-350. It only offers the most basic features: Gain, phase adjustment, low pass filter adjustment and a toggle switch for selection of on, off, or auto on settings. In addition to the usual unbalanced RCA type connections there are balanced XLR connections which I prefer to use whenever possible. The main power switch, socket for the detachable power cord and a fuse round out the amplifier back panel. The amplifier has no external heat sinks but does have a couple of small ones internally. During the high power outdoor testing the amplifier did get warm to the touch towards the end.

RBH constructed the enclosure for the SX-12 out of 3/4” MDF. The front baffle is countersunk to flush mount the driver and is double layered. The amplifier is not countersunk. The grill is your average black cloth covered affair. Inside the enclosure there is a pair of shelf braces tying the top, bottom and side panels into each other. The port is also flared on the inside of the enclosure and extends within inches from the roof of the enclosure. There is damping material applied on both sides and the top of the enclosure.