Introduction

When I attend CES, I always enjoy visiting the RBH Sound booth, because (1) they make a wide variety of speaker models, and (2) they have exotic wood veneers in which the models can be supplied. Also, they sound great, and I guess that is the most important thing.

At CES, 2004, RBH announced some new speakers, including the subwoofer reviewed here, the MS-10.1. It follows on the MS-8.1.

The Design

The MS-10.1 uses two 10" aluminum cone drivers, both active. One is front-firing, and the other is on the bottom, for downward-firing.

The front driver has a perforated metal grille, while the bottom one has no cover. There are four feet permanently mounted on the bottom of the enclosure. They are not very long feet, so you can place the sub on a short pile rug, but don't put it on a deep plush pile carpet, as the driver could impact the rug fibers.

You can see in the above photo that the MS-10.1 has a port on the side. The port is 5" in diameter and has a foam plug. The plug has a 1" hole in the center.

All designs that I have seen before, that use foam plugs in the port, allow you to use them either with the plug inserted, or with it removed. This changes the response, but lets you get a higher SPL if that is your need. As you will see below, in the bench test section, I tested the frequency response with the plug in, and with it out. However, I found later that the port plug is supposed to stay in, never removed. So I asked, "Why not just make the port 1" in diameter and do away with the plug entirely?"

The reason for this is RBH's specific design, called the "Tuned Aperiodic Vent", or TAV. The foam plug acts as a "membrane" that has some give to it, and the hole in the plug allows some air to come out. This configuration puts the design between a regular "ported" enclosure and a "sealed" one.

TAV is supposed to let you have a smaller enclosure, but still deliver deep bass, partially because it has two active smaller drivers instead of one larger driver.

The design appears to deliver on its promises, as you will see below.

The MS-10.1 has a 250 amplifier mounted on the back of the enclosure. For an $800 subwoofer, it has everything. The toggle switches in the top of the photo are for power-on and auto-power-on, and to let you switch the crossover in or out of the circuit (this is becoming more and more important as SSPs and receivers become more flexible in their bass management settings).

Inputs are line-level RCA unbalanced left and right, with corresponding RCA line-level out for daisy chaining to other subwoofers (full-range signal, not high-passed). There is also a set of speaker-level inputs and outputs, with the outputs high-passed at 100 Hz.

Phase is continuously adjustable from 0⁰ to 180⁰. The crossover is adjustable from 50 Hz to 180 Hz. The volume control is next to the crossover dial.

AC is non-grounded, with removable power cord.

The Listening

I set the MS-10.1 up with our Yamaha Universal Player, Lexicon MC-12, McIntosh Power Amplifiers, Balanced Audio Technology Power Amplifiers, Carver Amazing Speakers, Thiel Speakers, and Nordost Cables. I watched movies and listened to music, and the RBH courteously supplied the bass.

Frankly, I was very surprised that the MS-10.1 could keep up with this system, which is very big, and very powerful. Although we review RBH products regularly, it has been a while since I have personally reviewed them. It should remind me to get some RBH more often.

The 20 Hz stuff was really there! Now all subs will produce some sound with a 20 Hz signal. Even a car radio speaker will move a little bit. The question is how much? The MS-10.1 delivered the goods, and I have a very critical ear when it comes to deep bass. Sure, I could hear some harmonics when the RBH was asked to do too much, but within reason, it did more than I expected it to. It sounded clean and deep. I guess that odd-looking permanent foam plug in the port is not just marketing hype.

If I had not known the MSRP of this product, I would have thought it was $1,400, because it sounds like some others I have heard at that higher price.

On the Bench

The tests were performed with the foam plug in, except for the frequency response comparison, as noted below. The crossover was switched off (out of the circuit).

I measured 116 dB maximum output, 10" from the front driver, using a single input signal that contained 20 Hz, 31.5 Hz, and 50 Hz sine waves.

At 20 Hz, which is just below its rated response, and 100 dB output (10" from the front driver), there was 22.3% THD.

At 25 Hz, THD was reduced to 10.7%, a bit more manageable, but still pretty high with a 100 dB output.

At 31.5 Hz, THD was a reasonable 3.1%, with 100 dB output.

Going to 40 Hz, THD was a bit lower, at 2.5%.

And, at 50 Hz, THD was well in control.

Although the port foam plug is not supposed to be removed, I removed it anyway and measured the frequency response. It is not necessarily relevant, but it shows some interesting results. Below is the response with the plug in, as it is supposed to be. The peak is at 75 Hz, and rolls off 23 dB at 20 Hz. Notice how smooth the roll-off is. The MLS window is 50 ms. Note that this is the quasi-anechoic response, not the room response.

The initial part of the impulse response is negative, which means it is inverted. The phase adjustment dial does not affect this. Some subs are electrically inverting, some are not. Same thing with amplifiers. It seems like an electrical inverting toggle switch would be a nice addition to subwoofers.

With the foam plug removed, the response is no longer smooth. It rolls off more rapidly from 75 Hz to 40 Hz and then the slope is shallower to 20 Hz. So, now you see how this foam plug "aperiodic membrane" serves to improve the response.

Conclusions

I am pleased to say that the RBH 10.1 is a very nice product, especially at $800. It does a great job of delivering deep bass in a reasonably sized enclosure. It has connection flexibility and features of more expensive subwoofers. I have no reservations about recommending it highly.

 - John E. Johnson, Jr. -