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RBH Compact Theater CT-5 / CT-7  Print E-mail
Home Theater Loudspeakers Speaker Systems
Written by Richard Elen   
Wednesday, 01 May 2002
Article Index
RBH Compact Theater CT-5 / CT-7 
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Introduction
Utah-based RBH Sound has been around for a while: last year was their 25th anniversary. In the time they've been in business, they have produced some formidable loudspeaker systems, notably the impressive Signature Series. Now they have turned their attention to the needs of home theater listeners who have limited space, addressed with the release of the "Compact Theater" series. Though the new design is diminutive, RBH has managed to include the same design standards – and solid, durable materials, notably aluminum – that are utilized in their more up-market products. The result is a very satisfactory combination of high-quality audio and practicality that will suit the home theater and home surround audio listener who wants something way beyond your average grotty little satellite speakers (believe me, you do).

The system arrived in two boxes. One contained the MS-8.1 powered sub, a near-cube a little over a foot wide on all sides. The other carried four MM-4 mini monitors, each about seven inches tall, plus the 11-inch-long, four-inch-wide and four-and-a-half-inch-high C-4 center front unit. All the units feature solid, impressive and hefty die-cast metal enclosures, and are available in either black or white. The whole system exudes solidity and suggests that whatever it’s going to do, it will do it well. The price for the 5.1 system is $1,099; the 7.1 system is $1,349.

Installation and Operation
Installation was really easy, mainly because I already have a 5.1 system set up, so the cabling was already in place. There are two versions of the Compact Theater, incidentally, the CT-7 with six mini-monitors plus the center and the CT-5 (which I had). You can upgrade from the latter to the former by adding two more mini-monitors. The aluminum-coned MM-4 "mini-monitor" speakers and the C-4 center channel speaker have large, gold-plated screw binding posts. They are recessed in quite a small space, so it’s a little fiddly to get the cables in there, but it was not too much of a problem. The posts will take hefty cables fairly easily.

The powered sub is the most complex unit by quite a lot (with the MM-4s, you just connect the cable and you’re done). The ported enclosure includes a 200-watt amplifier driving a pair of eight-inch aluminum-coned drivers, one facing the front and the other facing down (it stands on four sturdy plastic feet that keep it a couple of inches off whatever surface it sits on). A rear panel power switch selects off/on/auto. Auto powers up the amp when a signal is sensed, after which it stays on for some time after the signal disappears, a sensible feature as most people will probably stick it out of the way in the corner. Also on the rear panel are the inputs and outputs, as there are two or more ways of driving this unit. It can be hooked up to systems which have no specific sub output by taking the front L-R pair signals either at line level or at speaker level into the sub box and then out again. For this purpose, there is a pair of RCA connectors for line-level left and right in, and another pair for out, plus four sets of binding posts for left and right high-level I/O. Three controls complete the rear panel: a level control, a phase knob, and a crossover frequency control variable between 50 and 160 Hz. In my case, I fed the line-level sub output from my receiver into the left line-level input and went on to the next thing.

The eight-ohm monitors feature a four-inch aluminum woofer and a one-inch tweeter. The center front unit includes two of the four-inch drivers (presumably parallel, as the unit has a four-ohm impedance), insuring that this channel, so important for movie dialogue (though of variable utility in a music listening situation) is taken care of properly. Remember that with mono sources, this speaker may well be handling everything above the crossover frequency on its own.

Once you have the speakers set up, you need to check that they are connected correctly, set their levels, and above all ensure that your receiver’s bass management is set up right. This is really important for anyone who does not have a room full of enormous full-range speakers. In my normal system, I have a powered sub and a pair of JBL 4311 studio monitors in the front (which I tell my system are "large") and JBL TL-series center and surrounds ("small"). In the case of the CT5.1 system, I had to tell the receiver that all the speakers were now small and that a sub had been added.

The purpose of bass management, as I so often tell people, is to make sure that any bass on any channel (not just the LFE low-frequency effects channel) is fed to any speaker that can handle it: the LFE is not the "sub-woofer" channel! In this case, the only speaker that can handle bass is the subwoofer. Get this wrong, and your system will sound thin and weedy. Get it right, and the system will spring to life.

With bass management correctly configured, I went on to test the speaker levels. For speaker testing, you can either use your receiver’s built-in test feature, if it has one, or use one of the many DVDs that include a set-up track. All of 5.1 Entertainment/Silverline’s DVD-A/V discs have one, for example. The usual format is to play pink noise out of each speaker in turn, allowing you to adjust the level of the speaker that is currently playing so that they all produce the same volume. Of course, they never do. Room position, for example, will vary the apparent level. Even perfectly matched speakers like these, for the same reason, never sound the same. So you do it by ear the best you can, unless you prefer to use a dB meter -- I have one, and I still prefer to do it by ear. It's virtually impossible to come up with a better method of setting up a sub, and you almost always need to tweak it on program material for best results.

Something you will also have in your receiver, probably, is a means of setting the crossover frequency between the sub and the rest of the system. The important thing here is to make sure that everything matches. In the case of the CT-5.1 system, we know that the mini-monitors are alleged to have a decent response down to 100 Hz. We also know that the sub’s crossover goes up to about 160 Hz.

The theory of a sub is that bass is not directional, so it doesn’t matter that you have a single source of bass end in the system. It also doesn't particularly matter where it is, because bass isn’t localized. I am not entirely happy with this conventional wisdom, but let’s assume it’s true for the time being. You therefore have two things to balance here. If you set the crossover frequency too high, you will be pulling frequencies out of the monitors into the sub that are high enough in frequency to be used in localization, so you could lose some of the directional information in a recording. Set it too low, on the other hand, and you could be giving those little monitors frequencies lower than they were meant to handle. This risks possible distortion and certainly a "hole" in the frequency range of the system between the crossover frequency and the lowest bass the monitors can reproduce at a decent level.

If you were running your front speakers through the sub, as you can with this system, it would be a bit less complicated, because you could feed full range to the front left and right speakers (tell your receiver’s bass management that there is no sub but that the front speakers are large, which should make all the bass come out of the front left and right channels) and then tweak the crossover knob on the sub until you get a smooth response. In my case, where I was using the sub simply as a sub, fed with a line level input from the receiver’s sub output, I had to be more careful, so I decided to set the powered sub’s crossover to its highest frequency, 160 Hz. This ensured it would get anything sent from the receiver. I then used the receiver’s crossover setting to choose the frequency at which bass signals would cross over from the monitors to the sub. My guess was that the best frequency would be somewhere between the highest frequency of which the sub was capable (let’s say 160 Hz or so at this setting) and the lowest frequency the monitors could handle (say 100 Hz or higher). So I went for 120 Hz initially, and messed with it later.


 

 
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