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RBH AC Series 5.1 Loudspeaker System

August, 2003

Colin Miller

 


Specifications:

AC-51
1 x 5.25" Polypropylene Woofer
1 x 1" Fabric Dome Tweeter
12dB/Octave Crossover at 3500Hz
8 ohm nominal impedance, 86dB sensitivity
8" x 11.25" x 10.25"
$299/pr

AC-525 Center Channel Speaker
2 x 5.25" Polypropylene Woofer
2 x 1" Fabric Dome Tweeter
12dB/Octave Crossover at 2000Hz
6 ohm nominal impedance, 89dB sensitivity
18.5" x 10" x 10.5"
$259 ea.

AC-10S Subwofer
1 x 10" Kraft Pulp Woofer
12dB/Octave lowpass 40-180Hz
15.5" x 17" x 18.25"
$499 ea.

RBH Sound

www.rbhsound.com
 

Introduction

One of the nicest things about playing equipment reviewer is the acquisition, albeit temporary, of a wide range of audio and video toys for the purpose of evaluation.  Some of us refer to the process of privilege as the “candy shop,” and most acknowledge it as the primary motivation for putting forth the effort to attend trade shows, make contacts, write articles, undergo relentless peer review, and wave signs on the corner during commute traffic.  Or maybe that’s just me.

Don’t get me wrong.  There is certainly a sense of civic duty attached to all of this.  After all, the marketing machines of the A/V industry will get their exposure and testimonials one way or another, and I figure I’m just as good an exploited, self-important hack as the next fellow who might just repeat manufacturer claims verbatim (as if reading some dubious “white paper,” makes one trustworthy on a subject) and then embezzles the review sample as a “fee” for the review, making a quick turn on E-Bay to liquidate.   Not making any accusations mind you.  I’m sure this never happens…. };>) I’m just happy to get a loan extension.

Personally, I really enjoy throwing my thoughts onto a notebook, and then translating the scribble into a keyboard to mull over and make coherent for anybody who doesn’t understand nonsense.  I find every topic I’ve written about in Secrets genuinely interesting and entertaining on some level.  Besides, the audio industry, though full of deluded “Gurus,” self-appointed experts, and purveyors of not so proven quasi-scientific charm bracelets, has its own collection of sincerely dedicated and occasionally exceptionally competent people.  Among them, RBH is one of the companies who doesn’t make me run looking for my manure boots every time we meet.

How This Came About

I’ve had two at home dates with RBH's MC series, which left me inclined to believe that they really had their feet on the ground.  A semi-private demonstration of their Signature Series after hours at a CES show a couple of years ago suggested they might even have a pretty good handle on what they’re doing, certainly better than many other factions.  A conversation or two with their head loudspeaker engineer confirmed the same.  Following unanimously positive experiences with the company and their products, I added them to my, “inclined to trust” list of loudspeaker manufacturers, the length of which wouldn’t fill half a page.

This last iteration of my RBH experience started at a CES cocktail party for dealers that Stacey Spears and I ungraciously crashed for the sake of shrimp, chicken, and beer. Joe Hageman, who represents RBH products, happened to catch me in the act, said his pleasantries, and mentioned this new “entry level” series. I asked if they were any good, and like he’s supposed to do, he said yes and suggested I might be interested in trying them out. With a belly full of shrimp, beer, and chicken wings, how could I not be?

“Entry level” loudspeaker systems are a dangerous place to go, almost as dangerous as “ultra high-end” models.  Much of the time, the entry levels downright suck eggs.  Granted, I’ve become somewhat of a practical snob about these things, but the truth is that once you get accustomed to the really nice stuff, most systems that squeeze in an entire “5.1” setup for less than a few thousand dollars can leave spoiled brats like us a little underwhelmed.  Aside from having invested all of that time in setting up the review arrangements, unpacking, setting up the system, and displacing the usual rig, you’ve then potentially got a very uncomfortable predicament should things go awry.  The manufacturer, and their rep, are looking for a glowing response in print, not only for publication, but perhaps for quotation in future ads, in return on their investment paid by pulling an “in-the-box” product from inventory to be dirtied by some cog masquerading as a journalist.

Having written a couple of, “It’s not really that bad, but I wouldn’t really want it” items in the past, I can vouch that the backlash isn’t so pleasant, both from manufacturers and disgruntled owners, even when I thought that the comments were even-handed and fair.

Should that deter our civic duty?  No, of course not.  If it sucks, it sucks.  If it’s just okay, well, so be it, even with as positive an intonation as ethically possible.  However, for my own purposes, I usually make an effort to avoid anything that I wouldn’t potentially want to buy myself, be for my own use, or for somebody else.  I take this approach in part because of my non-confrontational nature, partly because I think there’s more value to finding good products than stigmatizing bad ones, and partly because time is too valuable to spend getting gear in the door, unpacking, settting up, calibrating, repacking, and shipping off if the audition sours in the first few minutes, published review or not.

As I hadn’t even seen the target of this review, let alone heard any part of the system or known anything about it prior to agreeing to do a review based entirely on a few words of a PR guy, some shrimp, and a few beers, this was not necessarily the greatest idea.  I could have seriously set myself up for a whole bunch of angst.

The Sound and the Fury

I got lucky this time.  Let me put a lid on right here, before the balloons fly and the band begins to play.  Maybe I’ll offer up some quotable, ad-friendly text for those who stick it out at the end, but for now mere cursory comments will have to do.

Let’s start with cosmetics.  These speakers look really cool- avante garde enough for interior decorators, yet enough like a sports car to fill the manly man quota that many audiophiles call for. The units RBH sent me were of a kind of silver, speckled, shiny paint finish.  That itself is pretty smooth, though even smoother are the contours of the enclosure.  While the drivers mount on a flat baffle, the sides are tapered like a tear drop, much like the far more expensive Sonus Faber models that have become so renowned for their cosmetic qualities.  Some might obsess about the benefits of non-parallel walls and how that relates to internal standing waves, but after I remembered how standing waves do so well in a round bucket, I decided to only mention why I wouldn’t bring it up.  There isn’t any leather or fancy lacquer, but I didn’t ever miss it.

While the AC series lacks purse-quality leather upholstery, there are
threaded inserts for mounting brackets, which make installation of such that much easier, particularly if you use the optional brackets that RBH supplies. It’s a simple thing, but for those who want to mount speakers on the wall, it makes things much easier. Shiny, reasonable quality binding posts make the build quality that much more reassuring.

All of the speakers are of the bass-reflex variety, though if you’re using the ubiquitous 2nd order high-pass filter @ 80 Hz associated with the bass management of THX processors, as I did, the character and method of the lowest limits of extension achieved by the center, front, and surround speakers is pretty irrelevant beyond the fact that they extend substantially lower than 80 Hz, which these do.  As a result, it’s not an ‘ideal’ splice with the subwoofer when thrown into such a scenario as THX processors provide, though the problems are most likely deviating from a theoretical ideal than providing hurdles in any practical situation.  RBH provides foam plugs for the ports, should you like the system to behave in a more sealed fashion, but I opted to leave them out.  Should any of the L/C/R/Ls/Rs speakers be placed within an enclosed area (say inside a bookshelf type entertainment center, or other type of cabinet), it might be a good idea to employ the plugs, if only so as to avoid unnecessarily energizing the enclosed air behind the loudspeaker.  Better yet, fill the entertainment center with some fiber fill, like Dacron®.

The drivers in both the AC-51 and AC-525 are mounted flush to the front baffle, not only to look cool, but to avoid diffraction artifacts caused by the sound waves traveling along a quick transition in the baffle, particularly from the tweeter.  In addition, the tweeter inset into the ‘wave guide’ directs the output away from the baffle, so that less sound hits the baffle edges, which in turn would otherwise cause diffraction artifacts, or secondary arrivals resulting in smeared time response and high-frequency comb filtering.

The AC-51 bookshelf speakers used for front and surround speakers in this system don’t look very conventional, but underneath it all are pretty much a down home kind of design.  Soft dome tweeter, 5.25” poly cone mid-bass, and ported to the rear.  The binding posts are pretty, and the cabinet has the distinctive tear drop taper. 

The AC-525 center channel looks like two AC-51 speakers put together horizontally with the tweeters then turned to stack vertically. Multiple tweeters are usually stacked vertically to avoid lobing between the two tweeters on the horizontal plane where most listeners will have their ears located. Why they chose to use two tweeters, as opposed to a single one, I didn't know, though I eventually got my answer (see below). All of this fits nicely on a stand built to fit like a cradle, allowing the user to adjust the angle of the center channel speaker, critical in this case due to the stacked treble drivers.

I had concerns regarding the center channel. Because the vertical alignment of multiple tweeters might cause vertical lobing (narrow dispersion) of the treble, and the spaced horizontal placement of multiple mid-bass drivers could cause horizontal lobing of the upper midrange frequencies, not only would this make a very finite listening window in terms of angle, but the differences in dispersion between the center channel and the other speakers might result in a mismatch of sound at the listening position, regardless of how similar the on-axis response might be between the AC-525 and the AC-51. In practice, so long as I sat more or less in front of the center channel and angled the speaker so as to place my ears on-axis vertically with the center channel driver array, this wasn’t a problem. There was a good reason that arrangement I considered dubious on the surface worked out so well, explained by Shane, their head engineer:

"The AC-525 center channel is optimized for horizontal off axis dispersion when placed horizontally. The dual tweeter configuration of the AC-525 allows a lower crossover point to be used between the tweeters and mid-woofers. The result is better control of the off axis horizontal response and reduced lobing as compared to a single tweeter MTM center channel design . Since the AC-5T and AC-51 stand vertically and do not use a MTM type alignment,  the horizontal off axis dispersion is already very broad, and the use of dual tweeters is not necessary."

I would only add one comment to that in translation, that two tweeters allow a lower crossover point due to higher power handling (two drivers plus constructive summing of output on-axis). Paradigm takes a similar approach with their center channel speakers, except that instead of using two tweeters, they just beef up the power handling of a single unit. Anyway, mystery answered.

The A-10S subwoofer, in addition to being of the bass-reflex alignment, uses a downward-firing paper cone 10” driver. The downward-firing part is somewhat of an advantage in that it relieves the need for a grille, protecting the driver and port opening from children with, say, a few raisins to spare, but in that it also couples the output almost directly via a room boundary, eliminating the possibility of cancellation from that first reflection, and should you wish to put it in a corner, from all boundaries during the initial launch.  In addition, because the port is a fixed distance from the nearest surface (the floor plate), the designer can take the nearest surface into consideration when adjusting the loading characteristics of the reflex system.  So far, so good.

The amplifier/crossover module built into the subwoofer looks like a fairly economical unit.  No high-cost aluminum knobs or heavy toggle switches, but more than enough functions to get the job done.

There’s a switch to set the power manually to ‘On’ or ‘Off’, as well as an ‘Auto’ mode which senses the audio signal and turns on when it detects content, and turns off after a period of seeing none.  I found the ‘Auto’ setting annoying, as it could turn off in the middle of a movie when the bass content lacked, and not turn on quick enough when it came back.  This kind of annoying behavior is not unique to ‘Auto On’ circuits in subwoofers, and in the case of the AC-10S, is easily remedied by setting the switch position to ‘On’.  I left it there.

The subwoofer also includes a variable crossover with a range labeled from 40 Hz to 160 Hz, as well as a level control.  With the Onkyo TX-DS989’s own crossover, I turned the crossover all the way up to remove it from the equation, and set the level about half way and then did fine adjustments in the receiver’s configuration setup.

There are both RCA connectors for stereo input and outputs, as well as speaker level connectors for the same.  With this set up as a 5.1 system with a receiver that has onboard bass management, all that was necessary was a single line-level input, so I used the left RCA input connector exclusively with entirely satisfactory results, but it’s nice to have the options anyway.

The phase switch allows the user to switch polarity between 00 and 1800 relations.  I found that the 0 setting worked optimally, but again, nice to have the option.

From the Bottom Up

Generally speaking, I’m not a big bass reflex fan.  Please don’t infer that I mean bass reflex designs are of an inferior sort by their very nature.  Rather, that while the technique has potentially substantial benefits, more often than not (particularly with budget-oriented gear), the detrimental side-effects offset any benefits by a large margin.  While bass reflex can provide more extension in terms of the –3 dB cutoff point, more output at and slightly above the tuned frequency, and lower distortion over the same range, if it’s implemented poorly, the transient response sucks, the frequency response linearity sucks, there’s audible port turbulence, and the sound reflects week-old gruel growing green hair.  Poor outcome with bass reflex systems are usually the fault of poor design, poor manufacturing tolerances, or both.  Regardless, bad bass reflex implementation lends an identifiable character, be it muddy bass, or an artificially exaggerated punchiness that eventually exposes itself as a parlour trick.

If you’d like to get into it, we have a separate article entitled How a Hole-in-the-Box Works - A Big Dig into Bass Reflex.

The AC-10S subwoofer very much avoided the most serious issues that often plague bass reflex designs, so far as I could tell.  It didn’t have the last ounce of extension or pounding capability that more extravagant models, be it within RBH’s own offerings or otherwise, might provide, but it did tender a smooth, controlled roll of bass lines, and most importantly didn’t call attention to itself.  Throughout the audition period, it supplied enough low-end grip to lend a good sense of presence to movies and music alike, be it "Toy Story 2" during the street crossing scene, Tori Amos’ pedal work among the many singles my wife and I have collected, or the synthesizer bass of Sting’s "Brand New Day" album.  To be honest, it didn’t meet the same bar as the M&K MX-5000mkII in terms of dynamic might, infrasonic extension, or the extremes of articulation, but for 1/6th the cost, I think the AS-10S could certainly hold its head up with more than a few ounces of pride amidst any competition.

Within the confines of the $499 asking price, one could conceivably find an alternative that hit harder, but which might compromise the overall composure and poise that the AC-10S retained.   I certainly wouldn’t go that route.  On the other hand, you might be able to find another option that had slightly better transient performance for the same price, though it’s unlikely that it’d be able to meet the AC-10S’ well-rounded extension and output capabilities, which seemed pretty solid to about 30 Hz or so, maybe a little deeper depending on the room.  Bottom line, it’s got enough smack and slam to excite the senses, and enough control to make the rest of the performance worth it.

Moving onto the rest of the set, the AC-51 left/right/surround speakers and the AC-525 center channel speaker followed suit with a similar “liberal arts” kind of approach that touched all the right bases.

I couldn’t find much fault with the mid-bass.  I can’t claim that really I tried to, so perhaps if somebody more attentive did the same listening, some fault would emerge, but if it were there, it’d be minor, in my opinion.  The mid-bass, while full enough to balance out the weight of vocals, didn’t overcome the midrange spectrum to the point of unnaturally thickening the presentation, be it with the top spectrum of a kick drum, the body of a guitar, or the chest of a vocalist.  Mark it pass.

I initially screwed up the vertical angle of the front AC-51 speakers on setup, so that they were angled to aim slightly below my ears.  It’s interesting that the manual states a ‘higher order’ crossover, though I don’t think I remember seeing just how ‘higher order,’ to minimize driver output overlap.  Usually, this would make a loudspeaker not particularly directional in the crossover frequency, though it’s possible that the midrange driver itself is just directional at the top of its operating limit.

The results with the misalignment were OK with the improper vertical orientation, but a little underwhelming. The spectral balance overall was fine, though the upper midrange frequencies seemed a bit too laid back, if not recessed.  It sounded pleasant, but the AC-51’s didn’t seem to be able to open the window, so to speak.   It went a couple weeks this way, until I discovered my error while making out with my honey on the floor.  In the middle of a heated debate over specifically how dirty each of us really wanted it, I raised my head and realized the midrange output from the AC-51s sounded fine, great even.  I felt like such an idiot, repositioned the speakers, and went on to pop some more Tori Amos singles and a Sarah Mclaughlin’s "Surfacing’ into the player, admiring the AC-51’s reproduction of vocals-smooth, detailed, elegant, and bare.   Window of sound back open, sound stage focused, depth in recording apparent - all better now.  The AC 51’s portrayed the proximity of Tori Amos in relation to the microphone through her vocals on My Samurai from the "Talula" single without ripping my ears off with the sibilants.  Bravo grasshopper.

The treble, interestingly enough, shared more with RBH’s the top of the line Signature Series than the next step up MC Series, which I had the pleasure to dance with a couple times prior.  While the MC series uses a metal dome tweeter, and as such has the characteristic extra pep common to tweeters that use metal for a diaphragm, the AC series uses a soft dome, fabric diaphragm tweeter, not identical to the Signature Series, but closer, and so it seems, shares some of its more prestigious cousin’s treble neutrality.

Though I tend to be less fussy with cinematic material, in part because the picture and story tend to distract me from the audio quality, I do find it important that the quality of the playback does not serve as a detriment to the whole.  This means a good tonal match across the front, preferably a good match with the rear, low distortion, and intelligible dialog.  The AC system did this without a problem within the range of reasonable listening levels.  Throughout “Harry Potter and the Chamber of Secrets” or whatever else my kids wanted to throw in, it wasn’t a strain to understand the sophisticated dialogue, and when the troll fell down, we got a good thump out of it.  From the standpoint of delivering awe during the bombing scene of “Pearl Harbor,” it won’t match a THX Ultra system, but for the price, it’d be unreasonable to expect it to do so.  That’s not to say that this system can’t play loud.  It’ll certainly meet anybody’s requirements for achieving hearing loss.  It might just grunt a little more doing it.  Mark another pass.

If you want to get critical about it, I will say that neither the AC-525 or the AC-51 quite compare with the ultimate transparency or neutrality of the best speakers available, either RBH’s own signature series line or the S-150Ps I keep around for reference and personal pleasure.  That’s kind of like my required disclaimer to keep my high-end credibility.  Honestly, I don’t feel like I’ve any right to complain about where the AC series falls slightly short, considering what it does so well, and how little it cost to do that.

Conclusions

Granted, there’s no way I’m going to replace my “reference rig” with the AC series.  But, if you take into consideration that for what one of my surround channel loudspeakers cost, you could get two complete AC systems, either of which would deliver so much of the positive performance I appreciate with very little negative to go with it, it’d be a disservice not to recommend this system.  When prompted for a guess on what I thought these speakers sold for, I thought that the system, as provided, would be a good value at $2,000 to $2,500.  That you could land an entire set like this for under $1,500 seems absurd.

Looking over my ramblings, it seems that my praise might be seen as somewhat lackluster.  I mean, these things are darn good in terms of build and performance, and yet I keep mentioning that they’re not quite as best as some of my favorite things.  Well, perhaps I should offer this perspective.  While I haven’t ventured to do formal reviews of such, I have taken fleeting measure of similarly priced offerings from several other manufacturers and kept on walking, picking up the pace.

I don’t like to specifically address disparaging comments, but let me say that if you took the RBH AC series and did a direct, fair comparison with more established, mass market products that you typically see in chain stores of one type of another, regardless of how good those places may be, there’d be a whole lot of beating and stomping going on, with the AC series walking up and down each one of those clowns.

It’s no coincidence that I don’t have any examples of the AC series' most likely competition on hand for comparison.  As I mentioned before, I try to avoid letting substandard audio equipment in my house, and while the RBH AC series can run with the big dogs on many levels, much of their likely competition won’t even make it past the door.

Does that mean that they’re that good for the money, just plain good, or that I’m a pretentious audio snob that likes to give highly opinionated statements for others to assume as truth.  Probably all of the above.  Take it for your own appraised value.

 

- Colin Miller -

For the record, equipment used during the review period for operation, comparison, and/or pleasure:

Anthem AVM-20 Surround Sound Processor

Onkyo TX-DS989 Surround Receiver

M&K S-85 satellite speakers

M&K S-150P Active Monitors

M&K SS-250P Active Monitors

M&K MX-5000 mkII Powered Subwoofer

M&K MPS-2510 Studio Monitors

Aragon 8008bb Stereo Power Amplifier

Aragon 8008x3 3-channel Power Amplifier

Bryston 4B SST Stereo Power Amplifier

Dynaco ST-400 mkII Stereo Power Amplifier

Technics DVD-A10 DVD-V/DVD-A player

Related to the article above, we recommend the following:

Primer - Speakers

 

 

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