SMR logoAudioControl Richter Scale Review

Ever curious, John R. Potis has possessed a desire to audition the AudioControl Richter Scale sub-woofer equaliser for some time.  Is "equaliser" still a 'dirty word' in the world of high-end audio or have specialist EQs finally found their niche in the bass hungry home theatre era?

Many thanks go to Miss. Meaghan Muir and AudioControl for their help and for providing the review sample.

AudioControl Richter Scale III Specifications

THD: 0.005%
Frequency Response: 18Hz to 100kHz
Input Impedance: 100K ohms
Output Impedance: 150 ohms
Signal to Noise Ration (full output): -120dB
Meter Range: 7 Vrms
Crossover Slope: 24dB/octave
Subsonic Filter: 18dB/octave
Size: 17 2. 8.
Warranty: 5 Years
Price: $350
(All specifications as per manufacturer)

The Audio Control Richter Scale III Half Octave Equalizer/analyzer with
Subsonic Filter and Electronic Crossover


AudioControl Richter Scale     Now in its third iteration, the Audio Control Richter Scale may well have originally been a product way ahead of its time. My earliest Audio Annual Equipment Directory dates back to 1984 and the Richter Scale is listed, so I'm not exactly sure just how far back it dates. Before the advent of home theater though, I'm not sure how much interest there was in perfecting bass performance beyond what one could achieve with the popular graphic equalizers of the day. If you weren't satisfied with your speakers bass performance, you bought a10 band EQ and touched up the bass along with the rest of the spectrum.

     There was a time when everybody and his brother owned an EQ but then it happened- "Equalizer" became a dirty word. As a matter of fact, mere tone controls became a thing of the past on most audiophile gear. Just try to walk into a high-end stereo shop and find a display of equalizers today.

     But all things run in cycles. As quickly as it went out of style, up sprang another need for the Richter Scale. I speak of the aforementioned home theater. When I got into audio only the most well heeled and most ardent bass aficionados owned sub-woofers. They were large, expensive and rare to find in the home. But with the onset of home theater, they have become a downright necessity. No self-respecting "theaterphile" would be caught dead without the sub-woofer. Now the need for blending a subwoofer to the main speakers and giving it the "oomph" needed to bring todays movie soundtracks to life makes the Richter Scale a much more "fashionable" item to own.

     Of course, the Richter Scale is not only an EQ. It's a self contained bass "fix-it" machine. It comes with a microphone, a warble tone generator, a VU meter for reading the room response and a 7 band- half octave equalizer for fixing the bass response of your system in your room. But that's not all.

     In addition you get an internal crossover aiding in the addition of a sub-woofer to your system and you get the ability to turn your spare stereo amp into a monophonic sub-woofer amplifier. This is a cool thing. Oh, for those still spinning vinyl, there is also the subsonic filter and a rumble reducer.

Getting Hooked Up

     The AudioControl Richter Scale has a generous amount of possible hook ups with which to integrate it into your system. Unfortunately, the owner's manual was written with a lot less care than the designers took with the Richter Scale at the drawing boards. For example, you open it to page 3 and see a wiring diagram. However, you start reading and you realize that the words on the page do not match the diagram. They show you one way to hook it up, they walk you through another. Bluntly put, it's damned confusing. Even for a vet such as myself. Fortunately, an Audio Control "tech" is just a phone call away should you get lost in your sea of wires. I found them patient and helpful. Were AudioControl to either rewrite the manual or provide a toll free number for assistance (the phone call is on your dime), I could have gotten through this review with no complaints or reservations at all.

Once hooked up...

     I found the Richter Scale very easy to use and downright intuitive. Particularly when using it to equalize the bass in my systems, it was delightfully easy and used judiciously, it may be a real boon for your system. Fortunately for me, unfortunately for the review, I'm blessed with pretty good rooms where bass is concerned. But I put both my music systems through the paces with the Richter Scale anyway.

   Giving credit where credit is due, using the warble tone generator and setting EQ is explained very well within the manual. It was a breeze to accomplish. As I said, my rooms are very good for the reproduction of bass, but even so, it was nice to use the RS to verify this fact. When I EQ'ed my upstairs room, the sliders were almost ruler flat. I used it downstairs on my Genesis APM1s too and found it to be a little more constructive. While bass sounded good before the Richter Scale, I was able to affect improvement using the Richter Scale in the areas of articulation and slam, particularly down deep in bass's nether most regions.

AudioControl's not so dirty little secret!

     Take a look at the back of the Richter Scale and you find something interesting. There is a pair of outputs- one being labeled "invert", the second labeled "mono and bridging". But go to the owner's manual and you won't find anything at all about these outputs! What is it that AudioControl is trying to hide? I'm not sure. Perhaps they just want you to give them a call before you use these outputs because it's here that the unenlightened could get into some trouble. You see, what these outputs allow you to do is bridge the outputs of a stereo amplifier thereby creating a very powerful mono amp used to drive a sub-woofer. This is a great feature. The "invert" output does just that. It inverts phase on one channel of your stereo amp allowing it to be used as the second leg of a mono signal. Taking my Adcom GFA5500 as an example let me try to explain.

AudioControl Richter Scale      My Adcom puts out 200 watts per channel into an 8ohm load, 350 watts into 4 ohms. Now, what the Richter Scale does is combine the channels creating a mono block amp. In this case, when hooking up to an 8ohm bass speaker, what you get is a doubling of the 4ohm power rating -which, with the Adcom, means you get a 700 watt power amp (350 2). But here is where the unexpected twist comes in. When using the amp to drive an 8ohm load, what the amp actually sees due to the inverting of one of the channels is a 4 ohm load! Now the Adcom doesn't have any problems with 4ohm loads, but what if the sub-woofer speaker isn't an 8ohm driver? What if it's a 4ohm driver? Well, the amp sees a 2 ohm load and not many amps enjoy driving a 2 ohm load. Now you can see how it may be best to talk to someone from AudioControl before using this feature- particularly if multiple subs are going to be an option!

     I didn't use this feature, though I wish I had been in a position to. The only sub-woofer I had in the house with which to use it was the HSU Research TN1225HO. But it's a 4 ohm speaker and while I think the Adcom could have driven it within reason, I didn't want to torture it like that. Had I a second HSU on hand, I could have wired them in series thereby presenting the Adcom with a 4ohm load and that would have been some real fun!

     Of course, if you have a powered sub-woofer, you can also use the Richter Scale. You merely use the preamp outputs on the back in conjunction with the low pass filter. Oh, something else kinda neat here. The Richter Scale comes with a 90Hz crossover module built right in. If 90Hz doesn't do it for you, the Richter Scale comes with a certificate that you send in and get one at a value of your specification free of charge. They come in any value you could possibly need.


     As I mentioned, I really didn't need the Richter Scale in my rooms. But I very much wish I had had access to one in other places I have lived. I've experienced some really bad bass problems in the past and I wish I had owned a Richter Scale some time ago. It is for this reason that I requested the review sample. I'm sure that there are many people out there who can use this machine and will find this review handy. But I did install it in my systems and I found it to be a very clean machine. I found no obvious detriments with its use and found it to do its deed very transparently. Where EQs are concerned, you can't give it much higher praise than that because cheap equalizers have a reputation for coloring the sound, even with all sliders set flat to "zero". Again, I found the Richter Scale to add no obvious coloration to the music.

The Potis Bonus!

     OK, so I don't have problematic bass that needed heavy duty EQ. So I didn't have the appropriate sub-woofer to test the stereo amp bridging feature. Does that mean that I couldn't find a use for the Richter Scale? Heck no! I put the Richter Scale to very good use, thank you! It wasn't something that you would read about in the manual, just something that I kinda came up with on my own.

     If you are not familiar with the term "bi-amping", I'm going to introduce you to the reason that so many speakers on the market today have two sets of binding posts (connectors) on their backs. The first reason is that of "bi-wiring". Many audiophiles believe that sending two sets of speaker wires to the speaker from the amp, one for the high frequencies, the other to the bass driver, results in improved sound. Personally, I find that the benefits of bi-wiring is very speaker dependent and usually doesn't offer any appreciable benefit (maybe it should be spelled "buy-wire" because it results in selling twice the amount of speaker wire!).

     The second reason is that of "bi-amping", which is something I can get behind. Particularly if your speakers are not the most efficient or if you have speakers which benefit from different types of amplification, you may want to look into bi-amping at some point. Bi-amping is the use of two different amps to drive a single pair of speakers. One amp for the upper frequencies, a second (most likely more powerful) amp to drive the bass driver are most often used. Some like to use a tube amp on the upper frequency drivers because tubes have a liquidity and sweetness that many solid state amps do not. A solid state amp may be desired for the bass frequencies because most solid state amps have a solidity of bass and extension that few tube amps possess.

AudioControl Richter Scale      The fly in the ointment is that in order to bi-amp correctly, both amps must have exactly the same sensitivity for a given input signal. In other words, for the given setting on the preamp volume control, both amps must play at exactly the same loudness in order to keep the speaker in balance. This is a problem when combining different amps of different types from different companies. This is where the Richter Scale comes in.

     What I did was use the Richter Scale to split the signal and send the signals to two different amps. I sent the high frequencies to my Conrad Johnson MV100, and sent the low frequencies to my Adcom, then sent both sets of signals from the amps to a pair of NHT 2.9s. Using the low frequency output level pot on the front of the Richter Scale, I was able to balance two different amps by adjusting the volume of the bass amp.

     All one needs to remember is to replace the low pass filter in the Richter Scale (remember the free one you can get?) with one with a value higher than the crossover frequency of the bass driver. For example, if the woofer crosses over at 350Hz, get a filter that low passes at 400Hz, this way, the speaker's built-in low crossover will do the dirty work before the filter in the Richter Scale is even reached. This way, only one filter is at work at a time and you don't mess with the fundamental design of the speaker.

     As I said, I used the Richter Scale in this fashion with great results on the NHT 2.9s. If your speakers are crossed over low enough, such as the NHTs are (100Hz), you can even adjust the level of the bass driver just as you would the level of a sub-woofer -adding even more flexibility. If you are one of those who doesn't want to put any additional electronics in the path of the speakers, you can use a pair of "Y" connectors at the preamp's outputs, and send one signal directly to the upper frequency power amp and on to the speakers. Then you only send the signal destined for the woofers through the Richter Scale.


     The AudioControl Richter Scale half octave equalizer/analyzer/electronic crossover is an extremely cool unit. It's much better built and is more sonically transparent than is to be expected for its asking price of $350. Its extensive array of features makes it an extremely flexible machine and one that promises to come in very handy for at least one of several uses. If you have bass problems or just want to tweak bass performance or need help integrating a sub-woofer or bi-amp your speakers, I'll just bet that the AudioControl Richter Scale III can handle it. It's an audio accessory who's time has indeed come!

Good luck and listening,



More information about AudioControl products can be found at the Official AudioControl Web Site.

Text John R. Potis Jr.; HTML SMR Home Theatre and Images SMR Home Theatre & AudioControl cannot be reproduced without permission.

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Last updated 23 July, 1998

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