Feature Article

A Tale of Two Subwoofers: How I Achieved Bass Nirvana with the Velodyne SMS-1 Digital Drive Subwoofer Management System and MIC-5 Multiple Microphone System

Part I

October, 2006

John E. Johnson, Jr.


Secrets Home Theater and Audio Review - Vault


You may remember when I installed some room treatments in the Secrets lab, back in the latter part of 2004.

It worked very well, but one of the things that I noticed was that the huge amount of bass that I had before was diminished. Of course, much of what I was used to included all the reverberation from the room. The bass was now tighter and cleaner, but it was not as loud.

"Oh well," I thought, "it is more accurate."

This is part of the problem in high fidelity. You really have to get accustomed to the idea that less is more. In other words, reducing distortion and reverberation actually means less sound. That is not easy to deal with at first. I have had friends over to listen to great sounding systems, and they think that something is missing. Yes, something is missing. The bad stuff.

This is particularly hard to deal with in terms of bass. The reason is that distorted bass does not sound bad. It can actually be appealing. Just listen to some of the cars on the road at a stoplight. You can hear the pounding bass from big woofers in automobiles a block away. Most of it is harmonic distortion, but because the frequencies are so low, it does not bother the ears, and consumers can crank it up as loud as they want.

We would never put up with that kind of sound quality in the high frequencies. Such distortion is very unpleasant.

So, like many people, I had become accustomed to loud bass, much of which was reverberation and corner loading.

There I was, with more accurate bass, but it was not as much fun as it was before.

The SMS-1

In December of 2005, Roger Welch reviewed the Velodyne SMS-1 Digital Drive Subwoofer Management System for Secrets. It is one of a few outboard subwoofer EQ components that let you flatten the bass frequency response in your room.

The SMS-1 includes a microphone which picks up a sine wave sweep produced by the SMS-1, and generates a display on your TV, via an S-Video connection from the SMS-1, which shows the response as you add EQ in several parametric bands. The screen shot shown below is from Roger's original review.

This type of presentation is called an RTA, or Real Time Analysis. The SMS-1 generates a low frequency sine wave sweep, through your subwoofer, and the microphone (which is placed in your listening position) picks it up and transmits the sound back to the SMS-1, and the curve is shown on your TV screen. You simply move the sliders on the EQ bands until the response is as flat as you can get it.

OK, so, when Bruce Hall of Velodyne released the latest version of the SMS-1 software, which lets the SMS-1 automatically adjust the EQ bands to achieve a flat response (within 3 dB), I decided to see if this product might help me with my problem.

I have two Velodyne F-1800 subwoofers in the main lab, one in each front corner, behind and to the side of the main speakers, as shown below. Since they are configured as stereo, I needed two SMS-1s.

If you are wondering about the other equipment in the photo, that is a BAT VK-5i balanced tube preamplifier on the top of the rack at the left wall, with a Lexicon MC-12B SSP on the second shelf, one of the Velodyne F-1800s in the left corner with the SMS-1 on top, a Lamm M2.2 power amplifier on the floor in front of the left Carver Amazing Mark IV Platinum ribbon speaker, a computer for testing equipment, two McIntosh MC-1201 power amplifiers, then the right channel Mark IV Platinum speaker, Lamm M2.2, Velodyne F-1800, and second SMS-1. The component with the cables on top, on the floor at the right, is an Audio Precision test instrument. To the left of the left chair are components not seen in the photo, including McCormack CD transport and DAC, BAT VK-500 power amplifier, and McIntosh MC-602 power amplifier. Behind the camera are a pair of Carver Amazing Mark IV Silver ribbon speakers, which are smaller than the Platinums.

Another equipment rack is on the way, for placing a second preamplifier (Mark Levinson) and SACD player (McIntosh). The BAT drives the McIntosh power amplifiers, and the Mark Levinson preamp will drive the Lamms. So, there will be two complete two-channel reference systems which sound slightly different from one another. I have not decided on the speakers that the Lamms will drive. I took this photo with a 17mm lens on a 35mm camera, so the perspective is somewhat distorted. The room is not the tunnel that it looks like. Those Carver speakers are nearly 6 feet tall, and a 100" motorized projection screen will come down between them as soon as I can get the time to install it. The projector will, I hope, be a three-chip DLP 1080p.

I placed the two SMS-1s one on the top of each subwoofer. A photo of the left subwoofer with an SMS-1 sitting on top is shown below.

Right and left channel XLR outputs from my BAT VK-5 balanced preamplifier were connected to the XLR inputs on the SMS-1s, and the XLR outputs from the SMS-1s were connected to the XLR inputs on the subwoofers.

Room frequency responses before and after EQ with the SMS-1 have already been published in the original review. For the sake of this article, I decided to be a "busy consumer" who does not have the time or inclination to go through the manual EQ procedure with a TV connected to the SMS-1 and slide the parametric bands all around to get the flat response while watching the response change on the screen. I would be a consumer who wants to just connect it up, turn it on, get a Self EQ, and go back to watching movies.

So, what I did was use the SMS-1 remote control to select the Self EQ sequence (by pressing 321), which generated the sine wave sweeps several times, made its own adjustments to the EQ, and it was done!

I EQd each subwoofer separately, with its SMS-1 microphone sitting on top of my listening chair, approximately where my head would be.

Therefore, the left channel subwoofer was EQd from its position to have a flat response at my chair, and the right channel subwoofer was EQd from its position as well. The EQ was different for each subwoofer, obviously.

Click Here to Go to Part II.

Copyright 2006 Secrets of Home Theater & High Fidelity

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