Velodyne SMS-1 EQ Adjustment Evaluations

EQ Adjustment Evaluations: Manual EQ
In Reference System 2 we noticed some very enlightening and amusing room anomalies. While running the SMS-1 system in SYSTEM RESPONSE mode and allowing the system to provide real-time updates to the frequency response graph, I went around the room and opened and closed doors to see what would happen to the low frequency room response at the listening position. This is the standard configuration of my room with some minor optimization with the SMS-1 system.

Optimized Reference System 2 (we only took out -5dB at 34Hz and -4dB at 48Hz)

But notice what happens when we open a closet door in the rear of the room, effectively adding 4’ of depth to the room and changing the overall makeup of the system:

Room response at primary listening position with rear closet door opened.

Yowza! That’s roughly a 10dB suckout between 40 and 80Hz! It is important to pay attention to closets and anything that will affect the size of the room and how the subwoofer pressurizes the listening environment.

To give you an idea of the potential room modes you may have to deal with, we recommend using the following calculation to plot your trouble spots and map out any potential frequencies you will have to deal with:

F = m1130/2D

Where:

F = frequency of the resonance mode in Hz
m = mode harmonic (first = 1, second = 2, third = 3, etc)
D = distance between two parallel surfaces in feet
1130 = approximate speed of sound in feet/second

Here are the room mode points for Reference System 2:

The areas marked in red are the room modes that can be potentially troublesome since they compound between first, second, and third harmonics – making the net effect worse than if none of the frequencies overlapped.

EQ Adjustment Evaluations: Auto EQ

We knew what the best setting for the room was after evaluating the system manually and making our adjustments. Now it was time to see how the SMS-1 would treat the room when running in Auto EQ mode. We weren’t surprised when, like a doctor fresh out of medical school, the SMS-1 was a bit overeager in wanting to solve all of our low frequency problems. To give it a really difficult (but still real-world) task, I opened up the closet door at the back of the room and let the Auto EQ mode “have at it”.

We see here a nice deep cutout between 45 and 65 Hz. Typically in a room like this you would want to play with phase a bit before attempting to EQ-out a gaping hole of this size (which is honestly, impossible to fix via EQ).

Here is the SMS-1’s interpretation of the solution:

Does the graphed frequency response look better? Well, yes – but to understand more about what is happening we need to examine the settings. The Velodyne applied over 9dB of gain (in two bands) from 50-60Hz. This boosted frequency information that really wasn’t there to begin with – at least not in the way you think. In an attempt to smooth over the large hump from 25-40Hz, the Velodyne applies an equally aggressive cut in gain – this time over 30dB combined across the affected frequencies. The Velodyne SMS-1 system is simply applying its parametric EQ in an intelligent way to get the results to match a flatter curve. And, at that, it is doing an excellent job. What the user will need to understand is that it is IMPERATIVE to get the subwoofer integration as good as possible before allowing the SMS-1 to take over and adjust the levels to smooth out the response. Close those doors, move the sub, adjust phase – do what ever it takes to get a better starting point. Then, allow the SMS-1 to work its magic, or better yet do a manual adjustment and dial in the frequency response to a more realistic setting to avoid needless over boosting or cutting of frequencies.