Velodyne SMS-1 Measurements and Analysis
Test Case #2 – Compensating for Room Conditions
The following measurements and analysis was conducted in Family Room System #1 of the Audioholics Showcase Home. This is a most challenging room since it is open-ended, making it all but impossible to pressurize the room no matter how many high caliber subwoofers you integrate. Since the room is essentially a larger home theater room in terms of cubic feet, predominant low frequency bass modes aren’t quite as prevalent as one would see in typical rectangular shaped rooms with the listener within a few feet from a back wall. Suffice it to say, the listening position still incurs uneven bass response. Only passive room correction (ie. bass traps) and a PEQ system such as the Velodyne SMS-1 can improve upon, short of relocating the subwoofer or listening position which are two variables not able to be manipulated any more optimally than they currently are without severely sacrificing room functionality or aesthetics.
Measurements & Analysis
The subwoofer of choice used for these tests was no other than the Axiom EP500. The subwoofer response was set to flat via the back panel EQ’ing options. Its optimal location was found using our Crawling for Bass techniques in conjunction with the Sencore SP-295C FFT Audio Analyzer.
We settled upon a front left wall placement about six feet from the corner and directly behind the left couch. While the sub performed quite well on its own, it was obvious that further tweaking beyond level, crossover frequency and time delay was needed in order to linearize its in-room response and achieve a better splice between the bass-managed speakers. In this case all of the speakers in the system were bass-managed.
Figure 1. Screenshot of SMS-1 in bypass mode
The response here looks too good to be true showing 80dB +3/-4dB response from 20Hz to 200Hz. The response shown appears to be smoothed, perhaps 1/3 octave or so.
Figure 2. Screenshot of SMS-1 after Custom Calibration
With some fine tuning of frequency, Q and level at selective bands, I managed to smooth out the low end frequency response and reduce some of the bumps and dips in the response, particularly below 25Hz and at the crossover region (80-100Hz).
I wanted to see a more accurate representation of the system response, so I hooked up my LMS system to measure pre and post calibration.
Figure 3. Listening Position Measurement of SMS-1, 1/3 octave smoothed
Purple Trace: SMS1 Bypassed, On Axis Listening Position Measured response was +/- 5dB from 20Hz to 100Hz
Green Trace: SMS1 On Axis Listening Position response was 81dB +/- 4dB from 20Hz to 100Hz
The suckout from 30-40Hz was significantly reduced 3dB which required a boost of a couple of key frequency of the SMS-1 between 1 to 2 dB. A peak at 25Hz was reduced by 2dB while the response was flattened down 2dB from 80 to 100Hz, thus improving the splice between the subwoofer and bass managed speakers. The dips centered around 120Hz is a measurement anomaly caused by the mic position relative to the floor and satellite speakers woofers (more on this later). This dip is not a true response at the listening position and should be ignored. The 50Hz dip is a bit more complicated and will be discussed later on in this review addendum.
A note about boosting: use the boost option sparingly to avoid excessively overdriving your subwoofer or its amplifier. It’s usually not a good idea to boost, but if you see a null improve by adding 1-2dB of gain, then it might be a good idea to take advantage of it. As always, when making these adjustments take care to spot check adjacent areas to ensure that you are not creating large dips and peaks for seats outside the primary listening position.
Figure 5. Left Listening Position Measurement of SMS-1 System Response, 1/3 octave smoothed
Red Trace: SMS-1 Bypassed, Off Axis measurement
Blue Trace: SMS-1 Off Axis measurement
I picked the worst possible seat in the room which was about 2 feet from the subwoofer near the left side wall which incidentally has the worst viewing angle. This is the seat you stick your mother in law in, or your pesky neighbor who always unexpectedly shows up to watch a sporting event or movie on your system. You can see about a +12dB bump centered around 40Hz from a resultant room mode indicating this is not a good seat unless you are into gangster rap music, or want to feel the nauseating tactile response of the EP500 at full tilt during explosion scenes from War of the Worlds. Trust me I sat though this when entertaining some “invited “guests and it felt as if my couch was loaded with tactile transducers.
The point of this measurement was to show that even in the worst listening location, the SMS-1 didn’t muck up the response despite the fact I EQ’ed the sub in the optimal listening area. By doing so, it helped take away some of the energy in the room that would otherwise excite dominant modes, which is evident by the improvement in system bass response of -3dB from 40Hz down to 30Hz.
Although the system’s bass response sounded cleaner and had more punch to it, I wasn’t completely satisfied and decided the next day to spend more time tweaking it via more refining PEQ band manipulation, LMS, and a lot of patience. If you aren’t yet a believer of the Axiom EP500’s capabilities, then I suggest you get my neighbor’s dogs’ opinion. In the process of calibrating, about four of my neighbor’s dogs were going nuts, creating quite a ruckus. I could hear my neighbors yelling at their animals - not understanding why they were barking so much for no apparent reason. I didn’t have the heart to tell them why.
Figure 6. Optimized Subwoofer Response with SMS-1 Engaged, 1/3 octave smoothed
The response was a bit smoother than what I was able to accomplish the prior day. I did sacrifice a little low end response below 22Hz but moving my couch a few inches along with tweaking the PEQ helped to reduce a significant null in the 70-90Hz range which is much more perceivable than losing a few dB below 22Hz. The overall response from 22Hz to 100Hz +2/-3dB. Very good indeed!
