Without a doubt, the component with the single biggest impact on a system’s sound is the room itself. You can connect a flagship speaker system to a killer rig of electronics and feed it the highest resolution audio files through the purest silver cabling, but put it in a crappy sounding room, and you’re going to get crappy–or at least heavily compromised–sound.
For most of our installs, “audio calibration” probably starts and ends with plunking the sub in a corner, then running some pink noise generated from the receiver and using a handheld SPL meter. If the system supports some onboard correction like Audyssey, ARC, Dirac, YPAO, or other, then maybe we’ll put the included mic at a few listening positions and run the automated setup. Did the correction help? Does the room sound good? Generally this is an arbitrary, subjective answer.
|The miniDSP 2x4 HD DAC+DSP, UMIK-1 USB calibrated
microphone, and 2x4 HD1 software plug-in.
A visit from ARCOS Master Calibrator and Home Acoustics Alliance instructor, Adam Pelz, opened my eyes to the benefits of even moderate audio calibration. After Adam unloaded his Pelican cases of calibration gear, he ran some test tones and took some measurements in our theater. After looking at the results, he loaded some correction filters into a parametric equalizer, which he connected to our sub. The results were immediate and apparent.
While Adam has years of experience and training and travels with gear costing on par with a 7-Series BMW, he told me quick, “Turbo Cals” can be performed for far less while still delivering huge benefits to the system’s bass performance.
As I was reviewing the OEM Systems ICBM four in-wall sub system (review available online), it seemed like the perfect opportunity to bring in an audio calibration system for review as well, not only to measure but also optimize the bass performance and learn a bit more about audio calibration.
I reached out to miniDSP and requested a 2x4 HD DAC+DSP, UMIK-1 USB calibrated microphone, and 2x4 HD1 software plug-in. Along with this I used the free Room EQ Wizard (REW) Room Acoustics Software (download at www.roomeqwizard.com). This entire measurement and correction suite retails for $290 and you only purchase the mic and software plug-in once, just purchasing a miniDSP for each project as it stays onsite. As miniDSP is located in Hong Kong, the only real means of reaching them is through an email contact-us link. Even so, they were prompt in responding and shipping the product.
Beyond being an asynchronous USB DAC capable of handling up to 192kHz audio files, the 2x4’s main role for integrators will be room correction. The 2x4 has two inputs which could either be left and right audio or two separate sub inputs, with four outputs, say for multiple powered subs, or front left/right and two subs. Inputs and outputs are configured in a simple matrix
Though inexpensive, these are incredibly powerful and flexible tools that will let you go deep down the calibration rabbit hole if you desire, and there are a significant amount of notes and forum information for both the miniDSP and REW should you need help. Fortunately using the system for basic measurement and correction is simple enough once you get the hang of it.
Start by connecting the UMIK-1 microphone and an audio output from your computer to the audio system (I just used a mini-jack to RCA cable out of my laptop’s headphone out). After opening REW, go to preferences and select the UMIK-1 and load the microphone calibration file that comes with the microphone.
|The microphone carrying case
REW offers a ton of useful tools that will come in handy during audio installs. For example, a tone generator can play a variety of test tones that are terrific for locating rattles in a room or for demonstrating uneven bass performance and the SPL meter with calibrated mic is quite accurate. A “Room Sim” is helpful to plot a room’s dimensions and predict the best subwoofer/seating location(s).
A “Measure” tab brings up a window where you select the frequency range of the test tone (ie: 10 Hz – 100 Hz for a subwoofer). Once the measurement is taken, you will get a graph showing the dB level at each frequency. Take several measurements at different seating positions to get an idea of the in-room response, and overlay multiple measurements together to see an average.
An EQ tab within REW can automatically generate a series of filters to correct the response in the room that you can then save and load into your miniDSP. You set a target curve and then tell the program how closely to try and match the target and how much boost to allow.
Alternatively you can manually set up to 10 EQ filters for each channel in the miniDSP, selecting the frequency, amount of gain or cut, and Q (sharpness or width of filter). Calculate Q by looking at your target frequency, say a 6dB peak at 55Hz. Find the point where the signal is +/- 3dB from that point, say 52Hz and 60Hz. Subtract those numbers (60-52=8) and divide the target frequency by the result (55/8=6.875). So you would insert a -6dB cut at 55Hz with a Q of 6.88.
After you’ve loaded your filters into the miniDSP, go back and re-measure and compare the results. Fortunately filters load in real time so it is a fast process to go back and forth between measuring and EQ’ing until you get the best performance. When finished you can prepare a graph that shows the before and after measurements in the room and present to the client.
This is certainly no substitute for taking an audio calibration course such as those offered by the Home Acoustics Alliance. However, this is a terrific way to get your feet wet in audio calibrations for a minimal investment, add a justifiable “audio calibration” line item to your installs, and leave a client’s home with measured proof that you have made their system sound as good as possible in their room.
(Sincere thanks to Adam Pelz of REAL Audio for help with this review.)
Excellent low-cost way to definitively measure, correct, improve bass response in client’s rooms; great wealth of online community support
► Analog Devices SHARC ADSP21489 DSP
► 32-bit/192 kHz sampling
► Inputs: 2 RCA analog audio, Toslink optical digital, USB Audio; Outputs: 4 RCA stereo audio
► Parametric EQ on all input and output channels with crossovers up to 48 dB/octave and advanced biquad programming for unlimited range of filter and crossover types
► Requires miniDSP 2x4 HD1 plug-in module and UMIK-1 USB microphone (sold separately)
► Dimensions: 4.68 x 1.06 x 4.21-inches (WxHxD)