TECHNICAL SERVICES (Lab based AND on-site)
In addition to product development and management, we are able to do numerous on-site acoustical and electrical tests. I note some of my testing methods below and short discussions of their benefits.
I am a HUGE believer in the the KISS method (Keep It Simple Stupid). From a business standpoint we must constantly balance speed and quality in acoustical testing. The tools are available today to make very good "first shot" tests and 90% of the time they can point us to problem areas needing more review. If the time and money exists, then we can do some heavy lifting with in-depth testing.
The bulk of my preliminary testing is done with PC based software. It is fast, easy to setup, and usually gives very good first impressions of the system performance or problem areas. Once we know the target areas needed for further review, we can then pull out the heavy equipment such as the Audio Precision or LinearX LMS system.
I also begin my tests with simple, but effective USB based measurement microphones. Again, they are fast, simple, and often give us very good first indicators of performance. Once we have good initial data, the higher quality Bruel & Kjaer mics and dummy head are available for expanded measurements.
ROOM & SPEAKER FREQUENCY ANALYSIS (1/3rd, 1/6th, 1/12th octave) Like a doctor trying to make a first analysis on a sick person, a simple x-ray often gives quick answers or points them to a better test to use. The PC-RTA may not seem as technologically "elegant" to some field experts but I have found after many years it quickly strips away many of the obvious issues allowing more time to focus on root issues. My method is a "front-to-back" approach which may sound obvious but many people start at the listening spot and try to make assumptions working back to the source. This is loaded with variables and interpretive flaws. First I make a quick speaker analysis in a "semi" near-field measurements at 1/2 meter. This is certainly not an anechoic chamber quality test but it does give a quick snapshot of the speaker more as a confirmation of overall good performance. If something odd shows up in the data (e.g., severe peaks or dips) we can see that, and often hear it, right away. This approach also gives us some good data to subtract out of of far field, room influencing data. Next we move to our room measurements near the listening positions but I prefer taking many data sweeps at multiple locations around the listening spots then averaging out the data which the PC-RTA does beautifully and quickly. Rarely is listening done in one spot so this approach yields excellent room frequency response data once we reference the averages to the source data. Such "regional" sweeping gives us a nice and accurate view of room modes which are often ignored or misdiagnosed below the 100-200 Hz transition region. Speed is the key here helping point to the room issues that we can break down better in the frequency and time domains once we have a feel of the problem area which tends to show itself quickly in the frequency domain. |
Although many analyzers and methodology have surfaced in recent years offering a flood of testing options, I favor my trusty PC-RTA analyzer software on my laptop using a good USB powered mic. It just works well.
I have had good experience with time domain analysis using the TEF-20 and Audio Precision analyzers for years but lean more to recent, low cost software emulations for the PC. Why? Portability and flexibility. Surprisingly, many of these low cost software solutions have lead to data file formats that yield direct programming implementations into the DSP realm. There are several DSP hardware solutions that accept direct input from these files with inverse data transfers. As noted above, our time domain corrections are usually limited to adding absorption to the room to pull down reflections. These data files work very well in the frequency domain but they are also starting to be used in the time domain with some success per numerous writings. I have not had much interface with these but I can see the possibilities in at least identifying the reflection areas so we can try to modify the room where possible. Much more work is developing on high powered DSP time solutions but it continues at a glacial pace unfortunately. |
Using the LMS technique I can maintain high frequency resolution over many decades that are simply not possible with FFT systems. Here again, there is a huge advantage in simplicity of setup and speed of operation. Yes, an FFT approach can be just as simple and fast, but there is constant tweaking of data to ensure no outside poisoning of the signal. Still today, there are few other good ways to derive detailed frequency response resolution at very low and high frequencies without resorting back to conventional swept response data without a complex setup and few are very portable. Ironically, the ability to merge close mic data with far-field data remains difficult unless reverting to the LMS approach or going through substantial post-data acquisition manipulations. I remain a strong believer of the LinearX system when going into environments loaded with variables. The portable LMS system fits my requirements for portability and confidence in data, and again....it just works. |
I am able to do small signal measurements of any audio device in the analog or digital domain via the AP Dual Domain functions. My expertise has involved years of amplifier and electronic crossover testing for the home and car audio world. A complete study of high current power amplifiers is possible with a full report of gains, frequency response, THD+N, phase, crosstalk, Signal to Noise and numerous other standard audio testing. A sample test report is available upon request. There are occasions that I also use the LinearX LMS system due to its analog tracking capability, accuracy at low frequency, portability, and quick setup and overall speed. Again, simplicity prevails when deemed the best tool in the toolbox. |
NEUMANN HEAD ROOM AND HEADPHONE DATA ACQUISITION But, as an acoustical measurement tool, it was limited due to the odd frequency response characteristics and timing cues thus the fallback to conventional microphones for room measurements. Fortunately in the 1990's, thanks to the affordable developments in digital audio measurement modeling tools, the understanding and application of HRTF's (Head Related Transfer Functions) became popular. This refueled the interest, and value, in using the dummy head as a measurement tool. I feel the head is now a mandatory tool for taking acoustical measurements with multiple speaker locations. Even in smaller home theater installations, it is critical to measure the frequency response at the "shadowed" ear in a listening position. If the shadowed ear is receiving too much data bouncing off its wall from the opposite side, this destroys our image. If the shadowed ear receives too little information from the opposite side, this yields a listening experience that is too "anechoic" thus very dull or simply unenjoyable. With the huge increase in headphone acceptance in the last years thanks to the IPod, the head is regaining interest in characterizing a listening event that is enjoyable for a person with headphones only. Although the dummy head was originally intended for diffuse field measurements, the Neumann head is actually a very good tool for characterizing headphones and ear buds. We don't necessarily equalize for a "flat" response but the head is certainly a good tool for a "smooth" response. With the newer inverse equalization software available, we can measure a reference set of headphones, measure another set of headphones, and apply corrective equalization to match the reference set. No, this will NOT make $5 headphones sound like a $500 set but I have found it possible to make $100 units approach $500 units. Also, setting up adjustable EQ "presets" I can quickly simulate various headphones on the market and make recordings for a customer to quickly demonstrate their differences. |
During the 1970's and 80's the dummy head emerged as a very popular tool for life-like recordings. The Neumann head provided very low noise microphones that could now be used in recording of live events with remarkable realism when played back over headphones.