RBH T-2 Measurements and Analysis (cont)
Figure 5. LMS Full Bandwidth Frequency Response Comparison of T-2 and
(1266-LSE + 1010-SEP)
Pink: T-2 System
Blue: 1266-LSE + 1010-SEP Subwoofer
Note the apparent 3dB suckout from 1.5kHz to 3kHz seen in the T-2 response was mostly nullified by simply repositioning the speaker system with respect to my entertainment center as seen in FFT plot in Figure 3 .
While this plot doesn't look pretty, it is a realistic representation of how loudspeakers interact in a room when measured at the listening position using a high resolution measuring system ( > 1/18th octave resolution) such as LMS. Since my original reference system was more calibrated towards Home Theater (bass levels elevated), I attempted to closely match levels with the T-2 System to show a direct comparison. In reality, I usually cut subwoofer levels down a few dB when listening to music, particularly two-channel audio. Figure 4 gives a much better representation of how the bass levels were ultimately set for the T-2 System during my music evaluation.
I would consider the T-2 measurement to be more linear in the treble range. The reason being that the frequency response of the T-2 System fits within a tighter overall window of + or - 2.77 dB from 800Hz to 10KHz, where the 1266-LSE + 1010-SEP system measures + or - 3.85 dB within the same range.
Another important factor to consider is the overall trend of the curve. A general rising or falling trend to the curve is much more audible to the ear than an occasional narrow band peek or dip in frequency response. Now that being said, we are comparing apples and oranges to some degree. Both systems "play" into the room differently. The measurements taken do not distinguish the differences between direct and reflected sound. However, they do show the non-linearity that results from the interaction between direct and reflected sound. This is especially evident in the midrange and mid bass frequencies. Take note that the T-2 System has 4dB more output at 20 Hz when compared to the 1266-LSE + 1010-SEP system which may partly explain why the bass in with the T-2 System was both felt and heard more so than with the 1266-LSE + 1010-SEP reference system.
The on-axis response of the Vifa D27tg tweeter utilized in the T-1 satellite modules is almost ruler flat out to 30kHz. Notice the 30 degree off-axis response of the tweeter is similar to the in room response I measured at the listening position. This indicates the baffle and driver alignments are not interfering with the excellent off-axis response of the tweeter.
Figure 7. Impulse Response of T-2 System
A quick check of impulse response using LMS demonstrated that no nasty resonance anomalies due to poor driver/crossover integration, ringing, or cabinet vibration was present in this system as indicated by the short settling time and lack of bumps thereafter.
About LMS and FFT Measuring Methods
The Fast Fourier Transform (FFT) is a mathematical filtering process that determines the frequency content of a time domain signal. The dual-channel FFT is the transfer function comprised of the complex comparison between the electrical signal inputted to the loudspeaker and the acoustical signal produced by the loudspeaker.
LMS (Loudspeaker Measurement System) provides the ability to achieve very high log frequency resolution across many decades of frequency. Unlike FFT analyzers, LMS provides log resolution of frequency data points, while still maintaining the ability to gate signals for quasi-anechoic SPL measurements. LMS measures frequency response directly, requiring very little CPU overhead no complex FFT transform to solve. Excellent log resolution is obtained at both the low and high extremes of the frequency spectrum.
