RX-V2400 YPAO Automatic EQ
Another benefit would be increased dynamic capabilities of the small speakers by bandwidth limiting them to produce intended frequency range and lower driver excursions and stresses responsible for increasing non-linear distortions. Since the RX-V2400 only identified my back channels as small (which have very limited bass extension via their acoustic suspended 4" drivers), it set the crossover to 100Hz. This setting was too high for my particular set-up. I manually reconfigured the crossover setting to 60Hz which was optimal for proper bass integration of my speaker configuration in my listening room.
YPAO (Yamaha Parametric Room Acoustic Optimizer)
Perhaps the most distinguishing feature of the RX-V2400 is its inclusion of Yamaha's YPAO parametric active room correction equalizer. Unlike many of the first generation receivers implementing room correction, the Yamaha YPAO system is comprised of a ten band (seven user) parametric equalizer (not graphical) which adjusts level, frequency, and Q factor. Graphical equalizers adjust only amplitude response at fixed frequency bands, thus are not an effective tool for room correction at all in my opinion. Yamaha does offer a graphical equalizer as a programmable user option for every channel for additional fine tuning of your systems response in case you wish to forgo the YPAO system. When I selected the "Equalizing" portion of the "Auto Set-Up" feature of the receivers YPAO feature, it allowed for several equalizing options:
- Front - Applies equalization to all channels, except the mains, to attempt to achieve closest tonal response to the main channels.
- Flat - Applies equalization to all channels to attempt to achieve flat response.
- Low - Applies equalization to all channels with emphasis on low frequencies.
- Mid - Applies equalization to all channels with emphasis on mid frequencies.
- High - Applies equalization to all channels with emphasis on high frequencies.
I initially engaged the YPAO with the "Flat" setting to equalize all of the speakers in my set-up.
It was interesting to see how the YPAO altered the frequency response of even the similar speakers in my set-up, making one realize just how much of a profound impact the room acoustics have on a speakers sonic signature. It almost makes you wonder if using identical speakers for all channels for alleged perfect timber matching is really as critical as acclaimed giving how the room acoustics drastically affects speaker performance rendering identical speakers positioned at different locations to not sound so identical.
- Q Factor: 05 to 10.1
- Gain: -20 to +6dB (0.5dB steps)
- Frequency: 63Hz to 16kHz (1/3 octave)
Note: The RX-V2400's YPAO does not operate on the subwoofer channel, nor does it function below 63 Hz. This was a bit disappointing (but understandable) since active room correction is mostly needed in the low frequencies where simple room treatments (carpets, bookcases, furniture, acoustic paneling) have little to no effect.
Note: About the YPAO Yamaha Room Correction System
The YPAO system uses pink noise sweeps to map the response of the room at the listening position for each speaker. Pink noise delivers constant power per octave and the YPAO attempts to equalize the magnitude response accordingly. However, in attempting to achieve a "Flat" frequency response, this can have deleterious affects on impulse response and also reduce dynamic headroom in the amplifier if certain frequencies are boosted as opposed to being attenuated. If for example, the YPAO equalizes a +6dB gain centered around 3kHz, then the amplifier would be tasked to produce up to four times the power for that frequency band, thus reducing headroom and potentially causing compression, and/or distortion. Additionally, if the YPAO system attempts to compensate for a speaker deficiency by creating a boost because of improper crossover design and/or some other speaker anomaly or strange impedance characteristic, when coupled to an amplifier this can actually create a dangerous effect as it can potentially drive some amplifiers into oscillation when boosting under these circumstances. However, if the speaker is flat in performance and the amplifier is not taxed at the frequencies being boosted, then the this scenario is unlikely to occur, with the only possible penalty of compensating for the direct sound of the speakers as opposed to resolving a deficiency in ambient or reflected energy in the room. Ideally, these mid and high frequency issues should be dealt with at the source, namely the room (assuming the speaker and amplifiers are designed right).
If you consider the basic relationship of sound and propagation through air given the following formula:
lambda = v / f
(where v = velocity (speed of sound =1140 ft/s STP and f = frequency (Hz) ) then we see the wavelength of sound for 63Hz = 18 ft and for 16kHz = .86 inches!
Thus altering high frequency room response will affect only a very small listening area above a couple of hundred Hertz. High frequency harmonics are generally close together, if not overlapping, and their corresponding intensities are far less than the fundamental, making them more dependent on listening position. Another issue to consider with high frequency room correction is that the measuring microphone cannot accurately measure direct to reflected sound. The goal of room correction is to correct for room anomalies, not the loudspeakers (assuming the loudspeakers are of sound design). Altering the frequency response of the loudspeakers in this fashion changes the direct sound to compensate for a deficiency in the ambient or reflected sound field caused by the room. This may in fact alter the direct to reflected sound at the listening position further deteriorating imaging of the loudspeaker and corrupting the critical first arrival of sound. Ideally active room correction would best be applied at frequencies below 200Hz where sound is more difficult for the listener to localize. Utilizing a more precise parametric equalizer may be applied to analyze room modes to construct notch filters to reduce the excessive room decay times (RT60- # of milliseconds it takes for a sound to decay by 60dB).
Alternatively, a point to consider is that some room correction systems actually do address speaker non-linearities as well as room interaction affects. The problem is that most systems are not able to distinguish between the non-linearities of the speaker versus the non-linearities induced by the room. In some cases in may not really matter. For instance, in the bass frequencies smoothing out the response may involve changing phase and gain at certain frequencies. As long as the correction is made for the listening position we probably don't care how much of the problem is speaker or room related. For that matter, I can understand why the Yamaha YPAO system does not attempt correction at very low frequencies. It would take much more reserve power than the receiver is capable of delivering. In this respect limiting the correction to a moderately low frequency is understandable and in fact quite necessary. Of course that doesn't change the fact that we would all like compensation down to the very lowest frequencies. Practically speaking Yamaha could NOT put a correction filter on the LFE output because the power necessary for correction would way overtax most subwoofers (amplifier and driver excursion). It may however behoove Yamaha to introduce their own active servo subwoofer integrating low frequency room correction with a system much like many of Velodyne's latest product offerings. A system that initially measures nearfield power response of the speaker as well as impulse response and then takes into consideration a measurement which shows room decay time would probably make for an even more accurate correction system. Now if only a manufacturer would build such a system affordably!