In a previous blog post, I introduced YPAO R.S.C. (Reflection Sound Control), which is Yamaha’s room equalisation system. If you’re new to room equalisation, please read this post first. I will present some measurements below to show what R.S.C. is doing exactly.
Function of R.S.C.
According to Yamaha, the pure function of R.S.C. is to remove unwanted first order reflections from the sound. This should improve stereo imaging and intelligibility. As we will see there are other added benefits.
R.S.C. filters are applied before any Parametric Equalisation. In fact, all further measurements were taken using the following method on an RX-V3073 (the equivalent of the RX-A3020.
- Running a multi-position YPAO with all 8 speaker positions.
- Copying the flat curve over to the manual curve. This also copies the R.S.C filters as we will later see.
- Zeroing out the PEQ filters manually (to 0dB on all) as this will keep the R.S.C. filters but remove any parametric equalisation. This has also been confirmed by Yamaha Japan – and the measurements that follow.
YPAO succeeds in its goals – with some speakers and seating positions better than with others. I will show an example below with a centre speaker measurement. The centre speaker is located underneath a tensioned screen. The speaker is tilted upwards towards the listening positions. However, because of the room dimensions and multiple hard surfaces between the speaker and the listening positions on the sofa, the 70Hz to 250Hz region is a real issue with room modes – peaks and dips galore – that reduce intelligibility and are hard to deal with using PEQ alone.
The below frequency sweep has 1/6 octave smoothing so all that is visible that R.S.C. cut some reflections in the 60Hz to 200Hz region. The green line was measured in the “through” position, while the pink line in the manual setting with no PEQs applied. Please note that R.S.C. is applying some attenuation to the signal output. The attenuation is dependent on the filters applied by the system, so it varies from channel to channel. The graph below has been adjusted to take this into consideration.
It is interesting to note that there is some activity going on above the modal region (above 250Hz). This isn’t necessarily bad as long as the robustness of the correction is taken into consideration. For example, Dirac Live does this across the whole spectrum also, but the higher frequencies are corrected, the more correlation needs to be between samples.
Now let’s have a look at the modal region with less smoothing to see what’s really going on there. Now this is more interesting. R.S.C. actually dealt with a dip in the 70Hz to 80Hz region, where the subwoofer crosses over to the centre speaker and removed some frequency build-up because of the back and side walls between the 80Hz to 200Hz.
So what is actually going on in the 70Hz to 80Hz region? Obviously no PEQ filter would be able to fill that region in since waves are cancelling each other out – as that has been tried before on this set-up. Let’s have a look at what is going on in the phase of the signal to answer that question.
As can be seen in the below measurement without any R.S.C. filters applied, there is a phase shift in the crossover region. This is quite common.
As can be seen in the below measurement with R.S.C. applied, the subwoofer and centre speaker phase are better aligned in the crossover region, therefore removing the dip in the frequency measurement. So far so good.
Finally, let’s look at the spectrogram to see whether ringing has been improved. To be honest, ringing wasn’t much of an issue for this speaker / seating position. But as we can see in the after diagram, the crossover region looks a lot smoother and overall sound pressure levels have been better equalised in the modal region.
Subjective Listening Tests
After the above measurements were made, the PEQ filters got re-applied that smoothed the frequency response out, now having a much easier job of doing so.
Having the same PEQ applied over R.S.C. and no R.S.C. filters, though not a perfect test, the sound with R.S.C. filters applied just seemed more 3 dimensional with a better stereo image from the front and surround channel pairs. The sound of the centre channel is also improved in terms of smoothness.
What’s also clear is that the bass region is improved in terms of tightness. Even though amplitude was corrected with PEQ filters, the bass still sounded boomy in some listening positions without R.S.C. applied.
Tips and Tricks
The above does pose a challenge for those that like to have the Yamaha presence channels going along with the base 5.1 or 7.1 set-up and want to do a “full manual” configuration with R.S.C. applied. How do you measure the frequency response of these speakers after R.S.C. has been applied? Here’s a neat trick:
The easiest is to feed the left, right or surround left and right speakers with the frequency sweep signal while having the receiver in 9 channel / 11 channel stereo mode.
To hear the signal only come through the corresponding presence speaker, configure the 9 channel stereo to maximum high balance, maximum strength and maximum front / rare – left / right balance as needed. This will channel around 80% of the energy through the measured speaker, which is good enough to get an accurate measurement.