Chapter 4: CEDIA RP22
CEDIA RP22:
A New Era Of Uncertainty
New CEDIA RP22 tiers push for extreme, long-term loudness targets that may tempt buyers into massive SPL while sacrificing low-level audio clarity.
While I’m not seeking any grand jury indictments nor am accusing anyone of making deliberately misleading statements, if you consider the tendencies of human beings, when it comes to “Recommended SPL output capabilities”, misinterpretation is kind of baked into our decoders.
These ‘engineering-oriented objective recommendation standards’ (I’m paraphrasing, but I think it’s a fair summary), could lead to a chain of errors due to misunderstanding and misinterpretation. Consider these possibilities and factors.
Recommendations include ‘Performance Levels’, 1-4, and target metrics that have been selected from among expert input on the topic. Typically experts disagree about many things, because they deal in nuance, personal experience, and have different perspectives. I would guess that experts who contributed to CEDIA RP22 have some disagreements to some extent. And there is certainly remaining debate among experts within the industry at large. This is far from settled, or even completely spelled out in the document, because details matter.
In terms of SPL, reading off of the RP22 document on page 77, in this example screen speaker output capabilities delivered to the ‘Reference Seating Position’, “(post calibration EQ, within assigned bandwidth), without clipping. ” It provides a rough calculation example that basically factors in published voltage sensitivity, power rating, and inverse square law for ‘point source’ (as opposed to ‘line array’) propagation loss, the fall of SPL as a function of distance.
It is further clarified that these values are minimum long-term SPL capabilities, as per AES75-2022, or ANSI-CTA 2034-A, details not yet determined, nor specified how long qualifies as ‘long-term’…
It also suggests considering…
Additional speaker SPL capability at bass frequencies to allow for bass contours (for which there are no guidelines).
and
Additional speaker SPL capability to allow for +EQ (typically applied by ‘room correction, but could also be loudspeaker compensation, ‘transparent’ screen compensation, or just part of generalized tone controls.
These are important additional considerations, which we’re going to crunch numbers later, but for reference and consideration, these are ‘recommended’ targets corresponding to ‘Performance Levels’ 1-4 for ‘screen speakers’(aka, LCR), before additional SPL capabilities are considered:
Level 1: 99 dB Minimum, 102 dB Recommended
Level 2: 102 dB Minimum, 105 dB Recommended
Level 3: 105 dB Minimum, 108 dB Recommended
Level 4: 108 dB Minimum, 111 dB Recommended
Subwoofers:
Level 1: 109 dB Minimum, 114 dB Recommended
Level 2: 112 dB Minimum, 117 dB Recommended
Level 3: 115 dB Minimum, 120 dB Recommended
Level 4: 118 dB Minimum, 123 dB Recommended
People who seek a simplified understanding to make decisions, which is most of us, especially end users who are not seasoned cynical veterans of the industry, gravitate as much as possible towards collapsing reality variables into simplified, seemingly objective metrics. Then they may mistake these generalized (and debatable) recommendations as stringent requirements, assuming that the set of ‘Performance Level’ criteria the system meets will be a critical predictor of actual use benefit. In our circles within Harbottle Audio, we are seeing evidence of this, which is a little concerning for reasons to be mentioned.
These ‘Performance Level’ criteria are by definition a collapsing of nuance, for the sake of simplifying decisions, even if they are fantastic for general guidelines, becoming inflexibly attached to these sets of targets may actually prove detrimental. I. e. , “I want Level 4 Performance” instead of “I want performance that provides my optimal experience. ”
In peak SPL requirements, there is nothing that competes on a performance to dollar ratio with cheap PA equipment. Taking it one step further into loudspeaker requirements as represented in RP22, in areas where some PA equipment might fall short, you can simply reshape horns, maybe swap in equally cheap smaller drivers to improve directivity, lean even MOAR on non-linear port output and smooth out amplitude response with electronic correction, and according to RP22 guidelines, so far, you’ve got an ideal speaker. In fact, if I was only concerned with meeting performance standards for delivering sound related to RP22 recommendations, this would be my recommended course of action. Why pay for all other aspects required for comprehensive sound quality if the main purpose of the system is to simply get to ‘Performance Level 4’?
Manufacturer Perspective (Cody Hiebert). In PA gear a lot of it does not compress or distort horribly… At their maximums. PA is designed to be beaten on for extended periods of time. However, they are also not fidelity machines either. The very reason they can endure the beating is because they have very stiff suspensions and they limit stroke through the motor topology on the drivers. The drawback is that the distortion they exhibit is not THD. It’s generally IMD and Temporal distortions. So what happens when the signal deviates from the test signal averaging model, for example in the wormhole scene in Interstellar… which is like 75 seconds of pure insanity. So when the appearance of a room/system design target is ‘loudspeaker maximum linear sound levels’, we have to ask what kind of linearity we are looking for. A system that is optimized for high SPL is not automatically optimized for low SPL just because it is designed to go loud. Race cars are designed to go fast and suck at going slow. So what are we giving up?
To be clear: This is not a swipe at high sensitivity loudspeakers that use compression drivers or horns. In fact, one of the BEST audio systems I’ve ever heard was a Magico horn-based system that used horns not just for tweeters and midrange reproduction, but woofers. I am pointing out the reality that implementing techniques leveraged in cheap PA gear to standards that meet requirements of high fidelity playback preclude cheap, because there is in fact a lot about high fidelity audio reproduction beyond just loud. Such examples of ‘PA Style’ loudspeakers in the HiFi market are often exceptional in that they don’t just sound good playing loud, but they also don’t blatantly sound like PA equipment. In the same way that in other HiFi speakers you don’t hear the metal domes, the ribbons, the electrostatic panels, the paper, or the carbon fiber. You hear the audio, largely only the audio.
What I am concerned about is mistaking and fixating on a generally fine performance recommendation SPL level which is great, all else being equal, and throwing a lot of other performance capabilities under the bus because of the fixation on maximum SPL capabilities under test conditions. What happens when the content deviates from the test signal?
Something also interesting about these recommendations is that for Levels 3 and 4, they are advocating “minimum ‘long-term” output levels beyond what properly executed ‘reference level’ would ever require.
RP22 does not provide context as to why, other than for “predictable, distortion-free headroom” (Page 39), especially since content, by nature of the design of ‘Reference Level’, does not provide long-term peak output, especially to main channels. That ceiling was intended for short-term bursts that don’t sound as loud as they physically are due to the nature of our auditory system. ‘Reference Level’ ceilings were intended for brief transients, largely unused. Depending on what RP22 means by ‘Long-Term’, it is not only FAR more taxing on equipment, but also potentially causes hearing loss if the sound quality isn’t of a particular caliber, which they admit on page 14 of the Reference Audio Level and SPL Capabilities whitepaper.
As far as actual high-end users are concerned, and I mean people investing hundreds of thousands of dollars into just the audio reproduction equipment before we even address the room or video systems, I have NEVER spoken to a person who, when listening to system and content reference level output, wished to play louder. If anything, reference level comes out for a few demos, and then in real life, they rarely if ever go near it. I’m not saying anybody should or shouldn’t listen below, at, or beyond ‘reference level’ as a matter of correctness. I think people should do what they want.
However, from a ‘performance level’ recommendation standpoint, which implies sound quality as is their stated goal on page one of the RP22 document, it is interesting because it implies designing and paying for more of what you’re not going to use is a worthwhile investment for most people, when in fact it is a fringe real use case. If somebody is trying to put together an audio system with budget constraints, and blindly shooting for SPL ‘requirements’ because they incorrectly assume that they are a valid ‘standard’, that will go poorly for those seeking fidelity, detail, and true ‘immersion’.
Don’t get me wrong, EQ considerations I think are important, however, the recommendations mention EQ lifts applied to be taken in consideration in addition to these recommended levels beyond ‘Reference Level’. Moar on Moar!
Manufacturer Perspective (Cody Hiebert). Add to this, their statements about calculating the headroom needed to hit the SPL performance Level. Depending on the room design, they state typical +10dB for the LFE channel, then if you use bass management, there is another +4dB (approximate), now we need to add contouring, so if there is a +6 dB subwoofer contour, and we want Level 4: 123+10+4+6 = 143 dB at the RSP. This can include room and boundary effects as well.
My concern is that they refer to 20 Hz to 120 Hz. If someone is chasing the SPL bragging rights, this is pretty heavy stuff. For the sake of headroom and linearity, compression and coherence limits in AES75 do not guarantee sound quality. Compression is the loss of efficiency, it’s not the descriptor of linearity in all things system related. As I have stated before and many times, it is an indication. Coherence is a broad catch all of all kinds of distortions, but it will not be able to tell you which ones are the problem, therefore, when the signal deviates from M-Noise the odds of the same failure point manifesting in the same way are very low. If the program material provides the right kind of stress, it bypasses the distributed averaging of M-Noise and aggressively targets a single physical vulnerability which can cause early distortions and compression to show up when the system technically passes AES75. Like the wormhole scene mentioned above. In my opinion, CEDIA is trying to make a system for sound quality by using SPL at the worst case scenario as the metric. The issue is that those two things are not interchangeable and they do not express themselves the same way from an engineering perspective and in real use.
To be clear, depending on the equipment, there can be benefits to having more output than one might actually use, in that at maximum levels as defined by amplifier clipping, the speakers sound like utter garbage, and as you back down, things clean up, sometimes a bit, sometimes a lot.
This is the nature of loudspeakers in general terms: the further you operate away from the point of destruction, the less the system will sound like it is going to destroy itself. Is this always the case? No. Some systems just sound like they want to die after 10 watts, and some give no indication of stress until way past that.
I am not arguing against the logic or reasoning of having more than you would use, and for those who see it and would point that out, point valid. RP22 didn’t point that out, but that doesn’t mean it doesn’t exist, or won’t exist in future versions, only that I do not know the reasoning for those recommendation standards being lumped into a single index guide, ‘Performance Level’, when the thing that dictates usable sound is found outside of SPL.
Originally published by Totally Hypeless
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