CEA-2010 output: Room gain adjustment ready reckoner

Mr Wolf

Well-known Member
Not long ago I read this SVS article that explains how room gain works.

What is Subwoofer Room Gain

So, according to SVS, room gain starts at a frequency that is twice the wavelength of the longest dimension of the room which is almost always its length. For every octave below that starting frequency you should get 7-9dB of room gain which adds to the in-room SPL output of the sub. So the smaller the room and the lower the frequency the more room gain you should get. This gain is separate to boundary gain you get from corner loading.

Anyway, I used this logic to create this ready reckoner table that can be used by anyone in any room. The table assumes a 8dB per octave (i.e. mid-point of 7-9dB) so the actual result may vary +/- a few dB.

1629108421099.png


So to use this table, take the longest dimension of your room and find the closest one to it in the left hand column. The numbers in that row represent the estimated room gain dB you may get at different frequencies. The table has the same frequency points as CEA-2010 output testing so you can use them to see how room gain can flatten out the measured CEA-2010 maximum SPL output of a particular sub.

As an example, this is how it impacts the output figures for one of my PB-3000 subs in my circa. 5.5M long room (highlighted in blue in the table) .

1629108592706.png


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Anyway, hopefully you may find this useful when evaluating your next sub purchase decision.
 
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Dobbyisfree

Well-known Member
Really interesting, thank you. And, yes, useful for many members!

As you said to me recently, I need to look (at our listening levels) for a CEA with 20Hz at 100dB minimum (or perhaps 97dB as there are two subs). I assume I can subtract from this the room gain now?

As you've pointed out though, the complexity of the corner placement also affects this. And, on top of that in my case, it is two subwoofers one in each front corner :zonked:

Quick question while you are there, what is the frequency of the Denon test tone for subwoofer? The one in the manual "test tones" in speaker settings (not the Audyssey which is very different). Or is it a peaked curve (i.e. a wider spread of noise across the low frequencies)?
 

Mr Wolf

Well-known Member
As you said to me recently, I need to look (at our listening levels) for a CEA with 20Hz at 100dB minimum (or perhaps 97dB as there are two subs). I assume I can subtract from this the room gain now?
No, I said you a needed a pair of circa. 100dB capable subwoofers in-room at your MLP (not CE-2010 output) to cover your -15dB listening level. -15dB = 101.5dB max peaks and two subs gives you at least 4dB more so 97.5dB each, 100dB gives you 2.5dB headroom (circa. 3dB headroom is considered a good idea to avoid risk of compression).

CEA-2010 requirement will be less due to boundary gain and any room gain will reduce the output requirement further at the frequencies where you get it.

For "Medium" 1,500-3,000Ft3 rooms, Audioholics' Bassaholic room rating protocol states that to achieve reference level, if it is to be corner loaded in the room, a sub needs to be able to hit >100dB on CEA-2010 [email protected] basis. So at -15dB volume and with two subs (-4dB) that would be 19dB less than this so >81dB per sub. They're not allowing for any power headroom though so personally I would add 3dB to that so that would >84dB per sub (minimum of 2) on CEA-2010 [email protected] basis.

Where you get room gain this requirement may be less but also be aware of equal loudness curve so some people might want up to 10dB more output at 20Hz than say 80Hz. You'd need a suitable EQ system to implement a "House Curve" like this e.g. MiniDSP.

Quick question while you are there, what is the frequency of the Denon test tone for subwoofer? The one in the manual "test tones" in speaker settings (not the Audyssey which is very different). Or is it a peaked curve (i.e. a wider spread of noise across the low frequencies)?

Good question. I have no idea. It might be something like a 40-60Hz noise tone as all subs (even tiny ones) should have decent output level there.
 
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Dobbyisfree

Well-known Member
No, I said you a needed a pair of circa. 100dB capable subwoofers in-room at your MLP
Sorry that I had misunderstood you on that. I get you now. Thanks for taking the time to come back to me.

Good question. I have no idea. It might be something like a 40-60Hz noise tone as all subs (even tiny ones) should have decent output level there.
Compared to test tones (where it says the frequency although they could be a lie?) on Youtube, it sounds lower than that more like 30-35Hz. But it could be, as you say, a noise from 20-60 so what you hear depends on your subwoofer/s!

This may be the sort of thing that @dante01 would know please?

At the weekend, there were "more mature" people in our house (~70 years old) and they wanted to see if they could hear it. One could, one couldn't*. I raised it up to +2dB on master volume to see if they could hear it.

No matter how much you all think my Storms are wimp's subwoofer; at least this let me discover that they have more to them than the Quakes. I could take the Quakes only to about (roughly) -8dB on master volume before they would start "fumbling".

* - Sat after a few drinks, I thought to myself how scary it is that my hearing will fade and in my drunken state thought that I'd better go and borrow money now for more AV stuff while I can still tell the difference and get more pleasure out of it!
 

Dobbyisfree

Well-known Member
Cancel my comment of Quakes versus Storms, it appears from elsewhere on AVF that the manual test tones completely bypass Audyssey EQ. Therefore, it's not a fair comparison from sub to sub as it would depend on the settings on the actual subwoofers. You'd have to switch between them and listen for the difference.
 

IWC Dopplel

Distinguished Member
REW room simulation seems pretty good and did reflect my nodes and 34 an 68 and the null at 25Hz

As I now run all speakers full range and add with a Mini DSP 10x10HD the additional required bass from the subs, this I feel has really improved the bass response (more even and more dynamic) so if you can drive some more low frequencies in parallel with subs I personally think its a very good thing

Screenshot 2021-05-25 at 03.15.11.png
 

Conrad

Moderator
Cancel my comment of Quakes versus Storms, it appears from elsewhere on AVF that the manual test tones completely bypass Audyssey EQ. Therefore, it's not a fair comparison from sub to sub as it would depend on the settings on the actual subwoofers. You'd have to switch between them and listen for the difference.
Just run non-avr based test tones then. Youtube, Spotify, etc. have them
 

Gasp3621

Distinguished Member
This gain is separate to boundary gain you get from corner loading.

I think it`s also worth pointing out what you also get outdoor vs. in-room corner loaded using the Audioholics article. You can do the math depending how far the sub is from listener(s).



- Half space (ie.groundplane) is how Audioholics and most acoustic professionals measure subwoofers.

- In order for the sub to achieve the most output possible indoors, it is assumed the listener will corner-load the sub which puts it into 1/8th the volume as it sees in freespace. Each halving of the sphere the acoustical device sees corresponds to a +6dB increase in SPL assuming distance from the acoustical device to the microphone is held constant and assuming the walls are not lossy while also ignoring any additional room gain factors. Thus corner-loading a sub (1/8th freespace) increases the SPL output +12dB compared to our groundplane (Half Space) measurement.

- In real rooms the walls are not infinitely long and are also lossy so boundary additions are closer to +3-4dB for each surface added yielding a net gain of +9dB to +12dB for 3 surfaces instead of +18dB theoretical. However, SPL fall off in real rooms is more like 3dB for every doubling of distance instead of 6dB which happens in an anechoic environment.

- So we now know that simply adding +9dB (for RMS data) will give us an equivalent corresponding corner-loaded room output at 2 meters. Again, this does not factor in any room resonances which varies from room to room depending on room dimensions, position of the listening seats and room furniture, ceiling contribution, and the quality and kind of construction of the room.

- It is reasonable to assume the subwoofer will be (on the average) at a fixed distance of 4 meters from the listening area.

So in order for us to translate our 2 meter groundplane data to a corresponding 4 meter corner-loaded approximation, we can simply add 6dB (+12dB for two additional surfaces and -6dB for doubling of distance) to our SPL data. IE. If a sub measures 110dB 2 meter groundplane, the corresponding in-room output if the sub was corner-loaded would be roughly 116 dB at 4 meters.
 

Dobbyisfree

Well-known Member
that would >84dB per sub (minimum of 2) on CEA-2010 [email protected] basis.

And that doesn't include corner loading? So, if Gasp's corner loading estimations are correct then, even at 5.2m to MLP this may explain why my romcom subs are aren't actually that bad? And, estimation of course as no CEA data, but potentially something price/power/size equivalent of two KLH Windsor 12s would probably comfortably achieve this target?
 

Mr Wolf

Well-known Member
For "Medium" 1,500-3,000Ft3 rooms, Audioholics' Bassaholic room rating protocol states that to achieve reference level, if it is to be corner loaded in the room, a sub needs to be able to hit >100dB on CEA-2010 [email protected] basis. So at -15dB volume and with two subs (-4dB) that would be 19dB less than this so >81dB per sub. They're not allowing for any power headroom though so personally I would add 3dB to that so that would >84dB per sub (minimum of 2) on CEA-2010 [email protected] basis.
I had factored in corner loading.
 

Gasp3621

Distinguished Member
And that doesn't include corner loading? So, if Gasp's corner loading estimations are correct then, even at 5.2m to MLP this may explain why my romcom subs are aren't actually that bad? And, estimation of course as no CEA data, but potentially something price/power/size equivalent of two KLH Windsor 12s would probably comfortably achieve this target?

Windsor 12 FR 28-150hz -3db out of memory. It falls rapidly below this. It´s not true HT sub. Buy sub that has close to 20hz -3db spec. If money is issue then used BK Monolith (250-300£).
 

Dobbyisfree

Well-known Member

Mr Wolf

Well-known Member
To give you an idea of the minimum type of sub that can hit your estimated 84dB CEA-2010 requirement, an SVS SB-1000 Pro hits 88dB at 20Hz so that's the "ball park" minimum if you want ot cover the full acoustic spectrum. Note that this is being stricter than AH as its protocol only considers sub output >25Hz (not 20Hz) on the basis that >90% of movie content is >30Hz.

Something else to consider is that if you ever wanted to add some form of equal loudness "house" curve (definitely recommended at -15dB volume level and below) then that would bump the output requirement accordingly. House curves are very demanding output-wise e.g. an 8-9dB one is the equivalent of quadrupling the number of subs. In reality a pair of ported subs would make far more sense e.g. PB-1000 Pro hits 101.2dB at 20Hz so could cover off a House Curve requirement.
 

Dobbyisfree

Well-known Member
So I am a bell end. That 90% is the reason the Storms achieve as they are really competent down to there (by test at 30Hz I cant take them to their capable output as it hurts).
I am missing 10Hz though!
20Hz to 20kHz audible range... but that 10Hz is the best bit 🤣
 

ggwoodland

Well-known Member
thanks for the chart - good to know that if I want to dabble with Bass EQ sometime I'm getting some gain in the sub 20 Hz frequencies as my room is pretty large (> 10m width). I don't have my sub in the corner as JL worked out that the best place for it was 1/3rd along the front wall. But when I had my Arendal Sub 3 I did have it in the corner but it was really boomy until I got my soffit bass traps. I might move the JL into the corner one day and see what job that RoomPerfect can do with the sub in the corner, certainly as Audyssey really struggled when I had the Arendal/Marantz combo - George
 

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