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Analytical Analysis - Room Gain

abdo123

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This is the understanding I think most people have of what "Room gain" is: Spatial loading Pii, Pii 2, Pii4...

To me, this thread explains something else. But René also calls it "Room gain".

I really like to get a comment on when or what are we supposed to call Room Gain".

Indeed boundary loading is something else entirely. But a subwoofer placed in a room is subject to both.
 

Thomas_A

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there is just a gap in the wall to other rooms.
I get it; I was just joking...but from you post it seemed a bit "bunker-like" without a door.
 

DonH56

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René - Acculution.com

René - Acculution.com

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Room gain, meh. Now I am eagerly awaiting your article on how teleportation works! :D
That is what my wife is saying. Make a time machine or teleportation work, and cash in ;). Alas, I am stuck with vibroacoustics.
 
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René - Acculution.com

René - Acculution.com

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Anyway, let me know if a video meeting with a evening of discussing acoustics could be if interest. If people are confused then clearly the text is not enough.
 

GurvanBHC

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Anyway, let me know if a video meeting with a evening of discussing acoustics could be if interest. If people are confused then clearly the text is not enough.
Thank you so much for you post. But even with your clear post, i still have some question :facepalm: Will "room gain" apply if 4 sealed subwoofer play in a room that is greatly treated with enormous bass trap like "helmotz resonator" for example, and with an optimization like Dirac Live Bass Management for the 4 sub? Because the mode from like 20hz to higher will be really reduced by the treatement and the bass optimization. What i understand from your post, room gain exist beacause of the 0hz mode only, not those after?
I'm asking you this question because I have to buy 4 subwoofers, preferably sealed and I can't afford to buy them to be disappointed not to reach 20Hz at high volume... And I like to learn more about acoustics...
Thank you in advance (sorry for my english, I'm french.)
 
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René - Acculution.com

René - Acculution.com

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Thank you so much for you post. But even with your clear post, i still have some question :facepalm: Will "room gain" apply if 4 sealed subwoofer play in a room that is greatly treated with enormous bass trap like "helmotz resonator" for example, and with an optimization like Dirac Live Bass Management for the 4 sub? Because the mode from like 20hz to higher will be really reduced by the treatement and the bass optimization. What i understand from your post, room gain exist beacause of the 0hz mode only, not those after?
I'm asking you this question because I have to buy 4 subwoofers, preferably sealed and I can't afford to buy them to be disappointed not to reach 20Hz at high volume... And I like to learn more about acoustics...
Thank you in advance (sorry for my english, I'm french.)
Thank you, and good luck with setting up your room. I am not an expert in the practicalities of subwoofers in rooms, but I would guess that even it a treated room, you will still have the same very low frequency response. Your sound will probably depend much more on where you place the subwoofers and how the room is treated, than this particular effect. Also, Dirac may play with the phase of the subs, and so you could end up with very low output at low frequencies anyway, if they are not in-phase with each other.
 

GurvanBHC

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Thank you, and good luck with setting up your room. I am not an expert in the practicalities of subwoofers in rooms, but I would guess that even it a treated room, you will still have the same very low frequency response. Your sound will probably depend much more on where you place the subwoofers and how the room is treated, than this particular effect. Also, Dirac may play with the phase of the subs, and so you could end up with very low output at low frequencies anyway, if they are not in-phase with each other.
Thank you for the response René. I hope to have room gain even with Dirac I will post on this thread by the end of the year when my room is finished the measurement of my room.
 

JRS

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I am hoping you might comment on a related question, and that is where the woofer is infinitely baffled or at least an approximation by say making a crawl space attic or even a large closet the cabinet--in effect "eating" the back wave. My impressions on listening to 2 different systems was that it is the most articulate, clean, palpable bass I have ever had the pleasure of experiencing--not bloated, or boxy--a stand up bass sounded as if it were in the room. Devotees of the alignment are a bit fanatic and in fact the moderator where the subject is discussed is whimsically called the "Cult of the Infinitely Baffled." Granted the technique depends on employing massive amounts of driver disblacement--I had 2 extra long stroke 18" woofers coming up through a hole I had cut into my living room floor. It was pretty insane being able to watch the large plate windows flex at 10Hz.
 

Flaesh

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Devotees of the alignment are a bit fanatic
For example, I'm not a fanatic and now I have a room with boxes instead of a room with IB half the size.
For me, a good cause for fanaticism is good bass reproduction, regardless of how this is achieved.
The room "doesn't know" what's on the other side of the speaker. Room gain in the setup with IB is no different from the usual one. And modal issues too.
 
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René - Acculution.com

René - Acculution.com

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I am hoping you might comment on a related question, and that is where the woofer is infinitely baffled or at least an approximation by say making a crawl space attic or even a large closet the cabinet--in effect "eating" the back wave. My impressions on listening to 2 different systems was that it is the most articulate, clean, palpable bass I have ever had the pleasure of experiencing--not bloated, or boxy--a stand up bass sounded as if it were in the room. Devotees of the alignment are a bit fanatic and in fact the moderator where the subject is discussed is whimsically called the "Cult of the Infinitely Baffled." Granted the technique depends on employing massive amounts of driver disblacement--I had 2 extra long stroke 18" woofers coming up through a hole I had cut into my living room floor. It was pretty insane being able to watch the large plate windows flex at 10Hz.
Well, I don’t really know whether that is the way to go or not for you, but from a theoretical perspective the back wave adds some stiffness to the system and changes the Q, which should not be a problem if it is a good box design. And then you lose the freedom to move the subs around, which could be a big issue when it comes to bass response. But others here probably know more about it.
 

Flaesh

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And then you lose the freedom to move the subs around
For Cult of the Infinitely Baffled it is common practice to study the actual RTF (room transfer function) using a conventional closed loudspeaker(s) before cutting holes. Also one can do the same when building a conventional system (@GurvanBHC , ;)..).
Eh, it's a pity that the eldest child recently sold an apartment suitable for IB DBA :cool:
 
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So when we place a closed sub with a resonance frequency of 20 Hz in a smallish room, lets say a recording van with a 2 meter dimension, we get under about 80 Hz a 12 dB/oct soundlevel rise?
 
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René - Acculution.com

René - Acculution.com

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You get some kind of shelving filter but flat response at low frequencies assuming no leakage and such.
 
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You get some kind of shelving filter but flat response at low frequencies assuming no leakage and such.
I forgot this interesting lecture and apologize.
I have another question.
What is happening at the other modes? Assume a 8 x 5.5 x 3.5 room. We have axial modes at about 21, 31 and 49 Hz.
If we have a closed box tuned at 21 Hz we get a flat response under 20 Hz (which is nice for a visiting elephant or baleen whale). But we get 12 dB shelving under 31 and 49 Hz?
And what about the other fancy named modes?
 
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René - Acculution.com

René - Acculution.com

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I forgot this interesting lecture and apologize.
I have another question.
What is happening at the other modes? Assume a 8 x 5.5 x 3.5 room. We have axial modes at about 21, 31 and 49 Hz.
If we have a closed box tuned at 21 Hz we get a flat response under 20 Hz (which is nice for a visiting elephant or baleen whale). But we get 12 dB shelving under 31 and 49 Hz?
And what about the other fancy named modes?
The modes and the source characteristics and placement is basically what is needed to calculate the pressure. It generally varies widely across frequency and space. But below the first mode it gets notably easier to calculate the pressure and this is region can be called the room gain region. It only makes sense to talk about constant level or slopes or trends below that first mode. Above it, the pressure has to be calculated or measured and it difficult to say much in general about the pressure.
 

KLang1

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How would a (super-)cardioid woofer setup be effected by this? The cardioid setup results in a loss of 6dB/oct starting at f with 1/4λ = distance between the woofers (iirc). Would be nice if that's partially mitigated by room gain :) However attenuated sound to the sides and back will probably not help.
 
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René - Acculution.com

René - Acculution.com

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How would a (super-)cardioid woofer setup be effected by this? The cardioid setup results in a loss of 6dB/oct starting at f with 1/4λ = distance between the woofers (iirc). Would be nice if that's partially mitigated by room gain :) However attenuated sound to the sides and back will probably not help.
Interesting thought. Haven't looked at it, but if it realized via two drivers with one of them time delayed to the other as figure 5 in this reference (https://www.researchgate.net/public...libration_for_large-scale_sound_reinforcement), then at low frequencies the two will essentially be in-phase, as a time delay is linear phase and so basically zero phase at very low frequencies. But I would need to model it to be sure about the rest of the frequency range.
 

KLang1

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This is my setup, with all three subs in one corner of the room aimed roughly at the corner diagonally across.
1689341990657.png

1689342039374.png


I haven't measured the nearfield response yet, so I can't simulate the overall frequency response in the room, but the cardioid part works splendid.
It's a 3 woofer setup because initially multi-sub optimizer was intended to be used. It'd be easier to simulate with only 2 woofers of course.
 
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