Does room gain depend on number of subs?

[goldyrathore]

Hi All,

Does room gain change as more number of subs are added to a room?
Since the frequency at which room gain starts kicking in depends on the room volume that the sub 'sees', so the addition of another sub should make the effective room volume 'seen' by each sub into half thereby pushing the start of room gain frequency to a higher value.

Is my understading correct?

Thanks in advance,
Goldy

[bentoronto]

To my poor understanding, there is no such thing as "room gain" per se. Rather it is the collection of room modes and depends on their strength, distribution, etc. and where your head is.

These are bad, like any resonance or re-enforcement or multi-peaky boxes (no names to protect the guilty). Since we can't get rid of low frequency modes, the object is to hoax the ears by stimulating as many as possible, kind of like OB "theory."

Toole goes into some depth and data on the question in his turgid chapter. Well, the research is turgid, not his writing.

To make a long story short, mix and mis-match and multiply to work up those room modes. This is no place for purists.

I run a true horn bass in a corner plus a mid-wall giant OB sub with the same signal. Formerly, added a sealed box mid-wall. Both help charge the room modes and the OB better. With a glide-tone below 300 Hz, my sound level meter stays mostly on the same 12 dB range scale all the way. Good enough for me.

Funny the neurotic compulsive behavior making speakers followed by casual room installation (or the misfortune of having great speakers installed at the whim of circumstances or spousal taste).

My 2-cents.

[chris661]

Room gain exists as cabin gain in cars exists. It happens when the subwoofer output goes from waves (ie, ones that fit into the room) to pressure mode (where the wavelength exceeds the room dimensions).

I'd expect the subwoofers to ignore each other, as the tiny pressure differences you hear are nothing compared to the brick and motar of the walls, which dominate the frequency and magnitude of room gain.

[bjorno]

Originally Posted by goldyrathore

..Is my understading correct?..Goldy

Hi Goldy,

First I would like to comment bentoronto's:'To my poor understanding'
IMO, your understanding seems far above average.

No, room gain doesn't change for a specific speaker position but the SPL sum is altered when more speakers are added. See a simple program that will give you a trend hint of what happens:

Room Response Calculator - Reflective Accumulation Simulation Software

Note: This imaginary room is hermetically closed so to compare with a real room you must have real measurements to compare with.
To draw any conclusions: Using a RTA is OK, i.e. showing trends of any peak or other dips, typically several energy sinks affecting position dependent passive boundary gain.
If you have one of those boundary gain sensitive speakers like crappy TH designs*(large gldy at XO and typically when driver(s) is(are) placed close to TH mouth), this program would be a wast of time to use (Mains included) if trying to estimate in room Speaker System FR performance: That is trying summing one position for a main speaker and the other suggested for a TH(or any other speaker type with large untreated gldy) gives grossly erratic results.

*This exception don't apply to a normal T-TQWT, of course.

b

[tb46]

Hi goldyrathore,

The following thread has a lot of valuable information pertaining to the room-subwoofer interaction, and the setup (link in Post #5) and interaction of multiple subs:

Multiple Small Subs - Geddes Approach

bjorno has already stated the most important fact: "...with a real room you must have real measurements.... There are simply too many variables to generalize.

Regards,

[TerryO]

Originally Posted by tb46

Hi goldyrathore,

The following thread has a lot of valuable information pertaining to the room-subwoofer interaction, and the setup (link in Post #5) and interaction of multiple subs:

Multiple Small Subs - Geddes Approach

bjorno has already stated the most important fact: "...with a real room you must have real measurements.... There are simply too many variables to generalize.

Regards,

Room Gain is fixed by the room itself, the use of "Distributed Bass" as put forth by Dr. Geddes, and others, can... by the sheer numbers of drivers be capable of increased SPL levels and also by dividing the Bass Production chores among several drivers, result in less distortion as well as available headroom.

However the greatest advantage of "Distributed Bass" is the ability to deal sucessfully with "Eigenmodes" (the room modes) that have pressure nodes and nulls in the room. A correctly configured DB system allows consistant pressure levels which in turn allow far greater latitude in listener position without loss or dropout of bass.


Best Regards,
TerryO

[davygrvy]

Well said Terry!! +10!