how corner bass traps work....

[laagman]

This must be a very simple question for experts: why do corner bass traps work?

Looking at this sketch, one could think that only the axial modes that enter the absobers (super chunks in this case, orange) are weakened, leaving the axial modes that cross the mixing position (green) "untouched".
Therefore the room wouldn't improve on the mixing spot.

I know this is wrong, but why?

[bpape]

Corners are not a be-all, end-all solution to all of your bass issues. You still, at times, need to address things like center of rear wall, over your head, etc. to deal with direct axial buildup and cancellations.

Corners are just a very efficient place since they exist at the end of multiple room boundaries where bass tends to build up. Tri corners are at the end of all 3 boundaries. This can help with the longest single dimensions of your room - the diagonal corner to corner length.

In addition, the corners will also help bring decay times in line with the target curve for your application.

Bryan

[localhost127]

Originally Posted by bpape

Corners are just a very efficient place since they exist at the end of multiple room boundaries where bass tends to build up. Tri corners are at the end of all 3 boundaries. This can help with the longest single dimensions of your room - the diagonal corner to corner length.

but this would only be useful for pressure-based traps, correct?

i was under an impression that due to the LF wavelengths being so large, that they effectively diffract around any panel or absorber in its path (in small acoustical spaces). hence, by placing the panel in the corner, the wave is effectively forced into and then back through as it is reflected off 2D and 3D boundaries. is this correct, or is there more to the story?

[Starlight]

In your diagram your monitors are facing parallel to your axial mode lines. Not all sound runs perfectly parallel or perpendicular to walls. See Acoustic Primer. GIK Acoustics. Acoustic Panels and Bass Traps.

[bpape]

In theory, pressure based absorbers would be more appropriate. In fact, in real rooms, using only pressure based absorbers wouldn't be feasible as you'd need too many of them to cover the spectrum.

In reality, while the absorbers are small relative to the waves, you're still impacting them using velocity absorbers or light membrane absorbers over a wide range in terms of decay time and in terms of random angle of incidence.

Bryan

[boggy]

Originally Posted by localhost127

but this would only be useful for pressure-based traps, correct?

i was under an impression that due to the LF wavelengths being so large, that they effectively diffract around any panel or absorber in its path (in small acoustical spaces). hence, by placing the panel in the corner, the wave is effectively forced into and then back through as it is reflected off 2D and 3D boundaries. is this correct, or is there more to the story?

It's probably easier to understand this if you, for the moment, forget about sound wave behavior, and remember that sound is primarily movement of air molecules,... then... if we have subwoofer (some sort of "pump", or "fan") in (small) room, which generate movement of air at, about 50Hz, for example... this movement must reach our absorbers... because air in room doesn't have too much space to avoid our absorber and "difract" somewhere else...

For successful diffraction and all its effects at low frequencies we need (much) more space than ordinary small room.

Well, air movement is everywhere in room... but... when standing wave occur, there is a regions with large velocity of air molecules, and other regions with large pressure of air molecules. Both of it can be used for successful "bass traping", but in first place we must use porous absorbers, and in second place we must use pressure based absorbers.

Hope this clarifies the matter

Cheers,
Bogic

[Jens Eklund]

http://www.gearslutz.com/board/6773104-post8.html

[Dange]

Originally Posted by bpape

In theory, pressure based absorbers would be more appropriate. In fact, in real rooms, using only pressure based absorbers wouldn't be feasible as you'd need too many of them to cover the spectrum.

But, it is possible to tame just low frequency room modes using pressure based absorbers Studios and Labs for Acoustic Engineering, Audio and Video Engineering | University of Salford | Manchester

[Glenn Kuras]

Originally Posted by Dange

But, it is possible to tame just low frequency room modes using pressure based absorbers Studios and Labs for Acoustic Engineering, Audio and Video Engineering | University of Salford | Manchester

Any thing is possible, but smaller rooms have so many problems throughout the frequency range that it is pretty hard to just use pressure based. The other thing is if you don't build them totally right then you will fall all together.

[Ethan Winer]

Originally Posted by laagman

why do corner bass traps work?

Adding to what others said: Bass waves travel along the walls until they hit a corner. Corners are sort of like cupping a hand behind your ear, or the way a satellite dish works. Sound waves tend to collect in corners, which is why bass traps work well there.

--Ethan

________________
The Acoustic Treatment Experts

[laagman]

Thanks guys for the useful answers and links (that I'm reading now).

Would this be a good work plan / order to start with?

1. take measurements in empty room

2. build and install SSC's in vertical corners (floor - ceiling)

3. take measurements

4. build and install straddled porous absorbers in wall/ceiling corners

5. take measurements

6. buy (or maybe build) pressure devices

[boggy]

Originally Posted by laagman

Thanks guys for the useful answers and links (that I'm reading now).

Would this be a good work plan / order to start with?

1. take measurements in empty room

2. build and install SSC's in vertical corners (floor - ceiling)

3. take measurements

4. build and install straddled porous absorbers in wall/ceiling corners

5. take measurements

6. buy (or maybe build) pressure devices

Mark positions of measurement microphone and loudspeaker at floor, and try to measure always in same points, or you cannot get where are your hard earned benefits.

Also, measure only one channel... not stereo.

Good luck!

[laagman]

Originally Posted by boggy

Also, measure only one channel... not stereo.

Good luck!

thanks!

and place this speaker in the middle or in its normal position?

[boggy]

Originally Posted by laagman

thanks!

and place this speaker in the middle or in its normal position?

Place it in normal position...

Cheers.

[Dange]

Originally Posted by Glenn Kuras

smaller rooms have so many problems throughout the frequency range that it is pretty hard to just use pressure based.

I did say just low frequency

Originally Posted by Glenn Kuras

The other thing is if you don't build them totally right then you will fall all together.

Yup, I'm sure there definitely is a market for a home tuneable LF pressure based trap....you guys got anything up your sleeves?

[johndykstra]

Originally Posted by laagman

Thanks guys for the useful answers and links (that I'm reading now).

Would this be a good work plan / order to start with?

1. take measurements in empty room

2. build and install SSC's in vertical corners (floor - ceiling)

3. take measurements

4. build and install straddled porous absorbers in wall/ceiling corners

5. take measurements

6. buy (or maybe build) pressure devices

to add:

1.a - find a listening and speaker position via multiple measurements to find the optimum locations before addressing the room with treatments

5.a - a clarification to 5. etc measurements to determine which part and amount of first reflection points (side walls between you and speakers... same with ceiling) need to be addressed via absorption and/or geometric redirection.

5.b - multiple etc measurements to verify that you are creating a listening "zone"... meaning, ensure that you have good amount of room to move about the work surface with reflection free monitoring.

[Glenn Kuras]

Originally Posted by Dange

Yup, I'm sure there definitely is a market for a home tuneable LF pressure based trap....you guys got anything up your sleeves?

We already do them for custom jobs. Most of the time it is larger rooms or special cases. I still think all and all broad band for smaller rooms is the way to go though.