(sub)woofer dispersion patterns vs room acoustics

[Bending]

I had various loudspeakers (some diy) with various sound radiation patterns. One I got fairly early were Agogee speakers which were dipoles and the bass was quite impressive and impactful to a point: lowest octave was quite weak and distortions (especially playing a louder volume.) An other major restriction of that design was placement (>4ft from front wall) but it eliminated sidewall reflections. I used different woofers/subs since then mostly sealed but also ported and these have at low frequencies an omnipolar radiation pattern. Presently I have my woofers in a sealed cabinet mounted to the front wall, so no back radiation leading to interference and a boost at low frequencies (half space radiation). I was reading about cardioid dispersion woofers either by using multiple woofers in a sealed cabinet with a specific acoustic alignment (like Kjii) or using different version of folded open baffle like W, Ripol or PPD designs which are supposed to eliminate (or more likely reduce sound towards the side wall) and therefore improve room acoustics (similar to dipoles)

I could see that different low frequency radiation patterns could lead to different amounts of early reflections of the side walls and to some extends floor/ceiling. Once the sound is reflected from any room surface I don't see how the initial dispersion pattern matters.

Is there any good info about that question including how much early refection matter for low frequencies in room acoustics (below the Schroedinger frequency)? The audibility of early refections maybe also related to time resolution of our auditory system vs frequency.

 

[Philbo King]

Bass is pretty much omnidirectional unless you do something like use a bipolar sub with one speaker out of phase, which will create a lobed response if done correctly. The dispersion pattern is dominated by room nodes and nulls (created by acoustic standing waves) unless the room has acoustic treatment for those frequencies.

 

[Bending]

Bass is pretty much omnidirectional unless you do something like use a bipolar sub with one speaker out of phase, which will create a lobed response if done correctly. The dispersion pattern is dominated by room nodes and nulls unless the room has acoustic treatment for those frequencies.

Not initially, room modes need reflection from a wall so there is a difference between the initial sound generated by a woofer and what happens after it travels through the room. The question is can we perceive it?

 

[Flaesh]

how much early refection matter for low frequencies in room acoustics (below the Schroedinger frequency)? The audibility of early refections maybe also related to time resolution of our auditory system vs frequency.

Schroedinger frequency even more uncertain than the nominal Schroeder frequency!) I think that the term "early reflections" in its usual sense is not applicable in the frequency range under discussion. Here https://www.audiosciencereview.com/...ectivity-patterns-couple-to-room-modes.45518/ is exellent @NTK thread; the third axial mode used as an example.

Presently I have my woofers in a sealed cabinet mounted to the back wall, so no back radiation leading to interference..

I could see that different low frequency radiation patterns could lead to different amounts of early reflections of the side walls and to some extends floor/ceiling. Once the sound is reflected from any room surface I don't see how the initial dispersion pattern matters.

Is the rear wall behind or in front? This is a never-ending terminological question. Out of habit, I'll refer to the front wall as the front wall.
In particular case, the wave propagates in one direction without reflections from longitudinal surfaces:

For low enough frequencies, reflections will never occur if the drawn room continues infinitely. An infinite room is usually* not a very practical solution, so a passive absorber or "active absorber" is used at the opposite wall in real systems, SBA and DBA respectively. See DBA threads, including a link in the signature.

*I have been in finite low (say about 2.5 m) room about 5 meters wide and tens of meters long with loudspeakers (a bunch of cabs and subs) at the front wall. The bass sounded very good there.
Just for fun:

notice irregular trancducers at front wall. This is (assuming a width of 5 m) for ~35 hertz, and here is for ~70:

 

[Ellebob]

Early reflections don't really apply to bass and we can't think of it like higher frquencies. The wavelength at those frequencies are too long. If using an 80hz crossover the wavelength at 80hz is ~14 feet long and at 20 hz it is ~56 feet long. For reference at 20khz it is less than an inch. because the direct wave and reflected wave are reaching at the same tie it causes problems. We get different peaks and dips in the response that changes as we move the sub or the seating. EQ is almost always required. It is about finding the best location for seating and sub that is EQable. Which means no major dips and peaks than can be EQ'd.

Now, if we are using only 1 sub, a good bass response will practically only happen in 1 seating location. In theory you can have a similar bass response in other areas but not always practical esating locations. If you want consistent bass in all you seats, 2 or more subs are needed and you still need placement flexibility of the subs.

There are many tools that model bass room modes and sometimes can help to predict where your bass problems might occur. However, most of these are not practical in real rooms. If you have a perfect rectangular room that is sealed and not open to other areas and your room is built out of concrete or using methods to sound proof the room they are more likely to be accurate. In most rooms bass goes through walls, doors, windows or the room is open to other areas of the home. This makes these models less accurate and trial and error with measurements is required. While cardioid and other types of speakers can help they are not a magic bullet and measurements and good placements are still required.

 

[Bending]

Schroedinger frequency even more uncertain than the nominal Schroeder frequency!) I think that the term "early reflections" in its usual sense is not applicable in the frequency range under discussion. Here https://www.audiosciencereview.com/...ectivity-patterns-couple-to-room-modes.45518/ is exellent @NTK thread; the third axial mode used as an example.

Is the rear wall behind or in front? This is a never-ending terminological question. Out of habit, I'll refer to the front wall as the front wall.
In particular case, the wave propagates in one direction without reflections from longitudinal surfaces:
View attachment 550328
For low enough frequencies, reflections will never occur if the drawn room continues infinitely. An infinite room is usually* not a very practical solution, so a passive absorber or "active absorber" is used at the opposite wall in real systems, SBA and DBA respectively. See DBA threads, including a link in the signature.

*I have been in finite low (say about 2.5 m) room about 5 meters wide and tens of meters long with loudspeakers (a bunch of cabs and subs) at the front wall. The bass sounded very good there.
Just for fun:
View attachment 550333
notice irregular trancducers at front wall. This is (assuming a width of 5 m) for ~35 hertz, and here is for ~70:
View attachment 550334

thanks for that link. I think I should call it front wall, I will edit my post!