Seaton Sound SubMersive1 - Page 255

Hey Dad, how 'bout we cut a hole in the wall to make the bass better?





Hey son, how 'bout we just open the door?

 

LOL!  Voila! Instant hole!  I will perform this trick once more, this time in slow motion... Voiiiiiillllllllaaaaaa! Innnnnnstant Hoooooooooole!

Don't forget, to test the alignment of "fluid dynamics" with actual audio theory, you're going to have to flood the room. Better wrap the gear in plastic

Some acoustic theory is based on fluid dynamics, but has been refined - that's why we have a separate branch of science.

Regardless, I doubt based on your posts that you actually understand the science involved, fluid, acoustic, or otherwise.

+1. Fluid dynamics are useful when examining the behavior of an acoustic wave of a single wavelength. But since we don't listen to acoustic waves of a single wavelength one cannot use a simple fluid dynamic model to predict complex room response issues.

Please post the fluid dynamics equations which one would use to calculate the effectiveness of your proposed solutions for a given room.

Is that one of those cartoons you have running through your head?

Hey, you said it, I didn't.

Craig

The issue isn't thinking in three dimensions, it's doing so at 15,000 odd wavelengths simultaneously.

posts deleted: move on please

I have no idea what was deleted but just wanted to say this.

I don't think BeeMan is wrong here but I will say that properly opening up a wall is likely going to cost. There seems to be an adequate amount of literature supporting things like fluid dynamics not to mention finite element analysis when dealing with standing waves and the like. It seems to be a rather complex issue perhaps better left to comprehensive software packages designed to address these issues. And while it may seem flippant on BeeMan's part, I don't find it especially hard to believe that he can spatially visualize such concepts no more than I can find it hard to believe that there are some physicists who have visual concepts or multidimensional space, Rajon Rondo knowing just how and where to pass the ball, a mechanic porting and polishing things to improve fuel/air flow (same thing applies to rounding over the inside of the cabinet) or Gary Kasparov being able to assess a chess position 10 moves into the future.

I certainly don't have such an ability and would be rather loathe to start tearing down walls to address such problems but then my listening spaces tend to be open.

Hi Chu,

Obviously, if you change the reflecting surfaces, you change the acoustics of the room. Cutting a hole in the wall will "change" the acoustics. However, what we don't know is whether it will improve or degrade the acoustics. BeeMan didn't provide us with any of the higher level math or the computational flow dynamics to prove that opening a hole in the wall will actually result in an improvement. Therefore, it's a rather huge leap to suggest that Ashi go ask his Dad if he can cut a hole in the wall on the off-chance that it might make his subwoofer sound better.

You're 100% right that we don't know what the change would be. One could, if they were so inclined and happened to have a relatively sealed room with doors and windows that opened to conduct their own measurements under different scenarios. 'Course you just might muck up the speaker's responses too.

Hi guys,

Please cool off the attacks, and thanks markrubin for cleaning things up.

BeeMan458, the seeming attacks you are getting are not directly related to the ideas posed but rather how they are stated and delivered without the possibility of fault. I'm not saying this is what you are intending, especially having spoken, but this is what others are perceiving and inferring.

I have friends working on some of the most advanced CFD modeling of low frequency room behavior being done with multiple subwoofers solutions, and it's anything but intuitive at first glance.

Once you have real measurements from a few locations confirming what is happening in a room it is very possible to have some confidence in what changing a wall or surface will do to a specific problem, but it is very hard to know that other collateral effects will not come with it.

I've posted here and elsewhere that with a single subwoofer in a room, I first look to see what is the most structurally solid corner or wall. Windows and openings to other spaces are less confining than an exterior wall on a main floor, and in basements we often see what looks like a symmetrical room to only then find that some walls are backed by the foundation, while others are just 1-2 layers of drywall which pass low frequencies much more readily. In such cases you will see the observed response to the listening position change while moving closer to or away from the solid wall or corner. Most often we see a moving dip/peak which correlates well to the dimensions involved. For those rooms with left-right construction symmetry and subs on a front wall, this plays a big part in why 2 subwoofers at the front wall of the room tend to have minimal benefit over a single subwoofer in the corner or center of the front wall.

Once again, measurement is key if you want to get deeper into this level of system optimization. Without measurements of the real room, you're guessing.

OK, sure.. some sweet strokes from Mark and Chu... that's all nice... but you have still not unequivocally proven that cutting a hole in the wall will *improve* the acoustics in Ashi's dad's room. Mark's response demonstrates the absolutely unpredictable nature of this whole undertaking, and the unquestionable need for in-room measurements.

Please provide the higher level math, or the computational flow dynamics, or at least the 3-dimensional modeling, (which you proclaim to have the ability to visualize in your head, but not to communicate on the internet), that would prove there would be an improvement by cutting a hole in the wall. Does the complete wall of glass on the right side of the room have any impact on your recommendation? Where do you suggest he cut the hole in the wall? Also provide the optimal dimensions of that hole. Short of that, at least show that there is a better than 50/50 chance that there would be an improvement by cutting *any* hole in the wall.. Otherwise, it's all in your head, and it's probably one of those cartoons you visualize.

Craig

You also remove the cabin gain that the reflective wall causes. Few rooms will find that a positive change. It's a lot more predictable than one might think, but as there are so many calculations involved it's far from easy. But 20 years ago it took ten pages of calculations and a week's work to design speakers with T/S specs, and now software does it in a few minutes. That same ability is coming closer every day where room response is concerned.
Edited by Bill Fitzmaurice - 12/18/12 at 8:03pm

Hey guys,

Thank you for all the input on this complex matter everyone.

I am absolutely sure that Beeman wasn't trying to mislead anyone with his suggestion. He was just putting an idea out there. I never knew that opening up gaps in a room could solve these modal issues. But now I do!

Unfortunately I haven't been able to move the sub. Had some work to attend to. It shall happen tomorrow.

Sorry for the hold up. Not getting much further with the issue since I haven't changed the position. Bear with me a little longer please! Ill keep you updated.

Cheers guys
Ash

To be blunt, you've recently learned some new words but have no idea what they actually mean or how to apply the concepts behind them.

Bill, Craig, and others could help with that if you would slow down and think about their posts instead of being so utterly convinced you have a new and simple solution to a well known acoustical challenge.

This is a public forum - if you want to propose new "theories", they will get challenged.

Here's a way to solve the problem - validate your claims. Have an acoustical engineer model 10 rooms with diverse shapes and construction materials. You visualize the solution for where to best place a new opening to improve in room bass response across the common criteria. The acoustical engineer can run the computational flow dynamics and 3 dimensional modeling and come up with an answer using accepted science. If you consistently align with the math within a few inches in each dimension, then you can feel free to gloat all you like.

 

The main thing, Ash, is that it is easy for you to try. You have a pair of big doors in back of your room. Open them and see if it makes a difference. You don't need to knock walls down - just open the doors! Not very scientific, but it will take you 10 seconds and it's free.  Of course, the doors might be in the 'wrong place' but it's such a simple experiment that you could try.  Personally, I think you can probably get what you are looking for by repositioning the sub and/or MLP and applying some form of EQ to the bottom end - AntiMode, XT32 etc. I think it is significant that Mark has 'tuned' many rooms for his SubMs and, AFAIK, he hasn't yet knocked holes in anyone's house ;)

Edited by kbarnes701 - 12/19/12 at 4:01am

I am in my second home theater. The previous one had double doors in the back of the room. Opening either or both of the made a change. Just not a positive one. In my current theater, the door is on the rear left wall and opening it also makes a negative (but more subtle) change.

Arbitrarily opening up a wall in a room without knowing EXACTLY where, how large and what results moght be seen is not science. And that 's true even if you can visualize in 8 dimensions!

As Craig has asked multiple times, show us the math.

Absolutely. If adding subs is a viable option, it's usually quite an effective one. The main reason many (most?) of us go with multiples is for the benefit in smoothing out the frequency response, as opposed to compensating for lost cabin gain after knocking holes in the walls.

I think most folks considering multiple subs are more likely to sample how adding multiples in different positions in the room affect/even out the bass BEFORE making holes in the walls rather than simply trying to use multiples to compensate for a reduction in cabin gain after knocking holes in the walls.

Seems odd for someone to suggest doing it the other way round.


Max

Yes most of us got that when you explained setting your sound system at certain angles to walls and openings.