16 x 18's in a 1500ft^3 Space - Popalock's Sub Build - Page 5

I just have one of those Logitech Z550 sub/sat systems, but the low rumble of the sub from your video gave my sub a bit of a workout and the dogs ran, probably because they thought it was distant thunder!

I don't expect to see much diff with 16 vs 8 in the general room gain profile. There will def be differences in the specifics of the frequency response, but not the general trend.

The rooms openings to other parts of the floor plan is largely irrelevant as the brunt of the room gain profile washes over the mic (your seat) before it leaves the room. Still, where you sit in the room and in relation to where the subs are placed in the room matters, as Carp's placement differences show.

In my own room, there is a stairwell to the first floor in the back right corner. If I place there, the profile changes because a chunk heads down the stairwell before it can add the gain and/or hit the mic where the opposite is true of the LP vs the front right corner placement.

Haha, friggin awesome. You really will have car audio bass capabilities in your room.

This makes me look very conservative, because my room is twice the size but I have half the subs!!

Nice work, Bosso! (glad to see you around too )

I hope I can make the list soon.

If I could ever get measurements right, maybe you could add my 8 to the list as well! Jeez....

AVH, I am also running the 4outside/4inside approach, but perhaps you were talking about me anyways It seems to work quite well so far but I have contemplated doing the L/R deal as well as an "All-one" setup. Just to see how they all differ if at all...

Seeming as I am the only one with a solid concrete bunker, I would be interested as to how much room gain I am getting???

Dave,

If I wanted to figure out room gain profile in my setup, how would I go about it? Can you show how you derived popalock's RGP from the measurements he posted?

Thank you

Here's a long read about PVG versus the idea of wave interaction with the room. Bosso got into this thread right away and I didn't notice it until about the second page. Ever since that thread I've noticed how many people perceive room gain to be about sealing up the room. I agree with Bosso that's its about constructive waves at very long wavelengths.

http://www.avsforum.com/t/1422068/seperate-drivers-for-lf-and-ulf-or-one-driver

Thanks for your posts as of late Bosso. Good to see information based on actual data rather than hearsay.

I'm hoping you can GENERATE the list. I'm retiring.


Easy, just follow the instructions below...


It's very simple, see below. If you don't signal shape the response, just skip that step, the answer will be exactly the same. I have to mention that my ACO Pacific rig is indeed flat to 2 Hz. That rig includes a custom power supply, cables and high end outboard interface, so, I don't use cal files (B&K and others use my mic to create cal files) and the roll off part is very accurate. Otherwise, you have to pretty much ignore most of what's posted below 10 Hz. Cal files for mic and SC and the increase in noise as freqs decrease are a cluster f%$# below 10 Hz, IMO, and few actually know their systems signal chain roll off, which all muddies the waters down there quite a bit. Still, you'll know you RGP and working on signal chain bandwidth is the next step.




Yeah, I would have drowned in that thread if it weren't for you.

Hey Pop,

Now that I see the perspective view pics, did I see you commenting on theater chairs somewhere? Rings a bell for some reason.

"I agree with Bosso that's its about constructive waves at very long wavelengths."

it is not according to drs. rienstra and hirschberg who are at one of the most prestigious technical universities in europe. one is a physics and math professor, the other is a physics and fluid/gas dynamics professor.

paper: http://www.win.tue.nl/~sjoerdr/papers/boek.pdf

see sections 2.2.3. on compactness and 4.1 on plane waves (read through to the first footnote, about one page) where it is discussed how below the critical frequency, air, which is normally a compressible fluid, behaves as an incompressible fluid and pressure is pretty much uniformly increasing and decreasing everywhere at the same time.

if you'd like to discuss it some more, revive the other discussion thread.

LOL! In that case, you better make your room a true sealed room like mine. Seriously , my room is truely sealed, you could fill it with water up until the single small 4" hole in the concrete for the vent. If you blocked that hole off the whole room would be able to be filled with water and hold it!

@Boso, thanks I would take a look at that. How would you go about cabling for measuring roll off on a processor?

Yes it kind of was a one note wonder max SPL wise. Right around 40hz it a huge spike in decibels. From 20-60hz it was around 150-151 db so output was similar to your buddies car. I had a Bass Mekanic CD with test tones and at 40 hz would make vision go totally blurry and very very hard to breath. I have slight tinutus cause of that truck.

That what was when I was young and dumb but i still crave that chest thumping bass. I think you are gunna definitely have it. I have two HSU VTF 2mk4s, one in each corner behind my screen in my 13.5 X 20.5 X 7 theater, and I want MORE. I wanna either add a couple 18s or one for now, or just ditch the HSUs all together. I built a few car audio sub boxes with friends when I was younger but I dont own any saws or clamps and I haven't tried wood working in years. I should buy clamps and have HD do all the cuts for me. Any advice on what equipment to start buying to get into DIY? I'm gunna be learning a lot from your builds and others as I do research. Thanks bro.

Yo pop, you mean a CNC'd peice of MDF like a bud did right down the road from me? You mean like this? I think I can pull some strings, but you might be taking another drive to NC there friend...

http://www.avsforum.com/t/1323919/the-timelapse-theatre-planning-n-build-log/990#post_22389968

Apparently you haven't read that paper or much about propagation of sound pressure waves in general. Plane waves (surface waves, however they refer to them in whatever paper, all being the same 1-D waves) are not relevant to the discussion. You have to skip to the Spherical Waves section, where you see the appropriate disclaimer:



The paper even takes the spherical wave and reduces it back to a plane wave. ^^ Well and good for the purposes of the paper, but sadly, irrelevant to us.

In our rooms there are no "hard walls" (which don't exist except to make a formula work), there is no "far field", which means there are no plane waves to discuss and this rather lengthy paper does not address boundary reinforcement, transmission losses through various boundaries (that relate to us) and there is no such "critical (sound) frequency" formula for a lossy listening space.

This is a no-brainer. If the "critical frequency" is simply derived from the rooms longest dimension, why does that not jive with the actual responses posted by members here?

Twice the longest dimension in my room works out to below 20 Hz. So, why does room gain begin at nearly an octave above that, and why does everyone else's, regardless of the huge disparity in the "longest dimension" (the critical) part of the equation?

Here's the bottom line:

We have data posted by members. In order for the data to be of any use, we have to find a global explanation with variables resulting in a window, sized by the weight of the evidence (an average).

The facts are that progressively constructive reflections fits nicely with the data, the variables being (a) transmission losses variability due to the construction of the boundaries (which also works toward simplicity because there aren't infinite methods employed in the construction of boundaries in the national building codes) and (b) signal chain roll off.

This makes it simpler to predict in-room performance when attempting to expand the BW of your system. This is why I can predict the in-room response of a sealed system given only (a) the signal chain roll off, (b) the systems naked response and (c) the construction method of the boundaries far better than anyone else can with the PVG critical frequency, sealed vs open stuff, and will be happy to prove that any time someone is interested.

If we site white papers and endlessly discuss the irrelevance of them, we end up where we began... at Best Buy, or we throw displacement and amplification at the problem. Neither approach is illegal, but they certainly aren't optimal or a guarantee of success.

BTW, I really don't want to get into a generalized "everyone is right, everyone is wrong" circle jerk. I'd rather use the thread we end up in so that our discussion may be related directly to the OP's room/system/results. That's how we learn something of value, IMO. The OP has the right to yell "scram" anytime he wishes.

Oops, I raised the dead thread

Be careful of that rabbit hole there bro I assure you that you have enough firepower, it is just making it all play nice

Because there are 2 other room dimensions, and more [EDIT]complexity[EDIT] if your room is not a parallelopiped(sp?) (long time since HS geometry!).

JSS
Edited by maxmercy - 3/20/13 at 4:58pm

Without hesitation, I believe there is a correlation to the maximum physical dimension.

I answered Bosso's contention here, in Carps thread.

I do find the graphs intriguing, however not enough to dismiss the physics involved. I may be wrong, and Bosso your graphs have been extremely useful as learning tools for those paying attention for years. But prior to me even getting to visually discussing and intepreting measurements, I have to be mindful of the acoustics of residential sized spaces.

I believe what Bosso is attributing to PVG, an octave early, has got to be acoustic gain (for whatever reason). The modal range is defined by the spacing of the boundaries. If it's occuring above the first axial mode, 1, 0, 0, it's in the modal range.

Then by definition, it's not PVG.

Again, that's the theory, and I personally haven't seen anything compelling enough to dismiss it. That said, I'm thinking about it, because Bosso has a lot of experience in measuring, and correlating the results, so it'd be foolish not to contemplate any such new perspective.

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Popalock, goodness ... what you've created there ... I've got an interesting idea you could try, but it'll have to wait as it's complex, and I've got some PMs to get to. I hit you up tomorow. Enjoy that creation. Quickly though, unrelated note, you could likely benefit from much thick treatment panel right behind your LP.

Congrats, quite a rig.

next time i'm driving back from Blacksburg alone i'm going to have to swing buy and see this madness