16 x 18's in a 1500ft^3 Space - Popalock's Sub Build - Page 6

the authors are describing the same behavior in both sections bb.

either way, within 1/2 lamda (some would say 1/4) or alternatively when kr << 1, you are in what the authors refer to as the near field. that region has very different behavior (such as the incompressible flow behavior and resulting increased transmission velocity, v') than the traditional reflecting wave behavior that you are describing which is limited to what the authors refer to as the far field.

an extreme case of the concept is actually referenced again very briefly in 3.3.2 where the authors note that low frequencies of headphones work the same way. the sound is not radiated as sound in the traditional sense of waves traversing through the air, but rather an increasing and decreasing of pressure everywhere.

hope this helps.

When I had a Y splitter running out of the mini to the two clones I had to turn the volume knob on the avr up a lot higher to get the output I am getting with two separate rcas "in and "out" of the mini.

Bosso

Thanks! Never even thought about it like that.

What about when using the Phoenix balanced outputs on the minidsp 10x10 that spec at 8vrms (20dbu)? would it be optimal to really dial back on the dip switch? Just in my head that will be getting less output as I can turn the gain knobs on the front up to max pretty much with dip switch set to max without over driving the subs.

Lol yep

To adjust your clone input sensitivity to match 20 dBu/8 volts as closely as the dip switches allow for, driving a 4 ohm load to max output the amp has to give, set the gain limit switch to 23dB and the VPL (voltage Peak Limiter) to 195 (FP14000). That should allow you to run the FP gain pots to close to full on. If you're running the clone in bridged mode, I believe you have to go to 29dB gain limit setting because they attenuate by -6dB when switched to bridge mode (use caution until this is confirmed in actual use).

Again, if the gain limit DS is set to default 38dB and the VPL set to 195V, you can overdrive the amp with 8V from the mini.

That should work. LMK how it works out.

"...drastically new behaviour..." does not imply the same behavior. They're describing a behavior in a pipe for cryin' out loud. There is no plane wave behavior in our rooms at any frequency. The paper is irrelevant to the discussion and if it's the only card in your hand it's time to fold.

If the pressure is increasing and decreasing everywhere in Carp's room, explain the 6dB difference he (and all of us) measures by simply moving the subs. Does moving the subs to a new location change the longest dimension in the room?

I'm using the fp10k 220v


Papa and I were talking about the use of the Phoenix 8vrms output a few pages back and weren't positive how it would affect the amps.

"The paper is irrelevant to the discussion and if it's the only card in your hand it's time to fold."

the earliest reference to the hydrodynamic nearfield behavior that i have been able to find was in a paper to nasa in 1974, so its not like this is anything new to the physics community.

linkwitz describes the effect here as well: http://www.linkwitzlab.com/images/graphics/enclosure-spl.gif

no waves. no reflections. just pressure.

Unless.....popalock makes an ENTIRE FRONT WALL of subs!

JSS

So you're back on the ideal gas law? Well at least linkwitz is relevant. I'm not sure he's showing any research there, rather just some math musings scribbled down for fun maybe. And it's based on the ideal gas law which calls for the explanation of hall ways, open doors, etc. in my room I see gains below 30hz despite a long dimension of 33 feet, adjoining rooms, a stairwell to the upstairs, and a wide opening into a 12x10 furnace room. I should measure with my sliding glass door and windows open. But I'm pretty sure ideal gas laws don't apply to my room.

It does exactly what one expects. Of the varying attributes to utilization of multiple subs, selective mode cancellation.

The physical characteristics establish a room's modal behavior wrt frequency. This doesn't change, regardless where one places the LF sources. However, the placement does affect the magnitude of the modal excitement.


I see nothing inexplicable about Carp's measurements. Moving the LF source, changes the manner in which it couples too, and drives a particular mode. Just as one can minimize that excitation, one can similarly maximize it.


Where am I going wrong? It is late, my pharmacological cesspool of a self can't sleep, ... easily could've made a mistake.

Thanks

as you should

"So you're back on the ideal gas law? Well at least linkwitz is relevant. I'm not sure he's showing any research there, rather just some math musings scribbled down for fun maybe. And it's based on the ideal gas law which calls for the explanation of hall ways, open doors, etc. in my room I see gains below 30hz despite a long dimension of 33 feet, adjoining rooms, a stairwell to the upstairs, and a wide opening into a 12x10 furnace room. I should measure with my sliding glass door and windows open. But I'm pretty sure ideal gas laws don't apply to my room."

those are the same arguments that bb makes and we already covered that ground. he asked, how can a room be pressurized if there is a doorway? i'm not saying that isn't a good question. it is!

the answer is because the air in the room does not see the doorway the same way that you and i do.

even worse is the air in front of a speaker. it does not transmit a soundwave in the traditional sense when in the near field. the whole slog of air in the hydrodynamic nearfield is slogging back and forth. no waves inside the slog of air. that is what all that "incompressibility" stuff is all about. when the slog grows to the size of the room, waves in the room are done and it is just pressure.

i'm not sure, but i think the slog may be the physics explanation for things like flapping pants and the popular "hair trick". you can't get in the slog at 1khz, so no matter how loud the sound, no slog, just waves, and no hair trick.
Edited by LTD02 - 3/20/13 at 10:16pm

Sealed room is something we admire as well. Not concrete but it's sealed. The house is sitting over an all concrete garage 3 walls in ground. I think that helps for tactile feel being on a floating floor above it. We're reminded every time we cook on how sealed the room is cause our stove hood vent is a commercial fan venting to outside. Even when the fan is on low it will suck the cat door up that just happens to be in the wall next to the subwoofers leading to the front sunroom. Occasionally with healthy bass we'll see light from the cat door . We lock it closed during movies now. Main listening area shares open space with kitchen and dining totaling 4096cu ft. When the hallway door is slid open(sound deadened panels accordion door) to the rack area and rest of the house there's a notable difference in sound. It stays closed off to help keep from breaking things in other rooms.


On the car bass vid yes spl car competition is designed for certain peak freq and in a very small car space. Keith Miller the gent in the DC vid I posted said his is tuned for 41Hz.

"166.5dB (12) DC level 4 m2 12's in a 2:1 ratio 4th order
17 cu/in per cube on ported side. Peaks @ 41hz
Subs will start to unload at 24-25hz although it will play down to around 20hz if I watch the power.. Will play up to roughly 60hz before it rolls off. "


If you had enough to hair trick in a house i'm pretty sure it would need to be a bunker or it would fall down with you inside.

http://www.modulararts.com/

http://interlam-design.com/gallery/art-diffusion-gallery/

http://www.globaltrendsbuildingsupply.com/globaltrends-products/tiles/wall-tiles/3-dimensional-tiles/ecocarat.html

http://freshome.com/2011/08/30/three-dimensional-decorative-tiles-the-versatile-collection/ - really cool, but from Turkey and a bit pricey. YMMV.

At 33 feet long (not to mention the open room and stairwell making it more like 42 feet long) I should only get "PVG" below about 17hz. So something is up. I'm not sure how you can say I should get room gain from 30hz and down with the 2x the longest room dimension rule.


In the other thread you explained Bosso's window as a Hemholtz resonator. Now it doesn't "see" the stairway? Comparing the tactile feel of 10hz to the feel of 1khz and interpreting the papers you've read to explain hair tricks doesn't hold any water. The PVG theory relies on the ideal gas law, as shown in the Linkwitz link you provided. The ideal gas law demands the V1 is well defined. Adjoining rooms, stairwells, open windows, etc. create a V1 that approaches infinity. Once V1 approaches infinity, deltaP approaches 0. That's the physics.

I know you'll have some comment back on this, but I don't think it's worth discussing. You're using contradicting viewpoints, changing your theory on the fly, using invalid papers, and using personal opinions about hair tricks to advance you opinion. That's not exactly worth debating. The (now I'm gonna use Bosso's terminology because I think it's a good term) progressive constructive gain theory uses basic, well understood principles about sound waves that align well with the data and doesn't require complex explanations to explain away the problems of open windows and such. Sometimes simpler is better.

Bosso is saying there's an SPL change in the PVG region. If the PVG was explained by 2x the room length (or ideal gas law) moving the sub wouldn't matter. Bosso's progressive constructive gain theory says that even down at VLF there's reflections, except that nearly every reflection is constructive. Your post actually bolsters that view, thanks.

What you're expecting me to swallow is that the leading edge of the so-called Fm (frequency below the modal region) behaves in my room as this illustration shows...



...that the "leading edge" of the spherical wave has zero interaction with the 6 boundaries because it hasn't reached the longest dimension yet.

The hair trick and flapping pants are irrelevant.

The Linkwitz article discusses the pressure inside a perfectly sealed box. This has been my argument all along. IF you could seal a room like the box is theoretically sealed in Siegfried's example, I would be on board and all ears with the PVG theory. The displacement to sealed space is 20:1. My room is completely non-sealed and the ratio, using the 12" driver Linkwitz references, is 55,000:1. In a house, the room is not sealed in the sense of air pressure losses. The entire house is what is tested for air pressure leakiness when a fan is used to introduce pressure from the outside of the house, in which all rooms are affected equally. Rather the room is "sealed" against transmission losses to degrees that vary according to construction methods used to build the boundaries.

Poke a 12" hole in that box and see if the formulae and results change.

FOH,

Where you're going wrong is that, according to the theory, there are no modes below the magic frequency. There is only an increase and decrease in pressure "everywhere" which fluctuation somehow increases at a rate of +8dB per octave as frequency decreases below that point. LTD loves to cite various laws of physics so he must stick with the fact that there cannot be a (+/-) 6dB condition in the pressure that's "everywhere in the room" just because you move the point source location. Location is irrelevant if the PVG theory is valid.

Here's my room. Leaks like a sieve. Still get gain

Maybe setting up the clone's gains and vpl settings wrong are why they have some problems? I have no idea on what to set. I just set max gain and set the VPL to 120 V. I did this for both the 10Q and 14K. I think they were both set to hard as well.

Yeah.

Typically, with the exception of bass trapping, a well scattered, or perhaps full on diffusion is often the ideal approach from the LP rearward. However, in rooms whereby the LP is in relatively close proximity to the rear wall, acoustic absorption is the preferred method to pursue. As with any absorption, if you're going to absorb, you absorb as much as possible (ie., as broadband as possible). A thick 703 style treatment, or equivalent would work great. The destructive cancellation exhibited by comb filtering really eats away at the preferred smooth FR at the LP.

With all aspects of treatment, you really need to learn to be adequately proficient at measuring, and proceed with what the measurements dictate. Do nothing without measuring. Sure, there's always some "low hanging fruit" wrt acoustic treatment. But the science is well understood, and easily used to increase both the measured, and the subjective playback quality in our room's.

The theoretical component and basis of all specular treatment. Any treatment device inserted into a reflected sound path, whether it's an absorber, a diffuser or reflector, should execute it's duty uniformly well at all frequencies above the transition freq range (~150hz-300hz). Be mindful, this applies to the typical sidewall, and ceiling treatment positions as well. The reason behind this is all central to preserving the precedence effect. By attempting to preserve the spectral balance of the loudspeakers, via evenly absorbing as much of the full spectral content of the reflections, you establish a platform most conducive to assuring the precedence effect is most effective.

So the axiom is, absorb it all, or none at all. Otherwise you're merely EQ'ing the reflection. When individuals place 2" absorbers on the walls, they're essentially EQ'ing the response by removing HF content of the reflected content, allowing the remaining low-mid energy to re-combine, thus robbing the precious mid-high and high freqs, leaving a lifeless, dull level of reproduction. The highest freqs possess little energy when compared to the energy down toward the low-mids.

I'd recommend at least 4"of OC703 (or equiv) w/ 2-4" air-gap. Ideally, once you get up to a space available greater than 8", then you move to the loose, fluffy stuff. The thicker the treatment, the less dense the material needed. Most panels, like your application, sidewall reflection points, etc, need some structure to the panel, hence the 703 rigid. So for your behind the LP area, it all depends how much space/thickness you can devote to the issue.


Tell me, what is the approx distance from the your ears @the LP, and the back boundary?


Thanks

No, that's not what I said.

We're in agreement. Quite simple, I concurred, ... you should see gains below 30hz.

Without actually knowing your room, measuring or anything. Only considering your stated numbers, the 17hz PVG onset frequency, that said your modal range extends down into the 17hz region. So by definition, you can have boundary gain, modal influences elevating the level, destructive interference diminishing the level, all before even adding any reciprocal ULF gains that would be associated with the region below your 1, 0, 0, first mode.


When stating "something is up", what do you mean?

Yeah I agree. Me and papa had the entire convo by ourselves about 3 pages ago and thought we were on right track until bosso showed up. He definitely knows optimal setting just by the science part of it, without his in depth experiences which also help too. He knows these amps and the science of everything we could put in the signal chain. Me and papa came to conclusion that using Phoenix outputs and inputs must be better since would be more voltage but never realized the downside was our settings on the back which would need to be lowered quite a bit if using the 8vrms balanced outs from the minidsp. (Still hoping bosso will comment on that post)

Still need someone to verify that optimal inputs on the minidsp 10x10 is the Phoenix connectors and what (if any) changes need to be made on the mini's jumpers or other equipment in the chain.
Edited by audiovideoholic - 3/21/13 at 10:19am

There are 2 reasons I no longer post in the clones thread; a) there's no single source for purchases and b) the settings problem is indeed the #1 reason there are so many problems.

The clone amps have unprecedented flexibility. This is both a good thing and a bad thing. I've measured voltage out of every piece in my signal chain and 9-10V when playing WOTW or equal is not uncommon at reference level.

When you're feeding that hot a signal to an amp, most amps have a global input sensitivity and a crude version of voltage peak limiting, so they clip because the gain is nowhere near set up for that scenario. When you up the ante power-wise to the clone level and/or run stupid low impedances and include relatively hot single digit content, all sorts of bad things happen.

It's like getting a 60s muscle car to learn how to drive with and starting the engine, closing your eyes and flooring it.

AVH,

Sorry, I had no idea which amp, what loads or what configuration of the channels you're using.

The FP10Q rolls off at 7 Hz (hasn't been verified in the clones to my knowledge, so it's assumed) and the setting with the 8V/20dBu Mini would be the same, except to set the VPL one notch lower.

Again, this recommendation assumes the clone you use has circuitry that is accurately reflected in the dip switch demarcations. Always proceed with caution until you find the limits of your system using the heavy hitters.

I thought I had done that as thoroughly as a human could over the past 10 years, but along came Total recall with a single scene that caused my drivers to soft bottom HARD when I was running the SW out a few dB hot and 0dBRL:



If the Voltage Peak Limit lights flash, that tells you you've exceeded the voltage you set the limit for. OTOH, if the Current Peak Limit light flashes, that means you're clipping. If you're clipping, immediately readjust your system from the AVR to the drivers. If the VPL lights flash occasionally, it's OK. If they flash a lot, immediately readjust your settings from the AVR to the drivers. After readjustment, use the offending soundtrack and ease into it to find maximum (driver excursion or amp limits or signal limits.

On my new SEQSS signal shaper we've designed a circuit that is adjustable (not user-adjustable) and changes the color of the ON LED when input voltage exceeds the trigger point we set. Again, it will tell the user when these very hot scenes reach 'X'V input, which is OK occasionally but not OK constantly. There's also a trim pot to limit the output voltage to keep the signal within the amps gain/VPL settings window.

The whole thing with mega system DIY subwoofers is optimal performance. That means proper AC feed, signal chain bandwidth, signal chain voltage, power matched to EQ boost being factored into the equation, indicator lights to alert you of any need for readjustments and safe overall operation, etc. Otherwise, you're pi$$ing in the wind with high power amps and dozens of drivers.

You're welcome.




Prior to continuing, I need to determine that the aforementioned SPL change, is the same one I believe you're referring to; the one spanning the high 20's, to the low teens?



Again, I don't see the foundation of any disagreement. There's nothing on that graph that I'd consider falls outside of any convention I'm aware of. Maybe I'm wrong, but nothing inexplicable there.


The elements involved; the boundary impedances, the boundaries physical distance from one another. I'd suspect in Japan Dave's room, the Q of the 1, 0, 0 mode would likely be much better defined, thus, less influence either side of a better defined peak. When including less than robust boundary construction, room furnishings, and perhaps to a lesser extent the transitions to adjacent areas, maximum diagonal distances, I'd think the range included in the difference easily falls into the physics involved.



Bosso's take, sure makes me wonder. As I said before, I'd be foolish not to consider his opinion.

I have measurements that confirm a 7hz roll off though it's gradual and not a cliff down to 5hz before it gets bad. Not expensive measuring gear but does support it.