Seperate drivers for LF and ULF or one driver? - Page 12

How does one do this?

You already are MK! The phase/delay on your DCX

Not at all Max. As you mentioned it lines up very well with what I am seeing. I expected the peaking near 45Hz before I even turned on the measurement gear for the first time because I experienced it in my old room which had similar placements of the subs and LP and a similar length dimension. I keep ending up with long rooms in which I have to put the LP near center of the length and of the total room volume for that matter. The placements are what they are really so yes it is up to other DSP tweaks to smooth things out.


This is all from the main LP with all 4 subs operating and no DSP involved.

Impulse


Waterfall of the subs raw at LP 1.


Group delay


Excess group delay

Edited by Ricci - 9/7/12 at 1:00pm

FOH,

I view freq and time domain as the same thing. As far as subs are usually concerned, changes in one will effect changes in the other. Some people see a sharp drop in freq response, I look for the 1/4 wave reflection or mode. Absorb the reflection or use careful placement to avoid the mode or use multiple subs to cancel it, and you fix the problem. Peaks are much easier to fix with EQ. Freq and time; they are just a mathematical transformation away from one another.

Ricci,

Let us know what you end up with!

JSS

Agree 100%.

Great stuff with the calcs/graphic. I agree that it never works to sit in the center of a room. With that, it would be my suggestion to move the seat back as shown in the alternate layout shown below:



I would also experiment with stacking in the FR corner although Josh hasn't mentioned the sub box dimensions (or may have and I missed it). I very much prefer to move the LP than to dig that much of a hole in the signal.
Edited by bossobass - 9/8/12 at 7:20pm

Some great posts! I'm learning a lot for my own set up from this. Great to see the collaborative effort that I like so much about AVS

Dave...Each sub is 24Wx24Hx36L" roughly with an 18" on each end and weigh probably 250lbs each at least. Big heavy subs to say the least. I could maybe try your layout suggestion but I will have to build a stand for the back left surround to raise it up over the couch. All of the (rather large) mains currently sit on the subs to save on floor space. Anyway that would allow about 2 or 2.5ft to move the LP back. I may try some of Marks suggestions and / or this when I get the time to delve into it again.

That said I have been watching some movies and concerts with the 30-60Hz area battered down with EQ and it sounds pretty good to me really. I also took a few loud sweeps and distortion measurements. Even at a sweep that generates 115dB at the LP there is a lot of headroom left with the drivers barely doing 1" peak to peak and the amps nowhere near clipping. The distortion looks good through the deep bass but there is an uptick in H3 at 14Hz, H2 at 22Hz, etc. all corresponding with a huge acoustic boost of the harmonic at 40-45Hz. It is not too bad in the deep bass but there are a couple of large and sharp peaks in THD at 73 and I think 110Hz which are both the H2 and again are related to the room acoustics boosting the harmonic and diminishing the fundamental.

Ricci,

That's awesome you have that much headroom. With sound treatment/setup in small spaces, it's just like directors view films they work on. They are never really 'finished', only 'abandoned'.

Let's all harken back to the first time we took measurements with test tones and a pad and paper before we knew REW existed....when all we had was level controls for each channel on a receiver.....and the only thing we could do to help freq response was the subwoofer crawl? Remember your first REW sweep? Mine was Himalayan. But prior to this, the blissful ignorance convinced you that it was 'good'. Strange how we become accustomed to good presentation....

I still remember after EQ'ing flat (only had 30Hz extension at the time), I took out a 60Hz peak I had (which looked awful on REW), and remember the scene in Transformers 1 where Megatron first transforms inside the Hoover dam. With the 60Hz peak there, I remember a distinct chest/gut 'slam' when his engines fired up, which disappeared after EQ. I gained accuracy, but lost tactile feel, and lost a part of the movie I enjoyed due to the sonic impact of having a 9dB bump centered at 60Hz. All this was at a time in which I was mains/surround limited to -15dBRef playback.......

Ahh, how spoiled we sometimes get....All I am chasing down at the moment is a 45Hz dip, and some 100-200Hz 1/4 wave suckouts, and I have needed more capable mains/surrounds for years. I sometimes miss that old 60Hz peak sometimes and I think about it every time Megs fires up his engines, because I enjoyed that film with 7 other friends that evening, after an awesome WiffleBall tourney and a great dinner....and with a single sub, I can guarantee NO ONE got the same LFE presentation in that room.


JSS

First.... BALLLLLS!!! You're insane. Did I read that right... 8x18"? I have no doubts that you could easily get by with half that.

That's the rub with heavy EQ pull-down... the THD shoots up even though the FR is flat. Still, every test I've run with listeners who are listening for nothing more than to offer their preference between 2 systems almost always and unanimously prefer the higher 2HD system with music and no preference with heavy-ULF movies. Every year I doubt the fuss over THD is worth debating a bit more.

I have moved my main seats forward more so than I prefer regarding viewing and the surround placement in relation to the main seats to get a flatter response from cross down before any post EQ because it just sounds better in the end. That much of a hole in the signal sounds to me a bit like too much compressor on my bass guitar. You're prob right that it's a slight difference and a nit pick in the end.

All you really have to do is move your mic where the primary LP would be if you moved the furniture and see if the hump is less or not. I'd be interested to see the difference, if any.

Josh.... dude.... build thread.

What are you impressions josh of the RE's sealed and then the massive ported setup? That output just seems tasty, even though the box is massive, I am assuming there was a little added efficiency with the ported?

Max,

Post #338 = Exactly.

I think about this kind of thing all the time especially whenever I start getting too anal about the measurements or set-up. At the end of the day it's about how it sounds and whether it makes you happy. It doesn't matter if it is a big 10dB hump at 50-70Hz, the SW level ran +12dB, a broad midrange dip, boosted highs for that extra sizzle, shakers, or whatever floats your boat. It's your system, do what you like with it. Over the years I have come to like a flatter bass response shape but I remember at first that it sounded weak and uneventful. I was so used to the bass having huge peaks and being dialed in way too loud. Coming from car audio and live sound it is no surprise. Anyway 15 years ago in the late nineties I was jammin out on my Infinity SM112's and dual Velo CT-150's that I had saved up money for from many many hours working at a truly crap job and thinking that it was fantastic. All of my friends did too. I had no measurement capability at the time and nothing but a cheap SPL meter and the bare amount of controls offered in a middle of the road reciever back then. This is about the time that I heard about the sub crawl. The room I had back then was crap with windows everywhere, hardwood floor, drop ceiling that rattled with the bass, etc. I am pretty sure that if I measured it with the knowledge that I have now it would have been a real train wreck. But it was "the stuff" back then. Now I'm worrying about properly gain staging to minimise system noise and fretting over good time alignment. (I put about 5 hrs into the levels and gains on Sunday.) Comparatively small things that I would have been utterly oblivous to begin with back then. These are good days for audio.




Scott,
Meh...Most of it has been covered here and there in various threads over the past 4 or 5 years. If I get time maybe I will but it's mostly done until I get to new mains and eventually some treatments. It's nothing special compared to some of the systems some other guys have around here. Hell I'm rocking out a 73" Mitsu DLP still and probably will until one my TV's dies.



Beast,
The ported guy is truly ridiculous below 30Hz and does offer a big output and sensitivity advantage there but the cab is huge and it has to be since at minimum an 8" port is needed and a 10" port is really required IMO. Here's the rub, a sealed one is already pretty potent down low and using the cabs I currently am, 6 drivers are fitting in the same space as the single driver in the ported cab. Not to mention that this total space is broken down into smaller modules which are easier to place or transport. 4-6 sealed drivers outperform a single of the same driver vented every time. The downside is it costs a lot more $$$ to buy all of those extra drivers. This is why I didn't go with a pair of the giant vented subs. They would have taken up about 70% more room volume than what I have now.
Edited by Ricci - 9/10/12 at 10:30am

"Meh"?

"Nothing special"?

Wwwahhhhhhhhttt?!?!



"...if I get time maybe I will..."




*sniff* Ookayyy.

I tell you what Scott...You make a build thread for your ridiculous 1.71 giga-watt project and get those other RLP's up and running and I'll start a thread for mine.

Will do, sir! So I should be expecting to see an awesome writeup on them eight XXX18's pretty soon.

*wink wink*

*hint hint*

Yes 8 of them. The reasoning is a long story but let's just say that the plan was always either dual opposed 18's or 21's and I had assumed that it would be some other drivers with a better all around performance. I realized that when I did rarely run into limitations with 4 it was still in the <25Hz region first. I already had 5 acquired slowly over the years so instead of selling all 5 off and then purchasing 8 of something else it was just easier to buy another 3 as deals popped up. In my old room the amount of gain was not that great since it was very lossy and large so I could run up to about -7 to -5dB from REF for the big 5 star HTTYD, WOTW's, TIH type of movies before running out of clean headroom. I typically listen at -15 to -10 so that was truthfully plenty for my needs already. So then I doubled the amount of drivers, increased the amplifier power and moved into a 1,000cu ft smaller much more solidly constructed room. What would have simply been generous overkill is now transformed into unnecessarily excessive amounts of available headroom waiting to be unleashed. I do love sonic excess. But seriously...It's completely unneeded for any sane playback levels.


I will try moving the mic to the "possible" spot and see what it does around 40-50Hz. I could stack the subs all up front, left and right ,or 2 in the back right corner. It's a possibility.

I agree with you about THD. After listening to so many tests in an outdoor environment it really does take a very large amount of distortion before it becomes easily noticeable and even more before it becomes offensive and this is in a dead environment with back to back isolated measurement tones. In a vacuum of course we want distortion and noise to be as low as possible but I put it pretty far down on the priorities list now. A couple of % isn't worth getting worked up over certainly. I totally agree about the preference leaning towards a little higher THD as well. Adding some H2 and even a little H4 in suddenly makes everything sound 'fuller" or "fatter".

I understand your reasoning with going for the sealed setup as you were already a good ways there wrt the amount of drivers. So in my case, where I only have two, I'll either take two of yours off your hands since you dont really need them . If not I will maybe buy two more, or would you suggest I look into building out something similar to your vented cab to make my two be a little more robust and take advantage of the sens. increase? I had a little room to spare fitting two of lilmike's f-20's (depth and length wise) in there previously and actually liked the look as it basically created a "front stage" type look. two long enclosures spanning the full 11 foot width of the room doesnt bother me at all

EDIT: Or if you arent using that box, Id just love to demo it. we are only about 5 hours away from each other...
Edited by beastaudio - 9/10/12 at 2:06pm

You are in luck, PM Ricci!

I linked this thread in popalock's build after Bosso posted some interesting information that related to the discussion that formed here. I still stand by what was said by myself and Bosso, that at VLF sound behaviour remains as sound waves no different than LF, MF, and HF, except that in the typical home environment the wavelengths are so long they become no modal and entirely constructive, yielding increased SPL as frequencies decrease. The increase is proportional to the lossyness of the reflective boudaries, however. As a result of my post, LTD02 posted the below.

Thanks for your post LTD02. Previously in this thread we were told that the increased SPL as frequency decreases (relative to the anechoic response) was a result of Pressure Vessel Gain (PVG), then from a huge Hemholtz Resonator in the room, the sympathetic resonances. And now the above.

I've read the noted sections in the provided link and fail to see anything in there that changes my opinion of how sound works. Perhaps you could clarify LTD02.

In Section 2.2.3 the authors discuss "Compactness". What I get out of this section is that as wavelength becomes proportionally large, the Hemholtz number (He) becomes much less than 1 and the fluid can be treated as an incompressible fluid in the compact region. The section goes on to call it an acoustic field with waves.

In Section 4.1 on Plane Waves, the section describes wave behavious in a infinitely long pipes for the purposes of duct acoustics, and goes on to say that the acoustics may be approximated by that of an incompressible fluid.

I feel that these first and foremost don't offer support to the idea of PVG and also they are not applicable.

I hope raising up this thread was a good idea

I appreciate you digging it up. Looking forward to reading through it. Thanks for your feedback on my thread. Learning more and more every day.

I believe you are confusing the general simplifications under specific conditions as precise descriptions of operation. A good equivalent would be the assertion that a line source of sufficient length attenuates at 3dB/doubling of distance (more accurately 10dB/10x distance). In more detailed evaluation we find this to be a simplification of the resulting interference observed from an integration of a source of a given length. This simplification holds within a specific distance range and within some distance or angle from the ends of the line. In reality, each integral point on the line radiates as a point source with an attenuation of ~6dB/doubling of distance (more accurately 20dB/10x distance). The observed reduced drop off with distance is a matter of perspective. In fact at closer distances there is progressively more deconstructive interference, and every point behaves as we would expect, and at some distance far enough from any finite line we will see the equivalent delivered power of a point source with the total power of the integrated line.

Similarly, a 4th order bandpass with sealed rear chamber and ported front chamber is a specific case of a front loaded horn. It is mathematically wasteful to utilize a horn type model for specific cases of a bandpass, but it better encompasses the behavior. In fact I just finished up a very space confined design where I had to switch to a horn model to be confident in the behavior, as the port became close in area to the point where it entered the front chamber. The excursion and impedance was very closely related with some magnitude response variations which make sense and should be more accurate. We'll see for certain in a few weeks.

If I've understood what you mean correctly, you're saying that PVG theory is a general simplification and I'm confusing it with a precise description. That may be the case, but based on the previous posts it sure seemed to me that LTD02 et al thought of PVG as a precise description of operation and not a general simplification. If it is a general simplication, great. I believe there are better general simplifcations, but if PVG is an easier way for people to understand the precise description, I'm ok with that.

Have I understood you right?

"I've read the noted sections in the provided link and fail to see anything in there that changes my opinion of how sound works. Perhaps you could clarify LTD02."

the link explains what compactness is (where the enclosed wave is much smaller than a 1/2 a wavelength) and that in a compact enclosure air behaves like and incompressible fluid.

so, going further. there is a region relative to an acoustic source called the "hydrodynamic near field". in this region, which varies by definition but is generally <<1 wavelength, the acoustics are very different from the behavior in the far field--air particles behave differently, pressure and waves behave differently--it is a whole different physics from the far field acoustics which you are familiar with.

pressure vessel gain is simply a way of describing the effect of turning the entire room into the hydrodynamic near field.

an interesting thing about the hydrodynamic near field is that sound does not drop off at 6db per doubling of distance until you are outside of it.

I've wondered a few times that if a speaker/sub is producing 100db at one meter, then does that mean at 0.0625 meters it will be 24 db louder, never read anything about it, perhaps the above is at play here?