We Built it, We've measured it, HELP US TWEAK IT - acoustics of the BLACK CAT - Page 4

http://www.me.psu.edu/lamancusa/me458/10_osp.pdf



Not sure what this gives you.

Big clued me in - when measuring outside, the idea is to point the speaker up - duh!

Up is a good idea, but be mindful there will be reflections off the ground behind the speaker if you lay it down on or near the ground - just like rear wall reflections - making a comb filter for you.

Is that a concern when all he is trying to debug is the HF fall off?

No, just something to remember. It'd be nice if we had a picture and.or measurements of the setup so that the effects can be confirmed in the results - but like you suggest; it'll be pretty low compared to the roll off in question.

Nearfield Measurements! (Click on images for larger photos)

Suspended speakers on a soccer ball kick net pointing up into the sky:
Nearfield/Farfield overlays:
All nearfields measurements together:
Conclusions:

• all the speakers are look OK - the LCR (M&K) and the surrounds (Triad) are similar to each other
• the surround speaker's high-end roll-off is likely due to the tweeters being angled 45 degrees (link to speaker page)
• there continues to be a roll-off above 10KHz - likely a limitation in my measuring kit
• the room is having a noticeable impact on the LCRs between 4-10 KHz

I still have to redo to farfield measurement on the sub without the outside AC units running to test why there was a 60 Hz spike

Makes me want to move my build thread to the "Poser" Theater Design forum, because sadly, I will never be this "dedicated".

So will you be taking down some of the tratments affecting 4-10K and are you going to purchase a better mic?

Why boost the range, when you can take down/modify some treatments( assumption on my part), or as you said, add some reflective elements?

Exactly, the goal would be to treat the room first, removing as many anomalies as possible that way, and *then* apply equalization.

As of right now, I'm not sure what treatments are needed to boost the 4-10K range - I was hoping that someone would recommend a product or application...anyone know?

PS: I've been out of the country for a while, hence the delayed response

I agree with BIG about the linacoustic. I still haven't wrapped my head around the pertinent psycho-acoustic studies for early-arriving lateral reflections, but I think you're doing it somewhat backwards with the linacoustic. I hope someone will correct me if I'm wrong here.

As an observation, it seems that Dennis commonly uses BAD (Binary Amplitude Diffusor) Panels in the positions you have linacoustic. I don't have an image to compare the absorptive properties of linacoustic to an RPG BAD panel, but BIG's description of absorbing above 1K is pretty much opposite what RPG has designed into their BAD panel. They only publish data (in the graph at least) up to 5KHz, but the trend is clear, and I don't see any reason that the behavior should change patterns at any higher frequency range. (See RPG's data here.)

I still haven't found any way to price BAD panels without paying RPG for a consultation, which I don't even know if they do for HT on this sort of scale, but there are DIY versions of this out there. There is some research to do first (I might be able to help), should you consider trying to make one (several).

Those are not BAD panels. Those are another proprietary system from Quest Acoustics. Typically you see the PerfSorber which has holes and looks somewhat similar to a BAD panel. The BAD panel is a hard, semi reflective surface with holes creating diffusion and absorption by the underlying fiberglass. The PerfSorber is fiberglass with other engineered aspects to give a combination of diffusion and absorption. I am being a bit obtuse on the PerfSorber because it's design is not out in the public domain. The BAD panel on the other hand has been reverse engineered and there are DIY projects out there based on it, but both are patented.

Nice thread here.

At some point Jeff and I are planning on adding some additional content to the white paper and revising it to cover multichannel audio. Here's a link to the blog post containing the full PDF of the Acoustical Measurement Standards. I have had a few issues with it not downloading properly, please report back here on this thread if you have the same issues.

One particular area I think can be tightened up is the LF absorption metrics. The rooms I do now I try to get the 1/3rd octave within a 5dB window (not +/-5dB, more like +/-2.5dB) in the bass. I have also taken to giving more weight to the 1/6th and 1/12th octave measurements for linking the LF frequency response to how we hear. 1/24th is good to pinpoint issues but I do not think it links well to how we actually hear.

Lastly, it is perfectly possible to have a professional with the right knowledge and tools remotely design and calibrate a room. The most important factor is having someone on the other end who can operate the acoustical measurement gear for post build verification and calibration. This opens it up for people to use someone not located within their immediate geographical area without having to pay for travel and accommodation. Jeff does ALL of his work remotely, I do 2/3rds. I do agree that being remote is not quite as productive as being on site but on the flip side I find that when I'm onsite I end up doing most of the work myself, whereas when I'm remote I end up teaching the person on the other end much more of the theory and practice so they actually increase their knowledge and skills during the process.

Actually I do have one more thing to say about HAA. The training was awesome but really there is still a VERY steep learning curve after the training to get the Level II. So anyone who has the Level II should have the tools and knowledge to do a proper calibration as Sierra Mike Bravo said. Note that HAA doesn't teach you all that much about acoustic design and treatment, but they do teach you a very good calibration process. Like Dennis said the key is understanding how to interpret the measurements and understand how to tweak the design and /or calibration to improve things. I can say that Jeff and I are still learning new tricks and techniques with the acoustic measurement software and as the white paper should show it really requires a composite view of many different metrics to properly analyze a room.

Hi Nyal,

Thanks for posting! As you probably noticed, I'm following your "Acoustical Measurement Standards for Stereo Listening Rooms" point by point. I'd be absolutely thrilled to see an update for multichannel audio.

Right now, based on my measurements thus far as well as watching movies, I feel I want to address the low-frequency issues first - to flatten the response, increase SPL, and get deeper extension. My plan is to build a couple THT subs and put both of them behind the screen, replacing the M&K MX-150 that is there now. Those subs are very flat, have tons of SPL, and will reach down to 17Hz. If there remains a problem, it will likely be due to room modes, which might suggest bringing the MX-150 back into the room (perhaps along one of the side walls), adding some more broadband absorption or, if problem is just a specific range, a narrowband absorber (such as a Helmholtz resonator or a membrane trap). Another option might be to replace my "small" mains (LCR-850s) with "large" counterparts, but this is a last-resort type option for me.

Any thoughts about this plan before I start ordering and assembling?

Thanks!

To address a more in depth design element, HAA has had a Level III Design Certification for some time now.

Hey BIG. What adjustments did you end up making to the treatments, or are you guys still in testing mode?

Thanks!

I've almost completed the THT subwoofer build - just need to put the access panels on now... Once the sub is in place and I'm happy with the LFR, then I'll swing back to looking at the mid-range. So far there has been no change in the treatments...

HAA Level III? Maybe on paper, I've never seen a class offered or heard Gerry mention he was putting one on...

I've found the best education to be reading the AES journal and all the psychoacoustic studies. To me the areas still needing exploration are the links between what we measure and what we hear and low frequency modeling / optimization. We are making progress on those fronts but still a ways to go. It would be great if we could just get a computer to measure a room and tell us how it will sound! Maybe the scientific community needs to do a 'big data' project on listening rooms and home theaters. Big data (where you collect a ton of data and then mine it to determine relationships between elements) is what's hot right now in a whole bunch of statistical work.

BTW my numerical background is also atmospheric science... studied Climatology at college, my thesis was on 'the effect of El Nino southern oscillation on northern hemisphere storm tracks'

Awesome! That's great! Love colleagues in this field as well as the other one. HAA has had Level III on paper for sometime, but there are several issues that need to be addressed for it to move forward if it ever will. Hopefully, it will!

To address the LF, I built a 30.5"-wide THT (Tuba HT) subwoofer. I hooked it up to Behringer iNUKE NU1000DSP, which I put into Bridge mode, for roughly 750W RMS.

Subjectively, it's fricking awesome, but how does it measure? - that's what this thread's about


First, here's the farfield:


With equalization, I was able to get a pretty flat response between 20-80 Hz. My amp's cross-over is set for 80Hz, the the rest of the graph isn't too relevant. You can't see it very well, but it's +-2.5 dB, which is within the +-3dB range specified by Paul Spencer's Bass Integration Guide.

Notice the huge null at 90Hz. This wasn't there with my old sub:



And it's not in the sub's nearfield measurement:



My guess is that this null might disappear if I move the sub around a little.

Here are some more plots illustrating decay:





The lack of decay in the 20-40Hz range isn't too bad, considering that the dB drops 15 points within 150ms, but -20dB is the recommended target, so maybe I'm kidding myself about it...

More concerning is the lack of decay over 80Hz, but then again, my sub is crossed-over at 80Hz, so this somewhat disappears. I say "somewhat" as the main/surround speaker graphs I posted earlier (post #79) identified similar decay issues - specifically around 90Hz, 110Hz, 130Hz, 160Hz, 170Hz, and 270Hz.

So, it appears that my bass below 80Hz is in pretty good shape (anyone disagree?). That being the case, the next step is to try to address the decay issues between 80-300Hz - any ideas? - more bass traps I guess...

Oh, I forgot to post a new RC graph - this time I was sure to turn off all the HVAC units in the house



Notice that the spike at 60Hz shown in post #79 is no longer there.

I have a hard time understanding what RC number this is, but looking at other graphs, it seems that the dB level at 1000Hz is used, in which case this is RC-30. Does that sound accurate?

Thanks!

That Behringer amp looks like a nice piece - are you using unbalanced inputs to it? (ie. RCA to 1/4" TRS cables)

I had a subwoofer cable in the wall, so a RCA to 1/4'' TRS adapter was needed to plug it into the NU1000DSP.

This means that the iNUKE NU1000DSP is in my theater, which bring two small problems:

1. it's a little noisy
   
   • to be addressed by swapping the fan for the Noctua NF-R8
2. it's difficult to turn on/off, being behind the screen
   
   • this could be addressed by using using an IR or RF controlled outlet (e.g. this or this).
   • BTW, this is only an issue because the unit's "vampire" load is 20W - as the fan runs all the time...

Another alternative would be to move the amp to my rack and run a speaker wire from it to the sub. Running that speaker wire now could be challenging, as it would have to run through the supply duct. I don't currently have a ground loop hum, but this might prevent a future hum from showing up as I swap equipment around.

But never mind all that, how do the graphs look?

before doing any major revamp, why dont you "loan" some equipment some a forum guy if possible in some way, if you know any good souls near by.

like a parasound amps and processor or amps teamed up whit your sr9200 for processor, for the back and/or front. just to see if it would help

Ex run the fronts of a amp L/C/R and back of the SR9200 , if you get a 5Ch you can bridge 2x2 CH to drive R/L if you someday get bigger speakers.


ex of amps to get of used market, i would be looking for deal on one of these.


older but still great, prob aound 1k$ or lower
5 ch
Parasound 5125 / 5150

thise 500$ or lower
3ch - 5ch
Parasound HCA-1205A / HCA-1205A / HCA-2205AT /HCA-2205A older version
stereo
Parasound HCA-1500A /HCA-1000A Maby for you subs!? then no fans



Newer Halo versions
5 channels
Parasound A51 seen around 2k / A52 seen thise around 1300-1500$
stereo amps
Parasound A21 / A23 "maby get 3x for R/C/L" seen thise around 500$ +/- each

Or
Rotel Rotel RMB-1095
Nad M25 7ch / Nad T975 / T977
primare 30.5 ch/ 30.3 ch


then theres the new kids - > Emotiva xpr 5 /xpa 5 /Xpa 3 or Outlaw 7500 / 7125
i dont know about thise never heard or seen one, but they cheap,









Btw on the Behringer fans, this guys says they run 24v so you can´t just swap in a pc one, he got a guilde on how to make it silent here
http://www.avforums.com/forums/diy-subwoofer-build/1084750-behringer-ep2500-4000-silent-fan-upgrade.html
Edited by simple100 - 11/27/12 at 4:23am

The Noctua NF-R8 fan replacement in the NU1000DSP made it whisper quiet. Honestly, I didn't expect it to have such a dramatic effect, as the fan-replacement threads suggest needing to do more (trimming the shroud, installing an inline resister, installing heat-sinks, etc). One thing that may have made a difference is that I was able to use 2 (out of 4) of the rubber-mounts that came with the fan - these replace the screws thus providing more decoupling. Regardless, I'm very happy that I didn't have to do anything else. Still haven't decided about how to switch the amp on/off - at idle, it's consuming 16 watts. I think I might disable its lights and see where that gets me and if I really care about the two pennies a day it might be costing me

@simple100 - please note that the NU1000DSP comes with a 12v fan (the ep2500/4000 is a different beast)

You're suggestion to borrow equipment is interesting - I hadn't thought to do that yet. So far my research leads my to believe that equipment-selections should have little impact on room-accoustics. It has been said that even decent equipment in a great room will sound better than the best equipment in a mediocre room. That said, I will soon be interested in what EQ / Audyssey could do after I start reaching the end of what I think I can do with room treatments.

yea not many think of borrowing, its a cheap way to see what way to go, invite ones friend over , let him take some units whit him, and make dinner/movie and feed him beer. sounds like a success, room aint going nowhere, so might as well put research to practice and test yourself before buying alot of new stuff, i got the vibe you on a budget, so seems the next step forward as you also still playing whit the new room.

oki well thats good then, on the fan,