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Post by digitalchris on Oct 1, 2012 23:00:46 GMT -7
What should my graph look like? I will quadruple check my wiring tomorrow but everything should be correctly hooked up. What basic settings are you using to enjoy your IB? How hot are you running you LFE channel? How loud is your overall volume, reference level? Is your room treated for bad reflections, etc? A video would be cool to see as well  |
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Post by ThomasW on Oct 2, 2012 7:09:42 GMT -7
The LFE spec, due to the extra demand placed on the channel for huge effects etc., requires an additional cal setting of +10dB, thus the 115dB for subs. In bass managed use use, the redirected bass can add even more to where a calibrated flat system can hit 120dB plus @ the LP. Then add the house curve to taste. Different rooms need differing amounts due to decay time in my experience. My 2 cents, .... further thoughts? Thomas, Chris? +1 |
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Post by ThomasW on Oct 2, 2012 7:16:10 GMT -7
What should my graph look like? It shouldn't look like that. It should be a nice smooth curve with a gentle roll off, very similar to what's seen in a WinISD sim Is that plot from one of the drivers near the side walls of the theater or from one in the middle of the room? |
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Post by FOH on Oct 2, 2012 10:04:04 GMT -7
A nearfield measurement graph should appear nice and smooth, with a nice gentle arcing curve throughout the range. without any smoothing the graph may have some small ripple, but still has a characteristic of a relatively smooth arc. This is really step one, upon mounting and initially firing up the drivers and measurement rig. Here is an approximation of how it should appear. It was the first result from a Google image search; www.hifizine.com/files/2011/06/Figure-8-Nearfield-measurement-example-Rythmik-servo-sub.pngMy suggestion, you've got to establish a good baseline, execute solid methodology and scientific method, and proceed in an careful and orderly fashion. There's some modal issues in every room, but you've got some wicked strong rear wall SBIR interference, that can be lessened significantly with treatment. As you've seen, the MFWs can help as well. The bass traps are good for the ringing, tightening up the LF decay, and lessening the difference of the peaks and valleys somewhat. Small, intimate spaces such as yours benefit greatly from acoustic treatment. Your rear wall should be an acoustic black hole (front wall too). It's not always beneficial, but in your room it seems to me like that would help. The way the destructive interference works, just some modust attenuation of the reflected bass energy off the rear wall (or any surface), lessens the problematic nulls significantly. Likewise, as jman very astutely stated, our perception of the deepest frequencies is a function of overall playback volume. The higher in level at which you listen, the higher the perceived amount of bass is experienced. It's not a linear relationship. This is one reason why the film industry established a level, reference level, so that when played back at reference, the relative balance through a reasonably calibrated system is enjoyable and possesses the desired impact. However, few individuals listen at reference, few systems can achieve reference properly, so balance the system to taste. Enjoy it the way you want to. I like an impactful, bass heavy mix, as long as voices aren't overly and un-realistically warm. The problem is listening to that precise, warm balance at moderate levels requires a lot more bass level than the same effect cranked up at realstic, live playback levels. Also, as I stated in a previous post, different rooms require varying amounts of balance, to achieve the desired end result. I'm used to adjusting balance, it doesn't bother me a bit to make small adjustments for a variety of situations. Many (most) enthusiasts merely set the system once, and don't re-visit the balance settings again. That's fine too. They calibrate the balance to a set playback level, and forget it. Yeah, there's guidelines for balance, calibration, etc, but it's your system, so tune the bass balance in the manner in which you want. I like to keep handy some reference material in different formats. BluRay, multi-channel SACD, two channel Red Book CD. With bass management, the levels and relative consistency seems to be all over the place. So keep a BluRay with some significant LFE subwoofer energy. I like the big finale to the How to Train Your Dragon, because it essentially spans the entire spec bandwidth of the LFE spec. There's others discs that work fine too, but it's got high level energy from 5hz, all the way up toward the upper sub range. It's very, very demanding, in a broadband manner. I'm well aware of how it sounds, how the system deals with it, and how the balance of ULF, LF, mid bass and higher should be relative to one another,... at a given playback level. Anyway, get it close with measurements, then adjust to taste. Then enjoy and don't worry about level changes, adjustments,... until component changes, etc. ----- I'm a little confused FOH, are you saying that the +10 needs to be added by me and it's not already mixed in? I thought it was already mixed into the soundtrack. This depends on both your disc player and your pre-pro/AVR. Players have differing set-up guidelines, and AVRs/pre-pros handle it differently too. This is an oft mis-understood issue, for clear reasons. Below; www.avsforum.com/t/748147/lfe-subwoofers-and-interconnects-explainedis an AVS tutorial on the +10 issue. Bottom line, get the IB nearfield measurement down first, this assure both the subs and the measuring gear are operating correctly. If you're not, you could just be chasing your tail in some of these other "measured" issues. Balance the channels at 75dB, then add a bit more to the sub output as needed to achieve the "feel", or amount of effect you want. Small rooms like that can really use a ton of treatment, you can't really have too much bass damping. As I've suggested before, fortunately, the most effective bass trapping approach using fiberglass, is also the most reasonably priced. Real thick bass traps, constructed with fluffy fiberglass is the most effective avenue at taming the bass down into the deepest octaves. Downside,...the additional space needed. Sort out the nearfield measurement graph issue, determine what issues you have and keep choppin' that wood.  Good luck |
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Post by FOH on Oct 2, 2012 11:40:37 GMT -7
One additional item;
Resent research yields results that illustrate that there exists a strong and clear preference for smooth, flat response for loudspeakers when measured and listened to within a controlled, anechoic environment. Placing these loudspeakers into a typical listening space tilts the response toward the LF, due to acoustic loading, boundary reinforcement, etc. Thus, the general preference among listeners is for a smooth response, with a general tilt toward more bass energy and a downward sloping amount of energy in the upper octaves.
Fletcher and Munson would be proud,... there's nothing new under the sun. Measured flat, isn't equal to perceived flat. However, they do get closer as the the playback level increases.
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Post by digitalchris on Oct 2, 2012 18:22:56 GMT -7
What should my graph look like? It shouldn't look like that. It should be a nice smooth curve with a gentle roll off, very similar to what's seen in a WinISD sim Is that plot from one of the drivers near the side walls of the theater or from one in the middle of the room? One of the middle drivers. I checked the polarity again, all drivers move into the room when a 9v battery is placed across the terminals. I have no idea why the graph doesn't look correct  As far as room treatment go. I've struggled for months now with ideas on how to cure my issues. In order for treatment to be effective down low, it takes massively thick fiberglass traps or tuned absorbers. I don't have much room for such thick traps and no knowledge on how to build tuned absorbers. It's so hard to get specific help in the forums. There are so many ways to build tuned absorbers, so many kinds as well, I don't just know where to start  I'm at a point right now (one of many that I have encountered during this journey) where I wish I never built the room even with how great it turned out, I feel like it was a waste  I knew it wasn't going to be "easy" to get a great sounding room but mother of god did I underestimate how hard it would be. Plain and simply, it just isn't fun anymore. |
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Post by ThomasW on Oct 2, 2012 21:07:51 GMT -7
I have no idea why the graph doesn't look correct Could be a problem with the measurement system. In one post you talked about having AT material, are you using a AT screen? If not is getting a AT screen a possibility? If a AT screen is a possibility the you might consider what's called a double or single bass array for the sub drivers. |
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Post by digitalchris on Oct 2, 2012 22:55:54 GMT -7
If it's an issue with my test equiptment, I'm not sure what to do in this situation.
I have not thought of a SBA or DBA because I've never heard of it but now that I read a bit up on them, it sounds like a cool idea, just not for me because if my bottom subs aren't located at the 1/4 and 3/4 points on the wall, side to side and top to bottom, some serious modification will have to be done. But to answer your first question, I do have an AT screen.
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Post by chrisbee on Oct 2, 2012 23:05:22 GMT -7
That just ain't right. That graph does not look like any nearfield measurement I have ever seen. Consider borrowing or buying another SPL meter. Or another soundcard. There is no physical way to mess up a nearfield measurement to achieve that curve. Nor could a bass driver make that curve when measured nearfield. 105dB(C) at the listening position read directly on an RS SPL meter anywhere between 10 and 20Hz is very satisfying indeed. As anybody with a modest subwoofer will attest. My old SVS cylinder could just manage this level and it was great fun and downright scary for several years. Higher levels just add to the fun and the scariness. Let's not demand them as standard issue to be able to enjoy films and music. It just makes people feel inadequate and hungry for far more than they really need. Quality before quantity.  |
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Post by digitalchris on Oct 3, 2012 0:59:11 GMT -7
I'll try doing a sweep while holding my RS meter nearfield of the sub and see what that looks like for haha's. Also, maybe the cardboard box that I had the mic sitting on offered interference? The mic was hanging off the box a few inches but maybe the box still fedback some negative harmonics? I'm also thinking of taking the theater SR5005 and swapping it out for the upstairs SR5003 and then see what kind of graphs that produces. It'll be a PITA but might be worth eliminating as a reason for some of my measurements? Unfortunately, 105db peaks throughout that scene weren't very impressive. I could "feel" them I guess but no chair vibrations or floor rumble... My floor is on suspended plywood, it's not like I'm on a concrete slab so I don't know |
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Post by digitalchris on Oct 3, 2012 5:03:50 GMT -7
Ok guys, that close range sweep was my bad, I forgot to unhook my LCR speakers and up the x-over point. This graph is sub only with crossover raised to 250hz for the test. Not much better but more normal at least?  |
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Post by ThomasW on Oct 3, 2012 7:06:15 GMT -7
Also, maybe the cardboard box that I had the mic sitting on offered interference? The meter should be suspended at the end of a pole with no structure around it. The best thing to use is a boom mike stand. They're like $25 or so  BTW it's ok to use a little bit of smoothing for the plots |
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Post by FOH on Oct 3, 2012 9:09:48 GMT -7
Chris,
A nearfield subwoofer driver measurement is perform with the mic very close to the center of the cone. But not close enough for the cone to touch, perhaps within a couple inches. This renders the room's influence insignificant relative to the direct energy off the cone. The final measurement should be a nice gentle arc across the graph.
Yes, measurements require a mounting method for the mic. A cheapo Chinese knock-off will be just fine.
We really don't know what's going on until the close measurements are taken, then the process can begin. Until these steps have been taken, there's no sense in worrying about the response. I know, easier said than done at this point, but quite true nonetheless.
I doubt there's an acoustic related issue, especially a bass frequency response issue, that can't be adequately resolved in these pages, .... or over in your threads at AVS. However, if an inexplicable issue did come up, the pros at the GearSlutz acoustics forum would slice and dice your troubles away. When this first came up, I suggested the GearSlutz forum to you. This exactly what they do.
I also suggested EthanWiner's forum, which I follow. You posted your question and Ethan answered a couple items, and said he'd be glad to get to the bottom of it for you, but you never returned. Whatever forum you choose, I'd stick with it, not move around unless necessary. There's a wealth of knowledge at each respective venue, .... including this one here at The Cult.
I know this has been frustrating, that's clear. With a careful and steadfast approach, and with some modest gear (mic stand, EQ, separate amp channels, fiberglass) this is resolvable. What' transpired to date is history, move forward a step at a time. Identify issues, then one by one address the easy stuff, .... and then whatever issues remain, reduce them one at a time.
This is doable. You can achieve a nice listenable smooth response with all the impact you could ever need.
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Post by digitalchris on Oct 3, 2012 16:59:45 GMT -7
How this for a boom mic stand   Since this is only for my near field measurements, I decided to make way with what I had. I already have a rig for seat measurements. Let me head back downstairs and run another sweep and see what this setup yields  |
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Post by digitalchris on Oct 3, 2012 17:05:25 GMT -7
Well, same graph as expected. If I smooth by 1/6 or better, it looks ok but at no smoothing, very wrong as you've mentioned. Should there be that many hills with no smoothing?
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Post by digitalchris on Oct 3, 2012 20:14:48 GMT -7
Ok, after playing some more, I have some good news at first glance but not so good news once details have been said. After playing around with more settings and implementing the eq.2, I came up with some very nice graphs... the downside? I had to crank up the MFW's a bit much and added a boost of 4-5 db at around 30hz in order to get these graphs. I'm definitely worried about over driving the MFW's. What do you think?  Now what this does tell me is that with proper sub placement and eq, I can get some nice graphs. It get's me thinking about your other idea from my build thread Thomas. It wouldn't be hard at all for me to implement two of the IB drivers into the rear of the room but they would have to be in a manifold instead of a line array (unless you can explain how to mount them into 16" cavities again, super thick baffle?) and have to be in the right rear corner about mid way up the wall firing toward the opposite wall. I just have no way to test that exact spot without actually doing it. I did place both of my MFW's sort of against that wall and the graph went a bit sour so does that mean the IB's won't be as much of a help as I would hope for? Food for thought... time to go to work |
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Post by jman on Oct 3, 2012 21:45:28 GMT -7
Your first graph on page 1 would suggest that your mains are a bit out of phase with your sub (note the dip in the 60-80hz range) and how that vanished when you measured just the sub. Try adjusting the sub distance setting by add ~3'. So if you had the mains as being 10' away ad the sub, 11', make that 14'. There is an inherent group delay from speakers to sub.
You may find the MFW's are more of a liability than an asset since they can't keep up with the IB. If they help at lower levels, they can't possibly do so as the IB outpaces them at higher levels, making the exercise pointless.
If you have an eq for the IB, don't be afraid to add some boost down low. I had 1 band of boost at 20hz of about 6db and about half an octave wide.
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Post by digitalchris on Oct 4, 2012 2:51:07 GMT -7
Yeah, I too have a feeling that the MFW's will run out of steam, even though I won't be pushing the IB's anywhere near their limit. As far as my distance settings, you will see as of my most recent graph, I have no more dips up untill 80+ hz except for two smallish ones, one at 60hz and one at 82hz. I achieved this by playing with x-over points and subwoofer distance settings. My current graph was the result of boosting the MFW's up overall, adding a 3-4db boost around 30hz (to the MFW's) and dropping the overall subwoofer distance down to 2.8' I believe. Now, I still have some major funkiness going on above 100hz but that can be resolved a little later, I hope  Still contemplating a rear dual driver IB setup. Is there any reason why I can't go with a manifold back there for ease of install? One driver will be only 1-2 ft away from a sidewall which might be a problem? Do you also see any reason why that spot would be a bad idea? The drivers would be mounted about half way up the long wall in the rear right corner...  |
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Post by ThomasW on Oct 4, 2012 18:20:01 GMT -7
Still contemplating a rear dual driver IB setup Rotate the manifold so the drivers are horizontal If I were in this situation and had an AT screen I'd experiment with a single bass array. |
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Post by digitalchris on Oct 4, 2012 18:51:49 GMT -7
No, but how does that location test? Rotate the manifold so the drivers are horizontal Again how does the location test? If I were in this situation and had an AT screen I'd experiment with a single bass array. and have to be in the right rear corner about mid way up the wall firing toward the opposite wall. I just have no way to test that exact spot without actually doing it. I did place both of my MFW's sort of against that wall and the graph went a bit sour so does that mean the IB's won't be as much of a help as I would hope for? Also, the drivers would already be horizontal if built in a manifold, that way the manifold will seal up against the 16" stud spacing. If I install them into a manifold, one driver on the left and right side of the manifold, one driver will be very close to the concrete wall in the closet. Not sure how that would work out knowing the drivers need room to "breathe". And as far as a SBA goes, it can't be done, not with my IB drivers. My wall studs don't permit the install. |
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