SME

Hey @jay michael. If using the same amp when running everything together, definitely get the same drivers. Otherwise, it's not nearly as important.

FWIW, for the Denon and Marantz AVRs and processors I know of, if you have bass management enabled, they cannot pass a WCS signal at master volume "0" (or 80 for you) unless the subwoofer trim on the unit is set to the lowest setting of "-12". This assumes Audyssey is turned off. If Audyssey is turned on, it's still possible to clip. If you don't play higher than "70", then you should be OK with the trim as high "-2" without Audyssey. With Audyssey, you might still want to go with "-12" because Audyssey can boost (IIRC) by up to 9 dB. These days I use my Denon without bass management and without running Audyssey. I do it in my own processor downstream. Hence, I can get away with putting my sub-trim at "-2" in theory. (LFE channel alone needs -10 dB compared to LFE+LRCS.) In practice I have mine set to "-7" and mains set to "+3" as this let's me go as high as +5 dB vs. reference, in case I need that.

I think it means "no longer available". I don't have answer to the question though.

While I for the most part agree with you, I would ask then: why does bass so often end up different on different versions of a mix? If we presume that the mixes are being mostly let through untouched, why does the sub balance get touched so often? Do these mixers frequently identify undesirable bass (whether too much or too little) as a down-mix artifact? Oh yes! My HT system is definitely at its best, so far. And I find that this is a good defense against crummy content. Too little bass? I'm still feeling and enjoying it. Too much bass? It's heavy-handed but doesn't pull attention away from the presentation. The perfectionism I exhibit above has led me to realize that if I find a soundtrack annoying in some way, it's almost always partly a problem on my end. That's great, because it means it's worth striving for better. I don't have to give up because "most soundtracks suck and it's not worth more investment of time and effort". To connect this with above though, I suspect mixers aren't getting good bass if they are so inclined to make changes to it. That's unfortunate, and hopefully that will change for the better some day. One last thing about movie sound. I'm finding these days that I often enjoy the sound in lower budget movies more because they are likely to do a lot more recording on set rather than green-screened. My system is so transparent now that it's distracting when the acoustics in the sound don't match what's on-screen. I also have to give credit to the sound designers of many animations who clearly go through pain-staking effort to make the acoustic spaces believable. And then there are many 9 figures budget visual effects bonanzas with sound not much better than TV programs. This will really shock you, but it turns out that some entire movies are really quite terrible too. And yes, bad movies often get accompanied by bad soundtracks. Anyone remember "Mortal Engines"? There was some messed up stuff in that one!

Also what you measure is SPL at a point. What Hornresp simulates is basically SPL RMS-averaged over the 2 pi space (assuming you configure it for 2 pi space). So directivity effects will cause significant deviations in measurements vs. simulation at higher frequencies.

Two different mixes could very well be the case, and I'm thinking they may have an exclusive room for Atmos mixes that's different from what they use for the other mix(es). This is only a guess, but it's based on my impression from things I've read. It's also entirely possible that the two rooms use very different technologies including "room EQ" or whatever, so the greater bass in the Atmos mix certainly could be compensation under the mistaken assumption of being "calibrated". Or maybe the Atmos mixes are getting pumped bass on purpose in response to all the angry people on forums complaining about mixes with weak bass made for TV speakers. So they put a lot more bass in the Atmos mix to try to stop that. I guess people here would rather have a more balanced / less-loud mix. More extension instead of more 25-40 Hz would be great, right? Honestly the more I try to figure stuff out in audio, the less I'm convinced anyone knows what they are doing. :) It's unlikely any of these mixers are hearing what's on the track honestly enough (neutral enough) to make judgments about what kind of bass should or shouldn't be there, from an objective standpoint. And that says nothing as to what various people at home are using, which is probably also far from neutral and likely to be deficient in most respects, so they'll appreciate MOAR too, right?

What orientation was it in when you measured?

Can you plot your measurement against the simulation so we can see how they differ? There are definitely reasons why you're likely to see differences between the two.

Bummer, but thanks for donating the body for science!

I suggest turning off that EQ. Such dips are often caused by localized interference effects which listeners should largely be able to hear through. For me, those frequencies are felt at least as much as they are heard when they occur in complex music, so if you are feeling more sensation at those frequencies, it probably means you've got peaks there.

I'm not a perfectionist. I just have high standards. That's what I would say, anyway. However, perfectionism seems to actually be a virtue with audio, provided one is able to identify the aspects that actually matter. Under normal circumstances, nudging MBMs probably wouldn't change much of anything. This is true even for me when they are far from "optimal" placement (presumably close to where they were when last measured). I'm hoping I will be able to improve my optimization methods to reduce this issue. I am fairly confident I can, but we'll see.

Yes, but at 1/4 wavelength the loss will be pretty modest. And here again is a reason to have extra headroom to work with. For your situation, it sounds like 4 Skrams is plenty for output. Where 6 or 8 would come in handy is the increased placement flexibility and potential for sound-field control. Though I guess you have to decide whether it's worth hauling extra gear for each different situation. That's the real downside to having more gear than you need. Once it's setup, you can always turn the gains down on larger numbers of subs. And I agree that there's a lot more to good bass than sheer quantity. People routinely assume that high SPL is required for visceral impact, but that's not the case at all, especially if high quality is the goal. As far as I can tell, one can experience tactile sensations from bass that's barely above hearing threshold. The answer to the question of whether one can "feel the bass" depends more on the quality of information received by the brain than the SPL. Sure, one can always induce sensation given enough brute force, but I believe it's also possible to have sensations that are tight, rich, and detailed, and that you can still feel (albeit more subtly and with less "bottom") at low listening levels. We experienced as much in here with the Tool album, in which the rolling kick-drum sensations were still there at a "background level".

Excellent questions! My formula is for center-to-center spacing and it assumes point sources. The cabinets do radiate over a width, which can help but doesn't make much difference until they get pretty close together. Otherwise, I think you have the right idea. The 1/4 wavelength is really a fuzzy rule-of-thumb. What you *really want to avoid* is playing frequencies whose 1/2 wavelength is the distance between centers. Then the subs will be literally fighting one another. I swear, no matter how much we encourage newbies on this site to go bigger than they think they'll want, they practically always start talking about "adding more" soon after their first DIY project is complete. It really is a long running joke in the world of DIY subs.

OK! I re-did the FOTR:EE Tomb fight / Balrog comparison. This time, without the spider webs between my speaker terminals! Another factor that may have affected my earlier assessment is my low frequency response. It's a bit of a long story, but what I have now is not really stable vs. small environmental changes, particularly the precise locations of the MBMs which are light enough to be accidentally slid. You'all will think I'm *nuts* when I say that fractional millimeter changes to my MBM positions matter, without being able to hear a kick drum literally change tune upon such a manipulation. It's not subtle stuff, and I find that bass response has a *huge* impact on perception of higher frequencies too. (Really, every part of the spectrum interacts with every other part of the spectrum. As perfection is approached, new properties emerge.) This time I put one disc in each player and synchronized them, so I could bounce back and forth. This time, I perceived the sound to be much better overall and the differences between them to be much more slight. In terms of subjective loudness, they were identical. Both sounded "right" at -6 dB vs. cinema ref. The biggest difference is that the Blu-ray sounded more extended and just a bit brighter. I also noticed that the DVD sounded a bit warmer, and the bass had a bit more of a "rounded" quality. However, I suspect these differences could have had everything to do with the extra treble in the BD. Because of this interaction, I don't think I can reliably judge differences in the bass quality. For all I know, the bass in the tracks could have been identical. In a blind test under the circumstances, I think I'd lean slightly toward the BD version because the treble sounded more extended, but I think it would have been better if they'd toned it down just a bit, to let more warm mids (and mid-bass) through. Regardless, both tracks sounded fantastic this time. I'd never noticed before but when the cave troll swings the huge chain around, I could actually *feel it* as it swooped by overhead. The score was mixed very hot into the surrounds and hearing it was like being right in the middle of the orchestra, albeit surrounded by a bunch of timpanis which were pounding my chest like crazy. Again, I thought the DVD had a warmer sound, but the transient detail seemed to be there just as well in the BD as in the DVD. As I post-note, I want to point out that I spent easily thousands of hours trying to optimize my treble response (with particular focus on the top end) to figure out how to get the sound I have now. In that time, a lot of tracks that I'd found to be very harsh and loud sounding changed completely in character and now sound absolutely wonderful. It's convinced me that top-end response quality is a huge deal, and yet few if any transducers do it justice. I would guess that the DVD would sound cleaner than the BD for a lot of people, simply because the extra top-end on the BD is likely to add a lot of hash to the sound on less-than-ideal systems. I'm not sure how to judge this decision, from a mastering standpoint as it's a case where the extra treble does improve sound quality on "nice" systems but likely at the expense of enjoyment on lesser systems. The resolution I prefer is for everyone to have better playback systems, but I may be a bit of an idealist.

In a room that narrow, you might be able to get away with spreading the Skrams out evenly across the width of the room with "half-spacing" between the Skrams on the sides and the side-walls. Visualize each side-wall as a mirror, and then you can "see" that this effectively creates a very wide virtual horizontal line array. It'll likely work even better with 6 Skrams because of the tighter spacing. Ideally, you want spacing to be less than 1/4 wavelength (tighter still is even better). For Skrams set 5 feet apart, the 1/4 wavelength is around 57 Hz. (Simple formula: wavelength equals 1136 ft/sec divided by frequency; then divide *that* by 4 to get the 1/4 length.) If set 3.3 feet apart the 1/4 wave is at around 85 Hz. Nice! This is a big reason why it's very good to be over-provisioned. Recall that every +3 dB increase involves *doubling* of power and dissipated heat. Likewise, every +10 dB involves *10 times* the power and dissipated heat. I just love the mental image of the Skrams drawing people in like moths to a light, causing them to swoon in front of them.

Oh? I wonder how it detects that? I guess I'd have to read the manual or something to better understand what it's doing. Maybe. Like I said, that's only a short-term average, then you could be clipping a lot more than you realize. The peaks could be quite a bit higher and be clipping even though you don't see it go over "0" much. To avoid this complication, you need to use an artificial signal like a sine wave. You may want to do this with the speakers/sub(s) disconnected, if your amp is OK running like that. Then you can test using high level sine waves without breaking anything. Presumably REW lets you run a "worst-case scenario" sine wave by setting hte level to near full-scale (-3.02 dB in REW) and sending it to *all channels*. Start with the master volume low and watch the MiniDSP input volume. Slowly increase it and watch to see if it tracks the volume changes dB by dB. If the level shown in the MiniDSP does not increase as much as it should, then you know you are clipping, either in the Denon output or MiniDSP input. If your Denon is like mine, then MV "70" is the same as "-10". If you are using bass management but have Audyssey turned off, then you need to keep the sub trim at -2 dB or below to ensure nothing in the receiver clips on a worst-case scenario (WCS) event at MV "70". With Audyssey turned on, you need more headroom, and it's tough to say how much. IIRC Audyssey can apply boost as much as +10 dB, and that's not counting the extra headroom needed for other aspects of the EQ. If you are clipping on the MiniDSP side, IIRC you can set a jumper to attenuate the signal coming in so that it doesn't clip. My Denon puts about a bit over 4 Vrms, which may be too hot for the MiniDSP without the jumper set. Lastly, you want to optimize the MiniDSP output gain vs. the AMP gain/volume. Here you have two options. One is to ensure that a WCS signal will pass cleanly through the MiniDSP, repeating the process with the WCS signal and the gradually MV, monitoring the output level. Again, it should increase in step with the MV. If it doesn't it's starting to clip. This is tricky because the WCS may be hard to predict with a lot of EQ in use. This method may also lead to enough noise as to be annoying. Another method is to determine when the amp starts clipping and then dial-in some extra headroom. I do this, giving myself ~+3 dB. This requires knowing whether the amp is clipping/limiting or not. This method is simpler and minimizes noise, but it's still possible to clip the MiniDSP output if you are running beyond the headroom gap between the amp and the MiniDSP. For me that's not a problem. I've oversimplified the process a bit because the amp may not have very fine gradations in volume. So you may need to set the amp to the notch that is higher than required and then compensate by adjusting the MiniDSP and/or Denon output(s) down to maintain the right level balance right with the mains. Hopefully this makes sense? Another option which works to test the Denon and MiniDSP input and outputs for clipping but not the amp itself is to turn the amp down to its lowest setting and connect the sub(s) to it. Then when you adjust the master volume up with the WCS signal playing you should hear a sudden increase in distortion after you hit a clipping point somewhere. Question 1: I essentially answered above. You need to adjust output gain to optimize match with the amp and input gain to adjust match to the Denon. Question 2: That seems like that would work if you don't know how much you gain with each "tick". I'd guess that you get at least 1 dB per click on the Crown.

Totally OT, but I listened to parts of the new Tool album "Fear Innoculum" with a friend today with generous volume. The kick drums on this album really are phenomenal. "Chocolate Chip Trip" is particularly noteworthy and seems like good demo/show-off material. My only gripe is that it would have been better with no dynamics. The limiter on the drums was a bit obvious at times.

A D.O. 15" cabinet would not likely gain the benefit of having multiple subs in different parts of the room because they are too close together. There are pros and cons to using a coffee table sub. Usually the best place for a sub is as close as possible to the longest and most rigid walls. However, this location also tends to accentuate room resonances the most, which is an issue that EQ (or "room correction") might be able to help with. Placing it away from a corner, as would be done for a coffee table sub, will excite fewer resonances. However, you'll likely get a lot less low-end output/efficiency and potentially a major dip in response somewhere, depending on the distance of the "table" to your major wall. What other potential placement options do you have? The corner with your gear is likely to be the best location for output/efficiency. Because your room is so large and you don't have a big budget for subs and amps, I agree with the recommendation for a vented design. As far as woofer size is concerned, it's not that important by itself. What's important is how the particular driver fits into the overall design (including satisfying space constraints). Different drivers have different excursion capabilities, which affects overall output potential in addition to diameter. For the same "style" of driver, you typically get more bang-for-the-buck by going bigger, to a point. For home theater style subs, 18" seems to be the sweet spot for value. I am personally partial to pro-style drivers, which have less excursion than typical HT subs but which are easier to find in 21", which I'd say is their value sweet spot. I realize you probably weren't even considering 18" or 21". If only you knew whether or not you would be satisfied with two subs using 15" or smaller, you would have no reason to consider something bigger. However there is a very well-known tendency for DIYers, upon completing their first subs, to immediately decide they want *more* subs. Most consumer subs don't have the output to play movies even at medium volume without struggling. They may sound loud in the process but not good. When you have clean bass, you may be inclined to turn the volume up (or turn up just the sub) more than you used to.

Did they improve the level monitoring feature in the GUI? On my old MiniDSP 2x4 unbalanced and OpenDRC-AN, IIRC, the displayed levels were short-term averages. (IIRC on the 2x4 it wasn't even RMS average.) This would tend to miss momentary high output transients in movies that might clip the output. If it's indicating short-term average then "riding the ragged edge" means you might actually be clipping a lot. Here's one experiment you can try. Play a movie clip and note the highest level that pops up. Maybe play that part a couple times to make sure you get the same number. Then, add 3 dB headroom to the MiniDSP output by decreasing the output gain -3 dB and increasing the amp gain +3 dB. This should give the same average volume, but you'll have 3 dB more headroom. Now play the movie clip again and see if the highest level numbers you get are -3 dB compared to before or if they are higher. If they are higher, then you were probably clipping and may still be clipping. Sorry to make this a chore. It makes a big difference for sound quality to not clip or distort transients all the time. Depending on circumstances, this may not be nearly as obvious as with speakers because the sub output drops a lot in the high frequencies, meaning the clipping won't sound as harsh. IMO gain structure problems and internal clipping are also a very common problem in HT systems if they get turned up.

Sorry. I'd hoped to get around to redoing the FOTR:EE comparison this week but didn't get around to it. I'll try to do it early next week.

Each device in the chain can clip on either the input or the output. You'll likely only see clip lights on the amp when clipping on the amp output. You definitely could be clipping the MiniDSP output without seeing amp clip amp lights.

Thanks! I'm using Linux, and the 7.1 channels are ordered differently, even with HDMI output. So basically you are running sweeps on the LFE channel (not really "SUB" in this case) at "-12 dBFS", which is in terms of RMS level of the sine wave vs. peak output. That's actually approx. -9 dBFS in terms of how much headroom there is before the sine wave would clip. This is definitely quite a bit less than what you may encounter in an actual movie track. A movie track includes bass managed content from L+R+C and surrounds, which adds up to 10 dB vs. what LFE alone can do. Typical big effects in a heavy hitter may be "-5 dBFS" in terms of all the channels. A handful of movie effects go almost completely full-scale. So what does this mean? It means max output demanded when viewing a movie is likely to be quite a bit higher than your sweep level. Like "-5 dBFS" wrt all 7.1 channels playing is comparable to a sweep level that's 14 dB higher than you are doing. For ULF, it's not quite that bad because movies don't often use the whole bandwidth just for ULF, but I would say that based on your measurements and info, you're probably running pretty close to the limits with a heavy hitting film at "MV 50". If you ever want to play at "MV 70" you should get rid of all boost and maybe turn the sub down overall. But then why bother? Something else to look at is to make certain your gain staging is optimized between AVR/processor, MiniDSP, and sub amps. It's possible that your "MV 70" sweeps are clipping the signal before it even reaches the amp.

I see you're sweeping on "6: Display Audio Output 1 4". Is that just a single channel? Is it LFE? Or something else like center?

Let me ask again, a bit different: what kind of REW sweep is this? Which channels and what level in dBFS? If this is, say, "-10 dBFS" on left and right channels only, that's gonna be a lot lower in level than what a movie can do at the same MV.

Is your modeling with constant voltage or constant wattage? Depending on your amps, you might be able to get more useful output into the eminence.