Originally Posted by bossobass
Originally Posted by Archaea
Unfortunately concrete wall room gain is not all equal. I am on a basement slab with two concrete walls and my room has no perceivable room gain over riccis outside measurements at database (at least at my listening positions) as verified with omnimic and rew graphs at a couple meets I've hosted. I realize I am the extreme exception, but it is a datapoint that counters typical thoughts. By contrast, kc forum friendd scrappydue has probably more room gain than any other room I've measured out of dozens of rooms. He has probably over double typical room gain I've seen. He has to cut his four sealed si subs below 20hz by something like 6-8dB to have a typical house curve frequency response. I say this and will provide graphs for each when not on my mobile device to show all rooms are different on room gain.
You definitely have room gain. Every room does, bar none. In your 1st shootout, the only SEALED sub there that had a known native response was the SM. The measurements revealed room gain to 10 Hz with a dip at around 15 Hz (which is typical of many rooms, as both Josh & I have noticed over the years and some theories as to the cause have been lightly discussed to date). I do not consider most posted measurements to be reliably accurate below 20 Hz, but accurate enough to 10 Hz. So, the evidence was clear to me that with proper placement of listener and sub in your room you'll see similar gains to other members.
Unfortunately, in the 2nd round, Audyssey was used, rendering the data too skewed to compare to anything previously measured or known. But, I have no reason to suspect they would have shown any difference from the SM results in the 1st shootout.
Of course, all rooms are not equal. One may have either studs/siding, studs/brick, hollow masonry, solid masonry, hollow or solid masonry with backfill, more windows/glass doors with more or less transmission losses, an air return to a large network of supply ducts in other areas of the house, etc. But, of the dozen or so samples of known subs vs posted reliable in-room measurements I have examined, all have a far more similar room gain profile than otherwise.
For the record my 3,500 cubic foot theater room has poured concrete walls on three of the four sides - front, right, and rear, and is on a concrete slab. I know it is poured concrete because I took all the drywall down to refinish, and tiled the concrete floor myself. The ceiling height is 7ish foot. The left wall is concrete slab as well - but my theater room is only half the basement, and so the left concrete wall is lesser material for any room gain.
In my 2011 meet - no EQ was used on the subs. Bear in mind that the captures of the subs from my room is the average taken from the four main listening positions, which you can see my seating arrangement in my signature linked home theater pictures. AVSforum member counsil took the measurements with his calibrated microphone and REW gear. As an aside, I recall Mark Seaton, who attended the 2012 meet, stating that he had been in 7,500 cubic foot theater rooms that offered more gain than my room. Carp has submitted on public forum several times that his room gets a significant amount more room gain using four of his sealed SI 18" drivers when we demoed four of his drivers in my room in the last month. Post 176 being an example here:
These are old posts in another thread comparing room gain from subs measured in my room to subs measured in Ricci's outdoor testing. You've got to ignore the 50hz null in my room - that's a compliment of my seating positions and the sub position. Ignore that and then compare the graphs. Each individual subwoofer frequency response piece of evidence I'm presenting to back up my observation individually may not be sufficient, but when taken as a whole is more telling.
Post 35 - Epik Empire in my room compared to data-bass
Ricci's outdoor chart from data-bass on epik empire
Epik Empire in my room (taken from the 2011 KC Sub Shootout Thread) (rolloff at top end of FR due to AVR crossover)
here's another one -
Post 37 - SVS in my room compared to data-bass
not quite as apples to apples, but still same family.
Again - ignore the 50hz null - that's my room and sub placement conflict. But note the fall off at the low end is very similar for these two similar SVS subs.
Ricci's SVS PB12 NSD 20hz tune
Ricci's SVS PB13 Ultra 20hz tune
My room - SVS PB12+ 20hz tune from 2011 sub meet linked in sig. (roll off at top end due to AVR crossover)
Ricci has since measured one other subs that participated in our 2011 meet. The HSU VTF-15H.
Here it is in my room:
Sealed, EQ1, Q.3 was the configuration used:
Here it is on data-bass in sealed config with Q.7 (data-bass doesn't have a Q.3 to compare directly)
You can see all the other measurements from that 2011 meet here in post 3:
The Jamo D7 THX Ultra II sub is a sealed sub and was measured in that meet as well. Not very exciting for a sealed sub below 20hz either
We measured the Seaton Submersive at the 2011 meet, and while Ricci hasn't measured that one - many other well known AVSforum members have. You can see it falls off pretty hard at 20hz, losing about 15dB from 22hz to 15hz, but maintains steady from 15hz to 10hz, which may be an artifact of room gain as you stated - or it may be an artifact of the fact the graphs were the averaged measurement between the four different seats on the only sub in that contest that can actually meaningfully produce some sub 20hz content. (the theater chair in the right side by the fireplace has more gain than the other listening positions and would serve to boost that graph average a bit). BUT unfortunately - - - it could have also been the HVAC engaging. This meet was performed when it was quite cold outside, and my hvac system may have been engaged during the time the measurements were taken - it's impossible to know at this point. (I have no treatments and all hard reflective surfaces so my noise floor is typically higher than most rooms anyway) - and it certaintly goes up when the furnance in the room immediately next door turns on, and that furnace could have accounted for the appearence of room gain between 10-15hz. I was outside when counsil was taking the measurements - and being two years ago - - - who would now without measuring again. We took some recent measurements with carp's sealed SI subs in my room, and that info is linked here at post 146 and 147.
http://www.avsforum.com/t/1489801/bought-four-sealed-18-cabinets-on-a-wild-hare-direct-me-to-a-driver-setup-at-least-competitive-or-superior-to-jtr-captivators/120PERHAPS THE MOST DEFINITIVE EVIDENCE OF ROOM GAIN DIFFERENCE I CAN PROVIDE
As I mentioned previously, avsforum member scrappydue has absolutely RIDICULOUS room gain. He has the same SI 18" drivers that carp has. I was over at his house and demoed his four subs as we were getting them dialed into his basement room. He is in a conrete bunker that may only be rivaled by MKtheater. On his four SI 18" drivers double stacked in the left and right corners this is his naked - no eq frequency response graph - and then each side independantly.
Yes, scrappydue has to cut 6-8dB's at the 15 to 20hz range to even get a proper house curve. That and he has to apply zero boosting at 10hz, compared to my requirement of adding 15dB or more with the exact same four subs in my room. These subs are the same - - - the difference is the room. The subs are in the exact same four boxes (all SI 18" drivers, all DIY flatpack boxes from Erich). In my room boosting 10hz by 15dB fails to be flat. Both of our rooms are poured concrete basement theaters. My room is larger than his, but the difference is absurd. Both measurements taken using calibrated omnimic. I was present for both measurements and feel comfortable vouching for their accuracy having used the omnimic tool pretty extensively.
With this kind of extreme difference (even if outliers) in mind - how can room gain be calculated reasonably between unmeasured rooms?
In the end - - - if there's a lot of room beneficial room gain in my room - I fail to see it. Of all the dozens of rooms I've measured - I think mine is the worst for beneficial deep frequency room gain. (at least as is relative to my listening positions.)Edited by Archaea - 12/5/13 at 4:20pm