rms8
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Post by rms8 on Sept 23, 2012 6:33:57 GMT -7
Hi All ! The following was posted over at AVS. Posting here as well. We are having a new home built. Once the home is completed I will begin finishing the basement. One portion of this basement is under one of the garages (the 3 car) so it will have a SpanCrete ceiling. The whole theater will be a sarcophagus of concrete making for some great isolation. I have been planning this new build for the last 12 months or so. I have attached a link to the most current incarnation thus far. My question revolves around the basstraps I am planning. I have two in the rear corners which will be 2ft x 2ft column from the floor to the first soffit. They will be filled with fiberglass insulation. The traps will be a simple frame with a few wire mesh "shelves" on the inside supporting the fiberglass so it doesn't crush itself due to weight. The whole frame will be covered by a dark colored fabric. In the front of the room you can see I have planned for a 1ft x 1ft column (floor to 1st soffit). In between these front columns will be a shelf of sorts which extends in front of the screen wall. The face of this shelf will be the baffle for EIGHT 18" IB318 subs. Anyone see any cons with these basstraps?  |
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Post by FOH on Sept 23, 2012 10:09:59 GMT -7
Cons? No
Just the more the better, it's hard to add too much, as long as you have an eye on not attenuating precious MF/HF energy. If this becomes an issue (doesn't look like an issue with your sparse traps) you can always front the traps w/~6mil plastic.
The total amount needed is so interdependent on a variety of factors, so kinda depends on the composition of the boundary walls, ceiling, etc.
Rules of thumb for such absorption;
2" - use OC705
4" - use OC703
8" - 2" OC 703 with 6" R19 behind (fluffy) / or perhaps(2) layers of 4" Roxul Safe & Sound
12" or more, use R19/R30 (fluffy)
What other concerns do you have? Your best bet is measurements, then proceed accordingly.
Good luck
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rms8
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Post by rms8 on Sept 25, 2012 6:46:18 GMT -7
Thanks for the advice! I would also like to take advantage of my seating platform for use as a bass trap as well. I am getting a bit discouraged at the moment though. I am getting some negative feedback from Dennis Erskine over on AVS Fourm ( AVS Forum THREAD HERE). We've had a few PMs this week as well since I was considering using his service to help with the planning of the room acoustics. He posted in my thread over there with the following:
1. Bass traps as shown and placed are too small to do anything other than help the guy out who is selling the fiberglass;
2. Eight 18" woofers in an IB design? Why? What engineering specification did you follow to determine you needed that much low frequency energy ... and what engineering specification did you use to determine what your bass response might be like in those frequency ranges where 18" woofers are very inefficient? What will you be using for HF and MF drivers that will be sufficient enough to not be over powered by the subwoofers?
3. What method will you use to relocate the drivers when you discover they need to be relocated to improve in room response?
4. Since the drivers are facing the listening positions, what technique are you thinking of using so those in the listening area will not hear the higher frequency artifacts created by those drivers?In no way am I trying to start anything!!! I respect Dennis to the fullest; hence why I PM'ed him regarding his service. Maybe I'm reading into his post something which is not there, but it sounds to me that he thinks an IB setup is not worthwhile and actually more problematic than it's worth?  ? Like I said, I could be completely off base here. But his post and his PM's have me very discouraged from pursuing the IB route at this point. Thoughts/advice? ?? |
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Post by ThomasW on Sept 25, 2012 16:26:06 GMT -7
I am getting some negative feedback from Dennis Erskine over on AVS Fourm ( AVS Forum THREAD HERE). We've had a few PMs this week as well since I was considering using his service to help with the planning of the room acoustics. He posted in my thread over there with the following:
1. Bass traps as shown and placed are too small to do anything other than help the guy out who is selling the fiberglass;He's correct they are too shallow to trap bass Again he's correct, the best way to use that many 18"s is to space them around the room to even out the response Here he's just being 'catty' .... sarcastic [/i] Not a problem we're aware of Don't know if Dennis has heard a big IB sub My suggestion would be 4 drivers in the front of the room the remainder spaced appropriately to even out the in room response. |
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rms8
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Post by rms8 on Sept 26, 2012 6:00:37 GMT -7
Thank you Tom !!!!!!! Again he's correct, the best way to use that many 18"s is to space them around the room to even out the response My suggestion would be 4 drivers in the front of the room the remainder spaced appropriately to even out the in room response. Despite having not built a single wall yet, I don't know how one would space the drivers out appropriately once the room is built and mount them where they work the best? The baffle wall/walls would have to be reinforced prior to being built plus the cavity behind would need to be accounted for ahead of time. If one didn't know where they were ultimately going to mount each driver, how would one proceed to frame out the walls to support the driver locations? I suppose it's just too tricky to figure out ahead of time? What if I pull the front wall back and mounted 6 drivers in it, then built a baffle wall in the back of the room on the Right side wall (up to the wet bar) and mount 2 drivers in it? Any benefit of mounting drivers up high on the front wall? I know I've see IB's that were completely asymmetrical in location. I remember seeing one here that was four 15-or-18" drivers stacked from floor to ceiling on one side of the front wall. Of course, i have no idea of what that design sounded like either...... |
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Post by ThomasW on Sept 26, 2012 7:09:51 GMT -7
I suppose it's just too tricky to figure out ahead of time? Start with a little research, there's lots of info out there. Read what's written by Floyd Toole, Earl Geddes and the Harman multi-sub white paper, or pay Dennis, let him do the heavy lifting for you... You'll get the best sound quality with multiple IBs around the room. If that's not possible or practical do IB's where ever possible, augment them with sealed box subs. |
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rms8
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Post by rms8 on Sept 26, 2012 10:12:43 GMT -7
I suppose it's just too tricky to figure out ahead of time? Start with a little research, there's lots of info out there. Read what's written by Floyd Toole, Earl Geddes and the Harman multi-sub white paper, or pay Dennis, let him do the heavy lifting for you... You'll get the best sound quality with multiple IBs around the room. If that's not possible or practical do IB's where ever possible, augment them with sealed box subs. I had reached out the Dennis on Monday regarding his services. When you suggest multiple IB sub around the room, does that mean side walls too, or just front and rear? Also, do the drivers have to all be symmetrically mounted? I would think not, but really don't know. |
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Post by FOH on Sept 26, 2012 11:29:10 GMT -7
Dennis, by his own admission, can be quite the smart ass. He's well versed in nearly every aspect of HT, HT construction. That said, he's not beyond reproach and I've seen him give what I'd consider to be questionable advice on a couple occasions. Yes, his work is incredible, granted. I've seen him vastly under-spec a subwoofer system, and I've seen him advocate for strong, early reflections merely because Toole's data suggested that lay people felt like including early sidewall reflections helped intelligibility of the spoken word. Now, I believe he knows better in each case, however vociferously maintained that position despite being shown otherwise. Ok, no biggie, he's highly accomplished and quite knowledgeable, ....beyond reproach, no. But I'll tell you what, his body of work is phenomenal. Yeah, I pointed out a couple of things I felt like I'd approach differently, but I've read countless posts and contributions of his that are tremendously helpful to a vast amount of enthusiasts. He likely knows more about home theater HVAC, lighting, seating, sound proofing, etc., than most people in the business. If I was talking lottery winnings type of HT build, ....and as far as the last word in audio quality, I think I'd consider Keith Yates. Has Dennis been exposed to a state of the art IB, I don't know, but I'd guess he has. Everyone should  He may not fully grasp the excursion limited component of the equation. Eight Fi IB3-18s, driven to full excursion (30mm) at 10hz, is not equivalent to (8)18s small/sealed driven to full power at 10hz. Now, back to this issue. There are big, high profile, highly successful IB builds whereby all the drivers are located in one wall. It's not all about modes. SBIR, or in your case the back wall reflected energy is a strong consideration and can be diminished. Ethan winer;
If a reflection is 100 percent it will create a null of infinite depth 1/4 wavelength away from the boundary.
If you reduce the reflection by 1 dB the null is now only 19 dB deep.
Reduce it another dB and now the null is only 14 dB deep.
Reduce it again to -3 dB and now the null is only 11 dB deep.
If you reduce it to -6 dB the null is now only 6 dB deepWhat Dennis and Thomas suggested may be the best advice. However, I'm thinking the front wall IB isn't at all out of the question. Many builds, hell the majority of builds employ their subs this way. By using selective mode cancellation, you can mitigate the height, and width modes with driver spacing, and limit the rear wall's influence with significant treatment there. Much of this depends on you goals of how big a listening area do you want. Also, I don't think eight IB3-18s is excessive for the space. An IB build this size I'd build to the cubic room spec, not to the mains capability. That's my opinion. Another thing, I've never seen any good measured results of how effective riser bass traps can be. Doesn't mean anything but that, I've not seen before and after waterfalls, etc. WRT bass trapping, the more the better. Good luck, keep us informed btw; I like the idea of a full planar wave, wall of IB drivers, transferring their energy into the space |
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rms8
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Post by rms8 on Sept 26, 2012 11:38:20 GMT -7
What do you all think of this iteration? I have split the drivers up. Four in the front, and four in the rear. The air space for each set of drivers would not be identical WRT VAS-times-X (meaing one space may be 8x VAS, while another might be 9X VAS..... Should I stick with all eight on the front wall or would my room acoustics be better served via the plan below (or even something else?). Also, would it be a problem if the drivers were to be stacked in the rear, and/or even the front? EDIT: The thumbnail below does work, it's just not showing the image???  i441.photobucket.com/albums/qq137/rms8/Home%20Theater/Szewczyk-BasementPlan_9-18-2012HT-only_Printat100revised.jpg |
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Post by FOH on Sept 26, 2012 13:35:54 GMT -7
I think it's an important distinction to make, that the spaced drivers around the room, "Welti/DeVantier style", should help in less deviation of FR over a larger area of seating. That's different than stating you'd get the "best sound" from doing so. ---------- My opinion, and it really is merely an opinion; I'd utilize all drivers up front, spaced in both the X and Y axis, two high by four wide, and then utilize a significant thickness of trapping on the rear wall. This rear wall treatment, minus what space you need for the mini-bar, would be both velocity based and pressure based absorption of whatever energy needed to mitigate reflected nulls in the frequency response over the seating area. The reduction in ringing in the time domain is clearly a bonus. The velocity based, would utilize inexpensive fluffy insulation, with a thin plastic membrane to both heighten absorption of the LF, and help facilitate retention of the precious midband and HF energy to preserve and nice lively and immersive experience. This entire surface would be faced with, and possess whatever type of diffuse/scattering treatment you would choose. Sound has many characteristics, one being size. The big wavelengths needing absorption don't "see" or are they impacted by the diffusion or scattering treatment on the front of the treatment. the diffusion/scattering could be a variety of expensive, purpose built products, or a variety of artsy stuff, I've got tons of examples if you're interested. If you had 18-24 inches to devote to the bass trap that would be ideal. 18" of fluffy (loose fluffy is optimal for thick traps) would absorb outstanding down to 50hz, then it's attenuation tapers from there being decent down into the mid 30s. Attached is an 18" fluffy trap graph, no membrane (which increases effectiveness). This type of "pitch and catch" approach is what several studio mfrs like Genelec advocates, total rear wall absorption below a specific frequency. Above the bass range, into the midband and above, you can use a popular approach of simple wood slats in a math sequence. Below is the suggested math multiple of the slats and spacing. The first number is a slat, second number is an opening, third number is a slat and so on: 534435453534435 As I said, this is a well regarded studio technique to retain liveliness, yet gobble up the bottom end. Paul Right's Octagon; advanceddefinition.com/The%20Octagon.htm He got a killer LF result from (18) 15s in a planar array, with an absorptive rear wall. Thanks Attachments:
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rms8
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Post by rms8 on Oct 21, 2012 11:09:20 GMT -7
Hi All, I have an updated design in mind and wanted to run it by the members here to see if there could potentially be any problems with driver placement....  The front baffle wall will still have the eight 18" Fi IB318's. The front baffle will be angled in slightly on each side with four drivers per side. The left side "room" will have the 19" rack (in red). The left side "room" is just a void but built in to add symmetry and give additional air space for the IB side. At the rear of the room in each corner will be bass traps 6' wide floor to ceiling. The lower portion on each side will have a built in 11ft3 ported 15" Dayton Titanic sub tuned to 20hz. These would act as filler subs to help tame some bass peaks (hopefully). My plan is to go with a Denon AVR-4520 which has Audyssey MultEQ XT32 which provides equalization for two separate subwoofers. Anyone see anything wrong with this current idea? THANKS! |
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Post by ThomasW on Oct 21, 2012 16:09:19 GMT -7
The front baffle wall will still have the eight 18" Fi IB318's. ......... The lower portion on each side will have a built in 11ft3 ported 15" Dayton Titanic sub tuned to 20hz. These would act as filler subs to help tame some bass peaks (hopefully). Anyone see anything wrong with this current idea? Big problem is that the swept volume of rear drivers is a fraction of that provided by the front drivers. This means you have 8-18" front drivers and their output will be limited to that of a pair of modest excursion 15"s |
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rms8
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Post by rms8 on Oct 21, 2012 19:13:53 GMT -7
Thanks Thomas.
I had read some threads where the person added subs to the rear of the room to assist in taming bass peaks. I may have falsely assumed this would be a two'fer for me.....1) I would get to utilize the two Titanics I have and 2) their use would be to help with the room response.
Their intent was not to add anything but to "hopefully" help with peaks.
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Post by maxserg on Oct 21, 2012 19:45:23 GMT -7
I guess that what Thomas said is to tame the front sub power that it delivers, you need equal opposite forces to tame room null. Hope this is in line with Thomas's answer!  |
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Post by ThomasW on Oct 21, 2012 20:59:03 GMT -7
+1
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Post by FOH on Oct 22, 2012 8:43:34 GMT -7
I'd suspect they'd work better than being given credit, but I'm unsure. Here's my thinking; Wouldn't it depend on the frequency of the specific modal issue being addressed? As we know, the hallmark of a good IB subwoofer is effortless, efficient bottom octave extension. Also, we know that for every octave downward of additional extension, a quadrupling of displacement is needed to facilitate an equal SPL capability. That said, consider an IB w/(2) 18" drivers up front, mated with two balancing subs elsewhere in the room,...perhaps in the rear,sides, whatever. We pick a frequency below which modal concerns lessen. It depends on the room, but typically modal issues occur well above the lowest room mode, perhaps around the range between 30hz on up to the transition frequency 200-300hz. The room's first mode (1, 0, 0) is determined by the longest dimension of the space. In my 25 foot long space, that's about 22hz. In rms8's room, the axial modes theoretically occur beginning about 21hz length, and 26hz for width. Other modes don't begin until the 30s so the area of concern is the mid to low 20s,... on up. This would seem to be fundamentally key in my opinion considering the factors at play here. Eliminate the octave range below the mid to low 20s, we'll say 23hz, from our concern. Modal issues can't exist down below the first axial mode of 21hz, and likely won't have addressable swings until higher up. The hypothetical double 18 IB in the baffle wall, easily covers the subwoofer range between 23hz on up to the hand-off to the mains, with ample output to attain reference levels and keep up with even high output mains. Now, the quadrupling of displacement capability merely assures when the really deep material comes along below, the system maintains the same capability that the double 18 IB possesses, except now it has an extra full octave of extension way below any modal activity. All said, unless one operates the system extremely out of balance bass heavy, I suspect the balancing subs merely need the same capability as the original hypothetical pair of 18s, to address room modes, etc, as is typically done with such balancing subs. Thoughts? ------------------------------------- Now on a separate issue, I'd not opt for a vented/IB mix, as it may complicate proper blending and also may unduly draw attention to themselves via artifacts associated with such resonant systems. Done right, without audible group delay or detrimental port noise, the extra SPL capability added with a careful tune could be fine, I'm not sure. I've never blended vented with sealed with good results*, not saying it can't be done but I gave up. I like the huge bass traps, nice. Any more trapping? How about the remainder of the rear wall? What type of surface will it be? If I had a big space such as that, I too would have the mammoth corner absorbers, but with something like a slatted, rear wall w/both reflection above a design freq, and total absorption below. with the slats, with varying spacing between pieces, you maintain the elusive spaciousness yet you can control the bass. The wood is transparent to the lower frequencies, then a rear area behind the slats being filled with several inches of fiberglass/rock wool etc. This can be employed on any surface,..sidewalls, ceilings. It's very simple, very effective,...looks cool too. But, it does take up real estate. I'm not re-engineering your room, just throwing it out there for anyone. Good luck *(I once experimented over several days blending two vented Cerwin Vega 12's, with two sealed Velodyne 15's, the vented 12's, the distortion from the 12's was a huge obstacle) ... yeah CerwinVega  |
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Post by pitviper33 on Oct 22, 2012 10:14:04 GMT -7
Big problem is that the swept volume of rear drivers is a fraction of that provided by the front drivers. This means you have 8-18" front drivers and their output will be limited to that of a pair of modest excursion 15"s Thomas can you elaborate on this? Why would the output of the 18s be limited by what the 15s are doing? Clearly any null-filling ability of the 15s would disappear below tuning, and he'd be stuck with whatever the room and the 18s gave him below that. But couldn't there still be significant advantage above that frequency? Of course the problems that would come from sending the same signal to vastly different configurations and displacements are obvious. But in a case like this, where he's planning on sending a different different signal to the 15s anyway, I'm failing to see how the limitations of the 15s have to affect the 18s at all. |
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rms8
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Post by rms8 on Oct 22, 2012 10:31:39 GMT -7
Thanks FOH !
I think I follow what you were describing. Nothing has been set in stone (been through 20+ room designs since summer alone). I could just as easily build the cabinet for the 15's to be sealed. I was keen on my idea of hiding the "filler" subs in the rear bass traps. Also that I would actually be able to re-use the 15's.
I drew several designs shuffling the eight IB318's between the front and rear wall. I could still do these, but it eats up too much space and somewhat complicates the rear of the room for me with some of the ides I have been floating around.
I honestly thought I hit gold when I implemented the latest design integrating the 15's in the the rear basstraps. It seems it may not be as awesome an idea as I thought, but your input above is VERY insightful!
Regarding additional trapping/panels....
I will be incorporating DIY panels on all the walls and will try to design something for the bottom of the sofits. The front wall will be lined as well, but there will be a 60" TV on that wall for regular viewing when one doesn't want to fire up the whole HT to watch something insignificant.
I was going to implement your earlier idea on facing the traps with a plastic liner to help reduce the high absorption. Are you saying I might also want to have some sort of denser reflective surfaces to act more as a diffracter?
Thanks for all the really good info to date. It is all VERY MUCH appreciated!
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rms8
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Post by rms8 on Oct 22, 2012 10:36:16 GMT -7
Big problem is that the swept volume of rear drivers is a fraction of that provided by the front drivers. This means you have 8-18" front drivers and their output will be limited to that of a pair of modest excursion 15"s Thomas can you elaborate on this? Why would the output of the 18s be limited by what the 15s are doing? Clearly any null-filling ability of the 15s would disappear below tuning, and he'd be stuck with whatever the room and the 18s gave him below that. But couldn't there still be significant advantage above that frequency? Of course the problems that would come from sending the same signal to vastly different configurations and displacements is obvious. But in a case like this, where he's planning on sending a different different signal to the 15s anyway, I'm failing to see how the limitations of the 15s have to affect the 18s at all. That's what I was thinking/hoping/assuming.....that the 15's would just help lower some of the peaks which may show up once all is said and built. I should have mentioned that I will have a MiniDSP in the mix as well. So the 15's will have a higher cutoff than the 18's. Especially if I go with sealed 15's vs. ported as I originally stated. |
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Post by ThomasW on Oct 24, 2012 6:36:05 GMT -7
That's what I was thinking/hoping/assuming.....that the 15's would just help lower some of the peaks which may show up once all is said and built. EQ is used to lower peaks. Rear subs are designed to help fill nulls and as such need to have approx the same output level as the front drivers |
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