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Thread: HT Overhaul: JBL Pro Cinema L/C/R Build

  1. Back To Top    #1

    HT Overhaul: JBL Pro Cinema L/C/R Build

    Backstory:
    For the past year or so I've been working on my HT. I had a 110" screen, an Epson 8350 projector, my DIY 3-way Scan/Kef speakers, Kef r20c center, and some Kef Q100's for rear speakers. I 'completed' everything last summer.

    There were a few things that I didn't like about the room. Mainly, it didn't really have that "theater" vibe to it. I really didn't like floorstanding speakers in front of the screen (not physically blocking the view, but just forward of). I started thinking about the THX type baffle wall builds and really wanted to do something like that but I couldn't really justify it. Until...

    Around November a listing on Craigslist popped up. It had a lot of very nice JBL Pro Cinema gear. For practically free (literally) I obtained the following:
    (4) JBL 2035PHL 15" Woofers
    (4) JBL 2446J/2380A Compression Drivers/Horns
    (4) JBL 8330A Rear Speakers

    These all came from a theater which had closed down about 2.5 years ago. Some of the items were brand new and most were barely used.

    Now I have High Efficiency (the woofer is about 99dB @ 1w/1m efficient and the horns are ridiculously efficient at 111dB @ 1w/1m). I picked up all that and it gave me an excuse to build the baffle wall I'd been wanting to build.
    yes, these will almost certainly be toed in by some degree (I'll have to get these in the room to determine that), which means the baffle wall sides will be angled to support this. The center channel is the only one which will be firing through an AT screen.

    I'll be going active 2-way on each of the speaker so I have better control of the response, with each channel driven by a channel of my Crown XLS1500's (I have three of these amps already).

    And this is where the build begins...
    Last edited by erinh; 02-05-2015 at 02:00 PM.

  2. Back To Top    #2

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    I did some testing of the JBL 2035's and with help of Mayhem13 here I determined the optimal size to use for these.

    Here are the results of two of the 2035's impedance sweep:

    The first one was playing on the bench for about an hour at a low-mid volume. The second hasn't seen power in months, at least.

    #1:
    * Piston Diameter = 351.0 mm
    * f(s)= 56.52 Hz
    * R(e)= 3.98 Ohms
    * Z(max)= 34.30 Ohms
    * Q(ms)= 3.210
    * Q(es)= 0.421
    * Q(ts)= 0.373
    * V(as)= 130.600 liters (4.612 cubic feet)
    * L(e)= 0.85 mH
    * n(0)= 5.34 %
    * SPL= 99.38 1W/1m
    * M(ms)= 79.87 grams
    * C(ms)= 0.10 mm/N
    * BL= 16.38


    #2:
    * Piston Diameter = 351.0 mm
    * f(s)= 58.54 Hz
    * R(e)= 4.21 Ohms
    * Z(max)= 42.25 Ohms
    * Q(ms)= 3.581
    * Q(es)= 0.397
    * Q(ts)= 0.357
    * V(as)= 138.700 liters (4.897 cubic feet)
    * L(e)= 1.05 mH
    * n(0)= 6.68 %
    * SPL= 100.30 1W/1m
    * M(ms)= 70.12 grams
    * C(ms)= 0.11 mm/N
    * BL= 16.54



  3. Back To Top    #3

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    Modeling the response in various enclosures using BBP.


    This is just the #1 woofer.


    Red: JBL spec tuning/half box size (since it's one less woofer) @ 4 ft3, fb = 40hz

    Yellow = 3.84 ft3, fb 53hz

    Blue = 2.78 ft3, fb 60hz





    BBP let's me use an active filter as well so I just applied that to the 2.8ft3, fb 60hz model real quick.


  4. Back To Top    #4

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    I decided to go with the 4cube enclosure and these 4" ports. I finally got the time to assemble and route out the enclosures for the 15's. Each will house a JBL 2035HPL and will cover about 70-500hz for my L/C/R's. Fb is about 50hz, give or take. From 500hz and up, the horns will take over. The low end is all covered by the SI HT18's and JL 12TW1's.




    FWIW, I built the cabs from the PE 4cuft flat pack. I absolutely love that these things are available for guys like me (ie; guys who like to DIY but don't have the time to go buy all the wood and cut all the panels). They aren't as cheap to buy as they are to build but they save me a lot of time and effort so it's worth it to me to just go the flat-pack way. If I had to cut the wood for the enclosures, I'd probably only be half-way through just building one enclosure at this point. I put all three together in one day. I spent more time cutting out the speaker/port holes than assembling the cabs. Seriously.

    So now that the cabs are built the next step is to load each enclosure and run an impedance sweep so I can match the tuning frequency and try to get the best match I can. From there it'll be time to mate the big-ol' horn and start doing some testing to determine the best crossover point/levels/EQ to get the desired response. After that, they go upstairs and I start building the baffle wall.

  5. Back To Top    #5

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    Enclosures loaded and swept. Impedance matches pretty well on all of them (about 0.5 ohm difference on the odd-ball, which is fine since it's a straight level thing). The Qts values being different don't concern me at all because a) the differences are actually negligible, although the graph looks work and b) once the high pass filter is involved, these differences matter less.



    The resonances that show up at 700hz/1100hz are driver based; possibly edge or basket resonances... I'd have to measure distances to determine what it is exactly but it's not really important. The tuning frequency actually was lower than I was shooting for (which is fine) at ~45hz. I was shooting for 55hz but thinking there would be too much displacement with the bracing to achieve that, but it looks like there's a lot less than I had accounted for.

    The fronts were spray painted black so they wouldn't stick out (color wise) in the wall. Still, they will have black grill cloth over them as well as being covered with 2" wedge foam on the bare wood. Moral of the story: they ain't pretty but it doesn't matter.











    I should also note the above impedance sweeps were done with the drivers simply sitting in place and not torqued down (I hadn't even drilled out the screw holes yet). I did this so I could swap out a driver or adjust the fill easily until I hit the desired spec in an effort to better match each speaker. Once torqued down the values will change somewhat. The goal was merely to match the speaker impedance as best I could.


    Next step is to set up the horns and start testing crossover options via the Helix.

  6. Back To Top    #6

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    I've been chipping away at this overhaul over the past week. I've mainly been working on the amp rack, getting everything wired up and ready to go. The Helix DSP Pro is in between my Denon X4000 and the Crown amps. I wanted a cleaner setup and something that was easy to operate, so I'm using the Denon's 12v trigger to fire up the Helix which then will trigger a switched outlet to power up the Crowns. All in all, it works very well. And it looks nicer than the previous iteration:




    I wired up all the front speakers tonight and set some basic crossovers with the Helix between the horns/15's. Nothing too technical, just something to allow me to get everything wired up. Everything works... enclosures are good and horns are rockin'.



    But that's all just par for the course. The reason I'm updating this thread is here...

    I received my Sony PJ early last week which has been sitting in the office waiting to be used and I couldn't resist the urge to throw together a temporary screen to try the 40es on tonight. I got my photo backdrop setup (haven't used it in years, but so glad I hung on to it) and clamped the spandex I'm using for my AT screen at the corners and top. Fired up the PJ with the screen about 10 ft from the PJ. Given nothing in the current setup is the same as what I had I can't really give impressions based on an apples/apples, but I can say... WOW. The PQ of the current setup is astonishing. The AT screen I'm building is made up of two layers of milliskin (thanks to the research from Adam): silver as the back layer and white matte on the front layer. I was worried about loss of brightness and overall color/blacks but that's a non-issue. I wound up pushing the screen back to about 38" from the wall which now gives me ~120" diagonal. It looks fan-freaking-tastic! So, I'll build the wall about 30-34" off the real back wall and shoot for a 120" screen. This is a good example also of how doing a temporary setup just to test screen size is a good thing. Would suck to build a screen and it not be the right size. :/

    Here's a picture of my temporary rig:






    and here's a cell phone picture of Frozen (as much as I've grown tired of the songs, I really do like this movie )






    Picture of behind the screen:




    The other factor here is just how GREAT it is to be able to have the speakers behind the screen. I can keep all of the speakers the same so the tonality matching is dead on, panning seems more fluid, there simply are less visual distractions. Another big factor that I didn't really think about but turned out to be sweet is I can also move the screen lower to the floor (where I used to have to keep it up a bit higher to not project on to the center channel speaker when you don't have an AT screen). It takes you from having to look up to looking directly ahead.

    I'm stoked on the PJ choice as well as the decision to do this rebuild. Firing up the system, even in it's temporary state, tonight made me realize I made the right decision.

    If you have the opportunity to build a projection setup I HIGHLY, HIGHLY encourage you to explore the AT screen option. I know not everyone can do this because they may not be able to build a false wall or even just cut in to drywall to use in-wall speakers, but if you can or think there's a possibility of it, I really encourage you to look in to it. Easily the best decision I've made with my setup and it's not even done. Just understand that like everything there are trade-offs to a setup like this.

  7. Back To Top    #7

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    random info that someone may benefit from...

    Ground loop issues! Argh!!!!!

    I initially had an even higher system buzz that stemmed from my satellite ground not being tied to my house main ground. Running a 10gauge wire off the satellite coaxial cable distribution block to the common house ground reduced my initial buzzing by 70% (or something like that).


    The rest of the 30% was due to a ground loop issue between my Sony projector, Denon receiver, and the HDMI cord connecting the two. The Denon AVR is in a media closet on it's own 20amp circuit shared with a few power amps. There was a fairly strong 'buzz' that would occur when I'd plug my Sony projector in to the ceiling outlet in the room itself (so, two different circuits entirely). This buzz would go away if I ran an extension cord to the media closet outlet (in order to share a common outlet with all the gear). This was my way of verifying the issue was indeed the ground differential between the two components on two different circuits. The differential, it seems, was carried through the HDMI cable (as soon as I disconnected the HDMI cable the noise would go away). So, either put them on the same circuit or have no video... awesome. lol.

    I searched around on AVS and found some folks saying the ebtech HumX worked for them in this same scenario. So, I ordered the HumX, plugged it in to the ceiling out, then plugged my Sony projector in to the HumX. Noise = Gone. While it's not necessarily the 'best' solution (that would be to combine all components on the same circuit) and some may view the HumX as 'cheating', the fact of the matter is it works (for my application).

    The HumX took the remaining 30% system buzz and attenuated it to where I have about 5% system buzz (something I can tolerate at least for the time being).

  8. Back To Top    #8

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    Back to the baffle wall build, this may also be useful for others if you decide to do the same thing...


    For those who may be interested, this is a copy/paste of a post I made on avsforum last night. I spent a lot of time researching baffle walls for my upcoming build, looking at industry specs and what others have done. There are a few "professionals" there that prescribe X method which just seems to be an emulation of what THX spec is, which makes no sense for a home theater; the constraints aren't the same and even vary with build to build. The more I researched, the more I found that people just blindly do things others did and it seems to be without any effort to consider why, thus costing them more money and time.


    For example, acoustical treatment on the baffle wall. People are going out and spending hundreds of dollars on treating their wall in various manners. So, I posted the following last night, hoping to shed some light on the purpose of treating the wall. I posted this on AVSforum and didn't get a reply, but I think I managed to answer the question myself in the process of doing some research for the post, LOL.



    Let me ask this: what is the purpose of the acoustic material used on the wall? Is it to eliminate comb filtering between the speaker and the screen? Or should it be purposed to be more of a broadband absorber, absorbing both the front wall speaker/screen reflection and reflections from other speakers (ie; rear speakers)?

    If the former, I can understand using a thinner material or a material such as wedge foam because it's absorption ratio increases with frequency; in this case you are absorbing essentially what is reflected off the screen back to the wall and lessening comb filtering issues from these two surfaces (and even doing the same for speaker reflections from the rest of the room as they go through the screen, to the wall, and back out).
    However, why the need to treat an entire wall if the side speakers are a reasonable distance from the screen (notably, where beaming has occurred and the very high frequencies from the L/R speakers are not comb filtering off the screen/wall).


    The suggested standard for a 'THX Baffle Wall' is 1" acoustic foam. Here's an excerpt from this site for example: Welcome to CES Tech page!.
    The entire face of the baffle structure is covered with 1" (25 mm) Coated InsulSHIELD" Black, a product manufactured by Schuller International, Inc. This is a specific product.
    No substitutes are accepted unless the acoustical properties of the material in question are the same as that of the 1" (25 mm) Coated InsulSHIELD'" Black. In this case, a sample and specification of the material must be submitted to THX for approval.
    There must be a reason for this, right?

    So, what does the IS Black do in regards to absorption?...
    Well, I looked up the absorption coefficients for InsulShield Black 1" (1.5pcf (24kg/m3) via Bob Gold's site.
    (Note: The 1" Linacoustic that I see referred to a lot was close enough to not also include mainly because I didn't want to graph it again as you'll understand as you read further.)



    First, the graph from the IS Black 1":


    When you look at what is spec'd by THX the shape of the absorption curve indicates higher absorption with higher frequency (understanding that thickness plays a role here). This leaves me wondering if, again, the intent is simply to mitigate the comb filtering OR if the purpose is more broadband absorption. The latter seems not quite as plausible; otherwise I would think that THX would spec a thicker material such as 2" or more. Especially since they're (THX) the one driving the spec.
    But, that's just an assumption based on what I'm seeing. I don't know for sure that the goal wouldn't be broadband absorption, but it seems to me the logic lies in eliminating comb filtering more so than broadband absorption, based on what I'm seeing from the data and some of the other aspects.



    Next, for my own curiosity, I graphed the results of the IS Black 1" vs the various thicknesses of FoamByMail's Wedge Foam.
    (Note: I don't have Auralex's data. The best I have is FBM's discussion here which I can only assume is true, otherwise Auralex's lawyers would have them for lunch. BUT I'M NOT ARGUING PERFORMANCE OF AURALEX VS FBM.)




    Then I 'normalized' the wedge foams at 1khz by adding the difference of the IS Black to each of the (4) FBM wedge pieces so you could get an idea of the trend (not just the numbers):







    Comparing the wedge foam, the 2" version (once 'normalized' by adding 0.09 to each octave component) seems to be the closest match to the IS Black 1". I don't know what IS Black 1" costs, so the 2" wedge may be a nice cost/performance match if the IS is expensive. That said, you can still see the obvious skew of the IS Black to the higher frequencies.

    Of course, the screen material now is likely different than what it was when the spec was made. I've seen random posts here and there about the acoustical properties of (enter model of screen here), and it's pretty obvious all aren't created equal. I think the ideal situation would be to find a screen which drives the response in a linear fashion (ie; a smooth attenuation from x hz - xx hz as opposed to a jagged combing pattern) and match that up with an absorption material that follows the same trend. To me, that makes the most sense because you're essentially matching up the frequency range and pattern of combing caused by the screen to a material that can absorb those frequencies. You're not going to easily do this with a saw-tooth type comb, so based on what I came up with above I'd personally lean toward a screen design that filters out the response smoothly over a given passband than one that has very large comb-teeth and try to match absorption accordingly. If nothing else, it's easier to throw a parametric EQ curve at something and shelf the response opposite that of the attenuation as opposed to individually selecting bands to try to compensate for (if it's even possible).

    Given the above, it seems that for those who want to emulate the IS Black performance, albeit at a slightly lower level, might be interested in the 2" wedge foam from FBM. That's actually what I first considered and after this, I am leaning even more towards it.

  9. Back To Top    #9

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    and to get fully caught up...

    I bought all the materials for the baffle wall a couple weeks ago. About 8 sheets of 1/2" 4x8 OSB (cheap is the name of the game) and about 20-something 2x4's to frame out the wall. Haven't had time to really start building the wall, though. But, at least I have the materials.







    I went ahead and mounted the JBL 8330A's to the wall for the surround speakers. Being large, I was worried they wouldn't look right, but they actually look really good in the room. I mounted them right where I put the speaker cable in the wall (unlike the previous iteration of the HT which had the bookshelf speakers about 3feet from that position) so the wires are hidden and the install looks very clean. Right now all the speakers are powered up except for the subs. I currently still have the spandex taped to the big steel frame just so I can watch some basketball up there for the time being. I am totally pumped on how it's turning out, though. Very much looking forward to having the wall completed and then starting work on the rear seat area. Not really in a hurry on this project because it's at a place where I can kind of take my time. If anyone wants to come over and help me build this dang wall, though, I'd definitely appreciate it. My old-man back has a hard time with this stuff. lol.

  10. Back To Top    #10

    Re: HT Overhaul: JBL Pro Cinema L/C/R Build

    Lol.....old man back...............btw, you forgot the pics of the humongous surrounds!

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