| Theater room LCR [message #79637] |
Sat, 08 March 2014 19:49  |
LoveJBL
Messages: 4
Registered: March 2014
Location: SC
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Esquire |
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Hello all,
about a year ago my oldest son moved out and left me with a room downstairs in my house 24' x 11'. It didn't take me long to convince my wife that I could save about $200 a month if I built a theater room. of course she had no idea how much it would cost.
In any case I quickly started compiling a list of like to haves and must haves. Didn't take me long to realize that retail sound was not going to do it for me. So I started looking at what actual cinemas use for sound and I decided to go pro.
Here is my list of current equipment.
1 Each Integra DTC 9.8
4 Each Crown DSI 1000 Amps
1 Each Crown DSI 2000 Amp
2 Each JBL 4645C Sub Woofers
1 Each EV18B set up for mid Bass
3 Each JBL 3677 used for LCR behind a AT Screen
4 Each JBL 8330 used for L and R surround and Rear Surround
various source devices BD rom, Dish, Apple TV and a Media Center
OK so needless to say that I have the capacity to tear the paint off the walls and unhinge the ceiling joists. I do like to listen to movies loud.
My JBL 3677 speakers great as they are fatigue my ears after about a half hour of an action movie. I have tried many different things to tame them but just can't seem to get them in line.
A friend of mine suggested that I check out Pi speakers, he mentioned that he had read someones post on this forum about changing the CD in the 3677 to something that was much more pleasing to the ear. I looked at the forum and could only find a post where someone tested a few different drivers but did not come to a resolution inside the JBL cabinet.
So the real question is do anyone know if a direct replacement for the CD in the 3677 that just works? I know there is much more to it than that but I have to ask.
If the answer comes back no then of course I need to start cutting wood for My Pi 4 speakers and my question will be will the woofers in my 3677's work for a Pi4 build or would it be better to get the 2226's.
Where do I start? are there plans for the speaker box cuts or sizes available.
does it make a huge difference in sound quality if you buy the crossovers with the more expensive caps and resistors for the Pi 4?
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| Re: Theater room LCR [message #79644 is a reply to message #79640] |
Sun, 09 March 2014 12:02  |
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Wayne Parham
Messages: 18675
Registered: January 2001
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Illuminati (33rd Degree) |
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I'll send plans to your E-Mail account, so you can get started on the cabinets.
As others have said, the JBL 2226H is a best-of-class midwoofer. In my opinion, there are no better woofers than the JBL 22xx series devices, and in saying that, I am including the GPA and AE product offerings. Everybody is trying to catch the JBLs, but in my opinion, none are able to.
The CD we use is the B&C DE250. It also is a world-class driver, and most consider it to be the "one to beat." You can't do better for anything less than a grand. Next step up would be the TAD drivers, and the improvement you get is a tiny sliver of extension above about 18kHz. Not sure I'm willing to pay a grand for that.
You can buy kits from me, or you can source your own parts. Look around on eBay and you may find some good deals on refurbished JBL woofers. But make sure they have genuine JBL cone kits.
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| Re: Theater room LCR [message #79713 is a reply to message #79710] |
Mon, 17 March 2014 22:15 |
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Wayne Parham
Messages: 18675
Registered: January 2001
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Illuminati (33rd Degree) |
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I think if you're capable of configuring an active crossover so that its transfer function is exactly the same as the passive crossover we provide, you'll gain benefits from doing so. But there's the rub: I tend to warn people that they'll need to do some work to setup an active crossover, and not to think that they will enjoy improvements just by simply having one. It requires a crossover/processor that can be programmed to provide any transfer function, not just one that allows the user to select a set crossover frequency and slope. And it takes a little bit of time with an acoustic measurement system, to optimize the system at all off-axis angles. The process is shown in my "Crossover Optimization" thread. The basic process is described, and there is a link to a video that shows you how to find the vertical nulls, which mark the edges of the forward lobe.
The low-pass filter for the woofer is pretty straightforward, but the tweeter circuit is a little more complex. And of course, proper on-axis and off-axis summing through the crossover region requires careful selection of both high-pass and low-pass sections, both in terms of frequency and phase. This is usually set by slope and filter type, and sometimes standard types aren't even used.
The damping of the waveguide's high-pass filter circuit must be adjustable as well as the slope and frequency, because we set the lower "shelf" by setting filter Q. In most cases, it is slightly underdamped because (properly sized) conical horns and waveguides tend to rolloff a little down low. On the other hand, truncated conical horns and waveguides tend to have a peak down low, and in this case, the tweeter circuit can be overdamped to partially compensate. This is a very important feature of the π pad in the passive crossover - It provides a way to adjust the region just above crossover and to tailor it for any waveguide. You will need to provide this in an active crossover as well.
Most people tend to think an active crossover can be easily configured using "CD compensation" but I find this is rarely the case because of the lack of filter Q adjustability. The 6dB/octave compensation for mass-rolloff is the easy part, it's just a single pole RC or RL filter. That's what "CD equalization" in most active crossovers provides. But the result is a transfer function that's a diagonal line, and that doesn't work well in most cases.
Mass rolloff doesn't start to occur until around 4kHz, so we usually want flat response up to that point, followed by 6dB/octave rising response. And as I said above, each individual waveguide has its own unique charasteristics in the ~1kHz octave too, some needing a little more damping, some a little less. So for the active crossover to be useful, it needs to capable of adjusting the transfer function of the tweeter circuit accordingly, usually something like this:
π crossover tweeter circuit transfer function
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