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Discussion Starter · #1 ·
I'm converting to IB.
This morning I ordered four MJ-18s. :bigsmile::bigsmile::bigsmile::bigsmile:
The amp will be my Carvin HD1800.
The manifold will be a cube in my attic.
I'll keep you posted! :hyper:

 

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Discussion Starter · #4 ·
Yeah, the sale of my 10" just about covers the price of these drivers!
Does not compute...
 

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Are you in for a shock! :eek:

There is no way you can prepare yourself for what these things sound like! :D

Make sure you have the LOTR trilogy handy for your first test of courage. :devil:

If you survive that you'll survive anything! :T
 

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It's still hard for me to grasp that these drivers are so good for so little..

If I were ready for my IB, I'd think about a trip to British Columbia where I accidently buy 4-8 of these things!

JCD
 

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Congrats Naut... looking forward to seeing your progress.

Uh... before you begin, could you ease on over to my house and help me get mine all done first?
 

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Discussion Starter · #12 ·
So are you going back to receiver amplification for your mains?
Yes, for now. The amp generates a very low level hiss (beside the fan noise). My revciever's preouts clip at +0, so I'd like to dial them back to -12 and increase the gain on the amp, but that amplifies the hiss. I'm also picking up very high frequency noise from my CRT which is so high and quiet that its barely audible but its driving me crazy. The Carvin is more suited to living in my laundry room and powering the subwoofer. So for now I'm putting my mains back on the reciever power, and maybe around Christmas I'll pick up a new hi-fi amp.
 

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Discussion Starter · #13 ·
Make sure you have the LOTR trilogy handy for your first test of courage. :devil:
I've been very keen on an IB ever since I heard it described as a "religious experience."
 

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Discussion Starter · #14 ·
Uh... before you begin, could you ease on over to my house and help me get mine all done first?
Hurry up, or I might finish first. :run:
 

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Discussion Starter · #16 ·
I'm working out the plans.
This will be in the attic with a hole in the ceiling.
I'm sticking to a roughly cubic design to minimize the size of the hole (for WAF).
To accomodate the 18" drivers and the 16" joist spacing I had to be a little creative with the design of the "base."

The driver dimensions are:
Outside Diameter: 46cm (18 1/8")
Mounting Diameter: 42.4cm (16 11/16")
Depth: 20.3cm (8")

Q1. Should the driver cutout diameter be exactly the same as "Mounting Diameter?"
Q2. Should the inset diameter be the exactly the same as "Outside Diameter?"
Q3. How deep should the inset be? 1/4"?



 

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Q1. Should the driver cutout diameter be exactly the same as "Mounting Diameter?"
Q2. Should the inset diameter be the exactly the same as "Outside Diameter?"
Q3. How deep should the inset be? 1/4"?
A1. It depends if the mounting diameter is the actual diameter or has already taken into account some wiggle room. My rule of thumb is to take the actual diameter and increase it by 1/16" all around.

A2: The inset diameter should be exactly the same or a little larger than the surround diameter.

A3: 1/4" is perfect. Just enough to hold the driver in place and seat it.


Be sure to measure your proposed location for the IB to make sure your in room response will be desireable.
 

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Daniel,

You got the 8 ohm versions, right? I don't think Mark has ever had 4 ohm versions yet, but I could be wrong. I'm pretty sure I'm going to get four, I'm just not sure if I want 8 ohms or 4 ohms (he has eight 8 ohms left, and it's a six week wait for 4 ohm versions -- so I can get the 8s NOW!). Four 8 ohm in parallel will be 2 ohms, which I believe is fine for my EP2500. I can run that bridged, or I can run each channel with a 4 ohm load, which is also fine. Anyone see a good reason for me to wait for the 4 ohm versions, or should I just get started with the 8s?

FWIW, I believe I'm going to do my ceiling IB as two arrays of two in a vaulted ceiling (room's about 3,000 cubic feet, and open to dining and foyer areas). I won't be using a manifold. I'll start up another thread once I have a better plan and a bit of a start.

Good luck with yours!
 

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Running the EP2500 bridged into 2 Ohms is not a good idea according to two qualified engineers with whom I have discussed this matter.

4 Ohms per channel (2 x 8 Ohms parallel pairs) is a much kinder load on any amp.

The 8 Ohm version would have been my preference for my own drivers but only 4 Ohm models were available to me at the time.

So I use series pairs for 8 Ohms channel and still "enjoy" 120dB levels on demand from my EP2500 despite never having seen the clipping lights come on.

If you are going to use an array then make sure your baffle wall is stiff enough. You would not believe the forces an array can put into the surrounding wall once the cones really start moving. You may even find that the baffle wall is moving in the opposite direction to your driver cones. Not only does that increase noise dramatically but the wall moves in opposite phase to your drivers. This can't be good for the response curve and it becomes worse with falling frequency as cone motion increases. So you may lose your bottom end just because of baffle wall flexibility.
 

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Running the EP2500 bridged into 2 Ohms is not a good idea according to two qualified engineers with whom I have discussed this matter.

4 Ohms per channel (2 x 8 Ohms parallel pairs) is a much kinder load on any amp.
Yep, you're right... I had that backwards.

And I'll make sure that baffle is tight. I could still condsider a manifold, I guess.

Thanks!
 
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