Hidden HT

[hrockefeller]

Hey all, found this site when researching my project over at the Cult of the Infinitely Baffled on how to use 4 MJ-18's in an infinite baffle setup. I am pleased to see several others also seem to use this driver in an IB setup with the Behringer EP2500 and FBDP which I have also ordered.

My room is about 5000 cu ft and in addition is open plan, opening into the kitchen and there is a hallway coming off. I therefore don't anticipate much room gain. I am planning on using 4 MJ-18's arranged in a 2 per side stereo arrangement at the front of room where the screen is. I am just wondering how to EQ this system? I have read about the REW program but from what I can tell you need extra equipment - all I have access to is WinISD online and the REW program which I believe is free and generates tones. Can anyone tell me how to set the eq for the FBDP? Thought that if I had a room response curve I could just add the appropriate gain at the appropriate frequencies. Any help is appreciated. Thanks,

Philip

[Otto]

Hi Philip,

Ah, I see your message here...

As you know, I responded to you in a PM to a similar question. I figure I'll just copy that response here to start the conversation. Here's what I said:

Otto, in a PM wrote:

Hey Philip,

Well, EQing is a sub like that will be difficult to describe in a single message! In general, read up in the "REW | BFD" forum. There are lots of threads that describe various members' experiences with EQing subs, both large and small. I probably have one out there somewhere...

The EP2500 works great for my IB. As far as I can tell, I've gotten nowhere close "max" on either the amp or the subs. It can get quite crazy as to SPL output. You will enjoy it. Since my IB is the only "extreme" sub that I've ever experienced, I can't compare it to other IBs or LLTs, etc. I do think that the MJ-18s work very well for "budget" drivers. If I had it to do over, I might consider going with only two drivers, with those drivers being higher quality. Still, the MJ-18s pretty much crank it out!

I've found that the BFD is a great tool to deal with this sub, as well as my previous subs. You'll really get a lot out of it.

I think you might do better to post in the "REW | EQ" forum than the "DIY Subs" forum if you are asking about REW and BFD. They're definitely related to DIY subs, but it'll get more response in that forum. I imagine that a mod will move; I probably will if I get to it first. No problem with that, it's mostly just a matter or organization and accounting.

The first step in applying EQ to your sub is to learn how to use REW. REW will allow you to measure your sub's frequency response, and you will adjust from there. You'll just need an SPL meter, a PC with soundcard with line in and line out, and the proper cabling. These are all well-documented in the REW manual, available at the top of pretty much every "Home Theater Shack" page. Once you have measured you frequency response, REW will calculate the filters that it thinks should be applied to your signal. You don't need MIDI I/O from your PC to enter the filters into the BFD, although I do find it handy when I'm doing a lot of measurements and adjustments. The BFD can accept its filters through its front-panel user interface, as described in the BFD manuals at the top of this page. The BFD user's guide maintained at this site really describes the features that we're interested in for EQing subs and skips over all the other stuff that the BFD can do; it's really geared for everything you want to know. If you do want to use the MIDI connection between REW and the BFD, you can pick up a PCI sound card with digital output as well as a MIDI connection on eBay, I'm sure. Either way will work.

So, yeah, look around a little and ask questions in the forum! Feel free to PM me anytime, and I'll help as I can. Once you get everything up and running, it's pretty easy, and you can tweak all day and night!

Good luck!

I probably missed some stuff, but that's a good start!

[hrockefeller]

Hey Otto, thanks for moving my post, and for the very helpful reply. I didn't know about this alternate forum. Will try to pick up an SPL meter and go at this, have actually wanted to go down this road with my loudspeakers anyways. Would be very keen on seeing if this is a viable way to measure frequency response as all other methods have seemed complicated. Thanks,

Philip

[Otto]

Yep, REW is very effective for measuring frequency response, and it's free! Let us know if you have any issues with getting going.

Welcome to the Shack!