ebr's sub saga

looks like you're right around .707 on qtc...looking at the model indicates that everything looks good...no wonder you've found your midbass again...this 4x18 should be more than capable without upsetting things with venting...model shows 120-130 dB in 1/2 space from 20 Hz up...so you have enough to go deaf if you like...adding another ep2500 would give you another 2-3dB?...maybe not worth the trouble...you could tighten things up with EQ if you want to lower the qtc. a bit...there's "some" wiggle room with bass boost but not much, judging by the models...-7.5 dB @ 20Hz should put you right on the room gain curve and extend quite nicely with a reasonably built theater...besides shaping the Qtc., which is a personal taste, i see nothing wrong with this alignment...congrats to you...

Hello fellow North Carolinian!

I'd give EQ a good look.

Odd but I thought an experienced DIYer recommended building what you have....

With that much displacment there's basically no benefit to adding a port.

Might add a Behringer DEQ2496 or a Marchand Bassis. Either will allow you to lower the Qtc, tighten output, and boost the lowest frequencies without sacrificing SQ.

Sure, you can always gain more low end output and less low end distortion by porting. This should also make it easier to gain a flatter natural FR into the lower depths. Can you can post an in room FR taken at the seat before applying any EQ?

Nasty null @ 40Hz from the measurement position. For comparisions run a couple of plots from different locations in the room.

Do you still have your SVS? If so, as a test, place it at the back of the room and run both subs at the same time and retest.

Porting wouldn't fix anything above 20hz, but it would help extend solid response below it without needing to use any EQ boosting. With four 18" drivers and large enclosures, you could get away with a really low tuning.

Hi ebr,

You might also double check your correction curve for the RS meter you have. I'm wondering if your receiver or pre-pro has a high pass in the 20Hz range that you aren't aware of. In a closed room I'd expect a less severe roll of below 20Hz, but leaks could cause this as well.

That said, the response is plenty workable. I would suggest some further experimentation with filters on the 16-35Hz range. I would look to see if you can get a smoother, more rounded resulting curve. Try stacking a couple filters. I would start by cutting about 6dB from the peak in the upper 20s trying to smooth the response into the mound in that general region. You may need to closely spaced filters set to either side of the peak with 3-4dB of cut to best match the shape.

The next question is if this measurement is through the pre-pro and internal low pass filter, or direct into the BFD? You should be measuring through the pre-pro, and you should take measurements with and without the center channel, and then check the L&R. By sending the same signal to the L & R analog inputs on the pre-pro while in a DPL (cinema) mode, the signal will go to the center channel. It looks to me like you probably have to abrupt a roll off to the top end of the subwoofer's response, but "correct" is entirely dependent on what the center channel and the L&R are doing. The >55Hz range you have cut is precisely where a significant portion of the "kick/punch" you are describing lives.

Depending on if your measurement includes the low pass of the pre-pro I would probably suggest starting with first smoothing the dominant peak, and then set one or two very wide filters in the 50-90Hz range that you can use to tilt the entire response downward slightly and lessen the roll off from 16Hz to 10Hz similar to what you have already done on your own. If the measurement shown is through the pre-pro and low pass, you want to also add a filter up around 200Hz to kill the high frequency peaking in the response.

I would leave the 40Hz null to the end. You can't do much with that via EQ. You can either put a shallow EQ in that range after everything else is shaped to pull up the energy 2-4dB, or if you find that elsewhere in the room that null turns to a big peak, put a very narrow notch centered right on that frequency.

ebr,
so I'm confused here....you had the ssp's setting incorrectly when you were running the IB, or you meant that once you went to the sealed you forgot to setup the ssp again?

btw, great thread.....

I'm sure the 'wife' will appreciate that .......

Here's a URL for creating an LT circuit with the DEQ2496. If you get one of these you don't need the BFD because it contains all those functions.
http://home.comcast.net/~thomasw-2/S...EQ2496-LT.html

Marchand offers a stripped down mono version of the Bassis. If you use it you'll need to keep a BFD in the circuit.

The DEQ is designed by Behringer to be a high quality fullrange EQ. Remember the BFDs wee never designed with the intent of being used as EQs, that just something DIYers figured out they could do. The lowest hinge point on all Behringer products is 20Hz.

Here's more info on the DEQ, it's a pretty amazing device for the money
http://home.comcast.net/~thomasw-2/S...geDEQ2496.html

While my favorite and more flexible, but more expensive, and computer only GUI, DSP based EQ is the QSC DSP-30 (often found for around $499), the DEQ is well worth the difference for the addition of shelving filters to the available tools, especially with a sealed or IB system. The DCX2496 is similarly capable and not much more expensive, and adds the ability to include high and low pass filters as well as other room for playing with the additional outputs.

ebr,
I've been a fan of all three of your build threads and that is one impressive looking subwoofer. I'm in the process of adding a second cylinder to ours but it will only be an additional 18" cylinder w/15" TC Sounds drivers. We also have a screenwall covered in acoustically transparent fabric and a transparent screen. All my front speakers are behind that like yours. Looking at yours makes me want to go even bigger.

I just realized you're in Moorseville. As a wee lad, I lived on Lake Norman and then later just down the road.

At Thomas's urging I finally picked up a Rane PE17. All knobs and all can go low. Made it really easy so far to change things in my modest IB. Just a few more tweaks to make and I am pretty flat from 15 on up. I will be doing the front of the room soon into the attic with a second IB setup. I will definitely spring for another Rane PE17.

I agree that the big box gives you the low end without having to crank things way up.

Is that because of the shelf filters? Or some sort of electronics roll-off?

I see. I found the shelving filters on my Crown XTi 4000 to work magic, also.