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post #1 of 28 Old 02-03-2007, 02:52 PM - Thread Starter
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Well, its been a several month saga where I've gone from an SVS PB12+/2 to an IB to a pretty large sealed sub built into the room. The SVS was really pretty awesome but, of course, I wanted more. I read all the hoopla about IB and decided to try that route. That was more capable in some ways than the SVS but not by as much as you might think and I was never able to get the same "punch" out of the IB. The real killer, however, was the fact that the rearwave area was an unfinished portion of my basement and this caused waaay too much leakage of the sound to the rest of the house. I pretty much couldn't run the IB when my wife was home. So, I decided to build this huge box behind/under my screen:



The drivers are Fi Q18s purchased originally for the IB setup. The box is about 70cuft and they are driven by an EP2500 bridged into 4ohms. I'm actually quite happy with it now. I got the punch of the SVS back as well as some really good extension. I'm sure not as much as the IB but still it goes pretty low as my room has some good gain under 20hz. On music it is very natural and a movie soundtrack like the door banging in The Haunting will make any unsuspecting fool just about crap their pants. Plus, it doesn't leak nearly as badly to the rest of the house. On music it doesn't do much at all and only the most severe movie scenes cause rattling of the china cabinet and chandelier in the dining room above.

So, I think I'm happy, but I thought I'd ask the experienced DIY guys in here a question. Would I stand to gain anything by adding a port to this configuration? Or, anything else? Thanks in advance.
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post #2 of 28 Old 02-03-2007, 05:27 PM
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Quote:
Originally Posted by ebr View Post

Well, its been a several month saga where I've gone from an SVS PB12+/2 to an IB to a pretty large sealed sub built into the room. The SVS was really pretty awesome but, of course, I wanted more. I read all the hoopla about IB and decided to try that route. That was more capable in some ways than the SVS but not by as much as you might think and I was never able to get the same "punch" out of the IB. The real killer, however, was the fact that the rearwave area was an unfinished portion of my basement and this caused waaay too much leakage of the sound to the rest of the house. I pretty much couldn't run the IB when my wife was home. So, I decided to build this huge box behind/under my screen:



The drivers are Fi Q18s purchased originally for the IB setup. The box is about 70cuft and they are driven by an EP2500 bridged into 4ohms. I'm actually quite happy with it now. I got the punch of the SVS back as well as some really good extension. I'm sure not as much as the IB but still it goes pretty low as my room has some good gain under 20hz. On music it is very natural and a movie soundtrack like the door banging in The Haunting will make any unsuspecting fool just about crap their pants. Plus, it doesn't leak nearly as badly to the rest of the house. On music it doesn't do much at all and only the most severe movie scenes cause rattling of the china cabinet and chandelier in the dining room above.

So, I think I'm happy, but I thought I'd ask the experienced DIY guys in here a question. Would I stand to gain anything by adding a port to this configuration? Or, anything else? Thanks in advance.

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...

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post #3 of 28 Old 02-03-2007, 05:50 PM
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Hello fellow North Carolinian!

I'd give EQ a good look.
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post #4 of 28 Old 02-03-2007, 06:00 PM
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Originally Posted by ebr View Post

but I thought I'd ask the experienced DIY guys in here a question. Would I stand to gain anything by adding a port to this configuration? Or, anything else? Thanks in advance.

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.
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post #5 of 28 Old 02-03-2007, 08:56 PM
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Would I stand to gain anything by adding a port to this configuration?

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?
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post #6 of 28 Old 02-04-2007, 07:13 AM - Thread Starter
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Originally Posted by Thomas-W View Post

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

Excellent point, Thomas.
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post #7 of 28 Old 02-04-2007, 07:14 AM - Thread Starter
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Originally Posted by Willd View Post

Hello fellow North Carolinian!

I'd give EQ a good look.

Sorry, I neglected to mention it but I do have a BFD inline as well and have tuned it with REQW. I'll try and post a couple graphs today.
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post #8 of 28 Old 02-04-2007, 09:05 AM - Thread Starter
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Here are a couple of plots.

Uncorrected response:



And with my current set of BFD filters that I think sound best (so far):

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post #9 of 28 Old 02-04-2007, 09:24 AM
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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.
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post #10 of 28 Old 02-04-2007, 10:30 AM
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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.
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post #11 of 28 Old 02-04-2007, 10:45 AM
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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.

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post #12 of 28 Old 02-04-2007, 02:49 PM - Thread Starter
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Thomas - yes that is a nasty null and, unfortunately, it exists all across my back row (the prime seating). I still have the SVS but there is no option to put it in the room anymore. Just no place for it to live as I turned its "house" into a sub enclosure . I'm thinking I might ask Bryan if there is something we can build to attack that null, though.

Mark - Thanks for all the suggestions. I have actually done some of those things already but not quite as detailed as you laid out. I will try attacking them again tomorrow. FYI - I'm using an ECM8000 as my measurement mic. I'm not sure if my processor has a hi pass but these measurements are taken through the whole setup as it is used in practice. I am using a Pioneer Elite VSX84TXsi as a pre-processor (not using the amps in it).

Steve - I'm not one that sees much evil in EQ as I've used it all my life for both home hi-fi and when I had a recording studio. So, given that I will be using EQ to smooth my response regardless. If I can accomplish what I need with that, I don't really want to add a port. Given the amount of displacement I have, I was actually thinking a port would create the possibility of more distortion. As it is, I don't have to push these drivers or my amp very hard at all to get the output I want.
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post #13 of 28 Old 02-05-2007, 09:13 AM - Thread Starter
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[IDIOT ALERT]

Okay, so Mark's suggestions made me realize that I wasn't using the low-pass circutry of my processor because I was doing my tests through the sub input of the multi-channel input. So, I hooked up to a stereo input, put the AVR in a DLPIIx mode and ran another test. No sub output. Oops...

When I tore down the IB and re-built the current setup, I re-ran my processor's auto-setup routines to set levels and such. I forgot to go back in and re-set my main speakers to "small". Duh!

So, its back to the drawing board on my tweaking.
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post #14 of 28 Old 02-05-2007, 09:40 AM
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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.....
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post #15 of 28 Old 02-05-2007, 10:05 AM - Thread Starter
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Originally Posted by ssabripo View Post

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.....

It was correct with the IB. It was just when I built this new setup when I re-ran the auto routines I forgot to go back in and re-set the speakers to small.

As far as the plots of just the sub go, it shouldn't make much difference, but real life material will behave very differently with the mains low freq being re-directed to the big sub. I should get even more punch now.
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post #16 of 28 Old 02-05-2007, 10:43 AM
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Quote:
Originally Posted by ebr View Post

I should get even more punch now.

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.
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post #17 of 28 Old 02-05-2007, 10:55 AM - Thread Starter
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Quote:
Originally Posted by Thomas-W View Post

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

Funny man.... .

Quote:
Originally Posted by Thomas-W View Post

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.

Thanks for that link. In your opinion, is it worth the ~$200 upgrade price (assuming I can sell my BFD) to get the 2496? How much better than the BFD is this going to be? Its still limited to 20hz as the bottom filter, right?
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post #18 of 28 Old 02-05-2007, 01:28 PM
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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
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post #19 of 28 Old 02-05-2007, 01:47 PM - Thread Starter
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post #20 of 28 Old 02-05-2007, 01:52 PM
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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.

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post #21 of 28 Old 02-06-2007, 01:18 PM - Thread Starter
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Well, I started from scratch with REQW and the proper settings/hookups and got a much smoother response that fits the target graph better. It sounds awesome with even more punch and more consistent response across the seating area.

I still have a few nulls that look bad in some locations on the plots, but, in practice, I don't hear them as problems. Of course, you can't know what you don't hear. Anyway, I'm happy for now and will try to hold off upgrading my processing to the DEQ. Thanks all for your help.
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post #22 of 28 Old 02-09-2007, 04:45 PM - Thread Starter
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Just a quick update to note something I discovered today. I think one benefit to having the copious displacement I do with this setup is that I can fill in the low octaves even at very low listening levels.

With all my previous subwoofers, if you turn the overall volume way down you pretty much lose the really low stuff, and definitely don't get any of the tactile feeling you do when its louder. Well, this afternoon I was chilling out in the room with EC's "One More Car, One More Rider" DVD (my new favorite reference disc - its 750kbps DTS soundtrack is the best I've heard). I was basically resting so I put the volume down to a very quiet level (-35 on my AVR). I was laying there and was amazed that I was getting the full spectrum of sound. The really low stuff subtly moving my insides and the kick drum thumping me lightly in the chest. Absolutely beautiful.
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post #23 of 28 Old 03-02-2007, 02:59 PM
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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.

jeff

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post #24 of 28 Old 03-02-2007, 09:18 PM
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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.

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post #25 of 28 Old 08-29-2007, 07:33 AM - Thread Starter
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Just as an update, also at Thomas' urging, I found a good deal on a DEQ2496 and swapped it out for my BFD. Made a real difference in the low end extension. Thanks Thomas .
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post #26 of 28 Old 08-29-2007, 08:02 AM
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Is that because of the shelf filters? Or some sort of electronics roll-off?
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post #27 of 28 Old 08-29-2007, 08:04 AM - Thread Starter
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Is that because of the shelf filters? Or some sort of electronics roll-off?

I'm assuming the shelving but the electronics are higher resolution so maybe it doesn't roll of as fast under 20.
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post #28 of 28 Old 08-29-2007, 08:21 AM
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I'm assuming the shelving but the electronics are higher resolution so maybe it doesn't roll of as fast under 20.

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