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Discussion Starter · #1 ·
Well I am very late in posting my progress on my build.

After thinking about what I was really after with this build, I decided I was after trying to get as much low end extension as I could get and fit into my home theater room. I have a L shaped room that is about 2100 sq. ft. My main listening position is located about 2/5 within the long room depth. We only sit about 7 to 8 feet from the mains. So the theater room unfortunately has a narrow sweet spot.

After modeling several ported 18" and the sealed FTW-21, I decided to go with the FTW-21. Primarily because I wanted to see what could be achieved below 20 hz for movie viewing.

I am coming from a BIC PL-200 which is pretty good for a $270 sub for movies, and not nearly as great for music. It is now clear to me that the PL-200 is designed to punch up movie listening. My family enjoyed it for two years, and I would still recommend it for my room size, but for movies only. It is about a 7/10 for music, as I believe it humps up the 30 hz range and dies off quickly after 70 hz.

I just finished the FTW-21 build and it is powered by a Inuke 3000dsp as I wanted to play with a DSP and this was the cheapest amp I could find around 2000 watts. I am loving the Inuke, but is it very loud stock. I have already ordered a new fan and little heat sinks to quite it down. Will update after the quite-grade. So far I have not found the limits of the amp with the sub. I am letting the sub and my ears break-in to the power. So far have only once tickled the limit lights and that was during TRON legacy, which I have found has huge volume swings in BASS. Maybe not a good film to start with as I was mainly at -24 db and from there it once ticked the 0 db limit light!

I now need to quite the inuke amp and spend many hours listening to a variety of stuff. I need to get a better microphone for REW and to go around my Bat Cave and quite walls down. Stuff is shaking!

More updates later. I want to enjoy now. I spent 15 hours straight from last Friday evening to the wee hours of Saturday morning working on the box. First fired it up last night after work. Now have a cold, but am too excited to not try and have a listen!

I hope the photos upload in a vertical alignment. I can't stand when I have to scroll sideways... Very bad on a tablet...

Happy New Year!
 

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Discussion Starter · #3 ·
Thanks DougC.

The box is not perfect, but is good enough in my blacked out bat cave. It is going to be top covered with triple black velvet anyway. I don't like to see reflected light during movies.

This thing is soooo crisp so far with all of the tunes I like to play. Blues, rock, classical and jazz!. I had to borrow some thumping tunes from my teenage girls to dig deeper in music and it thumps it out so clean!

I would encourage anyone to go DIY and model and build either a strong ported or sealed box after the difference my build has made!

I have been playing a five string bass guitar for over 20 years in various very small time local bands. I have built over a dozen bass cabinets for bass guitar during that time and I have never felt as tight of bass as I have from this driver. It is clear to me that I now need to upgrade my live band bass power! I wonder how HT subs would do with live bass guitar frequencies?

Hope everyone has a safe and thumping night!
 

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Discussion Starter · #7 ·
The box ended up with the following external dimensions: H 25.875 x D 22 x W 28. It fits my space well. I could eventually build a duplicate as I have the space to the right of my center channel, but I doubt it is really needed for music or HT.

I calculate the internal volume minus bracing (& guessing a 1/2 a c.f. for driver) as 6.3 c.f.

Qtc: at 6.3 c.f. I model as .753

To start I put one 6" layer of R-19 fiberglass across the back of the box and then used the polyfill from three Walmart $2.50 pillows in the rest of the area. The polyfill was fairly loosely filling the rest of the space. I am curious on how to properly model stuffing. Do you both increase the box size 10% or so (based upon the amount of fill) and change the Qa parameter in Winisd to reflect the stuffing? The Qtc does not change a great deal either way.... A box of about 7.5 c.f. gives a Qtc of .708.

So far I have just been doing a great deal of listening to both music and a few movies. It is so much more sub than I have ever had before. Very clean sounding with more SPL than my family can stand. I will push the volume and play around with E.Q. this weekend when I am alone some.

I would like to get a microphone for using with REW. I have a few different music microphones such as a Sure SM58, but I don't know if that would work well with REW.

I don't think I need all of the SPL it can put out so I should be good with using some of the power to boost the low end with a Low Shelf filter or a PEQ at 20 hz. I wish the DSP could go lower than 20 hz. I went with the 21" sealed to try and get as much <20 hz as I could get. I wonder if boosting the low end will change the audible range much with the filter this DSP can deliver.

The sub has me spending a lot of fun time in the cellar! I need to chase down rattles also and maybe check my stone foundation :blink:.
 

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The box ended up with the following external dimensions: H 25.875 x D 22 x W 28. It fits my space well. I could eventually build a duplicate as I have the space to the right of my center channel, but I doubt it is really needed for music or HT.

I calculate the internal volume minus bracing (& guessing a 1/2 a c.f. for driver) as 6.3 c.f.

Qtc: at 6.3 c.f. I model as .753

To start I put one 6" layer of R-19 fiberglass across the back of the box and then used the polyfill from three Walmart $2.50 pillows in the rest of the area. The polyfill was fairly loosely filling the rest of the space. I am curious on how to properly model stuffing. Do you both increase the box size 10% or so (based upon the amount of fill) and change the Qa parameter in Winisd to reflect the stuffing? The Qtc does not change a great deal either way.... A box of about 7.5 c.f. gives a Qtc of .708.

So far I have just been doing a great deal of listening to both music and a few movies. It is so much more sub than I have ever had before. Very clean sounding with more SPL than my family can stand. I will push the volume and play around with E.Q. this weekend when I am alone some.

I would like to get a microphone for using with REW. I have a few different music microphones such as a Sure SM58, but I don't know if that would work well with REW.

I don't think I need all of the SPL it can put out so I should be good with using some of the power to boost the low end with a Low Shelf filter or a PEQ at 20 hz. I wish the DSP could go lower than 20 hz. I went with the 21" sealed to try and get as much <20 hz as I could get. I wonder if boosting the low end will change the audible range much with the filter this DSP can deliver.

The sub has me spending a lot of fun time in the cellar! I need to chase down rattles also and maybe check my stone foundation :blink:.
Well you need to decide how much boost you want...you can still affect frequencies below 20 Hz via the PA or parametric filter settings. You would choose the widest bandwidth (120/60) which is 2 octaves, meaning 10 hz to 40 hz either side of the 20hz center. The trick is to boost at 20Hz and then cut at a higher frequency in the midband area using the same 2 octave bandwidth. The end result is a net boost on the bottom end. From past experience a real world boost of 4-5 dB below 20hz would likely involve boosting 8 or 9dB at 20 and cutting 6 to 8 dB up higher.

When I had my 2x15 sub system, I used:

fbq2496...2 shelving filters for .5Q curve...20 Hz/.182/+6.5 dB...130 Hz/.182/-7.5 dB

Of course this is 5 octaves (Q = .182) and done with the much more capable FBQ2496. So the FBQ was boosting well down into the single digit frequencies, or whatever was available within the limits of the electronics. However you can still get some boost with the DSP1124.

My current modest setup uses a dsp1124 and I'm satisfied really because of the already low qtc. of the box, which is around .5 or critically damped. It does not require a huge amount of additional boost to run flat in a 1,200 cu. ft. space. The settings for the current box is 20hz +6dB and 63hz -8dB, both at 120/60 or 2 octave setting (Q = .6667), which of course is the max for the dsp.

If you have winisdpro, it will help you shape the response, but you must be sure to add the crossover filter into the simulation, which is typically fourth order, though you should check your receiver because sometimes the crossover rolloff can be different. Once the two shelving filters are put in along with the crossover filter, winisdpro will show a curve via the transfer function screen. You can then go back and forth to see how boosting and cutting will affect the curve. There is an optimal midbass frequency to keep a smooth line and it can't be too close to 20Hz or the lines will become squiggley and uneven. It is likely to introduce what is called ringing into the group delay response. Any sharp deviations in the response will cause this, although the room will have the final say in the matter.

Keep in mind that the in-room response will look nothing like the even lines in winisdpro but it represents an overall response curve, or best fit curve to use a statistical analogy. The ripples of deviation (outliers) in the room will need to be addressed further but the overall Q curve of the system will remain. That could mean a rising, falling or flat bottom end extension.

Finally, using 1 pound of polyfill per cubic foot of internal volume is about right. If you had an impedance analyzer, you could determine almost precisely what the qtc. is by the box frequency (with the help of Unibox). I put the numbers for the FTW-21 into Unibox and the lowest qtc. I could conjure up would be the aforementioned 1 lb./cu.ft. stuffing. It will be really tight (with 6.5 lbs. of polyfill) but the driver would squeeze right in for a Qtc. = .643 (6.3 cu.ft, Qa = 5 , Ql = 15) with heavy fill and minimal leakage. The measured box frequency via the analyzer should show Fb at about 39 - 40Hz if filled right. The lower the better. If you don't need all the SPL above the box frequency (~40Hz) then you can fill heavily and curve up a bit with the dsp...the FTW-21 has excursion for days! The sound with heavy fill will be a bit tighter as well.

As a further aside, I must add that I am currently in transition from an 18" to a 21" sealed driver and I may end up going 2x21 in the near future because it will take 2 neo-pro's to equal the mayhem of the FTW-21, but they can both reside in a much smaller cabinet with a dual-opposed setup. They might play a bit cleaner as well with two cones versus one. Good luck to you and enjoy the woofage!

Read more: http://www.hometheatershack.com/for...tc-3000-2x15-5q-sealed-sub.html#ixzz2pQLc1Y2u

This is a helpful Q/bandwidth calculator, though I don't think you need it with a dsp:
http://www.sengpielaudio.com/calculator-bandwidth.htm
 
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