My FI Q15 14.5Hz LLT Build - AVS Forum
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post #1 of 39 Old 09-10-2012, 11:52 AM - Thread Starter
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I just received my Q15 today and am still playing around with some designs, tuning in WinISD but this will be where I post my build. (sorry home theater shack was too prudish for me filtering words like 'heck')

Pictures of this beast to follow shortly.
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post #2 of 39 Old 09-10-2012, 12:42 PM
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Not bad, looking forward to it!!!! did you go with a traditional LLT or a sono-type enclosure?

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post #3 of 39 Old 09-11-2012, 12:47 PM - Thread Starter
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Still trying to see what fits best in the room. Sono would make it long but light, traditional box would give me more flexibility in design and shape. The biggest issue I'm having right now is port length vs port velocity vs port resonance. going to play around with it this week and hope to finalize design and start building next week.

I attached some picks just since I'm so impressed on how massive this beast is. On paper is one thing, but when you open the box, its another thing.

I used a beer can and my towers for comparison.





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post #4 of 39 Old 09-11-2012, 03:17 PM - Thread Starter
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Doing some hardware shopping and I'm wondering if any random binding post type connectors will do for a sub like this or if I should be looking into other options. I have the dual 2 ohm model of this sub so current might get a little high under heavy loads.
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post #5 of 39 Old 09-11-2012, 03:18 PM
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You won't need any special binding post for this unless you want to.

With dual 2ohm, you will hook the VC's in series for a 4ohm nominal load. Pretty average load for most amps. Don't worry.

My Dual 18" LLT subs 120dB down to 10hz

 

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post #6 of 39 Old 09-12-2012, 08:25 PM - Thread Starter
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So here is where I am, possibly a little stuck. Trying to keep my LLT in the 6CF range but I might have to rethink that. My current issue is # of ports vs port length vs air velocity.

I still haven't decided if going with a sonotube or not.

check out the attached screens shots. These are all 6CF and 15Hz as a starting point. no filters, 1000W for reference.





i can upload the winisd file if needed.
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post #7 of 39 Old 09-12-2012, 09:28 PM
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Somewhere in the WinISD options you can change air velocity measurement from Peak to RMS. That's more appropriate for "real world" use.

My build thread here (tall LLTs, 14Hz, 11.6 ft^3 internal) has a little info on using different tools (WinISD, boxnotes, flare-it).

BTW, I love Speakon connectors for subs. I'll never use binding posts again.

--Dan
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post #8 of 39 Old 09-13-2012, 10:49 AM - Thread Starter
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Dan, Thanks for the RMS recommendation in WinISD, now I have a more manageable port length.

I'm trying to use 2x 4" ports.

graph is of air velocity m/s rms with 1000w input power.

I see that you used a single 8" port.

Just from experience does this look ok or am I pushing it in terms of air speed?


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post #9 of 39 Old 09-13-2012, 02:03 PM
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Back when I built mine the recommended max velocity (rms) was 20m/s above 20Hz, and 25-30m/s below 20Hz. I don't know if that's still the consensus. Remember, a high-pass filter will reduce the velocity at the low freqs.

My final design used a single 6"x29" port with a max of 22m/s @ 12Hz. I've never heard any port noise.

--Dan
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post #10 of 39 Old 09-16-2012, 03:37 PM - Thread Starter
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So I'm itching to get building (and listening) and started to hash out final designs.

I decided to go with a regular box and not a sonotube, only for the simple fact that I could get the cubic footage I need with a cube, and it will be easier to make something the size of an end table fit into my living room / theater. I still want to build a sonotube at some point but that might be for when I own a house at some point later on in life.

Another reason to go with a cubed box was that I couldn't settle on a tuning frequency I liked. So i decided to go with all 3 tuning frequencies I liked. I plan on using external ports. This way I can relatively easily change the length of the port as I wish. See the graph below at 1000W power with no EQ or filters to see how much of a difference in SPL it makes by changing the tuning from 14.5Hz to 21Hz.

I will probably just keep it tuned low at 14.5Hz 95% of the time but I figure I have the option to change it if I feel like it. I will be using 4" PVC and will get/make flared ends for it.

Here are the graphs for the 3 different tunes I am looking at with 7.6 CF



why 7.6 CF? Simple 24x24x25 inch box equals easy cuts out of a 4x8 foot sheet.

(4x) 24x24 inch for baffle, back, top, bottom.
and (2x) 23x24 inch for sides.

I'm going with 1/2 inch to make box light with heavy bracing internally, since driver is about 50lbs already.
renders of the cad models to come shortly.

Comments welcome.
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post #11 of 39 Old 09-16-2012, 03:55 PM
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I would use no less that 3/4" wood and proper bracing. Weight is a good thing with long throw drivers like the Q. The thinner the wood, the more panel vibrations you will have and the less rigid the enclosure will be. The lighter the enclosure, the more likely you are to have the box walk across the floor.

Outside of that, it sounds like it is time to make some dust. smile.gif
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post #12 of 39 Old 09-16-2012, 05:14 PM - Thread Starter
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I might go with 3/4 as I have always done, it shouldn't change my cuts / dimensions too much. Either way I am planning massive amounts of bracing internally. Right now I'm focusing on trying to find an amp to drive this beast.
Only amp at a reasonable price I have found so far is http://geminiproaudio.com/xp-6000 which can do 4Ohm bridged. It might be overkill for what I need but I like to have the overhead.
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post #13 of 39 Old 09-17-2012, 09:21 AM
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Some points to consider before building:
1) What is your crossover frequency? Design to keep the port resonance well above that.
2) Tuning an LLT higher loses the extra output it gives vs a much smaller sealed sub, and you will have to use a high-pass filter or risk damage.

References:
llt-airspeed-vs-port-resonance
llt-explained


--Dan
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post #14 of 39 Old 09-17-2012, 12:34 PM - Thread Starter
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Quote:
Originally Posted by dhnjp1 View Post

Some points to consider before building:
1) What is your crossover frequency? Design to keep the port resonance well above that.

Yep, right now I'm using an 6 inch port and lowest resonance I get is around 150Hz so I should be OK there. I'm crossing over at 40Hz right now, might go to 50Hz depending on how it sounds when I integrate with my HT.
Quote:
2) Tuning an LLT higher loses the extra output it gives vs a much smaller sealed sub, and you will have to use a high-pass filter or risk damage.
References:
llt-airspeed-vs-port-resonance
llt-explained
--Dan

Thanks for the links, going to read those in a few.
With the 14.5Hz tune I think I will be ok without a HP filter but for higher tune you are correct I will need it. I'm still looking at those options right now. I looked at the minidsp but haven't pulled the trigger on anything. Idealy something that can do parametric EQ and adjustable high-pass filter would be great.

This is what I envision as far as integrating with my receiver.

[Onkyo Receiver]-->[speaker level to low level rca converter]-->[EQ/HPF solution]-->[1000W+ Bridged or mono Amp]-->[Subwoofer]
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post #15 of 39 Old 09-17-2012, 03:05 PM
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If you are at all worried about really low frequency and excursion, don't forget to extend winISD's frequency axis down to 5Hz or less. By default it only shows you down to 10Hz but some subs don't have a -3dB point till lower than that. I think I remember the behringer EP amps having a -3dB at 5hz roll off.
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post #16 of 39 Old 09-17-2012, 07:27 PM - Thread Starter
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Thanks for the tip Bushi.

I've been amp shopping.

Was thinking of this: http://geminiproaudio.com/xp-3000 or the larger XP-6000 model to power the sub.
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post #17 of 39 Old 09-21-2012, 05:55 PM - Thread Starter
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So I went a little over board and purchased an FP14000 Clone to power the sub, probably more power than I can ever use but ill have the head room and be able to use this for all my power hungry needs in the future if I upgrade.
Here is my design so far. I haven't done the bracing yet since its my first time using SketchUp and it took me a while to figure out the software.

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post #18 of 39 Old 09-22-2012, 06:32 PM - Thread Starter
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So one nice thing I did is settle on on 24x24x3/4 inch panels. Turns out they are pre-cut at Lowes in those dimensions. would of been cheaper to have it cut there or cut it my self but figure its worth the knowledge that they are pretty much perfect 24x24 cuts.

I bought 6 and will just have to cut 2 of them to make an almost cubed box in the 8CF range.

One thing I didn't buy was the 6 inch pvc pipe I was thinking of buying for the port. 40 bucks seems a little steep to me.

I was thinking maybe sonotube but that wold not let me easily adjust port length and i didn't see it there so looking for a solution this week.
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post #19 of 39 Old 10-10-2012, 10:21 AM - Thread Starter
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just a few pics to document my slow progress.

still haven't finalized my port configuration but box is almost done.

I wish there were a cheap flexible port solution. I want to attempt to fit 50" of port inside the box if I could.

I also broke up some heavy equipment cable I had laying around, 3 conductor 10awg (3/c 10) and i split it up and now have 10aws cable for each coil to go from the driver to the terminals inside the box.

















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post #20 of 39 Old 10-14-2012, 07:58 PM - Thread Starter
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Just finished the box this evening. There are still some minor things to be done like sanding, routing, sealing etc. but its testable. I ended up going with 4 ports as a test instead of one large 6 inch port that would extend out of the box. I figure whats the point of DIY if your not going to experiment. I figure if i get port noise I'll just modify and replace as needed.

here are some pics of the recent progress. too bad i finished it 3 min before 10pm but even at low volume I'm happy with the response in the garage.
Note that images don't seem to show up in the right order here when I upload.









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post #21 of 39 Old 10-15-2012, 04:36 AM
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Did you cut those ports down after installing them? Or is it ok to have them that close to the opposit wall? Also, are you planning on tuning this to 4 different frequencys? Is that the reason for the 4 ports? Or did you need to add multiple ports of the same length in order to get the total amount of porting needed for that tune?

I am new to this and am just wondering. Trying to learn as much about this kind of stuff as I can!
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post #22 of 39 Old 10-15-2012, 06:56 AM
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What's the diameter and length of those ports?

They do a look a little close to the back of the enclosure.
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post #23 of 39 Old 10-15-2012, 01:05 PM - Thread Starter
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So I was trying to avoid going with a large external port so I decided to use 4 smaller ports and just see how it works out.

I originally wanted to be able to adjust the tune so am going to experiment with these ports right now and when I'm happy I can setup a permanent solution with flares etc.

The ports are 3.25 inches internally and are about 20 inches long opening up about 3 inches from the bottom of the box. They are a little close to the back of the box on top but before I sealed them in, I bent them and adjusted them so they have about 3 inches between the opening of the port and the back of the box as well, and then I used a piece of wire to tie them together to keep them from rattling around.

with these 4 ports its tuned to about 22hz and i don't hear any chuffing, although I haven't pushed the driver to the limit yet.

I did a little testing to see how it sounds and I have to say I'm impressed there were no leaks.

I played some test tones, some music, and a little war of the worlds to see how it sounds and the garage door and who knows what else in the garage rattle and make noise but the box sounds fine.

I originally wanted a permanent low tune but like everything else its a compromise. you loose efficiency in the 20-30hz range by extending the box tune down to 15hz, that is why I wanted something tune-able.

Once I figure out what I want my permanent ports to be, I hope to be able to plug 1 or 2 ports to adjust the tune as I wish. 2 ports plugged brings it down to around 16hz according to my memory.

corrugated drain pipe is not the best solution for 10 bucks its disposable so I can cut/ replace / test etc and when i figure out what I want ill move to a permanent solution.

Now to figure out what I can stain the box with to have it match my mains which are black / simulated wood grain.
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post #24 of 39 Old 10-15-2012, 01:14 PM
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I have to say I am quite glad the corrugated drain is not a permanent part of that box...Whew. So you didnt use ANY glue to seal that box up? Try running a lighter around the creases and see if it blows with 20hz sine or something. you will easily be able to confirm no leaks this way, they arent always audible.

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post #25 of 39 Old 10-15-2012, 01:51 PM - Thread Starter
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Just wood glue on the inside. Like the lighter test. I'm thinking a candle or something.

I ordered some bolts to replace the 1/4" pan head screws holding the driver in (crappy selection at lowes)
so I'm going to have to get in the box anyway. Still need some kind of stuffing to staple into the walls and might add more bracing so I figure that is when ill make it "permanent" redo the ports etc.
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post #26 of 39 Old 10-15-2012, 09:38 PM - Thread Starter
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So here is the simulation for the test ports I used.

The idea is plug ports to get lower tune.

(other option is use something easy to extend like pvc pipe+ adapter to extend as needed)

4 ports 23Hz , 22m/s @ 500w
3 ports 20Hz, 27m/s @500w
2 ports 16Hz, 38m/s @500w

I have used flar-it and done lots of research and I feal that flar-it is very conservative with air speed.

I have read posts where 34m/s port air speed was built and there was no issue.

I originally was using 1000w for input signal in winisd for simulation but how much % of the time will I be listening to anything at that level of power. And when the sub is getting 1000w in a scene or with music, how much other sound is coming in at reference level?

Anyway, I'm going to live with the current setup for a month to evaluate and see what I want to do about the tuning. It may be that I go with a permanent tune that is not adjustable. lets see what happens.
Right now sounds great compared to the tiny 8" sub it replaced and I mean just in frequency response and quality, haven't been able to watch a movie at high levels yet. (its past midnight here.)
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post #27 of 39 Old 10-16-2012, 03:00 AM
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I am curious to know how much output your getting in the 25-65hz range with the 16hz tune?
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post #28 of 39 Old 10-16-2012, 09:21 AM
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can you take measurements of each of those tunings? I would love to see it all on a graph.

(European models do not accept banana plugs.)

 

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post #29 of 39 Old 10-16-2012, 12:01 PM - Thread Starter
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I have never done any graphing of my system, always by ear so this is definitely something I am looking to do. I have seen people using REW, is that what I want + a decent microphone?
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post #30 of 39 Old 10-16-2012, 12:27 PM
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REW is free, robust and can do virtually anything for testing your speakers and room. It is a little more difficult to set up but is worth it once you get the hang of it. OmniMic is also very capable and is a heck of a lot easier to set up, but doesn't have quite as much in the capability department. I love using the omnimic for quick measurements but for more in depth measurement sessions, I use the REW rig smile.gif

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