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post #61 of 292 Old 09-11-2014, 07:48 PM - Thread Starter
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Quote:
Originally Posted by FriscoDTM View Post
The two subs that I built have two different 2.5" port lengths, and I don't see a huge difference in the port tuning - the first one was done with the port running all the way up the back panel and the other is done as described in this thread. I checked tuning using sine waves and didn't see any appreciable difference - both were somewhere around 19.5Hz as LTD02 estimated.

I still have an open question about how to boost below 20Hz with the iNuke and if I'm somehow making a mistake - I modeled a variety of PEQ settings in WinISD (varying the gain and Q factor) and tested with REW sweeps. I ended up liking the 6dB, 20Hz, 1.5Q boost, and it seems to keep the excursion within the 34mm limit even at 2200W. I tested a variety of permutations (different gain and Q values) and this variant produced a relatively smooth dropoff between 10-20Hz. Is this setting overly risky?



And here are some corresponding sweeps after playing around with equalization settings. The right sub (red trace) has the longer port and is directly facing a 8'x6' door opening that connects an adjacent room.

As long as the amp isn't clipping I think your good. The uxl18 is a beast.
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post #62 of 292 Old 09-11-2014, 07:59 PM
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"I ended up liking the 6dB, 20Hz, 1.5Q boost, and it seems to keep the excursion within the 34mm limit even at 2200W."


PEQ doesn't supply free power. to model excursion at power, turn off all eq/high pass etc. enter power. that will give you the max the sub will do no matter how much eq is put on it. a more advanced method is to put a high pass filter on at or just under the tuning frequency, then add a compensating amount of eq, such a peq: gain=3.5db, q=2.0, freq=tuning frequency.


by adding 6db of eq at 20hz, it simply means that you are likely to run out of power at 20hz before other frequencies. 6db is after all 4x the power. that's no biggie. 3db of it is probably just offsetting the reduction in spl that you experience by setting the highpass in the first place.

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post #63 of 292 Old 09-11-2014, 08:11 PM
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I adjusted input sensitivity by running a 50Hz sine wave full signal - when the knob was turned up to max the input signal was just under clipping. I haven't tested the output anywhere near full volume but will play some more with it next weekend. What is the benefit of using the shelf filter over PEQ, and how do I model the high shelf in WinISD?
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post #64 of 292 Old 09-11-2014, 08:29 PM
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modeling a shelf in winsid is a pain in the azz. the linkwitz transform filter is used and the frequencies and q's are adjusted to create the filter.
if you really want to experiment with it, check the box in "advanced" to "force flat response" or somehow create a driver with a completely flat response. that is the baseline. from there start with a LT filter q=0.707 on both sides, and one frequency twice the other. that will give you a 12db shelf. by switching the high and low frequencies, it can be made into a high or low shelf. by adjusting the frequency spacing, the amount of the shelf can be changed. by stacking 2 or more filters, steep shelves can be created. winisd is actually a great tool for learning about filters for folks who are interested in that sort of thing.

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post #65 of 292 Old 09-11-2014, 08:31 PM
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"What is the benefit of using the shelf filter over PEQ"


minor, but since the shelf is specified by the corner whereas the peq is specified by the center frequency, the shelf can by "pushed" further down under 20hz without mucking up the frequencies above 20hz.

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post #66 of 292 Old 09-11-2014, 08:36 PM - Thread Starter
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I find better spl 17-25hz by boosting 3dbs at 20hz then using shelf. Measured with all sizes of cabs. When you want 15hz and below shelf was better.
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post #67 of 292 Old 09-11-2014, 08:40 PM
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+1.


also, it's generally bad practice to try to boost must of anything below the tune on a ported cab.

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post #68 of 292 Old 09-12-2014, 02:47 AM - Thread Starter
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Updated with proper cutlist.
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post #69 of 292 Old 09-14-2014, 04:15 PM
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Quote:
Originally Posted by LTD02 View Post
the port shown in post #38 will give about 19.5hz tuning. i just double checked it. that is with about 10% 'correction factor'.


if you want a little lower tune, the port can be made a little longer, but i would not go longer than 44" because of the effect on first port resonance getting too low. some have actually used very long ports without an apparent problems, so it is a little bit of a mystery that may depend on how many bends and the location of the bends in the particular design. more than 44" though and I'd have to say you are in 'experimental' zone, though you may still get a good result.


the only other option is to make the port a little less than the 2.5", but that will cause other problems, such as more audible chuffing. a 44" long 2.0" tall port will get it down to about 18hz, but that would require other modifications to the cut plan.


there are tradeoffs in these things and the designs that are presented are fairly well optimized, so trying to change one thing for the better will likely make another thing worse.
Thanks, I'll go with the 19.5 hz tuning that you've calculated. I'm sure I'll be happy with the subs
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post #70 of 292 Old 09-16-2014, 07:17 AM
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Just wondering if anybody has a built one of these boxes...
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post #71 of 292 Old 09-16-2014, 11:10 AM
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I posted this in my build thread but thought it should go in here too since it's based on the Johnny Sub.

Hopefully I will get to building this soon. The sub shipped out today.


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post #72 of 292 Old 09-20-2014, 06:17 AM
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Of the 2 Dayton 18s, is one preferred over the other?
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post #73 of 292 Old 09-25-2014, 07:27 PM
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Quote:
Originally Posted by Michael Mitten View Post
Of the 2 Dayton 18s, is one preferred over the other?
If i remember correctly the 460HO and UM will both work well.

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Last edited by squiers007; 09-25-2014 at 07:30 PM.
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post #74 of 292 Old 10-04-2014, 09:03 AM
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In 1 1/2 weeks my brother and I will be building two of these. I'm hoping someone can help with a bit of a mod. I want them to be end table high, so 24" high, and the driver and vent on the 24" 25.5" side. I'm using old Avalanche 15s so I know I have room on that side. (LTD02 said they will work.) As badly as I want 18s, I don't have a job right now so I'll re-purpose these!! I'll be using a iNuke 6000 and dial the power back.

Could someone please model a cut-list? Or at least explain the actual vent length I'd use on the 24" 25.5" side. The Fs of the sub is 15.7Hz, so if it can be tweaked a bit lower, cool.

I haven't had my HT setup for 1 1/2 yrs due to no sub. What's the point right?! LOL So I'm really excited to get these done.

Edit: Never mind. After further reading I'm going to model it after Gamecock24's design with a 45" length port.

Last edited by Michael Mitten; 10-04-2014 at 10:17 AM.
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post #75 of 292 Old 10-05-2014, 01:41 PM
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First complete johnny sub!
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post #76 of 292 Old 10-05-2014, 01:48 PM - Thread Starter
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Quote:
Originally Posted by whodunit23 View Post
First complete johnny sub!
Looks good but how does it sound ?
Can you take some measurements ? Interested in how strong it is around 17-18hz . Can you play war of the world pod scene ?

Thanks for feedback
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post #77 of 292 Old 10-05-2014, 01:57 PM
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Dont have a mic right now. I will have one soon tho. I would like to see the performance myself.
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post #78 of 292 Old 10-05-2014, 01:59 PM - Thread Starter
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Dont have a mic right now. I will have one soon tho. I would like to see the performance myself.
Do you have amp to run it ?
Enjoy
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post #79 of 292 Old 10-05-2014, 02:35 PM
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Quote:
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Quote:
Originally Posted by whodunit23 View Post
Dont have a mic right now. I will have one soon tho. I would like to see the performance myself.
Do you have amp to run it ?
Enjoy
I have an inuke3000dsp. I am really enjoying the 1 so far. Hope I can start the second one this week.
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post #80 of 292 Old 10-05-2014, 02:40 PM
 
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Quote:
Originally Posted by whodunit23 View Post
First complete johnny sub!
Awesome!! And you're building a second one ? Happy listening.
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post #81 of 292 Old 10-05-2014, 02:42 PM
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Quote:
Originally Posted by whodunit23 View Post
First complete johnny sub!
Awesome!! And you're building a second one ? Happy listening.
Yep! 2 of them. One day soon I hope to swap thes 15s out for some 18s
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post #82 of 292 Old 10-07-2014, 01:47 PM
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The struggle is real.

I'm so torn on using my Avalanche 15s, or getting the SI18s for this cab. Obviously either will work and fill my 12' X 23' room. LTD said they will work, but what I didn't ask and am wondering, am I leaving a lot on the table? Will it be a wow factor, or a oh yeah I can tell? I'll be using an Adcom GFA-555. I'm saving money where I can at the moment as I'm out of work.

Here are the specs on the 15s:
Fs 15.7Hz
Qms 3.5
Qes .334
Qts .305
Vas 300.6L
Re 3.2ohms (coils in series)
Znom 4ohms (coils in series)
Xmax 27mm
Sd 748cm^2
Mms 269g
Vd 4.04L
RMS 800w
Le 2.4mH
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post #83 of 292 Old 10-07-2014, 03:34 PM - Thread Starter
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Quote:
Originally Posted by Michael Mitten View Post
The struggle is real.

I'm so torn on using my Avalanche 15s, or getting the SI18s for this cab. Obviously either will work and fill my 12' X 23' room. LTD said they will work, but what I didn't ask and am wondering, am I leaving a lot on the table? Will it be a wow factor, or a oh yeah I can tell? I'll be using an Adcom GFA-555. I'm saving money where I can at the moment as I'm out of work.

Here are the specs on the 15s:
Fs 15.7Hz
Qms 3.5
Qes .334
Qts .305
Vas 300.6L
Re 3.2ohms (coils in series)
Znom 4ohms (coils in series)
Xmax 27mm
Sd 748cm^2
Mms 269g
Vd 4.04L
RMS 800w
Le 2.4mH
With that xmax and power handling the avalanche should be fine. I'd invest in the inukedsp amp before upgrading drivers.
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post #84 of 292 Old 10-07-2014, 04:55 PM
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Thanks for the input! I'll stick with the 15s.

I think I'll stick with the Adcom and try a miniDSP. After reading reviews on both amps, they seem to have the same RMS power and the Adcoms have done me well.
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post #85 of 292 Old 10-13-2014, 05:33 PM
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thanks for the easy cutout specs man. I think I'll be making a pair of these... most likely with the Dayton UM 18's and an Inuke 6000 to power them with....seems like even with the higher wind velocity of the UM 18's (about 23m/s) it still will be in reason. use these as rear near fields along with my SI 18 full marty's up front
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post #86 of 292 Old 10-19-2014, 09:01 PM
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Quote:
Originally Posted by Gamecock24 View Post
I posted this in my build thread but thought it should go in here too since it's based on the Johnny Sub.

Hopefully I will get to building this soon. The sub shipped out today.


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Is there a Cut List for This Design? If so can you please post it. Thanks.
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post #87 of 292 Old 10-19-2014, 09:02 PM - Thread Starter
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Is there a Cut List for This Design? If so can you please post it. Thanks.
Post one.
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post #88 of 292 Old 10-19-2014, 09:28 PM
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Quote:
Originally Posted by chalugadp View Post
Post one.
Thank you Chaluga...
Is that Gamecock's design without the Table Top? I would have to lay it Horizontal (32") to fit my needs.
Somehow I thought that Post one had it 32" High and the Port Still at the bottom.
The one in POST above has the Length = 32" and the Ports are still at the bottom.

Still thinking between the Flatpack vs the Finished :-)
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post #89 of 292 Old 10-19-2014, 09:31 PM - Thread Starter
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Thank you Chaluga...
Is that Gamecock's design without the Table Top? I would have to lay it Horizontal (32") to fit my needs.
Somehow I thought that Post one had it 32" High and the Port Still at the bottom.
The one in POST above has the Length = 32" and the Ports are still at the bottom.

Still thinking between the Flatpack vs the Finished :-)
One in post one is vertical .
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post #90 of 292 Old 10-20-2014, 03:31 AM
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Is there a Cut List for This Design? If so can you please post it. Thanks.

Here you go post #145 .
http://www.avsforum.com/showthread.php?t=1680218


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