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Discussion Starter · #1 ·
Hi, I am planning on building some new subs this spring. I currently have two AV123 Onyx Rocket UFW-12 subs with the small block upgrade that I am trying to sell (let me know if you're interested
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I ordered the two SI 18 HT's today and am planning a box using 1" MDF that I am getting from a local lumber yard. I am going to put each sub in its own separate enclosure.


Playing around with WinISD I think 8ft^3 with 20hz tuning looks pretty good. The box will be around 22" wide by 24" deep by 38" tall which will bring me a little over 9ft^3. After driver displacement, port and bracing I should be around 8 ft^3 I am hoping.


I was planning on doing a slot port, but WinISD is confusing me. I input two ports since I am going to put a brace down the middle of it. I entered 1" x 9.5", I then tried 1" x 19" with 1 port and it gave me different lengths and velocities. Isn't 1 port at 1x19 the same as 2 ports at 1x9.5, shouldn't the length be the same?


Here is the plot that it showed, any opinions and tips on what I'm planning so far?


 

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Discussion Starter · #3 ·

Quote:
Originally Posted by MemX  /t/1521030/diy-sub-build-2-si-18-ht-ported-1-mdf#post_24444518


If it's for HT use and not just music, you'll need tuning under 20Hz!

Really? SI recommends 20hz for HT use. I will play around with a lower tuning if you think so.


I am still wondering about the port thing, why having 2 of the same area as 1 made for different lengths. Just for kicks I installed WinISD Pro and put in the same parameters and got yet another recommendation, why?


I also checked cone excursion, looks like it is pretty minimal until around 15hz, is that expected, I put 600W as the input signal?


Finally, I made my first attempt at SketchUp. I did some things wrong but gives you an idea of the enclosure I am thinking, I will add bracing too, don't worry.






 

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Discussion Starter · #5 ·

Quote:
Originally Posted by sdaddy  /t/1521030/diy-sub-build-2-si-18-ht-ported-1-mdf#post_24447034


Two ports will have more surface to affect air flow.

Not by my math...

1X19 = 19sq"

2x9.5 = 19sq"


Why do I get different lengths? And why does Beta and Pro give me different length for the same driver, box size and enclosure?
 

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You have the same cross section. But you have more surface of wall area.


1+19 +1 +19=40 perimeter

(1+9.5+1+9.5)x2=42 perimeter
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by sdaddy  /t/1521030/diy-sub-build-2-si-18-ht-ported-1-mdf#post_24447320


You have the same cross section. But you have more surface of wall area.


1+19 +1 +19=40 perimeter

(1+9.5+1+9.5)x2=42 perimeter

Ah, interesting, ok. Still doesn't explain why Pro gave me a totally different length than Beta. Makes me think calculations are off in the program or something.
 

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Plenty of films have lots of content below 20Hz, check out the data-bass.com Movies with Bass thread for some graphs and ratings of a number of films. (That thread was born out of the Movies with Bass thread that's in the Subwoofers section of this forum.)


Check out the MartySub thread on here for a simple build with 16-17Hz tuning point, or you could look at doing an LLT (Large Low Tuned) enclosure to get to something like 11Hz tuning (Scott Simonian runs LLTs with that tuning - check out his signature if you find one of his posts).


Plenty of commercial subs run c.20Hz HPF to protect the drivers from over-excursion, but if you're going DIY then I would look to capture playback of as much content as you can afford / have the space for / have the amplification for
 

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If you want to stick to a 8cf enclosure 18hz tune is about it. The SI wants about 10cf internal if you would like a lower tune of around 16ish. 10cf would bring your two vents in at 2" x 9.5 in at 32" long after correction.
 

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Discussion Starter · #10 ·
Not sure how much larger I want to go, these will already be huge in my small living room. I know that a lot of movies have ulta low freq content. I tried lowering the tuning with the same size enclosure in WinISD and it starts to slope at a much higher frequency, the slope is more gradual and extends further but the 20hz graph looks so nice, flat until around 25 then it starts to drop off. I'd say this will be used 60% movies 40% music. I do have some Harrison Labs Fmods HPF at 20hz, not sure if it would be a good idea to use these or not. I will play around more with a lower tuning and enclosure size if you all recommend lower.


As far as port end correction, I searched extensively and came to the conclusion that Beta does everything for you, is that not true? What do I have to do? I remember reading something about taking half the height of the port and ..?
 

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No if you have a smaller room and other concerns go with less enclosure and use dsp the best you can. 18hz tune is pretty nice in that size enclosure imo if you have the space?.. especially since you will have to build it larger considering displacement.
 

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Discussion Starter · #12 ·
Played with dimensioning and out a sheet I can increase it to 24"x24"x38" which gives me 10 ft^3 but that is before displacement and bracing. I only want to order two sheets of the 1" MDF, I can make the finishing baffle out of 3/4" (1 3/4" total thickness) and the top port wall out of 3/4".


So, if you have a brace running down the middle of a slot port should you model two ports in WinISD? What about the end correction, do I need to do anything for that?
 

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Quote:
Originally Posted by DKAudio  /t/1521030/diy-sub-build-2-si-18-ht-ported-1-mdf#post_24451197


Played with dimensioning and out a sheet I can increase it to 24"x24"x38" which gives me 10 ft^3 but that is before displacement and bracing. I only want to order two sheets of the 1" MDF, I can make the finishing baffle out of 3/4" (1 3/4" total thickness) and the top port wall out of 3/4".


So, if you have a brace running down the middle of a slot port should you model two ports in WinISD? What about the end correction, do I need to do anything for that?

Yes two vents. http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm
 

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Discussion Starter · #14 ·
I spent some time playing with WinISD Pro. Call me crazy but the 8 ft^3 box at 20 hz still looks the best to me. Am I nuts? Here are photos of the 3 different boxes I modeled, the first is SPL, the second is cone excursion.

Gray is a little over 8 ft^3 at 18 hz

Blue is a little over 9 ft^3 at 16 hz

Yellow is 8 ft^3 sealed just to see what it looked like.


Excursion goes crazy under 15 hz in ported, I think my 20hz HPF fmods may be required. Excursion isn't even close to full at any other frequency, is that expected?





 

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Yeah they both look good depending how you want to look at them, not forgetting the room-gain profile of your room?? A guy can definitely build to large or to small. For some 8-9cf plus displacement just isn't a option.

EDIT.. there is a 6dB difference at 16hz but narrows as freq goes up?
 

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Quote:
Originally Posted by DKAudio  /t/1521030/diy-sub-build-2-si-18-ht-ported-1-mdf#post_24456256



Excursion goes crazy under 15 hz in ported, I think my 20hz HPF fmods may be required. Excursion isn't even close to full at any other frequency, is that expected?

Try and model in the high pass filter. Its under the EQ tab along with a host of other filter options.
 

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Quote:
Originally Posted by steve nn  /t/1521030/diy-sub-build-2-si-18-ht-ported-1-mdf#post_24457171


Yeah they both look good depending how you want to look at them, not forgetting the room-gain profile of your room?? A guy can definitely build to large or to small. For some 8-9cf plus displacement just isn't a option.

EDIT.. there is a 6dB difference at 16hz but narrows as freq goes up?

If you have a room with a lot of gain you can use the Q of the high pass filter to shape FR around the high pass. Example below. Same box, same 20 Hz tuning, 20Hz high pass but with 3 different Qs. You dont have to have the sharp knee just because you dont tune super low. I believe the Inuke DSP can do this.

 

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Quote:
Originally Posted by splotten  /t/1521030/diy-sub-build-2-si-18-ht-ported-1-mdf#post_24458556



If you have a room with a lot of gain you can use the Q of the high pass filter to shape FR around the high pass. Example below. Same box, same 20 Hz tuning, 20Hz high pass but with 3 different Qs. You dont have to have the sharp knee just because you dont tune super low. I believe the Inuke DSP can do this.


Can you explain a little more about the "Q" in the iNuke DSP? I have never fully understood what the "Q" actually is, and how do you know what to set it at? Is there a way of measuring "Q" to see what the optimal setting is?
 

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Its not easy to explain Q in a few sentences. For practical purposes you can use the Q to alter the shape of the filter in order to get a different FR like above. There is lots of free literature on the Internet about the subject that explain it in much more detail than I ever could. I have found this article use full:

http://www.****.de/Elektronik/AudioMeasure/UniversalFilter.html


(Cant seem to get the link working ?? )


Here is the shape of the the filters from post above. The red one is no filter, the peaked one is Q=1 and the bottom one is Q=0.5




I dont know how to measure the exact Q of a filter but I am certain that i have seen a screen shot of the Inukes DSP that showed that it was possible to change the Q of a high pass filter. In relation to what optimal is, I was merely pointing out, that if you are in a room that has strong gain in the lower bass it might not be such a good idea having the Sub completely flat all the way down and then cutting it off with a sharp filter. A better approach might be to use a lower Q high pass filter that makes the response slope a little like a sealed sub, only you can easily adjust it in the DSP. Try play with it in winisd. I believe a few commercial subs offer this functionality to compensate for room gain and boundary gain.
 

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Quote:
Originally Posted by splotten  /t/1521030/diy-sub-build-2-si-18-ht-ported-1-mdf#post_24458556



If you have a room with a lot of gain you can use the Q of the high pass filter to shape FR around the high pass. Example below. Same box, same 20 Hz tuning, 20Hz high pass but with 3 different Qs. You dont have to have the sharp knee just because you dont tune super low. I believe the Inuke DSP can do this.


Yeah I have seen LTD post quite a few times regarding using the inuke and have a link in favorites with him using the 2496 also. I've asked him about it VI PM and clearly see the benefit. ID would not be able to do what they do without it. There was a nifty little plate that was posted a few weeks back that I thought I saved the link to but cant find it. Anyway it didn't have the power we're generally looking for so irrelevant. No question regarding some subs coming with different dsp schematics in memory selection. It would be a nice function if they all did since digital is so cheap now. That being that it doesn't always translate out because of room suck out, nulls and so have you, but it's much better than just having the one option imo. Next pro I get will definitely have dsp. I always think of Q/hp as the teeter-totter affect though.
 
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