DIY Thx ultra 2 subwoofer - AVS Forum
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post #1 of 87 Old 08-31-2012, 07:52 AM - Thread Starter
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Hi i was wondering if its possible to build your own sub woofer that could meet Thx Ultra 2 standards?
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post #2 of 87 Old 08-31-2012, 07:59 AM
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Easily.

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post #3 of 87 Old 08-31-2012, 09:14 AM
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Most of us here consider that a very low bar to clear.

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post #4 of 87 Old 08-31-2012, 09:17 AM
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i think most diy subs meet that standard
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post #5 of 87 Old 08-31-2012, 09:42 AM - Thread Starter
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Ok where does a noob like me start?, i want to build 1. smile.gif
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post #6 of 87 Old 08-31-2012, 09:51 AM
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Whats your budget, size restrictions, and room size?

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post #7 of 87 Old 08-31-2012, 10:01 AM
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Easy to do for cheap! THX is 20-120 hz at 115 dBs. Build either a BFM THT or a Cinema F-20 and you will meet the spec at 1 meter outdoors which usually means it will meet the spec indoors at the seats(add boundary gain and subtract distance to seats and end up back at the same number). BTW, both will cost about $250-$300 to build depending on wood and driver. This is minus amp which a $200-$300 pro amp will power many of them if you wish. If you want small than sealed is your best bet but you will need at least two with better and more expensive drivers. Cheaper drivers and you will need more of them, the trade off is you can actually get deeper which is better than THX specs!

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post #8 of 87 Old 08-31-2012, 10:17 AM - Thread Starter
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My front room is 12metre long 6metre wide, budget about 1k, size something like 60 to 70cm sq.
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post #9 of 87 Old 08-31-2012, 10:24 AM
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Fairly large room.

You only want one sub that is less than 70cm x 70cm? Do I understand that right? How tall can you go?
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post #10 of 87 Old 08-31-2012, 10:27 AM - Thread Starter
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1 metre max, yes 1 sub for now, that is if 1 sub is enough lol?
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post #11 of 87 Old 08-31-2012, 10:29 AM
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Yeah. You could make a subwoofer that can easily exceed that of THX Ultra2 standards, which isn't saying much anyway. wink.gif

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

 

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post #12 of 87 Old 08-31-2012, 10:30 AM - Thread Starter
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I never realized, i thought it was the best you could get >< excuse my ignorance.
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post #13 of 87 Old 08-31-2012, 10:34 AM
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4 dual opposed Dayton 15HO (in 3cu) using an INUKE 6000DSP fits the bill according to my numbers. You may go slightly over budget though.
If you went ported you could save some money and do two of the 15HO's in 3.5cu ft each powered and high passed with INUKE 6000DSP.

The other option that comes to mind is running the Alpine 12's ported.
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post #14 of 87 Old 08-31-2012, 10:40 AM
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Are the full THX ultra 2 specs actually readable somewhere? Last I heard the specs were all secret still and therefore basically worthless.

From the THX website-

"For this reason, THX Certified Subwoofers must extend to 20Hz (-6dB) to handle the very highest bass levels with ease."

Only -6db at 20hz? That's a rather low bar indeed. Is it 115db@1m with any sort of distortion limit? What good is 115db@1m if you need reference level at the seats?

This is why most of us dismiss THX because it sets no firm requirements and the vague specs they give don't add up to much.
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post #15 of 87 Old 08-31-2012, 10:53 AM
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You're using metric units. Where do you live? Canada?

I think dual opposed is the way to go if you only want one box. These guys know subs better than me though. If you're from Canada, consider www.creativesound.ca, www.istonline.ca, and www.solen.ca for subwoofers.
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post #16 of 87 Old 08-31-2012, 10:54 AM - Thread Starter
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Quote:
Originally Posted by tgse3 View Post

4 dual opposed Dayton 15HO (in 3cu) using an INUKE 6000DSP fits the bill according to my numbers. You may go slightly over budget though.
If you went ported you could save some money and do two of the 15HO's in 3.5cu ft each powered and high passed with INUKE 6000DSP.
The other option that comes to mind is running the Alpine 12's ported.
Looks nice, but what is dual opposed and high passed?
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post #17 of 87 Old 08-31-2012, 10:59 AM
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Quote:
Originally Posted by BloodFX View Post

Looks nice, but what is dual opposed and high passed?

Dual opposed means one sub driver on one side and another on the opposite side. Driven in parallel they cancel out mechanical induced vibrations.

High pass means filtering out bass, pretty much. A vented subwoofer loses control under it's tuning point and mush be high passed in order to protect the woofer from mechanically overdriving itself.

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

 

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post #18 of 87 Old 08-31-2012, 11:04 AM
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Dual opposed is two drivers in one box and the drivers are installed on opposite sides of the box. High passed means that an inline filter is applied to the signal output to protect the drivers from overexcursion. The high pass filter can be set within the inuke for instance, so say, the driver with x amount of input power applied at x frequency the driver will exceed xmax. With the filter in place, the signal is rolled off before it can damage the driver.
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post #19 of 87 Old 08-31-2012, 11:11 AM
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dual opposed means you have a speaker on each side of the box and they fire at the same time, making the box not have any vibration. High passed means you will cut off the lowest of the low frequencies so the speaker doesnt try to produce them and blow.

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post #20 of 87 Old 08-31-2012, 11:12 AM
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Oh wow, well there's three explanations for ya. haha

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post #21 of 87 Old 08-31-2012, 11:21 AM
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lol, yeah...that should do it. tongue.gif

This one is for dual 10's, but you get the idea. Erich will probably have some dual opposed flat packs for some 15's too, don't know for sure though.http://www.diysoundgroup.com/flat-packs-1/subwoofer-flatpacks-1/dual-10-flat-pack.html
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post #22 of 87 Old 08-31-2012, 11:26 AM - Thread Starter
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Ok thanks for the explanations.
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post #23 of 87 Old 08-31-2012, 11:29 AM - Thread Starter
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Quote:
Originally Posted by robotbunny View Post

lol, yeah...that should do it. tongue.gif
This one is for dual 10's, but you get the idea. Erich will probably have some dual opposed flat packs for some 15's too, don't know for sure though.http://www.diysoundgroup.com/flat-packs-1/subwoofer-flatpacks-1/dual-10-flat-pack.html
Nice website smile.gif perfect for a complete noob like me lol.
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post #24 of 87 Old 08-31-2012, 11:38 AM
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Quote:
Originally Posted by Jesse S View Post

Are the full THX ultra 2 specs actually readable somewhere? Last I heard the specs were all secret still and therefore basically worthless.
From the THX website-
"For this reason, THX Certified Subwoofers must extend to 20Hz (-6dB) to handle the very highest bass levels with ease."
Only -6db at 20hz? That's a rather low bar indeed. Is it 115db@1m with any sort of distortion limit? What good is 115db@1m if you need reference level at the seats?
This is why most of us dismiss THX because it sets no firm requirements and the vague specs they give don't add up to much.

THX reference levels are for the seats so th subs need to hit their specs at the seats. Most THX subs only hit specs with multiples(sealed). The best THX subs I have ever used commercially are the KLipsch THX ultra 2 subs.

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sub amp-Sanway FP14K
LCR-Dual stacked BFM DR-250's
Surrounds- Dual stacked BFM W10's
subs-12 SI 18's ported 6hz.
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post #25 of 87 Old 08-31-2012, 11:40 AM
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BloodFX: Please do not repost your comments (even if they do not show up right away). You should be seeing a notice after you post a comment, that (since you are new) a moderator has to approve your post, before it shows up on the board. If you repeat the posts, it make more work for the moderators. They will show up in good time. My I suggest that instead of a lot of little "conversational" short posts, you edit a previous post and add comments to it, if time is of the essense.

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post #26 of 87 Old 08-31-2012, 11:49 AM - Thread Starter
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Ah ok sorry.
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post #27 of 87 Old 08-31-2012, 12:28 PM
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Build a jbl 4645c clone. With a b6 setup, its flat to 20hz.
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post #28 of 87 Old 08-31-2012, 02:26 PM
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Quote:
Originally Posted by Jesse S View Post

Is it 115db@1m with any sort of distortion limit? What good is 115db@1m if you need reference level at the seats?
It's actually 85dB with 20dB headroom, ie., 105dB maximum. The so-called 'ultra' bit has to do with the room size, the theory being that a larger room requires a louder/more powerful sub to reach the same levels at the LP. Of course that's just so much piffel, but the THX designation is pretty much just marketing hooey anyway.

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post #29 of 87 Old 08-31-2012, 03:09 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

It's actually 85dB with 20dB headroom, ie., 105dB maximum. The so-called 'ultra' bit has to do with the room size, the theory being that a larger room requires a louder/more powerful sub to reach the same levels at the LP. Of course that's just so much piffel, but the THX designation is pretty much just marketing hooey anyway.

105dB is the peak maximum output per channel for all non-LFE channels. The LFE (subwoofer) is 115dB peak.

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

 

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post #30 of 87 Old 08-31-2012, 03:39 PM
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Where do these numbers come from? I see them all the time. And I've read them in "old" (like 6 or 7 years old) dolby documents about setting up home av. But THX, dolby, dts, all those guys, their websites are soooo watered down. They show cute little HTIBs and it's like there is no standard other than $ now. rolleyes.gif
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