DIY Thx ultra 2 subwoofer - Page 2

I found it on the THX site, but it made no mention of a difference between mains and subs that I could see.

It's the standard that Dolby and DTS have been using for home and cinema for some 20 years now. No changes.

This is the article I have saved to my computer when ever I need to review setup requirements: http://www2.grammy.com/PDFs/Recording_Academy/Producers_And_Engineers/5_1_Rec.pdf

Just the main players don't have very good information on their sites anymore. Wish they wouldn't setup their sites like an advertisement. Then guys like BloodFX here would understand what he actually needs. I didn't even find as much as you did Bill. Your searching skills are better than mine.

I measured my system and at 95db-A it was physically uncomfortable to be within 15ft of the front speakers.
I normally do ~85db-a and ~120db-C and at those levels you can't hold a conversation even by yelling and I'm knocking cups filled with bolts onto the floor from 50ft away, and almost breaking light bulbs and drywall.

When my FP10kQ gets here, I hoping to expect an extra 3db

I consider 115db at the LP with <10%THD a decent target to aim, for a room of any size.
Not sure if that's Ultra2 or not...

^^^^^

Yeah, those 105dB/115dBLFE levels are for PEAK moments. Ie: dynamics, not constant.

I had a pair of THX Ultra II rated Jamo D7 Subs (servo controlled 15" drivers in a sealed enclosure - MSRP = $2k each and it took two to officially meet THX Ultra Spec according to Jamo and THX's website). They were nice subs, but the both of them compared pretty fairly to a single HSU VTF-15H when Luke Kamp and I compared them side by side in his room. When it was 2 Jamos on a single VTF-15H the SPL max levels were fairly comparable at max 'clean sounding' readings for both music and movie clips. THX Ultra spec isn't worthless because it at least guarantees some level of quality which you don't get if you don't have it at all.....but at the same time - like others have said - it's a fairly low bar for AVSForum enthusiasts. Many of the ID subs at $1000 and greater pricepoint could meet the THX Ultra spec if they simply wanted to pay the licensing cost.

Those LFE channel numbers only apply to systems that do not use bass management (AKA subwoofer = LFE channel).

True but I didn't feel the need to complicate my accurate description with all that. I was speaking purely of the standard on a per encoded channel basis in which case my description is 100% accurate.

it is actually a little higher than 115db.

the 115db is for the lfe channel by itself. in addition to the lfe channel, most folks re-route the bass from the other channels into the subwoofer channel.

we worked through the math before and it works out to around 117-118db required at the listening position from the subwoofer for full reference with re-directed bass. the ultra2 spec just means that this level can be hit in a 3000 cubic foot room or smaller.

i don't understand all the negativity directed toward thx. thx provided a minimum set of performance standards so that people going to see star wars (iirc) would all get a good experience. it still serves that purpose today and will hopefully save some folks from buying into htib or "small cube" marketing magic.

agreed with LTD02.

a 'certification' in the consumer market is better that marketing BS alone for the uninformed.

In the world of subwoofers if you buy a THX Ultra 2 certified sub you are going to have a decent experience. You'd not find a definitive technology 8" supercube claimed to 10hz flat finding its way onto the THX Ultra 2 rated list. So it protects the consumer from flat out marketing nonsense in the retail market.

for the origininal poster,

if you have a typical medium size home room, four of these: http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-468

properly powered, each driver in a 4 cubic foot sealed enclosure will get you to full reference unless your room is HUGE and the multiple subs will help smooth out room modes (peaks and dips caused by the room dimensions).
Edited by LTD02 - 8/31/12 at 6:48pm

LTD02....

don't know about that one with the Dayton drivers.

KCNitro07 bought 2 of those Titanik MK3 drivers and put them in 3.5 cubic foot sealed boxes. They are considerably shy of reference volume when you try to dsp them flat to 20hz. The most he can turn his system up with 2 of them in a very small room is about -8 before they start distortion with DSP flat only to 25hz.


Now if you didn't try to make them flat to 20hz or even 25hz you could obviously get louder, but i'm not sure even adding two more (6dB gain in total) would get him there in KCNitro's small room. He is considering building two more to have 4 himself, but I half wonder if he shouldn't have considered a bit more expensive driver with more excursion to get more clean low output.

Looks like I do 122.3db-C in 2ch+LFE mode in 3900cu ft @ 10ft with the THX Intro.
Every +6db requires (at least) double the number of subs and double the power in general, or half the listening distance/smaller room.

THX Ultra2 spec requires 105db @ 20hz @ 4% THD @ 3000cu ft+ (I assume that is a sinewave because of THD measuring?)
Additionally, let's agree to disagree, that anything sustained for more than 1 second is "continuous", rather than some sort of "peak" burp; because THX doesn't specify (unless I'm blind?) and most circuit-breakers pop after about 1 second if underrated

without knowing more about his system, we can't really know, but 2 titanics have 3-4db less spl in the excursion limited region than 4hf's. the 4hf's are excursion limited to about 117-118db around 25hz in 2pi space. in most medium home rooms, room gain will kick in around there and so will more or less provide full reference from that point down and significantly more above that point. that's where i was coming from. obviously all rooms are different, so it may or may not do the trick, but without more information, it is a reasonable (well, most people at "big buy" would say 4x15" subs is totally unreasonable!) approach.

how large is your room?

how much money you got?

do you have a wife?

:-)

btw, is that your car in your avatar?

oh, so you want *two* money pits. :-)

$3k is plenty for an absolutely killer home subwoofer system.

do you have some rough dimensions of the room? and, is it relatively open to other rooms or relatively sealed off?

how comfortable are you with woodworking?

based on your muscle car personality, i'm kind of thinking a couple of lilmike f20's might provide what you are looking for. that would come in way under budget and provide some money for a couple nice mains.

http://www.avsforum.com/t/1329971/lilmikes-cinema-f-20

He doesn't want it over 1m tall.

is this cheating?



and i see that he has a relatively large room.

two f20's and a couple of seos/360/2512's would be good for mains.

that might leave enough money for a receiver and a screen in the $3k budget.
Edited by LTD02 - 8/31/12 at 9:04pm

How about a klipsch THX ultra2 sub clone. Two high excursion 12s in slot ported boxes with 500 watts each. Thats what the klipsch system is. The klipsch drivers have 25mm one way Xmax. I'd say go for the tc sounds epic 12 with 23mm Xmax in a slot ported box and a yung 500 watt plate amp or pro amp of your choice. Put the epic in a larger cabinet with a slot port that has more surface area and you should no doubt best it, and that is saying alot because the klipsch is very impressive. It should actually be similar to a pair of SVS pb13 ultras. It's actually what I'm building. You'd be well under you $1000 mark

Dan

THX U2 slot port dado:

I guarantee that if you build a $1,000 sub using advice from this site, you will be so spoiled bass-wise that you'll probably go to you local high-end stereo shop so you can be amused by their demos of multi-thousand dollar subs.

"It should actually be similar to a pair of SVS pb13 ultras."

that is getting a little carried away, but mr. hurd's suggestion would certainly be a good one. i'd go with a little more amp, something around 1000 watts per channel. the behringer inuke 3000 dsp amp might be something to consider if two thx ultra 2 clones are the choice.

I don't think so. It's been said by many that a single infinity 120.9w can best pb13 untra in the rights box. This was said by a very knowledgable member about jinjuku's build:

"The potential output of one of these is so great, that it would be very similar to a PB13 Ultra, except that the PB13 would not have as much output in the lowest range, because the port on Andrew's design offers less compression due to the large cross section area, and the PB13 would potentially offer greater output by some degree, in the higher octaves, because of it's larger cone surface radiation area. But to realize the output potential of the Kappa Perfect cabinet design above, you would need to use a bridged EP2500 to deliver sufficient peak power. However, one does not need this level of capability in actual use. It's overkill. However, stereo units are always going to provide better ability to integrate with the main speakers, even if you don't need the output ability that is possible."

The tc epic 12 has more capability than the infinity 120.9w (supposed replacement for the perfect series). This is the older SVS model though. Not the new one with 1000 watt dsp.
Granted this may not be done with a pair of 500 watt plate amps but of he goes with a pro amp it could.

Dan

The one problem with the klipsch subs is volume. Their somewhat tiny. Klipsch isn't going to be able to convince as many people to purchase 6 cubic foot ported subs, that's why is should be fairly easy to best them with quality drivers.

Dan

the old amp in the pb13u was closer to 1000+ watts peak than 500 and the driver has something like 26-28mm of xmax. i forget the exact numbers, but i modeled it up pretty carefully a while ago in order to see what combination of power and excursion would be required to hit the ricci test numbers with a driver of its sd and a box of its size and tuning. the pb13u has more power, more sd, and more excursion than the epic 12/500 watt plate amp scenario, so it will be louder.

Like I said, more than 500 watts would be needed. The tc epic can easily take more than the 500 it's rated. The greater sd and Xmax of the SVS will surely make it louder at the higher frequencies. The down fall of the SVS are the ports. The recommended port for the epic is a 6". The SVS has three 3-1/2" ports which about equals a single 6" port. So if the driver has more sd and more Xmax that can't be good, there's going to be port compression. It is well documented that if even one port is plugged that the port chuffing is quite audible.

Dan