TC 2K LLT

[NateTTU]

I'm really new on diy speakers and design, but I have tried to read thoroughly and catch up on all the available info. Now I feel its time to begin construction on my own TC 2k LLT. However I have a few questions. But first, here is some background: 1 SVC TC 2000 15'' powered by EP2500.

The current plan is to build a sonosub with an effective volume of 270 liters and tune to 16.5Hz or lower. This brings up my first question, I have modeled the LLT using the sonosub program and it looks like even using the 270 liter volume I can still tune to 14.5Hz like the ones who use 320 liters. I attached the program I ran and everything came out ok and the first port resonance will be at 202Hz. I designed using a 22'' sonotube and a single 6'' port (2' 9 3/4'' length) that has a flared outer end. Attached are the pics of the sonosub program running the current setup.

I would rather go no larger than the 270 liter volume and wonder if its possible why do people go up to 320 liters to tune down to 14.5Hz instead of using the 270 liters instead? This is possibly where I'm getting mixed up so if you can help me please let me know. Thanks.

Nate

[Sonnie]

Hi Nate and welcome to the Shack!

I move your post to it's own thread so that it would get more attention and since it was not directly related to the LLT Explained thread.

[NateTTU]

Ok, thanks. I was wondering where it went. Although if you could do me a favor and delete the post off the LLT forum again as I think I may have added it again by accident.

[SteveCallas]

320 liters results in more output down low - 270 will start to rolloff a bit sooner. And while perhaps not a big deal, the shorter the port and higher the first resonance, the better. That said, if 270 liters is your limit, it will still work fine.

[WillyD]

I would rather go no larger than the 270 liter volume and wonder if its possible why do people go up to 320 liters to tune down to 14.5Hz instead of using the 270 liters instead? This is possibly where I'm getting mixed up so if you can help me please let me know. Thanks.

Folks tend to go bigger because A)they don't mind and B)It helps low end efficiency.

270liters at 14.5Hz would be fine. If the listening room you'll be using is relatively large, I might suggest raising the tune. If its pretty small (1500ft^3 or smaller) then the lower tune is kosher IMO.

[NateTTU]

Thanks for the response. Well how much would I lose/gain from doing the traditional 16.5Hz tune? If I'm gaining very little in the bottom end but losing a good amount of headroom by forcing the 270 liter to work for my environment I probably will be perfectly happy with the traditional desing.

[WillyD]

You'd just lose some headroom in the 20-30Hz region. How big is your room?

[NateTTU]

WillyD wrote:

Folks tend to go bigger because A)they don't mind and B)It helps low end efficiency.

270liters at 14.5Hz would be fine. If the listening room you'll be using is relatively large, I might suggest raising the tune. If its pretty small (1500ft^3 or smaller) then the lower tune is kosher IMO.

The current room it will be set in is roughly 2200^3 ft but eventually it will be moved and its difficult to say exactly but it will likely be less and not anymore. The sonosub will crossover relatively low at around 40Hz or so. The mains and even surrounds I'm building have very good extension.

[Ilkka]

NateTTU wrote:

Thanks for the response. Well how much would I lose/gain from doing the traditional 16.5Hz tune? If I'm gaining very little in the bottom end but losing a good amount of headroom by forcing the 270 liter to work for my environment I probably will be perfectly happy with the traditional desing.

Here's a comparison. I recommend 270L/16.5Hz.

[SteveCallas]

You'll really be limiting the sub's potential with a 40hz crossover - why so low?

[NateTTU]

The mains and surround channels I'm building have very good extension, even into the 30's. I could cross higher if necessary but I don't think it will really matter. The purpose of the sub was to reach into the realm of frequencies used only in movies. I could easily cross at say 50Hz and give the speakers a little more breathing room.

[NateTTU]

What type of foam, if any, do you use to put in the sub? If you guys have built other diy speakers what did you use in those?

[NateTTU]

Well, from what I have read it seems that regular pink and also rigid fiberglass are two great options. However, since rigid fiberglass is difficult to find and often more expensive, could I just use either 3.5'' or 6.25'' pink fiberglass and just line the inner wall and the top cap?

[thxgoon]

Ya, R13 is usually as thick as you will need to go. I actually used half the thickness of R13 as my tubes were a bit smaller diameter.

[mrstampe]

thxgoon wrote:

Ya, R13 is usually as thick as you will need to go. I actually used half the thickness of R13 as my tubes were a bit smaller diameter.

Are those egg crate bed pads a waste of time? Also, I've read about some using Dynamat from the car audio world.

[NateTTU]

Mrstampe,

While not useless, its difficult to say if the specific type of egg crate you pick up is indeed able to provide a good deal of acoustic damping. If you can blow through it then it will have at least some benefit. Through all my research I found if possible get the rigid, aka 703 or 705, fiberglass and if not use the fluffy pink stuff. Both work well and while the rigid is the best it is difficult to find and usually pretty expensive. Here is a great site that compares a ton of stuff:

http://www.bobgolds.com/AbsorptionCoefficients.htm
http://www.foambymail.com/Eggcrate.html (has values for the egg crate)

In all, the fluffy insulation found at the local hardware stores if the best option, providing more acoustic damping than most acoustic foams and is very cheap. The only downside to this application is the health hazards.

One question that I can't find an answer to is if the R-value of insullation has a direct realationship to its acoustic damping properties. For example, OC makes 3 types of 3.5'' insullation with R-values of 11, 13, and 15. Since they are all the same thickness I'm not sure if they all perform the same or if the higher R-value indeed helps.

Hopefully this more than answered your question.

Nate

[arande2]

I was wondering about the low crossover as well.

My mains extend to around 35hz and my surrounds extend to around 28hz (-6dB), but when I tried crossing my sub at 40hz, it didn't do much because it didn't have much low end output (UltraCube from Paradigm). I blew it very quickly because it had very limited output. With your design, however, it seems like a lower crossover would be fine. I'd probably stay closer to 50hz, though.

It really depends on how much amp power you have for your mains. At the time, I had only half as much power for them as I do now (Upgraded the receiver with store credit from sub).