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Re-design help for TL sub enclosure
Re-design help for TL sub enclosure
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Old 15th September 2012, 04:47 PM   #1
jb8812 is offline jb8812
diyAudio Member
Join Date: Mar 2012
Default Re-design help for TL sub enclosure

Just some background first, my questions are at the end.

I have done a lot of research on TL speaker designs; read through Martin King's alignment document and plenty of forums and other sources as well. Most of my experience is in ported design for car audio and I am proficient in winisd. I tried learning horn resp but just could not learn it and get into it. I have built a couple t-line speaker boxes (mostly as tests). I am satisfied with my mid-high range TL designs I have made (made a tapered design with 1/10 SL/SO). I used the alignment calculator tables (excel) from Martin's website for those as those were the most recent ones I made. My TL enclosure for my sub woofer however, was more of a design test and I want to rebuild it so that is where I'm asking for some advice and tips.

When I designed the sub woofer enclosure I read through Martin's alignment tables pdf and calculated each step manually (didn't know about the excel spreadsheet at the time, but I did later confirm that I calculated everything correctly by using the spreadsheet).

My subwoofers t/s parameters are as follows (listing same order as in the excel spreadsheet):

Re: 7.4 ohms
Fs: 32 hz
Qts: 0.36
Sd: 350 cm^2
Bl: 14.8 Tm

The subwoofer model is “believed to be” the Tang Bang wt-644f.
Spec page is: http://www.tb-speaker.com/detail/1208_03/wt-644f.htm

What I mean by “believed to be” is that my subwoofer is the logitech z-5500 and that is the model that everyone believes is correct based on actual measurements (not just by looking at it and saying “hey it looks like it”).

The calculated dimensions for the enclosure I calculated (TL straight):
Cross sectional area: 87.94 in.^2
Length (actual): 101.83 in.
Dz: 31.086

My actual build was different though as it was more of a test enclosure since it was my first time building a TL enclosure and I wanted to spend as little money and time as possible. Although I ended up keeping it because it sounded real nice after some tweaks lol.

Actual build I used 2 of those 12” diameter 4' height concrete form tubes duct taped together. The sub was bolted into a mdf faceplate and attached to the bottom of the tubes down-fireing into the floor. I used 2x4 legs to support the structure between the floor and faceplate of the sub. It is located in the corner of my room and has about 2' of clearance from the open port to the ceiling.

The actual dimensions are:

Cross sectional area: 113 in^2
Length: 96 in.
Dz : 0 (sub is at complete opposite end of the open end)
stuffed about 50-60% with about .5-1lb per cubic foot of volume of polyfill.

This monster is an eyesore which is one of the main reasons I want to rebuild it. Another reason I want to rebuild it is to allow driver offset to help even out the peaks and valleys. Because I am also using the logitech z5500 amp, the crossover on that amp is around 120hz and allows a large peak in the 90+hz range. I had to make drastic adjustments with my computers graphic equalizer to compensate for that, even with the amount of polyfill inside. The sound of this TL is still miles above what the stock ported box sounded like. I'm even tempted to buy a separate subwoofer plate amp to replace the logitech so that I can have better control of the crossover frequencies.

So now I am back in the planning phase and here is where I'm asking for some advice/tips.

1) I know folding a TL design can save vertical space and that would be something I'm seriously looking at doing. I want to know if I would lose out on the bass output as currently the open end is within 2ft of the ceiling which allows for nice ceiling loading from what I have heard (it is also in the corner of my room). If I would lose too much output by folding it then I would consider not folding it.
I have thought about blending it in under my tv to put my cable box etc on it without anyone actually know that it is a sub enclosure. (this would be the folded design). I have also thought about putting it under my bed as I have a good 14” clearance under it and my bed is located in a corner as well.

2) I like the deeper bass extension, the deeper the better for me, as this is mostly used for movies. I'm trying to remember the difference between tapered and expanding, if I'm not mistaken a tapered (smaller opening than the closed end) has deeper bass response at the expense of output. The expanding line (opening is much larger than the closed end) has more output but will not play as deep. The straight TL is in between. In simple terms that is. I'm not looking for an in depth explanation, but I'm trying to decide which one I should build for this subwoofer to allow the deeper bass extension without sacrificing too much output. I'm willing to experiment but right now I don't really have much time and would prefer to do it just once.

So any thoughts or tips would be much appreciated. I know this is long but I didn't want it to be one of those typical “I want to build a TL enclosure, show me how, I'm n00b” type of posts.

Also note that I do not have any way to model the response of my enclosure. I don't have MJK's mathlab programs etc. I was only going by ear when trying to find peaks/valleys and adjusting my equalizer on my computer.
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Old 15th September 2012, 05:38 PM   #2
Skiivari is offline Skiivari  Finland
diyAudio Member
Join Date: Sep 2011
Well, I can't suggest much more than I recommend learning Hornresp. It is probably one of the best programs I have ever used. The learning curve is a bit tough BUT there are nice tutorials, and I deeply recommend learning to use the program, as it will save lots of time and money in the long run.

I learnt with this tutorial: Hornresp for Dum... hmm... Everyone - Home Theater Forum and Systems - HomeTheaterShack.com

(I hope I'm allowed to link to other forums over here)

Some answers to your 1 and 2:
1: you will only lose output because of possibly losing the corner loading, the folds do not significantly reduce output.
2: I would recommend trying a straight taper sub, sacrificing output for depth and a smaller box. It's also easy to fold (you don't have to start thinking about angles and the like ) You can compare a ported design's sensitivity to the TL once you learn Hornresp

I'm simming this driver now and I want it I have to start to look for some broken Z-5500's. The design you have right now is surprisingly good, with relatively flat response to 30hz:ish.

I'm sure some other members can give their more experienced insights on the subject, I'm quite new to this stuff.
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Old 15th September 2012, 07:09 PM   #3
jb8812 is offline jb8812
diyAudio Member
Join Date: Mar 2012
Thanks for the advice and the link to the tutorial. I will give it a read. Yeah I picked up the logitech z5500 subwoofer with the builtin amp (no satellite speakers or control pod) from craigslist for $20. ebay has them too but not as cheap. the amp is just ok but the crossovers are around 120hz and then a subsonic at i think around 35-40hz. I had to boost the 31hz band in my equalizer to max in order to get a somewhat flat response down that low.
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Old 16th September 2012, 12:33 AM   #4
bjorno is offline bjorno  Sweden
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Join Date: Mar 2005
Location: Jacobsmountain
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