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Who knows transmission lines?

 

Silver Member
Username: Geekbike

Post Number: 176
Registered: Dec-04
If you do, have a look at this for me and see if everything lines up:

Driver: 15" SS RL-p
Fs: 27.487hz
Sd: 132.571cu.in
Speed of Sound: 13535.7997 (at my height and humidity with mean temp for the summer)
Calculated line length at Fs: 123.111"
Actual line length: 123.128"
Cross section: 15.5"x10.75" at start tapered to 15.5"x8.5"
No stuffing will be used
The corners will be rounded more than pictured to fit the line length better
The walls will be 0.75" HDF
There will be extra bracing on every panel except the top directly to the frame of the car

Upload
Upload
 

Silver Member
Username: Alpineuser

Winchester, TN

Post Number: 513
Registered: Mar-05
looks pretty and like u spent alot of time on it but i dont know enough about TL to help you out.
 

Gold Member
Username: Insearchofbass

Post Number: 2794
Registered: Jun-04
knacko ive been wanting to learn how to build one of them can you explain how you did it
 

Gold Member
Username: Insearchofbass

Post Number: 2795
Registered: Jun-04
im trying to understand your calculations here but i come out with 105 inches of line length when you said you came out with 123.128 actual length how did you derive this
 

Silver Member
Username: Addicted2bass

Miami, Florida USA

Post Number: 864
Registered: Nov-04
yea knacko can you also explain to me how to construct a TL enclsoure. I've also been wanting to know how to construct one. Do you AOL IM?
 

Gold Member
Username: Insearchofbass

Post Number: 2796
Registered: Jun-04
ok i redid the numbers the way i think they are done and i came up with 115.26 inches this time when you came out with 123.128 ....im the first to admit I dont know higher math well but i try but if you could explain id greatly appereciate it
 

Silver Member
Username: Alpineuser

Winchester, TN

Post Number: 514
Registered: Mar-05
i personally dont think a 15" sub with a TL enclosure would even fit in a car.As far as I know its 1/4 of the length taking from the FS of the speaker. Thats the total length through the center of the line to make it sound proper without stuffing. The cross section is supposed to be 1.25 of the SD at the beginning of the line and gradually get smaller to equal size of the cross section at the end. Use lots of angles and gradually decrease the cross section to avoid any straight areas that it would reflect on. Use of stuffing is for when you use a smaller design to enhance the "space" that you use, not for a line which is built to the actual size requirements. I'm sure there are more equations out there as well. I've written up designs but none would fit in a car unless its an 8 or 10" sub.
 

Silver Member
Username: Alpineuser

Winchester, TN

Post Number: 516
Registered: Mar-05
i wonder if your colon could be considered a TL enclosure :-)
 

Gold Member
Username: Insearchofbass

Post Number: 2797
Registered: Jun-04
aparently this one will fit plus i saw a xxx 12 in one heres where the video is click on reaudio 12xxx

http://www.realmofexcursion.com/videos.html
 

Silver Member
Username: Mixneffect

Orangevale, Ca. USA

Post Number: 114
Registered: Apr-05
Transmission lines seem like such a great idea in theory, but when it comes to functionality they produce lots of problems.

If you are looking for mathematical/calculation advice, then ALPINE THUMPING nailed it. Use his advice.

If you re looking to see if it is worth building it comparing time, design, money, and last but not least, outcome compared to a conventional bass reflex, then here are my two cents worth:

I have built a transmission line about 14 years ago. After I built it, I showed it off and was a huge show piece, because of it design and power at Fs, but there were lots of drawbacks. The design its-self has defects. The box will boom, I MEAN BOOM!!! at that tuned frequency, while the rest of the spectrum is soooooooooo damp and weak that it puts a sad frown on the listeners face. Just think that when you are kicking it and listening to tunes and when the bass line hits at the tuned frequency of your TL, it will sound like a level of 10 while the rest of the notes sound like a level of 4. Another drawback is the speed of the design. TL's are soooooooooooooooooooo slooooooooooooooooooowwwwwwwwww. They do not hit. They are loud at the tuned frequency but they are sloooooooooooowwwwwwwwwwwww. The response is very sloppy. No detail whatsoever.

If you plan on entering a competition and want to get high SPL at just a short frequency range, but do not desire to use this box for anything else then IMO it may be worth it, otherwise it will wear you out.
 

Silver Member
Username: Mixneffect

Orangevale, Ca. USA

Post Number: 115
Registered: Apr-05
Personally I think Tl's were intended for extended frequency designs, on the low end. Typically in 4 or 5 way design, because of its limited range. Perhaps in a home theather setup. It would be used as the lowest frequency driver.
 

Gold Member
Username: Insearchofbass

Post Number: 2798
Registered: Jun-04
you no mix i made the comment about the 12 xxx in the tl it played very powerfull and pretty acurate down low but on the higher transition note it was caught way off guard and became blurred but if you watch p4s and their videos in cars youll see quick controlled response with excellent low end my vote so far goes with the snail shell and apocolypse and i have ideas why they work so well...better than a tl
 

Silver Member
Username: Alpineuser

Winchester, TN

Post Number: 518
Registered: Mar-05
a snail shell is just a rear loaded horn
 

Gold Member
Username: Insearchofbass

Post Number: 2799
Registered: Jun-04
i think they modified it a little though if you look at the new designs but basically yes it is a horn
 

Gold Member
Username: Hdubb

Farmington, Nm Usa

Post Number: 1851
Registered: Nov-04
hey alpine your a rear loaded horn.
 

Silver Member
Username: Geekbike

Post Number: 178
Registered: Dec-04
TL's are rarely used in car audio, so I thought it would be a good project. The only downside is the 9cuft enclosure. Exterior dimensions are 42"x33.5"x17". The only way it can fit in a car is one with a deep extended hatch (specifically, an MX-3 as soon as my truck sells).

sean, recheck your numbers with the line length. The numbers posted for the corners are the radius.

Alpine was spot on for the general guidelines of TL's. There a few different theories for the cross section of the line, but it remains fairly similar. These are the sites I used:

http://www.t-linespeakers.org/design/classic.html
http://yu-ra.tripod.com/index_enc.htm
http://www.quarter-wave.com
http://www.diysubwoofers.org/tls/
http://ldsg.snippets.org/boxes.php3

mixn, from what I've read TL's response is comparable to sealed. This is off one of the sites I'd listed:

"No, a T-line will not act like a sealed box in terms of acoustic output. I mention the sealed box aspect for tuning purposes. Due to the back pressure of a properly tuned T-line at the resonant frequency of the driver IN THE T-LINE, the woofer will see an air load that is as if the open end of the T-line were closed, hence the need to match the line length and line volume using the woofer T-S parameters so that the line length tuning and the apparent enclosure volume the woofer sees end up in juxtaposition."

Snailshells are their own type of enclosure, as much as any other type is. They don't follow the rules of horns, compression and expansion chambers are way off and the mouth area is off a bit. They have the look of a modified rear loaded horn, but also follow some rules of tapered transmission lines. P4S seems to have figured out the exact equations, but doesn't seem to want to reveal them for the new design.




 

Silver Member
Username: Alpineuser

Winchester, TN

Post Number: 521
Registered: Mar-05
ever seen the p4s guys? they dont look that smart :-)
 

Silver Member
Username: Mixneffect

Orangevale, Ca. USA

Post Number: 116
Registered: Apr-05
http://www.audioasylum.com/audio/speakers/messages/19794.html

Some would say that it is 6 dB. However, these peaks are not as much the problem as are the dips, which occur in between the peaks, and they reach -40 dB or so !! While it would seem that loosing certain bass notes may not be that terrible, you must understand that since this is a casual system, the amplitude response will relate to the phase response and time domain response.

 

Silver Member
Username: Mixneffect

Orangevale, Ca. USA

Post Number: 117
Registered: Apr-05
I basicly copied and pasted your links and the first paragraph regarding transmission lines behaviour. this info is off of your links "Knacko"
 

Silver Member
Username: Geekbike

Post Number: 180
Registered: Dec-04
You are right, BUT I plan on setting my crossover at about 80hz, so it won't even apply. Here is the graph:

Upload

I don't think you need help interpreting it.
 

Silver Member
Username: Geekbike

Post Number: 181
Registered: Dec-04
80hz is a bit high. With the rolloff, it'll probably be set around 55hz.
 

Silver Member
Username: Mixneffect

Orangevale, Ca. USA

Post Number: 118
Registered: Apr-05
Well if thats the response you will get with your setup, and you want to cross it at that frequency, then its not bad, but I have experienced that same kind of choppyness, with transmission lines within the subwoofer range 20-100 hz.
 

Gold Member
Username: Insearchofbass

Post Number: 2800
Registered: Jun-04
knacko as i said im not educated on higher math thanks to a past teacher but could you explain how you calculated radius
 

Silver Member
Username: Geekbike

Post Number: 184
Registered: Dec-04
Circumference is just 2*Pi*Radius. To calculate the length of the corner, take the circumference and multipy it by the amount of the circle (1/2, 1/4).

My line length was calculated using completely rounded corners, so there will be a very small error percentage.

 

Gold Member
Username: Insearchofbass

Post Number: 2801
Registered: Jun-04
ok heres what i got using a calculator 31.416 28.274 25.133 28.274 = 113.097 line length. This was using your radius measurements. Why was I off from your 123.128
 

Silver Member
Username: Geekbike

Post Number: 187
Registered: Dec-04
These are the measurements I used.

The straight line lengths added together:

22.5+14+3+23.5+24 = 87

Length of corner 1:

(2*pi*5)*(1/2) = 15.708

Length of corner 2+4:

(2*pi*4.5)*(1/2) = 14.1372

Length of corner 3:

(2*pi*4)*(1/4) = 6.28319

Total:

87+15.708+14.1372+6.28319 = 123.128
 

Gold Member
Username: Insearchofbass

Post Number: 2802
Registered: Jun-04
ok thanks knacko i follow you now
 

Gold Member
Username: Insearchofbass

Post Number: 2803
Registered: Jun-04
knacko id expect you to win some spl comps with that box
 

Silver Member
Username: Geekbike

Post Number: 190
Registered: Dec-04
Well... I did some more calculations. The total area of wood I'll need is 55.9256 square feet of board. If you change that into a cube it would be about 3.4953 cubic feet. With the density of HDF, the weight will come to 192.02 pounds (this is assuming the minimum allowable density to be classed as HDF). Once assembled and everything installed, I'm going to be looking at about 250 pounds of stereo. Scary.
 

Silver Member
Username: Geekbike

Post Number: 191
Registered: Dec-04
Another small problem. I've seen that the price of HDF is usually about double what MDF is. That puts the price per sheet at around $60 or so (Canadian). With about 3 sheets needed... $180 for the wood alone.

Oh yeah, I've also read that HDF can be up to 80lbs/cubic foot. This means the enclosure could weigh an upwards of 270lbs. Eveything installed would be like 320 or so. Hmmmm.
 

Gold Member
Username: Insearchofbass

Post Number: 2806
Registered: Jun-04
wow knacko thats alot of weight and dough there has to be a cheaper lighter weight material you can use maybe wood with fiberglass overlay or something
 

Silver Member
Username: Mixneffect

Orangevale, Ca. USA

Post Number: 127
Registered: Apr-05
Knacko,

If you use 1" MDF it may be cheaper than 3/4" HDF. Bracing makes up for density. I have never used HDF in 17 years, but then again it may be worth it after all, who knows. The trick is to get rid of enclosure resonance, thats all. I used to spend 2-3 months on a project (reffrence systems only), before I got to cutting and building. I wish you the best.
 

Gold Member
Username: Jmloughrey

Farmington, CT

Post Number: 1283
Registered: Jul-04
I know i'm gonna get heat for this....

But personally, i find this idea to be stupid.

Its just a huge box that's gonna cost a ton to build and need a small army of people to move.

You'd be better off just building a wall.
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