EXPERTS ONLY PLEASE Building the perfect transmission line box, many questions

1995Tercel
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SW Utah
Vehicle : 2000 Honda Insight

Location in the vehicle: Terminus output behind driver seat, subwoofer facing rear of the car, under the package shelf

Space available (Length x Width x Height): Depends on what design I end up with, I'm going to try and fit the box we come up with.

Subwoofer make and model: Sundown Audio SA-8 V3

Subwoofer Size: 8inch

Number of Subwoofers: one

Amplifier make and model: Sundown Audio SAE-600D

Type of Port (Kerfed, Slot, Aero, etc.): circular

What type of music do you like?: all

Is your goal SPL or Everyday Music?: Goal is maximum extension (minimal Db taper past 20Hz), zero resonance, perfect bass. How loud the system gets is not a concern for me. Complete focus on quality.

Tuning Freq (Hz): I'm not sure, but the FS Hz for the subwoofer is 38.29

Volume : Also not sure

Questions: So, I'm attempting to make a straight tline box, but I just don't know where to begin. It is difficult to find practical information on this style box, as almost every single box i see, is done incorrectly. I also cant rely on calculations for those boxes, for the same reason. Many boxes I see have a parallel wall opposite the subwoofer (on top of zero sound deadening, with all parallel walls) which is all very poor design.

Just so people helping me are on the same page, Tline boxes exist to reduce or eliminate resonant frequencies, should be tapered wall, terminus output port 1/3 to 1/4 the area of the subwoofer radiating surface area, the first half of the transmission line lined with TL (not sure what this acronym stands for) second half filled with BAF Wadding. (If I'm wrong on this, please correct) I will also attempt to fit the box without compromising the design, so no internal turns or baffles, just straight.

1a. I think I need a bass chamber, that is 1/5th the wavelength distance, but I'm not sure what bass chamber means, what wavelength I need to use, or how to calculate volume of the box. Do I use the 38.29Hz of the subwoofer FS value? (Using that value I get a 1/5th wavelength distance of 69.40in at the calculated yearly average temperature of 50 degrees f where I live.)

1b. What is a bass chamber in a Tline box? Is "bass chamber"just referring to the overall structure of the box?

1c. I have read that I need to add a small distance to the overall length of the sub box to accommodate "end correction." How do I calculate this distance? This is another critical aspect, as the proper amount greatly increases low end extension.

1d. How do I cancel out the 3rd fundamental harmonic? the 5th one is done with the proper calculation of 1a.

2. What is the radiating surface area of my sub? I contacted Sundown audio, they just told me its 50.24 square inches, which is simply using a full 8 inch radius. I am very skeptical of this, as I've read this can be significantly different actual area among different subs. I need the exact area, because the port on the opposite end of the box needs to be between 1/3 and1/4th the area.

3a. How do I know what volume to use for the entire box?

3b. How do I calculate this volume?

3c. Are there separate volumes I need to calculate? Or is does this box simply taper from the subwoofer to the port?

Thank you for your assistance and expertise.

 
https://www.diysubwoofers.org/tls/

Do download and figure out how to use hornresp software.  EVERYBODY I have ever seen trying to build any type of horn, bin, or quarter wave box uses it. 

You can safely say you'll lose an inch from the diameter of the driver for surround, that should get you close enough.  Speaking of close enough if you're off on an end 3hz change in tuning of a box is inaudible in my experience and even 5hz is barely audible so don't drive yourself crazy there.

According to that source the unwanted high resonances that you think you want to tame with stuffing are only an issue in full range system so you should not need any batting unless you're trying to cheat a shorter line and from my experience with stuffing in general while you can change response slightly you pay for it with efficiency.

I do not believe you need a chamber for a true transmission line, that becomes more of a horn or just a ported box.  AFAIK true T-line is the woofer firing into the line which is consistent length throughout.  Having an odd size chamber puts you more into horn territory, though I suspect the hornresp software will have options where you can play with that.

Lastly I think if you want to play down to 20hz you will not be able to build this without a bend.   You are getting into a LONG wavelength, and that said I'm not sure how far below FS you can go with a t-line.   There have only been a handful of guys on this forum who have built these so if you want better, do a forum search and see who has done them, PM those guys and hope they're still active.  Good luck and please post a build log as you go.  I've heard one proper T line in person and it sounded very nice.   Almost worth the space and the wood.   Mind you, with today's EQ options and how cheap power is and how robust our woofers are there's no reason you can't get flat from 20-80hz in the same space a few different ways these days.   I'd consider T-line not something you "have to have" in order to get a particular sound but just an alternative as something to do if you like a good DIY woodworking challenge and interesting conversation piece.

Might even get better horn/tline discussion going at diyaudio forum or another home theater forum.  Home theater guys don't care about size of enclosure and are much more likely to have experimented with these sorts of designs... car audio guys these days lean heavily on cheap power and robust woofers to leverage the hell out of box size when wrestling Hoffman's Iron Law and the market has mostly focused on delivering options along that line of approach.

Good luck and please post a build log here.

 
https://www.diysubwoofers.org/tls/

Do download and figure out how to use hornresp software.  EVERYBODY I have ever seen trying to build any type of horn, bin, or quarter wave box uses it. 

You can safely say you'll lose an inch from the diameter of the driver for surround, that should get you close enough.  Speaking of close enough if you're off on an end 3hz change in tuning of a box is inaudible in my experience and even 5hz is barely audible so don't drive yourself crazy there.

According to that source the unwanted high resonances that you think you want to tame with stuffing are only an issue in full range system so you should not need any batting unless you're trying to cheat a shorter line and from my experience with stuffing in general while you can change response slightly you pay for it with efficiency.

I do not believe you need a chamber for a true transmission line, that becomes more of a horn or just a ported box.  AFAIK true T-line is the woofer firing into the line which is consistent length throughout.  Having an odd size chamber puts you more into horn territory, though I suspect the hornresp software will have options where you can play with that.

Lastly I think if you want to play down to 20hz you will not be able to build this without a bend.   You are getting into a LONG wavelength, and that said I'm not sure how far below FS you can go with a t-line.   There have only been a handful of guys on this forum who have built these so if you want better, do a forum search and see who has done them, PM those guys and hope they're still active.  Good luck and please post a build log as you go.  I've heard one proper T line in person and it sounded very nice.   Almost worth the space and the wood.   Mind you, with today's EQ options and how cheap power is and how robust our woofers are there's no reason you can't get flat from 20-80hz in the same space a few different ways these days.   I'd consider T-line not something you "have to have" in order to get a particular sound but just an alternative as something to do if you like a good DIY woodworking challenge and interesting conversation piece.

Might even get better horn/tline discussion going at diyaudio forum or another home theater forum.  Home theater guys don't care about size of enclosure and are much more likely to have experimented with these sorts of designs... car audio guys these days lean heavily on cheap power and robust woofers to leverage the hell out of box size when wrestling Hoffman's Iron Law and the market has mostly focused on delivering options along that line of approach.

Good luck and please post a build log here.
Agreed 100%.  Excellent response here.

I've built some and had luck.  I did not tune below driver Fs so I cannot comment on the effect.  I agree with having an efficient transition from the driver airspace into the T-Line.  I built enclosure-coupled T-lines but put focus on a good transition.

 
Yep. He has been telling everyone on Facebook the FU 750s will take 1500rms and the 300s will take 750. 
Of course if he said the SA12 will take 1500W, that's A-OK because everyone knows that Sundown uses magic unicorn tears to make their 2.5" coils handle double rated power.

I'd imagine most people could get away with running FU750 on a 1500W rated amp and be fine, same as SA or DD25XX.   My issue has always been if someone needs to ask how much power to use they have no business trying to exceed rated.

 
wow basically a whole thread about me and i said nothing and people do run 1500 to 750's guy here laughed at my amp because he ran a ppi 1800 to his for yrs.. also popwar u were running like 1300rms to 750's right? so how am so how am i wrong? either way idk why i was brought into this at all

 
Running a 1500 watt amp does not mean your subwoofer is seeing 1500 watts...

Everyone and their sister claims they are putting double rated power to their subwoofer yet have NEVER clamped actual power.  

 
Popwarhomie said:
You have no clue what impedance rise is do you...
right so why is it ok for u top tell me to run 1k to a sub but not ok for me to say 750? or 1500rms for a fu 750 when there are people running fsb 1600 to 1 or even a 3k amp on 1.. u may have seen guy just said he ran taramps 8k on 4 of them  a long time no problems.. don't tell me about rise when u are correcting me for tell people to "over power" subs because of rise

 
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