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3D printed T-line enclosure experiment  

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nicholascjs
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18/10/2019 6:46 am  

I recently saw a video on youtube of Hexibase 3d printing a t-line enclosure for a W3 1876S and it worked pretty well. I wanted to try it with a pair of W3-2141 because i really liked the idea of micro t-line speakers to what i read t-line and small package don't go well together , still worth a shot so i started to make some changes to his design. I did some homework on t-line but its best to ask around if this is a good idea because i don't have any experience with T-line enclosures.  Did some basic math and figured i need to scale it up by 19% to account for the SD difference, the piston area is 27 for 1876s and 32.1 for 2141. The resonant frequency of this drivers are also different at 55hz and 75hz, my thoughts are to reduce the wave guides from 152cm to 114cm. Is there anything i'm missing? Also im afraid that t-line enclosure will have a huge dip in certain parts of the range are there any sims for t-line?  i use winISD and Vituix they both don't do this well to what i've seen thus far.


123Toid
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19/10/2019 10:57 am  

I don't personally do a lot of T-line enclosures, but the best software for it is HornResp.  As far as having success with small speakers, that is basically the Bose wave radio.  Series 1, uses a small t-line for one of the drivers and while sealing the enclosure for the second.  I think their newer ones use a t-line for each speaker.  All this to say, that it has been done successfully.  I am really interested to see your build.


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nicholascjs
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20/10/2019 1:42 pm  

Thanks for the tip I'll try out HornResp, i dint know Bose made T-line speakers went digging and saw a few other models with t-line designs. Good to know its been done before, this is my 1st t-line build i'm pretty sure its going to take lots of trial and error to get it right. When i'm done with the design, i will remove my pair of W3 2141 from my 0.1ft.³ ported enclosure tuned to 75hz do a sweep and compare both enclosures.


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TVOR-Ceasar
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20/10/2019 4:33 pm  

Let me know what you come up with using HornResp. I'd like to see how the calculation info I obtained years ago stacks up. What I have is for just a straight line, not tapered. I'm working now, so it'll probably be later tonight when I could look at it.

-Charlie


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TVOR-Ceasar
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21/10/2019 9:38 am  

It was actually rather early this morning. Here's what I came up with from the info I found years ago:

3in x75hz tline

 

How does this match with what you've got or will get with HornResp?

BTW, this is a sketch of what a box could look like inside, though I'm a bit questionable on the placement of the damping material. I have seen some place it here, while others place in the main box area as normal.

-Charlie


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nicholascjs
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26/10/2019 3:43 am  

Sry for the late reply just got back form overseas, dint have time to work on it yet. I cant find the option for non tapered enclosure in HornResp ill poke around more there tomorrow. The calculations i use is slightly different for the crossectional area, i'm using the SD of the driver which is 4.97 sq inch and the line length is 3.7ft. I was thinking of going without stuffing if possible to get maximum efficiency, if needed ill try add a shot sealed line tuned to the dip in the frequency range to cancel out the quarter wave from the port fighting with the drivers output.


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TVOR-Ceasar
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26/10/2019 11:58 pm  

I did some digging and comparing what I had in Qbasic vs other calcs / formulae. Found this site which actually had the calcs spelled out. I had the correct info for length calc'd, but never used it. It's been many years, so I do not know why. Here's the corrected screenshot:

 

3in x75hz tline update

Also, the "stuffing I saw on other sites was described as being in the length of the t-line itself, with the last 1/4 to 1/3 left open. It is placed there to help damp reflections inside the line.

Also, you only need the diameter of the driver as it is the area of the surface plane of the driver used - in this case 3"D equates to:

(3/2)^2*PI

1.5^2 * 3.14159

2.25*3.14159

7.0685775

-Charlie


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bjaurelio
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28/10/2019 9:08 am  

Our understanding of T-line speakers has come a long way. Martin King did some excellent work clarifying the principles on which it works and provided the first accurate model for predicting output. Some of the old rules of thumb will apply, but modeling with hornresp is your best bet, because only it compares to the results from King's old mathcad sheets.

A few helpful rules of thumb:

1)  driver plaexperiment on driver placement along the line to tame peaks above the 1/4 wavelength resonance (ripples)

2) a 10:1 taper let's you get a smaller line and usually better controls the ripples

3) stuffing is also there for taming ripples. That's why you stuff just the first 2/3 of the line. Stuffing farther down the line reduces output from the primary resonance that you want for bass.


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TVOR-Ceasar
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28/10/2019 11:09 am  

@bjaurelio

The interesting thing is that the information I got back in the late 80's (most of which came from the 70's or earlier) actually comes up with the same result as the newer software (HornResp). The site that I linked to above, the thread was started in 2006. I needed that to verify my Qbasic program since I don't know exactly where my reference material is located, atm. 

As to the taper, the other article I saw (which I didn't save the link, damn!) showed an example driver with all 3 versions of T-Line: Straight, Tapered in, and Tapered out. All of the T-lines had the same equivalent volume - If you were to take the straight line and use the middle as a pivot and swing either end in or out, it's all equivalent. The tapers are used to either increase or decrease the laminar flow and acoustic matching to the room. Plus, the reduction of resonances due to non-parallel walls reduces the need for "stuffing". 

Another trait of T-line is that the bottom end roll-off is even more gradual than a sealed box (again, that was in the article I didn't save), which a sealed box is more gradual than ported. So theoretically you get more low end extension from the same driver - a smoother Bass presence / response.

All in all, what I remember from all that back then was the general classifications of where to use each type:

Ported - Rock n Roll high SPL types of music

Sealed - Jazz style where tighter accuracy is preferred (usually with a box Q between 0.5-0.8+-. Higher Q of 1.0 or more would be more suited to Pop music)

T-Line for Classical, where the bass lines are not pounding, but rather to be a complete fill for the music being played, ie, stringed bass played with a bow or wind instruments, and bass drums played with brushes or mallets, rather than standard hardwood sticks. Think Timpani (or Tympani, depending on where you are in the world).

-Charlie


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nicholascjs
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29/10/2019 9:11 am  

I was really close to your numbers, my calculations are almost same as this besides the port surface area i did mine without a online calculator using the speed of sound divided by FS of driver then divided by a quarter to get quarter wave which goes like this

Speed of sound 1120fps / 75hz FS =14.93ft 

14.93ft / 4 = 3.73ft port length

the software calculator uses 1130fps as the speed of sound that why its displaying 3.766ft but i dont think 0.03 ft matters 

My thoughts are that i only need the effective piston area (SD) of the driver not the overall driver diameter but since you mentioned using the overall diameter ill try making both and trying it out. The enclosure size will be significantly larger if i were to use the diameter of the driver , also plan to test out with stuffing and without. 

Just finished with the design of the enclosure ill post a picture of it, thank you for the check 

image


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nicholascjs
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29/10/2019 10:24 am  

@bjaurelio @TVOR-Ceasar dint refresh my page when i posted just now i missed your posts,this topic is quite messy indeed many different findings and results, i was thinking of doing a tapered enclosure also. hmm i guess i will need to test in person with my measurement mic to find out. this will take me quite some time to dial my drivers in to a quarter wave enclosure well its part of the fun, i guess when im done with it i can upload my designs and findings for other so refer to or perhaps if some one wants a t-line speaker without guess work they can just copy this build with the same drivers. im still waiting on my filament to arrive ill post updates, graphs and sample sweeps here when its done. now im also working on a 0.13cu ft boombox with 2 3" drivers and a 5" radiator ill post more details at the boombox section when the plans are done ill be moving back and forth between this 2 projects 


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TVOR-Ceasar
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29/10/2019 4:53 pm  

1120, 1130, the actual is 1125.33 FPS @ 20°C (68°F) @ Sea Level. I was using the # referenced way long ago, but as you so stated, the difference is minimal. It's all good. 

As far as the cross-sectional area of the TL, everything I have read has been in relation to the diameter of the driver, which has, in the past, been called SD. The info I read back in the 80's, the site listed above, and even this John Risch site say they all mathematically refer back to the size of the driver. I believe that even Hexibase says this in one of his videos. Of course, these are older sources, so if there is a new, definitive, explanation, I'd be glad to read it and accept it. 

-Charlie


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nicholascjs
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03/11/2019 1:48 am  

I think we are referring to the same thing, just that that in my case the driver is 3" how ever the SD is smaller then 3" because the mounting and surround is not counted. Depending on manufacturer some do use the effective Piston area diameter as drivers size specifications with a larger overall diameter. I think I misunderstood your earlier post.

Yesterday I have a light bulb moment, I was thinking if I could add a radiator or maybe another driver to further reduce the size of the enclosure that will be great sort of a isobaric setup but with a wave guide half the length of a ragular t-line. Have to look around see if I can find a PR with close enough cms and MMS that can be tuned to match the driver. I will complete my current enclosure that I'm working on before attempting this. This is just for my entertainment, it's fun to push limits and see what can I come up with, if it's good I might even make another to replace both my enclosures. 

Also this enclosure design have many folds so ripple might not be an issue, if there is noticable ripple in the frequency curve then I'll add stuffing. This is from what i read quite some time ago, the paper mentioned that folds in t-lines help to reduce (ripples, nulls, dips) don't know which is the correct term. 


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DIYAudiphileElliottBridge
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03/11/2019 4:22 am  

@nicholascjs

For a PR to work it needs to be in a sealed container. You can't combine a transmission line and a PR to get a shorter group delay. A PR is a good idea though as you will get less group delay and don't have to worry about excursion. Have a go at testing different PRs with your driver in winISD. Make sure to set it at the max W you'll be running the speaker at and then look at the excursion of the driver and that of the PR.


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nicholascjs
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03/11/2019 5:44 am  

@diyaudiphileelliottbridge

i was thinking of something like this 

image

my thoughts came from when i saw a compound setups with woofers facing each other, since I am working with a full range speaker not a woofer i will need it to face outwards or the same direction as the outside driver with PR or second driver coupled to the wave guide, the only thing that the sealed chamber between the driver and pr wont be constant pressure unless i use another driver in a push pull. I think a second driver will be better in this case well there will be definitely things that i dint foresee when im going to attempt this.


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