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An Improved Transmission Line Alignment.
An Improved Transmission Line Alignment.
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Old 5th October 2018, 04:52 AM   #91
GM is offline GM  United States
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Quote:
Originally Posted by teodorom View Post
I have to shorten it to 129cm.
Too much stuffing?
Incorrect stuffing model in the MJK worksheet?
Hmm using the pioneer's [Fs*1.56] rule-of-thumb, I get = ~34400 cm/4/[33*1.56] = ~167 cm, but is based on a non tapered pipe, so MJK's 1d wave equation is the more accurate when tapered. Regardless, tune it to suit your needs assuming it's not being driven with a high out impedance system where classical tuning is desirable.

By ~ a factor of 16+ based on the above Hornresp sim [0.741 kg/m^3]. FWIW, IME using his early worksheets, even light stuffing densities [< 0.25 lbs/ft^3] were often way too much in a wide performance range of MLTLs according to those relatively few folks that reported back to me with their final tuning/tweaking results plus don't recall going above 2 lbs/ft^3 since he stated he only charted this high IIRC.

Then again, 12 kg/m^3 = ~0.749 lbs/ft^3, so with Paul [P.Kitt] using this much in MLTLs with good accuracy and nowhere near the 32 kg/m^3 limit, your sim should be accurate enough.

Re driver offset, MJK listed some offsets for different tapers in his Classic TL Alignment Tables doc, so curious why you ignored them as they yield a smoother response with less damping.

GM
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Old 5th October 2018, 05:02 AM   #92
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Quote:
Originally Posted by Brian Steele View Post
With my PA310 driver with its 39 Hz Fs and 0.30 Qts, that will have me using a line with a un-stuffed resonance frequency of 130 Hz. That doesn't sound right...
Requires heavy damping, heavier than HR allows, though MJK's will sim them, but does work quite well, especially with low Qt drivers. Basically a pure TL variant of the Onken alignment.

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Old 5th October 2018, 06:13 PM   #93
teodorom is offline teodorom  Italy
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Quote:
Originally Posted by GM View Post
Re driver offset, MJK listed some offsets for different tapers in his Classic TL Alignment Tables doc, so curious why you ignored them as they yield a smoother response with less damping.
Don't worry about offset: my question would be the same whatever the offset is.
By the way, Alignement Tables are for people unable to use the Mathcad worksheets, or as a reasonable starting point.
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Old 19th February 2019, 06:22 PM   #94
Patrick Bateman is offline Patrick Bateman  United States
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Over on the SPL forums, there were a lot of people saying they didn't want to learn Hornresp to make a tline.

I can understand that thinking. I first learned hornresp over a decade ago. At the time, it was complex. The tricky thing about Hornresp is that it's become MORE powerful over time, so the learning curve is harder in 2019 than it was in 2009.

To address that challenge, I wanted to show how to make a transmission line in Hornresp AND NOTHING MORE. I'm not going to show you how to make a sealed box, or a vented box, or a multi-entrant horn or any of that.

I'm going to show you how to make a tline, and I'm going to show you that it can be done in under five minutes.

So, if you have five minutes to spare, and you want to build a tline, here's how you do it.

Click the image to open in full size.

First step is to look up the Thiele Small Parameters of your woofer online. I'm going to use an Alpine SWS 15D4 for this example. A nice cost-effective woofer that's available all over the world. I've highlighted the Thiele Small params.

Click the image to open in full size.

Second step is to plug your Thiele Small params into a vented box calculator. A lot of people like WinISD, but I like the calculator at carstereo.com because it's just so darn FAST. It will spit out what you need in a matter of seconds. Their calculator tells us that a Alpine SWS 15D4 works in a vented box that's 152.119 liters and tuned to 23.74Hz.


Some of you will notice that the calculator above says that the box requires 152.119 square feet. That's one of the neat things about the carstereo.com calculator - it doesn't care what units you use. If you give it liters, it will give back liters, if you give it cubic feet, it will give back cubic feet.

I'm working in liters because Hornresp is metric...

OK, steps one and two are done. We know about how big our box should be. These two steps shouldn't take more than about 30-60 seconds.

Up next, I'll put them in Hornresp.
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Old 19th February 2019, 06:33 PM   #95
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

Third step, you start Hornresp. Just run the program.

Click the image to open in full size.

Fourth step, you are going to ADD a record. Click "add." You can have a ton of records, I have no idea what the limit is. A lot.

Click the image to open in full size.

Click the image to open in full size.

Step five: you need to change this value so that it says "2.0 x pi" instead of "0.5 x pi"

I could explain why, but I won't bore you. Just double click on that box and change it from 0.5 to 2.0.

Steps 3-5 shouldn't take more than ten seconds at the most.

Up next, we'll put our woofer in Hornresp.
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Old 19th February 2019, 06:47 PM   #96
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

To put in your woofer parameters, you have to double click on the box labeled "Sd"

Click the image to open in full size.

When you do that, you'll see a screen where you can plug in your woofer parameters.

So there's a little data entry required here. Maybe 15-30 seconds to plug all this in.

At this point, you've spend about 90 seconds working on your transmission line.

A couple of caveats here:

1) The woofer that I am using has two voice coils. Due to that, we have to decide at this point if those coils will be in parallel or in series. In my case, I wired them in parallel. That's why my figure for resistance (Re) and inductance (Le) are half of what the spec sheet lists. If you're not doing a DVC woofer, you don't need to stress about that part.

2) Note that everything is in metric. One cubic foot is 28.32 liters. If you're spec sheet lists VAS in cubic feet, do the conversion.
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Old 19th February 2019, 06:49 PM   #97
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

Step seven. We're going to delete all this crap at the bottom.

What does this crap do? RTFM is you really want to know. These fields have no bearing on our transmission line. Just put zeroes in there. Or delete it. I don't care what you do, just get rid of them.

Doing that should take five seconds, we're still under two minutes at this point.

Click the image to open in full size.

Here's how things look at this point. I added a name to the project, but you don't have to. It's optional.

Last edited by Patrick Bateman; 19th February 2019 at 06:53 PM.
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Old 19th February 2019, 07:56 PM   #98
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.

Click the image to open in full size.

On the audio forums, most people are building transmission lines as pictured above. This style of folding is based on bad information that dates back for decades. Basically people have been building transmission lines for over fifty years, but there wasn't software to simulate them until about 2004. So see these foldings above? We're not going to do that. Because there's a better way. Hence the title of this thread.

Click the image to open in full size.

We're going to fold it like this. In this folding, there are three segments. The first segment is red, the second segment is green, the third is blue. The length of each segment is identical.

We are going to set the overall length of the segment to the value of "FB" from post 94 (An Improved Transmission Line Alignment.)

So we have to put values in those nine boxes that I've highlighted. You can safely ignore every other field there. We're just focused on those nine.

Each row represents one segment of our transmission line.
We have three segments, hence the nine values.

Our Fb from post 94 is 23.74Hz. We're going to set the length of our transmission line to 25% of this value.

Here's how we do that:

1) Sound travels at 34,000 centimenters in a second. So we can find out the length of 23.74Hz by doing the math:

speed of sound / frequency =
34,000 centimeters per second / 23.74hz = 1,432 centimeters

Now that we know the length of 23.74hz, we're going to set the line to ONE QUARTER of that, or 358cm.


We're *almost* ready to plug this into hornresp. The last step here, is that we need to divide that number by three... because we have three segments.

So 358cm divided by three is 119.33cm.

I know that was a lot of rigamarole, but our fundamental goal here is to figure out how long our transmission line will be, and how long each segment will be. That number is possibly the most important parameter in our transmission line design.
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Old 19th February 2019, 08:03 PM   #99
Patrick Bateman is offline Patrick Bateman  United States
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We're getting close to the finish line.

Click the image to open in full size.

In post 98, I showed how to find the length of each segment. In the case of this speaker, we're going to set each segment to 119.33cm. To do that, double click on "S1."

A menu will pop up. The menu asks you for L12. That's the length of our segment, so put in 119.33cm. S1 and S2 are the *area* of the segment.

Just to get in the ballpark, I am going to use the same size as our driver. In this case, that's 779.

NOTE: this value is only temporary. You could set it to 10 or a million or a thousand or whatever. We're going to change the area of the transmission line later. That's the beauty of using hornresp; we can tweak the parameters to improve performance, without making sawdust.

But in this case, we're going to use 779.

Repeat the process for S2 and S3. Same exact process:

1) double click on S2 or S3.

2) plug in the area in S2 or S3. In this case, 779.

3) plug in the length of the segment. In this case, 119.33cm.

4) Click "Calculate" and "Save."

That's it!

Click the image to open in full size.

Hornresp offers a bunch of different segment types. All we care about for our subwoofer is the "parabolic" type. To set our segments to "parabolic" just put your cursor in those three fields and type the letter "p" for "parabolic."

Poof, you got yourself a transmission line.

At this point, you should be able to complete steps 1-9 in under five minutes.
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Old 19th February 2019, 08:12 PM   #100
Patrick Bateman is offline Patrick Bateman  United States
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As noted in post #99, you should be at the five minute mark. You've plugged in your woofer parameters, you've figured out about how large the box should be, you've figured out how long the line is.

Now, let's see how things look!

Click the image to open in full size.

Click "Calculate." This calculates your subwoofer.

Click the image to open in full size.

The first window that Hornresp shows you is the "schematic diagram." The red line represents our driver, and the volume of our subwoofer is 278.874liters. That's 9.84 cubic feet. That's way too big, but I'll show you how to make (drum roll) an improved transmission line.

Click the image to open in full size.

Click on the "Window" drop down and select "acoustical power." That will show us our predicted frequency response.

Click the image to open in full size.

And there you go! You've just created a transmission line in Hornresp. This line has no taper and the woofer is mounted at the end of the line.

Click the image to open in full size.
In the real world, our transmission line would look similar to this. We don't want this. I'll show you how to make it smaller and smoother - in my next post.

In case anyone's curious, here's why we don't want a "traditional" transmission line:

1) We can make it smaller. A LOT smaller.

2) We can make the bandwidth wider.

3) We can make the response flatter.
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