Menu
Forum
What's new
New posts
Live Activity
Search forums
Members
Registered members
Classifieds Member Feedback
Car Audio Discussion
General Car Audio
Car Audio Build Logs
Car Audio Equipment
Subwoofers
Speakers
Amplifiers
Head Units
Car Audio Help
Wiring, Electrical and Installation
Enclosure Design & Construction
Car Audio Classifieds
Car Audio Classifieds
Car Audio Wanted
Classifieds Member Feedback
Gallery
New media
New comments
Search media
SHOP
Shop Head Units
Shop Amplifiers
Shop Speakers
Shop Subwoofers
Shop eBay Car Audio
Log in / Join
Test
Forum
Search
Search titles only
Search titles only
Log in / Join
Search
Search titles only
Search titles only
What's new
New posts
Live Activity
Search forums
Members
Registered members
Classifieds Member Feedback
Menu
Reply to thread
Forum
Car Audio Discussion
Car Audio Build Logs
T line build for Megalomaniac
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Message
<blockquote data-quote="Immacomputer" data-source="post: 5240405" data-attributes="member: 570419"><p>They're really not too difficult to design and to model. Martin J. King has done excellent work in the area of transmission lines and horns and has uncovered much of their mystery. His matlab simulations are pretty good at modeling transmission line behavior. I was able to get accurate models of not only the transmission line enclosure for my sub, but I was also able to get an accurate model of the sub when in my vehicle. It predicted one peak at 22hz and a dip at 30hz with a passband of 15-70hz and that's very similar to what I measured.</p><p></p><p>Transmission lines are not mysterious and they're not uncommon. They have been used for thousands of years. And transmission lines do NOT have to have a taper for them to act like a transmission line. The changing of line area from the open end to the closed end is a way of limiting the upper order harmonics of the 1/4 wave resonance to smooth out peaks and valleys in the frequency response.</p><p></p><p></p><p>If that is the case, then there has to be reduced cone movement at tuning right? The enclosure on my sub is very similar to this one in that it is a transmission line with a compression chamber. The tuning frequency if you were to calculate it as a ported enclosure would be around 35hz like this one. The problem is that I actually have a maximum of cone movement around 35hz and a minimum around 22hz. The sub also doesn't come anywhere near to unloading below 35hz and on the contrary, has quite a bit of acoustic loading controlling the cone below 35hz. Doesn't sound like a ported enclosure with a long port to me. Something else interesting is that when I model it using Martin J. King's t-line sections mathcad file, it tells me there should a cone movement minimum at 22hz and line velocity max at 22hz as well but it doesn't when trying to model it like a ported enclosure with his ported enclosure mathcad file.</p><p></p><p></p><p>Both of you have a fundamental flaw in your understanding of transmission lines. Every port in every enclosure has transmission line characteristics at certain frequencies. It's effects aren't normally noticed in subwoofer enclosures because they need to be very long to have transmission line characteristics (over 60" to get a 1/4 wave of 60hz... when is the last time you've used a 60" long port?). In this case, there will be some effects of a ported enclosure but the ported tuning frequency is equal to the 1/4 wave frequency which will dampen the oscillation of the port. Also, the air mass ratio of the port to net volume is far too large for the net air mass to effectively drive the port. Instead, the compression chamber will rise in pressure and try to drive the port. As the pressure from the chamber starts to compress the port, the inertia of the port air mass will reject this change and the pressure heading down the line will decrease but the velocity of the air will increase. That's also the exact same thing that happens in a transmission line enclosure.</p></blockquote><p></p>
[QUOTE="Immacomputer, post: 5240405, member: 570419"] They're really not too difficult to design and to model. Martin J. King has done excellent work in the area of transmission lines and horns and has uncovered much of their mystery. His matlab simulations are pretty good at modeling transmission line behavior. I was able to get accurate models of not only the transmission line enclosure for my sub, but I was also able to get an accurate model of the sub when in my vehicle. It predicted one peak at 22hz and a dip at 30hz with a passband of 15-70hz and that's very similar to what I measured. Transmission lines are not mysterious and they're not uncommon. They have been used for thousands of years. And transmission lines do NOT have to have a taper for them to act like a transmission line. The changing of line area from the open end to the closed end is a way of limiting the upper order harmonics of the 1/4 wave resonance to smooth out peaks and valleys in the frequency response. If that is the case, then there has to be reduced cone movement at tuning right? The enclosure on my sub is very similar to this one in that it is a transmission line with a compression chamber. The tuning frequency if you were to calculate it as a ported enclosure would be around 35hz like this one. The problem is that I actually have a maximum of cone movement around 35hz and a minimum around 22hz. The sub also doesn't come anywhere near to unloading below 35hz and on the contrary, has quite a bit of acoustic loading controlling the cone below 35hz. Doesn't sound like a ported enclosure with a long port to me. Something else interesting is that when I model it using Martin J. King's t-line sections mathcad file, it tells me there should a cone movement minimum at 22hz and line velocity max at 22hz as well but it doesn't when trying to model it like a ported enclosure with his ported enclosure mathcad file. Both of you have a fundamental flaw in your understanding of transmission lines. Every port in every enclosure has transmission line characteristics at certain frequencies. It's effects aren't normally noticed in subwoofer enclosures because they need to be very long to have transmission line characteristics (over 60" to get a 1/4 wave of 60hz... when is the last time you've used a 60" long port?). In this case, there will be some effects of a ported enclosure but the ported tuning frequency is equal to the 1/4 wave frequency which will dampen the oscillation of the port. Also, the air mass ratio of the port to net volume is far too large for the net air mass to effectively drive the port. Instead, the compression chamber will rise in pressure and try to drive the port. As the pressure from the chamber starts to compress the port, the inertia of the port air mass will reject this change and the pressure heading down the line will decrease but the velocity of the air will increase. That's also the exact same thing that happens in a transmission line enclosure. [/QUOTE]
Insert quotes…
Verification
Post reply
Forum
Car Audio Discussion
Car Audio Build Logs
T line build for Megalomaniac
Top
Menu
Home
Refresh