Perfect TL with MJK mathcad graph?

[Bricolo]

[christophorus]

Hi MJK,
Before I wrote this thread and Tl Basic Design Question.
thread, I knew very little about TL design. I tried to understand what Bob wrote, but it confused me because he made it so detail!
Based from yours and other guys answer in both threads, I reread Bob' TL site and now it's very easy and clearly to understand what to achieve and what to avoid in designing TL speaker.

BTW, is it true by extending TL resonant freq. below fs will change the sound from the original (colorization?) or it just boost the lower part of FR to flatten it?

see you.

Chris

[MJK]

Hi Chris,

BTW, is it true by extending TL resonant freq. below fs will change the sound from the original (colorization?) or it just boost the lower part of FR to flatten it?

In general, I doubt tuning below fs will flatten out the TL SPL response. You should model any geometry you are considering, in MathCad, and see what the predicted response looks like. Depending on the driver's T/S properties, I have found that tuning to fs works very well. This was the basis behind my alignment tables.

But having a MathCad model to try out potential designs allows you to be creative quickly and without spending any money. Then pick the design that appears to be the best. I usually have two or three designs worked out in MathCad to compare the different graphs before selecting the one I build. If there is a tie, I build the simpler design.

[christophorus]

Hi,
When we design ported enclosure one of the important thing is: Group Delay, even with T/S optimum design, it gets around 4 times longer than closed box and it gets more longer when we tune the box lower than Fs.

How about TL design? is it shorter same or longer than ported enclosure?
How can we calculate it for TL design?
Is there any graph to show it in MJK mathcad?

Chris.

[christophorus]

Hi MJK,
I have a question regarding impedance plot, there are 2 opposite achievement to make it right for TL, if I understood it correctly:

1. Your answer in this thread dated 01-07-2004:
(MJK) Watch the graphs as you move the woofer along the line and add or increase stuffing at different locations. The goal is to have a strong first peak in the terminus to augment the driver's rolling off bass bass, then damp out the other peaks to reduce ripples.

2.From Mini Mite ESL project by Sheldon D. Stokes, .Jordan TL Bass :
The line should be stuffed just until the lower peak disappears, and the upper peak becomes a smooth single peak.

You mentioned the second peak should be damped, Sheldon damped the first one (attached graph below), so I get confuse.
Would you mind explaining what the good/bad things happen for both answer?

regards,

Chris

[MJK]

Hi Chris,

The second peak I was refering to is in the terminus SPL response. You want the first peak to add bass but not the second which produces a ripple in the system SPL response.

I do not add stuffing until the first impedance peak is smoothed, this is an old rule of thumb that people typically apply to TL designs as a sign of correct damping material amounts. I don't believe this is correct and usually end up with two peaks in the impedance curve like a bass reflex design.

[tda]

A small question regarding the woofer displacement plot:
I assume the graph is for a 1 W. What is happening when you put 10 W? At 1 W, at 45 HZ the woofer displacement is almost equal with XMAS of my driver...this means that at 10 W the most lower frequency will be something around 90 Hz?

[Bricolo]

Originally posted by tda
A small question regarding the woofer displacement plot:
I assume the graph is for a 1 W. What is happening when you put 10 W? At 1 W, at 45 HZ the woofer displacement is almost equal with XMAS of my driver...this means that at 10 W the most lower frequency will be something around 90 Hz?

I was also wondering

[MJK]

Hi tda,

I assume the graph is for a 1 W. What is happening when you put 10 W? At 1 W, at 45 HZ the woofer displacement is almost equal with XMAS of my driver...this means that at 10 W the most lower frequency will be something around 90 Hz?

Do you plan on listening to your speaker at a single frequency and 10 watts of input? I never do this, I listen to music.

This is one of the reasons I don't like looking too closely at the displacement curve. When you are listening to music you are hearing a broad band of frequencies whose sine waves add and cancel as a function of time. If you are really putting in 10 continuous watts, you must like really loud music, only a portion of that will be in the low frequencies where displacement is a concern. You can even get into a situation where you are putting in enough power to exceed Xmax at a particular frequency if it acted alone but when combining with all of the other frequencies not actually exceed Xmax. For example look at the terms in a Fourier series that make up a square wave, the magnitude of the fundamental is larger then the magnitude of the square wave. For most normal acoustic music, I don't see Xmax being a huge issue.

[tda]

Hello MJK,
As usual, you are right. I read on Internet a few articles about Xmas that confirm your opinion. It seems that the problem occurs when you listen at really high input, which is not the case.
Again, thank you four your prompt replies.