Transmission Line Questions

[MJK]

Two responses :

Bricolo :

Martin, have you planned in a future version of your worksheets to enable us to enter the driver's efficiency?

The SPL of the driver can be calculated from the T/S parameters input. Inputting the SPL would require one of the other properties (Vas or BL) to be deleted to avoid an inconsistent set of parameters. I have no plan to make this change.

Matttcattt :

is this mathcad spreadsheet for a tube with the driver in one end? see picture 1. how could i change the results for use with a design like picture 2.

You can use the "TL Offset Driver.MCD" worksheet to model this geometry by setting E = 0.0001 or possibly a smaller value (where E represents that funny squiggle E in the input section). If you plan to run two drivers, as shown in the pictures, you should also read the two driver modeling article on my site under the "General Speaker Related Articles" section.

Hope that helps,

 

[Bricolo]

Two responses :

Bricolo :



The SPL of the driver can be calculated from the T/S parameters input. Inputting the SPL would require one of the other properties (Vas or BL) to be deleted to avoid an inconsistent set of parameters. I have no plan to make this change.

Hope that helps,

It's my fault. I tjought it was set to a fixed value. I haven't realized that it's calculated from the T/S params

 

[Matttcattt]

where can i find the densities of example stuffing materials?

 

[MJK]

I am afraid I do not understand the question. Could you be a little more detailed about what data you are looking for in your question?

 

[Matttcattt]

in the spreadsheet, i have to enter the stuffing density. where can i find some example values to insert here.

 

[MJK]

The worksheets are set up for stuffing densities between 0 and 1 lb/ft^3. A standard historical stuffing density is 0.5 lb/ft^3. Enter different values and see how the response changes. I am not sure what other advice to give you.

 

[kneadle]

The two extremes are given just to the right of the parameter input. They represent either an empty T-Line, or one that has been crammed to the gills with as much stuffing as is reasonably possible.

The T-Line design is a healthy compromise among line length, tapering, and stuffing. T-Line design is still something of an art, but MJK's worksheets make it a very scientific art.

I think of those worksheets as an advance in material, a better paint and paintbrush, so to speak, with which to create sound reinforcement and reproction masterpieces.

Dave

 

[planet10]

or one that has been crammed to the gills with as much stuffing as is reasonably possible.

You can say that again... i've got a prototype of GMs 40-1197 ML-TL that uaes 1 ib/cu ft and it is hard to get all the damping in.

dave

 

[Bricolo]

The worksheets are set up for stuffing densities between 0 and 1 lb/ft^3. A standard historical stuffing density is 0.5 lb/ft^3. Enter different values and see how the response changes. I am not sure what other advice to give you.

your answear brings me another question to mind: for what kind of stuffing is your worksheets optimised?

Every stuffing gives differents results, so, your worksheets have certainly be done according to your results with a certain kind of stuffing. But which one?

 

[MJK]

My worksheets were developed for Dacron Hollofil II (fancy pillow stuffing). I have used simple polyester fill from a fabric store and it also works well.

I did run the test line with long fiber wool and got almost identical results to the Dacron Hollofil II results.

Somebody sent me some test results using Miraflex and that also looked to behave in a similar manor.

The fibers that I do not have any data for, and which will probably not be equivalent, are fiber-glass and acoustistuff. I have been told that they provide better damping.

 

[kneadle]

FYI,

I used pillow stuffing.

Dave

PS--the TL threads are hot lately; a few old threads are being resurrected. Did they put something in the water last week or something?

 

[Matttcattt]

if i do stuff my TL, how can i keep the stuffing off the driver?

 

[kneadle]

You'll have to stuff the TL, and just put the stuffing far enough away that it doesn't touch the driver.

It's not necessarily WHERE you put the stuffing as much as it is that you put the right density in there.

In other words, if you designed for .3 lb /cu.ft., but you stuff the second third of your line (the middle third) with 1lb / cu. ft. of stuffing, it's the same effect as if you had stuffed the whole line evenly with .3 lb /cu.ft.

Hope that helps.

Dave