T-line with FE-103E as computer speaker?

[CD]

OK, bear with me a moment.

Goal: for $100 or so, get the most pleasant PC sound I can at a wall-facing table. (10'x10' room, home office) I've already ordered one of those $30 "Sonic Impact" digital amps that have been discussed elsewhere.

Simplicity and small size seem to point to (a) single drivers and (b) a t-line enclosure as described here (http://www.t-linespeakers.org/design/rules.html)

Were I to use the Fostex FE-103E, which seems to be the best that fits my budget and which has an Fs of 79.5 Hz, that indicates a 42.5" straight t-line, with an appropriate width and taper, a project that seems simple enough with mdf and some damping substance, plus the requisite stuffing. These things would be smack up against the wall (I'm happy to sacrifice imaging) and I'm hoping to manage w/o baffle-step correction.

Listening would be nearfield, like about 3 feet away -- the speakers would be more or less jammed between table and wall. I worry about the upper-treble unevenness of these drivers, being that close. Might it make sense to point the drivers at the ceiling instead?

More importantly, am I nuts? Am I overlooking something crucial? Thanks in advance for any sage advice.

[Dave Jones]

Been there. Done that. They sound great. Use the FE107E rather than FE103E. It has a smoother response, and a bucking magnet.

The Locust I

[CD]

Thanks! Much to think about. Did anyone ever build the Locust 2? It looks interesting too. There was also brief mention by GM of another taller speaker with the 127E (Locust 3?)

At a glance, I doubt I can improve on it without going large flared. I did an extended max flat alignment awhile back for someone that a false bottom filled with kitty litter/whatever can be added to get the driver up high enough, but AFAIK it wasn't built:
L = 39.46"
SO/SL = 43.785in^2
driver down 14"
1.875" dia x 0.5" long vent near/at the bottom

Any advice would be welcome; anything up to 48" high would work.


And a dumb question:

At what point does a t-line become a ported box, or does it matter? (More prosaically, are Locusts 1 and 2 being figured with the the ported box or t-line worksheets?) I notice Locusts don't taper; on the other hand I noticed with the open-end t-line worksheets that really small vents sometimes worked nicely, which is more or less what the locust 1 seems to have.

[CD]

I'm answering some of my own questions ... in Martin King's ported box worksheet, and FE127E specs produce nice-looking results for

L=40
zdriver=2
zport=36
S0,SL=60
Density=.9
rport=.75
Lport=.75

especially if you add a little resistance -- can I just up Re by an ohm or two to experiment with an added series resistor?

The bottom-end output is definitely better-behaved (at least in the model) than in the t-line. I can't figure out how to get the worksheet let me try different stuffing levels in different parts of the box ... or does that not matter?

Given that the worksheet only does top-to-bottom standing waves, should I worry about sideways waves? I'm thinking about say 12 inches wide and 5 deep as interior dimensions.

[planet10]

Originally posted by CD
(b) a t-line enclosure as described here (http://www.t-linespeakers.org/design/rules.html)

As i say in the Read-Me 1st i wouldn't recommend building a line based on these "classic" rules -- it will be hit or miss.

Use MJKs models or tables. Probably the smallest TL you can build will be a folded one based on a high taper rate (ie the 10:1 in MJK tables)

dave

[CD]

Sorry I missed the read-me-first! Where is it? And yes, you seem to be right about t-lines.

The worksheets are highly educational -- I know this is clear to most folks on this board , but I now understand why t-lines tend to use bigger speakers than 4" and why the smaller speakers work better with horns or ported boxes. And the exchanges between folks on this board that quote worksheet results are useful, as you get to see how people move between the model and the real world.

[planet10]

Originally posted by CD
Sorry I missed the read-me-first! Where is it?

First link in the ToC (right after the donations links)

http://www.t-linespeakers.org/readme1st.html

dave

[GM]

At what point does a t-line become a ported box

It depends on how you define a TL, something that seems to vary over the decades and folk's opinions. My description is a well stuffed 1/4WL straight taper tube that has an FR very close to the driver's IB response. Once it begins to exhibit 4th order roll off characteristics it becomes a ML-TL IMO.

especially if you add a little resistance -- can I just up Re by an ohm or two to experiment with an added series resistor?

Yes, but you must also change Qed and BL:

Qes' = Qes*(1+Rs/Rvc), where Rs is the series
resistance and Rvc is the driver's DC resistance, so:

Rs = (Qes'/Qes-1)*Rvc. Remember to include the series
resistances of your amplifier/cable/inductors in Rs,
so the actual resistor you buy may be somewhat
smaller than calculated value.

Qts' = Qes'*Qms/(Qes'+Qms)

Vas is unchanged

Then to find B*L:

Cms = Vas/(Sd^2*rho*c^2)

where:

Vas is in m^3 (liters*0.001)

Sd is in cm^2

c is in meters/sec*0.0001 to get Cms in mm/N

then:

Mms = 1/[(2*pi*Fs)^2*Cms]

BL = [(2*Pi*Fs*Re*Mms)/Qes]^0.5

Note that there's no need to calc Qts' since the WS will, I just copied/pasted this info from another post of mine on another TL thread.

I can't figure out how to get the worksheet let me try different stuffing levels in different parts of the box ... or does that not matter?

It can. Which version of which WS?

Given that the worksheet only does top-to-bottom standing waves, should I worry about sideways waves? I'm thinking about say 12 inches wide and 5 deep as interior dimensions.

Since these are 1/2WL, the dims have to quite large before they fall into the BW where the stuffing won't damp it sufficiently, or if little is used, like in most of my designs and why I use golden or acoustic ratios for width/depth in straight pipes.

GM

[CD]

Thanks GM! As far as the worksheet, I'm having difficulty with "Driver in a Ported Box (Bass Reflex) - Acoustic and Electrical Response 12/20/03" Variable section-stuffing was easy in "TL Sections," but in "Ported Box" it looks like I need to specify something else first before I can vary stuffing densities.

OTOH I can't find anyone out there who stuffs ported boxes variably so maybe it doesn't matter.

Thanks lots for the other guidance!

[GM]

Originally posted by CD
Thanks GM! As far as the worksheet, I'm having difficulty with "Driver in a Ported Box (Bass Reflex) - Acoustic and Electrical Response 12/20/03" Variable section-stuffing was easy in "TL Sections," but in "Ported Box" it looks like I need to specify something else first before I can vary stuffing densities.

OTOH I can't find anyone out there who stuffs ported boxes variably so maybe it doesn't matter.

Thanks lots for the other guidance!

Serious designers do!

You're welcome!

OK, this looks like the earlier version, so just highlight, right click on one of the '0.lb.ft^3' to copy it, then double click and paste it in the various 'density' fields. If you decide that some fields can always be the same, then change them back to 'density' and input it just once in the 'enclosure geometry definition' section.

GM