New T-Line box built. Now time to stuff it... help pls. (w/ pics)

[cossack23]

Greetings,

I'm a long time lurker, but a first time poster. Using the what I learned here, particularly from the likes of MJking and JimPA, I built my first 2 Transmission Line enclosures for JL 10" Subwoofers for Car Audio application (picture links below)

https://www.dropbox.com/s/ekq0ufl4odp3cn2/tline.jpg?dl=0
https://www.dropbox.com/s/t9ts8eh2copne42/2tline.jpg?dl=0

I'm only a med student, without a strong aptitude for mathematics, so I went with a basic "straight line" approach, without any so-called advanced techniques like driver offset and tapering. Perhaps I will try in future builds.

My goal -- smooth tight bass.

Given what you see in the 2 pictures, how would your experience guide you to stuff this enclosure.

Would you do as MJking did in on of his builds; 2/3 of the enclosure stuffed with Dupont Dacron II
https://www.dropbox.com/s/89dm77lbad60e84/MJking_build.jpg?dl=0

Or as the guys at PMC did, lining the enclosure with what i think is Open-Cell PU foam.
https://www.dropbox.com/s/xfdad4qspm1tmki/poly_stuff.png?dl=0

 

[sax6]

Building my own TL is a dream...

Seeing other ( like IMF and TDL ) stuffing... I would go with bumped styro cells .......

See attached

 

[cossack23]

Thank you sax6. Would you stuff the cross-section entirely, or as in the image you posted, simply line the walls?

 

[JimPA]

Thank you sax6. Would you stuff the cross-section entirely, or as in the image you posted, simply line the walls?

Take a look at my post and the photos in this thread.
index.php
You want to leave some space between the foam.
I would use a 65% density behind the driver in the first 1/3 of the line und taper to about 15-20% of the last part of the line.

I had to replace a tweeter resistor so I had my son take some photos.
Some of the foam had to me moved to get to the crossover.
There are 3 pieces of foam behind the 6.5" driver.
Two pieces are 2" wide and one piece is 1" wide.
You should use a piece between the bottom front of the driver.

Also what is the taper ratio of the Sd. [cone area of the driver] to the line terminus?

 

[JimPA]

After looking at the photo of the enclosure I would place by gluing a 1" thick piece of foam on the wood behind the driver.
This will help with reflections directly behind the driver.

 

[gdmoore28]

Want the hi-tech scientific answer to your question? Post it here:

http://techtalk.parts-express.com/forum/tech-talk-forum

These guys eat, drink, and sleep speaker technology.

GeeDeeEmm

 

[JimPA]

I suggest the OP uses a test Cd and spl meter.
Stereophile Test Cd 4 has oscillated warble tones to cancel out room models.
I would place the spl meter 1m from the woofer voice coil center.

Are you going to use a passive crossover?

BTW I have yet to find anyone that has developed a computer program for using low density polyurethane foam for stuffing transmission line designs.
You can also measure the woofer impedance at the driver terminals with a volt meter to find impedance peaks.

 

[cossack23]

Much love and respect JimPA. The details you provided is exactly what I was looking for. Last question: if I were to purchase foam from foambymail.com (or similar), is there any specific material that stands out as most suitable [according to mh-audio.com, i should opt for Dacron or Long Fiber Wool]

And to answer your crossover question -- I will be running an active crossover setup, via Helix G One amplifier with built in crossover.

To answer taper ratio -- The cross-section is slightly above the driver's Sd value... 15% greater which is below the traditional rule set of 25% min. My overall enclosure measurements were were ultimately restricted to the size of my car's trunk. [Cross-section of line is ~64 and the Sd of driver is 53.475].

 

[JimPA]

Much love and respect JimPA. The details you provided is exactly what I was looking for. Last question: if I were to purchase foam from foambymail.com (or similar), is there any specific material that stands out as most suitable [according to mh-audio.com, i should opt for Dacron or Long Fiber Wool]

And to answer your crossover question -- I will be running an active crossover setup, via Helix G One amplifier with built in crossover.

To answer taper ratio -- I don't have a great grasp on this topic. The cross-section is slightly above the driver's Sd value [Cross-section of line is 63.25 and the Sd of driver is 53.475] My calculations were based on Fs = 31.5; QTS = 0.485; Sd = 53.475; Driver displacement = 0.049 ft^3.

My experience is that foam is better then Dacron.
Most fabric stores carry foam.
types.php
You want to use the first type of foam listed as the low density type.

I have never used wool.
It would be much harder to glue wool to stay in place inside of an enclosure.
Gluing foam is much easier.

I have never used an active crossover with transmission lines.
Fried used a series crossover design.
Using a large air core inductor of 12mh 14 gauge added Re. to the crossover circuit.
It raised the driver Qts. to flatten the impedance.

 

[cossack23]

Truth be told, I have't given the crossover element much thought at this stage, but this will be a topic of extensive research on my part now that you mentioned it ... I'm guessing it matters much since you brought it up.

Thank you sincerely. Your contribution to my project is invaluable.

 

[Powertech]

Now this might be a bit long.
The answer to your question is ........ No idea! The reason is that there is no calculable way to do this. It is very much suck it and see.
It took me over six months to sort mine out, and I'm still not completely satisfied with them. After 2 years, I still fiddle with them from time to time.

It also depends on the frequency range you are running the drivers at. Let me try to explain.
If you are running full range or mid/bass drivers, as a lot of Lowther and PMC type designs do, you need to be absorbing all the high and mid frequencies with the stuffing while allowing a certain amount of the low bass to exit the port (as yours are open) without undue excitation of the cabinet walls. If you are using the TL units purely as bass units (as mine are) then the stuffing has no purpose with regards to high frequency filtering as there isn't any. Well, maybe some weak bass unit harmonics, but nothing of consequence. What you are trying to do is to use the wadding to change the speed of sound through it. What this does is to tune the perceived length of the line to an optimum value for the driver.
I concentrated on 2 layers of wool underlay glued and stapled all around the walls behind the driver to absorb initial reflections and reduce box resonance. I then started off fully packing the line with teased out Dacron wadding. I found that this overdamped the line. I have ended up with a 3" layer of Dacron next to the driver and just into the throat of the line, then about 60% of the line packed with Dacron teased out to about 1/2 the volume I thought was right to start with. There is also a layer of wool underlay glued and stapled around the first section of the line, but nothing thereafter. With mine I used a folded taper design with the open port end slightly larger than the CSA of the end of the line to reduce 'chuffing' at high volumes and to better impedance match to the external air in front of the port. When it comes to resonance reduction, I might add that my cabinets are made from laminated layers of MDF with a minimum wall thickness of 30mm (the baffle is 48mm thick) so these things are heavy. The drivers are 8" Peerless bass units with an Fs of 29Hz and cross over at 240Hz@24dB/oct.

One point to make is that it is a good idea to make the line accessible after completion of the cabinet as I can guarantee you will not get it right first time. On my cabinets the line folds front to back (if you think of yours being top to bottom) with 7 folds and I have rubber damped steel access panels in the back of the speakers so that I can still get to all sections of the line to adjust the stuffing.

I hope that some of this helps.

 

[Pete B]

What is your application, car audio or home?
What exact driver are you using, T&S parameters?
Stuffing is much more critical if you are running the driver up into the midrange
and less so if sub only.
How long is the line, do you know what to expect for the l/4 frequency?

It looks like the last section of line has more cross sectional area than the rest, is
that just an illusion?

 

[JimPA]

Now this might be a bit long.
The answer to your question is ........ No idea! The reason is that there is no calculable way to do this. It is very much suck it and see.
It took me over six months to sort mine out, and I'm still not completely satisfied with them. After 2 years, I still fiddle with them from time to time.

It also depends on the frequency range you are running the drivers at. Let me try to explain.
If you are running full range or mid/bass drivers, as a lot of Lowther and PMC type designs do, you need to be absorbing all the high and mid frequencies with the stuffing while allowing a certain amount of the low bass to exit the port (as yours are open) without undue excitation of the cabinet walls. If you are using the TL units purely as bass units (as mine are) then the stuffing has no purpose with regards to high frequency filtering as there isn't any. Well, maybe some weak bass unit harmonics, but nothing of consequence. What you are trying to do is to use the wadding to change the speed of sound through it. What this does is to tune the perceived length of the line to an optimum value for the driver.
I concentrated on 2 layers of wool underlay glued and stapled all around the walls behind the driver to absorb initial reflections and reduce box resonance. I then started off fully packing the line with teased out Dacron wadding. I found that this overdamped the line. I have ended up with a 3" layer of Dacron next to the driver and just into the throat of the line, then about 60% of the line packed with Dacron teased out to about 1/2 the volume I thought was right to start with. There is also a layer of wool underlay glued and stapled around the first section of the line, but nothing thereafter. With mine I used a folded taper design with the open port end slightly larger than the CSA of the end of the line to reduce 'chuffing' at high volumes and to better impedance match to the external air in front of the port. When it comes to resonance reduction, I might add that my cabinets are made from laminated layers of MDF with a minimum wall thickness of 30mm (the baffle is 48mm thick) so these things are heavy. The drivers are 8" Peerless bass units with an Fs of 29Hz and cross over at 240Hz@24dB/oct.

One point to make is that it is a good idea to make the line accessible after completion of the cabinet as I can guarantee you will not get it right first time. On my cabinets the line folds front to back (if you think of yours being top to bottom) with 7 folds and I have rubber damped steel access panels in the back of the speakers so that I can still get to all sections of the line to adjust the stuffing.

I hope that some of this helps.

A transmission line enclosure with no damping material is going to sound like a boombox.

The damping material flattens the response.

 

[JimPA]

What is your application, car audio or home?
What exact driver are you using, T&S parameters?
Stuffing is much more critical if you are running the driver up into the midrange
and less so if sub only.
How long is the line, do you know what to expect for the l/4 frequency?

It looks like the last section of line has more cross sectional area than the rest, is
that just an illusion?

PeteB I think you are correct about the last fold in the line having a larger cross section.
Also I wouldn't have designed the lines that way.
The piece of wood behind the driver is going to cause reflections.
That is why I stated to place a 1" piece of foam over it.

 

[cossack23]

CROSS SECTION: 5.5" straight line. I remeasured just to re-confirm that it is in fact 5.5" all around. The wide lens of phone camera may be warping the image a bit. Though the general structure is not ideal, I had to strike a balance between acoustically functional measures and trunk space dimensions.

UPDATE: I ordered the Open-Cell 1.2lb Polyurethane, which should be arriving later this week. I intend to stuff it as per direction of JimPA.

INTENDED USE: Subwoofer frequency range for car audio; inside sedan trunk. @Pete B -- the t-line is in fact calculated for 1/4 frequency, made for this driver: JL 10w3v3-4 (http://www.jlaudio.com/10w3v3-4-car-audio-w3v3-subwoofer-drivers-92151). I had them on hand, so I decided to built the box for them to educate myself about speaker building.

CROSSOVER: After some research, I remain firm on DSP driven "active" setup. Given my skill and budget level, this option seems best. It also allows me to tune my other drivers off same device (3-way door panels and 2-way center stage).

QUESTION (for future build): To avoid the reflections JimPA mentioned, should there be a certain type of driver offset in the design?

 

[JimPA]

CROSS SECTION: 5.5" straight line. I remeasured just to re-confirm that it is in fact 5.5" all around. The wide lens of phone camera may be warping the image a bit. Though the general structure is not ideal, I had to strike a balance between acoustically functional measures and trunk space dimensions.

UPDATE: I ordered the Open-Cell 1.2lb Polyurethane, which should be arriving later this week. I intend to stuff it as per direction of JimPA.

INTENDED USE: Subwoofer frequency range for car audio; inside sedan trunk. @Pete B -- the t-line is in fact calculated for 1/4 frequency, made for this driver: JL 10w3v3-4 (http://www.jlaudio.com/10w3v3-4-car-audio-w3v3-subwoofer-drivers-92151). I had them on hand, so I decided to built the box for them to educate myself about speaker building.

CROSSOVER: After some research, I remain firm on DSP driven "active" setup. Given my skill and budget level, this option seems best. It also allows me to tune my other drivers off same device (3-way door panels and 2-way center stage).

QUESTION (for future build): To avoid the reflections JimPA mentioned, should there be a certain type of driver offset in the design?

An enclosure design that is deeper behind the woofer.
Transmission_line_loudspeaker
This might not be a scientific reason but look at the IMF, TDL and the former Fried Products designs.

Dacron is less expensive than foam.
Why did John Wright of IMF and later with TDL as well as Irving Fried use foam instead of dacron?

 

[JimPA]

The sensitivity of the driver is very low.
It is going to take a lot of watts to obtain a high spl below 100hz in a transmission line enclosure with that driver.

 

[cossack23]

Well I got plenty of wood left and a decent pair of working hands. Now that I'm privileged to that wonderful schematic you posted, I would be remise to not rebuild before I apply the precious foam (haha). Thank you sir! I'll keep this updated.

QUESTION (depth) : What is the width measure on that speaker box? Seems like I could easily use my 10" subwoofer in your design. Any special consideration for me to take into account for possible measure adaptation?

QUESTION (port exist) : Does the port exist location matter for subwoofer application? If i place the port exist such that it is perpendicular to the subwoofer's driver face, would that produce unwanted consequences?

Once again, thank you!

 

[cossack23]

PS: @JimPA --- This calculator seems applicable: http://www.mh-audio.nl/bailey_tml.asp if I am not mistaken.

 

[JimPA]

Well I got plenty of wood left and a decent pair of working hands. Now that I'm privileged to that wonderful schematic you posted, I would be remise to not rebuild before I apply the precious foam (haha). Thank you sir! I'll keep this updated.

QUESTION (depth) : What is the width measure on that speaker box? Seems like I could easily use my 10" subwoofer in your design. Any special consideration for me to take into account for possible measure adaptation?

QUESTION (port exist) : Does the port exist location matter for subwoofer application? If i place the port exist such that it is perpendicular to the subwoofer's driver face, would that produce unwanted consequences?

Once again, thank you!

First of all I don't know how the Fried 04 subwoofer enclosure would fit inside an automobile?

Here is a photo of the front of the enclosure showing the dimensions.

The vent is at the bottom of the enclosure.
It is 12" wide and 3" high.
The inside enclosure width is 12"
The outside width from the plans using 3/4" industrial grade particle board are 13.5", 36" in height and 23.5" in depth.
Mine are 14" wide, 36.5" in height and 24" in depth since I used 1" thick wood.


You want the anti resonant sound to be able to exit the enclosure so it can't be blocked.
I know that low frequencies pass through foam.
If I place my hand in front of the vent while playing music I can feel the anti resonant bass exiting line terminus.

In Vance Dickason's Loudspeaker Design Cookbook 4th Edition he states that low frequencies do not pass through dacron as well as wool.
He never goes into enough detail about foam for transmission lines for stuffing.