Transmission line design

[Sponge]

I have a question about 1/4 wave length transmission line cabinet design.
Is it better or harmful to have the vent exit close to the woofer driver?
Most designs seem to place the exit as far from the woofer as possible.
I am not sure if that is for ease of labyrinth layout or a technical reason.

Thanks for any help.
Glenn

 

[Speedskater]

Transmission line loudspeakers are a rather specialized design. Someone at this foru might be able to help:

Full Range - diyAudio

Full Range -

www.diyaudio.com

 

[TLS Guy]

I have a question about 1/4 wave length transmission line cabinet design.
Is it better or harmful to have the vent exit close to the woofer driver?
Most designs seem to place the exit as far from the woofer as possible.
I am not sure if that is for ease of labyrinth layout or a technical reason.

Thanks for any help.
Glenn

It really is a matter of design convenience and practicality. The driver needs placing at the first node of the third harmonic, to help avoid exciting it. That is still a high pressure low displacement zone. The port is the open end of the close pipe. This is a zero pressure high air displacement zone. Generally there is one fold. This is to keep total enclosure length down, but more importantly to shut of port radiation of higher frequencies.

So that is really the reasons the designs look the way they do.

The length and volume of the pipe have to be carefully matched to the T/S parameters of the driver, and driver selection takes great care. In addition getting the taper, port size and the weight of the damping material correct is also crucial. Unfortunately their are a lot of opportunities to make serious errors along the way

Having said that though, the effort and resources involved are full justified by the end result. Properly designed these speakers eclipse all others in bass quality and especially even distribution of bass in the room due to inherent pipe properties.

Some pictures might help you.

The line.

Relationship of driver and port of this in wall sub.

End result.

 

[TheWarrior]

You can have the vent placed on the front, on the top,..... that does not matter.

It does matter to ensure a smooth taper from the coupling chamber to the vent, and that the full 'line' is the correct length, of course.

http://diyaudioprojects.com/Technical/Papers/Loudspeakers-on-Damped-Pipes.pdf
http://www.quarter-wave.com/TLs/Alignment_Tables.pdf

Those are probably the most comprehensive TL resources published on interwebz.

 

[Sponge]

Thanks for the replies.
This was my first attempt and I really liked the low end.
I want to make a 2-way unit and have the tweeter and woofer at the top front of a 42" high cabinet.
I was hoping to move the vent up close to the bottom of the woofer so the grill does not have to extend all the way to the bottom.

 

[TLS Guy]

Thanks for the replies.
This was my first attempt and I really liked the low end.
I want to make a 2-way unit and have the tweeter and woofer at the top front of a 42" high cabinet.
I was hoping to move the vent up close to the bottom of the woofer so the grill does not have to extend all the way to the bottom.




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Very nice work. I hope it sounds as good as it looks. The only way you could do what you want is to make another turn. The speaker would then be shorter but deeper.

One word of caution. At the mouth of a TL working properly there is a lot of air displacement (air movement). However the pressure is zero. There is always a node of pressure at the port. So that means there must be NO resistance at the port. Loudspeaker grill material should not be used to cover a TL port unless you can have a good deal of clearance between the grill and the box surface.

 

[Pogre]

Very nice work. I hope it sounds as good as it looks. The only way you could do what you want is to make another turn. The speaker would then be shorter but deeper.

One word of caution. At the mouth of a TL working properly there is a lot of air displacement (air movement). However the pressure is zero. There is always a node of pressure at the port. So that means there must be NO resistance at the port. Loudspeaker grill material should not be used to cover a TL port unless you can have a good deal of clearance between the grill and the box surface.

That was actually the thought I had when I read that part. I wouldn't think you'd want to cover the port opening like that.

 

[ryanosaur]

Very excited to see this thread! I’m still trying to get my life in order so I can start my first TL project. (Life in order means appropriate income, free time, and wife-on-board, and ability to problem solve the design! )
The Mass-Loaded TL Phil3s are wonderful. I suspect going all in on tapered 1/4 wave line designs will be very worthwhile based on all research and conversations I’ve had.
Cheers, all!

 

[ryanosaur]

That was actually the thought I had when I read that part. I wouldn't think you'd want to cover the port opening like that.

Would a metal mesh that is roughly 80% open air work?

 

[ryanosaur]

I have a question about 1/4 wave length transmission line cabinet design.
Is it better or harmful to have the vent exit close to the woofer driver?
Most designs seem to place the exit as far from the woofer as possible.
I am not sure if that is for ease of labyrinth layout or a technical reason.

Thanks for any help.
Glenn

Curious to see a more clear explanation if possible. I’ve read a lot of material and couldn’t find the source... *blushes
Thought I had read that the best location for the terminus of a closed line would be next to the driver itself. My understanding, at a novice level, is that the line should solve any phase concerns, thus terminus placement next to the driver results in stronger sound reinforcement.

@TLS Guy, if you might, please, offer any clarification? Many thanks!

 

[Verdinut]

Curious to see a more clear explanation if possible. I’ve read a lot of material and couldn’t find the source... *blushes
Thought I had read that the best location for the terminus of a closed line would be next to the driver itself. My understanding, at a novice level, is that the line should solve any phase concerns, thus terminus placement next to the driver results in stronger sound reinforcement.

@TLS Guy, if you might, please, offer any clarification? Many thanks!

In ny opinion, considering the wavelengths of the frequencies involved with the TL tuning and operation, the location of the vent with relation to that of the woofer is not important. It's the same situation with a bass reflex enclosure.

 

[Sponge]

Very nice work. I hope it sounds as good as it looks. The only way you could do what you want is to make another turn. The speaker would then be shorter but deeper.

One word of caution. At the mouth of a TL working properly there is a lot of air displacement (air movement). However the pressure is zero. There is always a node of pressure at the port. So that means there must be NO resistance at the port. Loudspeaker grill material should not be used to cover a TL port unless you can have a good deal of clearance between the grill and the box surface.

I agree there is lots of air movement but I owned ESS Amt towers and that was quite a heavy fabric they used and it was basically right against the cabinet.