Ultra compact 2-3” TL design?

[Linnaeus]

Hi all,

I have a 3d printer and am interested in building a small transmission line enclosure for a 2 to 3 inch driver. Because I will be using a printer I can experiment with very complex TL paths.

The requirement is that the box is no larger than 7"x8"x8" but would preferably be as small as possible.

I haven't quite picked up all of the language but have built sealed speaker boxes in the past.

I am hoping that someone can point me towards the most compact enclosure (theoretical or otherwise) for a small driver. And ideally, a driver which is particularly appropriate for small enclosures.

Best,
Rob

 

[Linnaeus]

It would also be very easy to produce hypercube enclosures like these: http://www.diyaudio.com/forums/full-range/265053-hypercube-loudspeakers-54.html if that is a valid small enclosure design.

 

[Xaborus]

Hi Rob.

Transmission lines work on quarter wavelength theory. Basically the longest path length inside an enclosure must be 1/4 of a wavelength for that wavelength and up to be re-enforced from transmission line effects.

8 inches would equal ~1.7Khz, which is much too high.

At 16 inches pathlength would equal ~850Hz, still too high.
At 24 inches pathlength would equal ~560hz, still too high imho.

With short pathlength such as these examples, you would be better off creating a skinny bass reflex which may or may not re-enforce the bottom octave due to MLTL effects. Pretty much any skinny bass reflex is in essence a MLTL- but it may or may not re-enforce the bottom octave depending on path length.


I'd suggest a skinny ported or sealed enclosure. Ported enclosures can easily be simulated with freeware such as WinISD.

If you're looking for something unique, a good start would be to check out the Hypercube TC9FD.

http://www.diyaudio.com/forums/full-range/265053-hypercube-loudspeakers-12.html#post4128571

http://www.diyaudio.com/forums/full-range/265053-hypercube-loudspeakers.html

 

[Linnaeus]

Thank you for the response and good ideas.

What about a folded transmission line? What would be the minimum viable cross sectional area?

 

[Scottmoose]

Using a basic 1/4 lambda derivation only works (although is questionable there also since it ignores end-correction) for untapered pipes, and falls apart when taper in either direction comes into play.

Cross section in terms of the broader functionality is in itself not the major issue; internal volume is. You often see CSA expressed as some multiple of driver Sd but in practice there is no real relationship between Sd and pipe CSA. TLs / QW variations are inherently larger than vented boxes for the same F3.

 

[Linnaeus]

Thanks Scott - that helps.

Is there a driver out there particularly well suited for a small enclosure?

 

[Linnaeus]

Looking at this driver Dayton Audio ND91-8 3-1/2" Aluminum Cone Full-Range Driver 8 Ohm

Product Specifications
Nominal Diameter3-1/2"Power Handling (RMS)30 Watts
Power Handling (max)60 WattsImpedance8 ohms
Frequency Response70 to 17,000 HzSensitivity82.1 dB 2.83V/1m
Voice Coil Diameter1"
Thiele-Small Parameters
Resonant Frequency (Fs)70.7 HzDC Resistance (Re)7.8 ohms
Voice Coil Inductance (Le)1.24 mHMechanical Q (Qms)4.29
Electromagnetic Q (Qes)0.53Total Q (Qts)0.47
Compliance Equivalent Volume (Vas)0.05 ft.³Mechanical Compliance of Suspension (Cms)1.05 mm/N
BL Product (BL)5.63 TmDiaphragm Mass Inc. Airload (Mms)4.8g
Maximum Linear Excursion (Xmax)5.1 mmSurface Area of Cone (Sd)30.4 cm²
Materials of Construction
Cone MaterialAluminumSurround MaterialRubber
Voice Coil Wire MaterialAluminumVoice Coil FormerKapton® / Polyimide
Basket / Frame MaterialSteelMagnet MaterialNeodymium
Mounting Information
Overall Outside Diameter3.35"Baffle Cutout Diameter3.01"
Depth2.22"Bolt Circle Diameter3.66"
# Mounting Holes4
Optimum Cabinet Size (determined using BassBox 6 Pro High Fidelity suggestion)
Sealed Volume0.02 ft.³Sealed F3139 Hz
Vented Volume0.04 ft.³Vented F375 Hz

 

[mikejennens]

These might suit what your after. I've built a pair with the Aura NS-3 and am amazed by them. I'm in the process of building another for a pair of Mark Audio CHN-70's. And then a Fostex, and then another Mark Audio, and then....... They are great designs!!!

http://wodendesign.com/downloads/Woden-BabyLabs-081015.pdf

Mike

 

[GM]

Thanks Scott - that helps.

Is there a driver out there particularly well suited for a small enclosure?

Since this is for experimentation, then for smallest, look for high Fs, low Vas & Qts tuned to Fs/Qts.

GM

 

[xrk971]

Your 3d printer can probably make a nice Nautaloss speaker. It's a closed end TL and the volume constraint you gave will probably let you make about a 36in spiral TL.

http://www.diyaudio.com/forums/full-range/247598-nautaloss-ref-monitor.html

 

[Scottmoose]

Depends on what's wanted I suppose, at least in terms of LF output. Not that it's going to have a huge amount in either case. Default would be per GM above. I suppose you could go for a slightly higher Q unit & a small peak in the alignment to give the impression of greater LF extension than is actually the case, although this rather goes against the point of using a TL, so not something I'd be inclined to recommend!

 

[Linnaeus]

Hmmm... Well seems like the size I would need for BR / TL would not be feasible. Physics and whatnot...

The Nautilus style is interesting, and would definitely be possible. If I wanted to go for that the largest I could do is 8"x8" - maybe I could square it up a bit for more volume or print it as two pieces. Another option is a ported tear-drop shape.

This is just a 10 minute sketch, but would a design like this be viable?