Narrow space - tube sub

[johnr66]

I have a desire to build a small sub for a narrow space. I was wondering about firing a 4" or 5-1/4" driver in to a tapered pipe so that the opposite end from the driver is a smaller port. This seems to be what Bose does with the wave radio except that in this case, the tube is not folded up.

The sub would be for general low level listening. Not expecting major SPL, just some reach down to around 40 Hz as the mains speakers are weak below 70Hz.
Thanks

[OscarS]

So pretty much a transmission line without folding the line to have the output on the same plane as the driver?

[cochleus]

You could scale this down a bit...

http://www.firstwatt.com/pdf/art_elpipeo.pdf

[bjorno]

Originally Posted by johnr66

I have a desire to build a small sub for a narrow space. I was wondering about firing a 4" or 5-1/4" driver in to a tapered pipe so that the opposite end from the driver is a smaller port. This seems to be what Bose does with the wave radio except that in this case, the tube is not folded up.

The sub would be for general low level listening. Not expecting major SPL, just some reach down to around 40 Hz as the mains speakers are weak below 70Hz.
Thanks

Hi,

Here is a suggestion of very small footprint subs (single-folded) both reaching below 40 Hz that should be listened at short distances:

b

[djk]

I would build a Bose Wave Cannon.

For 40hz the overall length should be about 84". The front pipe length should be about 1/4 the total length, or about 21". Ideally, the ends of the pipe would be 42" apart, as the Bose car systems do.



4" cardboard mailing tube, or 4" schedule 40 PVC pipe would be fine.

The original Bose radio-cassette boom-box used a single 4-1/2" driver driving an 84" (total length) plastic labyrinth, and it impressed me (other than the price).

[johnr66]

I decided to do a double fold TL in plexi. I built this box this afternoon. Internal length is 29" long with 5 x 5.5" folded tube. Calculated resonance is 39Hz and that is exactly the frq where the cone moves least. Driver is a 5-1/4" out of an old small speaker. I have no specs on it. Bass is really impressive from such a tiny driver. I'll have to try more TLs

Geez. Only 1 day into the new year and I already built a speaker.

Edit: I was playing some sine wave sweeps and get decent bass starting at 28Hz in my listening room.

[cochleus]

Nice job John! And fast too! I like the see-through look. Maybe some LED lighting?

Bose has stacks of patents on "pressure wave transducing" if your brain is up to it.

WARNING: TL's are addictive

[johnr66]

Originally Posted by cochleus

Nice job John! And fast too! I like the see-through look. Maybe some LED lighting?

Bose has stacks of patents on "pressure wave transducing" if your brain is up to it.

WARNING: TL's are addictive

Thanks! I have some acrylic fabrication experience and had a lot of those scrap strips lying around. I'll probably try a larger one in MDF. Thicker acrylic is very expensive and gets very heavy.

I need to put stuffing in the box as there is some pipe resonance, like the sound when talking into a long pipe. I do like the LED idea.

As expected, cone excursion goes huge below tuning. The single ended chip amp with single 9 volt supply makes the cone do 5mm which must me near the xmax of the small driver.

[cochleus]

Try rolling off the band-width (at both extremes) going into the waveguide. Also, you can drive the pipe at points other than the very end (at the closed end all of the possible standing waves have a common pressure node and are thus maximally excited). If the driver is positioned correctly this can also eliminate what is called "end-cancellation" where the wavelength that is equal to the pipe length emerging out-of-phase with the exterior pressure wave. Another option is that you could drive two separate waveguides, one on either side of the driver (what djk was referring to in post #5) Bose patent #4628528
I'll also refer you to Quarter-wave.com, a really awesome site.