A more interesting way that Bose deals with this (IMO) is U.S. Pat 6771787.
It doesn't involve off-setting the driver.
It doesn't involve off-setting the driver.
Off-topic:
But, if one does want to use driver location(s) to null pipe harmonics, refer to U.S.Pat 7886869, where they have it covered in spades.
I have verified it mathematically, and have taken it up to using 16 drivers. This cancels 8 consecutive odd harmonic modes, up to 17 times the fundamental. I guess beyond this point it becomes redundant.
But, if one does want to use driver location(s) to null pipe harmonics, refer to U.S.Pat 7886869, where they have it covered in spades.
I have verified it mathematically, and have taken it up to using 16 drivers. This cancels 8 consecutive odd harmonic modes, up to 17 times the fundamental. I guess beyond this point it becomes redundant.
Is there any work done on a tapered TL to handle the combing problems? Did B&W use this a tapered TL in their 1993 Nautilus design?
Oops! Ignore that! Apparently without waiting for the caffeine to kick in I had another 'senior moment'; the dip in question is the pipe's 3rd harmonic dip: http://hyperphysics.phy-astr.gsu.edu/hbase/waves/clocol.html#c1
GM
GM
If it's any consolation, I think I'm going to take out shares in Red Bull, the amount of the stuff I'm getting through. 
Scott's commiserating on the need for caffeine, which he's getting from energy drinks instead of coffee 🙂
Ah! Shows you how much attention I pay to advertising, I figured Red Bull was a local beer.
So RJB, long time no hear! How you been?
GM
So RJB, long time no hear! How you been?
GM
I bought a Red Bull once. One sip was all i needed to convince me to pour it out and never buy it again.
dave
dave
No, the wavelength in question is not a harmonic mode. The wavelength which causes the dip is equal to the line length. These wavelengths cause phase cancellation in the far field.
Bose dealt with the problem two ways; one was to amplify the pipe radiation to over-come the direct radiation, or to null the pipe radiation altogether (at that frequency).
There are several patents to back up what I'm saying. If you want the patent numbers let me know.
In post #3 the OP shows an example where the driver is off-set 0.25. This drive point nullifies wavelengths that are equal to the line length.
Bose refers to this as the 'end-cancellation frequency'.
Bose refers to this as the 'end-cancellation frequency'.
Right. Unfortunately I struggle with coffee, and since tea doesn't have enough caffeine these are the last resort.
Very well, thank you, GM! I've been here all this time, reading and studying your posts, but not posting myself. I've become obsessed (no exaggeration) with making round, curvy or otherwise alternatively shaped BiB's (for aesthetic reasons and for the challenge).
I've given away all my (previous) speakers to good homes (the various Klipsches etc.), and the current plan is to build a few simple "unfolded" BiB's with a few different drivers before committing to one "final" (ha ha) curvy build. The BiB is unfolded because of something you said years ago, (to "load the apex of the corner more directly"). Then the winner of that shootout will get built in a banana shape. Yes, a banana-shaped unfolded BiB. This will be the year I make a thread and post pics (*gulp*, I hope).
It's my white whale. I continue to be fascinated (and sometimes confounded) by your expert posts. Thank you for sharing them because it's the best hobby. 🙂
Bose patent number for 1wL cancellation solution
cochleus,
I'm aware of the Bose patents that null the pipe radiation altogether, but haven't seen one where they amplify pipe radiation; Could you please provide the patent number for that one?
Thanks!
James
cochleus,
I'm aware of the Bose patents that null the pipe radiation altogether, but haven't seen one where they amplify pipe radiation; Could you please provide the patent number for that one?
Thanks!
James
An old thread, I know, but this popped up in my feed again and I'd thought I'd add a few points:
1. Designing a TL for subwoofer duty is quite different to designing one for full range use. In the case of the former, you'd want to use as little stuffing as possible, as this introduces losses. In the case of the latter, it's best to design with stuffing in mind, as you'd want to attenuate any midrange sounds coming out of the vent. This can also be accomplished by using a chamber behind the driver.
2. Offsetting the driver in the TL to reduce or eliminate the "null" caused by the first harmonic works. However, the correct location along the line to locate the driver in order to accomplish this successfully can vary, based on the line's geometry. Hornresp however can be used to simulate an offset TL and locate the best position for the driver. I've built two such offset TLs, and they are documented at the links below:
The Subwoofer DIY Page v1.1 - Projects : The Boom Unit
The Subwoofer DIY Page v1.1 - Projects : Proof of Concept #6
3. Offsetting the driver in a TL is not without its consequences though. In this case for the gain in the useful passband width, you lose a little passband efficiency.
1. Designing a TL for subwoofer duty is quite different to designing one for full range use. In the case of the former, you'd want to use as little stuffing as possible, as this introduces losses. In the case of the latter, it's best to design with stuffing in mind, as you'd want to attenuate any midrange sounds coming out of the vent. This can also be accomplished by using a chamber behind the driver.
2. Offsetting the driver in the TL to reduce or eliminate the "null" caused by the first harmonic works. However, the correct location along the line to locate the driver in order to accomplish this successfully can vary, based on the line's geometry. Hornresp however can be used to simulate an offset TL and locate the best position for the driver. I've built two such offset TLs, and they are documented at the links below:
The Subwoofer DIY Page v1.1 - Projects : The Boom Unit
The Subwoofer DIY Page v1.1 - Projects : Proof of Concept #6
3. Offsetting the driver in a TL is not without its consequences though. In this case for the gain in the useful passband width, you lose a little passband efficiency.
.png)
Stuffing TL SUB
Hi Brian
I have som comments to your comments about TL for sub.
I do stuff TL sub, because it dampen the displacement and controls the cone movement. It is not a dense stuffing like a full range TL - but it is there.
Normally you only feed a sub with the lower frequencies and therefore the offset of the driver has little effect. The upper harmonics are filtered out anyway.
I use a coupling chamber in my HideAway sub, and idea I borrowed from G.L. Augspurger Loudspekaer on Damped Pipes.
Regards
Bjørn
Hi Brian
I have som comments to your comments about TL for sub.
I do stuff TL sub, because it dampen the displacement and controls the cone movement. It is not a dense stuffing like a full range TL - but it is there.
Normally you only feed a sub with the lower frequencies and therefore the offset of the driver has little effect. The upper harmonics are filtered out anyway.
I use a coupling chamber in my HideAway sub, and idea I borrowed from G.L. Augspurger Loudspekaer on Damped Pipes.
Regards
Bjørn