18 to 22mm is enough. It is open cabinet.
there are 3 different types of so called Voigt cabinets:
1. Voigt pipe. Cabinet is straight, driver position is at 1/3 lenght from St, Sm is open without port at the top, with the sealing.
I built one long time ago was explained in Elector magazine.
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2. Straight TQWT, driver is somewhere more than 1/3 lenght (can be calculate exact), the Bass reflex port is at the mouth. Could be position in reverse, so the port is with the floor. I didn't build this type
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3. Folded TQWT pipe, folded line. Everything is same as for Straight TQWT, but port is with the floor and shape of course is folded... I build several of these types even with 15in drivers.
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Stuffing is mostly in smaller part of the box below driver position, and there are more preasure in that part.
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Software to simulate optimum dimensions vs driver TS parameters is M. J. King Matcad sheets.
But I think that MCD sheets are not available for free any more?
http://www.quarter-wave.com
and link
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The sound of these designs is very very good, natural, good LF.
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Assuming parallel sides they're a parabolic expansion; technically a mass-loaded (to some degree) horn with an offset drive unit, though functionally they're a standing-wave generator since they're rarely impedance matched at any point in their usable BW. I wasn't going to say it, but like many of the Youtube projects, that 'World's second best...' isn't a particularly good example of the type.
Leaving the toxic aspects of lead aside, it's potentially difficult with bass cabinets until there's sufficient in there to lower panel Fs and its first 2-3 harmonic modes < the box operating BW. Since it's a bit of an inefficient solution to the problem, it's often easier / safer to use a decently rigid material, braced sufficiently to shunt the panel modes & their Q above the box operating BW to where they're no longer an issue.
Leaving the toxic aspects of lead aside, it's potentially difficult with bass cabinets until there's sufficient in there to lower panel Fs and its first 2-3 harmonic modes < the box operating BW. Since it's a bit of an inefficient solution to the problem, it's often easier / safer to use a decently rigid material, braced sufficiently to shunt the panel modes & their Q above the box operating BW to where they're no longer an issue.
The only use of lead is to overcome the bad attitude of wood in refracting sound i.e. to make it soundproof
If you want to inject into your veins some lead powder, why not some mercurium?
If you want to inject into your veins some lead powder, why not some mercurium?
I hesitate to dip into this can of worms again, but how can the panel modes be raised above the box operating bandwidth when the box contains drivers covering the full audio bandwidth?
I heard a few voigt pipes and all of them sounded nice. Also that TB fullrange is good.
But, when I hear that something is "the best in the world...or similar" I get an allergy 😀
Because the box is not covering the full BW. Bass enclosures are only acoustically functional for a very limited BW. So in this case, the object is to raise the panel modes above the region in which the enclosure is operating,where the maximum amount of energy is available to excite the panel modes. Since the actual amount of energy emmitted also drops rapidly as frequency rises, and by using high-rigidity panels with a high Q, there's very little left to excite them. That's why belting boxes with knuckles etc. can be a bit misleading -it's not really representative of actual operating conditions. Something like CRS is actually rather good in this sense -it rings like a bell if you hit it, but not anywhere it's ever likely to get excited, and what is left is quite easily damped out with much less material.
Agreed -I get a Herbert Lom twitch whenever I see 'World best' etc. There was a priceless one about 20 years back, allegedly with a UK patent (unsearchable, obviously) for a sealed TL with concrete deflectors, a cheap Alpine 6x9 car driver and an off-the-local-electronic-store-shelf EQ that was marketed as just that -IIRC it was even their site name, or something close. Says it all. 😉
The 1808 is a nice unit (less convinced by the 1772). There are quite a few dodgy pipes out there though, unfortunately.
Thanks Scott. So when you say 'the region in which the enclosure is operating' you're thinking primarily of quarter wave enclosures (of one kind or another), and of the range in which their resonant behaviour augments the driver's output? So, up to 2-300 Hz, typically? Or do you mean the region in which there are significant enclosure resonances? (Hornresp models tend to show lots of resonances right up to the max displayed frequency of 2K, most of the time, although that's without absorbent lining/stuffing.)
Pretty much. Basically, it's for any back-loaded bass enclosure -be it a Helmholtz, QW variation etc. Vented boxes, whether they're based around cavity resonance or standing waves will almost always be rolling off quite quickly above ~150Hz in practice, and bass horns are only really functional / usable up to the driver's mass corner, providing that falls below roughly 300Hz & then only if the expansion path isn't excessivlely long & you've got a decent acoustic LP in place -if you haven't, a bit of panel resonance is probably going to be the least of your troubles. 😉 So providing you can shunt the panel modes an octave (preferably more, but that's a reasonable minimum) higher than, say, the 3rd harmonic in the case of pipes, bass horns etc. then it's rarely an issue and quite small amounts of panel damping can generally kill off anything remaining.
Midrange boxes or HF driver supports on the other hand -that's a place where lowering panel Fs can be more practical, and are also less likely to put your back out...
Midrange boxes or HF driver supports on the other hand -that's a place where lowering panel Fs can be more practical, and are also less likely to put your back out...
Right, conical if tapered or parabolic if there's any parallel flat sides as Scott noted.
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It is easy to show that the energy available to excite a resonance decreases 2nd order, there are arguments for 4th order. The above curves are the right shape, where they sit on the x axis is an educated guess.
dave
I'm a professional commercial cabinet builder. Poplar plywood (poplar core layers) is not suitable for many things. Voids are common, and I have seen poor quality stuff that had severe core layer delamination that rendered it useless. It also doesn't take screws or staples well, and not even cut without failure.
An octave spread is a 2:1 ratio = +/-6 dB = 4th order, so why is there any debate? Regardless, the acoustically tiny air pockets will be in the HF whereas IME panel resonance ideally needs to be raised/lowered at least an octave from box tuning, so normally can't excite nor be excited by the mids, HF.
Fh = Fl*2^n
Fl = Fh/2^n
n = ln(Fh/Fl)/ln(2)
where:
Fh = upper frequency
Fl = lower frequency, or the XO point in this case
n = octave spread
ln(2) = 0.6931
Fh = Fl*2^n
Fl = Fh/2^n
n = ln(Fh/Fl)/ln(2)
where:
Fh = upper frequency
Fl = lower frequency, or the XO point in this case
n = octave spread
ln(2) = 0.6931
It's connected though, as GM (and to a much more limited degree I) mention. That's why you need that panel Fs to be an octave or more <> the XO (HP or LP as-relevant corner frequency), to ensure they're out of the way & unlikely to be excited.
I knew I should have left those worms in the can.
I asked a very specific question, Scott, about what you meant when you advised raising panel modes "above the box operating BW" - because this thread is about a plan to build voigt pipes with full-range drivers. So the OP's boxes will be "operating" over the full audio bandwidth. You explained what you meant, graciously and helpfully. I appreciate that. And I didn't express any disagreement with anything you said.
So I find it quite depressing that people pile in with posts that seem to want to put me right about something that I expressed no opinion about.
I asked a very specific question, Scott, about what you meant when you advised raising panel modes "above the box operating BW" - because this thread is about a plan to build voigt pipes with full-range drivers. So the OP's boxes will be "operating" over the full audio bandwidth. You explained what you meant, graciously and helpfully. I appreciate that. And I didn't express any disagreement with anything you said.
So I find it quite depressing that people pile in with posts that seem to want to put me right about something that I expressed no opinion about.
The same applies to a single driver enclosure, pushing resoanmaces above the BW would be impractical, as high as possible is what one should to attain — usng this approach.
The graph shows the okeihood of the input energy (mostrly reaction force from the driver movement) being able to excite any resoances — the amount of energy that is in the music at those frequencies.
2nd order is right iout of the physics of how a dynamic driver works. Adding 2 more is a not as obvious.
And if the Q of the resonance is high the music is unlikey to have sufficiently continuous HF notes to feed into it sufficient energy to excite it.
dave
The graph shows the okeihood of the input energy (mostrly reaction force from the driver movement) being able to excite any resoances — the amount of energy that is in the music at those frequencies.
2nd order is right iout of the physics of how a dynamic driver works. Adding 2 more is a not as obvious.
And if the Q of the resonance is high the music is unlikey to have sufficiently continuous HF notes to feed into it sufficient energy to excite it.
dave
OK, 2nd is +/-3 dB, but AFAIK 'we' normally design TLs, etc., in % of octave spreads, not its -F3 dB point.
If I may chime in:
I had the same exact plan as you and this video was my "gateway" into speaker-DIY. And let me tell you: The more you find out about speaker-DIY, the more you might dislike that guy. Not because his facts are wrong (they aren't), but because he over-engineers his speakers to extreme lengths. Yes you can calculate, design and buy the absolute best and execute a "perfect design for the worlds second best speaker".
But long story short: DIY is much more than "doing the absolute best. period".
it's about doing it yourself.
Concerning your Voigt Pipes:
I built them, same as you with W8 1772. I built them very very accurately according to his plan. And they sounded good, nice TMLs with a resonant bass. But they lacked the "sound-body", they lacked "oomph".
Then I went ahead, cobbled together some BIBs from MDF with the W8 1772.
And guess which speakers I will keep for the future? Right, the sloppily built BIBs.
Do yourself a favor and build the BIBs. If you have the space for a Voigt Pipe, you have the space for a BIB, so why not use it instead of "wasting" it?
https://speakerprojects.wordpress.com/cabinet-types/bib-loudspeakers/bib-calculator/