Voigt Pipe Design

Hi All,

Following the astounding success of my first full range design, I want to go onto something a little more interesting. I am trying to get my head around the Voigt pipe design and have a few queries and parameters I am hoping to confirm which will hopefully be clarified by the below picture.

1) The total internal height from apex to floor (including port) should be 1/4 of the driver's F0, correct?

2) The driver should be mounted about 50-60% of the way down the front baffle (by baffle I mean the front panel not including the port - see picture)? Is there an accepted standard position?

3) The pipe volume should be equal to or larger than the driver VAS, correct? Does the pipe volume used for this calculation include section B or only section A? Is a volume larger than the VAS preferable and if so, how big is too big?

4) Is the portion of the wedge above the driver normally stuffed or just damped?

5) Is the portion of the wedge below the driver normally covered with damping material? Is it ever stuffed?

6) How large should the port/mouth/hole be?

I am trying to model this thing in hornresp which is my first real attempt to use the package. I figure the TL design section is probably the bit to use. Regarding this...

1) Is the overall length of the TL in hornresp equal to the height of the Voigt Pipe or only the length above the port?
2) is the mouth area of the second interval in hornresp equal to the port hole area or the area of the wedge at the top of the port?

Any other thoughts or suggestions?

Any advice is much appreciated.

Regards,

Greg

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This is one of those 'Some say he only knows two things about ducks, and both of them are wrong' scenarios. ;) Not that there's anything wrong with that at all given how much bad information is out there on Voigt style tapered pipes. So, in order:
  1. No. The resonant frequency of a pipe is a function of its axial length and taper, and there is no requirement to tune to Fs. In many cases you'll be better off not doing so.
  2. Sort of, although it depends on the acoustic length & tuning of the pipe, and whether it's mass-loaded or not so there's no fixed answer per se, although when in doubt 50% is a good starting point & won't do anything catastrophic
  3. Usually, although in most cases Vas isn't used as the sole determining factor
  4. Stuffing is damping, so you're to a point answering your own question there. In more detail, depends on the design, but except in very particular cases, a good example usually only needs decent lagging on the rear and one side baffle as you'll be trying to minimise the pipe harmonics through geometry, driver, vent positioning & proportions etc.
  5. As per 4. above
  6. There isn't a fixed value as it depends on the type of pipe & alignment you're targeting (?)
If you can let us know what you're trying to do (and what driver) we can probably give you some more pointers.
 
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Hi Scott,

Thank you for taking the time to answer my questions. I see there is more to this than some of the sites I have seen make out!

Haha, I guess by stuffing vs damping I was trying to differentiate between something like polyfill stuffing and something more dense but thinner glued to the enclosure walls. Which I believe is the "lag" you refer to right?

I would probably use the Alpair 10P which I believe you are intimately familiar with. The 10M is tempting given its slightly lower Fs, but I very much like the sound of the paper and suspect it might have a more pleasant top end than the metal. I see you posted a possible design in my other thread, thanks very much. Is that what you would recommend for the 10P?

Sorry for the noob question but what exactly do you mean by alignment in this context? One speaker will be in a corner and one up against a wall. I am just seeking a little more bass extension than my QBB4 box. Not that I need it, but there's always the desire to improve and build the next thing.

I will likely copy your design as I imagine it is pretty close to optimum for this driver, thanks again for sharing. However, I'd love a better understanding of how it all works and how one goes about designing these things. Potentially even advice on modelling it in hornresp. So any advice and explanation would be most appreciated.

Thanks,

Greg

Greg
 
Thanks Dave and Leif,

Yes I am still considering the Pensils but something about the Voigt Pipe really appeals to me. Still contemplating.

Thanks for the Plans Dave, they look good. I will go have a read of quarterwave.com and see what I can learn.
 
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My daughter and I built a pair of folded voigt pipes for her dorm room when she left for college in 2002. We used the RS 40-1354 drivers and a back firing tweeter. They still sound great in her daughter’s ( my grand baby) bedroom.
 

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1) Is the overall length of the TL in hornresp equal to the height of the Voigt Pipe or only the length above the port?
2) is the mouth area of the second interval in hornresp equal to the port hole area or the area of the wedge at the top of the port?
 

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Note the pensil sim above is over-damped in the LF & with slightly more of a null at F3 relative to as-designed.

I'm certainly not going to chip in on using Hornresp with David here for obvious reasons. ;) However, as a general reference, the total internal volume excluding that taken up by the driver, any bracing or ducting etc. [as relevant] is functional and should be accounted for.

'Alignment' refers to the acoustic alignment i.e. tuning and shape of the rolloff, many of which are direct equivalents to those found in electrical filter theory; stock mathematical versions for vented boxes include QB3, B4, BB4, SBB4 & so on & so forth. There's no obligation to use them though, and typically they date from a time when most people would derive an alignment for a given type of enclosure load (e.g., sealed, Helmholtz-based vented) from available alignment tables or their underlying formulas, because modelling hardware / software and / or measurement gear was either unavailable or unaffordable, and many would find it impractical to manually calculate a few dozen spot-frequencies and draw out a curve on graph / coordinate paper for every variation they wanted to look at. Ditto for potentially building multiple test boxes.
 
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Hi All,

Thanks to the pointers above, I have been playing around with Hornresp and it is starting to make some sense. I would be interested to know if the design below looks viable and if I have properly set it up in Hornresp? I see the examples above did not use conical horn lengths, but I would have thought that would be what's required for a Voigt Pipe?

I still have some tweaking of the stuffing to do (probably a little needed in the lower half) and have not yet considered the bracing - that comes next. Also given the size, I might have a go at a folded design. It's a little large and I may shorten to 1.8m, still contemplating.

Anyway, any thoughts on the basics of the design and whether I have properly configured Hornresp would be great!

Thanks,

Greg
 

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At a very quick 1st glance (I'm off out in a minute as I've just hit 45 & to mark the occasion I'm going to wander around the local museum) it looks in the right direction.

I wouldn't bother with a folded Voigt. If you want a compact box for that unit, you might as well build a simpler MLTL & have done with it; there's no real functional advantage to the tapered design in this context other than the aesthetics.
 
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yes, sort of, likely not reach that high. Usually i would first try a bit longer (lower-tuned) terminus. It is the knee at the bottom you want to be less sharp. It is an anechoic sim and you are putting it in a room (i assume).

My usual 1st approximation is that in room F6 will become “flat” in room (not many rooms are “flat")

dave
 
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Hi All,

I would be interested to know if the design below looks viable and if I have properly set it up in Hornresp? I see the examples above did not use conical horn lengths, but I would have thought that would be what's required for a Voigt Pipe?

Greets!

Lacking the math skills and only knowing it from my decades long gone help from the local Altec distributor/pro installer, I had a 'Devil' of a time convincing folks that any horn with parallel sides was parabolic until DMB proved it in HR, so technically correct, though with damped pipes I can't imagine anyone hearing a difference in a blind A/B comparison.