Your original design is basically fine as is with bottom vent, just may need to shift the driver location, so figure at what floor height you want it and adjust taper to suit; no need to fold it unless wanting a horn tuned to a low Fs.
Re edit: ?? so will just say that yes, there will be some comb filtering between the driver's, vent's outputs that can be critically damped at the expense of reduced vent output.
Re edit: ?? so will just say that yes, there will be some comb filtering between the driver's, vent's outputs that can be critically damped at the expense of reduced vent output.
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Once you have the pipe geometry you can fold and bend (within limitations), and what you decorate it with on the outide just has to fit ther inside.
Lots if cheap drbivers: CHN//CHP-50, If your art installation needs more bottom, add separate woofers.
dave
Re EDIT:
This is only concept massing atm. The speaker mount facing is show sectioned here...so Im saying normally the back plane of the enclosure would be planar/reflective whereas in this case there are no planar surfaces so there should be no chance of retransmission through driver cone or freq nodes/nulls?
I was thinking of maop 11
So you are saying if I want eg 30hz I should use a sub or fold?
This is only concept massing atm. The speaker mount facing is show sectioned here...so Im saying normally the back plane of the enclosure would be planar/reflective whereas in this case there are no planar surfaces so there should be no chance of retransmission through driver cone or freq nodes/nulls?
I was thinking of maop 11
So you are saying if I want eg 30hz I should use a sub or fold?
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Hehe...no its not an installation...just making the enclosures as art 🙂
AURASPHERE..."The Art Of Sound"...that kind of thing.
I do hybrid QRD/Helmholz studio acoustics...although this was at a friends cafe...but a deaf lady with a cochlea implant could actually hear properly on a saturday morning breakfast whereas she couldnt before. This is tuned to 600hz but because of the surface scattering and some other stuff means you can sit almost on top of it without resonance
Acoustics of listening space is of course part of the speaker system
This is what I wanted as the most popular driver for the basic Voigt Pipe went the way of the Dodo Bird, he found a suitable substitute, which in turn helps with (hopefully quickly?) finding others:
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For those in regions where they're sold, the Monacor SPH-60X is about the nearest I've found in both spec. & general design. Not identical, but ~near enough on Fs, Qt & Vas to be in the ballpark once production tolerance, different measurement methods are factored in. It's not as good as the RS unit was, but that little guy punched way above its weight, and it's still decent for what it is, with the bonus that it's still available.
Have been watching a lot of Real World Audio which has such a wealth of information...based on the information in
Since the size of waveforms in the subs are so large, they of course are not directive but rather low/high pressure zones (omni) right?
Has anyone tried a downfacing port and rounded horn form?
1. Round is vastly superior to rectilinear for laminar flow
2. The down fire has no redirection of the flow and once connected to the external air body is pumping in a solar pattern and using the boundary plane of the floor (assuming the enclosure is tuned to the listening space) ie is capable of using a much larger propagation area.
3. For tuning into the room, the height off the floor is a simple way to tune the port size
4. The internal base edging of the pipe could be fluted so as to successfully mate to the external volume
Relating to laminar flow and velocity optimisation; in the voigt pipe application relying efficiency and speed of flow, why are the internal facings not variegated/dimpled to assist in reducing drag since the air is moving quite fast ie thing golf ball/hulls of racing yachts?
It may seem negligible but its effects can be easily heard in master made Djembes in mali, which as far as fluid dynamics go, have helix dimpling sculpted in by hand and create the best sounding of all...which we employ on our synthetic djembes, its also stops the annoying over bearance of head ring...like this
Maybe they are newb questions...and sorry if so but would love some help on these points
Cheers
Since the size of waveforms in the subs are so large, they of course are not directive but rather low/high pressure zones (omni) right?
Has anyone tried a downfacing port and rounded horn form?
1. Round is vastly superior to rectilinear for laminar flow
2. The down fire has no redirection of the flow and once connected to the external air body is pumping in a solar pattern and using the boundary plane of the floor (assuming the enclosure is tuned to the listening space) ie is capable of using a much larger propagation area.
3. For tuning into the room, the height off the floor is a simple way to tune the port size
4. The internal base edging of the pipe could be fluted so as to successfully mate to the external volume
Relating to laminar flow and velocity optimisation; in the voigt pipe application relying efficiency and speed of flow, why are the internal facings not variegated/dimpled to assist in reducing drag since the air is moving quite fast ie thing golf ball/hulls of racing yachts?
It may seem negligible but its effects can be easily heard in master made Djembes in mali, which as far as fluid dynamics go, have helix dimpling sculpted in by hand and create the best sounding of all...which we employ on our synthetic djembes, its also stops the annoying over bearance of head ring...like this
Maybe they are newb questions...and sorry if so but would love some help on these points
Cheers
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I'm strapped for time this afternoon, but very quickly, & FWIW:
It is, but laminar flow is mostly irrelevant with the wavelengths involved at LF frequencies. As you get higher -potentially.
More or less per above; LF wavelengths are too long to be significantly disturbed by simple bends, which are often used as functional parts of (acoustic) LP filters. By & large, smooth flow simply tends to promote efficiency at the top end of the operating BW, where you least want it.
Yes, been done since the 1930s & earlier if we step outside audio reproduction & look at other fields. Plenty of down-firing commercial & DIY designs with fixed or adjustable enclosure heights above the floor or preferably a plinth to remove variations in construction from the equation.
Variations on the theme have been done, although there is little in the way of comparative examples indicating benefits. More common would be a hybrid horn (or exhaust for that matter) with, for e.g., a very high ratio final expansion stage to cause an abrupt but controlled drop in pressure.
More or less per above. A 'Voigt pipe' (whatever is meant by that term) is basically an offset driver horn inasmuch as it's a pipe expanding from the throat to the terminus. But 99.99% of all such pipes are functionally speaking just standing-wave generators, no more. There is no horn loading (i.e. in this context impedance matching) over any part of their usable BW, and even less in mass-loaded types, so assuming you've optimised the offsets & alignment so it tracks the desired response, then providing the expansion is sufficient to avoid slap-echo with minimally damped types, it should be rolling off progressively above either Fb or, say, 1.41x Fb if you've targeted a broader band load.
As I recall, the bass fundamental of a djembe lies in roughly the 65Hz - 75Hz region, but being an instrument of equal / more relevance are its tone regions about 2 - 3 octaves higher up, which is significantly higher than you'd want any LF back-load playing or group delay & directionality would become major issues. It's certainly higher than almost any VP would be playing. Absolutely no harm in doing so of course, but the value is unlikely to be particularly high relative to the fundamentals of the design: alignment, inc. Vb, length / expansion & mass-loading as appropriate, driver & terminus offsets, and damping. Do those well & the rest largely falls into the window-dressing category. Which doesn't make it any the less fun to play with of course. 😉
Thanks so much @Scottmoose for your detailed response
I realise I would have to mod the VP formulas but is there any issue you could see using a rounded cone type shape vs the rectilinear?
Its useful to have broad area facings implement small exoskeletal "quilting" or pleating as it increases the rigidity of the structure signficantly...so there is no overhead in doing it.
Thanks for the info 🙂
I watch a lot of Hexibase; great vids and the outcomes are always well detailed, I guess because its his day job. There has been a lot of mention of laminar flow efficiencies in the subs project...so Im mostly going off that...Im always a noob...as there is just so much to know hehe
I realise I would have to mod the VP formulas but is there any issue you could see using a rounded cone type shape vs the rectilinear?
Im thinking much more in terms of turbulence, noise etc The kinetic energy of the airflow has often been problematic esp when I was first doing subs so I guess that has stayed with me. Interestingly curves are just what I do with all design now because Im not using wood but rather a masonry medium and it just does not like corners in so many ways.
The construction method is usually sub mm accurate. Internal mould lines are generally 100 micron which is of course irrelevant but its just the nature of this method. Likely I would have to use an aluminium or CF floor plate to do that and also stabilise the whole lot...will likely be close to 35kg at a guess even in wood stone which is 0.6 the weight of concrete
Yep pretty close. I tune 14" to tie in with E and at 432hz reference (either B@40hz or E@61) depending on context.
Indeed!
Its useful to have broad area facings implement small exoskeletal "quilting" or pleating as it increases the rigidity of the structure signficantly...so there is no overhead in doing it.
Thanks for the info 🙂
Is it possible/advisable to replace the round exhaust with a rectangular bottom exhaust ?
Possible, yes, if you're willing to sacrifice some performance. So advisible -not so much. But it depends where your priorities lie -performance or aesthetics / philosophy or something else. That's not a reflection either way -we all pick & choose which compromises best suit our own requirements.
Believe it or not, it's also my day job these days. You want the honest view? Acoustic relevance for LF applications is roughly nil. But as I say, that doesn't make it any the less fun to play with. I've included (functional) vortex generators in some designs before now for e.g. Audible? Yes -just. Would I do so again? Probably not -there are better ways of working.
No 'formulas' that I know of beyond the same laws of physics we all work within; a 'rounded cone' shape however really is a cone, whereas a rectilinear (assuming there is a pair of parallel sides) actually has parabolic expansion, although since as noted they're both standing wave generators the practical relevance is about zero in most cases, and particularly when Vb swamps Vas. Which is a bit boring, but unfortunately (fortunately?) is the reality. So the short answer is 'no -no issue' because assuming you're not working with an extreme case, there's no practical difference & if a cone is your goal, you'll be fine.
A slightly different scenario since with subs you're dealing with a much more demanding set of contions as far as pressures & air movement is concerned. A wideband based VP has much less in the way of LF volume velocity etc. to handle. Its own challenges, yes, but outright volume displacement and turbulance, no.
Despite what Scott suggests it is possible— maybe --but requires some trickery. The Terminus will probably have more R and depending on sizing, might not be of sufficient cross-section.
Or at least i think so. Been having thot eperiments with a similar issue. I could see if i can work it out if you would like.
x
dave
Indeed, with the pioneers concluding that the average ratio limit relative to circular area is ~1:1.273.
Right, but while we can convert to a recilinear easily enough, he mentioned down-firing; since I designed that pipe with an offset vent to help reduce some of the upper harmonics, it'd need a fairly large increase in ducting CSA to get the length necessary to maintain the offset internally without changes in the alignment. Since we don't know the floor condition & how much elevation is wanted to step it off either the ground or a plinth, I'd say 'not advisible' (on current information). Might be able to if we know those of course.