w15cy in a voigt pipe

[sergiof]

good evening (and by the way, happy birthday!)

it's been a while since i started to whirl my mind into a sound system of which i would really be proud of. my first idea was to prepare a 3way loudspeaker, using a transmission line bassbox, in order to reach as low as possible (with good quality, obviously). for this, i had the incredible help of pkitt, to whom i'd like to say "thank you" once again.

the problem started when i decided to show my idea to my girl... well, the boxes are huuuuuuge, so i believe you're understanding what the situation is...

therefore, i came up with the idea of building up a pair of 2way loudspeakers (seas w15cy + fountek jp3 - digital crossover), plus a huge subwoofer, also controled by this crossver (in a rectangular prism shape, that would be discretely positioned near a wall)...

for the subwoofer i'll continue asking the precious help of pkitt in the mentioned topic (fiberglass TL). for the 2way speaker, i was thinking on a voigt pipe made out of fiberglass (for the seas W15CY), that would look something like... the B&W emphasis...

the problem is i never made a voigt pipe loudspeaker before, and the info i found is not very helpful (for a rookie like me) to design it... can some of you please help me designing something that "not bended" would look very much like an icecream cone?

thank you very much!

[Scottmoose]

You could try this mass loaded horn (or Voigt pipe if you prefer) as a starting point.

60in long; St=0in^2 (i.e. it comes to a point at the top), Sl = 42.25in^2 (suggest 6.5in x 6.5in). Driver down 30in from the throat. Vent centre 1in up from terminus, vent 2in diameter x 3.75in long. Line entire cabinet with 1in 'stiff' acoustic fibreglass & adjust this & vent tuning to requirements.

[sergiof]

vent?
hummmm... i was expecting it to be completely opened in the throat... horn-like kind of pipe (maybe i'm really talking about a horn)

[EDIT: as an example of what i was expecting...]


[and these are the B&W Emphasis... gorgeous looking speakers]

[sergiof]

ah, i ended up finding the BIB calculator... that's what i intended...

just one question: i used the Thiele-Small parameters given by John Krutke, and then i compared to the ones given by Seas and... shock! one has nothing to do with the other!

Seas/ZaphAudio
Fs: 38Hz/53,70Hz
Vas: 14L/6,20L
Qts: 0,36/0,53

is this normal???

[Scottmoose]

Well, there you go, although a BIB typically is folded once, so the cabinet is actually rectangular.

As for T/S variations, yes, that's normal; it often depends on exactly how they were measured.

[sergiof]

i'm sorry, i really had the idea that these kind of boxes (the BIB ones) were voigt pipes... my mistake...

thank you for your patience!

[Scottmoose]

Oh yes; they're just a tapped conical horn set to 1/2 wave tuning rather than 1/4 wave. They're still essentially Voigt style cabinets. Note that the BIB is a corner-horn design; it needs corner-loading to work properly.

[GM]

Technically, they are tuned to a 1/4 WL of some predetermined frequency since all pipes/horns have a 1/4 WL fundamental, but an open pipe or an expanding or contracting horn is a 1/2 WL resonator, so must be acoustically a 1/2 WL long once any boundary loading is factored in to get max loading to the desired F3.

From this we see that both of the Voigt (pipe) horns shown above will have a relatively high F3 with the understanding that what makes them a Voigt patent design is their use of a point source driver to back load a horn. Apparently, RCA didn't bother to cross patent their decade plus earlier designs with other patent offices. What makes his patent unique though AFAIK is the concept of loading the (pipe) horn somewhere along its length that best matches the driver's electro-mechanical-acoustical properties to achieve the flattest/widest BW practical.

GM

[GM]

Originally Posted by sergiof

is this normal???

These days, unfortunately, though there are (were) some manufacturers that did/do publish specs that while what you bought doesn't match per se, will work fine in cabs designed using published specs and one reason why I have always preferred prosound drivers. For others I typically ignored any specs and designed based solely on driver Sd and measured Fs.

With the design routine I used, the cabs were initially over-sized to a greater or lesser extent, though all could be adjusted in-room via vent damping and/or some form of electrical bass tone control, so for me, the theoretically main advantage of the T/S way of designing is getting the minimum speaker bulk for a given gain BW, and yet the few A/B comparisons I made, I found that technically under-damped designs sounds more life-like to me once tuned in-room even if they may not measure as the most technically correct/efficient based on the driver's T/S specs.

GM

[sergiof]

the biggest problem in searching for new loudspeaker enclosures (seen by me, as i believe these kind of enclosures exist for ages), specially when i'm far to be an acoustic engineer, is that i always end up being a rookie in any new approach i try...

so please, i beg you your patience (and believe in me, i'm learning with interest)...

i understood most everything both of you wrote except the sentence: "Note that the BIB is a corner-horn design; it needs corner-loading to work properly.". i'm gonna search for info in the BIB website i went before, but on the meantime, may i leave this as a question?

thank you!

[I saw... still, as this is gonna be an expensive experience, do you recomend me this approach for the project in mind?]