calypso pvc boombox

[calypso]

hi all

i'm trying to build a boombox (= not so much audiophile play music for people outdoors) based on pvc pipes
if i'm able, the boombox would be enhanced by another pipe that will turn the speaker from *kinda* vented to *kinda* transmission line.

i'm a noob in speaker construction. yes, i already did some works, but always in a try&fail way. this time my approach will be somehow the same, but i will spice it with the little knowledge acquired by reading this forum.
a great thanks to all of you that sometime will toss an help to this. already a big help came from saturnus and his boominator concept, and arjenshenzen for some inspiring answers he gave to my silly questions.

anyway, i give you some idea of this
the final system will be (in the best hope) four "u" shaped pvc pipe.
on top of them there will be 4 coax 6x9 speakers for car audio.
those 4 coax speakers will be fed by two arjen's ta2020 mkiii amps.
the amps will be housed in a separate plastic box.
the energy source will be housed in a separate box/module.
all of this stuff shall be easily arrangeable, meaning that i will be able to bring music with a single pipe (losing a channel), the amp box, a battery. average use will be two pipes without transmission line extension, amp box, and if i'm lucky a solar panel.
intended usage is boombox for outdoor, transmission line for indoors.

the names i'll use:
1) speaker pipe - a 60cm long, 20 cm large pipe, ending with a reduction that acts as a 5cm circa vent
2) extension pipe - a 120 cm pipe composed of a 180° turn ending in a long straight pipe that shall realize a transmission line enclosure when joined to the speaker pipe.

---- strange/silly/poor man approach that may turn in big ups or big downs
- speaker pipe - housing will be pvc pipe. tricky: this won't harm so much for transmission line, where resonance doesn't matter. will harm instead for the speaker pipe, but i'll add car damping material and cross fingers.
- speaker pipe - 2 will have a 20cm to 16 cm reduction. 2 will have a 20cm to 12.5 cm reduction - tricky: i can combine them to have two identical behaviours in the two channels, or mix two different behaviours for bass, thus enabling a more sustained bass - graph will explain.
- extension pipe - two 90° degrees elbows - tricky: i can manage where to direct transmission end; risky: not really circular.
- extension pipe - will have a fixed width, so tapering will be only the reduction on speaker pipe - risky: everywhere is said that transmission line shall be tapered in the most progressive possible way.
- extension pipe - 2 will end with 82% of the piston area, 2 will end with 48,5% of the piston area - hazardous: even dwarves say that transmission line end shall be at least the piston area.
- amp box - plastic. risky for cooling and grounding, but can be managed. tricky for style - will have a transparent opening that claims "don't touch switches behind me - just look at them".

intended usage of this thread: people noob and dumb as me shall understand that building a pvc pipe boombox is easy.
all those details are to clarify ideas for better enhancement. when all this will sound, a webpage will summarize all of this.


+++ big question is: what will come out of this could be still called transmission line? or punky pvc pipe resonator? or silly speaker?

driver t/s specs
fs 67hz
qms 3,23
vas 25,2 liters
cms 0,337 mm/N
mms 16,79 g
rms 2,179 kg/s
xmax 3,5 mm
xmech 5,25 mm
dia 171 mm
sd 229,3 cm²
vd 0,9 liters
qes 0,77
re 3,2 ohms
le 0,62 mH @1khz
le 0,07 mH @10khz
z 3,84 ohms
bl 5,4 Tm
qts 0,62
no 0,949%
1-w spl 91,92 dB
2.8-v spl 95,9 dB

i choose this tuning for speaker pipe:
will use winisd pro for simulation
60 cm long, 192mm large cilinder, vented box with large diameter and 5cm vents. 17.3 liters volume.
vent will be circa 5cm, - the two reductions have different necks 'cause they reduce to two different diameters

winisd simulation for speaker pipe (not trasmission line)
scale is from 100hz to 600hz, up to 15db
yellow line describes what will happen at the speaker pipe with the 12.5 reduction. this reduction acts as a vent and will be long circa 5cm
green line describes describes what will happen at the speaker pipe with the 16 reduction. this reduction acts as a vent and will be long circa 5cm



looks like speaker pipes have an fs over 100 hertz. i was thinking to build a an input capacitors switch for a 100hz bass cut. this mainly for saving power outdoors. <--- is this still necessary? or the raised fs will be itself an energy saver for the amp?
by arranging two speaker pipes with different vents, i will obtain a complex response by the boombox. <--- help please! am i right?

how shall i see this if used outdoors? is there a way to tune winisd tu simulate outdoor behaviour?


i choose this tuning for transmission line
taper only once, 60cm after the driver
tune to 10hz less of my fs as suggested for high qts driver like mine: fs is 67hz - tune to 57hz: 6.0175m x0.9 woolstuff cofficient = 5.41575 /3 = 1.80525 ---> 180cm
1/3 wavelength to enhance bass response
180 cm long line, u shaped. starting with 126% of piston area, tapering and ending at 82%/48,5% of piston area.
first 60 cm have 20cm of diameters. then a small reduction tapers to 16cm/12.5cm diameter. after this point wool dampening, then a 180° turn that shall be long 40cm. then a straight line that is 60cm long. (where is the 5cm vent? inside the 180° turn!)
since with transmission lines resonance is not a big problem, i won't damp pipe sides. and i'll glue the joints as less as possible, to be free to orient them "depending on the stage".
a transmission line simulator that can accept my settings will be very tricky. do you know some?


pipe diameters
20 cm pipe has an inner diameter of 192mm, car damping foil is 1mm thick = 190 mm
16 cm pipe has an inner diameter of 154mm = 154 mm (car damping foil is not necessary, will be used wool for damping)
12,5 cm pipe has an inner diameter of 119mm = 119 mm (car damping foil is not necessary, will be used wool for damping)

amp module arrangement
i will put two arjen's ta2020 mkiii in a plastic box for house electric switches.
a panel mount fm/usb/mp3 player will feed them. player will have an aux input that can be passed to amp.
the aux input will be a mix of two input jacks. a four-or-more gang rotary pot will be arranged to act as fader between the two inputs.
>>>> intended usage should be: put usb key in the panel, hook cables, power on, and press play. second time: power on, press play.
intended voltage is 12v. a momentary on/off switch will feed a panel mounted voltmeter. i will put a 12v socket to light my cigarettes with a skeleton shaped or pool ball shaped electrical lighter.

solar panel - battery
best way shall be as saturnus did for boominator.
i already own three 12ah/12v sla batteries. shall be ok. but when i'll feel doomy i'll switch to lifepo: them say lifepo enhances class d amp behaviour, do you confirm this?

[calypso]

any help/answer/question/toss of a coin is warmly welcome.

[GM]

FYI, I was going to reply to your TL design thread, but now you want more help than I'm willing to devote time to ATM, so all I'll say is that for a simple straight pipe TL using > ~0.4 Qts drivers you can calculate a T/S max flat alignment to get its net Vb, Fb (Fp) to figure out its cross sectional area (CSA) once you calculate its length; or if using MJK's or Rick Shultz's TL designers, just use the calculated Fp to get the correct length/CSA.

Anyway, I re-did your WinISD driver file with Pe added and uploaded it to HTF's driver database: http://www.hometheatershack.com/foru...tml#post269574

GM

[chris661]

Hmmm...

If you shortened the TL, to tune it to more like 80Hz, then cut the bass below that, you'd get a smaller cabinet (handy if you want it portable). There's not many transmission line based small speakers out there. Perhaps it would be wiser to go with something that doesn't take up as much space?

[GM]

FYI: If you're going to recommend such, then a max flat impedance alignment is the goal or Fs/Qts = 107 Hz.

GM

[calypso]

thanks Gm, thanks chris661 for your reply.

will your reply be the same if i specify that the transmission line should be done to reach the lowest possible fs, for indoor listening, no matter how long will it be?
when i will go outdoors, what i will bring outside would be a third of it (a third of the pipe, not of the wave ). this third of the transmission line would be a pvc pipe 60cm long, tuned to match an fs of 100hz.

about tl tuning, i found out @ Pearls from Martin J King Quarter Wave Design that i should guess best tl-fs by my driver' qts, then arrange tl-length based on that guessing. is that right?
someone can give a clue on third wavelength vs quarter wavelength tl?

many thanks

[rjbond3rd]

Quarter Wavelength Loudspeaker Design

[GM]

Originally Posted by calypso

will your reply be the same if i specify that the transmission line should be done to reach the lowest possible fs, for indoor listening, no matter how long will it be?

about tl tuning, i found out @ Pearls from Martin J King Quarter Wave Design that i should guess best tl-fs by my driver' qts, then arrange tl-length based on that guessing. is that right?

someone can give a clue on third wavelength vs quarter wavelength tl?

many thanks

You're welcome!

Yes, since with a simple pipe loading it's not wise to load a driver lower than its specs indicate, especially with as low a Xmax driver as this one. It needs a relatively huge horn to go low.

?? Why guess when I gave you the T/S design routine theoretically correct way to calculate it? IME it works quite well and will be as accurate as the specs you use. That said, low Xmax drivers such as this one are best used in a max flat impedance (short) TL alignment or ~107 Hz in this case.

Bottom line, it's your design and well damped TLs are like sealed alignments in that they are relatively tolerant of inaccurate specs and/or misalignment, but again, with such a low Xmax driver even the short pipe will have marginal low distortion SPL output, so the long pipe will either need a lot of room gain and/or a high pass filter to protect it, somewhat negating the low tuning.

TLs are 1/4 WL resonators, i.e. only has odd order harmonics, so at its 1/3 WL its output will be 'buried in its fundamental.

GM

[calypso]

whoa! seems like i shall study a lot more before thinking a transmission line.

thanks again gm. i think i'll organize a shorter and more portable setup. but i would like to spruce the most bass possible from tl, 'cause i will listen to tl only at home.

however, next big mistery to me is to understand what effect will realize a cross sectional area end at 82% the piston area. hopefully, in shortt time, i'll be able to reply to myself.

today i did some work for the pipe speaker (the shortest part, intended as boombox). i took measures of pipe cap, where the driver will be mounted; and took measures of the reduction of the pipe, that will act as a vent.

i decided to contiune my project only with 20cm and 16cm pipes, tossing out the 12.5cm option. it will simplify things.

i did some simulation with winisd.
value i putted where corrected with some data
1) volume was calculated subtracting driver volume, then adding reduction volume. should be very precise.
2) vent measures 154mm diameter x 9 cm length, flanged vent
3) input signal is 20w (for simulating my ta2020) <- is ok?
4) highpass filter is "highpass - user SOS - fc 100hz - order 1 - q 1.2" for simulating a 100hz bass cut input cap applied to my amp.

winisd "transfer function magnitude" shows that reducing volume will raise db but in the same time have an higher fs. a 75cm long speaker pipe will have a total volume of 19.27l, a 119hz fs, and an affordable portability. but the maximum spl graph gave me doubts. from it looks like that the best setting should be 52.5cm total length, for a 146hz fs - too much for a boombox.

here is the maximum spl graph - why 80cm (blue) and 75cm (yellow) have this strange behaviour? starting from a 52.5cm long pipe speaker (146hz fs)
this won't happen.




as always, thanks for any coin you would toss

[borispm]

You can also try a dual chamber reflex with this speaker. Just like the KEF bassextender did. A normal down firing ported pipe enclosure for outdoor, a pipe with the top left open (to be attached by the ported plate) and the bottom ported will work as the extender (in fact just another Fostex dual chamber reflex). fb of smaller pipe (e.g. 3l) should be tuned at around 110Hz, fb of extender (e.g. 9l) at 55Hz.