We've Created a Monster
After a couple of weeks spent purchasing drivers, cutting pvc pipe, routing flanges from 18mm MDF etc and so on (work dramas not withstanding) today I finally got to run some test tones through the 5m long clone Acoustic Wave Cannon I've built.
Due to the "scrounged" nature of the parts incorporated, one side of the bass driver has a 1.25m long PVC tube that's 250mm in diameter while the other side of the driver has a 3.75m long PVC tube that's 300mm in diameter. No biggie it would seem, this design is pretty much all about path lengths and the proportion of a wavelength that they constitute (and how thay constructively combine with each other etc etc)
Bass driver used was a Vifa M26-WR-09 the numbers you need to know I guess are Fs25Hz, RMS power 160W, Peak power 500W and Sens 88.5dB (although in the low end where it's being used it's closer to 84-85). Can't recall the Qts but it's on the low side so things are pretty nicely self damped. No nasty "high excursion walkies" to be had.
A patient friend and I wing-nutted the sections together diagonally across my loungeroom today and hooked the driver up to a subwoofer amp of indeterminate specification (Jaycar specs are funny amorphous things sometimes) and fed the beastie with a series of test tones from 100Hz down to 10Hz.
I don't know how much power we were putting in and without knowing what (if any) eq was inherent in the circuitry of the sub amp I can't give you any idea of response flatness, I can tell you that we got tones that were cleanly audible to a level beyond what my house would tolerate.
Output from 100Hz down to 60ish was pretty normal. Below this we dropped the volume as the light fittings, sliding doors, windows, ceiling and plasterboard walls were joining in the fun.
Nice strong output was available down to 25Hz (house antics aside) with no evidence of doubling at all. I have to say that at this frequency we were beginning to get into the "bass you feel" region more than bass you hear and the house output was overpowereing the sub output.
Winding the wick up a little gave clean audible 20Hz and a decent impression of 15 was even on offer. Without knowing how much power we were applying (or what the house would take) I had no intention of pushing my luck.
The upshot is:
There's nice output from 40-25Hz where many normal speakers (and the lion's share of subs) are producing almost nothing .
Will i bother applying eq to bring the 20Hz section of the passband up to the same as the 25Hz (around a 10dB boost req)? I dunno. That would allow me to play a 90dB 20Hz tone with input power of around 100W. Personally i doubt the house would stand it anyhow and I'm more tempted towards subtle bass you notice when it's turned off than obnoxious bass.
Anyhow, I promised you folks some results and they are that the beast actually works. Having never heard anything producing 25hz in a pipe (or for that matter 25Hz most other places either apart from thunder) I can't say how "in a pipe" sounding it is. ....Didn't seem very pipe like.
One thing I will say, once you take away the flutter, port noise, box honk and so forth, these very low frequencies are kind of unimpressive in their impressiveness. Maybe it's the suff that's normally present that makes you go WOW! If it weren't for the output from the house I'd call the results subtly impressive.
As it is I'm just glad my wife was interstate.
For a first attempt I'm most impressed.
Drew
After a couple of weeks spent purchasing drivers, cutting pvc pipe, routing flanges from 18mm MDF etc and so on (work dramas not withstanding) today I finally got to run some test tones through the 5m long clone Acoustic Wave Cannon I've built.
Due to the "scrounged" nature of the parts incorporated, one side of the bass driver has a 1.25m long PVC tube that's 250mm in diameter while the other side of the driver has a 3.75m long PVC tube that's 300mm in diameter. No biggie it would seem, this design is pretty much all about path lengths and the proportion of a wavelength that they constitute (and how thay constructively combine with each other etc etc)
Bass driver used was a Vifa M26-WR-09 the numbers you need to know I guess are Fs25Hz, RMS power 160W, Peak power 500W and Sens 88.5dB (although in the low end where it's being used it's closer to 84-85). Can't recall the Qts but it's on the low side so things are pretty nicely self damped. No nasty "high excursion walkies" to be had.
A patient friend and I wing-nutted the sections together diagonally across my loungeroom today and hooked the driver up to a subwoofer amp of indeterminate specification (Jaycar specs are funny amorphous things sometimes) and fed the beastie with a series of test tones from 100Hz down to 10Hz.
I don't know how much power we were putting in and without knowing what (if any) eq was inherent in the circuitry of the sub amp I can't give you any idea of response flatness, I can tell you that we got tones that were cleanly audible to a level beyond what my house would tolerate.
Output from 100Hz down to 60ish was pretty normal. Below this we dropped the volume as the light fittings, sliding doors, windows, ceiling and plasterboard walls were joining in the fun.
Nice strong output was available down to 25Hz (house antics aside) with no evidence of doubling at all. I have to say that at this frequency we were beginning to get into the "bass you feel" region more than bass you hear and the house output was overpowereing the sub output.
Winding the wick up a little gave clean audible 20Hz and a decent impression of 15 was even on offer. Without knowing how much power we were applying (or what the house would take) I had no intention of pushing my luck.
The upshot is:
There's nice output from 40-25Hz where many normal speakers (and the lion's share of subs) are producing almost nothing .
Will i bother applying eq to bring the 20Hz section of the passband up to the same as the 25Hz (around a 10dB boost req)? I dunno. That would allow me to play a 90dB 20Hz tone with input power of around 100W. Personally i doubt the house would stand it anyhow and I'm more tempted towards subtle bass you notice when it's turned off than obnoxious bass.
Anyhow, I promised you folks some results and they are that the beast actually works. Having never heard anything producing 25hz in a pipe (or for that matter 25Hz most other places either apart from thunder) I can't say how "in a pipe" sounding it is. ....Didn't seem very pipe like.
One thing I will say, once you take away the flutter, port noise, box honk and so forth, these very low frequencies are kind of unimpressive in their impressiveness. Maybe it's the suff that's normally present that makes you go WOW! If it weren't for the output from the house I'd call the results subtly impressive.
As it is I'm just glad my wife was interstate.
For a first attempt I'm most impressed.
Drew
PENTIVENT DRIVERS
When i work with pentivent drivers i always use them on the front baffle of a vented box. I get good results evry single time. You could reconsider the size of the woofer your using, a dual 6.5 " pentivent sub is almost better than any sub using the 1030. If i remember the 1050 offers so much more... you could change driver to solve your problem.
When i work with pentivent drivers i always use them on the front baffle of a vented box. I get good results evry single time. You could reconsider the size of the woofer your using, a dual 6.5 " pentivent sub is almost better than any sub using the 1030. If i remember the 1050 offers so much more... you could change driver to solve your problem.
Drew has plans to post pictures but first will need to get digital camera from work (not till i'm well again, bloody Flu!).
Of course i need to figure out how too, I'm assuming i put the file on my machine and just stick its file name in "attach file"
further thought on the subject of crossovers has yielded the following idea:
If i build a low pass active filter with 12 dB/oct rolloff and the minus 3dB point at 22.5 Hz, then I have around 8dB of boost applied at 20Hz with respect to 30Hz and the right cut above that point too to integrate pretty well with most systems.
gonna need to hang the beastie in the roof cavity though. Firstly it's rather large, second, it can't be firing at any Gyprock walls or all hell (or the wall) breaks loose.
for safety reasons, i think i'll put a cct in the amp dfor the sub which monitors the input signal (post the filter and attenuator) and relay cuts out the sub for 5 seconds if the input signal would cause an output greater than 100W. That way, i know I'll nevr kill the driver and can't accidently clip the amp either.
Hope to get camera tomorrow.
Drew
Of course i need to figure out how too, I'm assuming i put the file on my machine and just stick its file name in "attach file"
further thought on the subject of crossovers has yielded the following idea:
If i build a low pass active filter with 12 dB/oct rolloff and the minus 3dB point at 22.5 Hz, then I have around 8dB of boost applied at 20Hz with respect to 30Hz and the right cut above that point too to integrate pretty well with most systems.
gonna need to hang the beastie in the roof cavity though. Firstly it's rather large, second, it can't be firing at any Gyprock walls or all hell (or the wall) breaks loose.
for safety reasons, i think i'll put a cct in the amp dfor the sub which monitors the input signal (post the filter and attenuator) and relay cuts out the sub for 5 seconds if the input signal would cause an output greater than 100W. That way, i know I'll nevr kill the driver and can't accidently clip the amp either.
Hope to get camera tomorrow.
Drew
Drew:
You can run the test tones through your sub amp and measure the output voltage of the amp. This will tell you what EQ, if any, the sub amp has.
Great job, though. The thing works. That alone should encourage others to try it.
Here's an incentive. The Bose Company people are going to get really, really mad if DIYer's figure these things out and build them themselves, for personal use.
You can run the test tones through your sub amp and measure the output voltage of the amp. This will tell you what EQ, if any, the sub amp has.
Great job, though. The thing works. That alone should encourage others to try it.
Here's an incentive. The Bose Company people are going to get really, really mad if DIYer's figure these things out and build them themselves, for personal use.
cannon
if it was filtered low,probably it wil sound abit better,since it wont ahve a chance to distort the 50hz signals,which wil have higher harmonics i n the 100hz+ range,
where as 2nd and 3rd harmonics if they occur ,on a 20hz fundamental,are just 40hz and 60hz noises
there is no free lunch 
SPL vs transients.
i have an old philips 12inch,Fs=44 Qts-0.17 measured.
i suppose i could try this?
for fun ofcourse in my holidays coming up
il read the posts on the theory and make a spreadsheet :-Di understand the theory,partially anyway :-D
i dont think msworks wil work very well
if it was filtered low,probably it wil sound abit better,since it wont ahve a chance to distort the 50hz signals,which wil have higher harmonics i n the 100hz+ range,
where as 2nd and 3rd harmonics if they occur ,on a 20hz fundamental,are just 40hz and 60hz noises
there is no free lunch
SPL vs transients.
i have an old philips 12inch,Fs=44 Qts-0.17 measured.
i suppose i could try this?
for fun ofcourse in my holidays coming up
il read the posts on the theory and make a spreadsheet :-Di understand the theory,partially anyway :-D
i dont think msworks wil work very well
Bother, I posted a big spiel earlier today but it looks like it's been sucked into no-where in cyberspace.
To DJ NUBZ, yes, any high level tests based upon sine wave test tones I'll be conucting OUTSIDE from now on. The house quite simply won't take it. Music/LFE effects and noise signals are fine but sine waves are bad news as far as getting things to resonate is concerned.
My plan is to use my regular KEF sub (the one that came with the "Egg" set) for bass down to 40Hz, the Cannon will only be in use below that. I expect it'll be a case of noticing it when it's turned off. I have no desire for obnoxious bass output to irritate the neighbours (although of course, testing on the front lawn with 100W in at 20Hz will likely raise a few comments).
Mikee, as I said below, I'm p-anning on hitting the output with a pretty hard filter. at 12dB/oct that 100W at 20hz will be 12.5 watts at 40 and only around 3 watts at 80Hz. And that's on the peaks.
who knows, I might even cascade a second filter to really kill any higher frequencies. With luck, being up in the roof will also acoustically filter those higher frequencies as well.
Being a drive unit intended for reflex cabinet (lowQ) it's prettty well damped anyway and the mass of the air column should also load the diaphragm pretty well. As i said earlier, didn't seem to have too many hassles with harmonics or doubling of notes, it all sounded pretty clean.
Not sure if the Fs of 44Hz will be low enough, if you can get he pipe cheap, i guess there's no harm in trying.
take care all
Drew
To DJ NUBZ, yes, any high level tests based upon sine wave test tones I'll be conucting OUTSIDE from now on. The house quite simply won't take it. Music/LFE effects and noise signals are fine but sine waves are bad news as far as getting things to resonate is concerned.
My plan is to use my regular KEF sub (the one that came with the "Egg" set) for bass down to 40Hz, the Cannon will only be in use below that. I expect it'll be a case of noticing it when it's turned off. I have no desire for obnoxious bass output to irritate the neighbours (although of course, testing on the front lawn with 100W in at 20Hz will likely raise a few comments).
Mikee, as I said below, I'm p-anning on hitting the output with a pretty hard filter. at 12dB/oct that 100W at 20hz will be 12.5 watts at 40 and only around 3 watts at 80Hz. And that's on the peaks.
who knows, I might even cascade a second filter to really kill any higher frequencies. With luck, being up in the roof will also acoustically filter those higher frequencies as well.
Being a drive unit intended for reflex cabinet (lowQ) it's prettty well damped anyway and the mass of the air column should also load the diaphragm pretty well. As i said earlier, didn't seem to have too many hassles with harmonics or doubling of notes, it all sounded pretty clean.
Not sure if the Fs of 44Hz will be low enough, if you can get he pipe cheap, i guess there's no harm in trying.
take care all
Drew
The house quite simply won't take it. Music/LFE effects and noise signals are fine but sine waves are bad news as far as getting things to resonate is concerned.
so music isnt bad on it?
also sinewaves reveal the other resonances of everything..
what about some pink noise/ i like it its rumbly if u filter it low haha it seems flat amplitude to 0hz...il send u some filtered,mp3 format if u want to test lol
although of course, testing on the front lawn with 100W in at 20Hz will likely raise a few comments).
lol 
who knows, I might even cascade a second filter to really kill any higher frequencies. With luck, being up in the roof will also acoustically filter those higher frequencies as well
that would work quite well! i dont know if youl need it that sharp,but perhaps ,im not the one whos heard the cannon lol
lol also,i have a JBL2226h,it is Fs=40hz Q=0.3 Vas 175l Eff 97db Xmax=7.5m,600watt rms :-D
just for an experiment . i dont know if i can get large enough diameter pipe! last time i checked it was 100$/metre so not possible,and making a huge long block of wood as a pipe lol,abit heavy.
im gona basshorn it sometime(oneday),but i can only fit 40hz mouth :-D
should i just model a tline in that guys mathcad files and see how it looks anyway..i will when im able to use that pc.
ive heard ppl with subs that go 20hz tend to listen to the bass range quiter cos they are gettn that LF rumble they want.
i did see an 18inch eminence TLine i lost the link though
so music isnt bad on it?
also sinewaves reveal the other resonances of everything..
what about some pink noise/ i like it its rumbly if u filter it low haha it seems flat amplitude to 0hz...il send u some filtered,mp3 format if u want to test lol
although of course, testing on the front lawn with 100W in at 20Hz will likely raise a few comments).
lol
who knows, I might even cascade a second filter to really kill any higher frequencies. With luck, being up in the roof will also acoustically filter those higher frequencies as well
that would work quite well! i dont know if youl need it that sharp,but perhaps ,im not the one whos heard the cannon lol
lol also,i have a JBL2226h,it is Fs=40hz Q=0.3 Vas 175l Eff 97db Xmax=7.5m,600watt rms :-D
just for an experiment . i dont know if i can get large enough diameter pipe! last time i checked it was 100$/metre so not possible,and making a huge long block of wood as a pipe lol,abit heavy.
im gona basshorn it sometime(oneday),but i can only fit 40hz mouth :-D
should i just model a tline in that guys mathcad files and see how it looks anyway..i will when im able to use that pc.
ive heard ppl with subs that go 20hz tend to listen to the bass range quiter cos they are gettn that LF rumble they want.
i did see an 18inch eminence TLine i lost the link though
Pro drivers like the JBL have high efficiency but the tradeoff is that to get it they usually have low moving mass and a higher Fs.
The Vifa's I'm using have an Fs of 25 or 26, not 40. Don't know what effect that will have on your results.
Go to a plumbing supplier. Locally i can get 250mm pvc pipe in 6m lengths for Aus $150. $100 per metre seems crazy. Even the 300mm pipe is only $250 for 6m.
Haven't tried playing proper music but we ran the whole "T Rex" scene from Jurassic Park and "The Fall of Carthage" from Gladiator with pretty good results.
Once up in the roof space, there won't be any parallel walls within 10m or so either side so the resonances should be a little tamer.
I doubt i would have attempted this if I hadn't had access to the pipe for nix. It was a gamble but it looks like it'll pay off.
Drew
yep it was about that much,at a plumbing place for 12inch sized pipe..
and about the JBL being low mass etc,,yes it is 88g,i know shiva etc are higher,and they are only 12inch,not 15!
the lab12 woofer is very heavy..
there is always a trade off
i dont particurly want to buy 2 shivas for no reason,just cos i want 20hz :-D
this image is just the cannon with some notes that another guy posted around it...
i want to know how music sounds lol,and is it jsut easier(and shorter) to make a normal tline,i was reading they roll off at 6db/octave around resonance ,but they are a few mroe db down there,than portedbox...audioasylum posts that is..
and about the JBL being low mass etc,,yes it is 88g,i know shiva etc are higher,and they are only 12inch,not 15!
the lab12 woofer is very heavy..
there is always a trade off
i dont particurly want to buy 2 shivas for no reason,just cos i want 20hz :-D
this image is just the cannon with some notes that another guy posted around it...
i want to know how music sounds lol,and is it jsut easier(and shorter) to make a normal tline,i was reading they roll off at 6db/octave around resonance ,but they are a few mroe db down there,than portedbox...audioasylum posts that is..
Attachments
The whole sinewave and tube diagram is on the right track visualisation wise but where you cross form the front to the rear of the drive unit you need to flip phase by 180 degrees. Neg peak on back of sine wave, not positive peak on both sides.
The dips i expected were not overly apparent, will need to do more testing in free air before i can give an appraisal of actual freq response.
drew
The dips i expected were not overly apparent, will need to do more testing in free air before i can give an appraisal of actual freq response.
drew
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