What pics. Great project, Drew!
One of the problems I can foresee with measuring is the fact that most measuring is done 1 meter from the speaker. Well, if you put measuring microphone one meter away from the center, either end is 2.7 meters away.
You can't put it toward either end because both ends have output.
Perhaps you can measure 1 meter from each end separately, and splice the curves onto each other somehow. But that might create problems by ignoing phase and the interaction the outputs might have with each other.
Perhaps the best thing to do is measure from 4 meters away from the center. Each end of the pipe will then be 4.7 meters from the microphone, yielding minus 1.4 difference from 4 meters away. Your readings should be 13.4 dB down from a 1 meter measurement, otherwise everything would be the way it is normally.
However, one of the concerns there might be length and height of the house. My understanding is that you would get diffraction if the walls are less than a half wavelength. Half a wavelength of 20 Hz is approximately 25 feet. The wall you are measuring against is probably 25 feet long, but how high is it?
But then, you are only 12 feet away-maybe the diffraction would not count. Hmm, anybody have any experience with this sort of thing?
One of the problems I can foresee with measuring is the fact that most measuring is done 1 meter from the speaker. Well, if you put measuring microphone one meter away from the center, either end is 2.7 meters away.
You can't put it toward either end because both ends have output.
Perhaps you can measure 1 meter from each end separately, and splice the curves onto each other somehow. But that might create problems by ignoing phase and the interaction the outputs might have with each other.
Perhaps the best thing to do is measure from 4 meters away from the center. Each end of the pipe will then be 4.7 meters from the microphone, yielding minus 1.4 difference from 4 meters away. Your readings should be 13.4 dB down from a 1 meter measurement, otherwise everything would be the way it is normally.
However, one of the concerns there might be length and height of the house. My understanding is that you would get diffraction if the walls are less than a half wavelength. Half a wavelength of 20 Hz is approximately 25 feet. The wall you are measuring against is probably 25 feet long, but how high is it?
But then, you are only 12 feet away-maybe the diffraction would not count. Hmm, anybody have any experience with this sort of thing?
There is also the possiblilty of indoor measurement. This would require precise tones to be generated, or else the two speakers would have to be played on the same settings.
Take a speaker of known frequency response, preferably sealed, if available, since we can count on a 12 dB/octave rolloff from it. We can call it the test speaker.
Put it next to the Cannon indoors, and go into the middle of the room. Run any tone through the test speaker, then the Cannon. Repeat any convenient number of times, from 16 Hz on up. If the test tone generator is analog, it is best to set it at one frequency for each speaker in turn, then move on to the next frequency. Room response can play big tricks even with slight frequency variation.
Compare the test speaker's output in your room with the frequency response curve you are supposed to get, and adjust the readings you get from the Cannon accordingly.
I am just guessing here. Good luck, Drew!
Take a speaker of known frequency response, preferably sealed, if available, since we can count on a 12 dB/octave rolloff from it. We can call it the test speaker.
Put it next to the Cannon indoors, and go into the middle of the room. Run any tone through the test speaker, then the Cannon. Repeat any convenient number of times, from 16 Hz on up. If the test tone generator is analog, it is best to set it at one frequency for each speaker in turn, then move on to the next frequency. Room response can play big tricks even with slight frequency variation.
Compare the test speaker's output in your room with the frequency response curve you are supposed to get, and adjust the readings you get from the Cannon accordingly.
I am just guessing here. Good luck, Drew!
Whoa there! Settle down folks, any measuring will be purely subjective.
1) How loud does it go at the low end (20Hz, 25Hz) with 28v RMS (100W) of signal being fed in?
2) How subjectively even is the volume at 15, 20, 25, 30, 35Hz. does it sound like there are suckouts or zones i need to EQ slightly?
There are precious few rooms smaller than 50M long that will have a linear low end response. Trying to get the perfect flat measurement response from something like this is futile. As soon as you put it in a real world house, the response flies straight out the window. not worth the effort.
If i can build a sub that will produce weight, awe, impact and majesty when the LFE channel calls for it then all well and good.
That's my goal. If a film uses a really low tone to give you that creepy "god is coming and she's not very happy" feeling, i'd like to be able to reproduce it to some degree.
It's funny really, for music, most of the time I'm happy with speakers that produce little output below 70Hz. I really don't care that much but for home theatre, alot of the cinema majesty (especially of late) is missing with my litle sub that only goes to 35.
Horses for courses huh?
Yes, very nice boltable flanges and a good amount of building adhesive and surface area with which to join the flanges to the pipes.
Drew
1) How loud does it go at the low end (20Hz, 25Hz) with 28v RMS (100W) of signal being fed in?
2) How subjectively even is the volume at 15, 20, 25, 30, 35Hz. does it sound like there are suckouts or zones i need to EQ slightly?
There are precious few rooms smaller than 50M long that will have a linear low end response. Trying to get the perfect flat measurement response from something like this is futile. As soon as you put it in a real world house, the response flies straight out the window. not worth the effort.
If i can build a sub that will produce weight, awe, impact and majesty when the LFE channel calls for it then all well and good.
That's my goal. If a film uses a really low tone to give you that creepy "god is coming and she's not very happy" feeling, i'd like to be able to reproduce it to some degree.
It's funny really, for music, most of the time I'm happy with speakers that produce little output below 70Hz. I really don't care that much but for home theatre, alot of the cinema majesty (especially of late) is missing with my litle sub that only goes to 35.
Horses for courses huh?
Yes, very nice boltable flanges and a good amount of building adhesive and surface area with which to join the flanges to the pipes.
Drew
You have to be aware that such "thingies" can be directional because of the large dimensions.
In a JAES article, where such tubular arrangements were discussed, measurements/simulations were done at the middle of the tube at some distance.
Additionally all Bose cannons I've seen installed so far were mounted that way (i.e. you were looking at it from the side).
So you'd rather take this into consideration when doing measurements.
Regards
Charles
In a JAES article, where such tubular arrangements were discussed, measurements/simulations were done at the middle of the tube at some distance.
Additionally all Bose cannons I've seen installed so far were mounted that way (i.e. you were looking at it from the side).
So you'd rather take this into consideration when doing measurements.
Regards
Charles
Test Results from the front yard
Folks, I borrowed a 150w subwoofer "plate amp" and a cd of LF test tones from a freind and fired the beastie up outside this morning with a digital volt meter hooked up to read RMS voltage applied to the drive unit.
Feeding the cannon with a 100W (28v RMS) input and produced smooth, non distorted and non boomy bass in the range 60 - 25 Hz, 100w at 20hz is not especially loud and is beginning to ask more of the drive unit than it would like to give. 50w (20v)is a better limit for the 20Hz tone. still audible but not giving any hassles.
15Hz produces a most disturbing sound with extensive non linearity and higher harmonics other than the raw tone if the signal is pushed above about 10v RMS in. below that it's barely preceptible anyway so these's no point in feeding a 15Hz signal to it.
Maybe a more robust and bulletprooof drive unit could handle this better (Lambda perhaps?) i don't know.
Of course, continuous sine waves will be making life far harder for the driver than any regular signal would, so perhaps none ofthis will be a problem in practice.
this week I"ll mount the driver with just the 300mm pipes hooked up as a 1/4 wave tube and see how that sounds. More like Nelson's "El Pipe O". Could be that the extra tube is just causing hassles.
Time will tell, thought I'd give you folks some feedback anyhow
drew
Folks, I borrowed a 150w subwoofer "plate amp" and a cd of LF test tones from a freind and fired the beastie up outside this morning with a digital volt meter hooked up to read RMS voltage applied to the drive unit.
Feeding the cannon with a 100W (28v RMS) input and produced smooth, non distorted and non boomy bass in the range 60 - 25 Hz, 100w at 20hz is not especially loud and is beginning to ask more of the drive unit than it would like to give. 50w (20v)is a better limit for the 20Hz tone. still audible but not giving any hassles.
15Hz produces a most disturbing sound with extensive non linearity and higher harmonics other than the raw tone if the signal is pushed above about 10v RMS in. below that it's barely preceptible anyway so these's no point in feeding a 15Hz signal to it.
Maybe a more robust and bulletprooof drive unit could handle this better (Lambda perhaps?) i don't know.
Of course, continuous sine waves will be making life far harder for the driver than any regular signal would, so perhaps none ofthis will be a problem in practice.
this week I"ll mount the driver with just the 300mm pipes hooked up as a 1/4 wave tube and see how that sounds. More like Nelson's "El Pipe O". Could be that the extra tube is just causing hassles.
Time will tell, thought I'd give you folks some feedback anyhow
drew
interesting!
i suppose the driver unloads above Fp ,like around 50hz,but you were going to filter it low??
it is a small driver isnt it? and it is a low frequency ,normaly you'd be using somthing more like a 15inch ,800cm^2.
low Freq+small driver+pipe UN-loading below Fp=super high excursion
so yeh i wouldnt expect anything amazing below Fp,was it 20hz or so
i wonder how the 1/4wave pipe will compare:-D
i suppose the driver unloads above Fp ,like around 50hz,but you were going to filter it low??
it is a small driver isnt it? and it is a low frequency ,normaly you'd be using somthing more like a 15inch ,800cm^2.
low Freq+small driver+pipe UN-loading below Fp=super high excursion
so yeh i wouldnt expect anything amazing below Fp,was it 20hz or so
i wonder how the 1/4wave pipe will compare:-D
I didn't actually try anything above 50 this time as I'm not aiming to use it there. gives great output up higher but you do begin to get pipe sounding resonances the higher you go
definitely for this driver (a 10 incher with Fs of 26) in the current tube, the optimum range is down to around 24 or so at 100W power and the highest reasonable top end would be 70 or so.
don't know how well it'd match other things seamlessly so I'm only planning on using it for very low end fill.
Drew
definitely for this driver (a 10 incher with Fs of 26) in the current tube, the optimum range is down to around 24 or so at 100W power and the highest reasonable top end would be 70 or so.
don't know how well it'd match other things seamlessly so I'm only planning on using it for very low end fill.
Drew
1/4 wave 3.6m V's 4.9m Cannon
Folks, again the results are purely subjective but there's a significant volume gain to be had by the use of the additional pipe on the front side of the driver. At the bass freq I'm interested in (20 - 45 Hz) nearly twice the volume is available with the front pipe in place as compared to a 3.6m long 1/4 wave pipe in the El-Pipe-O style.
Of course, alot of domestic acceptability is lost by doing things this way. A 3.6m pipe is alot easier to accommodate than a 4.9m long pipe. Fortunately, my cannon is destined for the roof cavity so domestic bliss is not destined for disaster.
We were running the Phloxton Paradise gun battle and destruction scenes from 5th Element and a friend of mine who's a notoriously harsh judge of sub quality was stoked with the results. If Jay McA is happy then I know I've got a good result
This next weekend the prototype sub moves into a friends house. I'd be building my own soon but the destruction of my car's crankshaft has put a couple of projects on delay.
Happy subbing folks
Drew
Folks, again the results are purely subjective but there's a significant volume gain to be had by the use of the additional pipe on the front side of the driver. At the bass freq I'm interested in (20 - 45 Hz) nearly twice the volume is available with the front pipe in place as compared to a 3.6m long 1/4 wave pipe in the El-Pipe-O style.
Of course, alot of domestic acceptability is lost by doing things this way. A 3.6m pipe is alot easier to accommodate than a 4.9m long pipe. Fortunately, my cannon is destined for the roof cavity so domestic bliss is not destined for disaster.
We were running the Phloxton Paradise gun battle and destruction scenes from 5th Element and a friend of mine who's a notoriously harsh judge of sub quality was stoked with the results. If Jay McA is happy then I know I've got a good result
This next weekend the prototype sub moves into a friends house. I'd be building my own soon but the destruction of my car's crankshaft has put a couple of projects on delay.
Happy subbing folks
Drew
I was wondering what pipe lengths to use for 20Hz, i have a JBL-2245H 18" woofer. I'm not quite sure that i have the calculations correct. Anyway here are the specs for the woofer, would this work well it has a low fs and qts so i would assume it would.
fs: 20 Hz
Re: 5.8 ohms
Qts: 0.27
Qms: 2.2
Qes: 0.31
Vas: 820 L (29 ft3)
Sd: 0.130 m2 (200 in2)
Xmax: 9.5 mm (3/8 in)
Vd: 1,230 cm3 (75 in3)
Le: 1.4 mH
no (Half space): 2.1%
Pe (Max): 300 W Continuous Sine Wave
DrewP i also noticed that the right quarter of you pipe (in the picture) ,which i assume is the length in front of the drive, is slightly thinner than the rest of the pipe, is there any reason for this?
fs: 20 Hz
Re: 5.8 ohms
Qts: 0.27
Qms: 2.2
Qes: 0.31
Vas: 820 L (29 ft3)
Sd: 0.130 m2 (200 in2)
Xmax: 9.5 mm (3/8 in)
Vd: 1,230 cm3 (75 in3)
Le: 1.4 mH
no (Half space): 2.1%
Pe (Max): 300 W Continuous Sine Wave
DrewP i also noticed that the right quarter of you pipe (in the picture) ,which i assume is the length in front of the drive, is slightly thinner than the rest of the pipe, is there any reason for this?
To my mind, the longer the pipe the better. The only reason Bose can get away with the 12 ft pipe they use is by setting a limit of 25hz in their specs and using a significant amount of EQ. I expect this is the reason their driver can handle 500W. It has to.
If my original calcs were correct then a 5.25m pipe ought to give above 75% of the drive unit's forward output at 20Hz.
The 6m pipe gives 93% at 20Hz.
In practice i believe that the 5m pipe i'm using at present starts to both lose output and get below the drive unit's Fs, hence the limited power handling and reduced output below 25Hz.
the section of 250mm pipe on the short section is because that's what i had access to. No scientific reason and it was still large enough to fit the driver basket.
I'll probably do the 6m pipe in 250mm the whole length. It'll be easier to install in the roof.
Drew
If my original calcs were correct then a 5.25m pipe ought to give above 75% of the drive unit's forward output at 20Hz.
The 6m pipe gives 93% at 20Hz.
In practice i believe that the 5m pipe i'm using at present starts to both lose output and get below the drive unit's Fs, hence the limited power handling and reduced output below 25Hz.
the section of 250mm pipe on the short section is because that's what i had access to. No scientific reason and it was still large enough to fit the driver basket.
I'll probably do the 6m pipe in 250mm the whole length. It'll be easier to install in the roof.
Drew
Assuming that the driver is producing usable output at that frequency, then yes, a 6m pipe should give you good 20Hz output.
It won't be boosted 20Hz output, for that you'd need a pipe around 8m long.
Nonetheless, it will give you better (and significantly less delayed) output than a reflex cabinet would give.
I've yet to see a reflex cab tuned down around 20Hz with less than 30ms group delay. The long end of the pipe is only 13ms away from the rear of the drive unit so you ought to get subjectively pretty fast bass from the cannon too.
drew
It won't be boosted 20Hz output, for that you'd need a pipe around 8m long.
Nonetheless, it will give you better (and significantly less delayed) output than a reflex cabinet would give.
I've yet to see a reflex cab tuned down around 20Hz with less than 30ms group delay. The long end of the pipe is only 13ms away from the rear of the drive unit so you ought to get subjectively pretty fast bass from the cannon too.
drew
More than likely suspended from okky straps so as not to put vibrations directly into the roof/ceilingstructure.
as far as getting the sound into the room goes, freq this low will happily go through the ceiling platerboard/Gyprock sheeting with no appreciable attenuation.
This theory is upheld by the doofy hatchback driveby audibility proof.
as far as getting the sound into the room goes, freq this low will happily go through the ceiling platerboard/Gyprock sheeting with no appreciable attenuation.
This theory is upheld by the doofy hatchback driveby audibility proof.
what's the best length though, i thought the optimum length 1/4 wavelength which for 20Hz works out to be just over 4m (haven't got my working with me so can't remember exact value), isn't this far to short. i will try the working you posted for 20hz at 8m and see what comes out. btw what are we aiming for, you found 125% in your working, are we trying to simply get the highest number here. Anyway thanks for your help.
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