Re: el pipe subwoofers
An easy way to achieve both stuffing and tapering that I've suggested from time to time:
1) Cut a sheet of foam (I've used 1/2" carpet foam...thicker works just as well, but gets harder to work with) into a right triangle.
2) Lay it out on the floor with the 90 degree angle next to your right hand.
3) Start rolling from the corner on your left--the small end of the foam. You want this on the inside.
4) Roll all the way to the right. You should now have a foam tube with an inverted cone on the inside. Look in the wide end and you'll see the cone taper towards the other end. Look at the narrow end and you'll see either a closed spiral or a small hole depending on the proportions of the triangle.
5) Slide the foam into the outer tube. You have now both stuffed and tapered the tube.
Simple.
Yes, there are better ways, but this is cheap, easy, and fast.
Grey
Professor smith said:
An easy way to achieve both stuffing and tapering that I've suggested from time to time:
1) Cut a sheet of foam (I've used 1/2" carpet foam...thicker works just as well, but gets harder to work with) into a right triangle.
2) Lay it out on the floor with the 90 degree angle next to your right hand.
3) Start rolling from the corner on your left--the small end of the foam. You want this on the inside.
4) Roll all the way to the right. You should now have a foam tube with an inverted cone on the inside. Look in the wide end and you'll see the cone taper towards the other end. Look at the narrow end and you'll see either a closed spiral or a small hole depending on the proportions of the triangle.
5) Slide the foam into the outer tube. You have now both stuffed and tapered the tube.
Simple.
Yes, there are better ways, but this is cheap, easy, and fast.
Grey
http://www.curran.co.uk/
I am in the UK. Is this the sort of thing I can use?
They state that the thickness of the tube can go upto 2.5cm so should i select this thickness?
The thicker the more dense no?
Many speaker cabinets are made using 2.5cm MDF board.
Also I am thinking of using the biggest woofer size such as 18 inch, and maybe a car woofer...is this ok?
thanks
I am in the UK. Is this the sort of thing I can use?
They state that the thickness of the tube can go upto 2.5cm so should i select this thickness?
The thicker the more dense no?
Many speaker cabinets are made using 2.5cm MDF board.
Also I am thinking of using the biggest woofer size such as 18 inch, and maybe a car woofer...is this ok?
thanks
the stuff your link shows should be perfect! I personally don't think that you need to get really thick walled tubes, the inherent strength of a cylinder does not require a huge thickness. On the other hand, I have not looked into the issue of resonance - I am using commercially available (in the U.S.) sonotube which isn't more than 3/8" thick. I have not experienced any resonance issues either. All the sound (air pressure) is coming out of the mouth of the tube. Use the cheapest stuff you can get. Also, using an 18" car sub would be great. I used a cerwin vega car sub because it is what I had unused, and it works fabulously. I also laid my tube on it's side because of space issues and I have heard that most speakers are not designed to be oriented in a horizontal plane. Anyhow, I think the main thing is that you just build it and experiment for yourself. I don't think you will be disappointed.😉
Any rigid tube will suffice. I tend to use MDF for my transmission lines, but I've used PVC pipe at times; other people prefer cardboard tubes. The thickness doesn't increase the density per se, but it does tend to increase the rigidity, which is what you want in the final analysis.
Be afraid...be very afraid of car woofers. They are far from flat. They tend to have a very pronounced hump ca. 80Hz followed by a strong rolloff. It's nothing to see a car woofer that's down by 15-20dB in the 20-30Hz range. Yes, it can be equalized, but why should you have to go to such strenuous efforts to get something like flat response? Also bear in mind the phase aberrations you introduce with the eq, etc. Ugh.
Hint: If all they show is a 'simulated' frequency response, don't buy the driver! It's junk. There's a reason they're cheaper than hifi drivers, and it ain't because they're out to do you a favor. Buy only drivers that show actual driver response curves in the spec sheets.
Grey
Be afraid...be very afraid of car woofers. They are far from flat. They tend to have a very pronounced hump ca. 80Hz followed by a strong rolloff. It's nothing to see a car woofer that's down by 15-20dB in the 20-30Hz range. Yes, it can be equalized, but why should you have to go to such strenuous efforts to get something like flat response? Also bear in mind the phase aberrations you introduce with the eq, etc. Ugh.
Hint: If all they show is a 'simulated' frequency response, don't buy the driver! It's junk. There's a reason they're cheaper than hifi drivers, and it ain't because they're out to do you a favor. Buy only drivers that show actual driver response curves in the spec sheets.
Grey
Drivers and Tubes
Hi Guys,
I'm with Grey on the whole car driver issue, it's probably not the best idea. There are some great car audio drivers out there, but also many terrible ones.
If it were me it would boil down to the following:
1. Do you have specs for the driver?
2. Can you measure the specs for the driver?
3. Are the specs any good for this application?
If the answer to the above is no, no and no/I don't know, then save yourself the trouble and buy another driver.
Prof. Smith:
Using a big driver is a great idea, but you'll need to design the pipe for it. That means you need a few key parameters for your driver to use MJK's sheets:
1. Fs
2. Qts
3. Sd
4. Bl
5. Re
Almost every respectable driver will have these specs published with it. If it doesn't, don't buy it. Just like Grey said.
Grey's suggestion of using the carpet foam is promising because a tapered pipe can be WAY shorter than a straight pipe, and also has generally better performance. For example, a straight pipe tuned to 30Hz would have to be 112" long, while a pipe tapered 10:1 at the same frequency is only 68.9" long.
If you don't feel like doing the design work, I'd be glad to do it for you if you provide the driver specs and what your size limitations/performance expectations are.
By the way, that pipe looks great. I'd say go for the thicker stuff just to be sure.
Cheers,
Owen
Hi Guys,
I'm with Grey on the whole car driver issue, it's probably not the best idea. There are some great car audio drivers out there, but also many terrible ones.
If it were me it would boil down to the following:
1. Do you have specs for the driver?
2. Can you measure the specs for the driver?
3. Are the specs any good for this application?
If the answer to the above is no, no and no/I don't know, then save yourself the trouble and buy another driver.
Prof. Smith:
Using a big driver is a great idea, but you'll need to design the pipe for it. That means you need a few key parameters for your driver to use MJK's sheets:
1. Fs
2. Qts
3. Sd
4. Bl
5. Re
Almost every respectable driver will have these specs published with it. If it doesn't, don't buy it. Just like Grey said.
Grey's suggestion of using the carpet foam is promising because a tapered pipe can be WAY shorter than a straight pipe, and also has generally better performance. For example, a straight pipe tuned to 30Hz would have to be 112" long, while a pipe tapered 10:1 at the same frequency is only 68.9" long.
If you don't feel like doing the design work, I'd be glad to do it for you if you provide the driver specs and what your size limitations/performance expectations are.
By the way, that pipe looks great. I'd say go for the thicker stuff just to be sure.
Cheers,
Owen
GRollins said:
Can you recommend any hifi woofers then? I dont know what to buy. I think 18 inch is abit much maybe either 12inch or 15inch will do.
I dont agree with your comment about flat response.
I am only covering from say 45hz down to about 20hz. Flatness will depend heavily on the room which will not be perfect anyway so I'm not bothered at all about flatness. Even the response of the human ear itself is not flat, it varies and actually isnt even symmetrical, as my audiogram showed.
The phase is again room dependent and it's silly to try to get it perfect in a domestic environment.
Do you agree or not?
Re: Drivers and Tubes
I dont understand why we need to taper it? and how that will make it shorter for a given cut off frequency?
I dont know if they will make a tapered pipe.
Id be happy if you could do the design work, in fact can you recommend the parts list?
I think a drive unit with dual inputs and around 15 inches.
My ceiling is 8 foot however, I could lay it on its side or diagonally.
My other hypothetical question is this. What would happen if we used a infinitely long pipe for a given drive unit?
Would it be the same as an infinite baffle?
How low could we make it go then?
opc said:
I dont understand why we need to taper it? and how that will make it shorter for a given cut off frequency?
I dont know if they will make a tapered pipe.
Id be happy if you could do the design work, in fact can you recommend the parts list?
I think a drive unit with dual inputs and around 15 inches.
My ceiling is 8 foot however, I could lay it on its side or diagonally.
My other hypothetical question is this. What would happen if we used a infinitely long pipe for a given drive unit?
Would it be the same as an infinite baffle?
How low could we make it go then?
Professor, I think you are trying to make it more complicated than it really is. After reading Mr. Pass' article, it seemed to me that the key to the whole thing is the Helmoltz frequncy/resonance that is set up in a cavity (pipe) of a certain length. Just use his formula to calculate the lenght the pipe needs to be to resonate at about the frequency you want, stick the woofer on the end, seal it, amplify it and then start tweaking it. Get a 14 foot section from your supplier, or 2 8 foot sections and have fun. Use the woofer you have or can obtain for a cheap price. The first time I tried it I duct taped the woofer to the end of the sonotube
After I tested it and saw that it worked well I had a friend make a wooden mounting plate that had a groove cut into it on one end to hold the tube and I screwed the woofer on the other end.
An infinitely long tube would resonate at 0hz.
After I tested it and saw that it worked well I had a friend make a wooden mounting plate that had a groove cut into it on one end to hold the tube and I screwed the woofer on the other end.An infinitely long tube would resonate at 0hz.
Re: Re: Drivers and Tubes
Aye, there's the rub...
Specs are worthless. Why? Well, for one thing there is no spec that shows cone breakup modes.
We stand at the edge of a perilous precipice, but being both brave and foolish I'll take a whack at it.
A good woofer will depend to some extent on what diameter you end up choosing. Some manufacturers have better 12s, some better 15s, or they may throw you a curve ball and have a great 12, but not even make a 15.
Diameter. Most people think of diameter in terms of how loud it will get (how much air it can pump), but there's more to it than that. All things being equal (they never are, but...) the less distance the cone has to travel, the lower your distortion will be. The price you pay is that larger cones have slower transient response and poor high frequency response. Use a low enough crossover point and those are less of a problem.
It's all a question of balancing one thing against another.
If you're not concerned with your frequency response, then any old thing will do.
Phase matters in the sense that your sense of...let's call it impact...is derived from having all the various portions of the waveform (subwoofer, woofer, midrange, tweeter) launch at the same time. Delay the sub and you'll get a 'light,' 'wimpy' sound because the midrange will get to you first, but the "whump" will arrive at the party late. It's a first arrival problem. Milliseconds matter.
Some of this will boil down to how the speakers are placed in your room. I begged a fellow I know to make some changes in his speaker placement for years. He finally did so. "You know, Grey, it sounds a lot better now!"
My response won't bear repeating. Just assume that it took somewhat from "DUH!" and "&#$%" and "YOU BLOODY IDIOT, WHAT TOOK YOU SO LONG?" in varying proportions until I ran out of breath.
Back up and do some basic reading on transmission lines. There's a good website, but I can't remember the URL. Ask Planet10, he does speakers all day long--he'll know the one right off the top of his head. Hell, it might even be his site I'm thinking of.
An infinitely long line will not get you response to 0Hz. Think more in terms of an extra octave of response, max. And even that can be screwed up by other factors. Part of the reason that transmission lines are as much art as science is because the free air resonance doesn't really tell you much about the response of the driver. In an ideal world, you'd take the point where the driver begins to roll off (I repeat, not[/] to be confused with the free air responance) and set the tube to begin working there.
A brief and oversimplified way of looking at a transmission line is to think of it as absorbing the rear radiation of the driver above a certain frequency. In other words, it's a low pass filter. You want the rear wave to start fading in right as the response starts falling off. In this respect, it arguably has something in common with a vented box, but it manages the trick in a totally different way. The quarter-wave part (Aha! My brain just woke up...try www.quarter-wave.com for a decent overview of the transmission line.) stems from the fact that it takes a quarter-wavelength of absorbtive material to attenuate sound. It also delays the sound somewhat.
I'm out of time. I'll try to get back to this later.
Grey
opc said:
Aye, there's the rub...
Specs are worthless. Why? Well, for one thing there is no spec that shows cone breakup modes.
Professor smith said:
We stand at the edge of a perilous precipice, but being both brave and foolish I'll take a whack at it.
A good woofer will depend to some extent on what diameter you end up choosing. Some manufacturers have better 12s, some better 15s, or they may throw you a curve ball and have a great 12, but not even make a 15.
Diameter. Most people think of diameter in terms of how loud it will get (how much air it can pump), but there's more to it than that. All things being equal (they never are, but...) the less distance the cone has to travel, the lower your distortion will be. The price you pay is that larger cones have slower transient response and poor high frequency response. Use a low enough crossover point and those are less of a problem.
It's all a question of balancing one thing against another.
If you're not concerned with your frequency response, then any old thing will do.
Phase matters in the sense that your sense of...let's call it impact...is derived from having all the various portions of the waveform (subwoofer, woofer, midrange, tweeter) launch at the same time. Delay the sub and you'll get a 'light,' 'wimpy' sound because the midrange will get to you first, but the "whump" will arrive at the party late. It's a first arrival problem. Milliseconds matter.
Some of this will boil down to how the speakers are placed in your room. I begged a fellow I know to make some changes in his speaker placement for years. He finally did so. "You know, Grey, it sounds a lot better now!"
My response won't bear repeating. Just assume that it took somewhat from "DUH!" and "&#$%" and "YOU BLOODY IDIOT, WHAT TOOK YOU SO LONG?" in varying proportions until I ran out of breath.
Professor smith said:
Back up and do some basic reading on transmission lines. There's a good website, but I can't remember the URL. Ask Planet10, he does speakers all day long--he'll know the one right off the top of his head. Hell, it might even be his site I'm thinking of.
An infinitely long line will not get you response to 0Hz. Think more in terms of an extra octave of response, max. And even that can be screwed up by other factors. Part of the reason that transmission lines are as much art as science is because the free air resonance doesn't really tell you much about the response of the driver. In an ideal world, you'd take the point where the driver begins to roll off (I repeat, not[/] to be confused with the free air responance) and set the tube to begin working there.
A brief and oversimplified way of looking at a transmission line is to think of it as absorbing the rear radiation of the driver above a certain frequency. In other words, it's a low pass filter. You want the rear wave to start fading in right as the response starts falling off. In this respect, it arguably has something in common with a vented box, but it manages the trick in a totally different way. The quarter-wave part (Aha! My brain just woke up...try www.quarter-wave.com for a decent overview of the transmission line.) stems from the fact that it takes a quarter-wavelength of absorbtive material to attenuate sound. It also delays the sound somewhat.
I'm out of time. I'll try to get back to this later.
Grey
Hi Prof. Smith,
The best explanation of all your questions is in Martin J. King's website:
http://www.quarter-wave.com/TLs/Alignment_Tables.pdf
Give that paper a read over at least once or twice, and give it time to sink in. It's fairly straightforward and very well written.
Tapering the pipe increases the impedance of the open end, and if you work through the equations on page 3 you'll see the relationship to pipe length.
You don't actually need a tapered pipe (although that would be really really cool if they would make you one). All you need is a straight pipe, and use the foam method that Grey described a few posts back to make it tapered. I've thought about this, but the best I could come up with was a cone shaped wedge supported in the open end of the tube that ran all the way down to the driver. That would also work, but it's a technical nightmare to build.
As far as a ballpark design goes, how about this:
- Dayton TIT400C-4 15" Titanic Mk III Driver
- Line length = 118"
- Driver end area = 161" square
- Open end area = 32.25" square
- Use 15" ID tube
- Taper down to 6.4" ID at open end
- Pipe tuning freq. would be 20Hz
If you don't like that driver, then AEspeakers makes something called an IB15 which is only $100 and would likely perform much better than the PE driver. I'd have to go back over the line calcs, but it would be very close to the above.
Also, don't limit yourself to dual voice coil drivers. It's much better to sum the channels at the input of the sub amplifier.
I've attached another one of my terrible drawings, which might explain what's going on. I have this strange ability to picture things perfectly in my head, but drawing them out the way I see them mentally always turns out to be a mess... I think I'm spatially challenged when it comes to drawing.
Let me know what you think, and we'll go from there.
Enjoy!
The best explanation of all your questions is in Martin J. King's website:
http://www.quarter-wave.com/TLs/Alignment_Tables.pdf
Give that paper a read over at least once or twice, and give it time to sink in. It's fairly straightforward and very well written.
Tapering the pipe increases the impedance of the open end, and if you work through the equations on page 3 you'll see the relationship to pipe length.
You don't actually need a tapered pipe (although that would be really really cool if they would make you one). All you need is a straight pipe, and use the foam method that Grey described a few posts back to make it tapered. I've thought about this, but the best I could come up with was a cone shaped wedge supported in the open end of the tube that ran all the way down to the driver. That would also work, but it's a technical nightmare to build.
As far as a ballpark design goes, how about this:
- Dayton TIT400C-4 15" Titanic Mk III Driver
- Line length = 118"
- Driver end area = 161" square
- Open end area = 32.25" square
- Use 15" ID tube
- Taper down to 6.4" ID at open end
- Pipe tuning freq. would be 20Hz
If you don't like that driver, then AEspeakers makes something called an IB15 which is only $100 and would likely perform much better than the PE driver. I'd have to go back over the line calcs, but it would be very close to the above.
Also, don't limit yourself to dual voice coil drivers. It's much better to sum the channels at the input of the sub amplifier.
I've attached another one of my terrible drawings, which might explain what's going on. I have this strange ability to picture things perfectly in my head, but drawing them out the way I see them mentally always turns out to be a mess... I think I'm spatially challenged when it comes to drawing.
Let me know what you think, and we'll go from there.
Enjoy!
Attachments
Wow... it put stars over the letters "T- I -T" which preceded the model name of that driver. Looks like the auto-filter went a little too far.
Grey posted while I was writing my post, so there's a bit of redundancy in the website suggestions.
I'm glad you commented on that "0Hz resonance" thing... I wasn't sure if it was intended as a joke or not so I didn't say anything.
By specs I meant FR measurements and waterfalls inclusive... so that would show you cone break-up. Most cones are pretty free from those types of problems between 20Hz and 45Hz however, so I'm not sure it's entirely applicable here.
Getting accurate data in that range would require buying all the applicable drivers, building enclosures for each, and actually testing them in your room. I'm not entirely sure that would be practical. I don't trust most published graphs when you get down around 20Hz.
Cheers,
Owen
Grey posted while I was writing my post, so there's a bit of redundancy in the website suggestions.
I'm glad you commented on that "0Hz resonance" thing... I wasn't sure if it was intended as a joke or not so I didn't say anything.
By specs I meant FR measurements and waterfalls inclusive... so that would show you cone break-up. Most cones are pretty free from those types of problems between 20Hz and 45Hz however, so I'm not sure it's entirely applicable here.
Getting accurate data in that range would require buying all the applicable drivers, building enclosures for each, and actually testing them in your room. I'm not entirely sure that would be practical. I don't trust most published graphs when you get down around 20Hz.
Cheers,
Owen
You would have 2 El Pipe-o's, and the outputs would be out of
phase. A lot would depend on where they were pointed.
😎
phase. A lot would depend on where they were pointed.
😎
And if you were to put a pipe on both sides of the driver cone, each pipe tuned to different frequencies, you get a variation on Dr. Bose Sound Cannon.
Peace,
Dave
Peace,
Dave
Yes this project reminded me of BOse.
By the way, I was quoted a price of 100 pounds for one 12 inch diameter 8 foot tube. It seems abit pricey. Is this normal?
Also If i only want to cover 35hz to 15hz, how do I do this?
By the way, I was quoted a price of 100 pounds for one 12 inch diameter 8 foot tube. It seems abit pricey. Is this normal?
Also If i only want to cover 35hz to 15hz, how do I do this?
Also just to be clear what would happen if I mounted this pipe diagnoally across the room? This is the only way for me to fit such a long pipe, of course it wouldnt look appealing having a pipe acroos the room from one corner to the other but is this acceptable?
Secondly can this pipe really shake the room? and cause damage?
Secondly can this pipe really shake the room? and cause damage?
No real problem with mouting the pipe the way you desire, it will have effects on the bass output. By mounting the pipe diagnonally you will effectively be corner loading the output ends of the pipe, this should further reinforce the bass.
Is it possible to shake the room, yup. Can you do damage with it, that depends on the SPL's coming out of the sub, and the structural condition of the building you are mounting it in. If there is sufficient bass output and/or the building isn't very well built, it can possibly damage things.
To cover the range of 15 to 35hz, calculate the pipe length needed for 15hz, that will give you the low end. Then use a crossover, either passive or active, to rolloff the frequencies above that which you want.
Peace,
Dave
P.S. can't speak for the cost of the tube, haven't built one yet, it's in the future though!
Is it possible to shake the room, yup. Can you do damage with it, that depends on the SPL's coming out of the sub, and the structural condition of the building you are mounting it in. If there is sufficient bass output and/or the building isn't very well built, it can possibly damage things.
To cover the range of 15 to 35hz, calculate the pipe length needed for 15hz, that will give you the low end. Then use a crossover, either passive or active, to rolloff the frequencies above that which you want.
Peace,
Dave
P.S. can't speak for the cost of the tube, haven't built one yet, it's in the future though!
But will the lowest note i can achieve depend on my room size or not?
and when you speak of damage, whats the worst damage that we can do in practice? Broken windows or damaged internal organs?
I tried a 15 inch box subwoofer at one point and it certainly rattled the windows and the door.
Is it true that the lower you go at higher spls the more damage can occur?
By the way does anyone know if damage to hearing can occur with ultra low vibrations such as below 20hz?
and when you speak of damage, whats the worst damage that we can do in practice? Broken windows or damaged internal organs?
I tried a 15 inch box subwoofer at one point and it certainly rattled the windows and the door.
Is it true that the lower you go at higher spls the more damage can occur?
By the way does anyone know if damage to hearing can occur with ultra low vibrations such as below 20hz?
Hello Professor Smith, the lowest note that will be reproduced depends on multiple factors. The size of the driver, the type of enclosure and the room all have an effect.
Damage that can be done varies also, if the bass is of high enough SPL and of the correct frequency, the building can go into resonance and this will cause structural damage. This is also true of the human body. It's not so much getting lower and lower frequencies as it is hitting the resonant frequency of something that creates a real problem.
Hearing damage can occur from any frequency, it's more a function of the SPL level. If the SPL is high enough (>80dB) and the exposure to the sound is long enough (duration decreases as SPL increases) then you can do damage to your ears. This is why many health agencies require employees to wear hearing protection when the SPL measures over 80dB.
Peace,
Dave
Damage that can be done varies also, if the bass is of high enough SPL and of the correct frequency, the building can go into resonance and this will cause structural damage. This is also true of the human body. It's not so much getting lower and lower frequencies as it is hitting the resonant frequency of something that creates a real problem.
Hearing damage can occur from any frequency, it's more a function of the SPL level. If the SPL is high enough (>80dB) and the exposure to the sound is long enough (duration decreases as SPL increases) then you can do damage to your ears. This is why many health agencies require employees to wear hearing protection when the SPL measures over 80dB.
Peace,
Dave
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