I have a $8 OB on cardboard setup in my workshop with the PC, and want to toss a sub into this. This is separate from the boxes on stands and 2 OB projects that are elsewhere in the house.
Just for fun I am going to take two 3" Chinese widebands, get a long length of PVC with 3/16ths thick walls, and place one on each end. They will be mechanically out of phase so that one on one end pushes out, the other is pushing in.
What I cannot find are calculators to figure this project as a sealed sub since it's a cylinder 75mm in diametre and 3 to 4 metres in length.
Maybe I will lay it down on the floor behind the PC and workbench, maybe I will stand it up in a corner. Who knows. It will cost under $15.
Drivers I will use have an Fs of 113-118 or so, will use a passive XO to feed the $8 high end upper octaves, and a SS amp to power the upper octaves and separate SS one for lower octaves.
What I expect is that with an amp and XO and a bass EQ on the amp, that I will be able to get this setup to extend well below 118 to the point of destroying these small drivers. Since they won't have any air pushing back as they will be out of phase, it's up to me to see if I will play them loud enough to separate the cone from coil. They will operate much as an OB in that regard. Over driving them is always a risk.
That said, I am trying to find calcs to model the FR of these.
Since my mids/woofers for the upper octaves roll off at the same frequency, [these are 3" $1.50 cheap-o yellow paper cone drivers scavenged from some old TV speakers] with a similar Fs for the drivers in the OB (not the ones that will be used in the sub) and all have very similar specs, I want to see what FR I can expect from a tube of 3 or 4 metres or so in length that is 75mm in diametre with 2 identical 75mm drivers 3 or 4 metres apart capping a long tube.
I suspect I will be able to 'ask' these drivers to do what they cannot, to the point of destruction. I want to calculate what that FR would be, how low/loud.
Any suggestions, tips tricks or hints will be most welcome!
TIA
Sub driver specs
Fms 118.5
Qms 3.75
Qes 0.99
Qts 0.72
Res 0.8ohm
Rms 0.2kg/s
Cms 1.40 mm/N
Mms 0.9gr
Nref 0.41%
Bl 1.7 N/A
SPL 88.1 dB
Vas 1.6L
Vas 0.05650347 cubic ft
Re 3.6Ohm
Rp 11.7ohm
Lp 3.9mH
Cp 622.4uF
Le 0.2mH
Max power 15W
vol of cylinder pi r2 h
3.75 - 3.50 cm2
300 - 360cm h
3.1416
15946.875cc 11545
15.947L 11.545L
4.21 US gallons 3.05 US gallons
Just for fun I am going to take two 3" Chinese widebands, get a long length of PVC with 3/16ths thick walls, and place one on each end. They will be mechanically out of phase so that one on one end pushes out, the other is pushing in.
What I cannot find are calculators to figure this project as a sealed sub since it's a cylinder 75mm in diametre and 3 to 4 metres in length.
Maybe I will lay it down on the floor behind the PC and workbench, maybe I will stand it up in a corner. Who knows. It will cost under $15.
Drivers I will use have an Fs of 113-118 or so, will use a passive XO to feed the $8 high end upper octaves, and a SS amp to power the upper octaves and separate SS one for lower octaves.
What I expect is that with an amp and XO and a bass EQ on the amp, that I will be able to get this setup to extend well below 118 to the point of destroying these small drivers. Since they won't have any air pushing back as they will be out of phase, it's up to me to see if I will play them loud enough to separate the cone from coil. They will operate much as an OB in that regard. Over driving them is always a risk.
That said, I am trying to find calcs to model the FR of these.
Since my mids/woofers for the upper octaves roll off at the same frequency, [these are 3" $1.50 cheap-o yellow paper cone drivers scavenged from some old TV speakers] with a similar Fs for the drivers in the OB (not the ones that will be used in the sub) and all have very similar specs, I want to see what FR I can expect from a tube of 3 or 4 metres or so in length that is 75mm in diametre with 2 identical 75mm drivers 3 or 4 metres apart capping a long tube.
I suspect I will be able to 'ask' these drivers to do what they cannot, to the point of destruction. I want to calculate what that FR would be, how low/loud.
Any suggestions, tips tricks or hints will be most welcome!
TIA
Sub driver specs
Fms 118.5
Qms 3.75
Qes 0.99
Qts 0.72
Res 0.8ohm
Rms 0.2kg/s
Cms 1.40 mm/N
Mms 0.9gr
Nref 0.41%
Bl 1.7 N/A
SPL 88.1 dB
Vas 1.6L
Vas 0.05650347 cubic ft
Re 3.6Ohm
Rp 11.7ohm
Lp 3.9mH
Cp 622.4uF
Le 0.2mH
Max power 15W
vol of cylinder pi r2 h
3.75 - 3.50 cm2
300 - 360cm h
3.1416
15946.875cc 11545
15.947L 11.545L
4.21 US gallons 3.05 US gallons
Last edited:
Only one way to find out, and it's a simply matter to reverse the polarity and have the air in the tube compress.
I'd go bipolar (opposite polarity) to get max SPL. Dipole doesn't have any advantage in your situation. Use a short tube to make Qtc .7, add moderate LF boost with a linkwitz transform, if you know or can measure the T/S parameters. But watch the power level so you don't burn the small VC. It might only handle 10W peak.
According to this calculator, the two small drivers will make only 78dB SPL at 50Hz at 2mm excursion, with LF boost. That should work OK. 50Hz is satisfying for a desktop system, and the sealed bass will rolloff at only 12dB so it will sound lower.
Piston Excursion calculator
Last edited:
there has been a experiment on adding the second driver to the open end of an sono-tube sub, I have read it some where. The result was not very good. I think the guy eventually put the two drivers face-to-face on the same end of the tube.
considering your drivers are very small, it is probably better to run them side by side to get larger piston area.
considering your drivers are very small, it is probably better to run them side by side to get larger piston area.
Last edited:
...thanks Richidoo!
Piston Excursion Calc...never would have thought of that one...
Running the calcs these types of drivers are better suited for a ported box, but I want to see what happens with a longer sono tube, and I can always cut the tube down to size and use it for something else. Will use one or two, bipolar or dipolar, etc, to hear the results.
QUESTION
What measurement for diametre would I use?
That of the cone before it connects to the surround? Of the middle of the surround? The outer edge of the surround? The face plate?
Piston Excursion Calc...never would have thought of that one...
Running the calcs these types of drivers are better suited for a ported box, but I want to see what happens with a longer sono tube, and I can always cut the tube down to size and use it for something else. Will use one or two, bipolar or dipolar, etc, to hear the results.
QUESTION
What measurement for diametre would I use?
That of the cone before it connects to the surround? Of the middle of the surround? The outer edge of the surround? The face plate?
Last edited:
It’s not really a sealed sub, but a dipole connected by a long ½ WL open cylinder that will resonate at ~1130 ft_sec/2/10 ft = 56.5 Hz, turning the driver’s output into a series of peaks, dips unless heavily damped, so not a good plan even if wired as bipole.
Resonances of open air columns
Resonances of open air columns
FWIW, using the more accurate Mms, Cms, BL, etc., specs, Fs = ~141.79 Hz, Qts = 0.8 and calculates a Sd = 28.4 cm^2.
GM
Attachments
![Chinese 3' wide bad [miragem3i] specs.gif](/community/data/attachments/378/378002-aa5e76819eb6467bdfbd60a530aa429a.jpg?hash=ql52gZ62Rn)
Diameter is measured from the middle of the surround. Diameter is only relevant to calculating the swept area (Sd,) which GM has kindly provided.
I actually just typed in 3" to the piston calc, and calculated SPL @50Hz. So your actual diameter might be smaller and the SPL at 50Hz even softer. It's hard to make subwoofer from 3", but where there's a will there's a way.
Last edited:
Hi,
There is nothing sub about 3" drivers and you are totally
wasting your time. Nothing good about an out of phase
pipe which would work better with a driver omitted from
one end compared to using two, unless it is in phase.
rgds, sreten.
There is nothing sub about 3" drivers and you are totally
wasting your time. Nothing good about an out of phase
pipe which would work better with a driver omitted from
one end compared to using two, unless it is in phase.
rgds, sreten.
Thank you for the input.
I am curious why so many members here 'shoot down'
and severely criticise other's builds.
It's very clear that there is 'an absolute sound' here that many agree upon, and attempt to force others to adopt.
You are not the 1st, nor 2nd (nor 3rd) member here to do this in one of my threads.
Perhaps you and I don't share the same values?
Perhaps my definition of 'a sub' for this particular install, is not the same as the guys who build 16 x 18" cabinets for their basement HT that cause everything in their house to fall down, and prompt the wife to scream at them to turn it down/off?
Really, curious why so many here are project killlers.
Some of you want members to have fun, as long as what we do meets your approval.
If it doesn't then the criticism is withering (and unwanted).
I think it is clear from this project/build, that I am not attempting to create a Sensurround Home Theatre Experience (which I felt first hand as a teen in North American theatres in the early-mid 1970's).
Last edited:
Addendum:
I found a source of sono-tube that would meet with the approval of some here.
Once I do this smaller 3" sub project, I will pursue the larger one.
Concrete storm runoff piping, made to order, various sizes.
I can get one made that's 3 metres long, 30cm or 40cm or 50cm in diameter.
I can then plug the ends with wooden discs, mount a driver or two in that (10' to 18"), and have a 'real subwoofer'. Fill with wadding, scare the neighbours, shake pictures off of the walls.
Overkill to the max.
Hauling a concrete pipe into the house will make a mess, I am sure.
I found a source of sono-tube that would meet with the approval of some here.
Once I do this smaller 3" sub project, I will pursue the larger one.
Concrete storm runoff piping, made to order, various sizes.
I can get one made that's 3 metres long, 30cm or 40cm or 50cm in diameter.
I can then plug the ends with wooden discs, mount a driver or two in that (10' to 18"), and have a 'real subwoofer'. Fill with wadding, scare the neighbours, shake pictures off of the walls.
Overkill to the max.
Hauling a concrete pipe into the house will make a mess, I am sure.
You might consider using a PVC "x" 4-way fitting at about 1/3 of distance from one end which is sealed. Leave other end open. Mount drivers on the cross and run drivers in phase (same polarity) and you may get a TL with reduced peaks and more output as dual drivers. I would suggest at least 5 in drivers that are sub woofers rather than full range. You can model this in Hornresp easily. The 3 in drivers will make bass down to 50 Hz and 30 Hz even but the excursion required for that is huge and forces the driver to operate near or beyond its xmax which means distortion will be high - about close to 100%. Using larger woofers allows large cone motions and relatively smaller movements to keep distortion lower.
Last edited:
That seriously sounds as a good project to me, especially the last one, put in a low sensitivity 18" driver and go..
Would go well with two 3" full range drivers each in a 1,5 meter PVC-pipe, with an open end. You could easily sim that by the way in Hornresp as well as the above suggestion (xrk971).
Now that I think of it, 3 meters would be a bit short for a real sub, 4 meters is where the fun starts.
Best regards Johan
Hoffman's Iron Law. It's possible but we have to sacrifice efficiency. OP, have you look at the Dayton Audio ND105? It's 4 inch but outperforms it's little brother significantly, so it's worth the size increase IMO.
Hi,
When the suggested project has no technical merit
whatosover and implies some severe misunderstanding
of one or more or many of the technical issues you
should be glad some of us are blunt enough to say so.
Its not remotely clear what you are trying do, or that
you have any understanding of what the build you
suggest will do, which is nothing much useful at all.
You can take or leave comments on a suggested build,
there is nothing personal involved, but imagining they
are, so you can carry on with the idea, when it has
received a serious thumbs down, is up to you.
Your suggestion has no technical merit in any respect,
other than being a ~ 50Hz boom tube still completely
limited by driver excursion, (why one driver with the
the other open is better, the open end is not), and
in all respects is an approach that makes no sense.
I can't think of of a single worthwhile feature.
It won't work at all vertically and quite ludicrous
as a form factor pointed at the listener to work.
rgds, sreten.
Last edited:
Since I have the materials and time, what I am going to do is this in this order
1) A 2900mm TL with one 3"driver
2) A 2900mm sealed tube with two 3"drivers
3) Cut the tube down to size to 1450mm and then 725mm and work with 2 and 1 driver on each.
The Fs for the driver is 118.5.
With 343.3 m/s based upon a temp in the listening room, a 1/4 wave calc results in:
343.45 / 118.5 / 4 == 0.7246 == 725mm which is what the length 'should' be.
Longer pipes will have various null issues and peaks and troughs, issues that I want to hear first hand and experiment with. A hack saw and 2 minutes can fix all of this as the length shortens and these drivers are widerange and can be used in the baffle-less hanging speaker frames that are yet another project.
Definitely, but the top octaves for this setup consist of 5EUR of drivers mounted in cardboard baffles from a shipping box, 15cm x 25cm wide and this is much more along the lines of ''see what happens'" and "work on my project building skills" than anything else.
Volume is going to be far below what most here would prefer and want (86), and the neighbours are very close and walls are very acoustically thin. The ceiling is also sprung and I suspect would not withstand any decently reproduced deep bass without structural failure.
This is not something I wish to determine experimentally.
rades and xrk those are some very fun ideas. I like the x-fitting partway down the pipe. That's an odd one I will pursue.
I am fine with the lowered sensitivity and low volume levels that won't exceed 80dB often.
I doubt I can get this driver down to 30hz even with aggressive EQ and a dB level of 60. Should be interesting to see. In an enclosed 3.5L box these drivers get down to 55hz at respectable volume levels. They roll off severely below 55hz.
- Status
- Not open for further replies.