I've also toyed with the idea recently of a servo rotary subwoofer which operates in OB mode. I'm not sure how you get a DC motor to work with an AC music signal though. I also wonder how the distortion can be low where there is a heavy large diaphragm. A cone is an efficient way of moving air since it is very light and strong, but whatever you use in a diy rotary design is not likely to have that advantage.
The concept has a lot of appeal - high SPL OB bass without spending absurd amounts on moving a lot of air with conventional drivers ...
But can a diyer do it without extreme cost or difficulty? Is it feasible? Does it work well enough to put aside conventional drivers?
I'm going to be watching with a lot of curiosity!
EDIT: if you can get the converter to work, then one idea is to use a lot of large passive radiators for the cone. Suppose you made an array of dipole W frames with 15" or 18" passive radiators.
The concept has a lot of appeal - high SPL OB bass without spending absurd amounts on moving a lot of air with conventional drivers ...
But can a diyer do it without extreme cost or difficulty? Is it feasible? Does it work well enough to put aside conventional drivers?
I'm going to be watching with a lot of curiosity!
EDIT: if you can get the converter to work, then one idea is to use a lot of large passive radiators for the cone. Suppose you made an array of dipole W frames with 15" or 18" passive radiators.
paulspencer said:
you MUST have the DC motor for the AC music signal... otherwise it would only spin one way... not the other.... it just works... don't ask me why 😛
it works amazingly well as I'm sure Tom will attest... the advantage is that you start with an already very efficent motor
light and strong are exactly what a carbon fiber cone element is... if you tried a solid piece of MDF like the parthenon used... you would find that it weighed far far more than two pounds...
the idea of the rotary is simple enough... and the most feasible thing for a DIYer... it's a realitively functional design... I finally came up with one of this size that will work in 10 cubes sealed and extend with an F3 of 13hz... problem is that efficency (if it was a conventional motor) is 80db/w...
the problem is trying to come up with a way to model these things... and sense it's so different than pistonic motors... I probably shoudl just build it and see what 2400 watts will do to a 2.25hp DC motor .....
You're whizzing right over the doppler distortion problem of such large excursion, which is going to make it sound like a helicopter.
I believe a giant cone is a much better answer for constructing something extreme if SQ is important.
I believe a giant cone is a much better answer for constructing something extreme if SQ is important.
johninCR said:
how do you get any bigger than 25x30?
45x45?
I think I might be able to do this...
what about keeping it under 100mm one way and 45x45?
the problem is you're running into a system that's going to give you diminishing returns as you increase the cone area to gain the SPL...
if I do this... and relinquish the movement to less than 30degrees rotation (lthe PG cyclone has 38degrees of rotation) this would yield 13.8 cubic feet of diplacement... would this be a better solution?
if so I can actually go far smaller on the sealed box and keep the design more compact in general
problem is to keep Vas low enough moving mass needs to be on the order of 20lbs... and motor strength to at least 50 N/A... not to mention suspension is nearly none existant
hmmmm
There is NO SUCH THING as doppler distortion in speakers. There's a thread all about it somewhere on the forum but I cant seem to find it(and there is experimental proof somewhere on the net)
The so called doppler distortion is caused by phase shifts from the source changing distance. At 30hz the wavelength is well above 20feet so if your speaker isnt moving half of that then the phase shift should be insignificant.
Its simple. A DC motor works so that when you apply a Direct current to it it will spin in one direction. Just like a speaker works when you apply a DC signal it, it will move in one direction. The problem with a speaker that a DC motor does not have is that the speaker motor runs out of it's magnetic gap and cant move any further after a point. A DC motor on the other hand will spin around and around. When you put a AC signal to the DC motor it will spin back and forth at the frequency being sent to it and at a magnitude proportional to the power imput.
A DC motor will also have fewer linearity problems(less distortion) because it's BL should be perfectly constant. The moving mass should have little effect on distortion if the "cone" is made well.
I don't believe that is correct at all. When you are talking about those kind of huge excursions doppler distortion can't help but come into play. For example, take a 30hz tone with a 10" ptp excursion and we'll ignore that the cone has to accelerate and assume that it is instantly up to speed in each direction (so we're understating the velocity), then playing that 30hz tone the cone is travelling at 34mph in each direction. Now while we're playing that tone, let's mix some 80hz in there too (since this is a sub). Are you trying to tell me that you aren't going to be able to hear the effect of launching that 80hz tone off of a surface that is travelling back and forth at 34mph .
Now let's throw into the mix the fact that the cone itself will be travelling at different speeds at different distances from the axis of rotation. This is also going result in distortion.
Now let's throw into the mix the fact that the cone itself will be travelling at different speeds at different distances from the axis of rotation. This is also going result in distortion.
johninCR said:
this speaker will never see anything above 32hz....
well the problems you state... IMD distortion... are present in all speaker systems... you can only do what you can to eliminate them
johninCR said:
a speaker like a 45x45" one would require far too large of a box and far too much cone weight... in fact over 13 lbs are needed to keep box size small... and the motor strength would have to be majorly beefied up
I'll try the large excursion design for now 😉
I think a lot of this sceptisism will be proven one way or another.
That is one great thing that Audiophilenoob does- actually make stuff. I applaud his efforts, and he IS in fact following a path that has been investigated before- apparently with some decent results.
Of course if it turns out to be "the greatest woofer ever made"
I won't know what to think
😉
That is one great thing that Audiophilenoob does- actually make stuff. I applaud his efforts, and he IS in fact following a path that has been investigated before- apparently with some decent results.
Of course if it turns out to be "the greatest woofer ever made"
I won't know what to think
😉
Variac said:
thank you variac
the esoteric and unique is what I care about... and if it turns out to smack me in the face I'm prepared for it 🙂
just don't judge me because of my enthusiasmif I can be the DIY community's guinnea pig I will be quite happy doing so 😀
Audiophilenoob,
How is your driver going to be aligned? Is it going to be like and opening/closing door (with the axis vertical)? Or is it going to be like a 'cat-flap' with the axis horizontal?
The second method would allow the gravity to do some of the work of your suspension (but there might be other problems).
I look forward to any results you're willing to share with us...
How is your driver going to be aligned? Is it going to be like and opening/closing door (with the axis vertical)? Or is it going to be like a 'cat-flap' with the axis horizontal?
The second method would allow the gravity to do some of the work of your suspension (but there might be other problems).
I look forward to any results you're willing to share with us...
Cloth Ears said:
oh I assure you I will post the process in detail
it will be axis vertical... like a door yes... the rear chamber will be 10 cubes sealed I think now... and this doesn're really add that much to the speaker size itself all that it will do is just make it a square when looking from the outside vs. this crazy "pizza pie" shape 😛
10 cubes should give very very good extension to 13hz... in fact the F3 point isn't till 12hz... this is with a low Vas and extremely high QTS... efficency drops to around 85db/w (if this was a pistonic speaker I guess)
MMs is 2lbs or so... and CMS is very very low... nearly none existant
Like I said before the distortion has NOTHING to do with cone speed, but the excursion distance and how that distance equates to a phase shift. There is a slight big of frequency shifting that does occur, but is because of a distance/phase shift. At bass frequencys where the wavelengths are extremely long the phase shift should be minimal because the excursion is small compared to the wavelength.... If I can find the thread about this, you will understand.
I'm not being skeptical, just pointing out what I perceive to be a flaw in the design. If I were building something similar, then I'd welcome anyone playing devils advocate. If he doesn't want input, WHY POST ANY INFO BEFORE IT'S BUILT ?
BA,
It has everything to do with speed. When the homeys go idling by at slow speed you don't hear the doppler effect, but when they go whizzing by you sure will. This is whizzing by back and forth.
BA,
It has everything to do with speed. When the homeys go idling by at slow speed you don't hear the doppler effect, but when they go whizzing by you sure will. This is whizzing by back and forth.
johninCR said:
at what frequency do they whizz by?
it's fine to point out possible flaws... hence why I posted... no problem here 😉
Audiophilenoob and others,
so, i have all these motors i want to try out. i really just want to 1) test them, 2) apply AC and see what happens.
all the motors i have are brushless DC servo motors. almost all would be beefy enough for this purpose, some would be INSANE, (2HP 230VDC servos).
anyways, most all of them have 4 large wires, and 5-6 wires (which are presumably the encoders). the large wires are always black, red, white, and green. how would i go about connecting those to an amplifier? or, better yet, how can i simply connect these in a manner to test them out?
this is something i would really like to tinker around with because i have the motors and i have a friend who builds large RC airplanes and has ability to vacuum carbon fibre and fiberglass. so, building a large, lightweight panel would be easy. i just want to toss something together to test it out and give it a whirl.
thanks!
so, i have all these motors i want to try out. i really just want to 1) test them, 2) apply AC and see what happens.
all the motors i have are brushless DC servo motors. almost all would be beefy enough for this purpose, some would be INSANE, (2HP 230VDC servos).
anyways, most all of them have 4 large wires, and 5-6 wires (which are presumably the encoders). the large wires are always black, red, white, and green. how would i go about connecting those to an amplifier? or, better yet, how can i simply connect these in a manner to test them out?
this is something i would really like to tinker around with because i have the motors and i have a friend who builds large RC airplanes and has ability to vacuum carbon fibre and fiberglass. so, building a large, lightweight panel would be easy. i just want to toss something together to test it out and give it a whirl.
thanks!
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