MJL21193 said:
No need to start ridiculing the religious beliefs of others here.
Admiral Adama would not approve.
Don't worry if you haven't seen te light, SpongeBob still loves you.
Mjl21193:
1: I live in a rental, cutting a hole through the wall / floor / ceiling is not an option.
2: I can't leave anything alone without tinkering with it, even ideas.
3: Rube Goldberg would be spinning in his grave at such an attitud, Shame on you.
4: we need more hamsters to power this thing.
1: I live in a rental, cutting a hole through the wall / floor / ceiling is not an option.
2: I can't leave anything alone without tinkering with it, even ideas.
3: Rube Goldberg would be spinning in his grave at such an attitud, Shame on you.
4: we need more hamsters to power this thing.
neededandwanted said:
Time for me to get serious here. Low frequency sound waves pass unobstructed through most material, especially fabric, due to the long wavelength. Ever notice how bass is the first thing you hear when you approach a closed room with music playing inside?
As far as I can see the fan sub has two BIG strikes against it:
1. It's a complex (overly so, IMO) device that is very difficult to build. Making the blades variable pitch is where the complexity is. Anybody think about making the whole fan assembly move back and forth like a speakers cone? Not as elloquent, but might be just as effective.
2. It's noisy. The only way to elliminate the noise is to shut it off.
Without going out on a limb here, I'll predict that it won't be in production in 5 years, as there are better (quieter) ways to reproduce low frequency. I have one here in fact. It's a Linkwitz transform eq'ed subwoofer, with lotsa cone area. WARNING!:Secure loose objects!
Then there's bass shakers. Attach a couple of those to your lazy boy, and away you go. I had an idea for a wall sized sub that uses an array of bass shakers.
Truely, there's lots of better ways to produce SILENT bass (you can't hear frequencies below 20Hz, or at least I can't) that would be simpler and cheaper.
Lots of VLF frequency info gets absorbed and reflected by loose material. There are lots of ways to think about this. Packing conventional boxes with fluffy fill (not to handle high frequencies). Blankets in a bass drum.
As a general rule, fabric passing LF works, but when the wavelengths start to get really long, the sounds starts to move the material.
Hearing LF sound from adjacent rooms usually has more to do with LF long wavelengths getting diffracted around corners and the fact that little phase cancellation occurs. Sound thru wall, plus sound thru crack under door, plus all other paths tend to add up.
With higher frequencies, lots of different length paths arriving at the ear tend to cancel each other out because of phase cancellation and the random arrival times.
Certainly the walls absorb a ton of HF, as do the furnishings. But the "sound coming around a corner" bit has mostly to do with wavelength being large compared to the obstacles.
The concept is simple. Some implementations could be very complex. Some could be nearly as simple as a conventional driver. That's what we are shooting for.
That won't work at all. It would just produce a bunch of wind and a tiny signal.
The entire benefit of a fan sub is that it generates many feet of excursion. In fact the excursion approaches infinity as the frequency approaches 0Hz. TONS of moving air is what fans and propellers do. The fan sub just modulates this.
There are lots of ways to eliminate noise, especially designing the device in such a way that it produces very little to begin with, but also absorbing it on the exit path, active cancellation, etc.
It's already in production and has been for a few years, at least. It produces infrasonics that are nearly unobtainable by other means (so far) and does it being driven by a 200 watt amp.
People listen to it and shell out $12,000 for one based on hearing it work.
Bass shakers and other tactile devices provide some acceptible effects, certainly. Bonesonics dance floors are amazing when you are standing on one, and they don't spread the bass all over the building and bother the neighbors.
Many implementations of motors shaking the walls have been employed in the past as well.
The problem with merely pumping energy into a wall or sofa is that the severe peaks in resonance make the sound very inaccurate. Loud? Yes. Felt? Certainly. Accurate? No way.
Shake a wall or a sofa and you also get sound that is higher in frequency as well.
Not too much different than most boomy car stereos you hear pulling up next to you; they existe some resonance in the car's suspension and you get one loud note. "Donk! Donk! Donk!"
Most people can hear bass much lower than 20Hz, but the rolloff of response usually requires significant increases in SPL to bring lower tones up to audibility.
It appears that your suggestions here are really just "don't build one of these" and "use tactile devices instead" and "use big conventional woofers instead."
Fans subs already work. We are looking at enhancements and simplifications to get them cheaper and better.
Jumping in randomly a bit here but how about modulating the airflow with something like a large camera iris?
Good idea. Don't know how the engineering would work on this.bigwill said:
What would be the differentce / considerations?
I can immediately think of a few.
--A simple iris-modulated flow of air would need somewhere for the blocked air to go.
--An iris may tend to go from lots of slow air (when open) to the smae amount of fast moving air (when stopped down)
--I tend to think of an iris as a rather delicate thing, with delicate blades that may be blown apart pr pushed tightly together whith an air load applied.
--Depending on how the blades fit together, there may be flapping, whistling, other noises
Other gate / valve designed have been tried, but I am not too familiar with them.
neededandwanted said:
Retort: If you have a problem with any of the following a little rsearch should set you staight.
1/ Packing a speaker box with wool or a drum with a blanket doesn't absorb low freq. sound, it damps the structure.
2/ Low freq. waves don't bounce off non-dense walls, they pass through it.
3/ What has this got to do with the topic?
4/ For the most part higher freq. waves are reflected off walls, not absorbed. Sound doesn't turn corners, it gets refracted/reflected.
5/ No, it's complex AND hard to build well.
6/ Maybe I'll build one and find out. Going by the remarks in the post of yours that I'm quoting, demostrating your vast knowledge on the subject, you don't know it doesn't work either.
7/ Yeah, but the best way is to not build it , therefore it will not be turned on. Silence.
8/ I said it won't be in production in five years. Obviously it's in production now.
9/ Any number of people shell out that much for speaker cables. Get my point?
10/ When I build a sound producing device, it's accurate. To talk about resonance, you have to understand it, you don't.
11/ No kdding? I said WALL SIZED sub, not wall sub.
12/ Human hearing range is generally 20Hz to 20000Hz. Most people can not hear below 20Hz. If you hear a sound from your sub when it is playing a 18Hz tone, throw it away and start again. That's distortsion.
13/ No, build it. I REALLY want to see and hear the results. I can see that you and the team are on the right track.🙂
Please either contributed to the thread in a positive manner or leave, MJL21193 🙁
edit - Good. Hope to see you in a more positive manner in another thread later.
edit - Good. Hope to see you in a more positive manner in another thread later.
I definitely wasn't trying to start a fight, but that may be how it seemed.NVMDSTEvil said:
I just wrote a reply and deleted it. I feel better.
I don't mind being corrected on technical points at all, and he did give me a few things to go and look up. For instance his comment that LF doesn't reflect off of non-dense walls. He's partially right on that of course, but if the LF sound didn't reflect, we wouldn't have severe nodes and high pressure in corners (and bass traps, etc.), right?
He also mentioned that stuffing in a cabinet "damps the structure." I'd like help on that one, if anyone can point me to relevant articles.
And of course he's 100% right about what people will pay for cables.
I was not targeting you neededanwanted, your replies were well within line.
His were confrontational.
Its all a moot point now though, he's gone.
His were confrontational.
Its all a moot point now though, he's gone.
NVMDSTEvil said:
Hi again.
NVMDSTEvil: Is this your thread? Are you a moderator? I have as much right to post in this thread as anyone else. I said nothing offensive, just pointed out a few inconsistancies. If you re-read neededanwanted's post that I quoted, you'll see who was being confrontational.
neededanwanted: It's big of you to admit you were inaccurate on a few of your points. I respect that.
Goodluck
John
I have nothing on being corrected. It's how I learn. Often the physical universe does it for me (10 mph was not fast enough to jump my bike off of that ramp, after all. Or, no, this giant 6th order bandpass enclosure that I made sucks.)
There are common oft-repeated ideas that I too have been corrected on, and I should remember to be nicer when I try to correct others. Often, on forums, it gets shortened to "no, that won't work because..." and this is often received as "you're wrong, and here's a bad explanation of why."
One of these items I have been corrected on is "human hearing doesn't go below 20Hz" and the 20-20K rule has been etched in stone for over 100 years.
I have been somewhat recently been shown extended Fletcher-Munson curves showing apparent loudness going down to about 10Hz or lower from experiments performed on hundreds of subjects. The biggest problem with ultra low freq is in the lower levels usually produced (certainly measurable, but not audible) because of the limitations on 'normal' drivers.
To get 130db SPL at 12Hz, an 18" driver needs an excursion of about 12 feet or something. (or 80 18" drivers with an excursion of 2 inches each.) You are right about tossing out any conventional woofer that play 18Hz that you can hear. (but I might push that number a few Hz lower)
You can see conventional drivers putting out content, just pumping away at 18Hz, but it is nowhere near loud enough to hear.
Real life events that produce these low and loud tones also contain signifcant content of higher frequency, so it usually isn't recognizable. I've been in earthquakes in LA and stood on flight decks with helicopters taking off and landing and never thought "I hear a 16 Hz note there." (and a helicopter makes a 4-6Hz tone that you can feel like someone punching you very quickly in the chest)
Now I am not saying that these tones are even directly heard with ear mechanisms only. I have no idea if the cilia in the inner ear get excited by these frequencies at all. It could be some body cavity resonance (chest, sinuses), or something else.
I have heard them, and know that they are audible.
Another aspect to these low tones is that they still provide sum and difference products with other notes. Just like playing any two other tones. This actually occurs at much lower volume levels as well.
Is it helpful for classical music? Don't know. I don't know of any acoustic instruments that have content of significant loudness that low. We have also spent the last 50 years filtering off the extreme low end to keep turntable noises from causing damage and robbing amplifiers of power.
You should listen to a fan sub if possible so you can hear some of this for yourself.
Have an effects track played with and without it to compare.
Also have a synthesizer play a chromatic scale for two octaves (from 44Hz to 11Hz) and see if you can hear that these are really the correct notes all the way down.
Then have some chords played on the synthesizer with and without an added bottom octave note.
Even if you don't think you can hear the actual notes that low, you would likely agree that sum and difference frequencies would be audible.
So that was my contention #1. It's not an entirely worthless activity to make sounds below 20Hz, and it is possible.
We also had an apparent disagreement that likely wasn't one on the LF going thru non-rigid materials.
On your side: tons of LF sound will go through a normal wall.
On my side: not all of it, and not without coloration
Getting sound to go through a wall involves several impedance mis-matches (air to first piece of drywall, drywall to trapped air and studs, studs and trapped air to second piece of drywall board, drywall to air) at each point are reflections and absorbtions. The result is a lower level and resonant peaks generated.
Here's an experiment to try: Place a loudspeaker on each side of a wall. Wire them out of phase (wire one backwards). Play low frequency content on the pair (mono). If you hear absolutely nothing, the wall is acoustically transparent.
Another one: Build a loudspeaker enclosure using 2 layers of drywall separated by studs. If it produces zero bass, the material is transparent. I guess it would be best to listen 90 degress off axis for this.
One more: cut a 12" round hole in your ceiling and mount a woofer in it. Put a low frequency signal into it. If you hear nothing, the low frequency sounds are passing unhindered thru that baffle.
I just can't imagine looking around a room and wondering where to put a subwoofer and thinking "on the other side of that wall!" You know?
All woofers tend to put out some higher frequency components. Many subwoofers can be localized on that basis. Disconnect the satellites and play 'find thesubwoofer' on nearly any system, and your ears will tell you where it is because of these HF distortions. That's part of the "gee whiz" factor of bandpass enclosures--they physically filter off the HF components emitted by the driver, so they tend to be hard to localize.
Having said that, I just can't imagine everyone putting blankets over their subwoofers to get rid of the HF components by blocking the out-of-band extra sound. That is exactly what was being proposed for this sub.
The fan sub goes from 20Hz to DC. At those frequencies, blankets will impede the sound like the green screening added to tennis court fences blocks wind.
OK, having rambled on about all of that, I will admit that I went and read a handful of your posts, mostly looking to see if you were confrontational everywhere, and came away with a better impression of you. (Since you joined the forums last month and have managed to place about 350 posts, I certainly didn't read even a significant percentage of them). I largely came away with the impression that you know what you are talking about, have really built some speakers, and are not just barging in with "you obviously don't know squat about..."sort of posts.
So take this as my apology for either lighting the first match match or throwing a log on the fire.
neededandwanted said:
neededandwanted: You seem like a very descent person. No apology is needed, I'm the one who stuck his nose in with my half-assed attempt at comedy.
No hard feelings.🙂
Sorry. Couldn't resist that one.
xplod, how would you use a hard drive head/magnet for a fan sub? Use the arm that positions the head over the platter to turn a fan blade or blades?
Hard drives use voice coils or stepper motors for this, and I think both of tese types of "motors" could be useful. The ones in hard drives move fast enough for this, but I think they are capable of only relatively low amounts of torque, since the heads are very low mass items.
I definitely welcome more ideas. We seem to have sort of killed this thread for a bit with playground antics, and I don't know if we scared everyone away for a few days.
I would really like to see some DIY'ers actually start building some of these. A fan sub is so different than existing drivers that it is sort of exciting to be involved in the early stages of it. Lots of room for radical new ideas on it.
It has been stated several times now that fan subs are complex and hard to build, but I think only if comparing it to making wooden boxes. If you compare it to DIY electrostatics and magnetic planars and actually making a DRIVER of almost any sort, it is of comparable magnitude, maybe even easier.
We need a head start with some already available materials.
A motor to spin the fan could be really simple. Possibly a one-speed motor of some sort would be fine initially, but it would need to be able to spin relatively slowly, like 200-800 rpm. It would also need to be able to maintain its speed stably, despite changing air loads.
Blades could be pretty home made and could be made to be easily replaced. For an initial try, flat blades may be best. If curved, they would likely need to be symmetrical front to back, so that they blow equally well forwards and backwards (can't use normal fan blades or propellers that are designed to blow only one direction.
Something to turn the blades on their axis. A linkage like a helicopter swash plate and lift arms could be used. Maybe some sort of ball bearing race that could go around the main motor shaft transfer the signal. Support it with something like a normal driver spider and attach it to a voice coil. The inner race of the bearing could rotate freely and be attached to the lifter arms that rotate the blades.
Thigpen's current fan sub has the driving mechanism around the axle, so the force that it twisting the blades is on the same side as the big motor. It would be possible, and maybe simpler to put the voice coil and other driving mechanism on the other side, especially since easily available parts might not fit easily on the fan shaft--the other side is wide-open space to play with.
I would also imagine that twisting the blades with individual motors could be an excellent effort. Basically, mount a few servo motors on the motor shaft and drive them with the signal from the amplifier. In this design, a big trick will be getting the signal to the motors. Possibly, circular contacts could be employed like brushes on a motor. Maybe a more advanced design could use something like a transformer in a circle--two round toroids placed near each other could let the power jump the gap, wth one spinning and one stationary.
Is anyone actually making some of these?
Is anyone ready to start taking a crack at it?
Does anyone have suggestion on where to get some parts?
It would be great to find already available parts.
xplod, how would you use a hard drive head/magnet for a fan sub? Use the arm that positions the head over the platter to turn a fan blade or blades?
Hard drives use voice coils or stepper motors for this, and I think both of tese types of "motors" could be useful. The ones in hard drives move fast enough for this, but I think they are capable of only relatively low amounts of torque, since the heads are very low mass items.
I definitely welcome more ideas. We seem to have sort of killed this thread for a bit with playground antics, and I don't know if we scared everyone away for a few days.
I would really like to see some DIY'ers actually start building some of these. A fan sub is so different than existing drivers that it is sort of exciting to be involved in the early stages of it. Lots of room for radical new ideas on it.
It has been stated several times now that fan subs are complex and hard to build, but I think only if comparing it to making wooden boxes. If you compare it to DIY electrostatics and magnetic planars and actually making a DRIVER of almost any sort, it is of comparable magnitude, maybe even easier.
We need a head start with some already available materials.
A motor to spin the fan could be really simple. Possibly a one-speed motor of some sort would be fine initially, but it would need to be able to spin relatively slowly, like 200-800 rpm. It would also need to be able to maintain its speed stably, despite changing air loads.
Blades could be pretty home made and could be made to be easily replaced. For an initial try, flat blades may be best. If curved, they would likely need to be symmetrical front to back, so that they blow equally well forwards and backwards (can't use normal fan blades or propellers that are designed to blow only one direction.
Something to turn the blades on their axis. A linkage like a helicopter swash plate and lift arms could be used. Maybe some sort of ball bearing race that could go around the main motor shaft transfer the signal. Support it with something like a normal driver spider and attach it to a voice coil. The inner race of the bearing could rotate freely and be attached to the lifter arms that rotate the blades.
Thigpen's current fan sub has the driving mechanism around the axle, so the force that it twisting the blades is on the same side as the big motor. It would be possible, and maybe simpler to put the voice coil and other driving mechanism on the other side, especially since easily available parts might not fit easily on the fan shaft--the other side is wide-open space to play with.
I would also imagine that twisting the blades with individual motors could be an excellent effort. Basically, mount a few servo motors on the motor shaft and drive them with the signal from the amplifier. In this design, a big trick will be getting the signal to the motors. Possibly, circular contacts could be employed like brushes on a motor. Maybe a more advanced design could use something like a transformer in a circle--two round toroids placed near each other could let the power jump the gap, wth one spinning and one stationary.
Is anyone actually making some of these?
Is anyone ready to start taking a crack at it?
Does anyone have suggestion on where to get some parts?
It would be great to find already available parts.
I just threw the hard drive head out as an idea. I have no idea how much torque those can put out, so that's why I asked. I was thinking of using the head assembly to rotate the blades. I have a couple of hard drives laying around, and now that I'm done with school, I have time to play around with a mini version of it. It might not even work, but it's worth a shot.
Had some free time today, so this is what I came up with. The fans blow in opposite directions, and the tunnel on the head is the output. The vid is shot at 5hz because the paper was flexing too much at higher frequencies. When I stick the cam in the output, it's pretty obvious that the air is changing direction.
http://youtube.com/watch?v=vL7u3zsbllA
http://youtube.com/watch?v=vL7u3zsbllA
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