Ultra Low Bass

[Rufe0]

Hi
I want construct a vari-pitch bass fan that works from something like 5hz to 50hz. Most music won’t have any sound at those frequencies so I was thinking maybe I’d have to compress all sound under like 250hz down to 50hz. What options do I have for making a circuit which will do this?

Thnx Rufe0

 

[audioguru]

A fan is not a speaker. Sound is frequencies above 20Hz. Frequencies below 20Hz are vibrations.
You need something to make vibrations or a good sub-woofer.

An electronic circuit can be made to divide the frequencies of sound into lower frequencies.

 

[Rufe0]

The fans blade pitch is vibrated by the speaker coil, creating far greater sound pressure than a cone speaker, but it oly works for low bass. There was a car company that made them a while back and more recently a guy who made one for his house, but that was far larger than i intend.

 

[evandude]

A fan is not a speaker. Sound is frequencies above 20Hz. Frequencies below 20Hz are vibrations.
You need something to make vibrations or a good sub-woofer.

An electronic circuit can be made to divide the frequencies of sound into lower frequencies.

Well, of course all sound is vibrations, so it's sort of semantics, but I agree, since you won't really 'hear' so much as 'feel' these frequencies.
For those not familiar with the technology the OP is referring to - it's a fan whose blades have their pitch controlled, allowing it to produce very low frequencies, down to the 1Hz range, with a lot of power; see:
https://gizmodo.com/gadgets/gadgets/worlds-most-powerful-subwoofer-134202.php

However, I think the entire challenge with that is in actually constructing the device, I don't think providing it a signal is much of a challenge. The estimated commercial price of the unit I linked is over $12000, that should be a pretty good indication that it is NOT going to be something easy to make.

I think your idea of "compressing" all sound below 250Hz down to 50Hz sounds pretty strange... surely it could be done, but it doesn't seem like it would produce much worthwhile - you'd just be artificially adding it to existing music - it seems pointless to build a device like this unless you actually had a useful signal to play through it... If existing recorded music doesn't have any signal below about 20Hz, then you'd have to re-record it in a manner that preserved the lower frequencies - if it's been cut out by the recording process then you can't "get it back" from the higher frequency information, you'd just be faking it. I'd also question whether most music even HAS any significant signal below 20Hz, regardless of what the recording process preserved... If it was never there in the first place, then you'd DEFINITELY be completely faking it.
It sounds more like you are trying to build it just to make music more loud and obnoxious, not to improve it...

 

[Rufe0]

If you cant beat em join em

Are there any off the shelf components that will do the job?

 

[audioguru]

The lowest note on a pipe organ is 16Hz. It makes a strong vibration.
The opening music in Pink Floyd's Dark Side of The Moon record starts with a 16Hz heartbeat.

 

[Sceadwian]

The main problem with bass is that the amount of power required to produce a perceptually equivilant sound increases exponentially as frequency decreases.
Mythbusters did a bit on this with a home hacked 'speaker' connected directly to the drive shaft of a couple hundred horsepower engine.
You're going to have to author this 'low note track' like you would the rest of the song, as there is no musically acceptable way of simple compressing a high frequency to one that low without beat frequency effects coming into play, which sound horribly bad. You're going to have to have two main tracks, the song produced on the normal audio hardware, and then create a 'subharmonic' track around it for your fan that sounds good when the musician makes it.

 

[HiTech]

The lowest note on a pipe organ is 16Hz. It makes a strong vibration.
The opening music in Pink Floyd's Dark Side of The Moon record starts with a 16Hz heartbeat.

Only the best woofers can faithfully reproduce that soundtrack without going into meltdown! I remember hearing a number of woofers caving in and popping from that heartbeat!

 

[audioguru]

My "not expensive but not cheap" Acoustic Research speakers and some I made all had 8" woofers and they produced 16Hz at a reasonable level.

 

[Nigel Goodwin]

My "not expensive but not cheap" Acoustic Research speakers and some I made all had 8" woofers and they produced 16Hz at a reasonable level.

'Reasonable' is a VERY interesting choice of word?.

I suspect it's far more likely you heard the harmonics of the bass notes, rather than the 16Hz itself.

 

[audioguru]

My speakers were flat down to about 50Hz then dropped off at 12dB/octave because they were sealed. So 70W at 50Hz gives about 98dB of sound and 25Hz gives 86dB then 16Hz gives about 80dB of sound. A reasonable level.

I don't think the speakers make much even harmonics, probably mostly odd ones. So the 3rd harmonic at 48Hz would be loud and clear.

 

[HiTech]

It's quite possible that AR speakers are capable of delivering very low bass, given enough power from the amplifier, since they are "power soakers"! I had a set of AR-3a cabinets driven by a 250w/ch Pioneer amplifier. They sounded great. But then they fell quite short of my former JBL Studio Masters! I can assure you that Pink Floyd's Dark Side of the Moon heartbeat opening heard through a set of 15" woofers is stunning to say the least, not to mention the air pressure felt on my face and throughout my body. It's not just listening to music, it's "experiencing" it!
Now, I'm down to a modest setup of two JBL bass reflex cabinets with two 12" woofers, two mids, and two titanium dome tweeters in each! The amplifier is a 600w Heath. I have a 150w Ramsa amp and an Ashley electronic crossover that would be good for a biamping set up... just an idea that's been gnawing at me over the years. Complicates things alot more, but sonically there should be a positive improvement (theoretically!).

 

[audioguru]

Bass reflex speakers have a response that quickly drops at 24dB/octave which is twice as fast as a sealed enclosure. If the enclosure is big enough then a bass reflex design can have its flat response lower than a sealed design. But very low frequencies can damage the woofer since the sound from the port is out-of-phase with the sound from the cone and therefore the cone is not supported by air in the enclosure like in a sealed enclosure.

 

[MadAlexis]

I don't know about compressing sound to a lower frequency - how can you create something that was not there to start with?

To answer one question though, maybe a class D amplifier will be able to drive these fans. Perhaps you could insert a low pass filter and amplify the remaining signal until your body vibrates...

Alexis

 

[Hero999]

I didn't realise that you could actually hear 16Hz. I thought 20Hz was the lower limit of human hearing.

There's certainly no point in producing sounds below 15Hz because you can't hear them. There is probably infrasound between 0.1Hz and 16Hz all around you but you can't hear it.

 

[Gaston]

i would think that you would feel the 16 hz and hear the harmonics.

 

[Ambient]

You would need quite high powered servos or some other device to change the pitch on the blades. The mass of the blades plus the volume of air the blades are moving will contribute to torque on the axis of each blade. Servos can go up to 300oz@1" last time I looked, but they are pricey, and you would need a micro controller to use them. Not a small project.

 

[Sceadwian]

Mind you even if you can't hear them directly they're still there and they're going to effect the surroudning audio. To what effect? Don't know. But simple heterodying says you're going to end up with base frequency plus modulation frequency and base frequency minus modulation frequency as the ouput. You can apply that to the outputted audio and just attach vibration mechanisms to whatever the people are touching in order to transmit the physical portion of it.

 

[mneary]

you're going to end up with base frequency plus modulation frequency and base frequency minus modulation frequency

Not always.... only if it's transferred through a significant non-linearity. Heterodyning is also called intermodulation (IM) distortion: This is a key spec for amplifiers and speakers, and they try to minimize this.

 

[cyb0rg777]

I tried to build one of these out of a fan ,but then I got hot and put my fan back together.

No really I was going to build one so I have a few thoughts about how it could be done. My main concern was balancing the whole thing and getting enough power to the coil. Here is a drawing of what I came up with.It uses a regular speaker magnet with a hole drilled through it and a coil. Should you choose to attempt to finish the project ,I wish you luck .Most of all let me know how it turns out.