Ultra-low frequency Rotary Subwoofer

[DanielT]

What a coincidence. That particular video has now been commented on in another forum. Or rather the principle itself with Rotary Subwoofers:

You are unfortunately stuck in a theoretical vise because the distortion increases quickly when the rpm is too low and the turbulence noise increases quickly when the rpm is too high. In practice, you have to stick to frequencies below about 20 Hz and also accept a certain amount of noise. However, it should be possible to reduce both noise and distortion via a bandpass solution, but the solution will be extremely space-consuming.

It makes far more sense to construct closed boxes with many and/or large conventional woofers and utilize the room support if one wants to generate high sound pressure levels at 7-8 Hz or so (but why would want to do that, when there is practically nothing to listen to at such low frequencies). For example two BMS 18N862 are fine for infra purposes in a normal sized room, although the differences for such low frequencies will be very large depending on whether the room is sound sealed or not.

faktiskt.io • Visa tråd - Roterande subbwofgfers.

BMS 18N862 - 18″ Subwoofer

18″ Subwoofer, 25 Hz, 3000 W, 93 dB, 8 Ω

www.loudspeakerdatabase.com

 

[Ciobi69]

What a coincidence. That particular video has now been commented on in another forum. Or rather the principle itself with Rotary Subwoofers:

You are unfortunately stuck in a theoretical vise because the distortion increases quickly when the rpm is too low and the turbulence noise increases quickly when the rpm is too high. In practice, you have to stick to frequencies below about 20 Hz and also accept a certain amount of noise. However, it should be possible to reduce both noise and distortion via a bandpass solution, but the solution will be extremely space-consuming.

It makes far more sense to construct closed boxes with many and/or large conventional woofers and utilize the room support if one wants to generate high sound pressure levels at 7-8 Hz or so (but why would want to do that, when there is practically nothing to listen to at such low frequencies). For example two BMS 18N862 are fine for infra purposes in a normal sized room, although the differences for such low frequencies will be very large depending on whether the room is sound sealed or not.

faktiskt.io • Visa tråd - Roterande subbwofgfers.

BMS 18N862 - 18″ Subwoofer

18″ Subwoofer, 25 Hz, 3000 W, 93 dB, 8 Ω

www.loudspeakerdatabase.com

I have 2 18n862 they are tremendous

 

[Keith_W]

This is capable of above 120 dB at 1 Hz and even does DC, i-e O (yes, Zero) Hz.! A concept I have some difficulties to wrap my head around . ,

Isn't 0Hz just no sound?

 

[DanielT]

It makes far more sense to construct closed boxes with many and/or large conventional woofers and utilize the room support if one wants to generate high sound pressure levels at 7-8 Hz or so (but why would want to do that, when there is practically nothing to listen to at such low frequencies). For example two BMS 18N862 are fine for infra purposes in a normal sized room, although the differences for such low frequencies will be very large depending on whether the room is sound sealed or not.

faktiskt.io • Visa tråd - Roterande subbwofgfers.

BMS 18N862 - 18″ Subwoofer

18″ Subwoofer, 25 Hz, 3000 W, 93 dB, 8 Ω

www.loudspeakerdatabase.com

There was probably a mistake in the translation of I-or's text. I think he means that the room should be air tight, closed so no air, thus sound cannot come out of the room. The room should work like a pressure chamber, roughly. If it should work with conventional woofers.
That's how I interpret what I-or writes writes anyway. In a direct translation: the room should be tight, which is not saying much.And sound sealed as I wrote last time doesn't sound quite right. It can be a bit tricky to use google translate sometimes.

 

[DanielT]

I have 2 18n862 they are tremendous

Two 18n862, with the right type of box, that will be SOTA subwoofers then.
BUT they will take up space. How big are your subwoofers?

 

[Scgorg]

Isn't 0Hz just no sound?

0hz (DC) would be static pressure. In a sense we can imagine sound to be AC pressure riding on top of the static DC pressure of our atmosphere, which is about 101kPa. This also limits our maximum SPL, as pressure cannot be negative, so at about 194dB (re 20uPa) the negative part of the waveform would clip. Higher static pressure would in other words allow louder playback.

 

[Keith_W]

0hz (DC) would be static pressure. In a sense we can imagine sound to be AC pressure riding on top of the static DC pressure of our atmosphere, which is about 101kPa. This also limits our maximum SPL, as pressure cannot be negative, so at about 194dB (re 20uPa) the negative part of the waveform would clip. Higher static pressure would in other words allow louder playback.

That's interesting, I never thought of it that way before.

 

[dasdoing]

pretty sure my ceiling fan is throwing 0Hz at me right now hehe

 

[DanielT]

I do not know. Exciting and fun but it seems a bit cumbersome to build. I had instead tried to buy a armchair at a flea market and motored in that some:

Bass Shakers

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There are quite a few threads about such bass ass shakers here on ASR:

https://www.audiosciencereview.com/forum/index.php?search/42549104/&q=Bass+Shakers&o=relevance

_____
Edit
OT. And if you still want to test with sound-related projects that are also simpler and cheaper things to do.
You can try these. Maybe it won't be the best HiFi with them, but for fun, why not:

 

[gnarly]

Two 18n862, with the right type of box, that will be SOTA subwoofers then.
BUT they will take up space. How big are your subwoofers?

Two 18n862's are in the sub box below the top white horn
46"W x 40"H x 29"D (not including built in castor wheels height)

 

[egellings]

Isn't 0Hz just no sound?

Yes, the atmospheric pressure in the room just sits at a steady higher or lower level at 0Hz.

 

[test1223]

Yes, the atmospheric pressure in the room just sits at a steady higher or lower level at 0Hz.

You can also argue that 0Hz is conistant air flow since sound consist of pressure and air flow. The type of microphone decides what was physically recorded.

 

[Ciobi69]

Two 18n862, with the right type of box, that will be SOTA subwoofers then.
BUT they will take up space. How big are your subwoofers?

They should be 60x56cm well they are not little but not very big for a ported 18 inch , considering they destroy like most of the commercial subwoofers existent I am very happy, main use is home theater and secondary music

 

[DanielT]

Two 18n862's are in the sub box below the top white horn
46"W x 40"H x 29"D (not including built in castor wheels height)
View attachment 310745

Impressive, what kind of white horn is that? Is it a custom build? Compression drivers in them I guess, what manufacturer and model? Crossover point between them and 18n862?

They should be 60x56cm well they are not little but not very big for a ported 18 inch , considering they destroy like most of the commercial subwoofers existent I am very happy, main use is home theater and secondary music

Nice work! Okay, 18n862 costs around $700. It may seem like a lot of money, BUT it is probably the other way around considering which SOTA killer for a subwoofer you then get with them. I don't doubt for a second that they destroy like most of the commercial subwoofers exist.

I have two Yamaha YST-SW300. Bought used at a really good price. Maybe not SOTA but surprisingly good (even really good) subwoofers. It may be due to the YST technology. Decent volume of the boxes, 85 litres. That helps with the rather modest power level of the amplifier in them. Measures nicely down to around 23 Hz f3.

I had an SVS SB12-NSD subwoofer for a while. A nice physically small closed sub with a 12 inch driver in it. Suitable for small rooms and not to be played at such a high volume. Small closed subwoofers literally eat power, so with 400 watts RMS continuous power (800 watts peak dynamic power) that the SVS SB12-NSD had, you didn't get far before the amplifier indicated that you were at or approaching maximum level. The amp clipping light started blinking red even at volumes not too much above normal listening volume.

SVS SB12-NSD Subwoofer Review

The SVS SB12-NSD is an affordable 400watt sealed powered subwoofer with a 12” aluminum cone driver in a tiny sealed cabinet to produce satisfying and exceptionally well rounded bass. Small but potent.

www.audioholics.com

Yamaha YST-SW300 Active Subwoofer System Manual | HiFi Engine

www.hifiengine.com

 

[egellings]

You can also argue that 0Hz is conistant air flow since sound consist of pressure and air flow. The type of microphone decides what was physically recorded.

Whether the air is flowing or still, the pressure could still be constant for a steady flow rate.

 

[gnarly]

They should be 60x56cm well they are not little but not very big for a ported 18 inch , considering they destroy like most of the commercial subwoofers existent I am very happy, main use is home theater and secondary music

Your sub looks like a very nice build to me, and makes good sense as a practical size. Quite elegant to the basic Duratex black stuff i always build.

Don't you just love the 18n862's? They are sooo dang easy to make work well.
I've put them in single sealed, single vented, dual push-push (clamshell) slot loaded vented, and lately the big dual vented box i posted above.
Heck, I've even put then in the big white horn in the pict on top that big dual.

I'm guessing your port area is maybe 40 sq in ? Have you measured the response outdoors ( i don't put much stock in indoor sub meas)

Here's the sub I posted above. Green is raw at 4m on driveway.
Blue and Red processed, 100 and 80 Hz low passes.
Port tuning goal was f-3 @ 25Hz.

 

[gnarly]

Impressive, what kind of white horn is that? Is it a custom build? Compression drivers in them I guess, what manufacturer and model? Crossover point between them and 18n862?

Thanks ! Yes custom, DIY. A B&C dcx464 coax compression driver, four 4" mids, two 12" lows, and two 18" woofers.
The woofers are either another pair or 18n862's or what I currently have in place, Dayton 18SW1200N's.

So four 18"s per speaker ! (and I still don't claim to have much response below 20Hz....like all the miracle home audio speakers do Lol)

Crossover points in the white horn are 100, 350, 750. and 4000Hz. Its 18"s high pass at 30-60 Hz (selectable via presets).
The big black sub low is f-3 @25Hz, f-12 @20Hz and low passes at 50-90 Hz (via presets)

 

[DVDdoug]

You feel (near) zero-Hz pressure in your ears when you drive up or down a mountain or fly up or down in a plane. Of course it's not something you'd want to experience as part listening, but you might be proud if your sound system is capable of it!.

I say "near" because after some time pressure difference between the inside and outside of the ear equalizes and you don't feel it anymore.

 

[LTig]

I have two Yamaha YST-SW300. Bought used at a really good price. Maybe not SOTA but surprisingly good (even really good) subwoofers. It may be due to the YST technology. Decent volume of the boxes, 85 litres. That helps with the rather modest power level of the amplifier in them. Measures nicely down to around 23 Hz f3.

This! I got the same answer from the Genelec support in 2006 when I asked them why the Genelec 7060b has only 150W amp power where typical hifi subs hat 500W or more. The smaller the volume the more power you need to get the same SPL, and as another downside distortion rises when you do this.

 

[test1223]

Whether the air is flowing or still, the pressure could still be constant for a steady flow rate.

Yes my intention was to point out that without any change in pressure or air flow there isn't any sound. It is constant air flow or air pressure and not any kind of wave.

A change in pressure introduces a change in air flow. Or a change in air flow introduces a change in pressure. Both is a sound wave.