What's it take for 20 Hz?

dayneger · « **on:** 19 Feb 2003, 05:18 pm »

I'm looking around for a powered subwoofer for my 2-channel system and would like to know what it takes to have solid output to 20 Hz?

I like to listen to organ and other stuff with deep bass, which is why I find 20 Hz so interesting (actually 16 or so would be more accurate, but realism kicks in

). I'm willing to consider new, used, mailorder only (Adire), kits, or complete DIY based on an established design if it's good enough.

My focus is definitely on pure musicality, not on SPL's. I unfortunately can't use the upper end of the SPL range in my apartment, and a musical sub is more than enough for my HT needs. I'll be crossing over at about 60 Hz or so.

I'd prefer to have a decent plate amp that I can switch between 115/230V, and a cabinet not much more than about a 22-25" cube, tube forms possible if advantageous. If I can I'd like to keep it under $600 or so, although we'll see where the compromises start!

I'd appreciate any thoughts you have on what it takes. Thanks!

Dayne

circularduck · « **Reply #1 on:** 19 Feb 2003, 05:45 pm »

I'm not sure if this will help you or not, but I just picked up an ACI Titan II kit (one of the few remaining) on the subwoofers.cc site. I haven't built the cabinet yet, but the plans show a 26" tall x 13.5" x 14.5" cabinet. I've read nothing but rave reviews of the sub for it's musicality. It has a -3dB of 20 Hz, and an adjustable crossover from 35Hz-250Hz. The people at ACI were a pleasure to deal with. If you do a search on some of the forums, you should get a good idea of why people like this sub.

dayneger · « **Reply #2 on:** 21 Feb 2003, 07:10 am »

Sounds like you'll end up with quite a subwoofer! I'll have to think about that one. I like the proportions, too--looks like it'd be easier to fit that in the room somewhere than the average subwoofer cube.

Anyone know what driver size and interior volume is necessary for <20Hz F3 if you use a standard 250W plate amp?

JohnR · « **Reply #3 on:** 21 Feb 2003, 07:24 am »

Since you say you're after a "musical" sub is it reasonable to assume that you want an "in-room" f3 of 20Hz, not an anechoic one?

I'd consider an Adire DPL12, anechoic f3 is around 30 Hz.

JohnR

JohnR · « **Reply #4 on:** 21 Feb 2003, 08:07 am »

Here's the response curve of a DPL12 in 84 liters sealed with 250W input:

Excursion graph:

Hantra · « **Reply #5 on:** 21 Feb 2003, 02:57 pm »

Wait a second. . .

Is it physically possible to reproduce a 20 Hz wave in most listening rooms?

Maybe you guys have a much larger listening room than I.

Dan Banquer · « **Reply #6 on:** 21 Feb 2003, 03:10 pm »

I think Hantra has a point. The ability of a subwoofer is one thing. The size of the room could well be a limiting factor because you can run out of acoustic wavelength. I don't have the formulas here at work, but I will guess you will need at least 25 to 30 feet from the subwoofer to the farthest wall. If you wish I can repost later on today with the minimum length needed to for reproduction of 20 Hz.

nathanm · « **Reply #7 on:** 21 Feb 2003, 03:30 pm »

I believe a 20Hz wavelength is 56.5 feet long. There's still debate about the issue of room size vs. bass ability. If the room were truly the limiting factor any sound beyond the length of our room would be completely inaudible, right? But we know it's not. I do notice that my sub sounds deeper from other rooms, though. Physics sucks...

I sure wouldn't mind visiting Bob Ludwig's place to find out though.

Dan Banquer · « **Reply #8 on:** 21 Feb 2003, 03:41 pm »

If Nathan is right about the 59.5 feet than the minimum distance needed from the subwoofer to the opposite wall is 1/2 of the 59.5 feet. (distance is calculated so that the 20 Hz wave reflects off the back wall and travels back) If I remember that correctly. The other fun problem here is where you happen to be in the room. Don't be surprised if the spl is all over the map at 20 hz.
Long wavelengths are just so much fun.
From my experience and others, the length of the room will limit the useable low end frequency response. My own listening area has a limit of 30 Hz. This matches up with the math and the tests. The middle of the room is also a null point for 30 Hz.
This leaves us one final question: DOES YOUR ROOM MEASURE UP FOR 20HZ?????

MaxCast · « **Reply #9 on:** 21 Feb 2003, 03:57 pm »

What about head phones? They can produce into the lower octaves with in a real small room (distance from driver to ear drum).

Also cars, that is a small room. Do we really have to have the full wave to hear the frequency? Or, do we need the original wave plus the rebound from a few walls?

Dan Banquer · « **Reply #10 on:** 21 Feb 2003, 04:13 pm »

Good question Max: I don't have an explanation as to why and how headphones manage to do real low frequencies.

Val · « **Reply #11 on:** 21 Feb 2003, 04:36 pm »

MaxCast is right, if deep bass is possible on headphones and inside a car, it is also possible in a normal room. That seems self-evident when you think about it. The wrong idea that room length equal to frequency wavelength is needed to reproduce it is a long standing one, and even J. Gordon Holt once wrote about it. My REL Storm III (faintly) reproduces a 20Hz tone in my 8' x 12' x 20' room, to say nothing of strong 25Hz and up!

What you have to be careful about is room gain, generally a sealed subwoofer with an anechoic F3 of about 35Hz will reproduce 20Hz in a typical room due to room gain more or less matching the sloping response.

Val

Hantra · « **Reply #12 on:** 21 Feb 2003, 04:50 pm »

Many times I have thought about an answer to the hadphones question, and I come up short on all accounts. It would seem common knowledge that for a wave to even be a complete wave, it would have to make a complete cycle at least once between trough, and peak. But what if that is not physically possible?

Who knows. Maybe I can play with my RTA software this weekend, and find out. . .

Val · « **Reply #13 on:** 21 Feb 2003, 05:05 pm »

Hmm. Let me put it this way. Is it not self-evident to audiophiles when they hear it, whatever the reasons why?

MaxCast · « **Reply #14 on:** 21 Feb 2003, 05:43 pm »

I think we hear the part of the wave that hits our ear drum. We do not need to hear the full wave to understand the note. If we had to hear the full wave the bass note would lag way behind the faster (shorter wave) of high frequencies. As the long wave is moving so goes the short wave, yet we hear them at the same time. Hell....I don't know.

Can we get an ENT in here?

ABEX · « **Reply #15 on:** 21 Feb 2003, 05:46 pm »

WHat recordings do you people use to see what effects of low Bass are coming through

I have Stereophiles Test Tones and my 2-Way Monitors go down to about 32Hz. if my memory serves me right.What through me off was I was playing something off Pink Floyd's Umma Gumma and "Through the Narrow Path" has a heartbeat that was not known to me unless I had the sub on.Did not know it was there till then.Freaked me out I first thought it was a Hum and I was pissed because I thought ,oh great what the &((% is that.Now I have a problem.

Other stuff like Jeff Beck\Terry Bozzio Guitar Shop and Bartok I use and let's not forget 1812 Overture.Lastly there's a Geni track on Roger Water's amused to death that seems to really make my speaker's and sub go nuts.Still can't figure out what he is trying to say.

Just a few thoughts!

nathanm · « **Reply #16 on:** 21 Feb 2003, 05:51 pm »

Has anyone ever listened to speakers out in the middle of a huge field with nothing around to block the sound aside from the ground? On a calm, windless day it would be interesting to try. Probably would need a generator, or battery power of some sort. Hmmm.

Another phenomenon I've noticed is that it is increasingly harder to identify pitch in those low octaves. Bass guitar for example, is difficult to tune by ear the less upper harmonics there are. If you roll off the mids and treble it can be pretty tricky to tune by ear. Perhaps the longer wavelengths are canceling and modulating each other, thus making the perceived tones much closer in pitch to our ear?

dayneger · « **Reply #17 on:** 21 Feb 2003, 07:19 pm »

The question about the room size is a good one, and I'm not sure I can add much. . .

As MaxCast mentioned, headphones can reproduce 20hz. As far as I can tell, it's clearly not necessary to have a full standing wave in a listening room, since we're not trying to make an organ pipe out of it. In fact, the standing wave can be undesirable, since the standing wave uses the room for reinforcement, which is why a lot of us with "normal" size rooms tend to have problems with mid-bass boom and need bass traps. The frequencies are being reinforced when the room dimensions near a nodal distance. Resonance in a room isn't the same thing as being able to hear a tone.

My limited understanding of the issue--sound and related percussive waves that require a physical medium to travel through. This is in contrast to electromagnetic waves like light and radio, that are happy to travel through a vacuum. Those explosions in space films are great for subs but don't actually produce sound.

The sound wave is transmitted by air molecules being set into motion by the speaker membrane, then they bump into each other across the room until they hit our personal organic microphones. Is there any reason why the speaker membrane can't force these waves to occur at audible frequencies? I think that's what headphones do. Obviously it takes quite a lot of energy for those lower frequencies.

I'm also intrigued about room reflections. Similar to Nathanm, I get sweet bass when I'm brushing my teeth in the bathroom, which happens to be around the corner and down the hall from the living room (and stereo). I'm clearly getting nodal frequency resonance down there although it's very much NOT a linear acoustic path. Exactly why it doesn't bounce around in the listening room until it hits a node in the same way?

Dan Banquer · « **Reply #18 on:** 21 Feb 2003, 07:26 pm »

For rooms, I still think it has something to do with wave length and distance. Coupling and room gain also play a part here, but I really wish we had someone well versed in acoustics on this thread. That person could answer a lot of our questions. I will e mail Mike McCall of Shamrock Audio to see if he can help.

mgalusha · « **Reply #19 on:** 21 Feb 2003, 08:16 pm »

There is a very good article on this in the current issue of AudioXpress. Unfortunately it's at home and I'm not, but it basically comes down to pressurization.

The author goes into detail about how B&K calibrates microphones to below 20hz and the device which does it has about a 5cm length.

Pretty interesting.

I can't say much more, since I don't have it as a handy reference but it was pretty well written and thought out.

mike