Purpose of flat response below 20Hz - Why does it matter?

Dolby spec actually accounts for an audio system to go down to 3hz in all channels.

Some amps may filter bass down low, others will not. That is usually something one would look into when designing a subwoofer system. Especially if the aim is to reach down as low as possible.

I love deep bass so I sought out to create a bass system that could go down to 10hz and produce very high SPL all effortlessly. You can check out my subwoofer system which is in my sig. I designed that system back in 2007. My system is a bit extreme but that is one way of doing it. The other option is to build a subwoofer system consisting of many sealed subwoofers with plenty of power and EQ. If you have a fairly small room (under 2,500cuft), reaching frequencies of 3-5hz is not very difficult.

You might as well sell your polk sub now, that isn't going to dig very deep. I would be surprised if it was doing anything in the low 30s. To be honest, I don't think it's worth chasing after anything below 20 hz. You can not hear it, and you can barely sense it at all unless it's at a very high amplitude. At those high amplitudes, things can break if they are not solidly braced and situated; plaster can crack, nails can loosen, sometimes even plumbing can develop leaks. If you are not getting lots of room gain, it also takes an enormous effort to get any serious output below 20 hz- the subs have to be huge and heavy or have a lots of power with a heavy duty driver or both. Consequently, the subs will eat of lots of space or lots of money or both. And in the end, it isn't for much more than the gimmick of making your windows rattle with your speakers.

Both my current systems go down to 15 hz with ease, but if I build another system, I am not going to concern myself with anything below 20 hz. The cost is just too high, whether in cubic feet or money.

A standard CD player and/or DVD player can play non Dolby content down to 3Hz as well. Just part of the basic digital technology.

In room response for the Polk psw505 is around 23-25hz.... Its one of those subwoofers that benefits from in room placement. It's not a lab test friendly subwoofer

I had my psw505 corner loaded and it got into the low 20's, however it was down 8db or so from bout 32hz. I don't know if I have that graph anymore.

I upgraded to a new sub instead of adding an additional psw505, I have 5000 cu/ft to fill and my beef with the 505 was it didn't have the spl for me in that room and subsequently I would overdrive it and it would fart and bottom out on the bass heavy scenes. I got a ss 18.2 corner loaded and it definitely provides below 20hz, **** rattles everywhere. I have it and I really don't know if I like it or not (my room definitely doesn't like it!), but I'm glad I did it because now I know. My in room response with it is pretty flat from 20 -80 hz and is down about 5db at 13hz. however, 80-150 is down like 10db, gotta play with it more and/or add a 2nd sub.

If your end goal is more even response and you are happy with the spl and response across your room, then get a 2nd psw505 and smile all the way to the bank with the money you are saving.

If you are looking for more spl than what your 505 can deliver and looking to go lower then time for a new sub.

1) Your amplifier specs for the powered channels may be 20-20K but your not supposed to drive the subwoofer with that kind of source. When you use the Subwoofer output on your receiver it should comply with the Dolby spec for the LFE channel which is 3Hz-120Hz.

2) Maybe a second 505 will do the trick, but most here would look for something better.

3) Something that will be flat at 20 Hz & 105 db would be something to grab hold of.

That's just how the manufacturer lists their specs. I can guarantee you that you could get bass <20hz from those amplifier channels. You won't get very much hooking up some run of the mill speakers to them and running full range. You would be better off with subwoofers for that but that is also a whole other discussion right there.

The subwoofer/lfe output on you Onkyo will more than likely have flat (or flat-ish) response down to under 10hz.

If you have strong interest in a subwoofer system that goes well below 16hz with lots of authority, drop by the DIY audio section here. Us DIY'ers will help you out. No problem.



Yes, this is very true but I was replying to the OP's question that specifically notes Dolby. Otherwise I would have mentioned DTS, PCM, etc.

Excellent, excellent, post.

As a good number in these parts know, I was considering an all-out assault on the 5-15hz range, but after experiencing it in a couple of maniacal (in the best sense of the word, of course) HT's, I walked away thinking very closely to what you detailed above.

To me, it seems as much "specsmanship" as anything else, and when you begin to consider the costs and space, it simply reeks a bit daft to me.

Now, I'll "suffer" with two Captivators, be good to around ~15 pretty darn strong in my room and laugh all the way to the bank. To each, his own though of course.

Again, great thought, thanks for it.

James

You know, I had a little enlightening experience as well. I had an AVS member over to my house for a little GTG and he wanted to experience 10hz in my room. I had dual dts-10's and dual CS 18.2 subs. I played some material for him and he said he noticed some lower stuff but nothing to get crazy over. He was using just a single THT in his room. I thought to myself I wanted to try something new and see if the experience is good enough. I have 4 F-20's right now and will see if 5-10hz was worth it to me. Again, if you want to be dead accurate, 3-10hz is needed as there are many scenes with it, but I want to see how much of it is noticed because most of the time during those very low scenes there is also 20-40hz material which we hear.

^ Like so much in this hobby, simply a question of cost/space/time vs $$$'s.

Ooops, my bad, I mean $$,$$$'s in this case. :P

Good luck.

James

yep, exactly what you said. Iam more interested in clean reference spl rather then the single digit stuff.

I have to be honest. I'm with most of you guys.

I got all setup in my media room with a calibrated mic and went out and traded my toy sub for a Rythmik F12....which is a great sub, by the way.

I started playing some low tones and measuring, and I quickly found out that, for me, anything below 25Hz is pretty much inaudible at reference levels. I would probably have to be +6 dB to 'hear' it flat. The curve said it was flat, but I couldn't hear it.

I also found out that anything below about 50Hz in my RIGHT ear is inaudible at reference levels.

At the end of the day, you can spend all the time in world making things flat, but your hearing is not flat, and it's just another variable in the mix...so is everyone else's hearing. I went to an ear specialist and he said my hearing was just fine, and that most people have similar responses to varying, especially low frequencies.

I think it is definitely worth spending time to have an 'even' response across the room to prevent nulls at audible frequencies, but IMO, flat below 20 is a bit ridiculous, and spending time on other aspects of the HT is more beneficial. I do like that I can still 'feel' the low end, but you don't need 'flat' response to get that.

MY first sub was a DefTech ProSub 200TL. It was a good sub...until I picked up an Energy S10.3 for a buddy and had a chance to demo it against my 200TL. The Energy dug noticeably deeper and played louder...and I was intrigued.

Since then, I've move to an SVS PB10-NSD, an SVS PB12-NSD and, currently, a CHT SS-18.T (dual subs). Each successor sub has dug deeper, and played louder and cleaner, than the one before it.

(I've also had the opportunity to hear - and to be impressed by - Paradigm's Servo-15 v1, Servo-15 v2, Sub-12 and Sub-25, and an AV123 MFW-15.)

In my current HT space, the SS-18.Ts are flat to ~17Hz, and I find that to be very satisfying. My buddy's CS-18.Ts are flat to ~12Hz in his ~1/3 smaller HT room, and the biggest difference I find is that his subs hit harder. (Their ability to dig deeper, although occasionally evident, doesn't make as much of a difference.)

Having said that, and IMO, I would stick to buying a sub (or subs) that play flat and clean to somewhere between 15-18Hz *AND* hit good and hard at volume.

Just my 2¢...

The fact that you couldn't detect much <20hz content probably has something to do with that fact that you are using a single 12" driver. You will need multiple sealed subwoofers and help from the room, itself to get you down to the single digits.

Anyone here with basic woodworking chops could build a pretty powerful subwoofer system for $1,000 that could go very loud and reach into the single digits.

The myth of needing super large and ultra expensive subs to produce bass below 20hz needs to die off.

This thought is akin to my own feelings about a good movie theater and the sound I strive to have in my own theater. In a proper commercial cinema (I'm talking a good one that's properly setup and well equipped), the low frequencies are great. Plentiful, dynamic, and clean.....while at the same time not going super low. High SPL that is clean and dynamic is more important to me than seeing how low I can get it. Not that I have anything against the single digits or anything. Mine is only flat to 16hz, but that was never the goal.

I had a calibrated microphone clearly indicating I had SPL 'nearly' flat to 20Hz and I had plenty of SPL below 20Hz, but I could hear NOTHING, as in ZERO.

BTW, it sounds like you contradicted yourself. I was going to get an F15 with the 500 watt RMS amp because I wanted to crush 20Hz, and Brian at Rythmik said I didn't need "super large and an ultra expensive" (as you said) sub to produce in my small room. I only have about 1400 cu. ft.

He was right...and I can't hear it anyways.

Not to speak for Scott, but he probably was talking about getting an appreciable SPL level below 20hz...which you'd have to have to detect it, rather audibly or by pressure in the room. Depending on room size that can be quite a task.

Purpose of flat response below 20Hz - Why does it matter?

I prefer to turn this question around.

Why on earth would it NOT matter to play what's on the disc?

It's always amusing to me to read the folks who say it's not important and their various reasonings for why that's the case, then to see that they don't have the capacity to play the first 2 or 3 octaves. I guess that's a pretty good reason to discount full BW playback in itself.

Would anyone here buy mains that roll off steeply at 5kHz and post why it's not important to have the last 2 octaves on the high end with a straight face?

There's no question of the importance of capturing everything that's sent to the SW output in my experience. But, I didn't stop there in asking the same question in the OP. I've set up exercises in which a scene is played with a steep roll off at 20 Hz, 18 Hz and 10 Hz vs letting her rip.

At 10 Hz and below, the consensus becomes more like 50/50, but anywhere above 10 Hz cutoff, it has been pretty much unanimous. Gender and age have no bearing on the results.

I recently posted this comparison from Hulk, the cop car bashing scene:


I also let people watch this scene from Terminator: Salvation with 20 Hz roll off and 3 Hz roll off:


Again, the result was unanimous; yes, there is a difference and yes, I liked the full BW presentation much better.

I'm in no way disparaging anyone's preference or subwoofer or opinions, just answering the OP, which is a question I've been asked countless times. It matters because a)it's what's on the disc and b)(according to me and nearly every person I've asked to listen and tell me if there is any difference and if so, which do you prefer) it adds a whole new dimension to the presentation.

Bosso

I don't have my graphs handy, but I read an absolute value off of my meter so I could get 'true' SPL. Not just relative.

My room with nothing playing (just my iMac and the lights on), it was about 30-35 dB. I calibrated my sub using frequency sweeps from about 200 Hz down to 10Hz, and I was getting around 80-85 dB. I could hear this (obviously) down to around 40 Hz (with both ears open). After that, although the graph stayed flat, it was noticeably dropping off, in my ears.

By 20Hz, my dB meter (Fuzzmeasure) was reading probably around 76 or so, but I couldn't hear anything. I played down to 10 Hz, and I measured around 60 dB, which admittedly is not flat, but should be audible, but I couldn't hear anything, but my microphone was clearly measuring ~60 dB SPL.

At 60dB, I could hear 50-60Hz, no problem in my left ear, but I noticed that my right ear not so much.

I guess my question is....can you guys even HEAR 20Hz and down? And if so, at what dB? and is your hearing flat?

To summarize, I guess you can 'hear' any frequency given enough SPL??? BUT...if you need 6-10 dB MORE below 20Hz to hear it flat, what good is flat?

Bosso,

That's interesting. I've never heard 'ludicrous' amounts of sub 20Hz content, so I can't really comment.

In your opinion, is this only because people 'feel' different, or they actually 'hearing' something different.

My biggest problem/hesitation is spending another couple thousand bucks and I don't get my return on investment because I can't even hear it.

Some people use a "house curve" (look up Fletcher Munson) when manual eq'ing their sub(s).

I found an frequency sweep from my F12.

This doesn't appear to be an absolute SPL, but looking at this graph, I'm actually flat to 20, and 10db down at 10Hz, and still have a little left below 10.

Again, my hearing starts to drop off around 40 or so, and I can't hear anything by 20. I also have a pretty small room.

Wow...now that makes more sense to me than 'flat'.

What's the use of flat when you read this article?

http://en.wikipedia.org/wiki/Equal-loudness_contours

To heck with flat, I want +80 dB at 20Hz!!

Yup, two of the lightweight non "super large" and non "ultra expensive" subwoofers like you own is the final proof that the "myth" needs to die off!

For other sample myth busters we could also reference Bosso's 8 -15" drivers that requires a nuclear power plant to run, or MKT's subwoofer systems (any of them), or a multitude of other systems that prove that the size "myth" for sub 20 hz playback is simply a myth.

Nice cherry pick there, J.

Do I really have to go and pick out all the dozens of small, sealed builds that are in the DIY section right now that are way, way smaller than my LLT's and were reasonably priced? Would you also like me to personally send you a PM linking my conversion of the LLT's to small sealed cubes?

C'mon.

Awesome subs there, btw.

What was the playback level of each test? You do have 8 15" drivers installed in that system!


Terminator Salvation only has about 5 seconds of sub 20 hz content on the entire disc, with no sub 20 hz content recorded on the LFE channel.

+ 1

+ 1

"Specsmanship" ,as you note, perfectly sums it all up.

Also two Caps are a fine choice. Two more would be nice

Another pointless post from the "mine rolls off at 25 Hz, so yours should too" guy.

Bosso