Oops, I lost my first attempt at my second post through not being logged in!

Here I go again …

Having read through threads pertaining to members comparing their subwoofer frequency responses (especially the SVS owners), I have a question.

The quest for powerful low frequency fun is a fine journey (exempting issues with neighbours, relations, small terrified animals and human hearing of course).

Why do decent subwoofers seem to play so low when the very deep bass frequency (whether at a high volume or not) doesn't seem to be encoded on the music CD's or film DVDs fed into them?

I might be wrong; my understanding is that most music isn’t all that low really,(unless you like organ music that is). It doesn’t reach down to the 20-25Hz levels that I regard as low. I had an MJA Pro 50 + 100 btw, so probably never even got that in my bedroom!

Blockbuster action movies may feature large explosions and moving vehicles, which are low in frequency. However, do subwoofers generally tend to play a little lower then the information they are fed with in order to sound more realistic? Do they just play to their limit when the bass is very low and become quiter/'drop-off'? I saw somewhere on this forum reference to subs using filters for preventing very deep frequencies and distortion problems, to an extent. The opposite of a high-level filter.

Does the nature of the subwoofer with ample power (speaking generally here) and large driver lead them into these low depths a little waywardly when they lose control at low depths?

Please feel free to set me straight. I am quite curious since reading SVS owners tuning tweaks (with bung ports and placement) to achieve very low frequency responses in-room.

In summary, perhaps I should ask:

Do subwoofers at any frequency level actually play accurately the frequncy of the orignal material played through them? Additionally, is more accuracy lost with either high SPL levels or the demand for very low level detail (beyond the subs ability).

Have I just partly answered my own questions?

To generalise somewhat, this has alot to do with distortion. With a lesser sub these levels of distortion at low frequencies can really affect the accuracy of what is actually on the disc etc. Moving to super-sub territory brings a wonderful sense of realisation.

Great post from a deep thinker!

Very low frequencies are increasingly found on CDs an DVDs. There are electronic music tracks that have content at 5-7.5Hz readily visible in "Spectrum Lab" waterfall charts. (free download)

Though very few subs can produce much volume at such low frequencies without considerable distortion. Frequencies below 20Hz are largely inaudible to most people anyway. Though they can easily be felt or sensed. (it varies a bit depending on volume and listener) Distortion will form harmonics at higher frequencies some of which will be audible. The ear/brain mechanism has the ability to conjure up the orginal fundamentals based on these audible harmonics.

As steve.EX rightly says the ownership of a serious subwoofer brings an effortless depth to much programme material that goes completely unmissed using smaller subwoofers.

It's all about moving lots and lots of air. Big drivers in large enclosures with large, low-turbulence ports help. Though there other ways involving electronic bass boost using large closed boxes which also have a following.

As (increasingly) do True Infinite Baffles. Where (usually) at least four 15" drivers are built into the wall of the listening room or Home Theatre.
This method uses the room behind the drivers as an enclosure to keep the sound from the front of the drivers from cancelling the sound coming from the backs of the cones.

Very low distortion is claimed for such systems. But not everyone has a suitable wall or the circumstances to use it. Since there is as much bass in the back room as in front. So the kitchen makes a very poor back enclosure for a True IB! But this very old is idea is having a real renaissance at the moment thanks to some superb drivers coming onto the market.

I'll leave some of your other interesting points for others to tackle.

Regards
Nimby

Hi Guys,

Thanks for replying. I was quite curious about this post.

Nimby, I'm not yet sure what the Waterfall Music is, but it sounds like it's worth checking out (no pun intended!). Not that I'd be in a position to appreciate the full spectrum of the sound of course. Surprisingly, I don't have a wall full of drivers either. Maybe one day though!

Great point about perception of sound by us mortals through brain processing of what are actually, higher frequencies created from distortion. The brain fills in the blanks then (to put it very crudely).

mrdark8.

Actually Spectrum Lab is a program, and waterfall charts a function within that which provides a real-time fourier transform of an audio signal so that you can see which individual frequencies make up the whole signal.

eviljohn2,

Oh right!

Well maybe I'll try the dload with my next subwoofer purchase (whenever that'll be?) as a curious mind like to know these things.

There's no need to wait for a new subwoofer. You can play CDs and DVDs through Spectrum Lab to get a waterfall chart of the frequencies as they play.

If you want a list of really bassy CDs and DVDs then check out this page on the SVS website. (Scroll right down to paragraph 10)

http://www.svsubwoofers.com/faq.htm#movidemoes

Nimby

To answer your question, Yes and No.

If we look at thing fairly simply from just a frequnecy response and SPL level people of view it comes down to you intereptation of "accuracy".

1) A subwoofer may not be "accurate" because it does not have the ability in frequency response to reach the lowest bass below 30hz, so you may be missing out on some frequnecys.

2) From another point of view a subwoofer becomes less "acurate" as is played neer its limits as if the music and movie demands additional 8db peak it but can't deliver it as subwoofer driver is in a power compression situation more power added makes little difference a smaller peak is generated, or in worse situations the driver bottoms or out blisters a voice coil on its thermal limits .

All subwoofers eventually compress on deeper end of bass at some SPL level.

At this point turning the volume of the subwoofer up past this point the subwoofer will give you more upper bass (often 45hz and and up) but no more lower bass.

micb3rd,

I liked your point (2) Re: Subs reaching a limit with deep bass material.

Adding volume indeed isn't going to help 'accuracy' at the extremes, when further "peaks" are required (a jump deeper/lower in frequency) which would be well beyond many a subs limit, as you have mentioned.

I wonder how subs manage all the input. Even on a regular 2-channel HiFi setups, as I have used previously. Infromation from both channels is being processed by a mono device (I used a HIFI Amp and so had no internal crossover settings on it).

I thought, well ... I'm getting a nice extension to my monitor sized speakers, but there are 2 of those receiving a dedicated channel from the source material. How is my sub making sense of it all without one note blurring into in inaccurate noise?

By "inaccurate" I mean a situation whereby the drivers efforts to reproduce the more dominant input (I assume this is favoured by the sub) blurrs with other bass information producing a kind of muddy sound.

Looking around the site at those with 2 sub systems seems interesting. I've seen accounts of people mearly splitting (Y-connector) the low level output from AV Amps. This must surely carry exactly the same signal but to 2 seperate subs. They're not really stereo are they?

On AV Amps they receive not only dedicated low level signals but may also take on low level information instead of the main speakers. The 80Hz crossover standard for example. I don't have an AV Amp btw!

It seems 2 sub set-ups (although perhaps tricky to setup) may help in larger rooms to create a more even sound (not the best way to describe this I know) and help pressurise a room. SVS owners don't need this of course


Oh, something else ... what is a FLAT RESPONSE when describing a frequency output such as 25Hz?

mrdark8

You make some interesting points regarding stereo reproduction via one subwoofer. The problem is that seperating subwoofers physically and then driving them individually opens up a whole new can of other kinds of worms.

I used a pair of DIY passive bandpass subwoofers for years in two different very large listening rooms. I was delighted with the performance provided each sub was placed very close to its standmounted speaker. (Mk1 Kans placed ten to twelve feet apart)

I found the clearly audible "cleanliness" and superior sound quality of the SVS easily overcame any limitation on monoing the stereo signal.Though I really wish I had two for true stereo. But I know from experience that the stereo placement would produce unwanted upper bass lift. Just because of the physical proximity of the large tubes to my floorstanders.

I keep wondering how my passive bandpass subs would perform with a BK plate amp each. But that's another story.

But perhaps it would be most sensible to lay a pair of SVS subs down end-to-end behind my speakers.

Nimby

1) A mono feed to 2 subwoofer is not stereo, it is just mono to a pair of subwoofers.

2) A by going to a pair of subwoofers by adding a extra subwoofer and rebalancing the gains, a less amount of compression will occour, thus you can have deeper uncompressed bass with two subwoofers over a single subwoofer unit on it's compression limits.

But a pair of subwoofers can have its own problems like extra cancelation or extra reinforcement (depending a tone of factors like frequnecy, placement, seating position and room etc).

3) Flat response to 25hz means exactly that.

e.g.

70hz - 90db
65hz - 90db
60hz - 90db
55hz - 90db
50hz - 90db
45hz - 90db
40hz - 90db
35hz - 90db
30hz - 90db
25hz - 90db


Now what has to realised is that rooms mess with the frequnecy response of a subwoofer, somtimes in a good way by reinforcing the low end due to room gain, sometimes in a bad way like adding a big peak (6db-10db) somewhere and a huge dip somewhere else in the response.

You can use equaliser to flatten the response but cutting the peaks or jently adding a little lifting but this can lead to other knock on problems like neighbouring centrer frequnecy phase issues.