Do we NEED subwoofers with full-range speakers, and how many?

[Alan Sircom]

Alan, you've focused precisely on what puzzles me. Performance above 200hz is placement critical for imaging, etc. Performance below 200hz is placement-critical as well, and proper placement can address lots of room issues. But often (usually?) optimum performance above and below 200hz requires different placement. So even if you buy great subs, and carefully place them in the room, you still have full-range speakers generating response way below 200 hz in the original, poor locations, yes? How can a sub(s) cure this? Let's say the room placement of your full-range speakers is causing a 6db hump from 60hz to 100hz. Does a properly placed, properly integrated sub cancel this out? How? If that sub, regardless of where it is placed in the room, puts out any sound from 60hz to 80hz, wouldn't it actually make matters worse? If it is crossed over well below that range, which is more likely, how would it effect that hump at all?

Tim

I'd say the situation was far, far worse with a smaller loudspeaker (especially a smaller ported) unless it was intended purely as satellite and had almost no content below 200Hz. A full-range loudspeaker might be in the worst-case nodal point where there's a 6dB hump at 80Hz. A bass trap will help. An active subwoofer acting in the same band but out of phase to the boom will do the same. But at least the full-range loudspeaker doesn't have a port chuffing away at the point where the room goes off.

You are really on a bit of a losing streak however you do this. If you use main speaker that have content below 200Hz, you run the risk of it interfering with the room. If you don't, you are dangerously close to putting the crossover point right where we can really hear it. So you compromise. The best compromise is to let the speakers be speakers and let the room and whatever else you put in there take up the slack. You just need to have the resolve to keep turning the sub down.

 

[JackD201]

In other words a sub or subs properly placed and in the correct phase, croosover, Q and output can smoothen response by providing active cancellation

 

[Alan Sircom]

In other words a sub or subs properly placed and in the correct phase, croosover, Q and output can smoothen response by providing active cancellation

Yes, but when you get used to being paid by the word, why use one word when you can knock out 10,000?

 

[microstrip]

(...)

In an ideal world, this is how it should be done, IMO:

1. Passive room treatment
2. System installation, with very great attention paid to the position of the loudspeakers on voice relative to the room. This can mean minute adjustments to position, toe-in and even angle of the speakers, and may not end up with a perfectly symmetric speaker paring in bad rooms. Which means a lot of trial and error
3. Subwoofer integration, starting with the subwoofer almost turned off, adjusting its controls carefully until the rest of the sound fills out. Use recordings with and without a lot of low-end component to test this. Once again a lot of trial and error
4. If at the end of this you are still unhappy, then start to look at DSP solutions

Alan,
Just one detail. The ways you are presenting it, it seems these sequential steps steps are independent - something that in my opinion seldom happens in real world.

My little experience is that once you introduce the sub-woofer you have to change the position of the main speakers. I have observed that subwoofer strongly affects the imaging and spacial properties, and as positioning is always a compromise between several different aspects they are really interactive.

I have experience with the Martin Logan Depth subwoofer with ML main speakers and the Wilson Watch Dog with Wilson Watt/Puppy VIIs - may be with other systems the situation is different. Even the acoustic treatment is dependent on speaker type and placement - sometimes you have to change some panels (or some furniture) after moving the speakers.

BTW, I always used a good spectrometer to make the first adjustments of the subwoofer - the bass balance of recordings is too variable, and unless you have a reference it will be a long time before you get an average. May be more experienced installers or users have a few references they can rely on.

 

[microstrip]

In other words a sub or subs properly placed and in the correct phase, croosover, Q and output can smoothen response by providing active cancellation

Jeff can surely help on this subject:

http://www.ultraaudio.com/twbas/twbas_20051215.htm

 

[andy_c]

Let's say the room placement of your full-range speakers is causing a 6db hump from 60hz to 100hz. Does a properly placed, properly integrated sub cancel this out? How? If that sub, regardless of where it is placed in the room, puts out any sound from 60hz to 80hz, wouldn't it actually make matters worse?

It's possible to get a reduction in the overall level over a limited frequency range by adding a sub because the outputs of the added sub(s) and the mains are correlated, and the net result is a phasor sum (addition that considers both the amplitude and phase of two or more acoustic pressures). As an example of real data showing this, check out Markus Mehlau's multi-sub page. Scroll down to the bottom to look at the four graphs. They can be enlarged by clicking on them. Note how the data change in the frequency band around 50 Hz. From "Mains only" to "First subwoofer added", the situation around 50 Hz gets worse. But look what happens from "First subwoofer added" to "Second subwoofer added" at around 50 Hz. Huge improvement there!

 

[Phelonious Ponk]

In other words a sub or subs properly placed and in the correct phase, croosover, Q and output can smoothen response by providing active cancellation

And this cancellation reduces the exact frequencies of the hump by the exact db of the curve? Good trick. But wouldn't it be a lot easier and more efficient to measure the hump and remove it surgically with a good parametric EQ?

Tim

 

[JackD201]

I wish it was so. As I have come to experience and thus understand it the issue isn't so much what comes out of the loudspeakers but where and when pressure builds up in the room once they have left it. From what I remember, most any room asked to accommodate speakers whose lowest output has a 1/2 wavelength greater than the room's length will have big humps and worse suck outs.

 

[LL21]

i would have also thought interjecting an EQ into the chain could also have deleterious effects by virtue of adding yet another component into the chain and further degrading the signal, if nothing else. and that degradation would have been inserted into a full range sound (ie, the entire range of the main speakers).

 

[JackD201]

Yes, but when you get used to being paid by the word, why use one word when you can knock out 10,000?

Hahahaha! I was in politics for almost a decade, I had to learn how to get the most out of a news soundbite. Hahahaha!

 

[RUR]

And this cancellation reduces the exact frequencies of the hump by the exact db of the curve? Good trick. But wouldn't it be a lot easier and more efficient to measure the hump and remove it surgically with a good parametric EQ?

Tim

The general idea is to even out the response as much as possible using bass traps+multiple, properly set-up subs. Whatever's left may then more easily be managed via EQ.

And don't forget, peaks are only one probable issue - nulls cannot be EQ'd away.

 

[Phelonious Ponk]

I wish it was so. As I have come to experience and thus understand it the issue isn't so much what comes out of the loudspeakers but where and when pressure builds up in the room once they have left it. From what I remember, most any room asked to accommodate speakers whose lowest output has a 1/2 wavelength greater than the room's length will have big humps and worse suck outs.

I see how that would call for bass traps, for example, but I still don't understand how subs work in this regard. I'm beginning to be glad I don't have much low frequency response .

Tim

 

[JackD201]

If I had limited space, I would definitely sacrifice low end extension first. The problem with passive bass traps is that they need to be larger the lower the frequency goes. They will eat up the living space. One could always open windows and doors but the cops will come

 

[andy_c]

And this cancellation reduces the exact frequencies of the hump by the exact db of the curve? Good trick. But wouldn't it be a lot easier and more efficient to measure the hump and remove it surgically with a good parametric EQ?

This will work at a single listening position, but as Earl mentions, it's possible for said EQ to make the response at a nearby listening position worse. With multiple subs, it's possible, at least in theory, to flatten the response at multiple listening positions - the more subs, the more positions for which this is possible.

And as RUR says, filling in a notch is not a viable solution with EQ, but can work very well with multiple subs. Also see Paul Spencer's multi-sub article.

 

[Phelonious Ponk]

Ahhh... I have one listening position and no bass. Never has poverty been such a blessing .

Tim

 

[andy_c]

Ahhh... I have one listening position and no bass. Never has poverty been such a blessing .

Hehe. That's my position at present too. I used to have some larger floorstanders that were flat in anechoic response to about 38 Hz. But my room has a mode at about 40 Hz, giving a huge peak of more than 10 dB. Now I have some monitors having higher quality midrange and highs, but their anechoic response is 3 dB down at 54 Hz, and about 10 dB down at 40 Hz. The room mode at 40 Hz is propping up the overall bass response of the monitors, giving an overall more realistic bass than the one-note jukebox bass at 40 Hz I had with the floorstanders.

I can't wait to move out of this apartment into a house, though. Time for some multiple subwoofage.

 

[amirm]

I see how that would call for bass traps, for example, but I still don't understand how subs work in this regard. I'm beginning to be glad I don't have much low frequency response .

Tim

The idea of multiple subs is to make the situation better by making it a lot worse!!!

Imagine the bass frequencies have peaks here and there based distance to reflective points. The problem is "here and there." If we could fill the gaps with more peaks then the overall sum would just look like the bass has increased but in a flat manner across all the frequencies.

That is what you can accomplish with multiple subs. By having more sources in more places, you start to fill in the gaps. If then the overall sum is too bass heavy, you can EQ it to shape since it is now more linear.

Earl's method relies on using the speakers full rang and hence have them look like more "subs." He says that below the first mode, there is nothing you can do to add more peaks. Therefore, the mains have enough low energy power to work since the first mode in most rooms is around 40 Hz or so.

Is this what you were asking? Or did you already know all of this .

 

[Phelonious Ponk]

The idea of multiple subs is to make the situation better by making it a lot worse!!!

Imagine the bass frequencies have peaks here and there based distance to reflective points. The problem is "here and there." If we could fill the gaps with more peaks then the overall sum would just look like the bass has increased but in a flat manner across all the frequencies.

That is what you can accomplish with multiple subs. By having more sources in more places, you start to fill in the gaps. If then the overall sum is too bass heavy, you can EQ it to shape since it is now more linear.

Earl's method relies on using the speakers full rang and hence have them look like more "subs." He says that below the first mode, there is nothing you can do to add more peaks. Therefore, the mains have enough low energy power to work since the first mode in most rooms is around 40 Hz or so.

Is this what you were asking? Or did you already know all of this .

I didn't know enough to be absolutely sure what to ask! Thanks.

Tim