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

[Mark (Basspig) Weiss]

I started to subscribe to the concept of at least one sub for every full range speaker, around 1982. I also subscribe to the technique of using all front-firing subs and the elimination of corner horns. I used to enjoy the advantages of tremendous room gain, by firing subs into the corners, but the delays and lack of immediacy in percussion sounds just ruined any gains in the deep bass for me.
When we listen to a live Classical concert, we are experiencing sounds from many sources. One of which is subsonic low level energy from HVAC and nearby subways/trains. So while the violin may not be producing any audible subsonics, they are present in the concert hall from other sources. Musically, we know that many instruments produce subsonics. Bass drums, pipe organs, etc. In studio recordings, kick drums have emphasized subsonics.
What we experience is a tactile difference in music. Not so much in terms of what we HEAR, but in what we FEEL.
For me, sitting on a 8" concrete slab in the cellar, I don't get the benefit of wooden flooring that easily vibrates with home subwoofers, adding a much more tactile effect on the cheap as it were. I needed much more power to get that concrete vibrating beneath the feet, and hence gain the physical tactile effect that second floor-dwellers enjoy with microscopic amounts of power, comparitively.
Watching a suspense movie takes on a more ominous dimension with some of the LFE in the single digits, rendering that uneasy feeling you get when you peer down an elevator shaft.
Pop/rock music, not to mention organ music, of course, enjoy a much more physically-involving experience with several good subs. The whole thing takes the strain off other components and allows them to operate with far less stress, rendering an overall better quality sound.

 

[amirm]

We have all read the Harman paper on subs. Here is an interview following it which has a few other tidbits: http://www.onhometheater.com/features/20040801.htm

In our showroom we are deploying JBL Synthesis system with 4 subs using their new DSP algorithm which first perfectly matches them in response. And then applies room correction. The system makes sense to me as opposed to throwing subs around which all produce random response and then having one room eq in front of it.

We will also have a Wisdom system in the same room with its room eq and multiple subs. Hoping all of it lights up in the next two weeks. Should be exciting!

 

[brianherlihy]

Amir, please post pictures when you open

 

[amirm]

Will do. Plan to also write an article on the whole thing from audio to video.

 

[microstrip]

Will do. Plan to also write an article on the whole thing from audio to video.

While we wait could you tell us the room dimensions and how the subs are placed?

 

[Robh3606]

Hello FrantzM

A reading of some works cited in this thread would give you the rational behind the use of multiple subwoofers ...

I am well aware of use of multiple subs to smooth bass response. In my 2 channel rig I want to keep it simple so I will stick to no subs. I use asymetrical placement anyway so I don't have 2 speakers that reinforce the same bass modes. That seems to help as it's mono down low anyhow.

Rob

 

[amirm]

While we wait could you tell us the room dimensions and how the subs are placed?

I will document these better later but for now, the room is roughly 19 feet wide by 22 feet deep. Don't recall the ceiling measurement but it is quite high perhaps 14+ feet. This is the dimensions of the box inside the larger box it was built into although we will lose some to secondary fabric covered walls as all the speakers on this theater are concealed (sans when we demonstrate floor standing speakers like Salon 2).

There are two parallel multi-channel audio systems as I mentioned:

JBL Synthesis: This one has all of its subs in the ceiling. It is composed of a single 15 inch plus six (6) dual-10 inch subwoofers. They are passive and driven by a bank of amps in the rack. If my math is right, all told there are 17 speakers being driven independently!

Wisdom: This has one sub in the ceiling close to the front of the room which is the S90i "in-wall" unit. We then have two of their "suitcase" subs (SCS) flanking the back walls. So the total here is 3, all self powered. All in all, there are 10 Wisdom speakers being driven separately.

The room is also designed to incorporate custom subs (e.g. Danley) in front (flush mount with the rest of the speakers). This was part of the original plan but we thought we bought enough speakers for now .

Again, all of these speakers plus more acoustic panels than you can possibly imagine are covered by fabric. As I mentioned in another thread, the focus of our business is to bring high performance and architectural/good looks together and hence this style of design.

 

[amirm]

Oh, even more insane. The original plan called for accommodating a complete Genelec system as the third option! The idea was to have a system for any taste at similar price points.

 

[microstrip]

JBL Synthesis: This one has all of its subs in the ceiling. It is composed of a single 15 inch plus six (6) dual-10 inch subwoofers.

Amir,

I am also speechless...

Do you know of Asterix the gaul? As far as I remember they always wear their helmets because they feared was that the Sky could fall on their heads. If they knew about your room they would also fear that the Bass could fall on their heads!

 

[Nyal Mellor]

One more thing for the thread:

Welti's original multi-sub approach was the solution to reducing seat to seat variability in bass response such that global EQ could be more effectively employed afterwards. Seat to seat variability is a big issue in home theaters but is non-existent in 99% of 2 channel setups since we only care about one seat.

So the optimal solution (best result at lowest cost) for bass in a 2 channel system may well be different than for a home theater setup.

 

[amirm]

Amir,

I am also speechless...

Do you know of Asterix the gaul? As far as I remember they always wear their helmets because they feared was that the Sky could fall on their heads. If they knew about your room they would also fear that the Bass could fall on their heads!

I must say, this will be the first time hearing bass showing from sky. Will report back on how it tall sounds when it is all together. It is a clever way of hiding these boxes though if you have a high ceiling as we do.

 

[Paul Spencer]

How many subs? I believe in the simplest solution that works. I could see anything between 1 - 5 subs working well, but there is no one size fits all solution and no magic number. One sub can work well, although it's probably only going to be a small area optimised, hence a 2 channel or small home theatre system. Usually you will want more than one bass source, because even in one seat you will usually get dips that you don't want to EQ. So you find another spot for another sub that fills in that dip. Sometimes the mains are in a good spot for bass - this is the case in my room. So if I overlap one sub and the mains, I can get a pretty good result. I have 3 bass sources then and if you tackle this using the Geddes 3 subs overlapped with the mains, you have 5 bass sources.

So how many subs in your particular room? The measurements can tell you. Put a sub in your listening position, ear level. Move the mic and measure every location you could actually use. Even different heights can be done (think bandpass with external vents). What I look for is two main things. Firstly, a spot for the first sub that has maximum bottom end gain. That first sub will produce most of the output as they don't all tend to sum together very efficiently. Next, I look at the mains and see how they perform. Next I look at other locations that don't have dips where the mains and first sub do. Ideally you use as many subs as you need placed where the dips are mostly gone. It's handy to keep in mind that peaks will sum but dips don't subtract, phase issues aside. So with that in mind, you can do a pile of measurements and pretty quickly pick out locations that can work pretty well. You try it out and start tweaking. EQ helps as you can bring down the peaks and the extra headroom is nice to have.

I find bass traps also essential. I can get a flat response without bass trapping, but adding bass traps was a giant leap forward. Would you prefer an untrapped room with EQ to get it ultra flat or a trapped room which is "acceptably flat?" For me it is an easy choice. I have found the slow bass decay of an untrapped room is quite annoying. I didn't recognise it before, it was just an impression that the bass could be better. Now it is something that I have to "listen through." So I'm more concerned about the room decay than I am about perfect time alignment, however, why not have both?

I've heard Terry's system at said shindig and it is something to experience. I was walking into the room when that demo of bass time alignment was going on. For me the subs made a big difference, adding weight and fullness to the sound. What impressed me most about Terry's system was the imaging. In the chair that sits over a spot literally marked X with masking tape, the imaging is like nothing else.

 

[andy_c]

You need subs with infinitely adjustable Level, Crossover and phase controls. The phase is particularly important, I am not sure and simple switch will do…

Hey Frantz, I assume you're using the Behringer DCX2496 as mentioned elsewhere in this thread? If so, I'd be interested in knowing how you are doing the phase adjustments. On page 18 of the manual, section 4.5.4 and 4.5.5 show two possible ways of doing a phase-oriented adjustment. Section 4.5.4 shows a phase adjustment called "polarity/phase", which may be some kind of all-pass filter, along with a straightforward normal/invert polarity swap option. It is described as follows:

Use the PHASE parameter to adjust the precise phase position at the upper X-OVER frequency of the currently selected output. This fine adjustment is necessary when two output signals are not perfectly displayed by 0 deg or 180 deg with respect to each other

Section 4.5.5 shows a delay adjustment, of which "short" looks like plenty for any home application. Which of these adjustments did you use, polarity/phase (4.5.4) or delay (4.5.5)? I wish they provided more information about what the phase adjustment in 4.5.4 really is. The polarity swap feature is straightforward, but it's not obvious what's going on with the phase - is it excess phase beyond the usual minimum-phase amount at the crossover frequency? It seems unlikely they could reduce the phase lag to below that of the minimum-phase result, LOL.

 

[Paul Spencer]

Andy, you can do it manually, using software to measure, or via auto align which can do both polarity and digital delay. I've used both but not the phase adjustment.

 

[Alan Sircom]

Going right back to the OP:

There's been a lot of discussion revolving around the use of subwoofers to augment the bass of "full-range" speakers. What are your thoughts/feelings about using subwoofers to supplement the bass of your main speakers, and how many subwoofers are necessary to assure good results?

Lee

The fundamental flaw in this logic is considering the subwoofer as simply augmenting the bass of a loudspeaker. If your loudspeakers resolve down to DC then no amount of subwoofer will augment that. In that case, a sub's role is to provide control over the lower end of the frequency range, and this has a peculiar perception effect in the listener. Properly integrated, a subwoofer (or subwoofers) will seem to open out the soundstage, bring out the speaker hidden in your speakers and may often make the sound appear lighter and faster than when used without.

There's a simple bit of thinking things through that seldom happens in audio. Here's the edited highlights:

1. The place you put your speakers for optimum performance from 200Hz and above is rarely the same place you would put them for optimum performance below 200Hz
2. A significant amount of the problems generated in room are in the region below 200Hz
3. Subwoofers work in the region below 200Hz

As a result, if you have a full-range speaker system, you should consider a subwoofer as part of the room acoustic treatment rather than a deliverer of bigger, better bass. I'd consider using one as the first or second line of defense, vying for the top slot with passive room treatment (passive treatment should come first, but this depends largely on the amount of high-frequency whine from the wife's upper regions you get when installing bass traps). 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

Personally, I'd consider steps #1 thru #3 to be mandatory for almost every system. I'd also recommend steps #1 and #2 for anyone before buying new equipment. A lot of the best gear goes in and out of people's rooms because they haven't done due diligence on the installation and room acoustics, and they mistakenly think the next product will solve an issue that has nothing to do with the products themselves. I've tried saying this every few years, but it falls flat because the new preamp or cable is crying out 'buy me!' and because audiophiles routinely dismiss subwoofers as 'home theater'. Fortunately, there seems to be renewed interest in room treatment at this time and maybe, just maybe, I can get this one across.

I doubt it though. I think some view room treatment and subwoofers (especially subs used effectively as active bass controls) as some kind of failure of manhood.

 

[FrantzM]

Going right back to the OP:



The fundamental flaw in this logic is considering the subwoofer as simply augmenting the bass of a loudspeaker. If your loudspeakers resolve down to DC then no amount of subwoofer will augment that. In that case, a sub's role is to provide control over the lower end of the frequency range, and this has a peculiar perception effect in the listener. Properly integrated, a subwoofer (or subwoofers) will seem to open out the soundstage, bring out the speaker hidden in your speakers and may often make the sound appear lighter and faster than when used without.

There's a simple bit of thinking things through that seldom happens in audio. Here's the edited highlights:

1. The place you put your speakers for optimum performance from 200Hz and above is rarely the same place you would put them for optimum performance below 200Hz
2. A significant amount of the problems generated in room are in the region below 200Hz
3. Subwoofers work in the region below 200Hz

As a result, if you have a full-range speaker system, you should consider a subwoofer as part of the room acoustic treatment rather than a deliverer of bigger, better bass. I'd consider using one as the first or second line of defense, vying for the top slot with passive room treatment (passive treatment should come first, but this depends largely on the amount of high-frequency whine from the wife's upper regions you get when installing bass traps). 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

Personally, I'd consider steps #1 thru #3 to be mandatory for almost every system. I'd also recommend steps #1 and #2 for anyone before buying new equipment. A lot of the best gear goes in and out of people's rooms because they haven't done due diligence on the installation and room acoustics, and they mistakenly think the next product will solve an issue that has nothing to do with the products themselves. I've tried saying this every few years, but it falls flat because the new preamp or cable is crying out 'buy me!' and because audiophiles routinely dismiss subwoofers as 'home theater'. Fortunately, there seems to be renewed interest in room treatment at this time and maybe, just maybe, I can get this one across.

I doubt it though. I think some view room treatment and subwoofers (especially subs used effectively as active bass controls) as some kind of failure of manhood.

Excellent!

 

[audioguy]

I agree.

Slightly OT, after I purchased my Watt/Puppies many moons ago, the dealer came down to help me get them to sound as good as they could. The room had a 15db hump at 65hz and his solution was to get rid of my Krell Amps and buy something else (that he was selling).

When I asked him why he thought a different amp would remove a 15 db bump, he yelled obscenities at me, physically threatened me and stormed out of my home.

Going back to the original topic, not unlike real-estate, to optimize bass, its all about location, location and location (with appropriateness room treatment first!)

 

[Phelonious Ponk]

There's a simple bit of thinking things through that seldom happens in audio. Here's the edited highlights:

1. The place you put your speakers for optimum performance from 200Hz and above is rarely the same place you would put them for optimum performance below 200Hz
2. A significant amount of the problems generated in room are in the region below 200Hz
3. Subwoofers work in the region below 200Hz

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

 

[Phelonious Ponk]

I agree.

Slightly OT, after I purchased my Watt/Puppies many moons ago, the dealer came down to help me get them to sound as good as they could. The room had a 15db hump at 65hz and his solution was to get rid of my Krell Amps and buy something else (that he was selling).

When I asked him why he thought a different amp would remove a 15 db bump, he yelled obscenities at me, physically threatened me and stormed out of my home.

Going back to the original topic, not unlike real-estate, to optimize bass, its all about location, location and location (with appropriateness room treatment first!)

I believe I would have returned my Watt/Puppies to that dealer and taken my business elsewhere.

Tim

 

[FrantzM]

Tim

I will leave more precise responses to your questions to those who know more about room acoustics than I do. I can however tell you however an anecdote.
I had a hump of about 10 dB at 75 Hz .. Sharp , at 80 hz, it didn't show up ... No amount of moving bass traps around the room would solve it or reduce it., in my old room. All concrete. Magnepan planar speakers that could as low as 25 Hz with vigor ... With a pair of subwoofer placed next to the speakers, I call that the traditional audiophile way The hump would simply get larger or disapeat with playing with the phase control .. The phase settings that made the hump disappear resulted in an unsatisfactory reproduction of the low bass, they seemed to come from a different speaker, not integrated with the mains at all ... Using the subwoofer in what I call the "Geddes variations on Welti papers" method .. more than 3 subs and one in one corner behind the front speaker, the second on the side wall and the thirs on the other side wall all subwoofer in the front speaker volume of the room , resulted in removing the hump while providing me with the best bass I have heard in my room or in others for that matter ...
Long Story short... The hump can be removed by adding subwoofers, even one , however counter-intuitive that this sounds (pun intended ) . I have some acoustic explanation ofhow this would happen but repeating myself leave it to those who know more.