Do you think you need a subwoofer?

@mke246 Great bass always brings a huge smile to my face, it is the part that makes you want to get up and dance.

Dear friends: I think this link belongs to this thread:

Microsoft Word - whitepaper10.doc

and this tinformation too:

" 

The ONLY correct way to add a sub to system is to define everything ABOVE the sub’s [frequency] range as an entity; clearly define the impulse, phase, and lastly frequency response of this entity; and then make a new "2-way" system where the sub is one way and everything above it is the ’other’ way. The parts must be combined correctly so that there are no cancellations and no smearing of time-related musical events.

This CANNOT be easily measured in the frequency domain, because you could have (as an example) an 80 Hz signal coming from both the mains and the sub, and if the sub is 12.5 msec late the two sources will "seem" to be in phase but the sub really will be 360 degrees, or one full wavelength late. It is the impulse smearing that this affects, but people don’t measure that because there is no simple "hand held" phase or impulse meter as there is an SPL meter.

The REASON this meter does not and essentially cannot exist is that in order to measure impulse response or phase response you need a starting REFERENCE point, (in time) and in a speaker system, since the signal has to travel through circuitry, amplifiers, passive crossovers inside the speaker box and then hit the driver; therefore the first reference point MUST be acoustic.

There ARE computer based impulse response systems such as the TEF, ( very quick technical blurb HERE; full story HERE ) but they are involved, require real instrumentation, are expensive, have a seriously steep learning curve, and they are absolutely not the kind of thing most ’consumers’ -- or audiophles, can be bothered with or have patience for.

So the overall view of adding a sub is this: In essence you are designing and assembling a new speaker system which is "2-way": the sub is one way and everything "else" above it in frequency is the 2nd way.

Simply connecting a sub to existing mains speaker (or amp) terminals ( or self powered subs. ) is the WORST POSSIBLE WAY to do this. EVERYTHING scientific and acoustic about this method is wrong, from the additive delay issues to the back EMF of the mains affecting the LF signal. However there are plenty of people who simply do not understand correctly integrated bass, and they will be reasonably happy simply sticking another box on to their system without regard to timing, phase and frequency issues, and they will think it sounds "ok" or "good" and for those people it doesn’t really matter.

Indeed the only thing that does matter is an individual’s happiness with their system, whether I or anyone else thinks it’s right or wrong.

But I want you to know and understand the truth, so to get purely technical...."

along this:

" 

TYPES OF "MAIN" SPEAKERS

In addition to all the above, there is the complex issue of the "main" speaker you are coupling to. There are essentially 6 types of speakers that exist:

1) sealed
2) port in the front
3) port in the bottom
4) port in the back
5) a dipole, which is a flat panel such as an electrostatic (Sound Lab, Magnepan, Quad, Beveridge, Martin Logan, etc.)
6) an true omnidirectional system such as the MBL or the BEOLAB 5.

Each of these speaker types couples somewhat differently to the room, and certainly to a sub in that room, and therein lie the problems in acceptable integration.

A port is ALWAYS nothing more than a cheap way to attempt to get free bass out of an enclosure and /or driver that's too small. It's a holdover from the 1930's when because of driver inefficiencies (especially when compared to today's units) you had to do everything possible to increase the useable output over the desired range of low frequencies.

At one level, all the guyz want 9 foot speakers in the living room (read "man-cave"). All spouses, of whatever gender, want tiny 3" speaker cubes that disappear, but expect 9-foot results from them. Since they haven't repealed ohms law or any other laws of physics while we were sleeping, the only way to get correct sound is to move a correct amount of air.

Lets examine ported speakers. We'll start with the worst case, the port in the front. At mid bass frequencies, say 50-80 Hz, the LF driver moves IN the cabinet, the air in the cabinet is elastic, and the port air moves out of the cabinet. Because of the frequency at which the cone is moving, by the time the cone moves out (forward) again, the port air is now moving out, so in front of the cabinet the two air pressure sources sum together and you get a fake bass "bump" or "boost".

As you go lower and lower in frequency, at some low frequency the air pressure from the LF driver and the air pressure from the port are exactly opposite each other, so they cancel, and there is no more audio at that frequency: it disappears.

When the manufacturer of a speaker cabinet defines the frequency response (i.e., 37 Hz - 20kHz +/- 3dB) this is what is defined by the entire arrangement of the port and the air in the cabinet and the driver. At some low frequency the port air is exactly out of phase with the driver air pressure and since they cancel, there is NO output from the cabinet into the room. Therefore with a ported cabinet, the entire sloppy concept is this juggling game between the response of the drivers under air pressure, the passive crossover inside the box, the port size and placement.

You must understand that ANY driver goes down to 0 Hz, or DC. If you put a battery across a speaker, the cone moves out and stays there. If you were to have a DC coupled power amp feeding a speaker - ANY speaker, from a 1" dome tweeter to an 18" rock n roll stage bass driver - and you put 4 Hz into it, it would simply move back and forth at 4 Hz. Of course in order to actually "hear" the audio it would have to be in the generally accepted passband of 20-20,000 Hz and the cone diameter would have to be enough to actually move some air in the room. So it is the overall combination of the driver size, the excursion, the box size, (therefore the air back pressure) and many other factors that determines the overall response of that "speaker" AS AN ENTITY.

That means IF you were to simply put those same frequencies through the mains and the sub (that means with no crossover, and this is the mistake that nearly everyone makes) you would now have 3 sources of LF energy and differing phase: the 'main' LF driver, the port, and the sub, all fighting with each other in the time domain. A further corollary is that since the air inside the [mains] cabinet is elastic, the phase relationship of the port air to the driver air is also a sliding one; that means it's "out of phase" — and smearing — over a wider range of frequencies than you might think.

If the port is on the back, again, a cheap attempt to use the back wave bouncing off a wall to give 'additional' bass, you have the ADDITIONAL issue of the transit time it takes for the back port pressure (already delayed because of the elasticity) to leave the cabinet, travel back, hit a wall, and bounce back around the front of the cabinet again; therefore this LF wave MIGHT be "in phase" with the front driver BUT BE 360 OR EVEN 720 DEGREES LATE; therefore it sounds like the bass frequencies are ok in the frequency domain but the IMPULSE RESPONSE is now muddied.

Also, in the case of back ported or (type 5) dipole speakers, since the path length from the back of the speaker to the wall and bouncing back around to the front of the speaker is a fixed physical entity, at some frequencies you are adding and at some frequencies you are canceling: you have simply made a physical/mechanical frequency comb filter that you can't do anything about. Sound Lab's answer to this (for use with their flat panel electrostatic speakers, which are dipoles) is they sell you a "Sallie", which is an absorber to absorb the entire back wave output of the electrostatic panel. Since now there is no comb filtering; all you are therefore hearing is the front signal.

PORTED SUBS

A ported sub for home use is even more wrong than ported mains. Now you would be attempting to acoustically add together in the room at least SIX low frequency sources with differing phase and frequency slope conditions: the LF drivers in your two mains, their ports, the sub driver, and its port. In addition, since it's a bandpass it cannot go down low enough for serious Home Theater effects. (that typically means a real 20Hz or close to it.)

In some cases such as a bandpass sub used in a club or on a modest-sized stage in your local pub, you are most concerned with efficiency and not with getting frequency response "flat" down to 20 Hz; therefore a correctly set up bandpass box that might roll off at 35 to 45 Hz is quite sufficient and also very efficient for the defined purpose. And again, as a point of reference, "flat" response in the frequency domain is FAR AND AWAY the LEAST important phenomena: impulse response in the time domain is the most important, but it cannot be measured with a handheld meter therefore almost everyone simply ignores it. If you're interested in learning about the newest (and evolving) pro sound system / stage methods of "steering" bass, Dave Rat has some very cool videos here:

part 1  www.youtube.com/watch?v=VwLH7zP6Lwo

part 2  www.youtube.com/watch?v=B-3pURYOwfw

part 3  www.youtube.com/watch?v=aSZK9Altvm8

There's a nice article here:
www.prosoundweb.com/channels/study_hall/tech-topic-friends-in-low-places

But back to our Home / HI-FI / 2-channel / Audiophile / Surround Sound systems: There is ONLY ONE truly correct way to "add a sub" to a system in an controlled listening room situation: you must correctly cross over the 2 sealed cabinets; and their timing must be correct. ANY other method will lessen the focus and clarity and imaging you have tried so hard to preserve.

I have many clients and customers with extremely exotic high-end 2-channel systems that are all chasing the holy grail of 3D holographic sound imaging, and until they follow my distinct guidelines they are never completely satisfied with the results.  "

Regards and enjoy the MUSIC NOT DISTORTIONS,

R.

Raul that was a very informative posting. The fellow you quoted, in simple language broke down a crucial concept to be more easily grasped at its basic fundamental level. I hear the voice of experience in the point he is making.

I have downloaded that PDF and will be reading it in the near future.

@theophile  :  Bass range is where MUSIC " belongs ". As better the room/system bass management as better the overal quality level MUSIC reproduction and only self powered dedicated subwoofers reproduce the "  rigth " Transient Response  that's where MUSIC starts.

R.