What causes the BOOM sound of bass?

[QuantumTheory]

What causes the "BOOM" sound of bass?

If you ever heard someone listening to their music with the bass up all the way you might understand what I mean. That "BOOM" from steoro systems . What is it caused by? The vibration of molecules?

 

[brewnog]

It's just low-frequency, high-amplitude sound waves. As you know, sound waves are merely vibrations. Low frequency, high amplitude vibrations can often make other objects resonate, - if I turn my subwoofer right up, it can often cause my floorboards and shelves to vibrate too. My housemates love me!

 

[exequor]

speaking of soundwoofers I know that they give you the lower "cleaner" frequencies, in other words the "true bass" sound over conventional speakers. Why aren't they used much in DJ equipment as regular speakers (that is what I've noticed where i live, could be different in other places over the world)?

 

[brewnog]

speaking of soundwoofers I know that they give you the lower "cleaner" frequencies, in other words the "true bass" sound over conventional speakers. Why aren't they used much in DJ equipment as regular speakers (that is what I've noticed where i live, could be different in other places over the world)?

They are!

In a typical club, you'll find that the subwoofers are generally hidden in big boxes on the floor. The location of subs is not nearly as critical as the location of normal speakers, so they generally just stick them wherever they can fit them.

DJs need to use normal speakers too, because their music isn't generally just bass. The normal speakers (woofers, drivers and tweeters) provide the moderately low, medium and high frequencies (instruments, vocals, cymbals etc) while the subs fill out the low frequencies from basses and drums.

 

[Rogue Physicist]

Just to put a face on the ranges,

subwoofers usually handle anything from 5 Hz to 30 Hz.

A bass guitar has a range of from 20 Hz to 500 Hz counting harmonics.

A female vocalist's output is mainly in the 1Khz to 5Khz range, with harmonics and sibilance (percussive sounds like 'p', 'k', 't', 's') all the way to 18 Khz.

An 'A' Note at 440 Hz is below middle 'C' on the piano, and so you can range a piano at about 100 Hz (doubling the frequency per octave) to about 6 Khz for the fundamental notes (ignoring harmonics).

Subwoofers can't 'substitute' for bass speakers, but only add extra low range.

 

[Cliff_J]

Rogue - is that a typo on your part?

By studying a Fletcher-Munson type of curve we know that our ear's sensitivity to low frequenices is poor and thus requires a far greater amplitude in order to meet minimum audible requirements.

Also, by studying the typical Thiele-Small parameters for transducers we can see that the lower the electro-mechanical resonance frequency of a driver the lower the efficiency by a cube factor.

And from a simple analysis of diaphram displacement versus frequency that for a given amplitude the displacement requirements go up by a square factor on the inverse of frequency.

So finding a subwoofer that can accurately produce an audible 20Hz note of level enough to carry any distance is difficult and not typical. Sure a couple dozen commercial examples can be quickly noted, but out of hundreds different models its a small percentage that are even capable of such a task, much less one two octaves lower at 5Hz!

So a subwoofer is better characterized as a driver being optimized for 20Hz to 100Hz with most designs being optimized for a lower bandwidth range of more like 30Hz or 40Hz to maximize output efficiency over the greatest range of materials. Not many people listen to a muscial selection like Planet Krypton, 1812 Overture, or other classical pieces that may have a kettle drum or something else with acoustic energy below 30Hz. So without the material to demand such extreme low frequency performance, most systems instead optimize for greater efficiency at the expense of a frequency band most people wouldn't miss.

On that note, most boom systems are optimized for 50Hz to 60Hz, a far easier freqeuncy range to achieve in displacement requirements and in efficiency. Add to that how well the small dimensions of a auto assist the speaker in achieving even greater efficiency with acoustic loading of the diaphram and you have the boom that can be heard for city blocks.

A 4-string bass has a low E fundamental of 41Hz and a 5-string has a low B of 31Hz, so unless you're counting undertones the range is a little different and a 6-string muddies the waters even more.

A subwoofer can be made to play from 20Hz to 2KHz - the Adire Brahma is an example of a commercially available driver that can do it and its low inductance plays a large part in that extended upper frequency response. Now it doesn't sound very good playing this wide bandwidth, but there are countless examples of home speakers where the woofer handling the bass portion plays up to the range where it handles most of the fundamental frequencies for vocals and most other instruments.

So its more like the commerical realities means its profitable to make subwoofers designed to satisfy consumer wants of exaggerated bass in the 40-80Hz range for both cars and home theaters. The number of audiophiles who want clean accurate reproduction of their music is another matter and a pretty small percentage of the market.

 

[FredGarvin]

I will back up what Cliff mentioned about bass frequency response. My current speakers, JBL 4412, are considered pretty good monitors and their low end is rated at 45 Hz. Other speakers I have looked at have had similar characteristics. I can also say that, when putting low freq. through my speakers, it is scarry to see just how much those woofers deflect. It amazes me that they can handle that level of alternating stresses and keep working for over 15 years.

 

[venuesystem]

Just a quick note from the pro audio slant. most big rigs used for concert sound operate from about 40Hz to anywhere from 100Hz to 200Hz. the upper cut off is determined by either
A. spectrum analysis of the room or space or
B. the techs ears
We try to set up the system to have the cutoff fall at the low frequency resonance of the room (helps keep the system from producing "single note' bass). In a typical 3-way system the speakers would be a sub (15" or 18') a bass speaker (usually a 15") and a high frequency horn. The crossover is set at 80 to 200Hz for the sub-bass, bass from 100 or 200Hz up to 1.2K or so and highs extending up from there. the bass speaker is usually capable of lower frequencies but not use for sub-bass information. Placement of the subs are very important due to the requirement for the sound at all frequencies to arrive at the listener at the same time and a problem with subs called the power alley. For small clubs, direct radiating systems are preferred, large stadium sound usually requires horn loaded boxes due to their efficiency and the ability to throw a longer distance. As with everything, all of this is room dependent, no hard fast rules apply, it's what sounds 'right" that counts.

 

[Danger]

Just a quick note from the pro audio slant

I have no technical knowledge along this line, but in my bartender capacity I used to help with sound-checks for bands that didn't have their own guy. I knew exactly what needed to be done, but not 'real' terms for it. Usually, I'd just say something like, "You need to drop the high-hat mike by about 10%, and bring the bass player's vocal mike up 20%." You would have loved the last place that I worked in. It's stylish here to have the sub-ceiling removed and the guts painted. So here was a room with pillars everywhere, tons of different types of glasses hanging from racks, and exposed 15" steel ventilation ducts that resonated with bass like you wouldn't believe. And this was a blues club! I saw more than a couple of very highly regarded nationally recognized sound engineers just give up and say "That's as good as I can get it."
As for sub-woofers, I'll never forget my first exposure to 'Sensaround' in the movie 'Earthquake'. The huge chandalier in the centre of the theatre ceiling was shaking fit to come apart, and the Coke boiled out of my cup. When 'Midway' came around, I made sure that I got a lid for my cup.

 

[justinreeves]

Another quick note also, In some system setups a person who does listen to tracks with extremely low frequency responses needs to remember that the human ear only hears down to roughly 20Hz but some insturments with low freq. outputs can have undertones that extend below the audible range. If these frequencies make it to your speaker what ever type it may be, you will not hear the sound but your sub will be working over time (hence why some have sub-sonic filters).

I wonder, I haven't looked at thiele small params for a 10+ years do you think they would apply to something like the Phoenix Gold Cyclone.
Its motor system is not comprised as a standard transducer.
The system is comprised of a oscillating motor which oscillates in a circular pattern, not in and out. the Diaphram consists of a composit membrane placed inside of a plastic cylinder, extremely strange setup, but supposed yields out puts equal to that of 4 12" drivers, even though its displacement is only equal to 1 12" driver roughly/
The main reason I would think is that both sides of the diaphram move air not just one side, similar I guess to a transmission line enclosure, but without the loss in amplitude for a given bandwidth.

 

[Cliff_J]

Actually you can hear below 20Hz, it just takes a lot of VOLUME. Neat pun huh, it takes high SPL levels and it takes some serious woofer xmax to make that happen. LOL I've heard 16Hz before, its weird because it doesn't sound very different than 17Hz and when I played the 15Hz track all that happened was too much woofer xmax and just all the noise from the coil leaving the magnetic gap. Even in a car is difficult to do even with the gain from the small space, the car is generally too leaky to make it happen.

The Cyclone was a licenced servo-drive woofer - it still behaves like a moving diaphram even though its rotating and not moving linearly. So the T/S parameters are there but look very odd.

Its biggest problem was that while it had the displacement of 4 18" woofers (assuming low xmax) its size and sealed box requirements were pretty big for any car, and the seals didn't work too well so it had extra noise. So it only made sound from one side of the twisted plate. There is a website out there where some guy is making his own carbon fiber tube with the same principle (with maybe plans only available, its not licenced) but the link escapes me at the moment.

Having both sides move air means cancellation unless you can delay it with something like a TL enclosure. But Dan Wiggins of Adire Audio made the Parthenon, a motor of a bunch of neo magnets on billet steel poles (looks like Parthenon) and $5k price tag but over 3" one-way xmax and with a 2'x2' diaphram it could generate 121db at 20Hz in a room even with cancellation as a dipole woofer! For some reason its gone from the website, but it was a odd looking beast.

Richard Clark went after the SPL competition scene in the late 90s and built a 5' woofer. Problem was that while it could do over 180db (unweighed) in the concrete room in the lab, the bread truck just shook apart and it was banned before he could get it sealed up and working.
http://www.autosound2000.com/gallery/images/Richard3-sml.jpg

If that isn't crazy enough for you, how about a massive dedicated concrete bass horn below the floor with sixteen 18" woofers for response down to 10Hz at 110dB 1W/1M!
http://www.royaldevice.com/custom.htm

 

[Hurkyl]

A minor correction: 440 Hz, or middle A, is above middle C. Fundamental frequencies on a piano go down to below 32 Hz.

 

[Rogue Physicist]

Well done to all who posted more accurate details and experiences with audio mixing and reenforcement. (Yes there was a typo here and there in my first post. )

Actually, just some cautions I meant to point out in the afterthink:

Frequencies between 0.4 Hz (not a typo) and 10 Hz are both dangerous (Tesla used such frequencies to damage a few buildings as a prank) and the subject of intense research into both directed body damage for military purposes and mind-control for the purpose of inducing or enhancing 'alpha-states' and such. These are not good frequencies to play with without careful precautions and extensive research into the relevant literature.

My current speakers, JBL 4412, are considered pretty good monitors and their low end is rated at 45 Hz.

Note that this is not a 'cutoff' frequency, but the limit of the range claimed to be 'flat' by the manufacturer: that is, the bass decreases in volume and power below 45 Hz. The speakers are probably capable of producing sounds down to 15 Hz, and the only danger to the speakers is the current load on the coils which can overheat and burn out, if too much power is dumped into speaker.