Subwoofers are just marketing hype?

Thu, 25 Jun 1998 15:30:02

From: Erik Olson
Subject: Re: How important is bass below 30Hz?
Newsgroups: alt.home-theater.misc

tom brennan wrote:
> sstrick---I think that for movie listening subwoofers are a big
> marketing hype. You now have full range, fairly efficient speakers with
> 15' woofers, you have better bass performance right now, in terms of low
> distortion and output, than most of the subs on the market.

Typically, efficient full range speakers with 15" drivers have small Xmax's.
The key to loud low bass is displacement.  Vd = pi * r^2 * Xmax.
That's the physics of the situation, vented/passive radiator alignments
do give you some gain, but it is still a matter of moving air.

Also, another advantage of subwoofers vs. full range speakers is doppler
distortion.  Example: a 12" full range driver cranking out a 100dB 30Hz
tone will have an excursion of about 8.5mm, now if it was also cranking out
an 90dB 500Hz tone which equates to an excursion of .010mm which is typical
duty for a full range drive.  The 30Hz tone will have a cone velocity of
about 1m/s.  This works out to about a 1.5Hz doppler shift.  Imagine
the 500Hz tone sweeping from 408.5Hz to 501.5Hz every 1/60 of a second!
Now that is something that is audible.

Check out my piston excursion calculator and other stuff on my quest
for more bass page:

> Then there's
> that fact that motion picture theater subwoofers don't really go much
> below 40 hz (check out the JBL, Altec-Lansing, EV and Klipsch 
> professional websites to confirm this) and the people that mix
> soundtracks are monitoring over motion picture theater speakers, the
> result is that there just isn't much super-low bass on movie
> soundtracks. 

Now this is true, THX movie theatre subs are typically vented units with
F3's in the 40Hz - 45Hz range.  So they don't mix in much really low
bass.  But there has been some activity in Hollywood dubbing theatre's
in replacing the THX vented subs with sealed BagEnd units that are
flat to some ridiculously low Hz at low volume levels.


> High output with low distortion is what is needed and 
> you're getting that now. I use Altec-Lansing Voice of The Theater
> loudspeakers in my HT, the basshorns cut off around 50hz but the impact
> is far superior to any "high fidelty" type home subwoofers.

Well loud bass is important to HT, no question about it, but typically
I listen to movies at the -20dB to -15dB level.  I have more loudness
volume than I need, what it important to me is a flat low end.  Personally,
for me, lowness is more important than loudness.


> There are soundtracks and music that "plumb the depths" but it's rare.

True it is not common, but I wouldn't call it rare.
Check out my list of favorite bass clips (movies and techno), I
used a spectrum analyzer to measure some low bass fundementals:

[deleted]


> Remember too that if you do get a sub you'll need at least 2 18" drivers
> to keep up with the 15" woofers of your CVs, otherwise why bother.

Check out the 5.1 mix of The Professional DVD.  It has some seriously
loud 26Hz thumps.

I challenge your 15" Altec full range drivers with the F3 of 50Hz
against my measly two sealed 12" subs to play the 26Hz thump on the
Professional DVD.  It'll be a no contest, it won't even be funny, so
then why even bother?

erik olson

--------------------------------------------------------------------------

From: Erik Olson
Subject: Re: How important is bass below 30Hz?
Newsgroups: alt.home-theater.misc

Erik Olson wrote:
> duty for a full range drive.  The 30Hz tone will have a cone velocity of
> about 1m/s.  This works out to about a 1.5Hz doppler shift.  Imagine
> the 500Hz tone sweeping from 408.5Hz to 501.5Hz every 1/60 of a second!
> Now that is something that is audible.

Opppps, that should be every 1/30th of a second.
 
Also I should note that the same percentage of pitch shift also
occurs at 250Hz or even 60Hz, but my point is that the ear is more
sensitive to pitch changes in the vocal regions than it is in the
sub 80Hz region.  
 
Also this same sort of thing goes on in the midrange and tweeter
drivers too but the frequency of modulation will be much higher than
30Hz, so it shouldn't be as noticable.
 
Also most movie soundtracks and modern music are bass heavy in that
the bass region is typically +15dB above the higher frequencies.
This means the cone velocities for the higher freqs won't be anywhere 
near what they are for the subwoofer freqs.

erik olson


Thu, 25 Jun 1998 15:30:02

From: Erik Olson
Subject: Re: How important is bass below 30Hz?
Newsgroups: alt.home-theater.misc

tom brennan wrote:
> sstrick---I think that for movie listening subwoofers are a big
> marketing hype. You now have full range, fairly efficient speakers with
> 15' woofers, you have better bass performance right now, in terms of low
> distortion and output, than most of the subs on the market.

Typically, efficient full range speakers with 15" drivers have small Xmax's.
The key to loud low bass is displacement.  Vd = pi * r^2 * Xmax.
That's the physics of the situation, vented/passive radiator alignments
do give you some gain, but it is still a matter of moving air.

Also, another advantage of subwoofers vs. full range speakers is doppler
distortion.  Example: a 12" full range driver cranking out a 100dB 30Hz
tone will have an excursion of about 8.5mm, now if it was also cranking out
an 90dB 500Hz tone which equates to an excursion of .010mm which is typical
duty for a full range drive.  The 30Hz tone will have a cone velocity of
about 1m/s.  This works out to about a 1.5Hz doppler shift.  Imagine
the 500Hz tone sweeping from 408.5Hz to 501.5Hz every 1/60 of a second!
Now that is something that is audible.

Check out my piston excursion calculator and other stuff on my quest
for more bass page:

> Then there's
> that fact that motion picture theater subwoofers don't really go much
> below 40 hz (check out the JBL, Altec-Lansing, EV and Klipsch 
> professional websites to confirm this) and the people that mix
> soundtracks are monitoring over motion picture theater speakers, the
> result is that there just isn't much super-low bass on movie
> soundtracks. 

Now this is true, THX movie theatre subs are typically vented units with
F3's in the 40Hz - 45Hz range.  So they don't mix in much really low
bass.  But there has been some activity in Hollywood dubbing theatre's
in replacing the THX vented subs with sealed BagEnd units that are
flat to some ridiculously low Hz at low volume levels.


> High output with low distortion is what is needed and 
> you're getting that now. I use Altec-Lansing Voice of The Theater
> loudspeakers in my HT, the basshorns cut off around 50hz but the impact
> is far superior to any "high fidelty" type home subwoofers.

Well loud bass is important to HT, no question about it, but typically
I listen to movies at the -20dB to -15dB level.  I have more loudness
volume than I need, what it important to me is a flat low end.  Personally,
for me, lowness is more important than loudness.


> There are soundtracks and music that "plumb the depths" but it's rare.

True it is not common, but I wouldn't call it rare.
Check out my list of favorite bass clips (movies and techno), I
used a spectrum analyzer to measure some low bass fundementals:

[deleted]


> Remember too that if you do get a sub you'll need at least 2 18" drivers
> to keep up with the 15" woofers of your CVs, otherwise why bother.

Check out the 5.1 mix of The Professional DVD.  It has some seriously
loud 26Hz thumps.

I challenge your 15" Altec full range drivers with the F3 of 50Hz
against my measly two sealed 12" subs to play the 26Hz thump on the
Professional DVD.  It'll be a no contest, it won't even be funny, so
then why even bother?

erik olson

--------------------------------------------------------------------------

From: Erik Olson
Subject: Re: How important is bass below 30Hz?
Newsgroups: alt.home-theater.misc

Erik Olson wrote:
> duty for a full range drive.  The 30Hz tone will have a cone velocity of
> about 1m/s.  This works out to about a 1.5Hz doppler shift.  Imagine
> the 500Hz tone sweeping from 408.5Hz to 501.5Hz every 1/60 of a second!
> Now that is something that is audible.

Opppps, that should be every 1/30th of a second.
 
Also I should note that the same percentage of pitch shift also
occurs at 250Hz or even 60Hz, but my point is that the ear is more
sensitive to pitch changes in the vocal regions than it is in the
sub 80Hz region.  
 
Also this same sort of thing goes on in the midrange and tweeter
drivers too but the frequency of modulation will be much higher than
30Hz, so it shouldn't be as noticable.
 
Also most movie soundtracks and modern music are bass heavy in that
the bass region is typically +15dB above the higher frequencies.
This means the cone velocities for the higher freqs won't be anywhere 
near what they are for the subwoofer freqs.

erik olson