Room nodes

Archived from groups: rec.audio.high-end (More info?)

I have been "fighting"an aggravating resonance in my stereo system for a
long time. I tried a sweep with a signal generator today and it appears
to be around 180 hz. This makes sense because my room dimensions
suggest a number of nodes at that frequency (22' X 30' with an 18'
cathedral ceiling). I tried suppressing it by setting the 120 hz slider
on my equalizer at -12. This helped a lot but I would like to suppress
the exact frequency. I know this would require either a parametric or
1/3 octave equalizer. Any suggestions?


---MIKE---

Archived from groups: rec.audio.high-end (More info?)

Were you the one using two subs?


"---MIKE---" <twinmountain@webtv.net> wrote in message
news:cinr520u2d@news2.newsguy.com...
> I have been "fighting"an aggravating resonance in my stereo system for a
> long time. I tried a sweep with a signal generator today and it appears
> to be around 180 hz. This makes sense because my room dimensions
> suggest a number of nodes at that frequency (22' X 30' with an 18'
> cathedral ceiling). I tried suppressing it by setting the 120 hz slider
> on my equalizer at -12. This helped a lot but I would like to suppress
> the exact frequency. I know this would require either a parametric or
> 1/3 octave equalizer. Any suggestions?
>
>
> ---MIKE---

Archived from groups: rec.audio.high-end (More info?)

"---MIKE---" <twinmountain@webtv.net> wrote in message
news:civp0u02ln1@news1.newsguy.com...
> No - FOUR subs! Two in corners and two along walls. The resonance is a
> room condition (I can hear it with the subs off).


How small are your subs? My one Sub capable of being heard 200 feet (my
opposite house )- if i were to push it to the max. Right now I am only using
a small fraction of its max.

Anyhow here's a link http://www.mhsoft.nl/Helmholtzabsorber.asp hopefully,
that will help you.

Cheers.

Archived from groups: rec.audio.high-end (More info?)

"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
news:cj1r3p02pu7@news3.newsguy.com...
>
> Hmmmm. Care to be more specific? What is your sub?
>
Why? you think it can't be heard that far? Even my car 10 inch Rockford
Fosgate Punch can be heard quite a distant if I push it to the max. But not
up to 2 miles as this gentleman
http://www.cardomain.com/reviews/l [...] ROCRFD2210 is claiming
but at least 120 feet.

My Sub is Boston Acoustics not a true High End but pretty much good for the
job.

cheers.

Archived from groups: rec.audio.high-end (More info?)

"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
news:cj40rc03cr@news1.newsguy.com...
> On 25 Sep 2004 02:10:05 GMT, "Chelvam" <chelvam@myjaring.net> wrote:
>
> >"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
> >news:cj1r3p02pu7@news3.newsguy.com...
> >>
> >> Hmmmm. Care to be more specific? What is your sub?
> >>
> >Why? you think it can't be heard that far?
>
> Not at 20Hz, no, but probably at the 60-80Hz peak common to many
> cheaper 'Home Cinema' biased units.
>
rest snipped for brevity....

My sub is crossed around 55 to 60 Hz. In my room it is certainly heavy and
full but felt more than heard. When I go to my bath it is definely louder
(more heard not so sure of felt) unlike in my room.

And in the case of my 200 feet neigbour who uses a mass market Home Theater
system the bass is not full or heavy but he was driving me nuts with his
"boom..boom ..boom" coming to my room. My sub on the other hand never heard
that far till I push it up the volume from about 10 oclock to 5 oclock and
crossed at 100khz.

So the question is:-

I always thought the lower the frequencies the further it is heard. Am I
wrong?

regards.

Archived from groups: rec.audio.high-end (More info?)

Hi Stewart,

> It's my 'intuitive feel' that in the 20-200Hz area
> which we may
> reasonably regard as 'bass', the propagation losses
> which accrue with
> increasing frequency are more than offset by the
> massive increases in
> input power which are required to generate the same
> 'muzzle velocity'
> SPL at the speaker cone as we dig down into subwoofer
> territory. But,
> I could be wrong. Anyone have some real data on this
> aspect of 'down
> range' bass SPL?

Did you happen to see the 3-part objective (i.e., based
on measurements) review of subwoofers in the last three
issues of Stereophile Ultimate AV magazine? It doesn't
answer your question, but does indicate that most
subwoofers (but I'm sure not yours ;^)) suffer from
compression in the lower frequencies as the power
increases, which will cause a relative increase in the
SPL of the higher frequencies as the power goes up.

Regards,
Tip

Archived from groups: rec.audio.high-end (More info?)

On 26 Sep 2004 22:18:09 GMT, "Tip" <Tip_Johnson@comcast.net> wrote:

>Did you happen to see the 3-part objective (i.e., based
>on measurements) review of subwoofers in the last three
>issues of Stereophile Ultimate AV magazine? It doesn't
>answer your question, but does indicate that most
>subwoofers (but I'm sure not yours ;^)) suffer from
>compression in the lower frequencies as the power
>increases, which will cause a relative increase in the
>SPL of the higher frequencies as the power goes up.

Knowing the basics of the drivers helps. My subwoofer design uses a
pair of Adire Tempests in an 'infinite baffle' situation using the
loft space above my listening room, and driven by a 250 watt 'plate'
amplifier. They are not in any way power compressed, but they are Xmax
limited below about 22Hz, although since this is at an in-room level
of about 115dB, I don't think it's a real problem.......... :-)

OTOH, if you run the numbers for virtually *any* driver in the sort of
2-3 cu ft box which is domestically acceptable, you certainly do run
into severe power problems when you get below 40Hz or so!
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Archived from groups: rec.audio.high-end (More info?)

"Chelvam" chelvam@myjaring.net wrote:

>"Nousaine" <nousaine@aol.com> wrote in message
>news:cj7nr5023hl@news2.newsguy.com...
>> Stewart Pinkerton patent3@dircon.co.uk wrote:
>snip..snip..
>
>
>>
>> What do you 'hear' when a boom-car travels down the street? It's not the
>20 Hz
>> information but the 40-80 Hz pounding plus the license plate and panel
>buzzes
>> even though a 10-inch woofer in a sealed box with a moderately large
>amplifier
>> will deliver 120 dB at 10-62 Hz in a car with less than 10% distortion..
>>
>> Of course, the reason that such a woofer can do this in a car even though
>it
>> takes 8 15-inch long stroke woofers and 5000-watts in my Home Theater is
>that
>> the auto cabin is a small reasonably well-sealed space with the according
>low
>> frequency reinforcement (my Corvette has 30 dB of 'cabin gain' at 10 Hz.)
>
>10hz? Do you mind telling the Subwoofer's name. The best I think that I
>heard/felt was 40 or 50hz. I have not teally tested but I doubt I could go
>below 20hz.

The system was described in the June '99 issue if Sound & Vision magazine. It
uses 8 TC Sounds 15-inch drives with a DUMAX tested 23.5mm Xmax. The system
measred at an optimal 2-meter listening position is capable of producing in
excess of 120 dB from 12 - 62 hz with less than 10% distortion at a 2-meter
listening position.

Further the system at full output was measured with a Crown VZ5000 and has been
implemented with an 18 dB 1 octave eq function centered at 12 Hz.

With the Crown full output is unattainable at some frequencies because the
double vinyl windows twist in the frames.

Archived from groups: rec.audio.high-end (More info?)

"Chelvam" <chelvam@myjaring.net> wrote in message news:<cj6l19024nd@news3.newsguy.com>...
> "Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
> news:cj40rc03cr@news1.newsguy.com...
> > On 25 Sep 2004 02:10:05 GMT, "Chelvam" <chelvam@myjaring.net> wrote:
> >
> > >"Stewart Pinkerton" <patent3@dircon.co.uk> wrote in message
> > >news:cj1r3p02pu7@news3.newsguy.com...
> > >>
> > >> Hmmmm. Care to be more specific? What is your sub?
> > >>
> > >Why? you think it can't be heard that far?
> >
> > Not at 20Hz, no, but probably at the 60-80Hz peak common to many
> > cheaper 'Home Cinema' biased units.
> >
> rest snipped for brevity....
>
> My sub is crossed around 55 to 60 Hz. In my room it is certainly heavy and
> full but felt more than heard. When I go to my bath it is definely louder
> (more heard not so sure of felt) unlike in my room.
>
> And in the case of my 200 feet neigbour who uses a mass market Home Theater
> system the bass is not full or heavy but he was driving me nuts with his
> "boom..boom ..boom" coming to my room. My sub on the other hand never heard
> that far till I push it up the volume from about 10 oclock to 5 oclock and
> crossed at 100khz.
>
> So the question is:-
>
> I always thought the lower the frequencies the further it is heard. Am I
> wrong?
>
> regards.

This is true and is basic acoustic science. There is a tiny bit of
loss in the adiabatic movement of air as the sound wave propagates.
This is +/- proportional to the wavelength. You could loosely
summarize that for every cycle there is a certain amount of loss and
therefore because lower frequencies have longer wavelengths that they
will travel more distance per cycle and thus per unit energy loss. Off
hand I believe the attenuation curve is quadratic against a
logarithmic frequency scale. (if I'm wrong someone will reply)

Your brain uses this principe, along with temporal left vs right
differences and reletive SPL differences, to tell you how far
something is away from you. In particular if something is pretty far
away then stereo preception will do you no good. You can hear this
phenominon all the time in music recordings.

Of course wind can skew this a bit. Ever wondered why a busy road in
the area only makes lots of noise sometimes?

Archived from groups: rec.audio.high-end (More info?)

Wessel Dirksen wrote:
>>
>> My sub is crossed around 55 to 60 Hz. In my room it is certainly
>> heavy and full but felt more than heard. When I go to my bath it is
>> definely louder (more heard not so sure of felt) unlike in my room.
>>
>> And in the case of my 200 feet neigbour who uses a mass market Home
>> Theater system the bass is not full or heavy but he was driving me
>> nuts with his "boom..boom ..boom" coming to my room. My sub on the
>> other hand never heard that far till I push it up the volume from
>> about 10 oclock to 5 oclock and crossed at 100khz.
>>
>> So the question is:-
>>
>> I always thought the lower the frequencies the further it is heard.
>> Am I wrong?
>>
>> regards.
>
> This is true and is basic acoustic science. There is a tiny bit of
> loss in the adiabatic movement of air as the sound wave propagates.
> This is +/- proportional to the wavelength. You could loosely
> summarize that for every cycle there is a certain amount of loss and
> therefore because lower frequencies have longer wavelengths that they
> will travel more distance per cycle and thus per unit energy loss. Off
> hand I believe the attenuation curve is quadratic against a
> logarithmic frequency scale. (if I'm wrong someone will reply)
>
> Your brain uses this principe, along with temporal left vs right
> differences and reletive SPL differences, to tell you how far
> something is away from you. In particular if something is pretty far
> away then stereo preception will do you no good. You can hear this
> phenominon all the time in music recordings.
>
> Of course wind can skew this a bit. Ever wondered why a busy road in
> the area only makes lots of noise sometimes?

Well, the most important factor is the decreasing sensitivity of our ears
for lower levels of deep bass, which is a necessity to suppress the sound of
our stepping feet on the ground.
At 20Hz the 0db-loudness is at 70dB SPL, below this level we cannot hear
anything any more, at 50Hz this threshold has gone down to 40dB SPL. If the
SPL is above this value its perceived loudness rises much faster than higher
frequencies. Look up "Fletcher-Manson" diagramm.
The SPL is 6dB down by doubling the distance, only high frequencies get
absorbed by the air, all bass frequencies are transported without loss, just
the bigger surface will cause the decrease in level. Deep frequencies
propagate equally into all directions.
--
ciao Ban
Bordighera, Italy

Archived from groups: rec.audio.high-end (More info?)

wdirksen@p-we.com (Wessel Dirksen) wrote in message news:<cjsnh507ev@news1.newsguy.com>...
> Think about being a few hundred years from an outdoor rock
> concert where the levels are still ....

Hmmm, "a few hundred years from an outdoor rock concert" would
put us right about in the middle of the Baroque era. Yes, yes,
that sounds MUCH better! :-)