Test tones into reflex cab
 

Just been here...

http://www.nch.com.au/tonegen/index.html

....and downloaded their tone generator prog to have a play. Turns out that
you can set up tones and save them as wave files, so I duly made a test tone
CD with the following frequencies played as 0dB sine waves lasting a few
seconds each...

100, 90, 80, 70, 60, 50, 40, 35, 30, 20, 20

I duly fired it onto the hifi and got the following impressions of volume
for each...

100 - 5
90 - 5+
80 - 5
70 - 4+
60 - 4
50 - 3+
40 - 2
35 - 1
30 - 1
25 - 2
20 - 1-

90Hz came across as a distinct peak amongst the upper frequencies which
otherwise seem to lose volume smoothly from 100 to 50Hz. There was a big
drop in volume going from 50 to 40Hz. 25Hz was a surprise peak at the lower
end - not mega loud, but clear and present compared to the other low tones,
which seemed to require listening for. 20Hz is there but barely audible.

The f0 of the driver is 25Hz, so perhaps that could explain the improved
volume at that frequency. They're old home-brew speakers using the KEF
Concerto drivers and baffle. They also use the Concerto reflex pipe, but
are built into larger cabinets. In other words, compared with the Concerto,
my reflex pipes are relatively small for the cabinet size. Could this be the
cause of the peak around 90Hz, and/or the dip below 50Hz?


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Wally wrote:

... 40, 35, 30, 20, 20

Oops- 30, 25, 20.


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Wally wrote:

... 40, 35, 30, 20, 20

Oops- 30, 25, 20.


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Wally wrote:

Just been here...

http://www.nch.com.au/tonegen/index.html

...and downloaded their tone generator prog to have a play. Turns out that
you can set up tones and save them as wave files, so I duly made a test
tone CD with the following frequencies played as 0dB sine waves lasting a
few seconds each...

100, 90, 80, 70, 60, 50, 40, 35, 30, 20, 20

I duly fired it onto the hifi and got the following impressions of volume
for each...

100 - 5
90 - 5+
80 - 5
70 - 4+
60 - 4
50 - 3+
40 - 2
35 - 1
30 - 1
25 - 2
20 - 1-

90Hz came across as a distinct peak amongst the upper frequencies which
otherwise seem to lose volume smoothly from 100 to 50Hz. There was a big
drop in volume going from 50 to 40Hz. 25Hz was a surprise peak at the
lower end - not mega loud, but clear and present compared to the other low
tones, which seemed to require listening for. 20Hz is there but barely
audible.


Apart from the 90Hz peak this is not a million miles away from the response
of the average human ear so the speaker may in fact be better than it
sounds. The 25Hz surprise may well be a room resonance artifact although
you would need a rather big room to get a large peak. Whereabouts was the
speaker when you did this test?

Ian

Test tones into reflex cab
 

Wally wrote:

Just been here...

http://www.nch.com.au/tonegen/index.html

...and downloaded their tone generator prog to have a play. Turns out that
you can set up tones and save them as wave files, so I duly made a test
tone CD with the following frequencies played as 0dB sine waves lasting a
few seconds each...

100, 90, 80, 70, 60, 50, 40, 35, 30, 20, 20

I duly fired it onto the hifi and got the following impressions of volume
for each...

100 - 5
90 - 5+
80 - 5
70 - 4+
60 - 4
50 - 3+
40 - 2
35 - 1
30 - 1
25 - 2
20 - 1-

90Hz came across as a distinct peak amongst the upper frequencies which
otherwise seem to lose volume smoothly from 100 to 50Hz. There was a big
drop in volume going from 50 to 40Hz. 25Hz was a surprise peak at the
lower end - not mega loud, but clear and present compared to the other low
tones, which seemed to require listening for. 20Hz is there but barely
audible.


Apart from the 90Hz peak this is not a million miles away from the response
of the average human ear so the speaker may in fact be better than it
sounds. The 25Hz surprise may well be a room resonance artifact although
you would need a rather big room to get a large peak. Whereabouts was the
speaker when you did this test?

Ian

Test tones into reflex cab
 

Ian Bell wrote:

Apart from the 90Hz peak this is not a million miles away from the
response of the average human ear so the speaker may in fact be
better than it sounds. The 25Hz surprise may well be a room
resonance artifact although you would need a rather big room to get a
large peak.

I've since had a play with a reflex cab design spreadsheet - I fiddled with
the desired cab resonance to get a reflex pipe about the same size as the
Concerto's - for my cab size, I got a close size match at 24.5Hz.


Whereabouts was the speaker when you did this test?

Played it through both speakers. Their sides are about 6" from the walls,
the backs have about 3' clear space behind. They're about 3'x2'x1 (H,W,D)
and sit on small concrete blocks. Concrete floors and walls.


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Ian Bell wrote:

Apart from the 90Hz peak this is not a million miles away from the
response of the average human ear so the speaker may in fact be
better than it sounds. The 25Hz surprise may well be a room
resonance artifact although you would need a rather big room to get a
large peak.

I've since had a play with a reflex cab design spreadsheet - I fiddled with
the desired cab resonance to get a reflex pipe about the same size as the
Concerto's - for my cab size, I got a close size match at 24.5Hz.


Whereabouts was the speaker when you did this test?

Played it through both speakers. Their sides are about 6" from the walls,
the backs have about 3' clear space behind. They're about 3'x2'x1 (H,W,D)
and sit on small concrete blocks. Concrete floors and walls.


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

On Sun, 21 Dec 2003 19:52:13 -0000, "Wally"
wrote:

Just been here...

http://www.nch.com.au/tonegen/index.html

...and downloaded their tone generator prog to have a play. Turns out that
you can set up tones and save them as wave files, so I duly made a test tone
CD with the following frequencies played as 0dB sine waves lasting a few
seconds each...

100, 90, 80, 70, 60, 50, 40, 35, 30, 20, 20

I duly fired it onto the hifi and got the following impressions of volume
for each...

100 - 5
90 - 5+
80 - 5
70 - 4+
60 - 4
50 - 3+
40 - 2
35 - 1
30 - 1
25 - 2
20 - 1-

90Hz came across as a distinct peak amongst the upper frequencies which
otherwise seem to lose volume smoothly from 100 to 50Hz. There was a big
drop in volume going from 50 to 40Hz. 25Hz was a surprise peak at the lower
end - not mega loud, but clear and present compared to the other low tones,
which seemed to require listening for. 20Hz is there but barely audible.

The f0 of the driver is 25Hz, so perhaps that could explain the improved
volume at that frequency. They're old home-brew speakers using the KEF
Concerto drivers and baffle. They also use the Concerto reflex pipe, but
are built into larger cabinets. In other words, compared with the Concerto,
my reflex pipes are relatively small for the cabinet size. Could this be the
cause of the peak around 90Hz, and/or the dip below 50Hz?

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Test tones into reflex cab
 

On Sun, 21 Dec 2003 19:52:13 -0000, "Wally"
wrote:

Just been here...

http://www.nch.com.au/tonegen/index.html

...and downloaded their tone generator prog to have a play. Turns out that
you can set up tones and save them as wave files, so I duly made a test tone
CD with the following frequencies played as 0dB sine waves lasting a few
seconds each...

100, 90, 80, 70, 60, 50, 40, 35, 30, 20, 20

I duly fired it onto the hifi and got the following impressions of volume
for each...

100 - 5
90 - 5+
80 - 5
70 - 4+
60 - 4
50 - 3+
40 - 2
35 - 1
30 - 1
25 - 2
20 - 1-

90Hz came across as a distinct peak amongst the upper frequencies which
otherwise seem to lose volume smoothly from 100 to 50Hz. There was a big
drop in volume going from 50 to 40Hz. 25Hz was a surprise peak at the lower
end - not mega loud, but clear and present compared to the other low tones,
which seemed to require listening for. 20Hz is there but barely audible.

The f0 of the driver is 25Hz, so perhaps that could explain the improved
volume at that frequency. They're old home-brew speakers using the KEF
Concerto drivers and baffle. They also use the Concerto reflex pipe, but
are built into larger cabinets. In other words, compared with the Concerto,
my reflex pipes are relatively small for the cabinet size. Could this be the
cause of the peak around 90Hz, and/or the dip below 50Hz?

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Test tones into reflex cab
 

Stewart Pinkerton wrote:

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

Yup, this is consistent with my subsequent fiddling with a design tool.
Should I be putting socks in the vents? :-)


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Stewart Pinkerton wrote:

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

Yup, this is consistent with my subsequent fiddling with a design tool.
Should I be putting socks in the vents? :-)


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Wally wrote:

Stewart Pinkerton wrote:

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

Yup, this is consistent with my subsequent fiddling with a design tool.
Should I be putting socks in the vents? :-)



Only if you want to *smell* the bass. Now if you used a pair of Felicity
Kendall's nickers that would be a different thing entirely.

Ian

Test tones into reflex cab
 

Wally wrote:

Stewart Pinkerton wrote:

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

Yup, this is consistent with my subsequent fiddling with a design tool.
Should I be putting socks in the vents? :-)



Only if you want to *smell* the bass. Now if you used a pair of Felicity
Kendall's nickers that would be a different thing entirely.

Ian

Test tones into reflex cab
 

Ian Bell wrote:

Yup, this is consistent with my subsequent fiddling with a design
tool. Should I be putting socks in the vents? :-)

Only if you want to *smell* the bass. Now if you used a pair of
Felicity Kendall's nickers that would be a different thing entirely.

I would need two pairs for stereo...


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Ian Bell wrote:

Yup, this is consistent with my subsequent fiddling with a design
tool. Should I be putting socks in the vents? :-)

Only if you want to *smell* the bass. Now if you used a pair of
Felicity Kendall's nickers that would be a different thing entirely.

I would need two pairs for stereo...


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

On Mon, 22 Dec 2003 14:20:56 -0000, "Wally"
wrote:

Stewart Pinkerton wrote:

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

Yup, this is consistent with my subsequent fiddling with a design tool.
Should I be putting socks in the vents? :-)

I usually do - I find that reflexes generally have 'loose' bass,
although this isn't inherent in the technology.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Test tones into reflex cab
 

On Mon, 22 Dec 2003 14:20:56 -0000, "Wally"
wrote:

Stewart Pinkerton wrote:

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

Yup, this is consistent with my subsequent fiddling with a design tool.
Should I be putting socks in the vents? :-)

I usually do - I find that reflexes generally have 'loose' bass,
although this isn't inherent in the technology.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Test tones into reflex cab
 

Wally wrote:

Ian Bell wrote:

Yup, this is consistent with my subsequent fiddling with a design
tool. Should I be putting socks in the vents? :-)

Only if you want to *smell* the bass. Now if you used a pair of
Felicity Kendall's nickers that would be a different thing entirely.

I would need two pairs for stereo...


pervert ;-)

Ian

Test tones into reflex cab
 

Wally wrote:

Ian Bell wrote:

Yup, this is consistent with my subsequent fiddling with a design
tool. Should I be putting socks in the vents? :-)

Only if you want to *smell* the bass. Now if you used a pair of
Felicity Kendall's nickers that would be a different thing entirely.

I would need two pairs for stereo...


pervert ;-)

Ian

Test tones into reflex cab
 

Ian Bell wrote:

Only if you want to *smell* the bass. Now if you used a pair of
Felicity Kendall's nickers that would be a different thing entirely.

I would need two pairs for stereo...

pervert ;-)

I'll take the one pair, then - could you send them in a plain wrapper? ;-)


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Ian Bell wrote:

Only if you want to *smell* the bass. Now if you used a pair of
Felicity Kendall's nickers that would be a different thing entirely.

I would need two pairs for stereo...

pervert ;-)

I'll take the one pair, then - could you send them in a plain wrapper? ;-)


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Stewart Pinkerton wrote:

Yup, this is consistent with my subsequent fiddling with a design
tool. Should I be putting socks in the vents? :-)

I usually do - I find that reflexes generally have 'loose' bass,
although this isn't inherent in the technology.

Are there any other materials worth playing with? Foam rubber? Something
solid?


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Stewart Pinkerton wrote:

Yup, this is consistent with my subsequent fiddling with a design
tool. Should I be putting socks in the vents? :-)

I usually do - I find that reflexes generally have 'loose' bass,
although this isn't inherent in the technology.

Are there any other materials worth playing with? Foam rubber? Something
solid?


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

On Tue, 23 Dec 2003 15:06:45 -0000, "Wally"
wrote:

Stewart Pinkerton wrote:

Yup, this is consistent with my subsequent fiddling with a design
tool. Should I be putting socks in the vents? :-)

I usually do - I find that reflexes generally have 'loose' bass,
although this isn't inherent in the technology.

Are there any other materials worth playing with? Foam rubber? Something
solid?

Yup, a solid plug is very effective in achieving that sealed box sound
from a reflex speaker! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Test tones into reflex cab
 

On Tue, 23 Dec 2003 15:06:45 -0000, "Wally"
wrote:

Stewart Pinkerton wrote:

Yup, this is consistent with my subsequent fiddling with a design
tool. Should I be putting socks in the vents? :-)

I usually do - I find that reflexes generally have 'loose' bass,
although this isn't inherent in the technology.

Are there any other materials worth playing with? Foam rubber? Something
solid?

Yup, a solid plug is very effective in achieving that sealed box sound
from a reflex speaker! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Test tones into reflex cab
 

Stewart Pinkerton wrote:

Are there any other materials worth playing with? Foam rubber?
Something solid?

Yup, a solid plug is very effective in achieving that sealed box sound
from a reflex speaker! :-)

Unfortunately, the original builder of the cabs put a bunch of narrow slots
in the back panels (to try and increase the apparent volume?). I tried a
sock last night, but can't say I noticed a great deal of difference. I'll
have another play...


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Stewart Pinkerton wrote:

Are there any other materials worth playing with? Foam rubber?
Something solid?

Yup, a solid plug is very effective in achieving that sealed box sound
from a reflex speaker! :-)

Unfortunately, the original builder of the cabs put a bunch of narrow slots
in the back panels (to try and increase the apparent volume?). I tried a
sock last night, but can't say I noticed a great deal of difference. I'll
have another play...


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

On Wed, 24 Dec 2003 14:15:23 -0000, "Wally"
wrote:

Stewart Pinkerton wrote:

Are there any other materials worth playing with? Foam rubber?
Something solid?

Yup, a solid plug is very effective in achieving that sealed box sound
from a reflex speaker! :-)

Unfortunately, the original builder of the cabs put a bunch of narrow slots
in the back panels (to try and increase the apparent volume?). I tried a
sock last night, but can't say I noticed a great deal of difference. I'll
have another play...

Aaaah, that's an old Gilbert Briggs trick from Wharfedale in the
'fifties. It's known as a 'distributed port', and is a variation on
the reflex theme. The idea was that the port area was distributed over
a large part of the cabinet, and made the port tuning less sharp.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Test tones into reflex cab
 

On Wed, 24 Dec 2003 14:15:23 -0000, "Wally"
wrote:

Stewart Pinkerton wrote:

Are there any other materials worth playing with? Foam rubber?
Something solid?

Yup, a solid plug is very effective in achieving that sealed box sound
from a reflex speaker! :-)

Unfortunately, the original builder of the cabs put a bunch of narrow slots
in the back panels (to try and increase the apparent volume?). I tried a
sock last night, but can't say I noticed a great deal of difference. I'll
have another play...

Aaaah, that's an old Gilbert Briggs trick from Wharfedale in the
'fifties. It's known as a 'distributed port', and is a variation on
the reflex theme. The idea was that the port area was distributed over
a large part of the cabinet, and made the port tuning less sharp.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Test tones into reflex cab
 

Stewart Pinkerton wrote:

Unfortunately, the original builder of the cabs put a bunch of
narrow slots in the back panels (to try and increase the apparent
volume?). I tried a sock last night, but can't say I noticed a great
deal of difference. I'll have another play...

Aaaah, that's an old Gilbert Briggs trick from Wharfedale in the
'fifties. It's known as a 'distributed port', and is a variation on
the reflex theme. The idea was that the port area was distributed over
a large part of the cabinet, and made the port tuning less sharp.

Oh right, it actually has a more technical name than 'a bunch of slots'. I
think I read years ago that it has the effect of making the apparent volume
of the cab a little bigger.

Been playing with more speaker design software, modelling my existing cab
and driver. Don't know if I have all the parameters in correctly (but it
knows about the B139). It shows two distinct peaks in the impedance at 16Hz
and 40Hz (about 50 ohms), with the dip between them centred on 26Hz (15
ohms). Although the software's numbers are hypothetical, these seem pretty
consistent with what I got with the test tones.

An 80L isobaric cab (sealed box) produces a single peak with a shallower
profile at about 34Hz (15 ohms compared to 4 ohms at 100Hz). Unfortunately,
to get the software to put the impedance peak at the driver's resonance (is
that the right thing to do?), I need something like a 300L cab. Even so, the
curve for the 80L looks better than that for the 130L reflex. In both
designs, lots of damping inside the cabinet made the impedance peaks much
smoother.


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

Stewart Pinkerton wrote:

Unfortunately, the original builder of the cabs put a bunch of
narrow slots in the back panels (to try and increase the apparent
volume?). I tried a sock last night, but can't say I noticed a great
deal of difference. I'll have another play...

Aaaah, that's an old Gilbert Briggs trick from Wharfedale in the
'fifties. It's known as a 'distributed port', and is a variation on
the reflex theme. The idea was that the port area was distributed over
a large part of the cabinet, and made the port tuning less sharp.

Oh right, it actually has a more technical name than 'a bunch of slots'. I
think I read years ago that it has the effect of making the apparent volume
of the cab a little bigger.

Been playing with more speaker design software, modelling my existing cab
and driver. Don't know if I have all the parameters in correctly (but it
knows about the B139). It shows two distinct peaks in the impedance at 16Hz
and 40Hz (about 50 ohms), with the dip between them centred on 26Hz (15
ohms). Although the software's numbers are hypothetical, these seem pretty
consistent with what I got with the test tones.

An 80L isobaric cab (sealed box) produces a single peak with a shallower
profile at about 34Hz (15 ohms compared to 4 ohms at 100Hz). Unfortunately,
to get the software to put the impedance peak at the driver's resonance (is
that the right thing to do?), I need something like a 300L cab. Even so, the
curve for the 80L looks better than that for the 130L reflex. In both
designs, lots of damping inside the cabinet made the impedance peaks much
smoother.


--
Wally
www.art-gallery.myby.co.uk
Latest addition: Early Works gallery

Test tones into reflex cab
 

"Stewart Pinkerton" wrote in message


Aaaah, that's an old Gilbert Briggs trick from Wharfedale in the
'fifties. It's known as a 'distributed port', and is a variation on
the reflex theme. The idea was that the port area was distributed over
a large part of the cabinet, and made the port tuning less sharp.

This was probably a good idea in days before Theil-Small, when people
really didn't have a lot of technical guidance about how to properly tune
ports.

Test tones into reflex cab
 

"Stewart Pinkerton" wrote in message


Aaaah, that's an old Gilbert Briggs trick from Wharfedale in the
'fifties. It's known as a 'distributed port', and is a variation on
the reflex theme. The idea was that the port area was distributed over
a large part of the cabinet, and made the port tuning less sharp.

This was probably a good idea in days before Theil-Small, when people
really didn't have a lot of technical guidance about how to properly tune
ports.

Test tones into reflex cab
 

In both designs, lots of damping inside the cabinet made the impedance
peaks much
smoother.


--
Wally

My preference was always for long haired lambs wool as a damping material -
vary the amount by ear with the speakers in the room until it sounds right -
then measure it! I always found it more "forgiving" than the acoustic foams
etc.

Never tried Felicity Kendall's knickers though.........

Test tones into reflex cab
 

In both designs, lots of damping inside the cabinet made the impedance
peaks much
smoother.


--
Wally

My preference was always for long haired lambs wool as a damping material -
vary the amount by ear with the speakers in the room until it sounds right -
then measure it! I always found it more "forgiving" than the acoustic foams
etc.

Never tried Felicity Kendall's knickers though.........