Bose 901

[gregz]

Scott Dorsey > wrote:
Yes that's 3 db down at 30 Hz from 1khz. My old boxes resonated at 100 Hz.
That was the peak.

Sure, if you do a swept sine test without a filter. Put 30 Hz into the box
and you get output, but none of that output is actually at 30 Hz.

>>

Not true.
If you put 30 Hz into a closed box speaker, sure you'll get some 30 Hz out.
I used to put 16 Hz in and rattle the window, but almost nothing heard
except the spiders.
You will also find a delay of the 30 Hz since it's below resonance, the
spider will slow it down and cause a phase shift.

Thats all I'm going to rehash about the 901, plenty of old stuff in the
archives.

Greg

[Trevor]

"gregz" > wrote in message
...
> Scott Dorsey > wrote:
> Yes that's 3 db down at 30 Hz from 1khz. My old boxes resonated at 100 Hz.
> That was the peak.
>
> Sure, if you do a swept sine test without a filter. Put 30 Hz into the box
> and you get output, but none of that output is actually at 30 Hz.
>
>>>
>
> Not true.
> If you put 30 Hz into a closed box speaker, sure you'll get some 30 Hz
> out.
> I used to put 16 Hz in and rattle the window,

Some "closed box speakers" perhaps, but not one with 4" drivers.

Trevor.

[MrTallyman]

On Sun, 29 Jul 2012 14:28:07 +1000, "Trevor" > wrote:

>
>"gregz" > wrote in message
...
>> Scott Dorsey > wrote:
>> Yes that's 3 db down at 30 Hz from 1khz. My old boxes resonated at 100 Hz.
>> That was the peak.
>>
>> Sure, if you do a swept sine test without a filter. Put 30 Hz into the box
>> and you get output, but none of that output is actually at 30 Hz.
>>
>>>>
>>
>> Not true.
>> If you put 30 Hz into a closed box speaker, sure you'll get some 30 Hz
>> out.
>> I used to put 16 Hz in and rattle the window,
>
>Some "closed box speakers" perhaps, but not one with 4" drivers.
>
>Trevor.
>
>
>
I still have a nice pair of circa 1972 Scott acoustic suspension
speakers. The 8 Inch driver 3 way model. Finding a sealed driver (cone,
button, and surround)is not easy. But they are still fine and still make
great surround speakers.

[gregz]

MrTallyman > wrote:
> On Sun, 29 Jul 2012 14:28:07 +1000, "Trevor" > wrote:
>
>>
>> "gregz" > wrote in message
>> ...
>>> Scott Dorsey > wrote:
>>> Yes that's 3 db down at 30 Hz from 1khz. My old boxes resonated at 100 Hz.
>>> That was the peak.
>>>
>>> Sure, if you do a swept sine test without a filter. Put 30 Hz into the box
>>> and you get output, but none of that output is actually at 30 Hz.
>>>
>>>>>
>>>
>>> Not true.
>>> If you put 30 Hz into a closed box speaker, sure you'll get some 30 Hz
>>> out.
>>> I used to put 16 Hz in and rattle the window,
>>
>> Some "closed box speakers" perhaps, but not one with 4" drivers.
>>
>> Trevor.
>>
>>
>>
> I still have a nice pair of circa 1972 Scott acoustic suspension
> speakers. The 8 Inch driver 3 way model. Finding a sealed driver (cone,
> button, and surround)is not easy. But they are still fine and still make
> great surround speakers.

I don't completely understand that. My first set of pre built speakers I
bought in1969 from allied radio, Utah components, acoustic suspension. Then
I had AR4x's. I still have small set of advents in the garage, and I recall
rebuilding a set of AR2ax's in the 80's. In the army in 1970' I really
wanted a set of AR3's but out of range for me. I settled for upside down
trash can's in the barracks, with radio shack coaxial's

Greg

[Trevor]

"MrTallyman" > wrote in message
...
> On Sun, 29 Jul 2012 14:28:07 +1000, "Trevor" > wrote:
>>"gregz" > wrote in message
...
>>> I used to put 16 Hz in and rattle the window,
>>
>>Some "closed box speakers" perhaps, but not one with 4" drivers.
>>
> I still have a nice pair of circa 1972 Scott acoustic suspension
> speakers. The 8 Inch driver 3 way model. Finding a sealed driver (cone,
> button, and surround)is not easy. But they are still fine and still make
> great surround speakers.

What has that got to do with the Bose 901's though?

Trevor.

[Dick Pierce[_2_]]

gregz wrote:
> You will also find a delay of the 30 Hz since it's below resonance, the
> spider will slow it down and cause a phase shift.

Uh, no. The spider does not "slow it down and cause a
phase shift." Whatever phase shift exists is not because
the "spider slows it down."

> Thats all I'm going to rehash about the 901,

That's good to know.

> plenty of old stuff in the archives.

And just like the Internet in general, some of it right,
some of it wrong, and much of it irrelevant.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

[Dick Pierce[_2_]]

MrTallyman wrote:
> I still have a nice pair of circa 1972 Scott acoustic suspension
> speakers. The 8 Inch driver 3 way model. Finding a sealed driver (cone,
> button, and surround)is not easy. But they are still fine and still make
> great surround speakers.

I remember Scott's ad compaign at the time: the basic theme was
"Where do Scott speakers sound best." I also remember Jim
Wilkinson taping the ad to the bottom of the lid of the
toilet in the bathroom at the hi fi store where he worked.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

[gregz]

Dick Pierce > wrote:
> gregz wrote:
>> You will also find a delay of the 30 Hz since it's below resonance, the
>> spider will slow it down and cause a phase shift.
>
> Uh, no. The spider does not "slow it down and cause a
> phase shift." Whatever phase shift exists is not because
> the "spider slows it down."
>

I guessed. When I was trying to figure out transmission line speakers, I
experimented with a 6.5 inch driver and a pipe. I was trying to figure out
delays along the pipe with stuffing. I first used the generator as sync and
measured various lengths along pipe. What was predicted was lower
frequencies having longer delays through stuffing. Until I placed a second
mic right behind the driver did I discover the delay was caused by the
driver. This was below resonate frequency of driver. I never found the
predicted longer delay at lower frequencies according to at least one
paper.

Greg

>> Thats all I'm going to rehash about the 901,
> That's good to know.
>
>> plenty of old stuff in the archives.
>
> And just like the Internet in general, some of it right,
> some of it wrong, and much of it irrelevant.

[gregz]

Dick Pierce > wrote:
> MrTallyman wrote:
>> I still have a nice pair of circa 1972 Scott acoustic suspension
>> speakers. The 8 Inch driver 3 way model. Finding a sealed driver (cone,
>> button, and surround)is not easy. But they are still fine and still make
>> great surround speakers.
> I remember Scott's ad compaign at the time: the basic theme was
> "Where do Scott speakers sound best." I also remember Jim
> Wilkinson taping the ad to the bottom of the lid of the
> toilet in the bathroom at the hi fi store where he worked.


I know nothing about Scott speakers, but I read about them from literature
in the 60's. What I do know, they had a small anechoic chamber. I was
staying in a motel in Maynard. One night I walked next door to Scott
through over a foot of snow. I looked in the window. I relived the visions
of the advertising flyer. Anechoic chamber right near the front window !
Just reliving a fond old memory of mine.

Greg

[Dick Pierce[_2_]]

gregz wrote:
> Dick Pierce > wrote:
>
>>gregz wrote:
>>
>>>You will also find a delay of the 30 Hz since it's below resonance, the
>>>spider will slow it down and cause a phase shift.
>>
>>Uh, no. The spider does not "slow it down and cause a
>>phase shift." Whatever phase shift exists is not because
>>the "spider slows it down."
>>
>
>
> I guessed. When I was trying to figure out transmission line speakers, I
> experimented with a 6.5 inch driver and a pipe. I was trying to figure out
> delays along the pipe with stuffing. I first used the generator as sync and
> measured various lengths along pipe. What was predicted was lower
> frequencies having longer delays through stuffing. Until I placed a second
> mic right behind the driver did I discover the delay was caused by the
> driver. This was below resonate frequency of driver. I never found the
> predicted longer delay at lower frequencies according to at least one
> paper.

And assuming your technique was oging to give you a reliable
measure of actual propogation delay is what's wrong with so-
called "transmission line theory". People have used these
measurements and derived completely absurd conclusions about the
effective speed of sound through such a line. I've seen claims
that the "speed of sound" in a transmission line drops by 75%.
Sorry, but that's just plain nuts.

The MOST the stuffing can do is drop the tranmission speed
by about .7 times, and that's assuming a PERFECT absorber,
capable of complete conversion from adiabatic to isothermal
conditions. And that just doesn't happen. You'll be lucky to
see a 15% actual reduction in propogation velocity.

And to talks about something that's shorter than a wavelength
as a transmission line itself is bordering on absurd. Consider
the fact that at those frequencies, you're actually looking at
the system as a Helmholtz resonator with a whopping large
acoustic inertance, a tinu effective acoustic cimpliance, and
a pretty high absorbtion loss, and then calculate what happens
to the effective pahse shift as you move through that overdamped resonance.

Bud Fried (of, among other things, IMF fame) did more to set back
the amateur's grasp of physical acoustics then damned near anyone
else: he, regretfuylly, was a very persuasive, charming personality
who was otherwise clueless about acoustics.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

[gregz]

Dick Pierce > wrote:
> gregz wrote:
>> Dick Pierce > wrote:
>>>> gregz wrote:
>>>
>>>> You will also find a delay of the 30 Hz since it's below resonance, the
>>>> spider will slow it down and cause a phase shift.
>>>
>>> Uh, no. The spider does not "slow it down and cause a
>>> phase shift." Whatever phase shift exists is not because
>>> the "spider slows it down."
>>>
>>>> I guessed. When I was trying to figure out transmission line speakers, I
>> experimented with a 6.5 inch driver and a pipe. I was trying to figure out
>> delays along the pipe with stuffing. I first used the generator as sync and
>> measured various lengths along pipe. What was predicted was lower
>> frequencies having longer delays through stuffing. Until I placed a second
>> mic right behind the driver did I discover the delay was caused by the
>> driver. This was below resonate frequency of driver. I never found the
>> predicted longer delay at lower frequencies according to at least one
>> paper.
>
> And assuming your technique was oging to give you a reliable
> measure of actual propogation delay is what's wrong with so-
> called "transmission line theory". People have used these
> measurements and derived completely absurd conclusions about the
> effective speed of sound through such a line. I've seen claims
> that the "speed of sound" in a transmission line drops by 75%.
> Sorry, but that's just plain nuts.
>
> The MOST the stuffing can do is drop the tranmission speed
> by about .7 times, and that's assuming a PERFECT absorber,
> capable of complete conversion from adiabatic to isothermal
> conditions. And that just doesn't happen. You'll be lucky to
> see a 15% actual reduction in propogation velocity.
>
> And to talks about something that's shorter than a wavelength
> as a transmission line itself is bordering on absurd. Consider
> the fact that at those frequencies, you're actually looking at
> the system as a Helmholtz resonator with a whopping large
> acoustic inertance, a tinu effective acoustic cimpliance, and
> a pretty high absorbtion loss, and then calculate what happens
> to the effective pahse shift as you move through that overdamped resonance.
>
> Bud Fried (of, among other things, IMF fame) did more to set back
> the amateur's grasp of physical acoustics then damned near anyone
> else: he, regretfuylly, was a very persuasive, charming personality
> who was otherwise clueless about acoustics.

I used a very short line and your probably right. Typical delay I measured
about 7 % . However, at 2.6 lbs per cubic foot, I got up to 35% , and was
hard to measure because it was a highly attenuated signal. at suggested
stuffing rates, 8 oz per cu ft., more like less than 3% delay. I don't
think its a transmission line if there is no signal at the end of the pipe.

Greg

[Trevor]

"Dick Pierce" > wrote in message
...
> Bud Fried (of, among other things, IMF fame) did more to set back
> the amateur's grasp of physical acoustics then damned near anyone
> else: he, regretfuylly, was a very persuasive, charming personality
> who was otherwise clueless about acoustics.

Great to see you back Dick, and help to counteract such BS that some claim
as "science".

Trevor.

[Dick Pierce[_2_]]

gregz wrote:
> I used a very short line and your probably right. Typical delay I measured
> about 7 % . However, at 2.6 lbs per cubic foot, I got up to 35% , and was
> hard to measure because it was a highly attenuated signal. at suggested
> stuffing rates, 8 oz per cu ft., more like less than 3% delay. I don't
> think its a transmission line if there is no signal at the end of the pipe.

How are you measuring delay? By using the phase shift?

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

[gregz]

Dick Pierce > wrote:
> gregz wrote:
>> I used a very short line and your probably right. Typical delay I measured
>> about 7 % . However, at 2.6 lbs per cubic foot, I got up to 35% , and was
>> hard to measure because it was a highly attenuated signal. at suggested
>> stuffing rates, 8 oz per cu ft., more like less than 3% delay. I don't
>> think its a transmission line if there is no signal at the end of the pipe.
>
> How are you measuring delay? By using the phase shift?


That's primarily how I did it, comparing wavefront near rear of driver with
microphone, then some distance away with identical microphone. I was using
a storage oscilloscope.

Greg

[gregz]

gregz > wrote:
> Dick Pierce > wrote:
>> gregz wrote:
>>> I used a very short line and your probably right. Typical delay I measured
>>> about 7 % . However, at 2.6 lbs per cubic foot, I got up to 35% , and was
>>> hard to measure because it was a highly attenuated signal. at suggested
>>> stuffing rates, 8 oz per cu ft., more like less than 3% delay. I don't
>>> think its a transmission line if there is no signal at the end of the pipe.
>>
>> How are you measuring delay? By using the phase shift?
>
>
> That's primarily how I did it, comparing wavefront near rear of driver with
> microphone, then some distance away with identical microphone. I was using
> a storage oscilloscope.
>
> Greg

Just thinking, I was using higher density stuffing amounts that would
ordinarily be used, but my short line was just that, short. A full line
would show more delay but using a lot less stuffing, so the delay would
probably be no more than 15%, perhaps closer to 10% .

Greg

[Dick Pierce[_2_]]

gregz wrote:
> Just thinking, I was using higher density stuffing amounts that would
> ordinarily be used, but my short line was just that, short. A full line
> would show more delay but using a lot less stuffing, so the delay would
> probably be no more than 15%, perhaps closer to 10% .

No, it wouldn't.

You're not looking at "delay" per se as in propogation delay
down a transmission line. You're simply looknig at the fact
that at those wavelengths, the line is acting as a simple
damped resonator.

In other words, all the bobonsense you read about lines
ignores that they are behaving just like a bass reflex
with a whopping big port, a tiny volume, and a lot of
damping.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

[gregz]

Dick Pierce > wrote:
> gregz wrote:
>> Just thinking, I was using higher density stuffing amounts that would
>> ordinarily be used, but my short line was just that, short. A full line
>> would show more delay but using a lot less stuffing, so the delay would
>> probably be no more than 15%, perhaps closer to 10% .
>
> No, it wouldn't.
>
> You're not looking at "delay" per se as in propogation delay
> down a transmission line. You're simply looknig at the fact
> that at those wavelengths, the line is acting as a simple
> damped resonator.
>
> In other words, all the bobonsense you read about lines
> ignores that they are behaving just like a bass reflex
> with a whopping big port, a tiny volume, and a lot of
> damping.


That's no fun.

I never tried to make one, but I guess they were interesting to me.

Greg

[cometodeal]

That is really useful information!
!!!
;960624']gregz wrote:
> Dick Pierce > wrote:
>
>>gregz wrote:
>>
>>>You will also find a delay of the 30 Hz since it's below resonance, the
>>>spider will slow it down and cause a phase shift.
>>
>>Uh, no. The spider does not "slow it down and cause a
>>phase shift." Whatever phase shift exists is not because
>>the "spider slows it down."
>>
>
>
> I guessed. When I was trying to figure out transmission line speakers, I
> experimented with a 6.5 inch driver and a pipe. I was trying to figure out
> delays along the pipe with stuffing. I first used the generator as sync and
> measured various lengths along pipe. What was predicted was lower
> frequencies having longer delays through stuffing. Until I placed a second
> mic right behind the driver did I discover the delay was caused by the
> driver. This was below resonate frequency of driver. I never found the
> predicted longer delay at lower frequencies according to at least one
> paper.

And assuming your technique was oging to give you a reliable
measure of actual propogation delay is what's wrong with so-
called "transmission line theory". People have used these
measurements and derived completely absurd conclusions about the
effective speed of sound through such a line. I've seen claims
that the "speed of sound" in a transmission line drops by 75%.
Sorry, but that's just plain nuts.

The MOST the stuffing can do is drop the tranmission speed
by about .7 times, and that's assuming a PERFECT absorber,
capable of complete conversion from adiabatic to isothermal
conditions. And that just doesn't happen. You'll be lucky to
see a 15% actual reduction in propogation velocity.

And to talks about something that's shorter than a wavelength
as a transmission line itself is bordering on absurd. Consider
the fact that at those frequencies, you're actually looking at
the system as a Helmholtz resonator with a whopping large
acoustic inertance, a tinu effective acoustic cimpliance, and
a pretty high absorbtion loss, and then calculate what happens
to the effective pahse shift as you move through that overdamped resonance.

Bud Fried (of, among other things, IMF fame) did more to set back
the amateur's grasp of physical acoustics then damned near anyone
else: he, regretfuylly, was a very persuasive, charming personality
who was otherwise clueless about acoustics.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

[Peter Larsen[_3_]]

Dick Pierce wrote:

> And to talks about something that's shorter than a wavelength
> as a transmission line itself is bordering on absurd. Consider
> the fact that at those frequencies, you're actually looking at
> the system as a Helmholtz resonator with a whopping large
> acoustic inertance, a tinu effective acoustic cimpliance, and
> a pretty high absorbtion loss, and then calculate what happens
> to the effective pahse shift as you move through that overdamped
> resonance.

So what you say is that a "transmission line speaker" is a bass reflex box
with a very small box volume and a very large port volume?

Kind regards

Peter Larsen

> Bud Fried (of, among other things, IMF fame) did more to set back
> the amateur's grasp of physical acoustics then damned near anyone
> else: he, regretfuylly, was a very persuasive, charming personality
> who was otherwise clueless about acoustics.

[Arny Krueger]

"Peter Larsen" > wrote in message
. ..
> Dick Pierce wrote:
>
>> And to talks about something that's shorter than a wavelength
>> as a transmission line itself is bordering on absurd. Consider
>> the fact that at those frequencies, you're actually looking at
>> the system as a Helmholtz resonator with a whopping large
>> acoustic inertance, a tinu effective acoustic cimpliance, and
>> a pretty high absorbtion loss, and then calculate what happens
>> to the effective pahse shift as you move through that overdamped
>> resonance.
>
> So what you say is that a "transmission line speaker" is a bass reflex box
> with a very small box volume and a very large port volume?

And a highly damped port.

A transmission line speaker can be considered to be a very wastefully
designed bass reflex.

[Dick Pierce[_2_]]

Arny Krueger wrote:
> "Peter Larsen" > wrote in message
> . ..
>
>>Dick Pierce wrote:
>>
>>
>>>And to talks about something that's shorter than a wavelength
>>>as a transmission line itself is bordering on absurd. Consider
>>>the fact that at those frequencies, you're actually looking at
>>>the system as a Helmholtz resonator with a whopping large
>>>acoustic inertance, a tinu effective acoustic cimpliance, and
>>>a pretty high absorbtion loss, and then calculate what happens
>>>to the effective pahse shift as you move through that overdamped
>>>resonance.
>>
>>So what you say is that a "transmission line speaker" is a bass reflex box
>>with a very small box volume and a very large port volume?
>
> And a highly damped port.

At low frequencies.

The notion of a transmission line involves the concept that
at the frequencies and wavelengths involved, the "line" is
long compared to the wavelength. At low frequencies, this is
decidedly not the case. A so-called "1/4 wave" line simply
acts as a system of lumped components. The old IMF Monitor used
a Kef B139, with a 25 Hz nominal resonance. At 25 Hz, the
wavelength is some 45 feet long, and 1/4 of that is almost 12
feet. That line is NOT 12 feet long.

And even considering absolute optimal absorbtive material that
fully converts the internal operating conditions from adiabatic
to isothermal (which it is FAR from doing), that's still over 8
feet.

People measure the output of the line and compare its phase to the
output of the woofer, and from that derive a bizarrely low
propogation velocity. The same can be done with a standard bass
reflex, which suggests a small bass reflex has an internal
propogation volecity FAR lower than that of sound in normal.
This simply ignores the phase rotation one goes through in a
normal 2nd-order resonat system.

At higher frequencies, it's a different story, in the sense
that the line is, indeed, long compared to the wavelengths
involved.

> A transmission line speaker can be considered to be a very wastefully
> designed bass reflex.

Well, careful. "Wasteful" is in the eye of a beholder.
A side effect of the traditional design of a transmission
line (the old IMF Monitor/Studio model) results in two things
that are very useful:

1. Midbass and up, the rear wave is lost, gone, forgotten
and never to bother us again,

2. The cabinet walls can be VERY stiff and inert (the rear
wall is problematic, but there are solutions to this).
Now, that in and of itself is not a feature unique to
transmission lines, but it is a useful feature,
nonetheless.

Some of Fried's designs (notably the ALS-50 and its
derivatives) were at best, well, interesting (a 5-legged
horse is interesting, too).

Some of the notions (I hesitate to call them "theories"
becasue their predictive power is pretty poor) surrounding
transmission lines falls into the same category that inspires
people to worry about the effective impedance of their speaker
wires, leading to bizarre (and, mostly, very expensive) wire
contrivances.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+