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Subwoofer drivers in series - reactive voltage

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Anonymous
a b \ Driver
January 1, 2005 8:42:22 PM

Archived from groups: rec.audio.tech (More info?)

Guys,

I'm in a discussion among friends about using multiple 15" large
excursion drivers in an infinte baffle configuration.

Some are saying you can't wire the nominally identical drivers in
series. The typical argument:

"Assuming a zero impedance of the amp output, then in serial
connection, when moving one driver's cone, the other should follow due
to the reactive voltage. But this is minimized for parallel connection
when the amp output impedance is very low. Even for same divers, the
manufacturering variation and operating condition may cause one moves
different from another, and therefore interferes with others in serial.
The effect can be positively fed back."
..
This doesn't sound right to me. Any comments?
Anonymous
a b \ Driver
January 2, 2005 1:03:59 AM

Archived from groups: rec.audio.tech (More info?)

In article <1104630142.376592.238160@c13g2000cwb.googlegroups.com>,
"Rusty B." <rustybx@knology.net> wrote:

> Guys,
>
> I'm in a discussion among friends about using multiple 15" large
> excursion drivers in an infinte baffle configuration.
>
> Some are saying you can't wire the nominally identical drivers in
> series. The typical argument:
>
> "Assuming a zero impedance of the amp output, then in serial
> connection, when moving one driver's cone, the other should follow due
> to the reactive voltage. But this is minimized for parallel connection
> when the amp output impedance is very low. Even for same divers, the
> manufacturering variation and operating condition may cause one moves
> different from another, and therefore interferes with others in serial.
> The effect can be positively fed back."
> .
> This doesn't sound right to me. Any comments?

There is no positive feedback. It's more like a severe loss of
dampening. You could get weird effects like each speaker resonating at
its own frequencies while reducing or enhancing those same frequencies
in the opposing speaker. That would sound strange for higher
frequencies where phasing is critical but it should sound OK for a
subwoofer. Differences in excursion shouldn't be a problem with an
infinite baffle because there's no enclosure resonance. Mechanical
dampening in the subwoofer should keep things balanced well.

I wouldn't put tuned enclosures subs in series. The speaker impedance
changes drastically with frequency.
Anonymous
a b \ Driver
January 2, 2005 1:37:10 PM

Archived from groups: rec.audio.tech (More info?)

Kevin McMurtrie wrote:
> In article <1104630142.376592.238160@c13g2000cwb.googlegroups.com>,
> "Rusty B." <rustybx@knology.net> wrote:
>
> > Guys,
> >
> > I'm in a discussion among friends about using multiple 15" large
> > excursion drivers in an infinte baffle configuration.
> >
> > Some are saying you can't wire the nominally identical drivers in
> > series. The typical argument:
> >
> > "Assuming a zero impedance of the amp output, then in serial
> > connection, when moving one driver's cone, the other should follow
due
> > to the reactive voltage. But this is minimized for parallel
connection
> > when the amp output impedance is very low. Even for same divers,
the
> > manufacturering variation and operating condition may cause one
moves
> > different from another, and therefore interferes with others in
serial.
> > The effect can be positively fed back."
> > .
> > This doesn't sound right to me. Any comments?

This common misconception is wrong on so many fronts that
it's difficult to choose where to begin to refute this
recurring nonsense.

First, there is never a situation where you drive one cone and
the other is not driven: they're both driven together.

Second, mounted in the same enclosure, and mounted in an
enclosure where the total system stiffness is dominated
by the enclosure, there are NOT significant variations
in driver parameters. One of the critical parameters,
moving mass, is actually quite well controlled in manu-
facturing, and the other, stiffness, is dominated by
the cabinet which, if the drivers are nmounted in the
same cabinet, minimizes
the apparent variations.

Third, they DON'T interfere with one another, their operating
parameters need only be close for them to work together. The
system losses (between mechanical and especially electrical
losses) are more than high enough to ensure that the system
is dominated by those losses and the resultant system Q is
low enough that the "out-of-synch" problems imagined simply
can't happen.

> There is no positive feedback.

Absolutely correct. FOr this nonsense about "positive feed-
back" to have any validity, the system has to have power gain
greater than 1, and I would challenge anyone espousing this
"feedback" problem to show that a typical speaker, with its
typical efficiency of less than 1%, to have a power gain
greater than 1.

The analysis is more properly done as two coupled forced
harmonic oscillators that are dominated primarily by resistive
losses (make that almost TOTALLY dominated), and the actual
behavior becomes obvious, and NOTHING like the description
above.

>It's more like a sevre loss of dampening.

No, you do not. If you're using two of the same model, even if
they are not EXACTLY the same, the total system damping is
exactly the same whether they are in series or not.

>You could get weird effects like each speaker resonating at
> its own frequencies while reducing or enhancing those same
frequencies
> in the opposing speaker. That would sound strange for higher
> frequencies where phasing is critical but it should sound OK for a
> subwoofer.

No, because at higher frequencies is where the impedance
variations between drivers is going to be at a minimum,
as the impedance is dominated by easy-to-control parameters,
notably the voice coil DC resistance and the voice coil
inductance.

> Differences in excursion shouldn't be a problem with an
> infinite baffle because there's no enclosure resonance.
> Mechanical dampening in the subwoofer should keep things
> balanced well.

No, the damping of the vast majority of drivers used for this
purpose is electrical, not mechanical. Secondly,

> I wouldn't put tuned enclosures subs in series. The speaker
> impedance changes drastically with frequency.

This has been debunked in the past. Take two speakers with
the same "drastic" frequency-dependent impedance variations
in series, and the operation does not substantially change
by putting them in series.

Below is a reprint of an article I did some time ago on this
topic. This is best read with a fixed-width font.

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

Damping: Loudspeakers In Series
Dick Pierce
Professional Audio Development

1 INTRODUCTION

An entire mythology surrounds the notion of damping in
loudspeakers. We have separately treated the oft-cited and
nearly useless "damping factor" specification in a separate
article. Here, we discuss much of the myth surrounding the
behavior of loudspeakers connected in series and the
seemingly intuitive effect on damping tat results. Of late,
this topic is relevant or several reasons.

First, we have seen a gain in use of multiple-woofer
systems, exemplified by the popular, so-called "D'Appolito"
configuration (often the woofers are connected in parallel,
but there are applications where a series connection could
be appropriate as well). Second, we have observed an
unfortunate trend in consumer electronics, especially in
home theater receivers. More and more, these receivers have
skimped on power supply and/or output stage design and are
quite unable to drive the lower impedances oft found in
today's speakers. The question often arises whether speakers
can be hooked in series, thus raising the impedance.

The answer often given to both of these scenarios is "Oh,
no, you can't do that. The damping of each speaker will be
severely reduced because of the series impedance of the
other speaker!

As you might have guessed, we're going to show why this is
wrong. We'll do this by taking an analytical approach, and
test our analysis by actually measuring actual systems.

2 WHAT IS DAMPING?

The term "damping" is has a very specific and unambiguous
definition: technically, it is a measure of how quickly
energy is removed from a resonant system. This definition
stands despite attempt to co-opt the term for otherwise
imprecise and often incorrect uses(1). It is a measure of
how quickly a resonant or oscillatory system is brought
under control by removing energy that would otherwise keep
the resonance going.

Energy is stored in reactive elements. These include masses
and compliances (or springs) in the mechanical world, and
inductances and capacitances in the electrical world.
Mechanically, energy of a mass is the kinetic energy due to
the motion of a mass. The kinetic energy of a moving mass
equal to the mass times the velocity squared. In a spring or
compliance, the energy is stored as potential energy in the
compression or extension. The potential energy is equal to
the spring constant times the compression or extension
squared).

Electrically, kinetic energy is in the magnetic field around
an inductor created by the current flowing through the
inductor. The energy is equal to the inductance times the
current squared. In a capacitor, it's the potential energy
in the electric field caused by the impressed voltage on the
plates of a capacitor, equal to the capacitance times the
voltage squared.

Energy is removed through loss mechanism, such as frictional
losses in the mechanical domain or ohmic losses in the
electrical. These losses convert energy to heat, and once
that happens, the energy is no longer available.

In loudspeakers, there is a direct measure of the ratio of
energy stored to energy lost, and that is the so-called "Q"
factor. And we find that in most loudspeakers, there are two
predominant loss mechanisms, each with there own Q
measurement. The due to mechanical losses is designated as
Qm, while that for electrical losses is designated as Qe(2).
We can calculate these factors knowing the energy storage
and losses mechanisms involved

The mechanical Qm results from the energy storage in the
moving mass of the cone and the frictional losses in the
suspension. It is calculated thus:

Mm
Qm = 2 pi F ----
Rm

where is the F resonant frequency of the system in Hertz, Mm
is the mechanical mass of the system and Rm is the
frictional loss in the system. Increase the mass, and more
energy is stored in the system. Increase the friction, and
more energy is dissipated from the system

The electrical Qe of the system results, again, from the
energy stored in the moving mass, but now dissipated by the
electrical resistance in the system. It is calculated as:

Mm
Qe = 2 pi F ------- Re
2 2
B l

Here, B represents the magnetic flux density in the voice
coil gap, l is the length of wire in the magnetic field, and
Re represents the DC resistance of the voice coil.

We can also speak, of course, of the total Q, or Qt, of the
system due to the combined mechanical and electrical
damping, and it's calculated by the familiar formula:

Qm * Qe
Qt = ---------
Qm + Qe

The lower the Q, the more damped the system is. The higher
the Q, the less damped.

3 THE INTUITIVE PREMISE

Here's the claim: putting speakers in series is a bad idea
because the series resistance of one speaker destroys the
damping of the other. Why, even the equation for electrical
Qe above says so: having two voice coils in series doubles
the voice coil resistance (assuming the voice coils are the
same, for simplicity). So it must logically follow that
adding two speakers in series must severely destroy the
damping, and the equation above shows that it should double.

It makes intuitive sense. It even seems to appeal to
technical authority. But will it stand up to analytical and
empirical scrutiny? Is this, perchance, another widely held
belief that might not be so?

4 ANALYSIS

We'll consider the case where we are connecting two of the
same thing in series, be it two identical woofers in an
enclosure or two identical speakers in series. We're using
identical woofers or systems to make the analysis
simpler(3).

Let's first look at the effects of two speakers in connected
together in the mechanical domain. It might seem obvious,
but since no electrical effects are considered in the
mechanical domain, it makes no difference on the mechanical
damping or Qm whether two speakers or two woofers are
connected in series or parallel. Indeed, it doesn't even
make any difference if they aren't connected at all
electrically.

In the mechanical case, we have doubled the moving mass Mm
to 2*Mm to (we have twice as many cones, after all), but we
have also double the amount of frictional Rm loss from to
2*Rm as well (twice as many surrounds and spiders, too).
Plugging these changes into the equation for mechnaical
damping, we find:

2 Mm
Qm = 2 pi F ------
2 Rm

We can simplify: in the equation 2/2 is equal to 1, and we
thus end up with:

Mm
Qm = 2 pi F ----
Rm

This equation, describing the effect on Qm of connecting two
speakers in series, is precisely the same equation for the
case of a single speaker by itself.

Now, let's look at the electrical damping or Qe. Here, we
have, indeed, doubled the resistance Re to 2*Re (the voice
coils are hooked in series), but we have also doubled the
moving mass from Mm to 2*Mn as well and we've also double
the length of the voice coil wire from l to 2*l sitting in
the magnetic field as well. Now, let's plug all those
factors of two into the equation for electrical Q:

2 Mm
Qe = 2 pi F ---------- 2 Re
2 2
B (2l)

The next step expands and combines terms:

2 Mm
Qe = 2 pi F --------- 2 Re
2 2
B 4 l

In another step, let's accumulate all these new factors (2
from the doubling of mass, 2 from the doubling of the voice
coil resistance, and 4 from the square of the doubling of
the length of the wire) together for the numerator and the
denominator:

4 Mm
Qe = 2 pi F - ------- Re
4 2 2
B l

And, since the fraction 4/4 is equal to 1, we can reduce
this equation to:

Mm
Qe = 2 pi F ------- Re
2 2
B l

Again, this result, showing the Qe electrical of two
speakers connected in series, is identical to the case of
just a single speaker.

Thus the analysis clearly shows that the damping is not
severely compromised by connecting two systems or drivers in
parallel, because the measures of damping, Qm and Qe,
remains the same for both the mechanical and electrical
domains, and thus the total also remains the same. Q.E.D.

5 EMPIRICAL SUPPORT

The intuitive premise makes one clear prediction: the
damping is seriously compromised by placing two speakers in
series. This must be manifested by a substantial increase in
the Q factors of the speaker. Specifically, the premise
predicts that the electrical Q factor should be much
greater. How much greater is not clear, because the premise
is woefully short of analytical precision. But let's say
that we should see at least a doubling of the electrical Q.
And since the electrical damping predominates in most
speakers, the total Q should be similarly affected.

On the other hand, our analysis above predicts that the Q
factors should remain essentially unchanged. Such an
unambiguous difference makes this discussion an ideal
candidate for falsification by experiment(4).

For the first experiment, I selected two woofers, a pair of
Seas PR17RC 6 1/2" woofer-midrange drivers. I measured the
relevant parameters, the DC resistance, resonance and the
mechanical, electrical and total damping of each separately,
and then with the two connected in-phase in series to see
the effect on damping of such a series connection. The
actual results are shown in Table 1:

Measurement Prediction
Parameter A B A+B Analytical Intuitive
------------------------------------------------------------
Resonance F 71.20 69.03 70.1
DC resistance Re 5.72 5.70 11.42

Damping
Mechanical Qm 1.29 1.33 1.32
Electrical Qe 0.88 0.92 0.91 ~0.90 >1.80
Total Qt 0.52 0.54 0.55 ~0.53 >1.06
-----------------------------------------------------------
Table 1: Driver Measurements

The data would seem to strongly support the analytical
method's predictions, and refute those of the intuitive
model. That's fine for single speakers, and this result has
been validated in numerous home-built systems using multiple
drivers in series. It might be a different question, though,
for complete speaker systems, often the situation found in
some installations.

So, I went to my storage room and grabbed a pair of rather
ordinary bookshelf speakers, some ancient ones made by the
old H. H. Scott company. I could well have used any two
speakers, but there were handy and fully functional. I
measured the resonant frequency, the DC resistance of the
voice coil, and the relevant Q factors for each speaker
alone, and the two in series. Along with these numbers, I
also present the predictions made by the two competing
theories, the "intuitive" premise, and the "analytical"
theory described above. The results are shown in Table 2.

Measurement Prediction
Parameter A B A+B Analytical Intuitive
------------------------------------------------------------
Resonance F 110.5 113.7 112.6
DC resistance Re 6.86 6.87 13.90

Damping
Mechanical Qm 2.77 3.06 3.15
Electrical Qe 1.02 1.09 1.14 ~1.06 >2.28
Total Qt 0.75 0.80 0.83 ~0.80 >1.6
------------------------------------------------------------
Table 2: Speaker System Measurements

It would seem that the empirical data strongly supports our
analytical model, and strongly refutes the intuitive
premise. Q.E.D.

6 FREQUENCY RESPONSE ERRORS

One problem with two speakers in series is that the
frequency dependent impedance variations of one will upset
the frequency response of the other, and vice versa. As it
turns out, this is not the case as well.

Consider how the attenuation arises. Take the case of two
resistances in series, R1 and R2. Given an impressed voltage
of Vs, we can calculate the voltage across . The current
through the entire circuit, will, by Ohm's law, be:

Vs
I = ---------
R1 + R2

Given that current, again, by Ohm's law, the voltage across
R2 will be:


Vr2 = I R2

And, combining these two equations and simplifying, we find
that:

R2
Vr2 = Vs -------
R1 + R2

Now, in the case where R1 = R2, this reduces to simply:

1
Vr2 = --- Vs
2

Now, this can be generalized for impedances. If the
impedances are the same, we can say that:

Z2
Vz2 = Vs ---------
Z1 + Z2

Z1 and Z2 represent the complex, frequency dependent
impedances of our loudspeakers. If Z1 = Z2, which would be
the case if our two speakers are the same (and this includes
the frequency-dependent impedance variations as well), then
our equation reduces to the fact that the voltage across
each speaker would be:

1
Vz = --- Vs
2

Notice the complete absence of any frequency-dependent terms
in this final equation: with two identical speakers in
series, the voltage across each is simply 1/2 that of the
voltage the amplifier is producing across the total, and is
independent of frequency. There are, thus, no
frequency-dependent variations in frequency as a result of
putting two identical speakers in series. Q.E.D.

-----------------------
Footnotes

(1) One often encounters hi-fi accessories, for example,
that utilize "mass damping" to control resonances. That
adding a mass will change a resonant system is hardly in
dispute, that it "damps" a resonance is altogether a
different and quite incorrect claim.

(2) There are other loss mechanisms, most notable the
acoustical losses. However, for direct radiator
loudspeakers, these loss mechanisms are quit
insignificant, most often representing less than 1% of
the total losses. Not coincidentally, this number is not
too dissimilar form the acoustical efficiency of such
speakers as well, because in order to produce sound,
real work has to be done, and it is the work done into
these acoustical "losses" that actually is the produced
sound. Eliminate the acoustical loss, say by taking away
the radiation load by putting the speaker in a vacuum,
and you've eliminated the sound. Not an entirely useful
exercise for something like a loud "speaker."

(3) While the case of non-identical drivers or systems is
more complicated, the general principles apply, though
there are confounding factors such as
frequency-dependent attenuation resulting from different
frequency-dependent impedances.

(4) "Falsification" is a vital part of the scientific
method. A theory must be falsifiable, that is, it must
make a prediction that, by experiment or observation,
can be clearly shown to be right or wrong. In the case
we have here, either one theory, the other theory, or
neither theory will be supported by the experimental
data. No data can support both. If a theory makes a
prediction that can't be tested, it's no good as a
theory. You might have a theory: "I can levitate myself
while no one is looking." It's impossible for anyone
else to construct a test, because they can never look at
you doing what you claim, thus the "theory" has no value
scientifically.
Related resources
Anonymous
a b \ Driver
January 2, 2005 2:20:37 PM

Archived from groups: rec.audio.tech (More info?)

dpierce@cartchunk.org wrote:
> Below is a reprint of an article I did some time ago on this
> topic. This is best read with a fixed-width font.

I just made this article available as a downloadable PDF,
which survives various text mungings of different hosting
services.

Check out www.cartchunk.org/audiotopics/SeriesSpeaker.pdf
Anonymous
a b \ Driver
January 2, 2005 8:50:11 PM

Archived from groups: rec.audio.tech (More info?)

Rusty B. wrote:
> Guys,
>
> I'm in a discussion among friends about using multiple 15" large
> excursion drivers in an infinte baffle configuration.
>
> Some are saying you can't wire the nominally identical drivers in
> series. The typical argument:
>
> "Assuming a zero impedance of the amp output, then in serial
> connection, when moving one driver's cone, the other should follow
due
> to the reactive voltage. But this is minimized for parallel
connection
> when the amp output impedance is very low. Even for same divers, the
> manufacturering variation and operating condition may cause one moves
> different from another, and therefore interferes with others in
serial.
> The effect can be positively fed back."
> .
> This doesn't sound right to me. Any comments?

If you put two identical N ohm woofers in series, you end up with
effectively an 2N ohm woofer. The increased load impedance will
significantly reduce the power that your typical power amp with no
output transformer can deliver to the speakers if the amplifier can
effectively drive N ohm speakers.

If you are properly designing a woofer, you will be using Thiel-Small
parameters to develop your design. Among the parameters that you put
into the design equations will be such parameters as driver DC
resistance, which will be doubled due to the series connection.

The explanation that you received is simply uneducated
psuedo-scientific double-talk. Ignore it. Instead devote your efforts
into developing a working understanding of Thiel-Small parameters and
how they relate to speaker and enclosure design. They will properly
include the effects of series and parallel driver connections.
Anonymous
a b \ Driver
January 3, 2005 5:23:07 AM

Archived from groups: rec.audio.tech (More info?)

Thanks for all the responses.

Arny, the reason for series connection is as follows:

Most of the high excursion drivers (like Stryke AV15 DVC - Xmax=23mm,
Xsus=30mm, Sd=830sqcm, Re=2.95 ohm each) have fairly low Re. For an IB
we usually use multiple drivers with 4 being the most common. So then
you have 8 voice coils of 3 ohms each. The most common configuration
is to parallel the coils on each driver (1.5 ohms) and put two drivers
in series for a pair of 3 ohm loads (Z=4 ohms). Then drive each pair
from a prosound amp like the Behringer EP1500 which would give 700Wpc
into 2 ohms and 450Wpc into 4 ohms. This is just enough power to drive
four AV15s to Xmax at 20Hz.

Obviously this has worked great for many people. However, there's been
some rumbling about the series connection not being optimum. I was
just looking for a good technical argument to counter.
Anonymous
a b \ Driver
January 3, 2005 11:25:08 AM

Archived from groups: rec.audio.tech (More info?)

Rusty B. wrote:
> Thanks for all the responses.
>
> Arny, the reason for series connection is as follows:
>
> Most of the high excursion drivers (like Stryke AV15 DVC - Xmax=23mm,
> Xsus=30mm, Sd=830sqcm, Re=2.95 ohm each) have fairly low Re. For an
IB
> we usually use multiple drivers with 4 being the most common. So
then
> you have 8 voice coils of 3 ohms each. The most common configuration
> is to parallel the coils on each driver (1.5 ohms) and put two
drivers
> in series for a pair of 3 ohm loads (Z=4 ohms).

Yup, that's how it is done (right).

> Then drive each pair
> from a prosound amp like the Behringer EP1500 which would give 700Wpc
> into 2 ohms and 450Wpc into 4 ohms. This is just enough power to
drive
> four AV15s to Xmax at 20Hz.

Yup, that's how it is done right (on a budget).

> Obviously this has worked great for many people.

Science works! ;-)

> However, there's been
> some rumbling about the series connection not being optimum.

Sound quality envy?

> I was just looking for a good technical argument to counter.

In this case its just a matter of calling a hand-wavey BS arguement
what it is! ;-)
Anonymous
a b \ Driver
January 4, 2005 10:50:53 PM

Archived from groups: rec.audio.tech (More info?)

>> Then drive each pair from a prosound amp like the
>> Behringer EP1500 which would give 700Wpc into
>> 2 ohms and 450Wpc into 4 ohms. This is just enough
>> power to drive four AV15s to Xmax at 20Hz.
>
> Yup, that's how it is done right (on a budget).

Are you saying this budget approach is done right or that one might do
it differently given a higher budget? A typical IB setup:

Basics:
1. Four Stryke AV15 drivers-$820 or eight Dayton IB 15"-$880.
.. Roughly 19 liters of Xmax displacement (25L at Xsus)
2. Behringer EP1500 amp $300
3. Construction materials $100

Fine Tuning:
4. Behringer DSP1124P EQ 1/60th octave step, 1/60th-2 oct BW. $120
5. Behringer ECM8000 Measurement Microphone. $50
6. Behringer UB802 mix (power for microphone). $50
7. TrueRTA software spectrum analyzer. $99

Total cost $1300-$1600.

Depending on room it's pretty easy to EQ for 125dB flat from 20Hz up
with rolloff to about 115dB at 10Hz.

Sustained output approaching 130dB can be achieved within Xmax if you
allow more rolloff at the low end.

How much would you have to spend on a traditional box sub to achieve
this extreme output of very low distortion bass?
Anonymous
a b \ Driver
January 4, 2005 11:33:09 PM

Archived from groups: rec.audio.tech (More info?)

Rusty B. wrote:

> >> Then drive each pair from a prosound amp like the
> >> Behringer EP1500 which would give 700Wpc into
> >> 2 ohms and 450Wpc into 4 ohms. This is just enough
> >> power to drive four AV15s to Xmax at 20Hz.

> > Yup, that's how it is done right (on a budget).

> Are you saying this budget approach is done right or that one might
do
> it differently given a higher budget?

People often do it on a far higher budget, but there's no guarantee
that they get better-sounding results.

> A typical IB setup:

> Basics:
> 1. Four Stryke AV15 drivers-$820 or eight Dayton IB 15"-$880.
> . Roughly 19 liters of Xmax displacement (25L at Xsus)
> 2. Behringer EP1500 amp $300
> 3. Construction materials $100

> Fine Tuning:
> 4. Behringer DSP1124P EQ 1/60th octave step, 1/60th-2 oct BW. $120

Thanks for the tip. I was unaware of the use of this inexpensive
product as a digital parametric eq as described at:

http://www.snapbug.ws/bfd.htm

and

http://www.snapbug.ws/brucekbfdbandwidthinfo.htm

Interesting reads!

> 5. Behringer ECM8000 Measurement Microphone. $50

Been there done that.

> 6. Behringer UB802 mix (power for microphone). $50
> 7. TrueRTA software spectrum analyzer. $99

> Total cost $1300-$1600.

> Depending on room it's pretty easy to EQ for 125dB flat from 20Hz up
> with rolloff to about 115dB at 10Hz.

> Sustained output approaching 130dB can be achieved within Xmax if you
> allow more rolloff at the low end.

> How much would you have to spend on a traditional box sub to achieve
> this extreme output of very low distortion bass?

Not necessarily that much more. The boxes can have minimal size, and
you can use eq to compensate for the bass losses due the small boxes.
Then, you'd probably want to move up to the larger Behringer amp
EP2500, which is as I recall about $100 more.
Anonymous
a b \ Driver
January 5, 2005 11:13:14 PM

Archived from groups: rec.audio.tech (More info?)

> 4. Behringer DSP1124P EQ 1/60th octave step, 1/60th-2 oct BW. $120
>
>> Thanks for the tip. I was unaware of the use of this
>> inexpensive product as a digital parametric eq as
>> http://www.snapbug.ws/bfd.htm
>> http://www.snapbug.ws/brucekbfdbandwidthinfo.htm
>> Interesting reads!

Yep, those are two of better guides for sub EQ with the BFD.

There's more good links and reading on the site below. FAQ, forum and
tons of photos of IB designs. One photo set is an install that pushes
over 50 liters using 18 15" drivers. Yikes!!!

'Cult of the Infinitely Baffled'
http://f20.parsimony.net/forum36475/

>> How much would you have to spend on a traditional
>> box sub to achieve this extreme output of very low
>> distortion bass?
>
> Not necessarily that much more. The boxes can have minimal
> size, and you can use eq to compensate for the bass losses
> due the small boxes.

Interesting.

I'm curious about how displacement affects SPL. For these IB's we
typically drive 19 liters of displacement to Xmax on the low end (20Hz
and under). Is it possible to get higher SPL with a box sub that has
lower driver displacement?

One of the most extreme drivers is the Acendant Audio Avalanche 18".
Over 6.5 liters of displacement is possible with Adire's XBL2
technology (Sd=1210 cm2, Xmax= 27mm). The recommended enclosure is a
ported cube 32" square (20 cubic feet). Would you still need three of
them to get the same displacement/SPL as the above IB? If so, this
would cost about $500 more and you'd have three largish boxes in the
room instead of just a hole in the ceiling. Of course, some might
prefer boxes to making holes ;) 

How hard is it to calculate power compression in a box sub? Since the
IB drivers are operating free air and multiple drivers are used the
power requirements are usually very low. With eight drivers you get a
gain of 9 dB...so 80 watts will get you to 120dB vs 650 watts for a
single driver (ignoring excursion limits and power compression).
January 6, 2005 9:29:33 PM

Archived from groups: rec.audio.tech (More info?)

As an aside, I continue to be amused at the "specmanship" of speakers
makers for car audio / home theatre. Eg Cerwin Vega quotes SPL "at
1W/1m", then in the fine print defines 1W at 2.83Vrms, even into a 4
ohm driver. Adire quotes Xmax at the -3dB flux, which makes the figure
grossly higher than that from a "reputable" maker. These makers
genuinely do seem to make good product, which makes it seem all the
more strange that they feel the need to deceive in their specs.

And of course for the current discussion, the result of that is
substantial errors in displacement volume and SPL.

But in spite of that I can't imagine in my wildest dreams that a dozen
or more 18" long-throw drivers can't produce enough bass for even the
most bizarre audio freak.

Tony (remove the "_" to reply by email)
January 7, 2005 12:07:50 AM

Archived from groups: rec.audio.tech (More info?)

On 6 Jan 2005 01:53:53 -0800, "Rusty B." <rustybx@knology.net> wrote:

>> As an aside, I continue to be amused at the "specmanship" of speakers
>> makers for car audio / home theatre. Eg Cerwin Vega quotes SPL "at
>> 1W/1m", then in the fine print defines 1W at 2.83Vrms, even into a 4
>> ohm driver.
>
>Agreed. No one I know uses CV for serious audio.
>
>> Adire quotes Xmax at the -3dB flux
>
>I don't see this as deceptive. The -3dB BL limit is the standard DUMAX
>test condition of 70% peak BL. Also, at -3dB BL the THD of Adire's
>XBL2 design intersects with the traditional long gap, long coil design
>(roughly 15% THD). Because of XBL2 at smaller excursions the THD is
>dramatically reduced. For example, backing off Xmax by 30% has XBL2
>under 1% THD while LGLC design is over 5%. Of couse, it's difficult at
>best to hear the difference between 1% and 5% THD at 20Hz.

Interesting stuff. I admit that the car audio world is quite new to
me, and I wasn't aware of the standard DUMAX test condition. But
neither did a google for
dumax "test condition"
show up any relevant hits, so I wonder if you could point me in the
right direction? Woofers I've used in the past quoted the ACTUAL voice
coil overlap as Xmax, as did even some cheap subs I recently bought
from Jaycar (I can see the overlap through a gap under the spider).

There certainly do seem to be circumstance under which XBL2 has
linearity advantages, but they are far from universal, and I was under
the impression that not all Adire's products used XBL2 anyway. And I
wonder which "long coil design" Adire's relative data is based on -
maybe an outdated competitive design, or maybe their own earlier
model?

But I didn't really want to single out Adire - as I said, I believe
they make a good product, and it's just a shame they have to express
the benefits of XBL2 in a market dominated by hype,
"pseudo-techno-speak" and lies.

Tony (remove the "_" to reply by email)
Anonymous
a b \ Driver
January 7, 2005 12:07:51 AM

Archived from groups: rec.audio.tech (More info?)

On Thu, 06 Jan 2005 21:07:50 +1000, Tony <tony_roe@tpg.com.au> wrote:

>me, and I wasn't aware of the standard DUMAX test condition. But
>neither did a google for
> dumax "test condition"
>show up any relevant hits, so I wonder if you could point me in the
>right direction?

"Xmag = Excursion limit due to the magnetic limitations of the driver's
motor. Xmag is defined as the displacement at which the BL product has
fallen to 70% of its value at the cone's rest position.

Xsus = Excursion limit due to the driver's suspension. Xsus is defined as
the point at which the compliance of the suspension has decreased to 25% of
the value at the cone's rest position.

From these two figures, Xmax is then derived as follows:

Xmax = The shorter of the Xmag and Xsus values, in each direction of cone
travel."

http://www.diysubwoofers.org/misc/dumax/dumax.htm
Anonymous
a b \ Driver
January 7, 2005 1:04:00 AM

Archived from groups: rec.audio.tech (More info?)

"Rusty B." <rustybx@knology.net> wrote in message
news:1104984794.112105.168970@z14g2000cwz.googlegroups.com
>> 4. Behringer DSP1124P EQ 1/60th octave step, 1/60th-2 oct BW. $120
>>
>>> Thanks for the tip. I was unaware of the use of this
>>> inexpensive product as a digital parametric eq as
>>> http://www.snapbug.ws/bfd.htm
>>> http://www.snapbug.ws/brucekbfdbandwidthinfo.htm
>>> Interesting reads!
>
> Yep, those are two of better guides for sub EQ with the BFD.
>
> There's more good links and reading on the site below. FAQ, forum and
> tons of photos of IB designs. One photo set is an install that pushes
> over 50 liters using 18 15" drivers. Yikes!!!
>
> 'Cult of the Infinitely Baffled'
> http://f20.parsimony.net/forum36475/
>
>>> How much would you have to spend on a traditional
>>> box sub to achieve this extreme output of very low
>>> distortion bass?
>>
>> Not necessarily that much more. The boxes can have minimal
>> size, and you can use eq to compensate for the bass losses
>> due the small boxes.

> I'm curious about how displacement affects SPL.

Basically, diplacement, frequency and SPL are tied together.

> For these IB's we
> typically drive 19 liters of displacement to Xmax on the low end (20Hz
> and under). Is it possible to get higher SPL with a box sub that has
> lower driver displacement?

Under certain conditions, particularly with bandpass enclosures.

The trick is to try to take advantage of air displaced on both sides of the
cone.

A vented box does that to a limited degree, and a bandpass enclosure goes
further.

> One of the most extreme drivers is the Acendant Audio Avalanche 18".
> Over 6.5 liters of displacement is possible with Adire's XBL2
> technology (Sd=1210 cm2, Xmax= 27mm). The recommended enclosure is a
> ported cube 32" square (20 cubic feet). Would you still need three of
> them to get the same displacement/SPL as the above IB?

A sealed box uses only the air displaced by one side of the cone. The air on
the other side is trapped inside the sealed box.

< If so, this would cost about $500 more and you'd have three largish boxes
in the
> room instead of just a hole in the ceiling. Of course, some might
> prefer boxes to making holes ;) 

In some cases the holes in the ceiling or floor are not feasible.

> How hard is it to calculate power compression in a box sub?

I think that would be something you'd want to measure.

> Since the
> IB drivers are operating free air and multiple drivers are used the
> power requirements are usually very low.

Most power is wasted in the driver.

> With eight drivers you get a
> gain of 9 dB...so 80 watts will get you to 120dB vs 650 watts for a
> single driver (ignoring excursion limits and power compression).
Anonymous
a b \ Driver
January 7, 2005 5:18:11 AM

Archived from groups: rec.audio.tech (More info?)

"Rusty B." <rustybx@knology.net> wrote in message
news:1105005233.149866.229360@z14g2000cwz.googlegroups.com...
> > As an aside, I continue to be amused at the "specmanship" of speakers
> > makers for car audio / home theatre. Eg Cerwin Vega quotes SPL "at
> > 1W/1m", then in the fine print defines 1W at 2.83Vrms, even into a 4
> > ohm driver.
>
> Agreed. No one I know uses CV for serious audio.

But nearly everyone uses 2.83V as the test level for 4 ohm speakers though!

MrT.
Anonymous
a b \ Driver
January 7, 2005 7:25:26 AM

Archived from groups: rec.audio.tech (More info?)

Arny Krueger wrote:
> Under certain conditions, particularly with bandpass enclosures.
>
> The trick is to try to take advantage of air displaced on
> both sides of the cone.
>
> A vented box does that to a limited degree, and a bandpass
> enclosure goes further.

Mo, it does not. This is a common myth, that somehow the air on
the rear of the cone increases the efficiency of reflex systems
because the rear radiation "enhances" the efficiency. It might
be intuitively correct, but it's wrong nonethless.

The reason a given reflex system with the same bandwidth and
enclosure volme CAN be more efficient is because the driver
itself is more efficient. That efficiency comes as a result
of using a motor assembly that's more efficienct. If the box
was sealed, that stronger motor assembly would result in the
same increase in efficiency at the expense of a significantly
overdamped system and the associated reduction in bass output
at and around resonance. The repesence of the port turns the
system into a 4th order resonant system. The effect is to, at
and around resonance, the output of the enclosure/port portion
of the system REPLACES the output of the direct radiation from
the front of the driver. It DOES NOT SUPPLANT it, it REPLACES
it.

Similarly, in bandpass systems, you're essentially building
a narrow-band resonant tuned system and simply depending upon
the gain of the system at resonance. Look at the efficiency
of a 4th order bandpass system as a function of resonance:
as the bandwidth gets narrower, the efficiency gets higher, and
at a narrow enough bandwidth, can exceed that of the driver's
free-air reference efficiency. Now, explain how taking advantage
of the air displaced on the rear side of the cone improves
efficiency when, in such a system, the enclosure on the rear side
of the cone is sealed from the outside world.

Reflex systems are more efficienct precisely because the DRIVERS
are more efficient, NOT because you stuck a hole in the box.
January 7, 2005 10:09:32 AM

Archived from groups: rec.audio.tech (More info?)

On Fri, 7 Jan 2005 02:18:11 +1100, "Mr. T" <mrt@home> wrote:

>
>"Rusty B." <rustybx@knology.net> wrote in message
>news:1105005233.149866.229360@z14g2000cwz.googlegroups.com...
>> > As an aside, I continue to be amused at the "specmanship" of speakers
>> > makers for car audio / home theatre. Eg Cerwin Vega quotes SPL "at
>> > 1W/1m", then in the fine print defines 1W at 2.83Vrms, even into a 4
>> > ohm driver.
>>
>> Agreed. No one I know uses CV for serious audio.
>
>But nearly everyone uses 2.83V as the test level for 4 ohm speakers though!

But most have the honesty to call it 2.83V rather than 1W.

Tony (remove the "_" to reply by email)
Anonymous
a b \ Driver
January 7, 2005 5:21:13 PM

Archived from groups: rec.audio.tech (More info?)

<dpierce@cartchunk.org> wrote in message
news:1105100725.971484.73800@f14g2000cwb.googlegroups.com
> Arny Krueger wrote:
>> Under certain conditions, particularly with bandpass enclosures.
>>
>> The trick is to try to take advantage of air displaced on
>> both sides of the cone.
>>
>> A vented box does that to a limited degree, and a bandpass
>> enclosure goes further.
>
> Mo, it does not. This is a common myth, that somehow the air on
> the rear of the cone increases the efficiency of reflex systems
> because the rear radiation "enhances" the efficiency. It might
> be intuitively correct, but it's wrong nonethless.
>
> The reason a given reflex system with the same bandwidth and
> enclosure volme CAN be more efficient is because the driver
> itself is more efficient. That efficiency comes as a result
> of using a motor assembly that's more efficienct. If the box
> was sealed, that stronger motor assembly would result in the
> same increase in efficiency at the expense of a significantly
> overdamped system and the associated reduction in bass output
> at and around resonance. The repesence of the port turns the
> system into a 4th order resonant system. The effect is to, at
> and around resonance, the output of the enclosure/port portion
> of the system REPLACES the output of the direct radiation from
> the front of the driver. It DOES NOT SUPPLANT it, it REPLACES
> it.
>
> Similarly, in bandpass systems, you're essentially building
> a narrow-band resonant tuned system and simply depending upon
> the gain of the system at resonance. Look at the efficiency
> of a 4th order bandpass system as a function of resonance:
> as the bandwidth gets narrower, the efficiency gets higher, and
> at a narrow enough bandwidth, can exceed that of the driver's
> free-air reference efficiency. Now, explain how taking advantage
> of the air displaced on the rear side of the cone improves
> efficiency when, in such a system, the enclosure on the rear side
> of the cone is sealed from the outside world.
>
> Reflex systems are more efficienct precisely because the DRIVERS
> are more efficient, NOT because you stuck a hole in the box.

Thnks for the correction.
Anonymous
a b \ Driver
January 7, 2005 6:58:50 PM

Archived from groups: rec.audio.tech (More info?)

"Tony" <tony_roe@tpg.com.au> wrote in message
news:27art0lqkva6fgln67lsgjgc5kl7iag56c@4ax.com...
> >> Agreed. No one I know uses CV for serious audio.
> >
> >But nearly everyone uses 2.83V as the test level for 4 ohm speakers
though!
>
> But most have the honesty to call it 2.83V rather than 1W.

Actually many don't, and don't even list it in the fine print!
IME this is slowly changing as 4 ohm speakers become the norm.

It's a bit like Hard Drive manufacturers calling 1000*1000*1000 bytes, a
gigbyte. It all started to decieve, now they all have to do it, but most
tell you that.

The fact is you can still cheat just as much with speaker sensitivity, by
using narrow band test signals at the most efficient frequency. Most don't
tell you what they use. I have even seen specs for 0.5 Metre, to make the
figure larger. It's not what measurement conditions they use though that is
the problem, it's what they don't tell you.

MrT.
Anonymous
a b \ Driver
January 7, 2005 10:25:35 PM

Archived from groups: rec.audio.tech (More info?)

> Mo, it does not. This is a common myth, that somehow the
> air on the rear of the cone increases the efficiency of
> reflex systems because the rear radiation "enhances" the
> efficiency. It might be intuitively correct, but it's
> wrong nonethless.

If I understand this correctly the often quoted saying "there's no
replacement for displacement" is true.

So, for the same frequency response and SPL a box sub would need just
as much displacement as an IB.
January 8, 2005 1:01:11 PM

Archived from groups: rec.audio.tech (More info?)

On 7 Jan 2005 04:25:26 -0800, dpierce@cartchunk.org wrote:

>Arny Krueger wrote:
>> Under certain conditions, particularly with bandpass enclosures.
>>
>> The trick is to try to take advantage of air displaced on
>> both sides of the cone.
>>
>> A vented box does that to a limited degree, and a bandpass
>> enclosure goes further.
>
>Mo, it does not. This is a common myth, that somehow the air on
>the rear of the cone increases the efficiency of reflex systems
>because the rear radiation "enhances" the efficiency. It might
>be intuitively correct, but it's wrong nonethless.

Any crossover, whether passive electrical, active electrical or
mechanical, has a finite crossover region in which both outputs
contribute to the final signal. A reflex box is a mechanical
crossover, and it DOES take advantage of air displaced on both sides
of the cone - one side for higher frequencies, the other for low
frequencies, and both in the crossover region (their respective
contribution always add vectorially, mostly constructively in the
crossover and resonant regions).

>The reason a given reflex system with the same bandwidth and
>enclosure volme CAN be more efficient is because the driver
>itself is more efficient. That efficiency comes as a result
>of using a motor assembly that's more efficienct.<snip>

Any given required combination of volume and bandwidth will require
specific driver parameters for each enclosure type/sub-type, and each
such driver will produce a specific efficiency (you don't get to
choose it independently); depending on how you integrate it, the total
overall efficiency from DC upwards probably doesn't vary much with
enclosure type. But sacrificing the extreme low frequency end, damping
and Q CAN allow higher efficiency in the passband for a given
bandwidth and volume, because the required driver parameters dictate
higher efficiency. So for the same volume and bandwidth, in this
respect a high Q design will have higher efficiency than a low Q
design, and 6th order bandpass beats reflex, which beats sealed.

Dick, I know your post was intended to explain that it is the driver,
not the enclosure that determines the efficiency; of course it does.
But I interpreted Arny's previous post to be more to do with the
potential "figure of merit" (efficiency/volume/bandwidth) of each
enclosure type; in no case can driver efficiency be chosen
independently.

Tony (remove the "_" to reply by email)
!