This is a recipe to construct some very simple diy speaker cables. I use these cables with my DIY Hi-Vi 3-Way Speakers. The following materials were used for these simple DIY Speaker Cables:

The materials for this project are available from Parts Express. Add banana plugs or spades of your choice to terminate the wires.

Photograph 01: Parts for DIY Speaker Cables

Photograph 02 below shows a test weave for the speaker cables. The idea here was to use multiple 16 gauge wires to lower resistance. Weaving the wires helps reduces asymmetrical field interactions since the wires are not on either the inside or outside of the cable more than any other wire.

Photograph 02: Test Weave of Speaker Wires

Once I was happy with the test weaves, I put together a short Test Speaker Cable.

Photograph 03: Short Test Speaker Cable

The pictures below show the final speaker cables.

Photograph 04: Simple Home Made Speaker Cable

Photograph 05: DIY Speaker Cable

The speaker stands is probably one of the most unappreciated item in a hifi setup. I would like to propose a probably outlandish idea to most audiophiles- that the speaker stand is more important than speaker it supports. This is an extreme thought but I feel that it is not that far from the truth.
Perhaps this truth would become clearer if some of the primary principles of speaker supports are discussed. The sole purpose of a speaker stand is to control the flow of vibrations away from the speaker.
Holding the speaker at the optimum height is the commonly accepted mundane, purpose of the stand. Notice that the keyword is “control”. In my own experience , I have found that attempting to suppress vibration by putting weights on top of the speaker, damping or clamping is a fruitless exercise. Vibration is like the other irrepressible force in nature – water. It seeks always to flow to the lowest point. Trying to stop vibration is like trying to stop a leak in a dam. Like water it will find another way to get through and often do it in a way we least expect and usually with dire consequences. I have found that suppressing vibrations in a speaker cabinet may apparently improve performance in such hifi parameters as tighter bass, better focusing , wider and deeper soundstage, etc. But without fail , I would notice that it has become less satisfying musically.

On the other hand , if the stand is ineffective in directing this flow of vibration away from the speaker it is supporting, the speaker can be overwhelm by the vibrations thrown up by the woofer. The speaker is left to cook in its own juice in a manner of speaking. This results in a boomy ,muddy, incoherent and smeared sound.

What makes a good speaker stands and why do they cost so much?

Maybe its better to look at the flipside. What makes a bad speaker stand? Maybe there isn’t any. Again ,the picture of matching comes in. A speaker stand that sounds bad with a particular pair of speakers may work wonders with another pair of speakers. The reason for this is simple. It all has to do with how efficient the stands can drain away the vibrations created by the workings of the woofers. If your sound system is muddy-sounding, lacking in focus and booms- your speaker stands could be at fault. If the stands are solid ,of high quality and expensive, and your system still sound this way ,it could be due to misuse because of a poor understanding of how the stands work.

If your speaker stand is one of those cheap, lightweight affair and thus not too efficient at the transfer of energy, the speaker it is supporting tends to trap the vibrations in the speaker’s cabinet creating that boomy and muddy sound. This is especially so if your speakers are of moderate quality where the cabinet construction are often lightweight. This problem affects not only the bass but also smear the highs as well. The tweeter produces frequencies whose wavelengths are in the regions of microns. If the entire tweeter itself is vibrating due to the woofer ,it will not be able to recreate those fine , delicate high frequencies properly. This situation is similar to the common experience of trying to read in a moving vehicle. The attempt will most likely give you a headache unless if you ride in a Rolls-Royce.

If your speaker stands are supposed to be the Rolls-Royce of stands and your system still sounds muddy , then maybe you are not using them properly. Maybe you have stuck blu-tack or some other soft compound under the speakers. Or instead of hard spikes on the base of the stands, you have replaced them with something that’s not so unfriendly towards your expensive floor. Most likely something soft again. Using a soft, dead material between the speaker and the stands, or between the base of the stands and the floor results in decoupling. This impedes the efficient transfer of vibration energy from the speaker to earth , which provides an infinite mass to absorb such disturbances. Replace these with some hard cones such as ceramics, hardened steel, crystals or tungsten carbide bits. Cones commonly make from aluminum, brass or mild steel are not really hard but are still better then blu-tack or rubber feet for the job of maximal coupling.

In certain situations, a “bad” speaker stand may actually sound better than a high pedigree unit. I can see this happening in some hifi system where the equipment have a tendency to sound thin, bright and without much bass weight. If the stands are too efficient at draining away vibrations away from the speakers, they may exaggerate the problem. Thus it may be a good idea to use blu-tack, rubber feet, sorbothane or some other soft compound to decouple the speaker from the stand. Personally I do not see this as a long term solution to such a problem because the speakers will never get a chance to sound their best.

To sum up the discussion so far, a pair of speakers sounds best on stands that drain away just enough vibrations. Not removing enough results in the system sounding muddy and boomy. Remove too much and the sound becomes overly tight, lean and less musical. The audiophile’s best bet is to buy the best pair of stands he can afford, that is one that is extremely efficient in removing vibrations, at the risk of making the speaker sounding lightweight. Then it is relatively easy to tune the efficiency of the stands down to a point where it matches the speakers. Whereas it is much harder to improve the efficiency of a poorly made stand.

Tip: How do you tell whether your present speaker stands are doing a proper job.

Play a piece of music with very strong bass. Place your hand very lightly on the speaker’s side which has the most vibrations. Place the same hand on the middle of speaker stand’s pillar. Compare the vibrations that you feel. You may have to do this several times to have an accurate assessment.

If the vibrations on the speaker is stronger then that on the stand. Your stand is not too good at its job. If the vibration feels about the same, your stand is doing a decent job. If the vibrations are stronger on the stands then on the speakers, you have one hell of a stand.

The next update will touch on how to recognize a well made pair of stands

Characteristics of a good , conventional speaker stands

The general perception is that a good speaker stand must be heavy and well damped so that it does not ring . Less well known is that the type and grade of metal used affects its performance. Which is why some stands cost a lot more than others. Other less obvious characteristic would be the effectiveness of the design in removing vibration from the
speakers. For example the flatness of the top plate. All the stands I have used in the past fail this point. Place a speaker on a stand and it will be rocking away. Hook up the speaker cable and see your speaker do a twist to face away from your listening position. The only solution would be to place blu-tack or three cones under the speaker to stabilize it. A flat top plate ensures maximal coupling of the speaker. A good stand is thus able to efficiently remove vibrations from the speaker and sink this into the stand itself, which thus has to be heavy.

This speaker was one of the speakers I have demonstrated at the VSAC 97. It has around 90dB of efficiency with a very, very easy input impedance.

I believe that the very best performance with SE amplifiers can only happen when the whole system of amplifier, output transformer, speaker driver and box is very well matched. This requires the loudspeaker be designed for that particular amplifier, or less frequently, the other way around. This includes taking in account the amp output impedance, distortion levels, the transformer primary inductance and who knows how many other interrelated things! This may explain why most of the time it is more effective (and a lot more fun!) to let past experience, some intuition and mostly the ear do the whole job and find this correct match. After all, the ear must be the final judge

But although this speaker was designed to be used with my amplifier it should work very well with most typical SE amplifiers. The bass alignment is targeted for amplifiers with an output impedance of 3.0 ohms, and it will work well with amps with Zout in the range of 2.0 to 4.0 Ohms. At the frequency range this speaker is expected to reproduce, any primary inductance bigger than 10H (for a 3K primary impedance) will work well. This means you may use good quality small transformers and get good sound. This speaker was designed according to some ideas that are presented in Glass Audio (3/97 and 6/97) and that were the subject of my seminar at the VSAC 97. For its size and efficiency you will have surprisingly deep and controlled bass when used with a typical SE amp.

THE BOX

The box is very simple. It can be made with MDF. I have used 5/8″ all around and 3/4″ for the fascia. This fascia should have rounded sides. After some tests I found these materials just right for this box size, with no need to further bracing. If you want to try, thicker materials and bracing may be used. Remember to keep the internal volume constant. If you decide to use thicker materials please change only the depth of the box. The frontal dimensions should remain the same. The box should be lined with 1″ foam of low density in all sides except the front baffle. Of course you can also experiment with this until you get the best results. The duct should be made of a 5cm (2″) curved PVC tube about 18cm (7″) long. It must be a curved duct otherwise it will not fit. Using a smaller diameter will allow you to use a straight tube. This will work but it is not the ideal. Always keep the duct as free as possible. Do not allow the foam to block the area close to the duct.

THE DRIVERS

I have seen no projects with the Audax HM130X0, but this speaker with a TPX cone is a remarkable mid/woofer for our application. It has a very smooth mid range and just the right parameters to be used with high output impedance amplifiers. It probably has not been used frequently because the calculated ideal box for commom low Zout amplifiers will be ridiculously small and the speaker could only be used as a mid range. But this driver has the Xmax and power handling to be used as a small woofer. The Seas T25-001, with its silver coil and very good subjective sound was my choice for the tweeter. It has complemented the Audax in a seamless way. Although not cheap these are not terribly expensive units each one being around $60.

THE CROSSOVER

This is a mix of the minimalist approach with some impedance correction. The Audax unit is connected straight to the amp.. The impedance correction network keeps the impedance curve in the mids and highs very smooth.with 8 ohms being just about the average. The measured frequency response is really very flat being within ± 2.5 dB at most of the range.

I have used no diffraction compensation in the crossover. This makes this speaker sound better placed closer to the rear wall, as it is expected to sit in a small room. The best position is something that only experimenting in your own surroundings can determine. I should also recommend that you put them on 24″ to 28″ stands placing the point halfway between tweeter and the woofer at ear level. This is not very critical, but certainly helps. The frequency curve shows the response from 400Hz up, without any smoothig. This response changes very little with high output impedance amps. At frequencies below 400Hz the response is affected by measurement setup limitations and by the value of the output impedance of the test amplifier.

CONCLUSION

I believe you should built this speaker with all the normal care that high performance equipment begs for. The drivers and crossover components should be very well fixed. The cabinet should be very well made and the drivers should be mounted flush with the front surface.

I should say that this speaker is intended to be used with high output impedance amplifiers and that it will be bass shy with the average transistor amplifier or tube amps using lots of negative voltage feedback.

I hope you try this little speaker. It has been the source of a lot of great listening for me and I believe it fulfills its intent very well.

(c) 1997 Electronic Tonalities/VALVE and Eduardo B. E. de LimaOne pair of these loudspeakers may be built by the reader for non
commercial purposes only. No parts of this article may be reproduced
without permission.

WARNING: The Audax HM130X0 has been discontinued and is not
avaiable anymore. The HM130Z0 has been suggested as a
substitute but requires a different crossover and other changes. We
intent to make the plans for a revised version avaiable whenever it
is ready.

Eduardo B. E. de Lima
(VALVE 12/97)

At that time, Dolby Labs leased Peter Scheiber’s patent for use in theaters. Dolby claimed it was theirs, but still pays royalties to Mr. Scheiber. Their audio matrix scheme at that time provide minimal channel steering, resulting in bleeding of audio from front to rear, and minimal separation.

Now enters a man named Jack Cashin. He also leased Mr. Scheiber’s patent and provided royalties. However, Mr. Cashin’s sound matrix provide excellent steering as well as a huge increase in channel separation.Utra Stereo Labs was founded by Mr. Cashin. Ultra’s first movie was Robert Altman’s ‘Nashvile’. This process was demonstrated for the Academy of motion pictures. It was so well received that Mr. Cashin was awarded an Academy Award for technical achievement in 1984.

After that, Dolby Labs started using the same steering scheme as Jack Cashin, called it their own, and it is what is currently used in theaters world wide. Once again, Dolby Labs provides a great contribution to the current status of motion picture audio, as well as home theater. But they did not invent surround sound.

Both Dolby Labs and Ultra Stereo’s theater equipment is THX approved.

To my knowledge, Ultra Stereo labs does not yet have a WEB site. Check the videos you rent and the marquee at the theater, and I am sure you will spot them from time to time.

by Steve Weiss

What you need is a sine wave generator with reasonably low distortion
(<1%), as flat frequency response as possible, and good, stable frequency.
You’ll need an AC voltmeter that is also flat over the indented range and
has the needed sensitivity. A frequency counter is also useful, since the
frequency calibration of most oscillators is pretty awful. You’ll need an
accurate means of measuring DC resistance as well. Add to that a precision
8-10 ohm resistor for calibration purposes, and a 1 kOhm resistor to turn
your frequency generator into a virtual current source.

Here’s how to proceed:

• Using either an 8 ohm precision resistor (or accurately measuring
  the resistance of the “calibration” resistor), turn your
  generator/AC voltmeter into an impedometer by driving the
  calibrated resistor from the generator through the 1 kOhm resistor,
  and adjust the output of the generator until you get a convenient
  voltage across the resistor. For example, if the calibration
  resistor is 8 ohms, you might adjust the output so that you
  measure 8 mV across it.
  Basically you make the current 1 mA so that on the mV scale on your
  voltmeter the reading is effectively both mV and Ohms.
  Your setup will look like this:

                     o---- 1kOhm -----+<-------+
                     |                |        |
                   Sine gen.       8 ohms   AC voltmeter
                     |                |        |
                     o----------------+<-------+

  This circuit is called an impedometer,
  where the voltage across the load is proportional to the impedance of the
  load. The 1 kohm resistor turns the oscillator into a pretty good
  approximation of constant-current source.

• Measure the DC resistance of the driver to test. This gives you Re. [Let's say it's 6.5 ohms]
• Replace the calibration resistor with the driver to test. Do not change the voltage from the generator!
• Adjust the frequency in the region of the specified resonance until
  the voltage across the driver is at a MAXIMUM. Record the frequency.
  This is Fs, the resonant frequency [let's say it's 32 Hz]. Also,
  measure the voltage across the driver. This is defined by Re+Res.
  [let's say voltage is 42 mV which means Re+Res is 42 ohms].(using an oscilloscope set for phase measurement, Fs will also be
  where the phase is 0).
• Calculate the ratio between the DC resistance (Re) and the maximum
  impedance (Re+Res), call it Rc. [In this case, it will be 42/6.5 or
  6.46]
• Find the two frequencies on either side of the resonant frequency
  f1 and f2 where the impedance is Re * sqrt(Rc) [in this example, that
  impedance will be 6.5 * sqrt(6.46) = 16.5 ohms, and let's say that
  occurs at f1 = 22.6 Hz and f2 = 45.3 Hz].
• Calculate Qms as:

                       Fs sqrt(Rc)
                  Qms = -----------
                          f2 - f1 
  
  [in the example, it will be: 
  
                         32 sqrt(6.46)      32 * 2.54      81.3
                  Qms = -------------  =  -----------  =  ----  =  3.58
                         45.3 - 22.6          22.7        22.7 
  

• Calculate Qes as:

                         Qms
                  Qes = --------
                        (Rc - 1) 
  
  [in this example, it will be: 
  
                        3.58         3.58
                  Qes = ---------  =  ------  =  0.66
                        6.46 - 1       5.46 
  

• Calculate Qts as:

                       Qes * Qms
                  Qts = ---------
                        Qes + Qms 
  
  [here, it would be: 
  
                        0.66 * 3.58      2.36
                  Qts = -----------  =  ------  =  0.56
                        0.66 + 3.58      4.24 
  

So, you have derived Fs, Res, Qms, Qes, Qts for the driver.

• Repeat the measurements in a sealed, leak-free, unlined test box, and
  determine the equivalent values of Fc, Qmc, Qec, and Qtc (use a box
  whose volume, Vb, is close to the expected Vas for maximum accuracy).
  [In our example, Vb = 20L, Fc = 80 Hz, Qec = 0.95]
• calculate Vas as follows:

                            Fc Qec
                 Vas = Vb [ -------- - 1 ]
                             Fs Qes 
  
  [In our example: 
  
                             80 * 0.95                76
                 Vas = 20 [ ----------- - 1 ] = 20 [ ---- - 1 ] = 20 * 2.62 = 52L
                             32 * 0.66                21 
  
  Our Vas is 52 liters]. 
  

You now have Fs, Re, Qms, Qes, Qts and Vas.

Information sources

The information in this article is mainly based on news articles from Dick
Pierce posted to rec.audio.pro newsgroup at 1998.

• Voice coil’s electrical impedance (resistance, inductance, stray capacitance)
• Driver’s mechanical impedance (stiffness, mass, damping)
• Driver’s acoustic radiation impedance (resistance, reactance)

Spaker nominal impedance

There is a convention to the use of the term “nominal impedance”, and if
the impedance over the majority of the bandwidth, specifically covering
the range in spectrum where majority of the musical spectral power occurs,
it’s 8 ohms. A single number cannot tell all there is to tell about an
impedance that varies with frequency.
You must keep in mind that ‘nominal impedacnce’ is not defined
in IEC. Indeed, the electronics industry was advised when the Trade
Descriptions Act was introduced, that the word ‘nominal’ should no
longer be used in specifications. That is why the IEC concept of ‘rated
value’ is so useful. There is a very detailed definition and explanation
of this term in IEC60268-2.
The IEC standard (IEC60268-3) allows any
“increase” above the rated value, but limits the “decrease”.
The standard does not allow the impedance to fall below the 80 %
of the nominal value at any frequency, including DC.

Practical case

In practice all loudspeakers are a compromise, the designer is therefore
free to allow the speaker to suck more power from the amp in order to optimise
other parameters. Most high-quality loudspeakers do dip well below
80% of their nominal impedance at one or more points in the audio
band. Speakers which attempt to present a flat impedance load using
conjugate techniques have sometimes been described as ‘flat and
boring’, which may or may not be connected to their excessively
complex crossovers. Speaker design is non-trivial!

Remeber that a specification is only of relevance when a product is claimed
to meet it. A specification is only of value when it lays down a minimum
standard which is of relevance to the intended purpose of the product.
A high-quality speaker may reasonably be assumed to be intended to be
driven by a high quality amplifier, hence minimum impedance is not an
important criterion in establishing sonic performance.

Measuring speaker nominal impedance

If you just want to find out the nominal impedence of the speaker e.g. ist
it 4, 8 or 15 ohms then there is a rough & ready way.
Just use your multimeter to measure the DC resistance of the voice coil i.e.
across the speaker terminals (with nothing else connected) and multiply the
answer by 1.3. So if the DC resistance is say 6 ohms then the speaker is nominally 8 ohm impedance.
More complete analysis with minimal equipments:

• a) Measure the DC resistance across the voice coil with the driver
  disconnected. The ohm value you get, is the lower impedance bound of
  the driver. Add an ohm or two to this value, and you should be at the
  nominal (rated) impedance of the driver.
• b) Connect a pot in series with the driver voice coil and then to the
  amp.
• c) Connect frequency generator or CD player with suitable test CD in
  it to the amp input, and start walking up the frequency scale in
  steps. For each step, measure the voltage
  across the voice coil terminals and then across the pot. Adjust the
  pot until both voltages match. Now shut down the amp. and measure the
  resistance across the pot. This is the driver impedance for the
  current drive frequency.

This approach is not the most accurate, but it needs minimal set of
measuring equipments: multimeter, signal generator and a potentiometer
of 50 ohms 5-10 watt. The clear advantage of this approach is that the
accuracy of the measurement is not affected by the multimeter frequency
response (their AC range is designed to show right values at around 50 Hz
range and at higher frequencies the accuracy can drop noticably depensing
on the meter construction, but this does not affect in this measurement
because the absolutely correct AC voltage values are not needed).
Warning, KEEP DRIVE LEVELS TO SPEAKER VERY LOW. High levels of
sustained sine wave can up the driver voice coil.

Speaker model

The single most dominant branch of the model is the voice coil DC
resistance, Re. It’s going to be in series with everything else we will
look at (you mentioned “stray capacitance”. Yes, there is some, but it’s
magnitude is absolutely miniscule compared to all other components so it
can be ignored).
Next we have the voice coil inductance (we’ll call it Lvc). Now, it, too,
is in series with everything else, but it’s no simple inductance.
So far, we have the two real electrical components, and they look like:

   o-----Re------Lvc----o

Now, the next major set of components are the electrical equivalents of
the major mechanical components of suspension compliance, cone mass and
suspension losses. The suspension compliance is modelled as an inductor,
Lces. The cone mass is modelled as a capacitance, Cmes, and the
suspension losses are modeled as a resistor, Res. These three are in
parallel and form a damped, parallel resonant branch called the drivere
mechanical branch.

Finally, in series with that, is the radiation impedance. No single
lumped-parameter synthesis comes close to approximating this.
Also the magnitude of the impedance of this branch is small
compared to the others, so for simulating the ELECTRICAL characteristics,
it can be safely eliminated.
The driver electrical model, then, looks like this:

     o------Re------Lvc------+   

                             |   

                      +------+------+   

                      |      |      |   

                    Lces   Cmes    Res   

                      |      |      |   

                      +------+------+   

                             |   

                            Xrs   

                             |   

     o-----------------------+

Now, the relative values of these components depends upon the magnitudes
of the physical values times a transformation factor. That transformation
factor is the electromagnteic transduction factor, proportional to the Bl
product (the product of the length of the wire l immersed in the magnetic
field B), measured in N/A (or T/M, if you will). So, IF we know the
magnitudes of the physical components, we can easily calculate their
electrical equivalents:

     Re -   don't calculate it, just measure it with a good ohmmeter!    Lvc -  measure it, but see below!Lces - depends upon the suspension compliance:   

                              2   

               Lces = Cms (Bl)   

where Cms is the mechanical compliance in m/N, and the resulting   

            inductance is in henries.   

Cmes - depends upon the cone mass:   

                              2   

               Cmes = Mms/(Bl)   

where Mms is the mechanical compliance in kg, and the resulting   

            capacitance is in farads   

Res -  depends upon the suspension losses:   

                         2   

               Res = (Bl) /Rms   

where Rms is the mechanical losses in 1/s, and the resulting   

            resistance is in ohms.   

Xrs - depends upon the air, the driver diameter, the baffle dimen-   

            sions, position of the driver on the baffle, etc., but has   

            little effect on the electrical impedance.

Typical characteristics

For example, a typical 8″ woofer with an Fs=30 Hz, Vas=60L, Qms=2.40,
Qes=0.42, Qts=0.36, Re=6.25 ohms, might have the following mechanical
parameters:

                      -3   

       Cms = 1.01 x 10  m/N,   

                      -3   

       Mms = 27.9 x 10  kg,   

       Rms = 2.19 kg/s   

       Bl = 8.84 N/A

Then, the electrical equivalents would be:

       Lces =  78.9 mH   

       Cmes = 356 uF   

       Res  =  35.7 ohms   

       Re   =   6.25 ohms

Effect of enclosure

One can construct a similar branch for the enclosure, using the lumped
parameters of a capacitive equivalent Cmep for the port mass Mmp, amd
inductive equivalent Lceb for the enclosure compliance Cmb a resistive
equivalent Reb for the system losses Rmb and the port radiation impedance
Xrp (which is, again, small). That branch looks like:

        o------+   

               |   

              Lceb   

               |   

              Cmep   

               |   

              Rmb   

               |   

              Xrp   

               |   

        o------+

The complete driver+enclosure+electrical model looks like:

     o------Re------Lvc------+------------+   

                             |            |   

                      +------+------+    Lceb   

                      |      |      |     |   

                    Lces   Cmes    Res   Cmep   

                      |      |      |     |   

                      +------+------+    Reb   

                             |            |   

                            Xrs          Xrp   

                             |            |   

     o-----------------------+------------+

Now there are some other complicating elements that would make for a
complete mechanical and acoustical model, such as the mutual coupling of
the driver and port, etc., but for the electrical model
the above suffices quite well for predicting reality.

Typical impedance characteristics of speaker element at different frequencies

Let’s look at the impedance of a very typical driver. It has the following
characteristics:

• At DC, the impedance is completely dominated by the DC resistance of the voice coil
• As you increase in frequency towards the fundamantal mechanical
  resonance, the reflected motional impedance begins to dominate
  and is inductive in nature. However, the total phase angle of the
  impedance RARELY exceeds 45 degrees and thus the resistive and
  reactive (inductive) parts of the impedance are just about equal.
• At fundamental resonance, the impedance is purely resistive, its
  phase angle is 0, and is determined by the effective series
  combination of the voice coil DC resistance and the reflected
  mechanical losses of (primarily) the suspension (Re + Res in
  standard Thiele/Small notation).
• Above fundamental resonance, the impedancs drops, has a negative
  phase angle (rarely exceeding 45 degrees) and is, surprise,
  capacitive in nature. The impedance drops until…
• In the midrange, it approaches the DC resistance of the voice coil
  it is SLIGHTLY higher than that DC resistance for a variety of
  reasons, typically about 10-20% (and THIS is the region that is used
  by MOST reasonably responsible manufacturers for specifying the
  nominal impedance). The impedance at these frequencies is
  predominantly resistive in nature and is dominated by the DC
  resistance of the voice coil.
• Above this region, the inductance of the voice coil begins to
  influence the impedance. However, it NEVER becomes purely inductive,
  or even remotely close. First, over the majority of the range of
  operation, the voice coil resistance still dominates. Second, eddy
  current losses in the pole piece (see Vaderkooy, et al) dominate
  quickly, such that the phase angle of the impedance asymtotically
  approaches about 45 degrees, and NEVER 90 degrees, which would be
  necessary if your assertioon that the impedance was almost a pure
  inductance were true.

Inmpedance of a speaker IS
NOT ALMOST A PURE INDUCTANCE. It is NOWHERE NEAR a pure inductance.
The impedance of a speaker is only a rough average of the impedance and
that the the voice coil dc resistance of most normal cone type dynamic
speaker is roughly 75% of its “rated” impedance as the industry rates
impedance. Most 8 ohm speakers will measure somewhere around 6+ ohms dc
give or take a bit. (When horn loaded, the impedance increases).

Impedance and effiency

Let’s look at the following situation:
Take an 8 ohm speaker and wind twice the length of wire onto
the voice coil. The resistance woul go up, for sure, but because there is
no more wire in thegap, the electromagnetic couping coefficient, the Bl
product, would also go up. And you would have, as a result, a 16 ohm
speaker with essentially the same efficiency as the 8 ohm speaker, all
other things being equal.
Or you could design a speaker with both a higher impedance (longer wire in
the voice coil) AND a larger magnet assembly with higher flux density in
the gap and get a higher impedance driver with higher electro-acoustic
efficiency.
Or you could design a higher impedance driver with a stronger magnet and a
lighter cone and get even more efficiency.
The point is, the rated impedance IS NOT the same as the efficiency, nor
is there any direct correlation between the two. Efficiency of a given
direct readiator driver is determined by the folowing relationship:

                   2  2   

                  B  l   

     n0 = k * ------------   

                    2    2   

               Re Sd  Mas

where

• k is a constant determined by the properties of air
• B is the magnetic flux density in the gap
• l is the length of wire in the magnetic field
• Re is the DC resistance
• Sd is the radiating area of the cone
• Mas is the effective total moving acoustical mass of the driver.

So, we can see that by doubling the length of the wire that’s in the gap
(doubling l) will, by itself, increase the efficiency by a factor of 4,
but since Re also doubles, it drops it by half, meaning that, all other
things being equal, lengthening the voice coil winding in the gap
increases BOTH impedance AND efficiency. Now, there ARE tradeoffs, and
everything CAN’T be equal. Lengthening the wire ALSO increases the mass,
though the voice coil is only part of a larger mass (it includes the
vouice coil former, the cone, and so on) so there is not a direct
relation. Also, the gap may need to be widened to accomadte the greater
winding diameter of the voice coil, and that may reduce B.
Add resistance certainly reduces efficiency all by itself. You could, for
example, just simply solder a resistor in series and, lo and behold, the
impedance goes up and the efficiency goes down. But we already have a
case where the efficiency goes up as the impedance goes up.
You could wind the voice coil with the same length of finer gauge wire.
The result would be the imepdance goes up, and so does the restistance,
but since l remains about the same, l^2, remains the same and the
efficiency goes down. But wait!, finer wire means less mass, so we can
gain some efficiency back from that and the finer wire means a smaller
thickness to the voice coil, and the designer may be able to close up the
gapand increase B.
Or, the designer may just design a TOTALLY difference driver with a
different B, a different l, a different cone diameter (changes Sd), a
different moving mass and a different resistance and get something totally
different efficiency wise.

The point being is that a statement like “The higher the impedance, the lower
then efficiency,” as a generalization has NO basis in physical fact.