Papyrus, Wood and Paper Cones

A Comparison

 

The purpose of this diatribe is to show the effects of a few materials use in the manufacture of loudspeaker diaphragms.  They are in no way intended to say which is better although it can be argued that a speaker without spurious harmonics would reproduce the original signal faithfully.  However, unless one has been to a live performance, one has no idea how the original; sounded.  The same band making the same recording ion different studios will sound different because of the acoustics of the studio, even if the person at the mixing board utilized the same mix.  In short, it all boils down to an individual's preference.  It's all subjective.

One man's meat is another man's poison.

The first person who is known to have made a record of it is the English musician Thomas Whythorne in his Autobiography, circa 1576.   The whole story can be seen here.

 

 

A one second sweep (20-20khz0 at 1w 1m.  The response curve of the papyrus is very similar to that on the manufacturer's data sheet The data sheet for the wood cone may still be here.  The speaker has been discontinued.  The merchant can be found here.

Despite the similarity inn these two up to 2khz, they sound different due to their harmonics which are filtered out during the sweep which looks only at the amplitude of the fundamental.

Note also that despite the phase plug in the wood cone speaker, the papyrus cone speaker does very well up to about 17khz. and down to about 200hz, making it a damn good choice for a two way system.  This speaker is used in such a system using a 12" bass guitar speaker for the bass below 200hz.

Papyrus  Fig.1

Wood Fig.2

 

A comparison between a gated response made with LMS and the one second sweep made with CLIO.  It's the same image as the upper left. Papyrus cone.
Fig. 3

Fig. 4

 

 

Spectrum analyses of the papyrus cone and the wood cone units.  There doesn't appear to be much difference between some of them yet in others, the difference is quite pronounced.  These are the distortions that make one speaker sound different than another.  These distortions include harmonic distortions, even and odd and any fractional multiples of them.  These are usually caused by a phenomenon known as cone break-up.  What's happening is that many areas of the cone are vibrating at multiple frequencies and different amplitudes depending on the frequency applied and the varying density of the cone.  The spectrographs shown here show the components of distortion with one sine wave frequency applied.  With music, the signal is much more complex.  The picture shown here is probably an extreme condition, obtained by driving the speaker hard.  the spectrographs shown here are obtained with about 1w applied and the first component of distortion is around 30dB below the fundamental.  the much shorter lines are around 50dB or more below the fundamental.

 

The last pair of spectrographs, at 10khz, show a large difference.  Odd as this may seem, the papyrus speaker does well to around 17khz whereas the wood cone speaker falls fast after 6khz despite its having a phase plug.  There are several reasons for this. These four are given in order of importance, from high to low.  Voice coil inductance, Fhm; cone mass, Fhvc and front cavity compliance, Fhc, the last being inversely proportional to Vfc, the volume of air in the cone.  The last may be of no consequence because the cone volumes are very close to being equal, even though the papyrus is slightly larger.  Then there's beaming effect at high frequencies, the microphone is only one meter from the speaker and the phase plug may affect this.

It's worthy of mention that these responses of both speakers were measured with the speaker in the same sealed box, thus negating any effect from rear radiation.

Table 1 gives the T/S parameters of each unit.

The 10kHz spectrographs are interesting.  Despite the heavier cone and coil assembly, Mms1,  the papyrus cone still gives a higher frequency response. The lower voice coil inductance is a contributing factor as is the lower Rms2. (See figs 1 & 2 at the top of the page and footnotes 1 & 2 below)  

Now we come to the wood cone.  This spectrograph is very clean compared to the papyrus cone.  The grain of the wood is in one direction only.  In this direction, it will allow traverse waves to propagate but against the grain, this traverse wave is highly damped.  Also, the wood cone is stiffer than the papyrus or paper.  See the paper cone  spectrographs at the bottom of this page.  It would have been nice to align them with the papyrus & wood spectrographs but that would require smaller images, rendering them difficult to read.

Judging by the similarity of Figs3 and 4 and knowing the LMS has 4th order filters applied to the microphone input to eliminate the harmonics, it's safe to assume the CLIO uses similar filtering.  Therefore, the higher frequency response of the papyrus unit has nothing to do with harmonics.  

1  Mms  Mass of the cone and coil assembly including the air load.

2  Rms  Load imposed by the suspension, annulus and spider.  Expressed in kg/s, lb/s or mohms, mechanical ohms.

 

TABLE 1  Papyrus cone on left; wood cone on right

MR16P-8

PAPYRUS

MW7065-8

WOOD

35.16 Fs  Hz 44.68
6.3 Re  Ω 6.3
30.75 Vas  L 15.47
7.18 Qms 3.06
0.43 Qes 0.34
0.40 Qts 0.31
119 Sd  cm2 119
6.2 Xmax  mm 7
6.5 BL  NA - TM 9.12
0.41 Rms  Ωm 1.49
1.5551 Cms  mm/N 0.7847
13.1784 Mms  g 16.2
86.91 Sensitivity  dB 1w1m 88
0.16 L(1khz)  mH 0.24
0.06 L(10khz)  mH 0.10

 

 

Papyrus Wood
400hz

 

400hz

 

700hz

 

700hz

 

1200hz

 

1200hz

 

2000hz

 

2000hz

 

3000hz

 

3000hz

 

4000hz

 

4000hz

 

5000hz

 

5000hz

 

10000hz

 

10000hz

 

 

 

 

Treated paper cone  Dayton PS180-8

Now, here's a spectacular 7" point source speaker.  Can be seen here in detail

Despite the myriad of distortion components which are some 50dB below their fundamentals, these little guys sound incredible; they virtually disappear when playing and sound good even at levels around 95dB, depending on the music, of course.  A female vocal wouldn't sound realistic at that level unless she was a rock-a-billy gal.

These spectrographs show what was meant by traverse waves and cone break-up.  As for jazz, they'll place the clarinet, trombones, trumpets, sax and cymbals right into the room.  They are, IMHO, the closest thing to well designed horn loaded midrange and tweeter.

 

400hz

 

700hz

 

1200hz

 

2000hz

 

3000hz

 

4000hz

 

5000hz

10000hz

 

 

 

 

 

Impulse responses

Papyrus has lighter cone by 3g; better compliance; lower mechanical resistance (spider & annulus); lower cone mass; top plate 5mm   vc=11.2mm; less force factor BL by 0.5T

In view of the above noted parameters, the following results almost seem counterintuitive but consider the following.  First, the impulse signal is one half cycle at the specified frequency and at a level of about 20 watts driving the cone a few mm.  This will drive the cone in one direction like a plucked guitar string where the force applied to the string pulls it in one direction and it is released to oscillate.  The initial pull (pluck) is the longest, after which each succeeding oscillation is less than the previous, a damped oscillation.  The half cycle applied to the voice coil behaves the same way as can be seen by the initial vertical peak in each spectrograph with exception of the first, at 400hz.  It is possible the time base on the scope wasn't set correctly.  This method was used with a PICO Scope prior to acquisition of the CLIO, which does this easier and most likely, more accurately than my manual method.

The decay can be best seen from 2000hz and above; the irregular decaying oscillations at 500hz is not understood - yet.  The last three show a regular decay with  more oscillations as well as a higher initial peak in the wood cone.  This is attributed to the inverse or opposite of the above parameters despite the higher BL force if the wood cone speaker.  That higher mass, once set into motion, is harder to stop due to a higher momentum.  It's similar to a moving ship; it hard to set into motion and equally hard to stop.  A stronger power system will help as it does with the higher BL force of the wood cone motor.  In the case of the papyrus vs the wood, the lower cone mass and better compliance of the papyrus cone seem to be the major contributing factors for the faster decay of the impulse.

Despite all the above, none of that will tell anyone how it sounds or better yet, if one likes that which one hears.  The only way to make that determination is to listen to the music.  Many focus too much attention listening to the system and miss the music.

 

 

 

Papyrus Wood
100hz

 

100hz

 

500hz

 

500hz

 

2000hz

 

2000hz

 

3000hz

 

3000hz

 

4000hz

4000hz

 

 

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