Alpair 10, Outstanding Low-end Performance

Finally I have implemented a Markaudio Alpair 10V2 into my powered sub-woofer system for assisting low-end range of Alpair 6Ms, after tried two other conventional 13cm class woofers. Those woofers could never overcome or replace boosted bass generated from two Alpair 6Ms because I felt some unpleasantness in their sounds. Now, I’m completely satisfied with my desktop 2.1ch configuration (Alpair6M x2+Alpair10 x1) and have decided to finalize the development.

Current System Configuration

- Main System (ZAP)
   Driver: Alpair 6M, 2.5L sealed box/full damped
   Amp.:  NuForce Icon AMP (24W x 2) or
              Elekit TU-870R (6BM8 single, 2W x2)

- Subwoofer System (ZAP BASS)
   Driver: Alpair 10 V2, 4.0L sealed box/full damped
   Amp.: Dayton Audio plate amp. (100W x 1, with built-in low-pass filter)

In this article, I will demonstrate the outstanding low-end quality and performance of Markaudio Alpair 10V2 (FULL RANGER!) comparing with two types of conventional 13 cm WOOFERs.

History of Bass Drivers in my system
I started with a powered subwoofer from Victor. Its sound quality was quite poor (due to maybe high amount of distortions). The digital boosted bass generated from tiny Alpair 5s was much better. I threw it away.

Victor Powered Sub-Woofer


Then I tried two types of conventional 13cm Woofer, Dynavox LW5002PPR-S (PP cone) and Dayton Audio DA135-8 (Metal cone). However, they also could not overcome or replace the boosted bass from Alpair 6Ms. I felt something unpleasant with those woofers, too.

Dynavox LW5002PPR-S

Dayton Audio DA135-8

Absolute SPLs are unknown. Levels are adjusted in the range of 200 to 500Hz.

Finally I have adopted Alpair 10V2 as the bass driver, although it’s a pure FULL RANGER. To confirm or identify the measurable advantages of Alpair 10, I performed a series of tests on my desktop.

Definition of Xmax
Before presenting the results, I would like to clarify the definition of Xmax (maximum excursion of diaphragm) as below:

In this article, “Xmax” refers to “maximum linear excursion” (center to point “D” (or “C”) in above figure).
           Xmax = (Hc – Hg)/2
                   Hc: Coil length
                   Hg: Gap height
  Markaudio Alpair6: Xmax=1.6mm (Hc=7.2mm, Hg=4mm)
  Markaudio Alpair 10: Xmax=5.5mm (Hc=16mm, Hg=5mm)
  Dayton Audio DA135-8: Xmax=3.0mm (Hc=12mm, Hg=6mm)
  Dynavox LW5002PPR-S: Xmax = 3.0mm (Hc=12mm, Hg=6mm)

Alpair 10’s Xmax(5.5mm) is much larger than conventional 13cm woofers (typically Xmax=3.0mm).

Test Results

1. Open Air Condition
The diaphragm displacement (p-p amplitude) and sound pressure curve were measured at the same time using below setup.

The displacement (p-p) was read from a scaled sticker attached on the voice coil bobbin via a digital photograph (1sec exposure time) or just visually.

a) Alpair 6M
As a reference, I’ll show you the results from Alpair 6M first. 
 Common Test Conditions:
    Signal: sinusoidal 40Hz/0dB
    Xpp=Peak-to-peak amplitude of displacement
          (i) approx. at half amplitude of Xmax
         (iii) approx. at Xmax
         (iv) amplitude > Xmax

Typical 2nd and 3rd order contents can be seen. As Xpp increases, 3rd order increases more significantly than 2nd order. This 3rd order distortion seems strongly related to unpleasant feeling. My personal subjective and rough criterion for allowable distortion is: 3rd < 2nd. If the 3rd exceeds the 2nd, then the sound pressure wave form becomes triangular and it sounds clearly different from a sinusoidal tone. With Alpair 6M, this limit roughly corresponds to its Xmax (1.6mm x 2 = 3.2mm p-p)(see (iii)).

b) Dayton Woofer

It violates my criterion already at half amplitude of Xmax (see (i)). At Xpp=4mm, the wave form becomes completely triangular (see (ii)). At Xmax, its slopes become “S” shape. Additionally, higher order distortions (4th, 5th,….) also appear while Alpair 6M has almost no higher order contents. These high amount of 3rd order distortions seem to be the main reason why this driver could not overcome or replace the boosted bass from Alpair 6Ms, in other word, why I didn’t like this driver.

c) Alpair 10

I think no explanations are necessary. Very less 3rd order distortions in the entire operating range. The 3rd never exceeds 2nd even over Xmax condition (see (iv)). Very less higher order distortion even at very big amplitude (Xpp=10mm, near Xmax) (see (iii)).

2. Sealed Box Condition
I compared the Dynavox woofer and Alpair 10 on a 4L sealed box because Dynavox has no space for the scaled sticker.
Test Conditions:
    Amplifier Volume: Full (NuForce Icon AMP, 24W)
    Signal: sinusoidal 40Hz with level from -18dB to -6dB

Again, Alpair 10 demonstrates very low 3rd order distortions up to tremendous amplitudes while Dynavox generates high amount of 3rd order already in very low signal levels.

Why the 3rd order distortion is generated? Why the pressure wave form becomes triangular?
To understand the phenomena, I performed very simple simulations.


This is no distortional condition. Blue curve is a pure sinusoidal wave that corresponds to “Displacement of Diaphragm”. Green curve corresponds to “Sound Pressure” that is derived by differentiating the displacement with respect to time. 

Then 3rd order contents are added to the displacement.



Form the results above, we can assume that the 3rd order distortion of sound pressure is derived from the 3rd order distortion in the displacement which is generated when peaks of the displacement curve are rounded or cut. It is clear that the 3rd order distortion is unavoidable if the diaphragm moves beyond Xmax (due to non-linearity of magnetic driving force). This is OK. …
However, within Xmax range, it should be reduced as much as possible. The 3rd order distortion within Xmax range could be mainly caused by mechanical losses (due to spider and edge) that disturb or pull-back the movements of the diaphragm more strongly as the diaphragm excurses more from the central position. Especially if the mechanical force has a strong nonlinear characteristic (i.e. increases drastically at larger displacement), the 3rd order distortion will be more serious.

Such low 3rd order distortions in Alpairs (especially in Alpair 10) could be attributed to their very less mechanical losses thanks to ultra thin and soft spiders and edges. On the other hand, conventional woofers with harder mechanical suspensions could generate larger 3rd order distortions even within Xmax.

2nd =7.5%

When 2nd order is added, the sound pressure curve inclines toward right. This tendency can be clearly seen in Alpair 10’s sound pressure curves at high Xpp. The 2nd order distortion is generally inevitable with “dynamic” loud speakers and seems not so critical as 3rd order distortion in view of subjective unpleasantness. For example, many people feel something pleasant with single tube amplifiers even though they generate relatively high amount of 2nd order distortion. The 2nd order distortion could be compensated easily via digital signal processing if necessary.

- The main reason why I could not be satisfied or felt some unpleasantness with those conventional woofers could be attributed to their large 3rd order distortions.

- Both Alpairs demonstrated excellent sound quality with much less 3rd order distortions within Xmax range comparing to conventional 13cm woofers. One of primary reasons for this could be attributed to Alpairs’ low mechanical losses thanks to ultra thin and soft spiders and edges.

- “Low mechanical loss (High mechanical compliance)” must directly improve the quality of music reproduction in entire frequency and amplitude range because of higher sensitivity and linearity (thus lower distortion) of the diaphragm movements. I believe this must be one of the most important advantages of Markaudio Alpairs.

- In addition to reduction of mechanical losses, following measures could be effective to reduce 3rd order distortions.
        1. Increase magnetic force relative to mechanical loss:
               Stronger magnet
               Thinner air gap clearance
               Rectangular wire for voice coil (Alpair 10 use this)
        2. Increase geometrical Xmax: (for expanding linear range) 
                Longer coil
                Thinner gap height
I will soon report comparisons of several 3” drivers including Alpair 6M/6P/ 5, FOSTEX FE83E, Aura sound NS3-193.