Alibaba 28mm Tweeter with Black Flange Testing

I’ve recently been provided three different sets of tweeters for testing by a member of the audio community.  Each set of tweeters are from an overseas seller of numerous audio components.  Essentially, what many would call a “build house”.

The first of these tweeters up for testing is the 28mm dome tweeter with a black flange as shown below:

This driver’s approximate dimensions are:

  • Outer Diameter: 60mm
  • Mounting Diameter: 50.5mm
  • Mounting Depth: 10.2mm

Physically this driver looks pretty nice from the from.  A shallow mounting depth and a nice aesthetic black flange.

With that, let’s move on to the data.  If you want to see the graph in full 1600×1200 resolution, simply click on it and it’ll pop up in full-res.

 

 

Thiele-Small and Impedance Data

Electrical Parameters
Re 4.11 Ohm electrical voice coil resistance at DC
Le 0.035 mH frequency independent part of voice coil inductance
L2 0 mH para-inductance of voice coil
R2 0 Ohm electrical resistance due to eddy current losses
Cmes 117 µF electrical capacitance representing moving mass
Lces 0.17 mH electrical inductance representing driver compliance
Res 3 Ohm resistance due to mechanical losses
fs 1131.7 Hz driver resonance frequency
——————
f ct 1186 Hz driver resonance frequency in enclosure
Mechanical Parameters
(using test encl.)
Mms 0.372 g mechanical mass of driver diaphragm assembly including air load and voice coil
Mmd (Sd) 0.349 g mechanical mass of voice coil and diaphragm without air load
Rms 1.065 kg/s mechanical resistance of  total-driver losses
Cms 0.053 mm/N mechanical compliance of driver suspension
Kms 18.81 N/mm mechanical stiffness of driver suspension
Bl 1.787 N/A force factor (Bl product)
Loss factors
Qtp 1.436 total Q-factor considering all losses
Qms 2.485 mechanical Q-factor of driver in free air considering Rms only
Qes 3.403 electrical Q-factor of driver in free air considering Re only
Qts 1.436 total Q-factor considering Re and Rms only
Other Parameters
Vas 0.0043 l equivalent air volume of suspension
n0 0.175 % reference efficiency (2 pi-radiation using Re)
Lm 84.64 dB characteristic sound pressure level (SPL at 1m for 1W @ Re)
Lnom 84.53 dB nominal sensitivity (SPL at 1m for 1W @ Zn)
rmse Z 11.62 % root-mean-square fitting error of driver impedance Z(f)
Series resistor 0 Ohm resistance of series resistor
Vbox 0.296 l volume of enclosure
Sd 7.55 cm² diaphragm area

 

The impedance shows an Fs at roughly 1186hz.  Rather high for a dome of its size, relatively speaking.  For example, look at the Scan Speak D3004/602000 I just tested.  Physically, these drivers are very close to the same size.  However, the Scan has an Fs at about 730hz.  Quite a bit lower if you need to cross low.  Of course, Fs isn’t everything, so let’s keep looking.

 

Large Signal Analysis

Displacement Limits thresholds can be changed in Processing property page
X Bl @ Bl min=82% >0.175 mm Displacement limit due to force factor variation
X C @ C min=75% >0.175 mm Displacement limit due to compliance variation
X L @ Z max=10 % >0.175 mm Displacement limit due to inductance variation
X d @ d2=10% 0.919 mm Displacement limit due to IM distortion (Doppler)
Asymmetry (IEC 62458)
Ak -16.75 % Stiffness asymmetry Ak(Xpeak)
Xsym 0.18 mm Symmetry point of Bl(x) at maximal excursion

 

This data, truth be told, isn’t as complete as I would like it to be.  To be honest, the fragile nature of tweeters makes it a bit harder to measure than that of a woofer and since these were donated tweeters to test, I chose not to stress them like I normally would a woofer.

What you can see, however, is that the suspension is the more dominant source of distortion.  The other graphs gives you some idea of the internal workings of the motor, suspension and inductance.  You can see the xmax parameters did not converge.  Again, this is simply due to the fact I did not continue to test these drivers.  I heard audible buzzing during the test and was concerned I was going to damage them so stopped the test at this point.

 

Fundamental and Harmonic Distortion Taken at 2.83v/1m

Nearfield Harmonic Distortion Test Results approximating 96dB at 1 meter.

The fundmaental response curves at 0 and 30 degrees are fairly smooth in a nominal passband of 1khz to 10khz with a mean sensitivity of approximately 84dB at 2.83v/1m.  There is a dip in response in the mid section, likely made more obvious by the increased top end response.  The 30 degree off-axis measurement mimics very closely the on-axis (0 degree) measurement.  At 60 degrees, however, the response takes a relatively sharp decline and at 12khz is roughly 7dB down from the 30 degree measurement and 9dB down from the 0 degree measurement.  So, the polar response of this driver isn’t great when getting to the very high frequencies.

The HD testing shows a very steep increase in non-linear distortion; reaching 10% at 1.6khz and 5% as high as 2khz for the high output testing (5v).  Even at more moderate levels of 2.83v, as shown in the first picture, 1% THD is reached by 3khz with a steady incline in to higher distortion the lower in frequency it plays.

All in all, while the FR looks good, the HD results indicate this is not a driver that should be crossed low.  The imlications are that this driver would likely be best served when crossed above 3khz with a fairly steep filter.  From personal experience, relating objective data to subjective thoughts, this looks to be even better served as a tweeter relegated to a 3-way system where a higher crossover is permitted.

Intermodulated Distortion Testing (Voice Sweep)

Note:  See Klippel Application Note 24 for details of test parameter and setup.

  • Fixed Bass Tone at ~ 0.1*Fs
  • Voice Sweep from 800hz to 10,000hz
  • Voltage Range from 1v – 4v
    • There was audible buzzing of the driver which caused me to not increase the test voltage output higher than 4v
  • Mic was located in the nearfield – approximately 4.75 inches from the driver – to mitigate environmental related anomalies

The data above again indicates a driver not well suited to a low crossover.  It also shows the effect of compression.  Based on the relative 1v test, nearly 1.8dB is lost at 4v due to thermal effects at the voice coil below 3khz.  In other words, there’s a pretty big loss in efficiency the more power you throw at this driver.  Compare this to the Scan Speak D3004 test mentioned above where only 0.45dB is lost due to compression.  However, above this 3khz mark, the compression is only about 0.2dB from the 1v measurement to the 4v measurement.  This is more data that show this driver’s ineffectiveness as a capable transducer above 3khz.

Motor Stability

Note:  See Klippel Application Note 14 for details of test parameter and setup.

Conclusion

As noted above, this driver’s Fs and non-linear performance indicate it should not be used to be crossed low and mate with a larger woofer for a 2-way system.  While I am sure some might say it sounds just fine, all the data points to egregious issues when used below 3khz.  In regards to linear distortion (frequency response), this driver would likely perform well mounted slightly off-axis.  However, the large rolloff in response above 10khz might give me some cause for concern.  If you’re in the hunt for a driver that can be used in a 3-way system with a higher crossover of around 4khz, and can mount it a bit more on-axis than 30 degrees, it’s worth a shot.  If you’re looking for a tweeter to cross below 3khz, I wouldn’t really look at this as a contender.

If you like what you see here and would like to contribute to the fund toward additional test gear, hardware, or just buy me lunch, it would be greatly appreciated.  Just click the “Contribute” button to the side or bottom of this page.

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