The Scan-Speak Illuminator D3004/6020-00 1″ Textile Dome Tweeter has become a pretty regular staple in the audio community. Especially for the automotive hi-fi hobbyist due to its Scan Speak name, community based subjective reviews, and small form factor.
I have owned a set of these tweeters for a while now and have had great results with them. At any volume I play them, using a 3.15khz/LR4 (24dB/octave) crossover, they handle it very well. I wanted to see just how my subjective thoughts and others’ translate in to objective performance.
For dimensions and accompanying manufacturer specs, please see the link above.
On to the test results…
Thiele-Small Parameters and Impedance
|Re||3.21||Ohm||electrical voice coil resistance at DC|
|Le||0.013||mH||frequency independent part of voice coil inductance|
|L2||0.021||mH||para-inductance of voice coil|
|R2||0.45||Ohm||electrical resistance due to eddy current losses|
|Cmes||167||µF||electrical capacitance representing moving mass|
|Lces||0.28||mH||electrical inductance representing driver compliance|
|Res||7.14||Ohm||resistance due to mechanical losses|
|fs||735.8||Hz||driver resonance frequency|
|f ct||756.7||Hz||driver resonance frequency in enclosure|
|(using test encl.)|
|Mms||0.189||g||mechanical mass of driver diaphragm assembly including air load and voice coil|
|Mmd (Sd)||0.169||g||mechanical mass of voice coil and diaphragm without air load|
|Rms||0.159||kg/s||mechanical resistance of total-driver losses|
|Cms||0.248||mm/N||mechanical compliance of driver suspension|
|Kms||4.04||N/mm||mechanical stiffness of driver suspension|
|Bl||1.064||N/A||force factor (Bl product)|
|Qtp||1.714||total Q-factor considering all losses|
|Qms||5.506||mechanical Q-factor of driver in free air considering Rms only|
|Qes||2.473||electrical Q-factor of driver in free air considering Re only|
|Qts||1.706||total Q-factor considering Re and Rms only|
|Vas||0.0164||l||equivalent air volume of suspension|
|n0||0.254||%||reference efficiency (2 pi-radiation using Re)|
|Lm||86.24||dB||characteristic sound pressure level (SPL at 1m for 1W @ Re)|
|Lnom||87.2||dB||nominal sensitivity (SPL at 1m for 1W @ Zn)|
|rmse Z||2.41||%||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|
You’ll note the low impedance. The common rule of thumb for tweeter crossovers is to double Fs and use a steep slope; typically LR4 (24dB/octave). Many people who run 2-way setups (a midwoofer + tweeter) prefer to have a tweeter that can be crossed low in order to better match the power response of each driver, giving a nice overall polar response. Dr. Earl Geddes has a very good writeup regarding the importance of matching directivity, found here:
If you’re paying attention, you’ll also see the difference in T/S values measured vs that of the manufacturer spec. T/S values are to be measured in one given environment, typically at room temperature. This keeps them all on an even keel for comparison purpose. Some manufactures adhere to IEC specs for defining T/S parameters and others do not. If they do, they will state it. For the time being, I am measuring in my garage and thus am making note of the fact that my results will not always mimic those of a manufacturer when it comes to parameters influenced by the environmental conditions such as humidity and temperature. Specially, these parameters are Vas, Bl, and Cms. However, Fs, Qts, Qms, Qes, Le, and Re are not affected by the environment and thus can be compared to that of other sources with more latitude. This particular test was done in an ambient temperature of approximately 85 degF; humidity undetermined. The tweeter was mounted on a scaled IEC baffle. It is important to always be aware of the test methods when making comparisons across different sources.
Frequency Response and Harmonic Distortion at 2.83v/1m
At the standard measurement conditions of 2.83v/1m, this driver exhibits a sensitivity of approximately 85.9dB.
The frequency response on axis has a trough from 1.5khz to 3khz dipping to ~81dB and then rises to the height in SPL from 6.2khz to 9khz at 88.2dB before dipping again at 13khz and rising one more time at 15.5khz.
The off-axis response of this driver is smooth with no severe drop off as the driver is angled away from the listener. The graph above depicts a smooth response at 30 and 60 degrees off-axis with a very nice linear gap between the two response curves.
The corresponding Harmonic Distortion results show a very nice distortion profile. There is clear separation in 2nd order from third order distortion. The 1% THD threshold is crossed at 1631hz with a small blip above 1% at 6.25khz. Realistically, the audibility of 1% THD is a far fetch, so I often adhere to the 3% THD value (which corresponds to -30dB down from the fundamental). My own personal subjective testing and data points on the internet have shown me this is a fair median value to use. While some cannot hear 1% THD, others cannot hear 10% THD. What’s more, the source material being played will cause variance in the audible threshold of distortion. And going beyond that, it is being stated that masking plays a large role in perception of distortion. To again point to Geddes, you can read this for further information:
Having said all of that, the 3% distortion mark for this DUT does not occur until approximately 1.1khz at this particular output level. While these values are great, consumers often listen louder than at the standard measurement above, so …
Harmonic Distortion (measured in the Nearfield)
This test was done in the nearfield, with the mic located about 4.75 inches from the mic, with a 5.2 volt output applied. This equates to roughly 114dB in the nearfield, or 96dB at 1 meter.
Zoomed in Results:
As you can see above the 3% THD mark occurs roughly at 1.5khz. Notice the clear separation of 3rd order distortion; it’s below even 1% distortion until 650hz. Well beyond the typical crossover range for any tweeter of this size; below Fs even.
There is a couple areas that have a higher 2nd order distortion, however, at approximately 5.5khz and 6.5khz. These make up the THD percentage of 1.75% and 2.75%, respectively.
So, what do the two sets of data above really tell you? Not quite as much as you might think. While HD testing is great, it’s not a stand alone in non-linear distortion testing because it’s a swept sine test. However, you can often get practical use information out of this data and that’s why it’s still important to analyze a driver in this context. From the above, you can see that crossing below 2khz at even loud volume (96dB at 1 meter distance) will net you distortion levels well below 3% for a typical crossover passband as low as 2khz. So, this tweeter can be crossed relatively low. However, I would not advise crossing below 2.5khz with a 12dB/octave slope simply to play it safe. I use mine in a 3-way set crossed at 3.15khz/LR4. Of course, you should use your own judgement. The data is here only to help you and should not replace your ears and a little common sense. 😉
Intermodulated Distortion (Voice Sweep)
Now that we have some basic non-linear data from the Harmonic Distortion plots above, let’s see what happens when we apply a more real-world situation. By using the Klippel IMD Voice Sweep, I can play a single “bass” tone (defined by 0.1*Fs) and sweep a nominal passband at the same time. The output voltage can be dictated by the user. For this test, I chose 1v to 4v, in 1v increments. This excites the voice coil with a bass tone while playing higher frequency content and therefore gives a better idea of the performance of the DUT when music is applied and at varying levels.
For this test, the bass tone is fixed at 75hz and the swept tones range from 800hz to 10,000hz.
First, let’s look at the Harmonic Distortion components. In many ways this data can be used to correlate with the HD above. The real benefit, however, is the ability to more easily see the effect of increased voltage to the DUT on distortion where in the previous HD test, the applied voltage was singular.
What you can see from the above is, since third order distortion is so low, the overriding factor of THD (1st picture in this set) is from 2nd order distortion.
It’s interesting to note the third order distortion values are not linear with applied voltage. To be honest, I’m not exactly sure what is the cause of this but will investigate further.
Let’s look now at the intermodulated distortion results.
Second order IMD seems to increase at a linear rate (compared to input voltage), whereas third order seems to increase more non-linearly.
Again, as with the HD results, you can also see that 3rd order distortion is kept to a minimum here. It is worth nothing that odd-order distortion is often referred to as the distortion that can be most offensive to the listener, whereas even order distortion is acceptable and reportedly sometimes preferred.
Compression of a driver is what happens when the coil is heated and the dissipation of the heat is not very efficient. This ultimately results in a loss of SPL at varying input voltage. In an ideal system, if you increased the voltage by 3v you would expect the output of the system to reflect this; essentially input/output linearity. However, this is not the case with real world drivers. They all suffer compression. Some just do a much better job at reducing the effect. So, it is important to understand the limits caused by compression. Klippel presents this in a VERY easy way to understand: if the output is linear with input voltage, all result data points should stack on top of each other. As thermal compression increases, however, these lines will separate and the lines further down (referenced to the original, smallest voltage, measurement) will be shown as the relative SPL difference. Confused? It’s harder to explain in type than it is to see, so let’s look at this tweeter’s performance as an example:
Pick a frequency. Let’s say 2000hz.
The 1 volt input measures about 90.9dB.
The 2 volt input measures about the same at 90.9dB. This means there is no compression because the output is linear.
The 3 volt input measures about 90.79dB. Very little compression.
The 4 volt input measures about 90.45dB. This delta means there is roughly 0.45dB loss from the 1v input. Ideally, if the driver had no compression, these lines would all stack on top of each other and show the same value because they’re all referenced to the initial measurement. However, with the little compression suffered here, there is some loss in SPL output from 1v to 4v input.
Think of it like this. With 1v applied to a 4ohm (nominal) driver – measuring 86dB @ 1w/1m – you would expect to get 80dB output at 1 meter. If you put in 4v, you would get 4 watts, making your theoretical expected output at 1 meter to be 92dB. In this particular case, we lose 0.45dB at 4v from theoretical. So, your final output at 4v would be maxed at 91.55dB at 1m.
Finally, here is the measured voice coil delta Temperature (Tv) from 1v to 4v.
You can see from the above that as the input voltage increases, the temperature of the voice coil does as well. It’s interesting to note the dip in Tv at 4.5khz. Compare this to the Frequency Response measurements above and you can see the driver seems to gain efficiency at this point. I’m sure this is not a coincidence. However, I will have to explore this further to determine just what the relationship may be.
The Scan-Speak Illuminator D3004/6020-00 1″ Textile Dome Tweeter is great tweeter that can be crossed low enough to mate with most nearly any 6.5″ woofer. The frequency response on and off-axis is very smooth, while the on-axis rise in response lends to a better slightly off axis response as shown at 30 degrees. For the car audio crowd where on-axis mounting is not always easy in order to remain ‘stealth’, this is a benefit. However, I’ve not necessarily been a fan of a driver that deviates from a flat response. In fact, while using these in the car on-axis, I had the passband of about 6khz to 10khz attenuated via my graphic EQ. This was without knowing of this near 3dB rise in the same passband from the measured mean of 1khz to 10khz. Maybe a more off-axis aiming would have kept me from having to attenuate this band, though I prefer the method of having a driver on-axis to gain in the direct vs reflected avenue. It’s been my experience that a sense of ambiance is more prevalent when this is done. For the home audio crowd, this is namely a moot point. Unless, of course, you prefer to toe out your loudspeaker or even cross fire inward. Some have spoken of the benefits of a wider soundstage in the home when doing this. Personally, I’m more fundamentally rooted in car audio so my experience toward aiming trickery in the home audio realm is minimal.
The non-linear measurements show this driver to be higher in 2nd order distortion and marginally limited in 3rd, and subsequent, orders of distortion.
Bottom line: A great driver objectively and my own subjective experiences have resulted in the same conclusion. I dare not mention “value”. I’ll leave the data for you to determine that.
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