Tweeter Mishmash
About the Test
All response curves are with the drivers on an infinite baffle. Don't forget that in the real world, baffle step and diffraction will affect the curves. These curves are measured with a close mic, but not so close that the response curve is affected. I use a small amount of gating to keep room effects from showing up. All drivers are countersunk, or in the case of few neo tweeters, rear mounted and surface mounted if they are designed for that.
Cumulative Spectrum Decay (CSD) charts are 1/12 octave smoothed. Time slices are taken up to 3ms with the start marker right at the beginning of the impulse. All levels are equalized to 30dB to accurately show comparitive energy storage regardless of individual driver efficiency. The CSD's are closely related to the frequency response, and just as important.
Harmonic distortion charts are taken near field at roughly 4". In relation to the dome size, this is far enough away to be considered far field. Amp output level was adjusted for each driver so that 0dB is equal to 90dB at 1 meter, at a frequency best representing the driver's average. This is normally somewhere between 1.5 and 3kHz. Harmonics F2 thru F5 are tracked. F2=Green, F3=Blue, F4=Purple and F5=gray. In general, the higher the order of harmonic distortion, the more offensive the sound. The range is 400Hz to 10kHz and the level is +15 to -110 dB.
The critical range of harmonic distortion is the 1kHz to 3kHz range. This range determines how low you can cross over, and high order harmonics are easily heard this low in frequency. As you go higher in frequency, high order harmonics begin to be unimportant as they occur above audible frequencies. For example, a peak in the F5 at 5.3kHz actually occurs at 26.5kHz and is inaudible. A peak in the F2 at 5.3kHz would be audible at 10.6kHz however, possibly causing brightness, edgyness or "false air".
• Special measurement issues: In this grouping, older harmonic distortion sweeps have dips in the response of the fundamental on the HD charts. This is an artifact of the way my SE was originally setup to measure harmonics, and does not affect the harmonics themselves. It's a function of the mic distance and related phase shift - the recorded signal internally summed with the original signal before plotting to the chart. Only the fundamental is affected, and the harmonics are accurate. For an accurate fundamental here, just take a look at the response curves. Rest assured however that all testing levels in this grouping were set the same for new and old, and the harmonic distortion can be reliably compared.
And finally, note - Do Not compare these harmonic distortion plots to others anywhere else, including on this site. The test method was different for this particular set. Make comparisons within this test group only.
There are two general types of harmonic distortion tests - Single frequency spectrum and fixed harmonic sweeps. I do sweeps, while many others do single frequency.
Single frequency has two primary benefits. First, the level at the fundamental frequency can be adjusted to the same level as other drivers tested, making easier a direct comparison at a single frequency. Second, very tall order harmonics can be seen. For example all the harmonics above F6 can be seen, along with other spectrum noise.
Fixed harmonic sweeps have several benefits. The first and foremost is that distortion is shown for all frequencies at once, rather a single selected frequency. Single frequency testing requires *many* tests to get a complete picture of distortion across the spectrum, and even then, sharp peaks in distortion could hide between 2 tested frequencies. With a sweep however, the primary harmonics F2 through F5 will be clearly shown at every frequency.
For example, if speaker with a large and very audible peak in the 3rd harmonic at 1.5kHz had single frequency tests done at 1kHz and 2kHz, the harmonic distortion would be completely missed. This is particularly important when testing stiff drivers with breakup nodes within the audible band. This is the primary reason I choose sweeps for harmonic distortion testing. There is a lot more information in one image.
We can't have everything with sweeps, and we loose the ability to see harmonics above F5. In my opinion, this is a fair trade off. Taller order harmonics far above the fundamental frequency are more audible than a low order harmonic of the same level. But tall order harmonics are typically at a much lower level. Looking at the data with trending in mind will help see around these limitations.
Reading harmonic distortion sweeps is fairly easy. This section will deal with interpeting the data and "reading between the lines" to help see around the limitations of this type of testing.
These sweeps are not EQ'ed to flat. Nor are they filtered or crossed over in any way. This is both an advantage and a disadvantage depending on how the driver is used. It is an advantage if the frequency in question falls within a range that is intended to be run without any sort of response shaping or crossover. For example, the top two octaves of a tweeter or the midbass of a woofer. In that case, what you see is what you get. It is a disadvantage when the response curve will be modified to reach a target response shape. For example, an extended low end of a tweeter will have it's harmonic distortion reduced in the area where the crossover begins to take effect. A woofer crossed over to a sub will have it's audible distortion reduced as the woofer rolls off.
Related to the above, the enclosure tuning for woofers affects the low end distortion. The baffle dimensions and driver location for all drivers will also affect the distortion level due to baffle diffraction ripple response and baffle step response due to 2pi to 4 pi conversion. The most important thing to remember when looking at these harmonic distortion sweeps is how the drivers will be used.
There's a lot more information in these F2-F5 sweeps than may first meet the eye. You can get a pretty good idea of what's going on further up in the spectrum by looking at the level of the F4 and F5 in relation to F2 and F3 respectively. This is a form of trending. For example, to take a guess at tall odd order harmonics, draw an imaginary curve from the fundamental to the F3 and F5, and it's almost guarenteed that the F7 and F9 are going to fall close to where that curve extends.
For intermodulation distortion, there is nothing more definitive than looking at a 2 or 3-tone spectrum, but in my experience an F4 or F5 of a relatively high level almost certainly points to high IMD as much as it points to high spectrum noise. While I do not provide IMD plots, be aware that drivers with high HD are probably going to have high IMD and high spectrum noise also. All these forms of distortion are closely related.
All parts of this test are done with Soundeasy 12.0. This is a modeling package with a lot of extra testing applications included. It is not a full acoustic measurement system such as CLIO or Praxis however, so take these results with a grain of salt. What is important however is that all of these drivers were tested in the same way. Because of this, my test results should not be compared with tests done elsewhere by other people, but comparisons within this group of drivers are perfectly valid. That's why tests like this are best done in groups.
This test represents tweeters from "all walks of life". There's nothing like comparing a $4.60 tweeter to a $260.00 tweeter. It truly is a mishmash. The purpose of this test is not just to point out the best tweeter, but to give you an idea of what your money will buy.
When I add tweeters to this test, I start by re-testing a previously tested tweeter. If neccessary, I make adjustments to match previous measurements. This is done to insure accurate, repeatable results when testing all the drivers at one time is not possible.
There are a few types of tests that are important, but not shown here in the interests of brevity. Keep this in mind and know that these results need careful interpretation.
Page done by John "Zaph" Krutke © 2007 Also visit -Zaph|Audio-
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