Driver distortion measurements?

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The only distortion measurements I've seen for drivers are at zaph audio

Zaph|Audio

Also linkwitz has also done some woofer measurements

It shows how at low frequency and excursion at half xmax distortion is fairly high, and it is unacceptable by xmax.

Has anyone done distortion measurements at lower levels? I'm wondering if keeping excursion down to 10% of xmax, 1% of xmax, or .1% of xmax keeps distorton down as well or if there is a minimum. It seems that distortion would just keep decreasing as especially with subwoofers I believe the main cause of distortion is the magnetic Flux decreasing as it leaves the gap and also non linearity in the suspension as you increase the excursion so it seems that the lower the output the lower the distortion would be, to diminishingly low levels
 
The only distortion measurements I've seen for drivers are at zaph audio

Zaph|Audio

Also linkwitz has also done some woofer measurements

It shows how at low frequency and excursion at half xmax distortion is fairly high, and it is unacceptable by xmax.

Has anyone done distortion measurements at lower levels? I'm wondering if keeping excursion down to 10% of xmax, 1% of xmax, or .1% of xmax keeps distorton down as well or if there is a minimum. It seems that distortion would just keep decreasing as especially with subwoofers I believe the main cause of distortion is the magnetic Flux decreasing as it leaves the gap and also non linearity in the suspension as you increase the excursion so it seems that the lower the output the lower the distortion would be, to diminishingly low levels

Forgot to link linkwitz measurements...lol
 
Forgot to mention also I'm building a 4-way speaker with a subwoofer to handle the low end. I'm deciding between 2 infinity 1262w'so which are cheaper lower end units, 2 Dayton rss315ho-44's, or a 15 inch Mach 5 ixl 15.2.2. They all have similar piston volume, box size and xmax, the infinitys are cheapest, the Mach 5 in the middle and the Daytons being most expensive. The mach is sort of a different beast being a single 15 but between the infinitys and the Dayton, is there really double the cost in quality difference? I feel like the infinity while most definitely not designed as well, has similar distortion at say 9mm excursion as the Dayton has at maybe 14mm, but at 1mm excursion where most of my listening will happen or quiter, do they really have much difference? I just can't seem to find anywhere where anyone has measured anything like this...and I understand it's hard also because boxes are often vary different, but still nothing?
 
I've measured some 2-3" drivers:
Timothy Feleppa's Pages

I plot my results in a similar fashion to SoundEasy even though I use my own custom scripts/software because I learnt how to interpret distortion plots from Zaph's data. That said my results and Zaphs should not be directly compared - my mic, test levels, baffle setup are different. I have tested a few of the same drivers though (check in particular his 'blog' page for newer drivers such as the Vifa TC etc), so that provides some points of reference.

I don't think it makes much sense to measure distortion at levels much below 85dB/1meter because with the better drivers the distortion products are already disappearing into the noise floor of the average home.

Also since you seem to be particularly interested in low frequency performance, take into consideration what happens when you put a low-Fs, low-Q woofer on an infinite baffle like Zaph and my own testing - the excursion goes way down compared to a high-Q driver so the harmonic distortion does too. Compare for example the RS180 and the 8945A in Zaphs data. At first glance the 8945A looks like the clear winner below 100Hz until you check out what the frequency response of both drivers are doing - the RS180 is 10dB down at 30Hz from the midrange level while the 8945A is 15dB down. This means much less excursion from the 8945A at 30Hz in the harmonic distortion test which is going to make the distortion go way down. As a result you can't directly compare the cleanliness of the bass from Zaphs results. It is also why the distortion doesn't just keep increasing as the frequency gets lower and lower - in the 8945A test it sort of flattens off because the excursion flattens off.

If I get into woofer testing what I'll probably do is use a DSP to EQ all woofers to a target response, then a direct comparison of distortion can be made.
 
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A few measurements collected from here and there

1) ScanSpeak Illuminator 18WU (a well-respected and expensive "audiophile" 7" = 18cm mid-woofer)

2) Monacor SPH-KE300 (a relatively affordable 12" = 30cm kevlar woofer)

3) B&C 15PS100 (a relatively affordable 15" = 38cm woofer designed for "Pro"/PA applications)

4) Fostex FW405N (an expensive, high-end 15" = 38cm woofer designed for Hi-Fi applications)

I'll let you draw your own conclusions.

Mine are:
1) Low frequencies DEMAND a large Sd
2) Within the same Sd class, you tend to get what you pay for

Marco
 

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  • 1) ScanSpeak Illuminator 18WU.gif
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  • 2) Monacor SPH-KE300.gif
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  • 4) Fostex FW405N.gif
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The only distortion measurements I've seen for drivers are at zaph audio

Zaph|Audio

Also linkwitz has also done some woofer measurements

It shows how at low frequency and excursion at half xmax distortion is fairly high, and it is unacceptable by xmax.

Has anyone done distortion measurements at lower levels? I'm wondering if keeping excursion down to 10% of xmax, 1% of xmax, or .1% of xmax keeps distorton down as well or if there is a minimum. It seems that distortion would just keep decreasing as especially with subwoofers I believe the main cause of distortion is the magnetic Flux decreasing as it leaves the gap and also non linearity in the suspension as you increase the excursion so it seems that the lower the output the lower the distortion would be, to diminishingly low levels

Hi,

I always include distortion plots in my driver measurements.

www.audioexcite.com

Regards

/Göran
 
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