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Old 29th December 2009, 03:33 PM   #31
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Quote:
Originally Posted by planet10 View Post
vlado,

I'm not sure where you are getting that from... it starts falling off above 20 kHz (the graphs go to 30k). I've seen 1" dome tweeters without as extended or as smooth on-axis response.

Now it is true that on-axis response tells us only about the on-axis performance, and little about the overall driver performance.

dave
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vlado
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Old 29th December 2009, 06:18 PM   #32
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I know where you got the graph. The question was your interpretation of the graph.

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Old 29th December 2009, 10:50 PM   #33
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Hi Vlado,
The new generation CHR-70's graph is near RAW data. I'm trying to move to RAW data since it's the more honest approach. Most audio guys on this forum know driver makers apply smoothing to the data on their graphs.

When I started with my first generation drivers, I produced RAW graphs. Sadly a few forum members with limited understanding made critical comments. They made a fundamental error by comparing RAW data with smoothed. They were quite vocal in their comments, thus I was sadly cornered into following other makers and applied smoothing.

The second generation CHR-70 benefits from the Multi-form cone making process. Its resonance performance is more stable in the high range than the first generation. In particular there is a +5dB peak at around 12-kHz in the old model. At the request of the German market, the new model has a smoother response to 20-kHz.

You need to exercise much care when comparing data, it's not a level playing field.

Cheers,

Mark.
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Old 29th December 2009, 10:54 PM   #34
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Amen to that.
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Old 30th December 2009, 08:23 AM   #35
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thank you Mark
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Old 30th December 2009, 08:54 AM   #36
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I dont understand the Xmax rating
It says 4.5mm 1way
Alpair12 says 9mm 1way

Xmax to me means linear Xmax, not max bottom limit before destruction
Roughly, 1way linear Xmax to me is voicecoil length, minus polplate, divided by 2
4.5mm 1way, is to me like 4.5mm+/-, or 9mm(p-p), linear
9mm 1way, to me would be like 9mm+/-, or 18mm(p-p), linear

Numbers seems strange to me
Are they linear Xmax both ways, or Xmax limit one way

Last edited by tinitus; 30th December 2009 at 09:02 AM.
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Old 30th December 2009, 02:35 PM   #37
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Tinitus

This reference may enlighten you:

Xmax
Specified in millimeters (mm). In the simplest form, subtract the height of the voice coil winding from the height of the magnetic gap, take the absolute value and divide by 2. This technique was suggested by JBL's Mark Gander in a 1981 AES paper, as an indicator of a loudspeaker motor's linear range. Although easily determined, it neglects magnetic and mechanical non-linearities and asymmetry, which are substantial for some drivers. Subsequently, a combined mechanical/acoustical measure was suggested, in which a driver is progressively driven to high levels at low frequencies, with Xmax determined at 10% THD. This method better represents actual driver performance, but is more difficult and time-consuming to determine.


The first method that you suggested is best described as "simplistic", the second mentioned in the reference has more merit but is arbitrary @ 10%THD where some FR drivers are concerned.

As a general rule, high and ultra-high efficiency FR drivers (>90dB) will have limited usable short Xmax values. This is due to their damping and low power handling characteristics. Conversely, lower efficiency FR drivers usually offer larger serviceable Xmax values. Much depends on the mechanical/operational design properties of the power-train relative to the driver's moving mass. This is especially particular to delivering extended oscillations in progressing near limit loads.

My drivers have wide serviceable X loads. Power-train design is a particular speciality of mine. A good example of Xmax in action is the Alpair 10. There are numerous comments on its ability to deliver bass on progressive loads. I'm now working with Tadashi Matsubara san to further develop suspension systems, the latest of which are incorporated into the Alpair 7 and Alpair 12 drivers.

Realistically, it's unlikely that you'll consistently operate any transducer close to any of its Xmax constituents. Aside issues of distortion, the potential damage to human hearing will become significant.

like Vlad's situation, its all too easy to get hung up on some aspects on the interpretation and evaluation of driver data.

If there's more interest in this topic, I'll create a new thread and move the related posts to it.

Mark

Last edited by markaudio; 30th December 2009 at 03:36 PM.
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Old 30th December 2009, 03:29 PM   #38
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Hi Vlado,
Glad to help. Sorry I can't bring you a complete solution. There's no industry wide agreement on the presentation of frequency data. That's why I like to be part of the DIYAUDIO forum. Its a great place to seek out the practical experience of drivers in regular use by enthusiasts.

Rest assured that I always try my best to deliver reliable and usable data for all my drivers.

Cheers

Mark.

Last edited by markaudio; 30th December 2009 at 03:33 PM.
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Old 4th January 2010, 04:01 AM   #39
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My first CHR-70 desktop speakers using real oak wood cabinets sound natural and balanced. They have very beautiful mid range and high range.

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Old 4th January 2010, 04:20 AM   #40
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Default Chr-70

Remember to use good accessories and can make the sound of speakers much better.

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