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Old 10th June 2014, 07:26 PM   #1
DIM is offline DIM  Russian Federation
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Default Xmax A12p

Hello, Mark!
Is it possible increase Xmax for Alpair 12P? Want try it with Linkwitz transform in Closed Box.


Best regards, Dmitry.
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Old 11th June 2014, 05:46 PM   #2
Scottmoose is offline Scottmoose  United Kingdom
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Not a good idea, hammering a driver as hard as you seem to be implying. The FMD etc. will be crippling. That's just the laws of physics at work.
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Old 11th June 2014, 06:21 PM   #3
DIM is offline DIM  Russian Federation
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I would like to hear Mark.
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Old 11th June 2014, 09:10 PM   #4
Scottmoose is offline Scottmoose  United Kingdom
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You're very welcome. Nice to know you appreciate feedback / people trying to help.
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Old 11th June 2014, 10:11 PM   #5
DIM is offline DIM  Russian Federation
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Please do not be offended! But I used to check everything myself.
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Old 12th June 2014, 01:26 AM   #6
markaudio is offline markaudio  Hong Kong
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Quote:
Originally Posted by DIM View Post
Hello, Mark!
Is it possible increase Xmax for Alpair 12P? Want try it with Linkwitz transform in Closed Box.
Best regards, Dmitry.
Hello D,
What amp are you using (power rating)? How large is your room? What types of music do you play?

Xmax on the Alpair 12P is already large but not to be used all the time. Reminder, it isn't a high power driver.

Thanks
Mark
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Old 12th June 2014, 02:25 AM   #7
DIM is offline DIM  Russian Federation
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Hello, Mark.
I'll try to use your driver with Holton amp for experiments. As you know, the more Xmax, the lower the frequency, which can reproduce a speaker with a Linkwitz transform. In this variant, I can get 35 - 38 Hz. I would like to enlarge.
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Old 12th June 2014, 02:55 AM   #8
Bob Brines is offline Bob Brines  United States
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I don't think that you understand the magnitude of the power and excursion that a LT requires. I have a sealed 12" driver that does essentially what an LT does. At 30Hz, the 12" driver runs out of excursion -- +/*12mm at 500 watts to do 30Hz @105dB @2.5m. That's a 12" driver. The A12P is a 6" driver. There is simply no way to get 30Hz out of a sealed A12P at anything above say 70dB.

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Old 12th June 2014, 03:40 AM   #9
markaudio is offline markaudio  Hong Kong
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Quote:
Originally Posted by DIM View Post
Hello, Mark.
I'll try to use your driver with Holton amp for experiments. As you know, the more Xmax, the lower the frequency, which can reproduce a speaker with a Linkwitz transform. In this variant, I can get 35 - 38 Hz. I would like to enlarge.
I think you're confused between the driver's frequency in free air (Fo) and the practical (actual) limits of box alignments when applying the same driver.

Take note of Scott, Bob and similar senior forum members who have a large understanding on using full-range drivers. They have much knowledge and experience.

Ask them nicely for their help to get a sealed box alignment that will work.

Thanks
Mark.

Last edited by markaudio; 12th June 2014 at 03:52 AM.
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Old 12th June 2014, 10:33 AM   #10
Scottmoose is offline Scottmoose  United Kingdom
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Quote:
Originally Posted by DIM View Post
...As you know, the more Xmax, the lower the frequency, which can reproduce a speaker with a Linkwitz transform...
Not so. Not by itself anyway, without major caveats. LT requires the drive unit to possess very high power-handling levels (especially if you require more than whisper-level SPLs) since you are pumping considerable current into it. With a relatively small wideband drive unit like the 12P which is not designed for woofer duties, you'll fry the voice coil if you try pushing it particularly hard. LT was primarily intended for bass drivers -big voice-coils, high power-handling & to allow more practically sized sub-woofers. Also good for line-arrays.

Quote:
...In this variant, I can get 35 - 38 Hz. I would like to enlarge.
Check the power-handling and the SPLs that will be available. Which brings us back to the next points.

-The 12P is not designed to be constantly hammered to, or near, rated Xmax like that; a point Mark regularly makes with all his drive units. It has wide excursion, but it's there to handle occasional LF dynamic swings when reproducing music at a more 'normal' average SPLs. If you run it to the limit of travel, you have nothing left to handle these dynamic peaks. And ultimately, you'll reduce its lifespan. You don't run a car flat out all the time -same deal with drive units. All of them.

-Xmax per se doesn't mean much since there is no industry standardised definition about what it is. There are numerous ways of defining it & the calculations all give different results for the same drive unit. Smashing. Personally I think distortion levels (2nd - 7th) at different drive levels to be rather more useful, with a figure given for maximum excursion beyond which the driver should not be run (especially if travel is not limited by the suspension before the VC smacks into the back-plate).

-Even if you could get around the above, as previously noted FMD (Doppler distortion if you prefer, although it's arguably not the right terms) comes into play. The HF in particular can get rather odd when reproducing a signal on a cone that is moving nearly 1/2in back & forth. This cannot be engineered out; it's not a matter of driver design, it's the laws of physics. It's not an issue for a bass / sub-bass driver, since they are functioning over a very narrow BW, but it can be for a single unsupported widebander.
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