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Old 2nd July 2014, 03:41 PM   #1
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Default ultra low Qts drivers as much as .1 pros and cons?

well the application is towards the midrange driver for 5.5 inch. The reason behind is

There are important factors to be considered that drivers which has high Qms and low Rms gives better details. My goal is that to make a low Rms driver with high Qms and with very low Qts as much as .1 i believe the cone is in much control by electrical signal than the mechanical compliance of the driver. Lets consider a 5.5 inch driver is designed to a Fs of 50Hz and with super low Qts of .1 when loaded into a box the fs will go higher and I am very happy for it for two reasons one low box size and another is no need of capacitor in the path rather use just a low pass filter for the upper cutoff and lower cutoff is taken care by the natural rolloff for the driver. The bass is being handled by another driver.

Please let me know if there are any pros and cons of this kind of low Qts driver.
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Old 2nd July 2014, 07:17 PM   #2
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my thought would be what is the driver offset caused by any DC in the signal if there is no DC blocking capacitor ?
will the diaphragm be pulled out of alignment thus adding distortion?
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Old 2nd July 2014, 07:19 PM   #3
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Do you mean something like the (existent?) Accuton C153-4-082 pdf, Accuton C153-8-082 pdf, Fostex FE168EZ pdf, Lowther DX55 and Scan-Speaks 15M/W/WU
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Old 2nd July 2014, 07:45 PM   #4
Lojzek is offline Lojzek  Croatia
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This is basically what you want.
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File Type: jpg Imaginary driver.jpg (162.5 KB, 421 views)
File Type: gif Rhythm FR.gif (17.5 KB, 413 views)
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Old 2nd July 2014, 08:02 PM   #5
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I got the impression that the OP was to take a low Qts driver, then mount it in a small box such that the system Qtc would then be raised up to something like 0.5 to make a good natural 2nd order roll off to mate with the woofer.

It's not that this cannot be done, but you'd still be better off using a high pass. This serves a number of purposes. 1) Separates the impedance of the mid and bass creating an easier load than with both drivers in parallel down to DC. 2) Reduces the power that the mid range drivers voice coil will see, reducing thermal compression. 3) Reduces the excursion of the mid ranger driver reducing distortion.

If you have the mid ranges system resonance, tuned to say 300Hz with a Qtc of 0.5 and you use this as a natural filter to cross to the bass driver then you will be operating the mid driver, at the bottom of its range, where it will be controlled by the amplifier and the systems own tuned resonance. If however you decide to place it in a larger cabinet, say tuned to 100Hz, but with a Qtc of 0.25 and cross it with a proper crossover still targeted at 300Hz with a filter Q of 0.5, then the drivers motion will now largely be controlled entirely by the amplifier as it is operating away from the natural system resonance.
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Old 2nd July 2014, 09:05 PM   #6
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A driver having a very low Qtc when in a closed box has a behavior quite similar to an order 1 high pass filter (6 dB/o). Its response can be used as the order 1 section of an order 3 high pass filter (18 dB/o).
My three-way system is based on this property but with the difference that the driver does not need to have a real low Qtc, a well adjusted parametric equalization is able to give the required apparent Qtc.
The driver resonance is now taken in account in the transfer function and the response is very close to the intended theoretical one.
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Old 2nd July 2014, 11:44 PM   #7
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Quote:
Originally Posted by Lojzek View Post
This is basically what you want.
yeah the graph would look something like that. The main intention is to get best midrange out of it.

I had a doubt regarding the excursion of such driver will there be any problem with such ?
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Old 3rd July 2014, 07:04 AM   #8
Lojzek is offline Lojzek  Croatia
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Hi rhythm,

I don't think getting the best midrange out of it has anything to do with
the idea of driver's Qts being 0,1.

Assuming available power of 30W and Xmax 4 mm:
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File Type: gif rhythm excursion.gif (9.3 KB, 345 views)
File Type: gif Imp.gif (10.7 KB, 345 views)
File Type: gif Consumed Power.gif (10.6 KB, 345 views)
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Old 3rd July 2014, 11:43 AM   #9
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Quote:
Originally Posted by rhythmsandy View Post
well the application is towards the midrange driver for 5.5 inch. The reason behind is

There are important factors to be considered that drivers which has high Qms and low Rms gives better details. My goal is that to make a low Rms driver with high Qms and with very low Qts as much as .1 i believe the cone is in much control by electrical signal than the mechanical compliance of the driver. Lets consider a 5.5 inch driver is designed to a Fs of 50Hz and with super low Qts of .1 when loaded into a box the fs will go higher and I am very happy for it for two reasons one low box size and another is no need of capacitor in the path rather use just a low pass filter for the upper cutoff and lower cutoff is taken care by the natural rolloff for the driver. The bass is being handled by another driver.

Please let me know if there are any pros and cons of this kind of low Qts driver.
The only way to get a Qts this incredibly low is to have a simply diabolical motor force for the size of the driver. Typically, that's not needed. It's especially not needed for a sealed, low volume midrange as the driver should, as you said, be controlled by the box stiffness at the bottom end. In its passband, it won't use the box stiffness to much effect other than isolation (assuming you're not crossing over at like 150Hz).

For a detailed mid, a very low mass diaphragm is definitely a plus. A very large motor is not necessary and does indeed come with its own bag of issues. Since we're talking next to minimal excursion here, you'd have very successful results using a fully underhung midrange driver instead. Lower distortion, albeit lower Bl than the design you propose.
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Old 3rd July 2014, 11:44 AM   #10
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Quote:
Originally Posted by Lojzek View Post
Hi rhythm,

I don't think getting the best midrange out of it has anything to do with
the idea of driver's Qts being 0,1.

Assuming available power of 30W and Xmax 4 mm:
Agreed
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