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New B&C 18DS115-4 in Keystone sub
David Winners:
The new B&C 18DS115-4 looks like a good candidate for the Keystone sub.
+2.5 mm (16.5 mm) xmax over the 18SW115-4 (14 mm)
Same 97dB sensitivity
My main concern is the 3.3 ohms Re, though in all honesty, I don't know enough to know what to be concerned with...
Any thoughts?
Thanks for your time,
David
Edited to correct sensitivity... A couple times
Art Welter:
--- Quote from: David Winners on May 17, 2018, 09:13:13 AM ---The new B&C 18DS115-4 looks like a good candidate for the Keystone sub.
+2.5 mm (16.5 mm) xmax over the 18SW115-4 (14 mm)
Same 97dB sensitivity
My main concern is the 3.3 ohms Re, though in all honesty, I don't know enough to know what to be concerned with...
Any thoughts?
--- End quote ---
David,
Although the BC18DS115-4 specifications look like it would work well in the Keystone, it does not look like it would work any better than the BC18SW115-4.
The two drivers have the same Re, the 18DS115-4 more Xmax, the 18SW115-4 more Xvar.
The 1dB sensitivity increase is above 100 Hz, the 18DS115-4 is slightly less sensitive below.
The 18DS115-4 has more Bl & Mms and lower Fs (below the Keystone's Fb) which may result in less output near Fb but slightly less steep cutoff below.
The Keystone's mouth exit was specifically designed for optimal response with the 18SW115-4, enough reason to use it rather than another driver unless there is a compelling cost difference or large increase in excursion.
Art
David Winners:
Thanks for taking a look Sir.
I appreciate your time.
David
Ivan Beaver:
--- Quote from: David Winners on May 17, 2018, 09:13:13 AM ---
My main concern is the 3.3 ohms Re, though in all honesty, I don't know enough to know what to be concerned with...
--- End quote ---
The Re is the DC resistance-NOT the impedance load presented to the amplifier.
In almost all cases the impedance (opposition to AC current flow) is higher than the resistance (opposition to DC current flow).
In some cases (specifically horns) the actual impedance load on the amplifier is higher than the rated impedance of the driver.
In some cases it is actually twice what the rated impedance is.
I would not give Re a second thought.
Art Welter:
--- Quote from: Ivan Beaver on May 17, 2018, 05:15:30 PM ---The Re is the DC resistance-NOT the impedance load presented to the amplifier.
In almost all cases the impedance (opposition to AC current flow) is higher than the resistance (opposition to DC current flow).
In some cases (specifically horns) the actual impedance load on the amplifier is higher than the rated impedance of the driver.
In some cases it is actually twice what the rated impedance is.
I would not give Re a second thought.
--- End quote ---
Ivan,
In almost every FLH, TH or BR design, the impedance drops to very near Re at Fc or Fb.
The average and peak impedance may be much higher, but the impedance minima is still there, presented to the amplifier.
As an example, the "4 ohm" TH-118 is less than 4 ohms from around 55 Hz to almost 80 Hz (dropping to 3 ohms)- plenty of EDM droning frequencies in that region to heat things up.
But don't give it a second thought, with the 3.3 ohm Re B&C18SW115-4 instead of the 2.5 ohm Re of the 18NLW9600-4, the TH-118 impedance hardly drops below 4 ohms ;^).
Art
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