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In the Forum: Audio Discussions
In the Thread: Exceptional loudspeakers drivers
Post Subject: Don't forget the wheels!Posted by jessie.dazzle on: 4/7/2007
Hello NBC,
If you have the space, and the sense of humor, go with a large pair of SEALED enclosures.
If done right, it will change your life.
Regarding the Northcreek Audio version of the 1808 : According to some research I did a while ago, this driver has not been available for a long time.
Some say that Northcreek simply glued on a second cone, thereby adding mass, and bit of stiffness (depends how they glued the cone). I was also told that at one point they got the mass up by adding weight under the dust cap.
Adding mass will certainly lower the free-air resonance of a driver, but it is just that much more mass the motor will have to "articulate".... accelerate, stop, and re-accelerate in the opposite direction... in this case, anywhere from 15 to 60 times per second. Even with the neodymium-cocaine magnet, this is not easy... something like jumping rope immediately after gorging yourself on an XL pizza...
More moving mass for the same effective piston area has to result in soggier bass.
If you don't already have the drivers, you may want to consider a pair of 18" McCauley 6174s. This is a paper cone driver (at 222 grams the moving mass could be lighter ; the rear surface of the cone is coated). One or more of the same people who came up with the 1808 participated in the creation of this driver. The McCauley specs list Fs at 20Hz, but they have not updated this figure since changing to a different suspension material a long time ago.
These drivers are not perfect, but in a way, they are closer to the original 1808 (paper cone model) than the current Aurasound product. I would guess the McCauleys could be made even better if it did not have to take into account the demands of the "Pro Audio" world.
I use a pair of them in sealed enclosures (15 cubic ft each) made from concrete. In these boxes, with no EQ, they roll of at 40Hz. With some help (this is the only place I use EQ) from a Velodyne SMS-1, they can be EQed flat (or rising) down to 18Hz. This is because the drivers have a lot more excursion than is normally required for home use. They can handle, but DO NOT REQUIRE a lot of power (94dB/watt @ 1m)... A pair of Lamm M1.1s drives them very well (as a reference for power, this is more than enough to simulate Sunday mass in a cathedral... not that its your thing, but they will also effortlessly best even a good discotheque in both quality and quantifiable pressure).
In my opinion, the SMS-1 is almost mandatory... Not only does it allow you to completely control crossover frequencies EQ, phase, etc, but it also allows you to SEE a real time plot of the repeating swept tones it generates... you can see what is going on, and how it relates to the rest of your speakers. But it is not idiot proof... you can of course make a mess.
Last point : Before finishing the enclosures, I did a little testing with the lids off... The pressure from these drivers is out of proportion to what you might expect could come from a piece of paper... it was enough to lift and rattle two concrete slabs (2 X 36 lbs) I had placed over the top in a futile attempt to create a temporary seal.
Good luck,
(if you go with concrete, at a half a ton, you will want wheels in place of spikes)
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