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Seismic Quad 18ís

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Al Rettich:
https://www.seismicaudiospeakers.com/collections/live-sound/products/the-quad-18-4-x-18-inch-subwoofer-cabinet#

This past Sunday ran into a company who had ten of these cabinets laid end to end in front of the stage.  Powered them with Crown MA3600ís.

Not the worst sounding sub Iíve heard. However, something just didnít sound quite right.  Now that Iím looking at the online specs, if the drivers are facing each other, Iím assuming one would be flipped out of phase. However, there would still be a bit of delay from one voice coil to the other yes? I understand that yes there is about 6Ē from coil to coil, there would still be a slight delay, affecting the performance? Or am I crazy. Iím wondering if this is what I heard.

Mike Caldwell:
Looks like their using compound isobaric speaker loading. The speakers are either mounted together cone to cone or one directly in front of the other with a sealed chamber between them, the cone to cone version flips the polarity of one of the drivers.

The cone to cone version cancels out the mechanical distortion produced by the drives, the design overall lets you cut the box size/volume in half while maintaining the low frequency cutoff.

The blurb on their website is actually fairly correct but it's Seismic Audio so their published specs are really any ones guess. Kind of funny to see a speaker like that with 1/4 inch jacks on it.
I wonder if it holds together any better than their snake cables and rack mount splitters!!!!

Ivan Beaver:

--- Quote from: Al Rettich on February 05, 2024, 10:11:57 PM ---https://www.seismicaudiospeakers.com/collections/live-sound/products/the-quad-18-4-x-18-inch-subwoofer-cabinet#

 Now that Iím looking at the online specs, if the drivers are facing each other, Iím assuming one would be flipped out of phase. However, there would still be a bit of delay from one voice coil to the other yes? I understand that yes there is about 6Ē from coil to coil, there would still be a slight delay, affecting the performance? Or am I crazy. Iím wondering if this is what I heard.

--- End quote ---
You cannot "flip something out of phase".  You can only flip the polarity.

Yes there is a big difference.  "out of phase at one freq will be in phase at other freq".  Out of polarity will be out at all freq.

You need to think in terms of wavelength.  50Hz is roughly 20' long.  6" is nothing at that freq.  At 2Khz, that is a completely different issue.

John Schalk:

--- Quote from: Al Rettich on February 05, 2024, 10:11:57 PM ---https://www.seismicaudiospeakers.com/collections/live-sound/products/the-quad-18-4-x-18-inch-subwoofer-cabinet#

This past Sunday ran into a company who had ten of these cabinets laid end to end in front of the stage.  Powered them with Crown MA3600ís.

Not the worst sounding sub Iíve heard. However, something just didnít sound quite right. 

--- End quote ---
Let's say that each sub is 4' long if deployed horizontally, which is how I take your "end to end" comment.  That would make a subwoofer "line" that is 40' long which will greatly narrow the dispersion pattern horizontally.  To offset this effect, the sound company may have delayed one or more of the subwoofers in the line to generate a wider dispersion pattern.  Dave Rat says that this type of delayed line can result in a smeared image which means that there is a trade off in sound quality for this deployment configuration.  Of course, that is true for almost any subwoofer deployment configuration.  I'm just spit-balling here as I finish up the last of this morning's coffee :)

Chris Grimshaw:
Clamshell isobaric loading will reduce even-order distortion from drivers, but IIRC odd-order increases. Even-order distortion is harmonically-related to the input signal (ie, sounds fine from a musical perspective), but odd-order is not. It's possible, then, that a listener used to a certain amount of harmonic distortion will find those cabinets a little odd-sounding, depending on how hard they're pushed.

The "delay" between the cones isn't a concern - the two cones and lump of air in-between are acting in unison at subwoofer frequencies.


In terms of that particular setup, I can see a few potential issues/factors:
- The Crown MA3600 wasn't a wonderful sub amp in its day, and its day has long since passed. We don't know how well they've been looked after. The cabinets present a 2x4ohm load, so they might well have been wired for 2ohm/cab, just to really give the amps some pain.
- We don't know how long the cable runs are. If, as I suspect, they've gone for 2ohm use, then there'll be a serious loss of power and damping factor over anything other than a very short cable run.
- Along a similar line, I haven't seen how those amps react to a squishy mains supply, but it could be another consideration.
- The drivers in those cabinets don't appear to be anything special - 600w RMS per driver isn't much these days. While high power handling doesn't automatically make one driver better than another, the other technology that gets included with higher-end drivers (like double spiders, shorting rings/sleeves, etc etc) does make a difference to performance.
- Quad-18" cabinets might evoke some image of having crazy output per cabinet, the maximum output of those cabinets will only ever be the same as a pair of 18" drivers in a larger enclosure. Isobaric loading does not increase the radiating area.
- The short tunnel in front of the drivers will result in standing waves. That'll put a spike in acoustic output which is way above the passband of the subwoofer itself, but will also have an imprint on the harmonic distortion profile.

Finally, unless we have access to all the settings of all the processing from desk input to power amps, there's a million other ways for the operator to screw up the sound as well.

Chris

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