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Author Topic: Seismic Quad 18ís  (Read 3235 times)

Al Rettich

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Seismic Quad 18ís
« 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.  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.
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Mike Caldwell

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Re: Seismic Quad 18ís
« Reply #1 on: February 05, 2024, 11:24:04 PM »

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

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Re: Seismic Quad 18ís
« Reply #2 on: February 06, 2024, 08:19:53 AM »

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.
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.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
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John Schalk

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Re: Seismic Quad 18ís
« Reply #3 on: February 06, 2024, 10:51:49 AM »

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. 
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 :)
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Chris Grimshaw

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Re: Seismic Quad 18ís
« Reply #4 on: February 06, 2024, 11:37:24 AM »

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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Bob Faulkner

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Re: Seismic Quad 18ís
« Reply #5 on: February 07, 2024, 09:58:19 AM »

hmmm... looking at their specs and the wording that is used to describe the cabinet, this looks like a 4-speaker cabinet with 2-speakers on one pair of wires and the other 2-speakers on another, separate, pair of wires.

CONNECTORS:Two 1/4" and Two Speakon per side

The power ratings shown on their website and on the back of the cabinet appear to point to two independent "pairs" of speakers.

POWER RATING: 2 x 1200 Watts RMS; 2 x 2400 Watts Peak
NOMINAL IMPEDANCE: 2 x 4 Ohms

Looks like the cabinet would need two separate amplifier channels for its full utilization.

The term "Quad-18" is correct; However, it may not mean all 4 speakers work together.

I do NOT trust anything Seismic puts on their website. 

As a side note on speaker cabinets, many (many) years ago, I swapped out a Peavey 18" speaker (from a Peavey 118 sub) with an RCF 18" speaker.  This was so I could run my Crown PowerTech 3 amps in bridge-mode (1500 watts @8ohms) on each cabinet.  The cabinets only had 1/4" inputs (2).  The pressure from the speaker blew the 1/4" cables out every time.  I changed out the 1/4" to Speakon... which resulted in the cables staying in, but the pressure from the driver eventually destroyed the cabinet (blew it apart slowly), over about 2 years. 

There was nothing wrong with the Peavey 118 cabinets; I'm sure it just wasn't designed to handle that level of pressure.
« Last Edit: February 07, 2024, 10:01:14 AM by Bob Faulkner »
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Steve-White

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Re: Seismic Quad 18ís
« Reply #6 on: February 07, 2024, 01:26:58 PM »

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.

Thanks for this Ivan.  ""out of phase at one freq. will be in phase at other freq".  Out of polarity will be out at all freq."

I used to mix the term phase with polarity.  This puts it real clearly why not to do that as they are in most cases vastly different.
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lindsay Dean

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Re: Seismic Quad 18ís
« Reply #7 on: February 07, 2024, 02:07:48 PM »

Well they had them set up correctly in the beginning forward-facing The only problem was they didn't  have them forward faced into the dumpster 👍
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Steve-White

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Re: Seismic Quad 18ís
« Reply #8 on: February 07, 2024, 04:20:06 PM »

Well they had them set up correctly in the beginning forward-facing The only problem was they didn't  have them forward faced into the dumpster 👍

The Bose/Pyle dumpster?  :)
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Chris Hindle

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Re: Seismic Quad 18ís
« Reply #9 on: February 10, 2024, 07:01:09 AM »

The Bose/Pyle dumpster?  :)
.... to give a soft landing to Accordions and Banjo's. 8)
Chris.
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Ya, Whatever. Just throw a '57 on it, and get off my stage.

ProSoundWeb Community

Re: Seismic Quad 18ís
¬ę Reply #9 on: February 10, 2024, 07:01:09 AM ¬Ľ


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