JBL PRX618S-XLF vs. JBL SRX718s

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Mario Pollio

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Jan 18, 2012
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Hey all. I'm new to these forums, I hope I'm posting in the right section. I'm a mobile DJ with 2 PRX618s-XLF's and 2 PRX615m's. For the price and weight, I think these things sound pretty damn good. For a larger rig sometime in the future I wanted to add 2 more XLF's and a pair of 625's with the 615's as side fills. My question regarding the XLF's vs. The SRX718's is mostly about the specs.

The max spl of the XLF's is rated at 133 db, but it doesn't state if that's at half space, full space etc. Same goes for the SRX718, which is rated at 130db. Does the XLF really get louder then a properly powered SRX718? Owning the XLF's, they do get pretty loud. I like them a lot more then the QSC HPR181i's I used to own. They seem to get louder and deeper. The HPR181i's also seemed to get a little sloppy at their limit while the XLF seems to hold up better.

Basically my question is, are both the XLF and SRX718 subs rated the same way? And if so, why is it that the XLF would have a 3db higher spl rating then the SRX718? Is that all because of the box size? Has anyone actually listened to and compared the two as far as output goes?
 
Re: JBL PRX618S-XLF vs. JBL SRX718s

Does anybody know if the SRX718 was rated in full space or half space? When I search for this I get mixed answers. The JBL VRX918 is said to be tested in full space, and the box size, components (driver etc) as well as specs are all nearly identical. That would make me assume that the SRX718 IS tested in half space, but am not completely sure
 
Re: JBL PRX618S-XLF vs. JBL SRX718s

Many are the arguments...

I would say it doesn't really matter. If you like the PRX, I would just add those, up to 3-4 per side. That should give you a nice scaleable system.
 
Re: JBL PRX618S-XLF vs. JBL SRX718s

Thanks guys. Yeah I've noticed the SRX spec threads. You do a google search and there are endless threads over many different forums about it, just with no certain/accurate answers. I do like the XLF's, I think they sound quite good for what they are. I think I'll just end up adding an addition 2 (total of 4) for larger rooms/parties. If my math is right, you get a 6db increase in max output when coupling subs, and I was planning on having 2 coupled on each side. So 133 plus 6 would be 139. Another 139 on the other side would be like having 2 dual 18's so 139 plus 3 would be 142db max output for the subs.

One more thing I was wondering. Do the benefits of coupling end just with the SPL increase? I've noticed dual 18's like the SRX728 not only get that 6db bump in spl, but also go lower in their frequency response. Would coupling also give you that lower frequency response as well?
 
Re: JBL PRX618S-XLF vs. JBL SRX718s

Mario Pollio said:
One more thing I was wondering. Do the benefits of coupling end just with the SPL increase? I've noticed dual 18's like the SRX728 not only get that 6db bump in spl, but also go lower in their frequency response. Would coupling also give you that lower frequency response as well?
Click to expand...

Adding boxes will not lower frequency response. The only time that happens is with true horn subs where the LF cutoff is governed by the size of the horn mouth. Adding more flex style subs merely increases output at all frequencies the box reproduces. The increased low frequency extension of the single vs. double 18 using the same components is likely due to a change in box volume and tuning.
 
Greg Cameron said:
Adding boxes will not lower frequency response. The only time that happens is with true horn subs where the LF cutoff is governed by the size of the horn mouth. Adding more flex style subs merely increases output at all frequencies the box reproduces. The increased low frequency extension of the single vs. double 18 using the same components is likely due to a change in box volume and tuning.
Click to expand...

Actually, it doesn't happen with horn subs either, that would break superposition. You may get more LF output due to coupling, that you may want to EQ out and thereby turn into headroom, but you will get no additional extension. This myth comes from the days of modeling phonograph horns with simple equations, and making an incorrect assumption about the impedance at the diaphragm.
 
Re: JBL PRX618S-XLF vs. JBL SRX718s

Bennett Prescott said:
Actually, it doesn't happen with horn subs either, that would break superposition. You may get more LF output due to coupling, that you may want to EQ out and thereby turn into headroom, but you will get no additional extension. This myth comes from the days of modeling phonograph horns with simple equations, and making an incorrect assumption about the impedance at the diaphragm.
Click to expand...

You do get additional extension. HOWEVER additional means different things to different people. It is not as much as some think.

Here are graphs of a single-dual-triple and quad Danley DBH218 array. All have the exact same input signal and the mic stayed in he same place (10m) while the other cabinets were stacked (2x2) together.

The DBH218 is a normal horn (not a tapped horn)-so the additional cabinets help to not only lower the extension, but also to smooth out the response-due to better impedance coupling of the larger effective mouth.
 

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Re: JBL PRX618S-XLF vs. JBL SRX718s

Interesting. I see that adding a second seemed to make the biggest difference, when adding a 3rd and 4th, the result seems less dramatic, although still a bump
 
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