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Author Topic: Replacing the JBL PRX 718XLF  (Read 1401 times)

Patrick Cognitore

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Re: Replacing the JBL PRX 718XLF
« Reply #20 on: June 17, 2019, 10:01:08 pm »

I really liked the size of the PRX (compared to my SRX728s); it was easy to move in/out and around.  But after the disappointing moments with it,  actually ended up using one of my 728s for smaller events.  The PRX has a 1500 watt amp... I powered the single 728S with a bridged PLX1602 (1600 watts). 

I actually think the PRX is 1500 "marketing" watts.  ;)

...but when it came to needing to feel the kick in your chest, it just didn't do it.  It always felt/sounded like the thump was getting lost.  The sub was never run at its maximum; I always ensured head-room was available to manage the "thump".

...the difference (in thump and other things) with the 728 was so much greater, that I ended up lugging a 728 around for smaller events. 

This get's me back to thinking that you just appreciated the higher output of the bigger, more powerful sub. It'd be a shame to be searching for a single 18" sub with 'thump' but what you really need is the output of a 2x18 in a single sub.

It always seemed loud enough.

Did you ever get to compare the two models using normalized output? Even if the PRX seemed loud enough in the feel, it could've been the case that when you brought and setup the SRX you naturally had more output (even at similar upstream drive levels) and that was the main difference.

The PRX has an internal LPF set at under 90hz so it's possible the tonality you were looking for was out of the range. And having an external DSP handling crossover duties before the sub could've been confounding the response of the sub. I realize you no longer have that sub so some of this discussion is moot.

If you can get a hands on demo of the active SRX818 that'd be a good option to hear your price point.
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Bob Faulkner

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Re: Replacing the JBL PRX 718XLF
« Reply #21 on: June 18, 2019, 07:00:12 am »

Very possible with the marketing watts!

Never did compare the models.  The differences between them were so obvious, I never felt there was a need for a comparison.  The SRX had more output, but (as referenced before), it was more about the tone of the cabinet and it's ability to reproduce an "impact" tone.
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Geert Friedhof

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Re: Replacing the JBL PRX 718XLF
« Reply #22 on: June 18, 2019, 08:07:41 am »

I own some 8004's for 3 years now, and can tell you that any decent 12 or 15" top will outrun a single 8004. I can also tell you that you are producing a lot of sound and vibrations at that point. They really sound much bigger than they are. I always use the 90Hz crossover. I would not recommend the 120Hz setting.

Regarding the prx7: I have to use a prx735/2x718xlf rig a few times per year in a low ceiling, 50'x100' room, and i too think it is near impossible to make it sound 'big' without excessive eq. Granted, it is grindcore/metal 'music' with double kick etc, but still...

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Bob Faulkner

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Re: Replacing the JBL PRX 718XLF
« Reply #23 on: June 18, 2019, 01:44:21 pm »

I own some 8004's for 3 years now, and can tell you that any decent 12 or 15" top will outrun a single 8004. I can also tell you that you are producing a lot of sound and vibrations at that point. They really sound much bigger than they are. I always use the 90Hz crossover. I would not recommend the 120Hz setting.

Regarding the prx7: I have to use a prx735/2x718xlf rig a few times per year in a low ceiling, 50'x100' room, and i too think it is near impossible to make it sound 'big' without excessive eq. Granted, it is grindcore/metal 'music' with double kick etc, but still...
My level settings for top cabinets are to accommodate the sub; I will throttle back the top cabinets to ensure a good balance... before adding more power to the sub.

I'm interested in your input on why don't recommend the 120Hz setting.  Sometimes, I will xover that high to keep some of the upper bass out of the top cabinets (depending on the top cabinets: ie PRX-710).

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Geert Friedhof

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Re: Replacing the JBL PRX 718XLF
« Reply #24 on: June 18, 2019, 03:08:06 pm »

On 90Hz the sub produces composed, dry, deep notes, with a very tight kick. A kick sounds like "Bonk!" On 120Hz the sub starts to ring a bit. The kick starts to sound like "Boink!" if you get what i mean.

About levels: Ofcourse you set your levels to make the combo sound good. But that is all it does. When you need the volume you just raise your faders a bit more, and by doing so give the speakers more power output. There will always be a point that either the sub or the top can't give any more output. This is where the rig is to small.
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Luke Geis

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Re: Replacing the JBL PRX 718XLF
« Reply #25 on: June 18, 2019, 03:48:05 pm »

I too believe that higher X-Over settings for subs make the kick sound tubby and hollow sounding. I.E. more work to make it sound right.

I am in the camp of getting the Main PA doing as much work as it can, I will cross the subs over as low as I practically can. Typically for me, this is between 80hz and 60hz. This does two things. It allows the PA to do more work on the sound everyone actually hears. Second, it gets the frequency low enough that major phase issues between the subs and Mains are reduced. Third, it reduces the separation between subs and Mains that most complain about when doing subs on an aux. Since the Mains almost outrun the subs in most cases, making the Mains do a little more work can make it so that the subs have a little more room to work. My big thing is that below about 80hz, humans have a tough time locating the source of the sound. So if the Mains are pumping out a decent amount of energy at 80hz and the subs are filling in mostly around 60hz, the sound we perceive is more natural and filled out from the predominant source.
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Bob Faulkner

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Re: Replacing the JBL PRX 718XLF
« Reply #26 on: June 18, 2019, 07:23:06 pm »

On 90Hz the sub produces composed, dry, deep notes, with a very tight kick. A kick sounds like "Bonk!" On 120Hz the sub starts to ring a bit. The kick starts to sound like "Boink!" if you get what i mean.

I do know what you mean.  Were your experiences specific to the 8004 sub, or in general?

Some of the systems I have mixed on, the tops have been too small (and sometimes under-powered); crossing over at 120 kept the tops from running out of gas.

Most of the time I xover around 90.

I too believe that higher X-Over settings for subs make the kick sound tubby and hollow sounding. I.E. more work to make it sound right.

I am in the camp of getting the Main PA doing as much work as it can, I will cross the subs over as low as I practically can. Typically for me, this is between 80hz and 60hz. This does two things. It allows the PA to do more work on the sound everyone actually hears. Second, it gets the frequency low enough that major phase issues between the subs and Mains are reduced. Third, it reduces the separation between subs and Mains that most complain about when doing subs on an aux. Since the Mains almost outrun the subs in most cases, making the Mains do a little more work can make it so that the subs have a little more room to work. My big thing is that below about 80hz, humans have a tough time locating the source of the sound. So if the Mains are pumping out a decent amount of energy at 80hz and the subs are filling in mostly around 60hz, the sound we perceive is more natural and filled out from the predominant source.

Yes, setting the crossover too high makes a hallow/shallow tone.  Having mixed on various systems (some "frakensystems", I found the need to move the xover settings up/down to accommodate limitations of the speakers.  I keep my system around 90hz.
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Caleb Dueck

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Re: Replacing the JBL PRX 718XLF
« Reply #27 on: June 18, 2019, 08:12:37 pm »

I am in the camp of getting the Main PA doing as much work as it can, I will cross the subs over as low as I practically can. Typically for me, this is between 80hz and 60hz. This does two things. It allows the PA to do more work on the sound everyone actually hears. Second, it gets the frequency low enough that major phase issues between the subs and Mains are reduced. Third, it reduces the separation between subs and Mains that most complain about when doing subs on an aux. Since the Mains almost outrun the subs in most cases, making the Mains do a little more work can make it so that the subs have a little more room to work. My big thing is that below about 80hz, humans have a tough time locating the source of the sound. So if the Mains are pumping out a decent amount of energy at 80hz and the subs are filling in mostly around 60hz, the sound we perceive is more natural and filled out from the predominant source.

Totally agree.  I'm starting to drift toward thinking the mains should reproduce as close to full range as possible, without any sub-bass 'haystack'.  Then let the subwoofers on an aux be used for effect, IE haystack.  This also helps with instruments/voices that have LF but don't need the big LF boost, such as super deep bass male vocals, bass guitar, keys, etc.  Other more artificial sounds (kick drum) can have as much or as little LF 'effect' dialed in. 

This is another vote for flown subwoofers - much less physical offset between the LF from the mains vs subs.  With lower than normal crossovers this isn't as huge a concern as it seems.
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Bob Faulkner

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Re: Replacing the JBL PRX 718XLF
« Reply #28 on: June 19, 2019, 11:11:11 am »

Thanks all for the input and suggestions.

After a "vision-quest" moment this morning, I'm needing to change direction a little with how I approach subs.  Powered cabinets are great (my tops and full-range cabinets are powered), but for my setup, the subs will need to be passive.

I'm looking at a few passive options.
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Steve Crump

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Re: Replacing the JBL PRX 718XLF
« Reply #29 on: June 19, 2019, 11:42:27 am »

Thanks all for the input and suggestions.

After a "vision-quest" moment this morning, I'm needing to change direction a little with how I approach subs.  Powered cabinets are great (my tops and full-range cabinets are powered), but for my setup, the subs will need to be passive.

I'm looking at a few passive options.


The JTR Captivator 212 comes as a passive also. Here is a link to the Data-Bass test.

https://legacy.data-bass.com/data?page=system&id=142
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ProSoundWeb Community

Re: Replacing the JBL PRX 718XLF
« Reply #29 on: June 19, 2019, 11:42:27 am »


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