JBL PRX715XLF Powered Subwoofer - Excessive Fan Noise

Bob Harvey

Freshman
Aug 18, 2012
90
0
0
Central VA
I recently picked up a pair of these powered 15" subs to use at small venues. And yes, you can indeed pick them up since they weigh only 56 lbs. !

Both easily stacked on the hand truck and made load-in almost pleasant. I'll generally use QSC K10s on top.

The sound from these is nice and tight, as you would expect from a 15, and there's ample punch for most any type of program material ... live or recorded.

The DuraFlex finish on the cabinet appears rugged and I really like the security of the threaded pole mount.

However ...

The noise from the cooling fan is quite excessive. At 2' from the back of the cabinet the fan noise at idle is 74 db with the droning sound of the motor resonating the cabinet at 350 Hz.

The fan noise can even be heard throughout the room along with the program material.

I just can't imagine that JBL let this go out the door without noticing.

My point of reference for quiet is: 4 QSC KW181s, 2 QSC KW153s, and 2 QSC K10s.


Has anyone else heard these subs?

Did I just get lucky and get two that slipped by QC?


- Bob
 
Last edited:

KEITH ERICKSON

Freshman
Jun 24, 2011
5
0
1
Re: JBL PRX715XLF Powered Subwoofer - Excessive Fan Noise

Hey Bob,

I just went and measured one of mine. At 2' from the rear of the speaker i was only getting a reading of 60db. This was set on a C weighting with a fast response although the slow response didn't really change it since it is a steady sound. I basically had to put the mic right up to the fan in order to get 74db.
 

Bob Harvey

Freshman
Aug 18, 2012
90
0
0
Central VA
Re: JBL PRX715XLF Powered Subwoofer - Excessive Fan Noise

Hi Keith:

Thanks for checking yours. Does the fan noise seem louder than what you would expect ?

I just don't think the fan should be making that much noticeable sound. I don't even hear the fans in my QSC speakers.
 
Sep 12, 2012
645
4
18
SW Ontario
Re: JBL PRX715XLF Powered Subwoofer - Excessive Fan Noise

Hi Keith:

Thanks for checking yours. Does the fan noise seem louder than what you would expect ?

I just don't think the fan should be making that much noticeable sound. I don't even hear the fans in my QSC speakers.
Have you contacted JBL?

Sounds odd, could be that something is loose and just needs to be tightened. Could also be that some part that was used to isolate the fan from the enclosure was forgotten on some early units (or the regular guy was sick that day), JBL tech support would have a good idea of things to check.
 

Bob Harvey

Freshman
Aug 18, 2012
90
0
0
Central VA
Re: JBL PRX715XLF Powered Subwoofer - Excessive Fan Noise

Hi Spenser:

The isolation (or lack thereof) of the fan from the enclosure and/or amp panel may indeed be the culprit. Where's my screwdriver? ☺

I have filled out the "contact us" form on the JBL website, but no reply yet. Also, my dealer is going through JBL's rep to follow up on the excessive fan noise.

After Keith said that his db reading was somewhat lower, I noticed that the fans run at two speeds ... idle and faster when there is program audio present.

My readings were just when audio program had stopped and the fans were at full speed. Both subs had similar readings.

Thanks
 

Bob Harvey

Freshman
Aug 18, 2012
90
0
0
Central VA
Re: JBL PRX715XLF Powered Subwoofer - No Audio at Low Level

I noticed another annoyance this week.

At low program levels the subs will go into an idle or sleep mode and shut off the audio.

I'm using QSC K10 tops and they don't demonstrate this at the same program level.

At first I thought the power to the subs had gone off. Then, I noticed that the program indicator light on the front had switched to red indicating no audio present.

I spoke with "Sam" at JBL tech support and asked if there was a trim pot adjustment for this. He said it was controlled by the DSP chip and not adjustable.

Apparently, the DSP threshold is set too high and is telling the amp to enter standby mode even when audio is still present.

This really makes it challenging to provide low level sound reinforcement for certain dinner club environments where background audio is required prior to the band playing.
 

Ben Lawrence

Senior
Mar 2, 2011
1,052
20
38
Vermont
vtaudiovisual.com
I have a bunch of the 700 series and dealing with the same thing. Talking head events in small spaces are the worst. Running 710s in smaller rooms the fan noise clearly audible. I am wondering if it might be possible to wire in a kill switch.

Edit: Oops didn't realize this was a 2013 thread. Carry on.
 
Last edited: