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[George Friedman-Jimenez]

Gordon's explanation makes some big and unverifiable assumptions like linearity on a semilog scale. Also, we really don't know, other than the slope, what type of crossovers are being used (LR, Butterworth, FIR, etc) and the number of dB down at the crossover frequency can be very different for each of those, even given the same slope (in dB per octave). Just turning up the sub will shift the acoustic crossover point to a higher frequency but will not necessarily create a smoother crossover. I am looking for very musical bass rather than slamming bass for the type of music we play. Also, not all JBL systems sound great, so predicting that this particular one will is a big assumption as well.
The tech support guy at JBL that I spoke with yesterday did not know the answer to my question and referred me to another guy's voicemail, I am still waiting for a call back.

Gordon and Scott, have you heard the PRX710 / PRX715XLF system?
Tom, have you used your system out yet? Any more observations?

I am trying to get as much information as I can before I go listen to them in a shop like GC where the salesperson is unlikely to know the answer, the acoustics are unpredictable, and they may not let me play my test tracks or do even simple measurements. And I really dislike buying stuff and returning it if I don't like it.

[Scott Wagner]

Gordon and Scott, have you heard the PRX710 / PRX715XLF system?

I am trying to get as much information as I can before I go listen to them in a shop like GC where the salesperson is unlikely to know the answer, the acoustics are unpredictable, and they may not let me play my test tracks or do even simple measurements. And I really dislike buying stuff and returning it if I don't like it.

I own both of these boxes' big brothers and have listened extensively to the 710/715XLF combination in a demo (but have not driven it in anger).  I heard no obvious holes during my audition (and that is an area where the holes would be obvious).  I think you'll be happy with the sound of this system as long as you're reasonable with your expectations of output.  These two products were specifically designed to work together.

[George Friedman-Jimenez]

Thank you Scott. In the demo, were the 710 tops using the 120 Hz high-passed output signal from the 715XLF or an external crossover?

This will be for my tiny system for small venues in NYC and a small car, and my expectations for SPL are realistic. I also own the PRX618XLF and PRX612M combination for bigger gigs, and the crossover is pretty smooth using the 90 Hz built-in crossover which has a 90 Hz low-pass for the sub and a 90 Hz high-pass for the top. That is why I am concerned that a 120 Hz high-pass for the top would leave a hole between 90 and 120, especially since at performance SPLs the 710 would be expected to have less strong SPL to begin with in the 90-120 Hz range than the 612. Also, buying more 612/618XLFs would not be my preference as size is important. In addition, I don't particularly care for the sound quality of the 612s on either vocals or monitors and am hoping the 710 will sound a little better.

[Scott Wagner]

Thank you Scott. In the demo, were the 710 tops using the 120 Hz high-passed output signal from the 715XLF or an external crossover?

This will be for my tiny system for small venues in NYC and a small car, and my expectations for SPL are realistic. I also own the PRX618XLF and PRX612M combination for bigger gigs, and the crossover is pretty smooth using the 90 Hz built-in crossover which has a 90 Hz low-pass for the sub and a 90 Hz high-pass for the top. That is why I am concerned that a 120 Hz high-pass for the top would leave a hole between 90 and 120, especially since at performance SPLs the 710 would be expected to have less strong SPL to begin with in the 90-120 Hz range than the 612. Also, buying more 612/618XLFs would not be my preference as size is important. In addition, I don't particularly care for the sound quality of the 612s on either vocals or monitors and am hoping the 710 will sound a little better.

Yes, it was using the internal crossover from the PRX715XLF.  Not that I think this is a good idea, but you also have the option to run the tops full-range with the push of a button.

[Samuel Rees]

Am I silly for being completely willing to assume that Harmon knows what they are doing?

Doesn't JBL and crown have some similar 24/48 crossover settings in the 700/800 series?

[George Friedman-Jimenez]

I was not questioning the difference in slopes of the 2 crossover filters (24 dB/octave vs 48 dB/octave), which is very commonly done. My question was about the 30 Hz difference in the -6 dB crossover frequencies for the low-pass (-6 dB at 90 Hz) and high-pass (-6 dB at 120 Hz) portions of the crossover, which is very unusual.

[Samuel Rees]

I was not questioning the difference in slopes of the 2 crossover filters (24 dB/octave vs 48 dB/octave), which is very commonly done. My question was about the 30 Hz difference in the -6 dB crossover frequencies for the low-pass (-6 dB at 90 Hz) and high-pass (-6 dB at 120 Hz) portions of the crossover, which is very unusual.

I don't think its reasonable to question it unless you graph the slopes and prove there is a hole. Gorden provided a good explanation which has been ignored. Is there an issue with that explanation?

[George Friedman-Jimenez]

I certainly did not ignore Gordon's explanation, I just have some concerns about it that I chose not to express. But since you ask, Gordon's explanation does not seem to include the fact that the signals are already down by 6 dB at the 90 Hz low pass frequency and the high pass 120 Hz frequencies. The sketching needs to be done on horizontal 2 cycle semilog paper for the lines to be straight and the estimates to be correct. The conclusion of Gordon's explanation conflicts with that from David Morison's calculation, which predicts an 8 to 12 dB hole. Gordon's explanation also conflicts with my own experience constructing sub/top crossovers using a DSP. When I separate the high pass -6 dB frequency from the low pass -6 dB frequency by even 5 or 10 Hz, there is an audible hole. I have never tried separating them by as much as 30 Hz. Although I am not a competent crossover designer, the few crossover design calculations I have seen for passive crossovers use the same frequency for the high pass and low pass filters, I have not seen crossover calculators or equations that let you choose a different frequency for each filter. The classic Linkwitz Riley 4th order (24 dB/octave) crossover certainly assumes the same frequency. Modern DSP-based crossovers give more flexibility but I still have not seen such a wide gap between the low pass frequency and the high pass frequency. Flexibility to use a subwoofer with different tops would be a plus and even if somehow the PRX710 / 715XLF pair is designed to sound good with a 30 Hz gap, trying to use different tops would probably not work too well with the 120 Hz high-pass and 90 Hz low-pass, unless I used an adjustable external high pass filter instead of the high-pass loop through output from the 715XLF. But one of my main purposes in purchasing a tiny system like this would be to minimize complications like having to bring a DSP or external crossover along to gigs.

I think those are more than adequate reasons to raise the question. And in my opinion it is not necessarily a good assumption that although this crossover configuration seems somewhat bizarre that it will work perfectly just because it was designed by Harmon/JBL.

Of course the bottom line will be listening to and testing the actual 710/715XLF combination at performance level SPL in a store, in my studio, and in a performance venue, but I think it is reasonable to do my due diligence and try to clarify a perplexing theoretical question before investing my time and a salesperson's time setting up a demo.

[Tom Burgess]

Gordon's explanation makes some big and unverifiable assumptions like linearity on a semilog scale. Also, we really don't know, other than the slope, what type of crossovers are being used (LR, Butterworth, FIR, etc) and the number of dB down at the crossover frequency can be very different for each of those, even given the same slope (in dB per octave). Just turning up the sub will shift the acoustic crossover point to a higher frequency but will not necessarily create a smoother crossover. I am looking for very musical bass rather than slamming bass for the type of music we play. Also, not all JBL systems sound great, so predicting that this particular one will is a big assumption as well.
The tech support guy at JBL that I spoke with yesterday did not know the answer to my question and referred me to another guy's voicemail, I am still waiting for a call back.

Gordon and Scott, have you heard the PRX710 / PRX715XLF system?
Tom, have you used your system out yet? Any more observations?

I am trying to get as much information as I can before I go listen to them in a shop like GC where the salesperson is unlikely to know the answer, the acoustics are unpredictable, and they may not let me play my test tracks or do even simple measurements. And I really dislike buying stuff and returning it if I don't like it.

Unfortunately I've not had the opportunity to use them live yet.  I was using the crossover on the sub.  The track was Gaslighting Abbie from Steely Dan's Two Against Nature out of my Focus S phone into a Soundcraft EPM mixer.  It's a high res file but I didn't use my ProCo iFace like I normally do just for the lack of time but I will do so the next time I plug it up.  Even without it the pair seem to play very nicely with each other.

As to the technical question... fortunately for all of us I'm not the one trying to answer the technical questions, lol!    There are folks here way smarter than me that have already chimed in but as someone previously stated (I'm paraphrasing here) the only thing that really matters is how they sound and, after hearing one of my "go-to" tracks on them I think they're going to work quite nicely.

As far as auditioning them goes, if GC won't let you do what you need to do then I would strongly recommend finding another dealer... there's bound to be plenty of them in the NYC area.  If you find yourself in OK you're welcome to give me a heads-up and we can rock the joint with whatever track you want.

[George Friedman-Jimenez]

Thank you Tom for the details, and for the invite!
I look forward to auditioning them in a couple weeks, after I get back from travel.

[ProSoundWeb Community]