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JBL 708i Monitor Review (DSP: Part 2)

Rate this speaker:

  • 1. Poor (headless panther)

    Votes: 28 22.8%
  • 2. Not terrible (postman panther)

    Votes: 69 56.1%
  • 3. Fine (happy panther)

    Votes: 23 18.7%
  • 4. Great (golfing panther)

    Votes: 3 2.4%

  • Total voters
    123

amirm

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This is a follow up to my part 1 review of the JBL 708i speaker (monitor) using active DSP amplification. A Crown DCI 4/300n four channel amplifier with built-in DSP and profiles for 708i was used in bi-amp configuration.
index.php

The process of configuring the amplifier DSP with the profile for 708i is not overly complicated but made more tedious by missing information in the manual and even bad links. It you can survive through it, you will face a problem in that the gain for the Crown amp is set using analog trim pots. These are notoriously inaccurate. In the normal course of using the amplifier for stereo or multichannel use, this is not a big problem. But when using one channel for woofer and another for tweeter, such mismatch completely messes up the frequence response of the speaker. This is made more complicated by the fact that near-field measurements are highly impacted by where you place the microphone, i.e. the distance relative to each driver. Through some trial and error, I managed to get it close but I think it may be off by 1 dB or 2. I don't know how an end customer can perform the matching without proper instrumentation.

Another problem is the loud fan in the Crown amp. During setup, it seemed to shut off after being powered on. Alas, once testing was done, I realized it had was running (I could not hear due to my hearing protection). This may have impacted the measurements a bit.

I was also disappointed that Harman has locked the EQ settings for the speaker. I see that others have figured out a way to display this but out of the box, the icons are grayed out and the manual tells you the same.

All in all, I think you are buying yourself fair amount of grief here relative to 708p which comes as a packaged deal, ready to go.

Note that the passive crossover is active at all time, whether you use the speaker in one-wire or bi-amp mode.

JBL 708i DSP Speaker Measurement
Here is our frequency response measurements: (actual SPL = 86 dBSPL@1 meter)
JBL 708i Speaker Monitor Active DSP Crown Frequency Response.png

I must say, I expected flatter response. The boost in the treble region of 5 kHz is out of place and seems to be caused by corresponding EQ boost in the DSP. Looking at the Harman measurements, we don't see this:

JBL 708i Speaker Monitor Active DSP Crown Harman Frequency Response.png


Both measurements share a distinct sharp dip but their frequencies are different. Mine is at around 780 Hz whereas Harman's is at 600 Hz. I am wondering if there are differences in production of speakers vs the original samples/design. If we look at the 708p with its integrated amplifiers/DSP, we don't see the error in treble:
index.php


And the dip is at 600 Hz which matches Harman measurements. I would imaging in the case of the 708p, the whole package is tested and measured at the factory to generate the desired result.

Another error is lack of bass extension/flattening in my 780i DSP. I expected this to be resolved as well.

Anyway, moving on, here is our near-field response:

JBL 708i Speaker Monitor Active DSP Crown Amplifier near-field frequency response.png


Compare this to the passive measurement:
index.php


We see that the area around the bass resonance is pulled down as it should be. But there is an extra boost around 5 to 6 kHz that should not be there.

Unfortunately both early window and predicted-in-response look unrefined:
JBL 708i Speaker Monitor Active DSP Crown Early Window Frequency Response.png


JBL 708i Speaker Monitor Active DSP Crown Predicted in-room Response.png


Distortion as before remains excellent at 86 dBSPL but tweeter gets unhappy at 96 dBSPL:
JBL 708i Speaker Monitor Active DSP Crown Amplifier Relative THD Distortion.png


JBL 708i Speaker Monitor Active DSP Crown Amplifier THD Distortion.png


Overall directivity and beam control in horizontal axis remains superb:
JBL 708i Speaker Monitor Active DSP Crown Horizontal Beamwidth Response.png

JBL 708i Speaker Monitor Active DSP Crown Horizontal Directivity Response.png


Vertical is not but it is to be expected in 2-way design:
JBL 708i Speaker Monitor Active DSP Crown Vertical Directivity Response.png


Finally here are CSD and step responses:
JBL 708i Speaker Monitor Active DSP Crown CSD Waterfall.png

JBL 708i Speaker Monitor Active DSP Crown Amplifier Step Response.png


I have not listened to the speaker yet. When I do, I will add a section to this review.

Conclusions
At high level, the 708i provides more flexibility compared to integrated 708p. In practice, at least in the setup I tested, it proved fussy and rather difficult to optimize. Worst part is that it seems that the EQ profiles as provided by Harman are not accurate/representative of actual speaker samples. I wonder if the production of speaker takes into account its response variations and whether they match what the equalization attempts to do. If not, it is basically an impossible task to optimize as I don't see how end-users are capable of creating anechoic measurements for every sample.

Another miss is not having true active operation with crossovers in the amplifier rather than speaker. More efficiency can be had by doing that.

I leave slight possibility that there is a pilot error here, or an odd sample. But with 708p standing by, ready to go, I am not sure it is worth our while to keep testing and testing another configurations.

As is, I can't recommend the JBL 708i active DSP speaker. I really enjoyed the 708p which produced more correct objective measurements.

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As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

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Χ Ξ Σ

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Emmmm, active DSP could actually worsen the directivity test result.:oops:
 

Mario Sanchez

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Emmmm, active DSP could actually worsen the directivity test result.:oops:
I imagine this has something to do with the drivers' interaction around crossover, that'd be the only place where filters could affect off-axis and thus directivity behavior. It is very similar to the 708P though.
1672816256910.png
 

martijn86

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Very interesting (and disappointing) result. I'm a big believer in DSP and active crossovers but it should really be sample specific. My bet is that a set of 708p's with a MiniDSP Flex Balanced and 2x Sabaj A20a is going to be significantly better.
 
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Absolute

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Interesting, but not surprising. It seems like there's a bit of hit and miss with the EQ settings in the various dps-platforms when it comes to speakers from Harman.
I don't find any problems with the tweeter and it's happiness, though. Compression drivers generally have higher 2nd harmonics than regular tweeters, but look at the non-existent 3rd and higher! It should probably be measured at 106 dB also.
 

Mario Sanchez

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I somehow fail to understand this one.
Were they trying to make a good active design and turned back halfway, or vice versa?
And, either way, why? :oops:
I think the I stands for Installation, and this one is likely trying to cater to the bigger studios and such. When the setup is big or complicated, it's probably easier to drive all the loudspeaker units from a rack of amplifiers than to bother trying to get to the power of every unit, servicing is also arguably easier with passive speakers that use external crossover+ampllification since it's usually the electronics that go first, and one can just pull the faulty electronics off of the rack in the case of passive speakers, while active will need to physically remove the speakers from their mounted position. That said, the 708P seems to be so much flatter than the 708I, even with the DSP profile applied, and I just don't see the attraction of these for the average enthusiast. Perhaps there is some per-unit calibration on the 708P?
 

Tangband

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Very interesting (and disappointing) result. I'm a big believer in DSP and active crossovers but it should really be sample specific. My bet is that a set of 708p's with a MiniDSP Flex Balanced and 2x Sabaj A20a is going to be significantly better.
Its a passive crossover inside this speaker thats not very well made , without a passive notch filter . No DSP can save this . If you combine a less good passive crossover with a less good DSP , the sum of its part will be less than the two of them , ie : -1 -1 = -3 .

I have tested this approach in DIY, and its much better to go active all the way with the dsp , also doing the crossover .
Dont combine two bad things !
( If you must do it , both the passive crossover and the dsp must be correctly done .)

As shown by Amirm, 708p is a much better speaker .
 

YSC

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much better than the part 1, but the DSP being fixed I would expect it to be factory calibrated for each driver to make it sound like the 708P, but hack, that amp analogue pot tuning for the driver balance is kind of crazy in my book, why on earth you would do that in the analogue domain risking (or to be more correct, guaranteeing) messing up with the balance??? if one want an analogue EQ pod, especially for those who would dare spending so much money on this external DSP solution, why don't you just get the integrated, fixed cross over bi-amp module and attach the EQ interface?
 

respice finem

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I think the I stands for Installation, and this one is likely trying to cater to the bigger studios and such. When the setup is big or complicated, it's probably easier to drive all the loudspeaker units from a rack of amplifiers than to bother trying to get to the power of every unit, servicing is also arguably easier with passive speakers that use external crossover+ampllification since it's usually the electronics that go first, and one can just pull the faulty electronics off of the rack in the case of passive speakers, while active will need to physically remove the speakers from their mounted position. That said, the 708P seems to be so much flatter than the 708I, even with the DSP profile applied, and I just don't see the attraction of these for the average enthusiast. Perhaps there is some per-unit calibration on the 708P?
But even then, why the passive crossover, if it's meant to work only with its dedicated DSP/amp anyway?
 

Robbo99999

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"Flawed", my overall impression of this implementation! (including complications & issues re setting up of the amps) I'm not a fan of the 708p either based on it's measurements. Both are kind of messed up from 600-1000Hz. Tweeter distortion at 96dB is disappointing. They could have been a lot better for a high tier product.

(I was very harsh on this product in the voting, mainly because of the large cost associated with the product itself let alone the additional propriety amps you have to buy and the silly poor user implementation issues). JBL do a whole lot better than this!
 

Tangband

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"Flawed", my overall impression of this implementation! (including complications & issues re setting up of the amps) I'm not a fan of the 708p either based on it's measurements. Both are kind of messed up from 600-1000Hz. Tweeter distortion at 96dB is disappointing. They could have been a lot better for a high tier product.

(I was very harsh on this product in the voting, mainly because of the large cost associated with the product itself let alone the additional propriety amps you have to buy and the silly poor user implementation issues). JBL do a whole lot better than this!
The compression driver used in 705/708 would be better crossed slightly higher at 1,9 KHz or/and with a steeper dsp crossover. Jbl has a habit of crossing their compressiondrivers far to close to their resonance frequency . That was the case in their studio 5 series and it seems to be the case here to. The result is higher distortion at the crossover region at 96 dB level or higher . Having perfect directivity ( meaning crossing low in freq with this speaker ) is always a tradeoff regarding higher distortion in a big two way speaker .

2CC8101D-C129-4290-8B68-8FCCD6139411.jpeg
 
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audio2920

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In line with @Mario Sanchez 's comments....

I've mixed on these on several Atmos Home Ent mix stages and always been happy, but never installed them myself (but do own the "p" version).

Always seen the 708's used with the 4|600 rather than the 300, and with the attenuators wide open. Not sure if that alleviates some of the LF/HF channel imbalance issue? (Like I say, never installed myself.) Moreover, the more modern rooms I've seen use the Dante variant of the DCi which obviously doesn't have the analog input trim pots. I think in some cases the room designers have probably used "i" rather than "p" JBLs purely for the simplicity/cleanliness of Dante'ing straight in to the DCi. Well, that and not needing mains runs all over the room maybe.

One would assume this "i" version is rather specifically for "pro studio installs" so fan noise not a consideration as it would always be in a machine room of course.

The 708P wasn't the most reliable speaker for me in terms of remembering it's DSP settings, where-as the DCi amp does seem better at working day in, day out.

Surprised the HF distorts so much so early, but I guess in Atmos HE film/tv mixing the spectral balance will often be toward LF when things are loud so maybe I've just never noticed. Or maybe, going on my theory that I need a little bit of monitor distortion to maintain an even keel with my levels across a working day/week, maybe that's why I'm OK on the 7 series....!? :)

Anyway, I think there's plenty of small mix stages using this product to good effect.
 

Neale

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JBL once again waste their brand and their excellent tech and skills ... consider their PA gear: PRX, SRX, VP/VRX all with same branding. The tier 1 brands don't do this, so ... be very careful of JBL brand
 

beatelund

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1. 708p have no passive crossover
2. 708i in bi-amp mode does not have a passive crossover for the woofer just for the tweeter.
And the tweeter has a 1uf condensator in series and a 11ohm resistor in parallell.
3. 708i in single amp mode have passive crossover for both drivers
 

Dennis_FL

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A little off subject, but why do frequency response graphs have dB as linear? Is a 2dB difference at 70dB sound level the same as a 2dB difference at 60dB?
 

Robbo99999

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The compression driver used in 705/708 would be better crossed slightly higher at 1,9 KHz or/and with a steeper dsp crossover. Jbl has a habit of crossing their compressiondrivers far to close to their resonance frequency . That was the case in their studio 5 series and it seems to be the case here to. The result is higher distortion at the crossover region at 96 dB level or higher . Having perfect directivity ( meaning crossing low in freq with this speaker ) is always a tradeoff regarding higher distortion in a big two way speaker .

View attachment 254761
That's interesting, but that would shift the crossover closer to the woofer resonance which is at around 2.6kHz.....but like you say a steeper crossover to help mitigate that influence. I guess you're thinking the tweeter is playing too low and causing distortion at high levels, although the higher crossover wouldn't solve the 5-10kHz distortion and it wouldn't do anything to affect the messed up 600-1000Hz region that is being affected by bass port resonances. To be honest there's multiple fronts where this speaker looks like it needs to be improved on a design level, not to even mention the poor user integration related to the analog trim-pot ridiculousness.
 
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