JBL Professional 708P Bi-Amplified 8-Inch Master Reference Monitor

  • Sunday, May 23, 2021

Foreword / YouTube Video Review

The review on this website is a brief overview and summary of the objective performance of this speaker. It is not intended to be a deep dive. Moreso, this is information for those who prefer “just the facts” and prefer to have the data without the filler.

However, for those who want more - a detailed explanation of the objective performance, and my subjective evaluation (what I heard, what I liked, etc.) - please watch the below video where I go more in-depth.

Information and Photos

The JBL 708P is a powered 2-way Studio Monitor featuring the JBL 728G 8-inch woofer and JBL 2409H compression driver in the JBL Image Control Waveguide. It features 1 x XLR-1/4” balanced combination analog audio input and 1 x XLR AES3 format digital input with 1 x XLR pass-through output. The following is from the manufacturer’s website:

JBL 708P is the self-powered reference monitor for critical music recording, film post and broadcast production applications. The 708P leverages new patent-pending driver technologies and JBL’s renowned Image Control Waveguide to deliver extraordinary output, stunning detail, an expansive soundstage, and greater accuracy in a broad range of rooms. 708P delivers several times the output of other comparably-sized studio monitors, providing significantly greater dynamic range and greater working distances. 708P features analog and digital inputs and sample rate converters. AES/EBU digital inputs allow connectivity with a broad range of production hardware, including digital audio workstations (DAW), mixing consoles and digital playback hardware with sample rates of up to 192 kHz.

MSRP is about $1800 USD for a single speaker.



CTA-2034 (SPINORAMA) and Accompanying Data

All data collected using Klippel’s Near-Field Scanner. The Near-Field-Scanner 3D (NFS) offers a fully automated acoustic measurement of direct sound radiated from the source under test. The radiated sound is determined in any desired distance and angle in the 3D space outside the scanning surface. Directivity, sound power, SPL response and many more key figures are obtained for any kind of loudspeaker and audio system in near field applications (e.g. studio monitors, mobile devices) as well as far field applications (e.g. professional audio systems). Utilizing a minimum of measurement points, a comprehensive data set is generated containing the loudspeaker’s high resolution, free field sound radiation in the near and far field. For a detailed explanation of how the NFS works and the science behind it, please watch the below discussion with designer Christian Bellmann:

The reference plane in this test is at tweeter.

Measurements are provided in a format in accordance with the Standard Method of Measurement for In-Home Loudspeakers (ANSI/CTA-2034-A R-2020). For more information, please see this link.


The On-axis Frequency Response (0°) is the universal starting point and in many situations, it is a fair representation of the first sound to arrive at a listener’s ears.

The Listening Window is a spatial average of the nine amplitude responses in the ±10º vertical and ±30º horizontal angular range. This encompasses those listeners who sit within a typical home theater audience, as well as those who disregard the normal rules when listening alone.

The Early Reflections curve is an estimate of all single-bounce, first-reflections, in a typical listening room.

Sound Power represents all the sounds arriving at the listening position after any number of reflections from any direction. It is the weighted rms average of all 70 measurements, with individual measurements weighted according to the portion of the spherical surface that they represent.

Sound Power Directivity Index (SPDI): In this standard the SPDI is defined as the difference between the listening window curve and the sound power curve.

Early Reflections Directivity Index (EPDI): is defined as the difference between the listening window curve and the early reflections curve. In small rooms, early reflections figure prominently in what is measured and heard in the room so this curve may provide insights into potential sound quality.


Early Reflections Breakout:

Floor bounce: average of 20º, 30º, 40º down

Ceiling bounce: average of 40º, 50º, 60º up

Front wall bounce: average of 0º, ± 10º, ± 20º, ± 30º horizontal

Side wall bounces: average of ± 40º, ± 50º, ± 60º, ± 70º, ± 80º horizontal

Rear wall bounces: average of 180º, ± 90º horizontal


Estimated In-Room Response:

In theory, with complete 360-degree anechoic data on a loudspeaker and sufficient acoustical and geometrical data on the listening room and its layout it would be possible to estimate with good precision what would be measured by an omnidirectional microphone located in the listening area of that room. By making some simplifying assumptions about the listening space, the data set described above permits a usefully accurate preview of how a given loudspeaker might perform in a typical domestic listening room. Obviously, there are no guarantees because individual rooms can be acoustically aberrant. Sometimes rooms are excessively reflective (“live”) as happens in certain hot, humid climates, with certain styles of interior décor and in under-furnished rooms. Sometimes rooms are excessively “dead” as in other styles of décor and in some custom home theaters where acoustical treatment has been used excessively. This form of post processing is offered only as an estimate of what might happen in a domestic living space with carpet on the floor and a “normal” amount of seating, drapes, and cabinetry.

For these limited circumstances it has been found that a usefully accurate Predicted In-Room (PIR) amplitude response, also known as a “room curve” is obtained by a weighted average consisting of 12 % listening window, 44 % early reflections and 44 % sound power. At very high frequencies errors can creep in because of excessive absorption, microphone directivity, and room geometry. These discrepancies are not considered to be of great importance.


Horizontal Frequency Response (0° to ±90°): specs

Vertical Frequency Response (0° to ±40°): specs

Horizontal Contour Plot (not normalized): specs

Horizontal Contour Plot (normalized): specs

Vertical Contour Plot (not normalized): specs

Vertical Contour Plot (normalized): specs

Additional Measurements

On-Axis Response Linearity


“Globe” Plots

These plots are generated from exporting the Klippel data to text files. I then process that data with my own MATLAB script to provide what you see. These are not part of any software packages and are unique to my tests.

Horizontal Polar (Globe) Plot:
This represents the sound field at 2 meters - above 200Hz - per the legend in the upper left. specs

Vertical Polar (Globe) Plot:
This represents the sound field at 2 meters - above 200Hz - per the legend in the upper left. specs

Harmonic Distortion

Harmonic Distortion at 86dB @ 1m: specs

Harmonic Distortion at 96dB @ 1m: specs

Dynamic Range (Instantaneous Compression Test)

The below graphic indicates just how much SPL is lost (compression) or gained (enhancement; usually due to distortion) when the speaker is played at higher output volumes instantly via a 2.7 second logarithmic sine sweep referenced to 76dB at 1 meter. The signals are played consecutively without any additional stimulus applied. Then normalized against the 76dB result.

The tests are conducted in this fashion:

  1. 76dB at 1 meter (baseline; black)
  2. 86dB at 1 meter (red)
  3. 96dB at 1 meter (blue)
  4. 102dB at 1 meter (purple)

The purpose of this test is to illustrate how much (if at all) the output changes as a speaker’s components temperature increases (i.e., voice coils, crossover components) instantaneously.


Long Term Compression Tests

The below graphics indicate how much SPL is lost or gained in the long-term as a speaker plays at the same output level for 2 minutes, in intervals. Each graphic represents a different SPL: 86dB and 96dB both at 1 meter.

The purpose of this test is to illustrate how much (if at all) the output changes as a speaker’s components temperature increases (i.e., voice coils, crossover components).

The tests are conducted in this fashion:

  1. “Cold” logarithmic sine sweep (no stimulus applied beforehand)
  2. Multitone stimulus played at desired SPL/distance for 2 minutes; intended to represent music signal
  3. Interim logarithmic sine sweep (no stimulus applied beforehand) (Red in graphic)
  4. Multitone stimulus played at desired SPL/distance for 2 minutes; intended to represent music signal
  5. Final logarithmic sine sweep (no stimulus applied beforehand) (Blue in graphic)

The red and blue lines represent changes in the output compared to the initial “cold” test.



Parting / Random Thoughts

If you want to see the music I use for evaluating speakers subjectively, see my Spotify playlist.

  • Subjective listening varied between the nearfield at 1 meter and the midfield from 1-2 meters. Subjective listening was conducted at 80-95dB at these distances. Higher volumes were done simply to test the output capability in case one wants to try to sit further away. Since I only have one unit on hand for testing, listening was done in mono only (mixed stereo to mono through PC). Speaker was out in the open area of my living room, about 1 meter from the wall behind it and multiple meters from any other adjacent walls.
  • Higher Love - the bass is incredibly potent from a speaker this size. Looking at the data, the f10 shows as 35Hz and with this track containing such a thumping kickdrum it makes sense that what I heard translated so well with these speakers as even the f3 is below the 50-60Hz area of kickdrums. I did feel like the cymbal crash was missing just a touch of air. Looking at the data, maybe this is attributed to the 10kHz dip. Maybe it’s just my imagination.
  • Lauryn Hill’s “Doo Wop”… first “bookshelf” sized speaker I’ve had that can play this song at 90dB+ without exhibiting issues (mechanical or distortion/compression). I was sitting at 2 meters registering peaks of 105dB with average of 90dB. This is much higher than I would ever listen to for extended periods of time. And the clipping indicator would only occasionally flash. This passes my ‘stress test’ for a speaker of this type and use (bookshelf, nearfield/midfield) without issue and bests every other similar-sized speaker I have tested to date with this track.
  • In line with the output capability, the distortion even at 96dB @ 1m is within 1% THD above 100Hz and less than 3% below 100Hz.
  • Long-term compression testing is impeccable. At 86dB this speaker exhibits the ideal performance; no deviation from “cold” to even 4 minutes of continuous output of 86dB. And even at 96dB the difference is less than 0.10dB from cold to 4 minutes!
  • Tell Yer Mama - this track typically gives many speakers problems because it highlights cabinet resonance very well (it is one reason I use this track, other than just liking it). Listening to this on the 708P, however, made me go back to my trusty headphones to make sure I wasn’t missing something. There is no resonance. I have grown so accustomed to hearing resonance with various speakers that it actually threw me for a loop and prompted me to make a sanity check.
  • No audible hiss even when sitting right in front of the tweeter with the input sensitivity set to max.

All in all, I have zero issue recommending these speakers. They perform excellently (as they should at $3600/pair). The frequency response isn’t completely flat - though mostly within ±1.5dB - and exhibits a couple resonances at ~700Hz and 900Hz. However, these didn’t seem to be troublesome to me in my listening. It may be that the level is relatively low (~1dB above the mean) or maybe I am just not “tuned” for these frequencies as well as I am other issues. Aside from this, I do think the HF could use a single PEQ with a very wide Q at about 6.5kHz and knocked down about 0.5dB to take a little edge off.

Back to the price, I have to say that $3600/pair seems very steep. And I would expect to not see the resonances I mentioned. That said, with the built-in EQ, one could knock these down.

As stated in the Foreword, this written review is purposely a cliff’s notes version. For more details about the performance (objectively and subjectively) please watch the YouTube video.

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