JBL 308P MKII Studio Monitor Review

[Muelli]

Regarding the Mackie HR824, here you can find a review with measurements from german magazine Sound&Recording.

The attached graphs are supposed to be from Harmann.

 

[turbotuff]

You could always send a pair in!

Just busting your chops. I'd love to see that old venerable design measured as well! I wonder if they've moved to Class D as many others have.

Edit: It appears that the new version is the XR line, using Class D amps, same driver complement though, it appears.

The original HR824 are class AB design, linear power supply, low distortion, made in USA with Vifa woofers and Seas tweeters.

But yes, I'm working on getting one to amirm

 

[SpaceMonkey]

HR824 MK2 from here: https://www.resolutionmag.com/wp-content/uploads/2016/03/Mackie-HR824-Mk2.pdf
FR

 

[jcebedo11]

HR824 MK2 from here: https://www.resolutionmag.com/wp-content/uploads/2016/03/Mackie-HR824-Mk2.pdf
FR
View attachment 92539
View attachment 92545
View attachment 92546

the MK1 seems to have a flatter response

 

[SpaceMonkey]

the MK1 seems to have a flatter response

This or it is scaling at play

 

[DavidMcRoy]

Very interesting review and comments. I’m running 305P MKIIs up front and LSR305s as surrounds and overhead in an 11.1 channel system with multiple subs, everything on DSPs. This discussion of the 308s has revived my threat to hotrod a spare pair of LSR305s I have, converting them to passive speakers and using outboard DSPs and “known dead quiet” 125 watt + external Class D amps to see what’s what. Each unit would be biamped, of course with DSP for each driver. Every unit I have has some barely audible hiss, but I have to put my ear within a few inches of the tweeter to hear it. I did find it necessary to float the power cord ground pin on every single one to alleviate ground loops. Overall I’m very pleased with what I’ve done, crossing over at 80Hz and never wanting to listen at insane levels, anyway.

 

[AnalogSteph]

This discussion of the 308s has revived my threat to hotrod a spare pair of LSR305s I have, converting them to passive speakers and using outboard DSPs and “known dead quiet” 125 watt + external Class D amps to see what’s what. Each unit would be biamped, of course with DSP for each driver.

I bet you'll need DSP, too.

I did find it necessary to float the power cord ground pin on every single one to alleviate ground loops.

Not exactly to code, this. At least use some chunky antiparallel diodes or something (25 A bridge rectifiers are good for this sort of thing).

 

[JRAudio]

This is a review and detailed measurements of the JBL 308P MKII 8-inch Monitor (powered speaker). I purchased this from a member a few months ago. New, they cost US $249.

The 3 series look the same for good or bad:

View attachment 91937

The large plastic waveguide is really in your face. Wish JBL would provide a matt version of it.

Back panel has the usual controls:

View attachment 91938

Drivers are powered using dual 56 watt class D amps. Crossover is stated at 1.8 kHz.

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in ordinary rooms yet results that can be more accurate than an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

I performed over 800 measurement which resulted in error rate of less than 1% throughout the range.

Temperature was 60 degrees F. Measurement location is at sea level so you compute the pressure.

Measurements are compliant with latest speaker research into what can predict the speaker preference and is standardized in CEA/CTA-2034 ANSI specifications. Likewise listening tests are performed per research that shows mono listening is much more revealing of differences between speakers than stereo or multichannel.

Reference axis was the tweeter center.

JBL 308P MKII Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker is and how it can be used in a room. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:

View attachment 91939

I must say, this is a better response than I expected! On-axis is essentially flat from 45 Hz to above 15 kHz. There is a resonance near 20 kHz but most of us don't hear that high so probably OK. There is a tiny dip around 1.4 kHz. Measuring each radiating element tells us why:

View attachment 91954

As you see, there is a small "dead" region between the woofer and tweeter crossover region. I wonder if this sample variation. Regardless, if the woofer was 100 Hz higher or tweeter was 100 Hz lower, it would cover that gap.

Early window which is more representative of far field listening sums quite nicely as well:

View attachment 91953

Putting the two together, this is our predicted in-room far-field response:

View attachment 91952

Man this is good! It is very hard to get this kind of precision in a passive speaker.

Beamwidth and directivity are excellent:

View attachment 91943

View attachment 91944

Even vertically it is good compared to most 2-way designs:

View attachment 91945

You have ±20 degrees vertically before you get in trouble much.

The only downer is distortion:

View attachment 91951
During the sweep even with my ear protection on, I could hear anomalies at 96 dB. There is electronic limiter which when kicks in, creates all kind of noises and squeals.

Here it is in absolute level:

View attachment 91950

I could get it to produce around 105 dBSPL at 1 meter before it would severely limit levels (not shown).

JBL 308P MKII Listening Tests
Ah, what a joy this speaker is to listen to. It has plenty of warm and impactful bass, yet is almost perfectly neutral. I say if I had to listen to it for a long time, I might take down the highs just a bit but that is it.

Gradually turn up the volume with deep bass though and at first, everything sounds wonderful. When you get to pretty loud levels, the sound gets muddy at first before reaching quite distorted levels. It is not distortion you are used to due to limiter. But it is there. Suspecting it was very low frequencies that was giving it trouble, I dialed in this quick filter:

View attachment 91949

This is helped fair bit but also cost me a bit of that wonderful bass.

And oh, yes, there is hiss from the tweeter. It is very audible with your ear at the tweeter level but is gone at about 2/3 of a meter/2 feet or so. Turning down the gain reduces it a bit but note that this speaker does NOT want to have too much driving it. Setting the gain low and them pumping up the source generates severe distortion. Shame as this would be a good way to reduce the impact.

Conclusions
If you want to get a taste of accurate sound production that manages to delight, the JBL 308P MKii is a wonderful entry into this world. You would quickly learn that what research says about preference and accuracy being two sides of the same kind is very much true.

As with many powered speakers, amplification for the woofer is the limiting factor. This speaker with 100 watts or more to power the woofer would be so darn perfect. As it is, it will get quite loud and present ton of bass. Just don't expect miracles in overall loudness.

I am very happy to recommend the JBL 308P MKii.

------------
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/

Dear Amir

I bought this speaker for our guestroom as a planed update to the 16 years old M-Audio BX-5. After I installed it I noticed, that there sound something „wrong“ with the treble area. So I measured this speaker (with 1 Meter distance with a calibrated Earthworks M30 with 96 kHz Sample Rate) and noticed, that the frequency response drops like a rock above 22 kHz. So it looks like, that this speaker does AD at the input with 48 kHz. I am „surpriced“ that I did not find any information about that in the data sheet or user manual. I further measured the phase response and group delay of this speaker and this confirmed an AD converter at the input compared to an regular low pass behavior of a tweeter (as for the M-Audio BX-5). So I will send this speaker back.

I think it would be great to measure at least for one measuring point up to 40 kHz (or at least up to 30 kHz, similar to what John Atkinson does for Stereophile), in order to be able to see such behavior of a active loudspeaker. I would be very happy, to see this in your measurements. Thank you.

Juergen

 

[Robbo99999]

Dear Amir

I bought this speaker for our guestroom as a planed update to the 16 years old M-Audio BX-5. After I installed it I noticed, that there sound something „wrong“ with the treble area. So I measured this speaker (with 1 Meter distance with a calibrated Earthworks M30 with 96 kHz Sample Rate) and noticed, that the frequency response drops like a rock above 22 kHz. So it looks like, that this speaker does AD at the input with 48 kHz. I am „surpriced“ that I did not find any information about that in the data sheet or user manual. I further measured the phase response and group delay of this speaker and this confirmed an AD converter at the input compared to an regular low pass behavior of a tweeter (as for the M-Audio BX-5). So I will send this speaker back.

I think it would be great to measure at least for one measuring point up to 40 kHz (or at least up to 30 kHz, similar to what John Atkinson does for Stereophile), in order to be able to see such behavior of a active loudspeaker. I would be very happy, to see this in your measurements. Thank you.

Juergen

Why does frequency response matter over 20kHz? You can't hear that high in frequency.

 

[JRAudio]

Why does frequency response matter over 20kHz? You can't hear that high in frequency.

I also do not hear any frequency above 20 kHz (as fundamental frequencies), but I personally do hear group delay / phase shifts of the overtone in relation to the fundamental in that area.

But the reason why I wrote here was not to judge that tones above 20 kHz are audible or not, my reason was to add a 40 kHz measurements, to see if there is any 48k AD in the system.

With that JBL, I measured 90 ms group delay shift above 25 kHz, that means that the overtones of a violin are about 30 Meters behind the fundamental (where the violin stands).

 

[andreasmaaan]

I also do not hear any frequency above 20 kHz (as fundamental frequencies), but I personally do hear group delay / phase shifts of the overtone in relation to the fundamental in that area.

But the reason why I wrote here was not to judge that tones above 20 kHz are audible or not, my reason was to add a 40 kHz measurements, to see if there is any 48k AD in the system.

With that JBL, I measured 90 ms group delay shift above 25 kHz, that means that the overtones of a violin are about 30 Meters behind the fundamental (where the violin stands).

Do you have a phase response or group delay measurement you could share please?

 

[Xyrium]

HR824 MK2 from here: https://www.resolutionmag.com/wp-content/uploads/2016/03/Mackie-HR824-Mk2.pdf
FR

I've always liked the addition of step response and group delay measurements. We've seen them here a few times, and I've always felt that when units fare well in these areas...subjectively there's a rightness in the sound. The lf matches the hf output (skin to port) of a bass drum...etc. Anyway...nice find!

 

[Pio2001]

I also do not hear any frequency above 20 kHz (as fundamental frequencies), but I personally do hear group delay / phase shifts of the overtone in relation to the fundamental in that area.

Hi,
This is physically impossible. It is not possible to define, let alone to hear, the group delay or phase of a signal that doesn't enter a system.

and noticed, that the frequency response drops like a rock above 22 kHz.

With that JBL, I measured 90 ms group delay shift above 25 kHz, that means that the overtones of a violin are about 30 Meters behind the fundamental (where the violin stands).

Since, according to your measurement, the signal was extremely low at 25 kHz, the group delay measured is probably associated to the noise of the microphone rather than to an actual signal coming from the speaker.

 

[DavidMcRoy]

I bet you'll need DSP, too.

Not exactly to code, this. At least use some chunky antiparallel diodes or something (25 A bridge rectifiers are good for this sort of thing).

I know, but here in North America we have 120VAC/60Hz in the wall, not 230 and everything in this installation is safe, otherwise I wouldn’t have done it. I worked in radio and TV broadcasting for 40 years, and there are stations that wouldn’t be on the air without the odd “cheater plug” here and there! LOL

 

[JRAudio]

Hi,
This is physically impossible. It is not possible to define, let alone to hear, the group delay or phase of a signal that doesn't enter a system.





Since, according to your measurement, the signal was extremely low at 25 kHz, the group delay measured is probably associated to the noise of the microphone rather than to an actual signal coming from the speaker.

I am well aware how to measure the passband and stop-band behavior of anti alias filter, as I am doing this on my daily work basis and have developed some methods for it,

And I am also aware of the different effect and audibility of different type of antialias filter, when mixing and mastering classical music, as a certified engineer,

but this all are not my points here. As the spinorama measurements are really a great tool to judge the sound of a loudspeaker, when placing them at home,

I really would appreciate and like to see just one extended measuring when testing speakers, too see, if there is an additional AD process at 48k.

 

[ctrl]

I really would appreciate and like to see just one extended measuring when testing speakers, too see, if there is an additional AD process at 48k.

To get a complete impression of the DUT, a measurement far above 20kHz would certainly be interesting. Beside possible (low-pass) filters (with active speakers) one would also be able to see the break-up modes of the tweeter.

@amirm has to decide if the additional effort for such a measurement is worth the possible findings.

With that JBL, I measured 90 ms group delay shift above 25 kHz, that means that the overtones of a violin are about 30 Meters behind the fundamental (where the violin stands).

Here I can not follow your arguments any more.

How should the 90ms group delay come about and how should these 90ms (if they are correct) be determined from the frequency response measurement, if the absolute phase is not known and only the minimum phase can be calculated from the frequency response measurement?

In your shown measurement in post#270, a filter seems to limit the frequency response (of the JBL-308P) above 20kHz.
The resulting acoustic order of the filter should be somewhere around 16th order (at 21kHz) if we consider the filter slope of your JBL-308P frequency response measurement (red straight line in the diagram).

How should a low-pass 16th order at 21kHz lead to 90ms group delay?
Let's look at an example of an ideal loudspeaker with a typical LR4@2kHz crossover. The FR, phase frequency response and the group delay is as follows (red - woofer, green - tweeter):

Everything as expected. The 4th order filter shifts the phase around the allpass filter crossover frequency by 4x90° = 360°. The resulting group delay is about 0.3ms. The higher the crossover frequency, the lower the effect on the group delay.

Now we provide the speaker with an additional low-pass filter 16th order at 21kHz:

The new filter results in an additional phase shift of 16x90°. However, the influence on the group delay is negligible. So it is not possible that the additional filter creates a group delay of 90ms.

 

[hvbias]

I have this speaker and I wouldn't want it sitting on my desk whilst I work on my computer, because of the hiss when no music playing on them. I have them at about 2m listening distance for TV/movie/music use and the hiss is a complete non-issue at that distance (can't hear it), but I wouldn't want them on my desk.

I'm using 306 MK2 on my desk at work and I can hear the hiss with some very quiet sections of classical music.

I think I paid about $180 including shipping for a pair from Amazon on sale so I can't complain too much, I don't think there is anything remotely in this price that will compete with them. And I don't really want to spend more in case of theft.

The one thing I have considered is DIY as there are many threads on DIY Audio on speakers made on foam core, could essentially build something really nice for about twice the price of these JBLs once you factor in the cost of a MiniDSP. But four channels of amps would be another expense.

 

[Robh3606]

I have a pair in my office on my desk top and really enjoy them. I use them with a subwoofer JBL Sub 550p and use a JBL M552 active crossover @80Hz with my Ipod as a source. I have no issues with hiss. Can listen to them all day long.

Rob

 

[amirm]

I think it would be great to measure at least for one measuring point up to 40 kHz (or at least up to 30 kHz, similar to what John Atkinson does for Stereophile), in order to be able to see such behavior of a active loudspeaker. I would be very happy, to see this in your measurements.

I can increase the measurement bandwidth for the distortion tests. It won't be calibrated though so not very accurate. It will show the cut off due to ADC though.

Increasing it for the spin data substantially increases file size and slows down the measurements and computation so I rather not touch those.

 

[JRAudio]

I can increase the measurement bandwidth for the distortion tests. It won't be calibrated though so not very accurate. It will show the cut off due to ADC though.

Increasing it for the spin data substantially increases file size and slows down the measurements and computation so I rather not touch those.

Hi Amir

Great to hear. I totally agree, the high bandwidth is absolutely not necessary for the Spinorama data, in my opinion even not for the THD measurements, but just a „check“ if this active speaker does have internally a 48k or 44k1 digital „bottle neck.“

The natural low pass behavior of the tweeter itself is fine, or 88k2 / 96k DSPs in active speakers or room processors, but I would like to see up front, if an active speaker has a 48k digital bottle neck, if this isn't even mentioned in the manual.

Thanks, Juergen