JBL 708i Monitor Review (Passive: Part 1)

[Tangband]

Well, as close/tight/sealed as you can get


For the near field measurements of BR port and woofer (as in the example above) this is not necessary and would even make the result useless (you would sum up a sealed speaker with a BR port)


I use speaker analysis (say bad things about other speakers and their insights) and simulation for my own projects.
But for others to build my own projects, I would have to pay them money. For me, only function matters; aesthetics hardly play a role.
Nobody wants to build something like that.
View attachment 254086

But nevertheless I plan to publish my next project here in the forum (so you can all shi.. over me) if it sounds good and has no serious errors. And if there is really interest I would also make detailed construction plans - but I doubt it

I would build one

 

[pierre]

@amirm updated the data, thanks. Here is an EQ that flatten the LW. The 708i is then very close to the 708P.

Let's compare to 708i with the above EQ and the 708P:

Looks close to me. I don't think you need a sophisticated EQ to make them sound well.

EQ for JBL 708i computed from ASR data
Preference Score 3.8 with EQ 5.5
Generated from http://github.com/pierreaubert/spinorama/generate_peqs.py v0.18
Dated: 2023-01-02-09:16:27

Preamp: -3.9 dB

Filter  1: ON PK Fc    63 Hz Gain +2.99 dB Q 0.50
Filter  2: ON HS Fc  1674 Hz Gain +2.78 dB
Filter  3: ON PK Fc   842 Hz Gain -4.04 dB Q 2.87
Filter  4: ON PK Fc  9442 Hz Gain -1.91 dB Q 0.49
Filter  5: ON PK Fc  1734 Hz Gain +2.20 dB Q 2.99
Filter  6: ON PK Fc  9894 Hz Gain +1.49 dB Q 2.94
Filter  7: ON PK Fc  3148 Hz Gain -1.18 dB Q 2.93
Filter  8: ON PK Fc  7011 Hz Gain -0.77 dB Q 2.82
Filter  9: ON PK Fc 14428 Hz Gain -1.38 dB Q 2.98
Filter 10: ON PK Fc  1046 Hz Gain -0.97 dB Q 2.97
Filter 11: ON LS Fc  3959 Hz Gain +0.72 dB
Filter 12: ON PK Fc   651 Hz Gain -1.23 dB Q 2.97
Filter 13: ON PK Fc  2702 Hz Gain -0.72 dB Q 2.43
Filter 14: ON PK Fc  1098 Hz Gain -0.62 dB Q 2.98
Filter 15: ON PK Fc   862 Hz Gain +0.68 dB Q 2.86
Filter 16: ON HS Fc  7853 Hz Gain +0.50 dB

You can also compare with JBL's spinorama of the 708i (with their EQ of course) which again shows the quality of Harman anechoic room. Concordance between
Klippel data and JBL data is good. Curves with dashes are JBL's, curves with continuous lines are @amirm's data.

 

[Toni Mas]

Surely I'd stick with Dynaudio or Focal Be active speakers for home listening

For people who do not need an extra 10db of headroom, those JBL are totally overkill and a waste of money...

 

[Tangband]

As I see it , when constructing good active dsp speakers one can go in two directions :

1. Make the construction as it would also function as a kick-ass passive speaker with optimal cabinet volume, rounded sides and a big enough bass reflex tube ( or slotport ) . The acoustics are not fooled in this way and avoiding eq for the baffle step will provide 3-6 dB of extra acoustic output.
Then, - apply the dsp crossover and the dsp eq to do minor corrections .
Low sensitivity drivers can be used with flat frequency response , and without using big DSP corrections .

2. Or this way : Construct for maximal sensitivity with the drivers , use a smaller closed box with Linkwitz transformer and make massive corrections afterwards with a dsp .

Personally, I havent tried this later approach in a DIY speaker , but it seems to be very common . Using high efficient drivers ( with unflat frequency response ) is interesting because maybe one can get away with some of the problems afterwards with the dsp correction, and still have rather good sensitivity left .

Using good PA drivers and compression driver - horns in a DIY project, it wouldnt be to expensive to try this.

 

[Toni Mas]

2. Or this way : Construct for maximal sensitivity with the drivers , use a smaller box and make massive corrections afterwards with a dsp .

Personally, I havent tried this later approach in a DIY speaker , but it seems to be very common . Using high efficient drivers ( with unflat frequency response ) is interesting becase because maybe one can get away with some of the problems afterwards with the dsp correction, and still have rather good sensitivity left .

For bass reproduction efficiency does not matter, only driver size and mechanical excursion capacity. Add power compression if spl matters...

I routinely apply linkwitz transform to small midwoofers mounted on small closed cabinets and am totally happy this way... No more BR, back loaded horns, tls, etc...

 

[Robbo99999]

For me, this thread is off the rails.

This is not intended to be a speaker used without the PEQ/DSP portion of the design.
It uses a 2 part crossover, part passive components(inductors, caps, resistors) part active (DSP, PEQ)

This speaker is designed for specific applications.
The passive portion of crossover is in the speaker for three reason as I see it and only these three.
1. To allow 1 channel of amplification per speaker vs 2
2. To protect the drive units in case some one cranks them before properly loading the DSP filters.
3. Is a continuation of #1, to allow the speaker to be connected with speaker wire and not require AC nearby. It can now be amplified from a distance.(&centralized)

Again these are designed to be installed with DSP.

Beyond allowing for 1 channel of amplification and protecting the drivers from accidental overload, the only thing the passive components need to get right is maintaining good directivity. They do that and so now the PEQ/DSP based portion of the 'crossover' can do it's job.

If you think anything else about the passive part of the 'crossover' is important in a design like this be my guest but please don't design my next set of speakers. If DSP/PEQ doesn't make sense to you as a useful part of contemporary audio design, but is rather a hack, be my guest but please don't design my next set of speakers.
I appreciate the hobby of those who choose analog, however I am not a someone who scrapes rocks on PVC so I could care less about preserving whatever DSP/PEQ is supposed to be ruining/hacking up. The final product is what matters to me and I see DSP/PEQ as powerful primary design tool not an afterthought.

The below is from JBL

• Centralized amplification and processing eliminates the requirement for power source at each speaker location
• BSS BLU link Networked Audio for ease interface and reduced system noise
• Harman HiQnet equipped components can be centrally controlled via hardware, software or wireless tablet

I think people who are criticising this speaker are really just saying the resonances that occur around 900Hz is due to poor design and could have been solved by better design to start with, because as it stands DSP can correct those resonances to a large extent but can't correct them perfectly - better results could have been achieved by a correct design in the first place before DSP was applied. Some people think that this compromise or oversight is not acceptable in such a high tier product.

 

[sarumbear]

I don't get, that you don't get it!

I get it but not able to explain myself, clearly.

Hope this helps you understand why even "50 year old methods" are sometimes still useful

My comment on near-field measurement is for the full FR of a speaker. My reply was about level matching the nearfield responses as per the emitter sizes. That is only required if you are going to create a summation to achieve the complete FR. As Klippel gives us the full FR, and as there is no summation on the near-field charts why bother with level matching? That is my point. Do you disagree?

 

[sarumbear]

Surely I'd stick with Dynaudio or Focal Be active speakers for home listening

You should as JBL clearly says they are for professional use. They are even on their separate pro site. Why assume they are meant for home use?

Next Generation Systems for Post and Broadcast Production in Control Rooms and Trucks​

The first in JBL’s new 7 Series line, the 705i and 708i models answer the call for next generation multi-channel monitoring in post rooms, broadcast facilities and trucks.

JBL Professional 708i

Next Generation Systems for Post and Broadcast Production in Control Rooms and Trucks The first ...

jblpro.com

 

[sarumbear]

I think people who are criticising this speaker are really just saying the resonances that occur around 900Hz is due to poor design and could have been solved by better design to start with, because as it stands DSP can correct those resonances to a large extent but can't correct them perfectly - better results could have been achieved by a correct design in the first place before DSP was applied. Some people think that this compromise or oversight is not acceptable in such a high tier product.

I think it is the same people who was educated by @amirm who very correctly says that a designer should pay attention to every detail of the design and make sure that everything they do is SOTA. This is why @amirm praises those DACs that reach the theoretic limits. In that aspect that port resonance is certainly nowhere near what is achievable. Will it matter depends on the answer to this question: is 110dB SINAD DAC a bad design when we know that 124dB is achievable?

 

[Toni Mas]

You should as JBL clearly says they are for professional use. They are even on their separate pro site. Why assume they are meant for home use?

Maybe the trouble is the reviews systematically test any speaker following the same process based on klippel measurements, and based on these data a small Cantón monitor may look as good or better than Big pro midfield monitors. Of course there is nothing wrong about this, except that we only get the picture for small signals, and for pro stuff this is far from being enough to assess the real life performance. Of course we home audiophiles with limited power requirements for domestic use, have very little interest on large signal behaviour, but all sorts of equipments are being tested here.

 

[sarumbear]

Maybe the trouble is the reviews systematically test any speaker following the same process based on klippel measurements, and based on these data a small Cantón monitor may look as good or better than Big pro midfield monitors. Of course there is nothing wrong about this, except that we only get the picture for small signals, and for pro stuff this is far from being enough to assess the real life performance. Of course we home audiophiles with limited power requirements for domestic use, have very little interest on large signal behaviour, but all sorts of equipments are being tested here.

Even though @amirm called those posts as Reviews they are mainly excellent acoustic tests of the speaker punctuated with his subjective opinion on their sound and sometimes on their build quality. You should use these posts along with other reviews found elsewhere, and of course the manufacturer's websites to get the complete picture. These are certainly not what the dictionary would have defined a review. As they are (to you) free, they get as good as it gets.

 

[beagleman]

I'll be frank: Brute forcing a speaker with obvious mechanical issues to measure well with DSP is just not good design. EQ can't fix stored energy problems beyond reducing the energy input - which doesn't fix the problem, it just masks it. Are Genelec et al guilty of this? Maybe, maybe not. I know for a fact that Neumann has done some clever things to knock down the resonances in the KH120 that aren't just electrical notch filters, and I'd bet good money Genelec does something similar.

But either way, it's just sloppy for a company that otherwise does really well - their drivers are excellent and so are their waveguides/horns, and it's not as though they're incapable of designing good ports. The "bones" are good, there's just some... questionable tradeoffs being made.

Besides - we know what it looks like post-DSP, it's the 708P, which still has port issues that you corrected with EQ and reported positive effects.

So you are asking basically, "Does the final sound matter" or is it more important how they "Get to" the final sound.

In this forum, I think if we found Genelec had to use all kinda DSP to fix largish issues, some would say they lose some/lot of their appeal.

 

[beagleman]

I have noticed something that "may" be important.

When listening or measuring a port up close, with my ear close or the mic right against the port, the resonances several hundred Hz up, Appear to measure and sound louder than when at a distance from the port.
Of course that makes sense, but I mean in "relation" to the bass output, they seem more elevated up close and at a distance they dwindle down a good bit.

Possibly Phase related, so in the end they are not directly additive or subtractive to the final output, but merely vary it a small bit.
So what measures BAD up close or sounds Horrible with your ear against the port, is actually not as bad a foot or more away.

Polk audio went into this 20 years ago with their ARC ports. (Anti resonance control) where they would use 2 ports of different sizes front and rear and resonances would cancel due to being out of phase with each other at the typical listening positions used.

 

[Toni Mas]

So you are asking basically, "Does the final sound matter" or is it more important how they "Get to" the final sound.

In this forum, I think if we found Genelec had to use all kinda DSP to fix largish issues, some would say they lose some/lot of their appeal.

Yes, purists are strongly biased against processing... Bit perfection rules!

 

[sarumbear]

I'll be frank: Brute forcing a speaker with obvious mechanical issues to measure well with DSP is just not good design.

Almost every speaker has a form of EQ, even the passive ones. There’s nothing wrong with EQ as long as there are no measurable issues. The issue we are seeing on this speaker is the port resonance is within the range of the woofer. No EQ can correct that as it’s excited by the woofer. The only way to reduce the resonance is not to activate the port. It means the woofer level at the port resonance must be reduced, which will create a dip in the woofer response.

Those resonances cam be and should reduced by geometric corrections. JBL must have other reasons for not doing it. Production cost or enclosure size comes to mind.

 

[Tangband]

So you are asking basically, "Does the final sound matter" or is it more important how they "Get to" the final sound.

In this forum, I think if we found Genelec had to use all kinda DSP to fix largish issues, some would say they lose some/lot of their appeal.

The Genelec 8030c is an analog active speaker with no dsp, and it measures great.
How they have done it in the s360 model , it might be a different story and they have probably used the help of dsp to optimize it, but the measurement of this monitor is better than for the 708p. The price is higher to.

 

[Toni Mas]

I have noticed something that "may" be important.

When listening or measuring a port up close, with my ear close or the mic right against the port, the resonances several hundred Hz up, Appear to measure and sound louder than when at a distance from the port.
Of course that makes sense, but I mean in "relation" to the bass output, they seem more elevated up close and at a distance they dwindle down a good bit.

Possibly Phase related, so in the end they are not directly additive or subtractive to the final output, but merely vary it a small bit.
So what measures BAD up close or sounds Horrible with your ear against the port, is actually not as bad a foot or more away.

Polk audio went into this 20 years ago with their ARC ports. (Anti resonance control) where they would use 2 ports of different sizes front and rear and resonances would cancel due to being out of phase with each other at the typical listening positions used.

Trouble is that port resonances are not only emitted by the port (which might also be mounted at the back of the cabinet, since bass is omni directive), but as the port interacts with the driver, its output is also afected by those resonances.

 

[pierre]

Yes, purists are strongly biased against processing... Bit perfection rules!

i am guessing you are talking about home listening? for studio use, processing is everywhere and 99% of the time in the box (computer) v.s. analogue.

 

[Toni Mas]

i am guessing you are talking about home listening? for studio use, processing is everywhere and 99% of the time in the box (computer) v.s. analogue.

Sure, i am joking about a few audiophile tabous...

 

[sarumbear]

@amirm updated the data, thanks. Here is an EQ that flatten the LW. The 708i is then very close to the 708P.

They share the same drivers and enclosure. One has the EQ inbuilt the integral active crossover and amplifiers, the other has a passive crossover and you EQ the external amplifier.

In fact JBL expects you to use an active crossover and separate amplifiers for each driver. Their positioning of 708i is an active speaker where the amplifiers are central instead of integral to each unit. @amirm tested these speakers against the manufacturers suggested use. The results may be interesting but not to be used to judge these speakers nor compare to competitors.

I was concerned that this review will go off the rails from the beginning as majority of my fellow members have difficulty in interpreting speaker tests.