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JBL 708i Monitor Review (Passive: Part 1)

617

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Sorry this is not entirely correct. It should be said quite clearly that the BR port is a faulty design and that no DSP can correct this. You can correct the FR which reduces the audibility of the BR port noise, but it does not solve the problem.
Especially when used as a monitor, the BR port resonances will be audible - with DSP (less) or without (clearly).

If one realizes that the near-field measurement of the BR port is not baffle-step corrected and roughly draws in the correction (blue line), it becomes clear that JBL absolutely has to improve it - IMO.
View attachment 253590

I don't entirely disagree but the argument can be made that port resonance is a legitimate design tradeoff when you are making a very small speaker with significant bass extension. In this form factor, passive radiators are not possible, so if you want a deep tuning in a high SPL speaker you are going to end up with an undersized port, and no amount of sculpting is going to help that. I would bet it is even worse than in the 705, but these port resonance issues are almost ubiquitous with two-way speakers, especially front ported monitors (and remember why they front port them to begin with - portability).

If this was a size-is-no-object design it would be shameful, but in a speaker with this kind of SPL and bass capability in this size it is expected.

I do agree that DSP is not the proper tool for mitigation as well, and this is especially problematic in a hybrid speaker that cannot equalize the woofer in that region without also equalizing the tweeter.
 

ctrl

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I don't entirely disagree but the argument can be made that port resonance is a legitimate design tradeoff when you are making a very small speaker with significant bass extension. In this form factor, passive radiators are not possible, so if you want a deep tuning in a high SPL speaker you are going to end up with an undersized port, and no amount of sculpting is going to help that. I would bet it is even worse than in the 705, but these port resonance issues are almost ubiquitous with two-way speakers, especially front ported monitors (and remember why they front port them to begin with - portability).

With a passive monitor that is priced in the 4-5000$ (pair) segment, one can be a bit more critical ;)

Amir recently tested the Neumann KH 150, also with a front BR ports. The quality differences (only with regard to the BR ports) are clearly evident:
br-port.gif

The BR port resonances of the KH150 are always at least 6-7dB below the woofer signal. With the JBL, the port resonances reaching the SPL of the woofer.
 

Dj7675

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First, thanks to Amir for measuring these (I sent them in). This is quite a lot of work, measuring with and without DSP. But thought it may be interesting to see ..
-Raw response if others wanted to develop their own EQ for them
-See the corrected response to see if EQ was different than the 708P
-By looking at the corrected response of the 708p and comparing it to the raw 708i response (as well as the upcoming v2 review of the 708i with EQ) it is interesting to see what Harman chose to EQ. The 708P is not EQ'd perfectly flat like Genelec.
Purchased new, both the 708i and Crown amps such as the DCI 2/300N, 600N are very expensive IMO. Used,, both tend to be a better value. Used 708i you can usually find them as low as around $700 each. A used 2 channel 300n can be $6-800. I found a 4 channel DCI 4/300N for $1000. Or an mentioned you can use a BSS processor and your own amps. Of course if a good EQ is developed, it would negate the crown amps or BSS Processor if one had a minidsp, roon, or other processor already in their system.
Look forward to the second part of the review with the Crown amps.
 

TonyJZX

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Because they know they will make corrections in DSP. Otherwise it would require more complex crossover to correct.
but surely for $2,000 per unit they should have more then enough 'fat' for the 'right' crossover???

as people have pointed out, no one person is buying this right?

like $4,000 for a pair just makes no sense... makes even less sense in euro or pound sterling

the corporations buying these are buying a total auditorium 'solution' so if you're spending $50k $100k for this then you have the jbl electronics to fix all this when you deliver the keys to the company... i'm sure they sound amazing in a fixed room
 

jhaider

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I suspect this is going to continue be a grab-the-popcorn kind of thread…

as people have pointed out, no one person is buying this right?

I did, and new at that (not as tested; originally with BSS processor to complete the EQ, though currently used with Crown DCI* processor amps.) The reason was I listened to them. Like them or not, they don’t really do anything wrong (when used with the complete hybrid crossover) and they do some things no other speaker their size does. Dynamics is one - look at Erin’s compression measurements of 708P. Also, I’ve not heard another speaker - including the Revel Gem2’s in our secondary system - that sound correct in the treble over such a wide listening area. Look at the horizontal polar map in the top octave. No other speaker does that, except maybe the Philharmonic designs with their super narrow ribbon, and their ribbon offers neither the dynamic fidelity this compression driver can, or the ability to stand up without the treble going to hell.

like $4,000 for a pair just makes no sense... makes even less sense in euro or pound sterling

In the EU there’s definitely stiff competition from Neumann KH 310, but in the US less so due to relative pricing differences. Neumann easily beats 7-series in fit/finish too, though the grilles come with these and are an expensive add on from Neumann.

* @amirm I hope you can test the Crown DCI independently as well; I don’t expect NC400/ ATI Siggie/ Benchmark/ Purifi performance - I’m more curious if the amp section is any lower in noise/distortion than Crown’s much cheaper XLS line.
 
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Blumlein 88

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I am unaware of that listening session. Assuming it was well done, that is a very interesting comparison.

I like your premise. It certainly makes sense to me.
Another possibility is that we need additional tests or other interpretations of our speaker measurements.

FWIW: Not too long after the M2 was released I was talking with Kevin Voecks and he had taken a pair of M2s home to listen to them in his own listening room. He spoke very favorably of them. I never heard him speak that favorably about any of the other JBLs at any price point. Of course in his position at Harman, he had to speak favorably about all of them, but reading between the lines, he was extremely impressed with the M2s. I did not ask and he did not volunteer a comparison between his own Salon2s and the M2s.
Here is a thread on the M2 vs Salon. First post by Amir has links to the thread over at AVS.

 

ROOSKIE

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With a passive monitor that is priced in the 4-5000$ (pair) segment, one can be a bit more critical ;)

Amir recently tested the Neumann KH 150, also with a front BR ports. The quality differences (only with regard to the BR ports) are clearly evident:
View attachment 253619
The BR port resonances of the KH150 are always at least 6-7dB below the woofer signal. With the JBL, the port resonances reaching the SPL of the woofer.
Yes but factor in Maximum SPL.
Port turbulence increases very quickly in small diameter ports as SPL starts to reach loud. I guarantee you that is an important consideration is a speaker like this which is obviously meant to be/designed to be used very loudly at times.

I'd MUCH rather have some midrange pipe resonances vs port turbulence or chuffing. Port turbulence and chuffing are 100% distortion and a 100% go away you are being returned deal breakers for me.

Unless what I currently know is wack (and I believe it comes from Toole's book among other DIY sources) Pipe resonances are just more output (or if out of phase less output) at the frequency they present at. There is zero reason why this matters at 750hrz that I can see. The port is just acting like another driver operating in a narrow band adding to the output of the woofer. If the port adds 3db to much and you reduce that frequency via PEQ or (passive component) you now have flat response. It is all just air being moved. This is not distortion in the sense the port is only emitting the 750hrz frequencies when the content has them.
Now, I could see more of an issue if the port was far away from the woofer and then comb filtering could occur and weird effects from the extra sounds radiating from, say the back. Certainly not when an inch away at 750hrz. Which a very good reason to design speakers with the port right next to the woofer and I'd bet JBL is aware of this.

As well stated by @617 the other option is passive radiators which can still have resonances and in this box would have to be very capable to match the output of the active woofer (at least 2x the swept volume, 2.5x is best) and would very likely not be able to be tuned as low as the port, at least not in a passive but would rely a bit on DSP bass boost like a typical DSP based sealed box.
 
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jhaider

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Not competitive with Neumann KH150: they offer amplification for $ 150 less, and a ruler flat fr response, among other SOTA qualities. Thank you Amir for another most excellent review!

KH150 looks like a fantastic and admirable loudspeaker design, and is also at least a 5 year old newer design than 708i. (I looked mine up, and the receipt is dated 3/2017. They weren't purchased at launch.) Yet, there are some objective differences that favor 708. First, KH150 will give you a lot less bass headroom. In that regard its peer in the JBL 7-series lineup is the teeny-tiny 705, not 708. JBL's 7-series drive units are still IMO best-in-class. (Look up Erin's compression testing!) Second, the aforementioned constant treble directivity all the way to 20kHz.

There's also an interesting difference in horizontal radiation pattern: basically constant (708) vs. smoothly narrowing (KH150). Which is "better" is likely a matter of placement and preference, but I would expect them to have subtly different presentations based on the differences in directivity optimization.
 
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ROOSKIE

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First, thanks to Amir for measuring these (I sent them in). This is quite a lot of work, measuring with and without DSP. But thought it may be interesting to see ..
-Raw response if others wanted to develop their own EQ for them
-See the corrected response to see if EQ was different than the 708P
-By looking at the corrected response of the 708p and comparing it to the raw 708i response (as well as the upcoming v2 review of the 708i with EQ) it is interesting to see what Harman chose to EQ. The 708P is not EQ'd perfectly flat like Genelec.
Purchased new, both the 708i and Crown amps such as the DCI 2/300N, 600N are very expensive IMO. Used,, both tend to be a better value. Used 708i you can usually find them as low as around $700 each. A used 2 channel 300n can be $6-800. I found a 4 channel DCI 4/300N for $1000. Or an mentioned you can use a BSS processor and your own amps. Of course if a good EQ is developed, it would negate the crown amps or BSS Processor if one had a minidsp, roon, or other processor already in their system.
Look forward to the second part of the review with the Crown amps.
Thank you for sending them in.
This is indeed a very cool review and doing it in 2 parts is pretty fun. Thanks to Amir as well for being game for throwing down effort on this one.

I think it will also help me confirm that I made good choices with PEQ on my 4309's which have similar issues in their purely passive form.
 

Tangband

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This is very interesting for me to read about. My jbl 530 was converted DIY to active dsp mode some years ago with massive gains in soundquality. In a passive speaker like this 708, it takes a very complicated passive crossover network to equalize the tweeter horn, and you will loose sensitivity. Much easier to do within +-1 dB with the help of a dsp crossover.

My hybrid loudspeaker project was a mix of passive crossover components and active dsp crossover. In the end of the project I conluded that its much easier in the first place to use well behaved woofers that dont need any notch filtering or such, - the Neumann KH150 seems to point in the right direction. :)

Doing the baffle step correction with a dsp is a much better solution than doing it with passive components , you gain more than 3 dB, up to 6 dB of amplifier power by doing it with the dsp , and the correction can be done more exact.

Edit:
One could also argue that using only one really good dsp doing everything, including crossover duties, volume control, baffle step compensation and using steeper crossover slopes, ( this design needs it ) might improve the sound instead of going the hybrid ( mixing a passive crossover with corrections from dsp ) approach.

A Minidsp flex would be perfect for this, and together with two class D Purifi amplifiers would probably be even better and cheaper than the active JBL/Crown approach. Only a step further from this would also be building new, rounded cabinets for less diffraction, making the cabinet slightly larger and put a slot port on the upper back.
 
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GXAlan

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@amirm, @Dj7675

It would be really interesting to see how a regular receiver would EQ this.

What if Dirac or Audyssey or ARC Genesis (or even YPAO) are “good enough”?

Alan
 

Frank Dernie

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Personally I am disappointed the correction must be being applied to "solve" resonances in this model.
The magnitude of any resonance will depend on for how long it is excited and damping, so making a correction which is adequate for a flat frequency response under steady state or a certain sweep speed does not convince, me at least, it would be always correct on music.
 

Cars-N-Cans

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I'm sorry but this is objectively flawed. That port is a mess. That kind of midrange ringing is exactly what Toole considers the worst offender for sonics (if I'm remembering correctly).
The principal use looks to be monitoring and in a mobile application as they state there will also be a need for simplicity, low weight, and ruggedness, not to mention tolerating high playback levels. Since its not being used for critical listening or purely for mixing its likely ok for a few boogers to be there that can then be tidied up later with some form of EQ or DSP. If you are looking for an end game speaker your princess is definitely in another castle, but for the usage case they offer acceptable performance for the intended application. For us it would be nicer if they didn't have those issues, but we are not the target audience for these.
 

ctrl

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Pipe resonances are just more output (or if out of phase less output) at the frequency they present at. There is zero reason why this matters at 750hrz that I can see. The port is just acting like another driver operating in a narrow band adding to the output of the woofer. If the port adds 3db to much and you reduce that frequency via PEQ or (passive component) you now have flat response. It is all just air being moved.
The difference is that a resonance oscillates in and out depending on the Q of the resonance. And if the woofer does not itself has massive resonances in the frequency range of the BR port resonances, it follows the input signal much better.

The severe BR port resonances are simply a disadvantage of the speaker, which cannot be eliminated by using DSP or EQ, since the sound level ratio of woofer to port resonances remains almost the same.
Of course, everyone must decide for themselves how audible this is.

Nevertheless, this should be clearly pointed out, because the "recording people" are obsessed about transients and in the frequency range with severe port resonances, the speaker can no longer follow the signal perfectly ("ringing").

Of course, this is only a small part of the speaker's overall rating, which is likely to be very positive.


Yet, there are some objective differences that favor 708. First, KH150 will give you a lot less bass headroom. In that regard its peer in the JBL 7-series lineup is the teeny-tiny 705, not 708.
I only cited the KH150 as an example of a good front BR port design. Did not mean to equate a 6'' woofer LS with an 8'' woofer LS - obviously ;)
 

abdo123

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Not competitive with Neumann KH150: they offer amplification for $ 150 less, and a ruler flat fr response, among other SOTA qualities. Thank you Amir for another most excellent review!

The horn implementations that JBL typically has are significantly superior. So it's not flat out superior. This is showcased by the incredibly smooth directivity and lack of weird behavior in the highest octave.

Neumann doesn't even bother with horns or extensive waveguiding because they're not targeting the high-end PA world. This speaker is capable of 117 dB / 1m peak output from 80Hz to 20KHz. Something I'm sure the KH150 is not even close to achieving.
 

Cars-N-Cans

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The difference is that a resonance oscillates in and out depending on the Q of the resonance. And if the woofer does not itself has massive resonances in the frequency range of the BR port resonances, it follows the input signal much better.

The severe BR port resonances are simply a disadvantage of the speaker, which cannot be eliminated by using DSP or EQ, since the sound level ratio of woofer to port resonances remains almost the same.
Of course, everyone must decide for themselves how audible this is.
Be interesting to see how it stacks up once the required EQ has been applied in the second part of the review. Obviously once there is less energy to excite it, it will die away more quickly. Yes its true that it will still impact the sound but if the ringing is not too severe it may not be a significant issue in the end. That is probably the part I don’t like the most, namely such resonances audibly carrying on when there is a lot of energy there. The previous review for the powered version does not have the same scale for the CSD plot so it’s hard to say, but Amir did say he had an impression of improvement when he put a notch in the EQ to help remove it further beyond what was already done in the DSP tuning of the speaker.
 

Toni Mas

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Meh... If the brand were a chines noname, votes would show no mercy...
 
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