JBL 708i Monitor Review (Passive: Part 1)

[changer]

Why would there be an adjustment for the size of a sound emitter.

I assume this is a result of the characteristics of a measurement microphone, which is always positioned at center of the radiator, versus how big the surface of the radiator is. The mic probably does not see the full emitting surface of the radiator, its SD. Check @napilopez manual for speaker measurements / bass near-field https://www.audiosciencereview.com/...amas-with-rew-and-vituixcad.21860/post-726171

 

[MAB]

I agree this speaker has an issue with port resonance, but think your conclusion is incorrect: it appears to me that @amirm usually does not adjust the near-field measurements for size of the radiators. This leads to a higher than actual SPL level of the much smaller port.

To align woofer and port output at actual SPL level, the radiator surface SD for woofer and port opening must be used to calculate an offset. This offset is global, which means it also reduces the level of the port resonance in the mids, as opposed to baffle step.

I could be wrong, but an adjusted for so size port measurement is usually lower in level than the woofer. Only when summed, they together create the higher in level, preferably flat response.

Yes I follow. I think we need to normalize these near-field measurements to get the net impact of the port resonance. The resonance is still there and is still large but the impact is much less dramatic than the raw near-field results suggest.

 

[Toni Mas]

Agreed. Pro gear is often better than Hi-Fi gear. You maybe mistaken with cheap PA as pro gear. Besides, most Genelec speakers everyone loves are pro gear.

Genelec? I don't...

 

[Cars-N-Cans]

The 708P is exactly the same in terms of cabinet, port, drivers - and those are absolutely marketed as professional monitors for critical listening.

Well yes they are the same speaker sans the “p” part. It also has overlap in application with the passive version from the marketing material.

But, given the line is intended to be modular in some fashion it’s not surprising to see some form of compromise and optimization. Also those worrying over the resonances forget that while they will be the same relative output as the woofer, their overall levels relative to the rest of the response will be lower and fall below the threshold of hearing sooner once EQ/DSP is in place. The active version was reviewed here and Amir did not explicitly find it to be an issue. If we find the same again, then the resonances are a non-point. If they are inaudible 99% of the time then addressing them will be largely pointless other than a prettier measurement, and could even be detrimental if it comes at the expense of some other aspect of performance. It ideally shouldn’t be there, but we have no explicit knowledge of the design analysis and decisions that was done. Maybe it was penny-pinching, maybe they felt it didn’t really matter, maybe fixing it would have had some other effect. But, it makes sense to see what the second part of the review has to say before everyone gets their briefs in a bunch over it being there. In that regard its nice it was done as a two-part even if some feel it’s irrelevant. It gives Amir a good opportunity to quantify the effects of the resonances pre and post-corrections. This is hardly as bad as some inexpensive floor and bookshelf speakers that have a port resonance that just towers over the rest of the response. Those are bad as they are genuine high-Q resonances much of the time, and will just drone on and on once something excites them.

 

[YSC]

Interesting.
If I put the 708p and 708i side by side, the port resonance looks identical. So nothing new, but not well controlled.
From the two reviews, adjusted for similar y-scale:
View attachment 253606
edit: I assume after DSP the woofer response will match and the port response will have identical responses. Perhaps I assume too much...

indeed, but kind of disappointed for such research based company with a not budget friendly offering still have this strong a port resonance IMO.

 

[dfuller]

Well yes they are the same speaker sans the “p” part. It also has overlap in application with the passive version from the marketing material.

But, given the line is intended to be modular in some fashion it’s not surprising to see some form of compromise and optimization. Also those worrying over the resonances forget that while they will be the same relative output as the woofer, their overall levels relative to the rest of the response will be lower and fall below the threshold of hearing sooner once EQ/DSP is in place. The active version was reviewed here and Amir did not explicitly find it to be an issue. If we find the same again, then the resonances are a non-point. If they are inaudible 99% of the time then addressing them will be largely pointless other than a prettier measurement, and could even be detrimental if it comes at the expense of some other aspect of performance. It ideally shouldn’t be there, but we have no explicit knowledge of the design analysis and decisions that was done. Maybe it was penny-pinching, maybe they felt it didn’t really matter, maybe fixing it would have had some other effect. But, it makes sense to see what the second part of the review has to say before everyone gets their briefs in a bunch over it being there. In that regard its nice it was done as a two-part even if some feel it’s irrelevant. It gives Amir a good opportunity to quantify the effects of the resonances pre and post-corrections. This is hardly as bad as some inexpensive floor and bookshelf speakers that have a port resonance that just towers over the rest of the response. Those are bad as they are genuine high-Q resonances much of the time, and will just drone on and on once something excites them.

No, I think this is just a JBL "thing" - every last one I've seen measured here has weird chewed up mid response going on.

As for "hardly as bad as inexpensive [...] speakers", I should hope not considering their cost. It's still not something I would consider acceptable. The price range these compete in ($2000ish per speaker sans amplifier(s) and DSP) has a lot of competition from other manufacturers that don't have these problems.

 

[RobL]

… It's also worth noting that none of this is new information. People have been kvetching about the 7-series port resonances for as long as I've been reading about these speakers, because JBL provided reasonable data from the start. Most of these kvetchers through all that time, it should be said, have not tried to personally evaluate the audible significance of these port issues. Dr. Toole often writes about features in graphs that are more offensive to the eye than the ear. I think this is one of those features. …

+1
It’s almost comical the amount of caterwauling about JBL’s “horribly designed” 7 series. Interesting that I’ve really never heard anything but praise from those who have been able to actually listen to a pair. I have a pair of 705’s with that horrible (looking) notch.
They sound superlative.

 

[Toni Mas]

Whatever the issues with port resonances, the predicted in room response above these is not pretty...
Sorry to have to say these speakers measure rather like PA/DJ stuff than studio/audiophile gear...

Probably another issues is the use of this ridículous tiny compression tweeter impossible to crossover low enough...Hence a tonal balance probably closer to pretencious PA standards than true high fidelity...

 

[sarumbear]

I assume this is a result of the characteristics of a measurement microphone, which is always positioned at center of the radiator, versus how big the surface of the radiator is. The mic probably does not see the full emitting surface of the radiator, its SD. Check @napilopez manual for speaker measurements / bass near-field https://www.audiosciencereview.com/...amas-with-rew-and-vituixcad.21860/post-726171

Your assumption is not correct. It doesn’t matter what generates the wave, which are alternating pressure deviations from the equilibrium pressure.

 

[jhaider]

Whatever the issues with port resonances, the predicted in room response above these is not pretty...

So what? Even ignoring that PIR is a vastly overrated metric.

You do realize this test is of a speaker with half of its crossover inactive, right? Kind of pointless to evaluate the measurements as if it were a finished product used as intended.

 

[Toni Mas]

So what? Even ignoring that PIR is a vastly overrated metric.

You do realize this test is of a speaker with half of its crossover inactive, right? Kind of pointless to evaluate the measurements as if it were a finished product used as intended.

Dont understand what this silly thing is really about... Will never understand the JBL way of understanding audio... Vastly overestimated brand by truly purist hifi standards, just good enough for casual and profesional musical entertainers...

 

[changer]

Your assumption is not correct. It doesn’t matter what generates the wave, which are alternating pressure deviations from the equilibrium pressure.

Does not matter for what? Size does not matter for sound pressure level, if power is constant?
Anyway, it was a guess and marked as such, find a better explanation instead and share it.

It remains a fact that port output and woofer output, when measured near field, must be corrected by an offset that was mathematically defined as:

Now that we have our two measurements, we need to reduce the port's SPL to match the woofer's.

The 'proper' way, as noted in Jeff Bagby's whitepaper, is to follow this formula if both port and woofer and circular: 20 Log ([port diameter]/[woofer effective diameter]). If one of them is not circular, you can use this generalized formula by calculating the area: 10 Log ([port area]/woofer effective area]).

VCad merger tool does the same for you without the need to scratch numbers.

 

[jhaider]

Dont understand what this silly thing is really about... Will never understand the JBL way of understanding audio...

Conceptually JBL here is just going down a path blazed by, e.g., KEF and Thiel (and Bose), who long ago sold passive speakers with part of the crossover in an active box to offer superior performance than they could from an all passive design.

KEF called their box “KUBE.” I don’t know about the others. See https://www.stereophile.com/content/kef-r107-loudspeaker-page-2.

 

[sarumbear]

It remains a fact that port output and woofer output, when measured near field, must be corrected by an offset that was mathematically defined as…

Maybe in your universe but not on this.

 

[Toni Mas]

Conceptually JBL here is just going down a path blazed by, e.g., KEF and Thiel (and Bose), who long ago sold passive speakers with part of the crossover in an active box to offer superior performance than they could from an all passive design.

KEF called their box “KUBE.” I don’t know about the others. See https://www.stereophile.com/content/kef-r107-loudspeaker-page-2.

For the price they cost these things should measure and sound good enough without any dsp aid....
As i said before, if were marketed by an unknown asian maker, they would have been labeled directly as junk... But as the maker is semi god...

I insist, this design is good enough for half deaf by db over doses professional users only...

 

[jhaider]

For the price they cost these things should measure and sound good enough without any dsp aid....

There’s no “DSP aid.” There was a deliberate design choice to bifurcate the the crossover between passive and DSP elements.

Note they can also be run biamplified, with the appropriate Crown or BSS electronics, if the passive components offend.

If an “unknown maker” regardless of origin (no need to inject ethnoracial bigotry) shot out of the gate with something like 708i…they would soon be well known!

 

[Toni Mas]

There’s no “DSP aid.” There was a deliberate design choice to bifurcate the the crossover between passive and DSP elements.

Note they can also be run biamplified, with the appropriate Crown or BSS electronics, if the passive components offend.

I use an active DIY system and do not need at all JBLs, Crowns, Bss and the likes... This stuff can only justify their flaws in praise of high spl and power, sacrifying sound quality... A no deal and a total waste for me...

 

[MAB]

Maybe in your universe but not on this.

I believe @changer referenced Jeff Bagby.
If you didn't find it, here is a link:

White Paper - Accurate In-Room Frequency Response to 10Hz.pdf | Powered by Box

app.box.com

The important bits:

It seems pretty clear. It occurs to me the need to normalize near-field to far-field measurements isn't unique to audio.

 

[changer]

Not worth the time to reply to a rude boy who does not care to read. Ignore lists are not nearly appreciated enough around here.

E: Notably Jeff Bagby is basically saying the same I did: The mic cannot see relative surface area, hence the measurement of the smaller radiator needs to be adjusted for true levels.

 

[sarumbear]

I believe @changer referenced Jeff Bagby.
If you didn't find it, here is a link:

White Paper - Accurate In-Room Frequency Response to 10Hz.pdf | Powered by Box

app.box.com

The important bits:
View attachment 253830

It seems pretty clear. It occurs to me the need to normalize near-field to far-field measurements isn't unique to audio.

I believe @changer referenced Jeff Bagby.
If you didn't find it, here is a link:

White Paper - Accurate In-Room Frequency Response to 10Hz.pdf | Powered by Box

app.box.com

The important bits:
View attachment 253830

It seems pretty clear. It occurs to me the need to normalize near-field to far-field measurements isn't unique to audio.

Have you wondered why there’s not a single formula on that paper?