JBL 708i Monitor Review (Passive: Part 1)

[ROOSKIE]

The near-field chart is shown for analysing individual driver & part responses only. There’s no summation offered, hence no level error exists. What is it that people are asking for adjustment?

Because there is a typically accepted method for accurately aligning the port output levels and the woofer nearfield bass levels when taking manual nearfield measurements.

Therefore they could be overlaid so that they more closely approximate the actual output levels of the port and woofer.

In this case the port would be overlaid lower then it currently is.
The whole level would be lower.

I believe these are eyeballed so the ports maximum level is close to the woofers, however that is not likely accurate in very many cases.

This port still has high output in the midrange, however it would be wise to eventually use the 'standardized' method, that does take some added effort though.

This is the common method described in two different articles from reputable sources with published calculations and the logic behind the method well documented.

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If you want to measure the very low frequencies or a bass reflex port, your best bet is to do a near field speaker measurement.

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[sarumbear]

Because there is a typically accepted method for accurately aligning the port output levels and the woofer nearfield bass levels when taking manual nearfield measurements.

They could be overlaid so that they more closely approximate the actual output levels of the port and woofer.

Measurements are for a purpose. That "accepted" method is for generating a the FR of the full speaker using near-field measurements. When there is a proper Klippel measurement why would anyone needs to "closely approximate" a FR? Yes, it "could" be done but it is not done here because the close-field measurement's only purpose is to show each driver's response, not the speaker's overall response.

 

[Descartes]

It seems better to stick with Genelec!

 

[Toni Mas]

Measurements are for a purpose. That "accepted" method is for generating a the FR of the full speaker using near-field measurements. When there is a proper Klippel measurement why would anyone needs to "closely approximate" a FR? Yes, it "could" be done but it is not done here because the close-field measurement's only purpose is to show each driver's response, not the speaker's overall response.

The sum of port + driver would also be interesting, though both responses cannot be summed directly without taking into account the port and driver size ratio.
But more interesting is showing the 2 curves, the driver's one showing the BR tuning freq, and the port's one showing those spurious resonances that else might be intérpreted as driver's non linearities if only the sum were shown.

 

[sarumbear]

The sum of port + driver would also be interesting, though both responses cannot be summed directly without taking into account the port and driver size ratio.

You have that on the Spinorama chart. No need to use a calculator. Speaker measurements progressed since Keele published his paper in 1974, almost 50 years ago!

But more interesting is showing the 2 curves, the driver's one showing the BR tuning freq, and the port's one showing those spurious resonances that else might be intérpreted as driver's non linearities if only the sum were shown.

You can see the port resonance frequency and the spurious resonances on the near-field chart. You also see the driver separately. What more do you need?

 

[Toni Mas]

It seems better to stick with Genelec!

Question is what Genelec? ... KLH, or whatever...

More important question is what the case use is, near field or midfield monitoring?

Midfield gear is not intrinsically better than nearfield, rather a waste of money for no improvement at BEST, if the case use is nearfield listenning.

And of course small nearfield gear are totally incompetent when the listenning position and área expand to midfield conditions, with much higher power and spl requirements

Imo these JBL are intented for enourmously big midfield set ups, but not especially refined ones compared with the best and much cheaper nearfield available gear.

 

[sarumbear]

More importante question is what the case use is, near field or midfield monitoring?

This is what the manufacturer suggests. Post #6.

 

[Toni Mas]

This is what the manufacturer suggests. Post #6.

Yes It is clear... As clear as bigger is not intrinsically better...

 

[jhaider]

Interesting compression measurement comparison from Erin's data, that might shed some light on the quality of the drive units used in this speaker:

708P (same drivers as 708i, I think the same cabinet volume as well).

Looks a whole lot more like this:

M2 (15" woofer 2-way)

Than this:
Wharfdale Linton 85 (larger standmount with 8" woofer)

Or this:
Ex Machina Pulsar (studio monitor with 8" Seas woofer and a coax)

 

[Toni Mas]

Interesting compression measurement comparison from Erin's data, that might shed some light on the quality of the drive units used in this speaker:

708P (same drivers as 708i, I think the same cabinet volume as well).

Looks a whole lot more like this:

M2 (15" woofer 2-way)

Than this:
Wharfdale Linton 85 (larger standmount with 8" woofer)

Or this:
Ex Machina Pulsar (studio monitor with 8" Seas woofer and a coax)

Yes those JBL look like tanks... And the rest like almost toys...

But the real question is what are the needed power and Max Spl?

And of course who needs such db monster factories for home listenning...

 

[MAB]

because it's intended as a guide to a layperson

you'll find the basis for this (with formulae) in https://www.pearl-hifi.com/06_Lit_A...apers/Keele_D_B/LF_Near-field_Measurement.pdf

Thanks for this reference! Much better than the one I provided.
But still the debated rages!

 

[sarumbear]

Interesting compression measurement comparison from Erin's data, that might shed some light on the quality of the drive units used in this speaker:

708P (same drivers as 708i, I think the same cabinet volume as well).

Looks a whole lot more like this:

M2 (15" woofer 2-way)

Than this:
Wharfdale Linton 85 (larger standmount with 8" woofer)

Or this:
Ex Machina Pulsar (studio monitor with 8" Seas woofer and a coax)

The difference between a decent professional speaker and home Hi-Fi speakers is like night & day when it comes to SPL capacity.

 

[cbrworm]

Those compression graphs are very enlightening. You may not need 102db in your living room, but you might need/want more than 96db + headroom without a noticeable change in response. Not for long-term listening at those level, of course.

 

[Toni Mas]

Those compression graphs are very enlightening. You may not need 102db in your living room, but you might need/want more than 96db + headroom without a noticeable change in response. Not for long-term listening at those level, of course.

I don't! Well under 96 headroom included!

With low efficiency equed drivers and mini amplifiers under 50wmax / Channel for the "headroom"...

 

[ROOSKIE]

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.

Oh man.
Well by that logic, then what is the point of looking at any typical frequency response graph for any speaker at all?
What is the point of reading Toole's book or the numerous sources of information presented by extremely talented people.
What is the point of all of the PEQ/DSP filters used by thousand of people and many top quality designs(and certainly every active design).

Yes they all probably behave in some unpredicted ways when playing actual content but there are always resonances corrected for in the design in various ways and at various stages.

Have you designed a few speakers?
Every speaker has problems that have been 'solved', that is what designing is.

Beyond that it is 2023. Why on Earth would anyone not use DSP in a design when possible? The way I see it, that is like saying I am really disappointed that my car requires electronically controlled fuel injection when perfecting the carburetor would be preferred to me.

Measurements are for a purpose. That "accepted" method is for generating a the FR of the full speaker using near-field measurements. When there is a proper Klippel measurement why would anyone needs to "closely approximate" a FR? Yes, it "could" be done but it is not done here because the close-field measurement's only purpose is to show each driver's response, not the speaker's overall response.

I am not talking about summing the drivers overall response, as yes the Klippel NFS has done that well. But that method will allow you to understand the ports SPL relative to drivers when given a particular input level.
I was discussing more correctly over-laying them as a way to make the chart more technically correct for the average person who looks at it.
So the ports actual output level is laying on top of the woofers actual output level, generally that needs to be calculated and is different for different speakers and can't be eyeballed.
This would be for some a minor thing but in the context of the conversation being carried on here it was pointed out that this is something to consider if someone is really going examine this particular chart.

Personally I don't care much either way but I understand what I am looking at in the ASR nearfield chart and it's limitations as source of information.

But the real question is what are the needed power and Max Spl?

And of course who needs such db monster factories for home listenning...

I don't! Well under 96 headroom included!

That 708p in that chart is an active speaker, who cares about power requirements here as the driver is not measurably stressed yet and the internal amp is doing its thing and providing enough power to cleanly sweep 102db@meter.
What we(at least I'd) need to see is if this speaker can handle 106db@1m maybe even 110db@1m. That would be helpful to know.

I don't know about you but I am not 1meter away from my speakers. @12feet/3.7meters away 102db@1meter is now approx [email protected].

Add the 2nd driver in for stereo and we do have fairly loud @[email protected] but I exceed this regularly with loud passages when doing a louder session.

If you don't value the output levels above, and/or sit in the nearfield then you can pass on these and many other speakers. You will be fine with a small speaker with modest output ability.

Distance Attenuation Calculator

The distance attenuation calculator finds how the sound level in dB decreases with distance from the sound source.

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[jhaider]

The difference between a decent professional speaker and the home Hi-Fi speaker is like night & day when it comes to SPL capacity.

Not necessarily. “Studio monitors” (which this is) and “hifi” speakers often use the same parts. One of the comparisons posted is, like 708, marketed as a studio monitor. It uses a Seas woofer, like one may find in a “hifi” speaker. Amphion is another that uses the same types of drivers (also Seas in that case.) Genelec’s previous flagship subwoofer (the 4x12 ported monster Keith Yates measured for his “way down deep” series) used Peerless XLS woofers just like any number of commercial and DIY home subs.

For another example, as previously discussed Sound und Recording found Neumann’s brand new KH150 to have bass capabilities equivalent to the the smaller speaker in this series, 705, despite the Neumann using a 6.5” class woofer and 705 using a 5” midwoofer in much smaller cabinet.

Point is the drive units in 7-series are stars. I haven’t looked at all of Erin’s tests, but I suspect you won’t find another speaker with an 8” woofer that’s close - and maybe not one with a 10 or even 12 either. It’s too bad we don’t have comparable compression data between, e.g. 708 and Neumann KH420 or Genelec 8351. Erin hasn’t measured the other two, S-u-R hasn’t measured 708, and Amir doesn’t do compression testing.

 

[Toni Mas]

If you don't value the output levels above, and/or sit in the nearfield then you can pass on these and many other speakers. You will be fine with a small speaker with modest output ability.

I listen at less than 2 m from the speakers, mainly acoustical program chamber music or jazz solos duos or tríos, and like to experiment the spl sensation of listenning to the live performance with the musicians playing quite far in front of me... This is my personal concept of realistic listenning level... No need for PA reinforcement...

 

[sarumbear]

Oh man.

I was discussing more correctly over-laying them as a way to make the chart more technically correct for the average person who looks at it.

As you have experienced “the average person” has no reason to look at any chart until they educate themselves and become a learned person.

Personally I don't care much either way but I understand what I am looking at in the ASR nearfield chart and it's limitations as source of information.

Because you are a learned person, you are not interested in chart cosmetics.

 

[Toni Mas]

Not necessarily. “Studio monitors” (which this is) and “hifi” speakers often use the same parts. One of the comparisons posted is, like 708, marketed as a studio monitor. It uses a Seas woofer, like one may find in a “hifi” speaker. Amphion is another that uses the same types of drivers (also Seas in that case.)

For another example, as previously discussed Sound und Recording found Neumann’s brand new KH150 to have bass capabilities equivalent to the the smaller speaker in this series, 705, despite the Neumann using a 6.5” class woofer and 705 using a 5” midwoofer in much smaller cabinet.

Point is the drive units in 7-series are stars. I haven’t looked at all of Erin’s tests, but I suspect you won’t find another speaker with an 8” woofer that’s close - and maybe not one with a 10 or even 12 either. It’s too bad we don’t have comparable compression data between, e.g. 708 and Neumann KH420 or Genelec 8351. Erin hasn’t measured the other two, S-u-R hasn’t measured 708, and Amir doesn’t do compression testing.

These pro hifi small monitors have been there almost since ever. My first ones were Rogers LS3/5A, designed by the BBC in the seventies as monitors for mobile set ups in their vans... An audiophile vintage classic...

The "professional" label is generally a meaning less one...

 

[sarumbear]

Those compression graphs are very enlightening. You may not need 102db in your living room, but you might need/want more than 96db + headroom without a noticeable change in response. Not for long-term listening at those level, of course.

Not to mention that it is around 96dBSPL at a typical listening position. Nothing spectacularly high.