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JBL 708i Monitor Review (Passive: Part 1)

ctrl

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Howdy, I showed this type of chart earlier Post #135 and it was largely ignored & to be fair with this speaker even with some large adjustment, the JBL speakers port leakages(pipe resonace) will have influence on the frequency response, so the question is ---------->
Sorry, somehow completely overlooked your post. So much the better for @sarumbear he now can read the argumentation from different sources ;)
 

changer

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I guess that this is exactly the thing they have done in the true active model, 708p.
View attachment 254175

708p -> https://www.audiosciencereview.com/...measurements-vertical-directivity-png.109993/
708i -> https://www.audiosciencereview.com/...vertical-directivity-measurements-png.253575/

Crossover appears to be the same, as apparent from vertical sonograms. Slightly asymmetrical slopes somewhere around 4th order.

A question for @ctrl: How to measure and combine phase if port is back-or down-facing and not co-located with the woofer?
 
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sarumbear

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sarumbear

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Before we condemn the JBL's designer(s), need to consider whether some of the issues shown here might be other defective parts, manufacturing problems or induced by other shipping/handling that has happened along the way to get to Amir.
Yey! The broken unit excuse has finally arrived. This time it took 194 posts :)
 

ctrl

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A question for @ctrl: How to measure and combine phase if port is back-or down-facing and not co-located with the woofer?
[off-topic]
Easy, as briefly mentioned in post#141, you have to integrate the additional "time of flight" as a delay into the impulse response of the BR port measurement.

For this you can use VCAD and integrate the delay into the phase frequency response. The FR will stay the same. For example if the path of the BR port to the microphone is longer by 0.2m compared to the woofer, then you would enter 580µs delay and get additional phase shift.
1672685116723.png

As already mentioned, always remember that at high frequencies, rule of thumb >300Hz, the resulting frequency response will deviate more and more from reality.
 
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Rick Sykora

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Toni Mas

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A question for @ctrl: How to measure and combine phase if port is back-or down-facing and not co-located with the woofer?
Just my 2 cents.... I would only combine the driver and port response in the bass region, to check the BR reinforcement and considering the wavelengths at those freqs (several meters) port location and corresponding delay are not a matter for concern, at least with this small cabinet.
If the port response is noisy and interacts with the driver, i would not trust near field measurements summing in the midrange, but rather would take an anechoic measurement of the whole speaker, typically at 1m
 

uwotm8

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they are for professional use. They are even on their separate pro site. Why assume they are meant for home use
I was talking about pro range of Focal and Dynaudio as well. Basically it's a right way to get a pair of decent active speakers. And I believe that 708P sound great. My cup of tea is just different (still good enough for FR graph possessed persons tho). Partially being a measurement zealot, I admited that non-DSP and DSP Neumanns beat 708i and P respectively in flat FR graph drawing discipline.

Answering the quoted - if I can connect it to source and it sounds great, who cares if it's pro or not?:)
 
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Robbo99999

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Yes, I am aware of what a number of people think. My viewpoint is that there is no 'before DSP was applied'.
The speaker was always intended to intergate DSP.
There is no 'before'.
It only appears that way because we can measure it before connecting the entire intended product.
The use of a complex ' crossover' using both passive and active(DSP) capability is seemingly very confusing for a lot of folks.
That's silly, that's like you saying that speaker design doesn't matter and we'll just DSP all defects.
 

ROOSKIE

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That's silly, that's like you saying that speaker design doesn't matter and we'll just DSP all defects.
Hi, I am curious if you would be willing to read what I wrote in my several post in this thread again.

I am certain I did not say or suggest anything even remotely close to 'speaker design doesn't matter'. Actually my viewpoint is that speaker design does matter and that if you know you will be using DSP then you make different choices vs when not using it. Who on Earth would make the same design choices for a fully passive speaker vs a speaker that will have active elements.
DSP is part of some speaker designs, like tweeters, woofers, MDF, cabinet shape, ports, inductors and all myriad parts one might chose for a speaker design.

At no point did I even remotely suggest 'we'll just DSP all defects'.

It sure seems like you are being disingenuous here @Robbo99999
 

Robbo99999

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Well Dsp, or Asp (for analogue, active or passive) is part of what loudspeaker design is all about...
Hi, I am curious if you would be willing to read what I wrote in my several post in this thread again.

I am certain I did not say or suggest anything even remotely close to 'speaker design doesn't matter'. Actually my viewpoint is that speaker design does matter and that if you know you will be using DSP then you make different choices vs when not using it. Who on Earth would make the same design choices for a fully passive speaker vs a speaker that will have active elements.
DSP is part of some speaker designs, like tweeters, woofers, MDF, cabinet shape, ports, inductors and all myriad parts one might chose for a speaker design.

At no point did I even remotely suggest 'we'll just DSP all defects'.

It sure seems like you are being disingenuous here @Robbo99999
Well our conversation started when you replied to following post of mine:
Some people think that the defects around 900Hz should have been designed out rather than using DSP to partially fix the problem (as that area is not totally solvable with DSP). That's all I'm saying, that's the issue and argument that non-fans of the design have been saying.
 

MAB

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Here is the distortion plot...

index.php


It shows a major rise in distortion in the same range as the "port" resonance(s). You might argue audibility but cannot claim this speaker is linear in this frequency range.
Hi Rick. Lots going on around 900Hz for sure. But the 3rd order IM peak seems to be coming from the cone's breakup mode at 2.6kHz. Here are the HD and FR graphs aligned and with my comments added:
1672689033431.png

You can see the 3rd and even the 5th order modes at exactly 1/3 and 1/5 the primary breakup mode at 2.6kHz.

This is common. For instance frequency response and harmonic distortion data (with my annotations) on a Dayton 8" woofer from Zaph Audio:
1672689216807.png

It's easier to see on the raw driver with no crossover. You can actually damp out these harmonic modes with a passive notch filter. DSP is of no use except to reduce the magnitude of the fundamental. For instance:

I note that it appears the passive crossover is simple with no notch to tame the cone's breakup mode of the harmonic distortion components. So this bump in the harmonic distortion is there and is not addressable with DSP. That being said, it is the only notable HD feature on this otherwise incredibly clean speaker, and I don't know if it is audible.
 

sarumbear

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So this bump in the harmonic distortion is there and is not addressable with DSP. That being said, it is the only notable HD feature on this otherwise incredibly clean speaker, and I don't know if it is audible.
Passive crossover is not how the speaker is marketed. The speaker is designed to be used with a DSP acting as EQ and active crossover, feeding two amplifiers, one for each driver. Why can’t you then EQ the woofer separately and reduce any anomalies?
 

Rick Sykora

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Hi Rick. Lots going on around 900Hz for sure. But the 3rd order IM peak seems to be coming from the cone's breakup mode at 2.6kHz. Here are the HD and FR graphs aligned and with my comments added:
View attachment 254286
You can see the 3rd and even the 5th order modes at exactly 1/3 and 1/5 the primary breakup mode at 2.6kHz.

This is common. For instance, frequency response and harmonic distortion data (with my annotations) on a Dayton 8" woofer from Zaph Audio...

This all seems very plausible and like the way you stepped through your thought process but is still an educated guess without having all the real parts in hand...

Amir's near field measurements are affected by some crossover parts that are unknown at this juncture. Will be interesting to see how JBL applied active filtering in the next pass. The 2.6 kHz resonance is a narrow Q one at 20 dB down from the fundamental. Would agree it is not likely audible.
 

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abdo123

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A question for @ctrl: How to measure and combine phase if port is back-or down-facing and not co-located with the woofer?
Hi Rick. Lots going on around 900Hz for sure. But the 3rd order IM peak seems to be coming from the cone's breakup mode at 2.6kHz. Here are the HD and FR graphs aligned and with my comments added:
View attachment 254286
You can see the 3rd and even the 5th order modes at exactly 1/3 and 1/5 the primary breakup mode at 2.6kHz.

This is common. For instance frequency response and harmonic distortion data (with my annotations) on a Dayton 8" woofer from Zaph Audio:
View attachment 254287
It's easier to see on the raw driver with no crossover. You can actually damp out these harmonic modes with a passive notch filter. DSP is of no use except to reduce the magnitude of the fundamental. For instance:

I note that it appears the passive crossover is simple with no notch to tame the cone's breakup mode of the harmonic distortion components. So this bump in the harmonic distortion is there and is not addressable with DSP. That being said, it is the only notable HD feature on this otherwise incredibly clean speaker, and I don't know if it is audible.

I’m not very experienced so I didn’t really get what’s “the solution” for these break-up modes harmonics.
 

Jaimo

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Is it safe to say that the only reason someone would go down this 708i route versus the 708p is for potentially higher SPL and easier repairability?
Repairability yes, SPL’s no. For Hi-Fi listening, the 708P active speaker goes extremely loud.

There is a ASR thread that discusses the reliability issues folks have experienced with the Active versions and if my 708P’s should ever fail, I will seriously consider modifying them to some form of passive speaker.
 

dfuller

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For Hi-Fi listening, the 708P active speaker goes extremely loud.
Even for pro usage, they go extremely loud. About the only thing they're not going to do is sub-bass at 105+ dB.
 
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