JBL 708i Monitor Review (DSP: Part 2)

[jhaider]

I’m sure you know that bi-wire is a single amp connection type. However, we are discussing the bi-amp use of the speaker.

My point is they chose the term "biwire" rather than "biamp" more likely than not with intention.

I read the manufacturer documents too but cannot see anywhere it says it’s bi-wire.

HINT: look at the file names for the tuning files, which are clearly posted on the product page.

What is the benefit of using a separate amplifier for each driver then?

That's the point! Basically there isn't any advantage to using two amp channels here. As I keep repeating, the engineers responsible for this loudspeaker have said it's preferable to use one stronger amp channel over two weaker channels. So all of the talk of biamping or whatever is just an irrelevant sideshow.

However, so far not a single bit of information or proof was posted that shows information about an active crossover,

Here what actually matters: look at the manufacturer provided spin and compare it in the crossover region to the measured response. It is clear to anyone possessed of the intelligence and knowledge to interpret such graphs that all of the intended filtering, whatever that is, is in place. Moreover, the woofer response is not causing the major noted deviation from the published measurements; the native frequency response of the tweeter is. So instead of bitching and moaning about active whatever, maybe focus on that. Everything else is just a goddamn circle jerk. That kind of thing is of zero interest to me, so I'm out. Cheers.

 

[sarumbear]

My point is they chose the term "biwire" rather than "biamp" more likely than not with intention.

If you cared to read the tests or looked at the manufacturer’s documentation you would see the following. Since when Bi-amplified is understood as bi-wire. Shall we believe you or the manufacturer?

https://jblpro.com/en-US/site_elements/7-series-set-up-guide

As I keep repeating, the engineers responsible for this loudspeaker have said it's preferable to use one stronger amp channel over two weaker channels. So all of the talk of biamping or whatever is just an irrelevant sideshow.

This is how the manufacturer suggested to use these speakers. Is that what you call a sideshow?

https://jblpro.com/en-US/site_elements/7-series-data-sheet

So instead of bitching and moaning about active whatever, maybe focus on that. Everything else is just a goddamn circle jerk. That kind of thing is of zero interest to me, so I'm out. Cheers.

Not only you are a rude person but you are showing how badly informed you are. Magazine viewers like you have no clue but act authoritatively.

This is why ASR exists so that we rely on facts not on hearsay from a magazine reviewer having spoken with some engineers.

 

[changer]

The most factual remark by @jhaider you just skirted in your direct reply, which comes to no surprise to me.

It is obvious that the crossover of the 708i was in place and working as the response in the crossover region is not showing deviations from the all active 708p version of the speaker. I wonder how an acoustic engineer could have missed this.

 

[MAB]

If you cared to read the tests or looked at the manufacturer’s documentation you would see the following. Since when Bi-amplified is understood as bi-wire. Shall we believe you or the manufacturer?

View attachment 255941
View attachment 255945

https://jblpro.com/en-US/site_elements/7-series-set-up-guide

This is how the manufacturer suggested to use these speakers. Is that what you call a sideshow?

View attachment 255942

https://jblpro.com/en-US/site_elements/7-series-data-sheet

Not only you are a rude person but you are showing how badly informed you are. Magazine viewers like you have no clue but act authoritatively.

This is why ASR exists so that we rely on facts not on hearsay from a magazine reviewer having spoken with some engineers.

I just measured my friend's 708i passive crossover with and without the single-/bi-wire jumpers in place. It has a passive crossover that is always enabled and cannot be bypassed no matter what. It is a 1uF capacitor with an 11 Ohm resistor. That is it. Visual inspection also confirms.
The 3rd order passive crossover for the woofer is bypassed in bi-wire mode. I confirmed that.
I understand this isn't clear in JBL's documentation, and I had to take the speaker apart to explain to you.
I also understand this is not the crossover you expected.

Several members have tried to point this out. Some of the members own the speakers, and seem to have spoken to JBL's engineering support, which I respect those conversations, I certainly hope that JBL engineering and support is telling customers correct and actionable information beyond the insufficient owner's manual. I respect the observations and conversations of many of the members who have posted here.

For instance:
The actual passive crossover explains how the tweeter level is reduced to the woofer without padding. This was mentioned.
And how the tweeter unit's HF response is leveled, this was also mentioned.
And explains how the 3rd order rolloff of the tweeter is obtained to match the woofer's, which was mentioned too.
And (likely) explains the rise in 2nd order harmonic distortion in the tweeter at ~2kHz as the volume is increased. That's my observation, with the help of some of my friends.
And confirms just about everything @jhaider said.

I've only heard the single-wire version of this speaker. I like it very much. I imagine that JBL decided the tweeter's response will limit max SPL, but got the tweeter to operate all the way down to below 2kHz, and it seems to do that really well on a number of fronts. I've heard these several times now, I actually can't hear the rising distortion, but maybe I get so blown away by the sheer volume my brain locks up, or am not turning it up much beyond 96dB.

 

[sarumbear]

And confirms just about everything @jhaider said.

Other than there’s no proof that JBL calls the “active” mode bi-wire and they prefer the single-wire mode over bi-amp. Everything published by the manufacturer refutes that.

As we do not have the bare tweeter response we do not know how an otherwise 20kHz 1st order LP filter works in this speaker. I have never seen such a filter on a driver. Has anyone?

The woofer crossover you mentioned is not used in the “active” mode hence not relevant to this thread.

 

[Naturlyd]

Now, where do I find the "ignore" button..

 

[jhaider]

I just measured my friend's 708i passive crossover with and without the single-/bi-wire jumpers in place.

Curious - do you know about how old they are, and did the tweeter measure above ~5kHz like this DUT, like mine, or like neither one? It would be interesting to get another data point to help identify if there was a running change to the tweeter or just poor QC.

I actually can't hear the rising distortion, but maybe I get so blown away by the sheer volume my brain locks up, or am not turning it up much beyond 96dB.

Or maybe harmonic distortion, within reason, isn’t actually all that important. I do wonder if aspects such as compression matter more for realism in audio reproduction.

 

[MAB]

Curious - do you know about how old they are, and did the tweeter measure above ~5kHz like this DUT, like mine, or like neither one? It would be interesting to get another data point to help identify if there was a running change to the tweeter or just poor QC.

I didn't measure the tweeter acoustic output, just used an LCR meter to measure the crossover component values and verify the functionality of the different jumper configurations... Sorry. Then we watched a movie!
I helped my friend build these into his home theater 2 years ago, I don't know how long he may have been hoarding these. He was interested in the bi-amp configuration and I looked into that a couple years ago. But he decided to stick with single-amp anyway. Having looked at both DSP configurations and now understanding the passive crossover functionality, I probably maxed out my time measuring my buddy's speaker. I would have rather done some sweeps with REW rather than haul out the crossover to sort out the passive crossover confusion. At least I'm not confused.

Or maybe harmonic distortion, within reason, isn’t actually all that important. I do wonder if aspects such as compression matter more for realism in audio reproduction.

I think I agree. But I don't know where the threshold for something like this is. And, it may be a non-issue until you get to very high volume.

 

[thewas]

Guess that 1uF capacitor is used as a linearisation of the horn/waveguide response (and to drop its sensitivity), here I simulated a typical 1" tweeter with waveguide (unfortunately not a similar horn in the database), black curve is the amplitude response of the driver and waveguide in an infinite baffle, blue curve in a typical enclosure and red curve with just a 1 uF filter:

Since it is starting quite high it is also sufficient as a high pass and protection despite being first order.

 

[GXAlan]

*Cough*

Onkyo/Takamine D-TK10 vs JBL 708P

Onkyo D-TK10 “Vintage” Speaker Review (vs. JBL 708P) TLDR? They’re great. No they’re not really vintage but they are the last flagship speaker from the pre-bankrupt Onkyo. Eighteen years ago, Onkyo launched a statement pair of speakers, the D-TK10. Using an enclosure made by Takamine (the...

www.audiosciencereview.com

 

[Ra1zel]

So speakers where ports play as loud as transducers at random midrange frequency are now fine? This is what is considered good accoustic design these days? ASR is wild place sometimes, there was a lot of criticism towards "British monitor apologists" but funnily enough there is just as much JBL/Harman apologists, after all every mistake of theirs can't be an actual mistake right? "Nuh-uh ackshually you are just reviewing/measuring it wrong, and you didn't consider that it should be used in [insert irrelevant use case]"

Btw slightly off topic I remember when Greg Timbers was criticised for not wanting to adapt to "modern acoustical design", he was kicked from JBL and now what we have? Flawed ports, plenty of diffraction, random spikes of distortion... and this is supposed to be this magnificent modern era of accoustic design?

 

[Naturlyd]

So speakers where ports play as loud as transducers at random midrange frequency are now fine? This is what is considered good accoustic design these days?

Are you thinking of this illustration?

 

[GXAlan]

Btw slightly off topic I remember when Greg Timbers was criticised for not wanting to adapt to "modern acoustical design", he was kicked from JBL and now what we have? Flawed ports, plenty of diffraction, random spikes of distortion... and this is supposed to be this magnificent modern era of accoustic design?

The 7 series is a Charles Sprinkle design and Charles Sprinkle is one of the engineers that Greg Timbers went on record to acknowledge as someone he really respects.

I think we are seeing a combination of
- inconsistent quality control. Would be great to know if this unit was pre or post COVID (@Dj7675)
- the way the ports are measured vs. the way they actually sound
- one instance where the preference score under-rates the subjective performance of this speaker

see this comment
https://audiosciencereview.com/foru...vento-826-2-speaker-review.40475/post-1427410

 

[changer]

At least with these speakers, the port might not play as loud as woofer at mids. It might be playing maybe some 6 dB lower in volume.

Some portion of this thread was dedicated to the representation of near field, individual driver responses in the current graphs by Amir. In many cases, the SPL response of the port is not adjusted. I have also found some graphs where he did the adjustment. This case here, however, is particularly difficult to read because we also seemingly miss the baffle step compensation.

All things considered, we should use this graph to interprete the combined driver response.

 

[Ra1zel]

- the way the ports are measured vs. the way they actually sound
- one instance where the preference score under-rates the subjective performance of this speaker

...

Nuh-uh ackshually you are just reviewing/measuring it wrong

 

[changer]

I do not think this thread needed this sort of energy to return.

Yes, the port is obviously flawed. It is still possible that the port response is masked. To rule this out would require further listening, testing and measurements, whereas picking on brand images is lacking methodoloy.

 

[Ra1zel]

- one instance where the preference score under-rates the subjective performance of this speaker

I just simply can't agree with that, so far my experience has been exactly opposite, Olive Preference Score Formula tends to over rate all speakers, especially small ones since it doesn't take into consideration effects of:
- THD
- IMD
- hidden resonances
- diffraction
- driver compression (power handling/thermal management)

All of this leads to confused newbies when they conclude a Genelec 8331 is just as good as Revel Salon2 and a headache for me when explaining why it isn't so and why it's nonsense to even compare them.

 

[Naturlyd]

my nearfield rew measurement IR window 20ms.

Roon is doing the dsp in its convolution processing.
I have exported thoose from REW, where i did a measurement of the bss outputs from the 708i settings.

I think they line up very well with amirs on axis measuerments

Thanks for the measurement. Have to ask, is this really the measurement of the BSS output? Not the 708i with the BSS doing the processing?

 

[thewas]

I just simply can't agree with that, so far my experience has been exactly opposite, Olive Preference Score Formula tends to over rate all speakers, especially small ones since it doesn't take into consideration effects of:
- THD
- IMD
- hidden resonances
- diffraction
- driver compression (power handling/thermal management)

I agree that the score is a limited representation of the loudspeakers performance, on the other side though audible resonances and diffraction issues make the on- and off-axis responses more ragged which has a negative impact on the score.

 

[Naturlyd]

Even if this is the review of the biamp/biwire mode of the speaker, a comparison I found of the differences between the filters for single amp use included with the Crown amps and the filters in the BSS unit is quite interesting. The forum where I found this picture has a lengthy thread on the subject of the JBL 7-series. Those differences will not be subtle.

Edited for the sake of completeness, added the FIR filters from the DCi Crown amp: