JBL 708i Monitor Review (DSP: Part 2)

[Jaxjax]

Good to know - thanks. I have five refurbed 6328s in service plus two 32s - still wonderful.

After reading the JBL literature on these it surely makes me want a pair. The used market price is fair to me.

 

[jhaider]

I highly doubt i'm the first to ask, but my searches aren't fruitful so far. Is there a significant benefit to using the JBL EQ when you plan on using Dirac or Audiolense anyways?

Two totally different things. The JBL EQ is a part of the loudspeaker’s crossover. Dirac does things based on whatever it measures in the room. I presume the same goes for audiolense.

I would use other loudspeakers before using these with an incomplete crossover with some “correction” based on in-your-room measurements. And further note that you can’t just plug n’ chug the BSS EQ values into a miniDSP or wherever. The shelf filters work differently. I’ve measured the outputs of a BSS BLU-50 vs 2x4HD and Monoprice HTP-1. (The latter two were identical, within the resolution of the HTP-1’s EQ.)

 

[tifune]

Two totally different things. The JBL EQ is a part of the loudspeaker’s crossover. Dirac does things based on whatever it measures in the room. I presume the same goes for audiolense.

I think that's part I'm struggling to understand - whatever abnormalities are introduced by an incomplete crossover would manifest in-room, so why wouldn't a sufficiently powerful room correction system compensate for both the crossover and the room issues in aggregate? The room correction simply knows "this is wrong" and attempts to correct.

 

[jhaider]

I think that's part I'm struggling to understand - whatever abnormalities are introduced by an incomplete crossover would manifest in-room, so why wouldn't a sufficiently powerful room correction system compensate for both the crossover and the room issues in aggregate? The room correction simply knows "this is wrong" and attempts to correct.

Because in-room measurements are not sufficient to correct speaker problems. They are useful to correct room problems and make broad tonality adjustments. To correct speakers performance reasonably you need anechoic measurements. That’s why Amir and Erin etc go to the trouble of characterizing speaker performance.

Otherwise you could just run anything that gets loud enough and auto-DSP the hell out of it by sticking a microphone in the room.

 

[Jaxjax]

Because in-room measurements are not sufficient to correct speaker problems. They are useful to correct room problems and make broad tonality adjustments. To correct speakers performance reasonably you need anechoic measurements. That’s why Amir and Erin etc go to the trouble of characterizing speaker performance.

Otherwise you could just run anything that gets loud enough and auto-DSP the hell out of it by sticking a microphone in the room.

But from my readings on asr isn't below schroeder ok for the willy nilly auto correct filters. & above using anechoic for precision EQ adjustments if at all. Or just shelve it as is in the no touch above schroeder anechoic area. ? In room response at MLP in the end is everything isn't it. I am asking is all. Learning.

 

[MAB]

I think that's part I'm struggling to understand - whatever abnormalities are introduced by an incomplete crossover would manifest in-room, so why wouldn't a sufficiently powerful room correction system compensate for both the crossover and the room issues in aggregate? The room correction simply knows "this is wrong" and attempts to correct.

But from my readings on asr isn't below schroeder ok for the willy nilly auto correct filters. & above using anechoic for precision EQ adjustments if at all. Or just shelve it as is in the no touch above schroeder anechoic area. ? In room response at MLP in the end is everything isn't it. I am asking is all. Learning.

The tweeter and woofer have separate DSP for the bi-amped configuration.
Some of that is to linearize the individual drivers in the crossover region.

Yes, the filters for the bass driver and the tweeter that are far away from the crossover frequency can be provided by another method. But Dirac etc. won't be able to replace JBL's specific driver EQ in the crossover region. The tweeter tilts down 5dB and the woofer has a 3 dB swerve, each seems really significant.

For the Single-wire setup, I don't think there are any issues.

https://www.avsforum.com/threads/jbl-705i-708i-7-series-master-reference-monitors-725g-728g-subwoofers-jan-2015.1724906/page-139#post-57945990

 

[GXAlan]

In room response at MLP in the end is everything isn't it. I am asking is all. Learning.

Conceptually, in-room response at the MLP is indeed what we care about, however in-room MEASUREMENT at the MLP is not the response.

This is why the target curve is really the result curve. Your mic at the MLP hears omnidirectionally while your ear might not. Second, the UMIK is +- 0.5 dB so you have the variability of the mics.

So 708p or 708i with BSS x Dirac is better than 708i with Dirac alone. Certainly, 708i with Dirac is better than 708i alone…

 

[Rahan]

I used APO to set up the cracked JBL filter and compared it with my personal version on the MiniDSP Flex HTX, based on REW measurements. In theory, you should set the speaker flat in an anechoic room before applying room corrections. However, with the 7 Series, the crossover is already in place when single-wired. The BSS does not affect the crossover in this configuration. In real-life conditions, in a partially treated room, making your own corrections works great—you can’t really tell them apart.

 

[Tom C]

I think the problems arise when you try to generalize. Things may be fine for your speakers in your room, when you have a known set of anechoic measurements to refer to. But are they fine for most speakers in most rooms, when spins are not available, or are ignored? Maybe, maybe not. We can be confident that in-room measurements to create a crossover will not always work well for all speakers in all rooms. What to do if you happen to be in a situation where the result isn’t good, or you’re not sure if you’re getting the best possible result? Well, you can have confidence in a set of high quality spinorama measurements and base the EQ on that.

 

[beefkabob]

Let the profile get the speaker to how it should be to begin with, and then let Dirac or whatever correct for the room.

 

[Nimrod]

This is a follow up to my part 1 review of the JBL 708i speaker (monitor) using active DSP amplification. A Crown DCI 4/300n four channel amplifier with built-in DSP and profiles for 708i was used in bi-amp configuration.

The process of configuring the amplifier DSP with the profile for 708i is not overly complicated but made more tedious by missing information in the manual and even bad links. It you can survive through it, you will face a problem in that the gain for the Crown amp is set using analog trim pots. These are notoriously inaccurate. In the normal course of using the amplifier for stereo or multichannel use, this is not a big problem. But when using one channel for woofer and another for tweeter, such mismatch completely messes up the frequence response of the speaker. This is made more complicated by the fact that near-field measurements are highly impacted by where you place the microphone, i.e. the distance relative to each driver. Through some trial and error, I managed to get it close but I think it may be off by 1 dB or 2. I don't know how an end customer can perform the matching without proper instrumentation.

Another problem is the loud fan in the Crown amp. During setup, it seemed to shut off after being powered on. Alas, once testing was done, I realized it had was running (I could not hear due to my hearing protection). This may have impacted the measurements a bit.

I was also disappointed that Harman has locked the EQ settings for the speaker. I see that others have figured out a way to display this but out of the box, the icons are grayed out and the manual tells you the same.

All in all, I think you are buying yourself fair amount of grief here relative to 708p which comes as a packaged deal, ready to go.

Note that the passive crossover is active at all time, whether you use the speaker in one-wire or bi-amp mode.

JBL 708i DSP Speaker Measurement
Here is our frequency response measurements: (actual SPL = 86 dBSPL@1 meter)
View attachment 254728
I must say, I expected flatter response. The boost in the treble region of 5 kHz is out of place and seems to be caused by corresponding EQ boost in the DSP. Looking at the Harman measurements, we don't see this:

View attachment 254729

Both measurements share a distinct sharp dip but their frequencies are different. Mine is at around 780 Hz whereas Harman's is at 600 Hz. I am wondering if there are differences in production of speakers vs the original samples/design. If we look at the 708p with its integrated amplifiers/DSP, we don't see the error in treble:

And the dip is at 600 Hz which matches Harman measurements. I would imaging in the case of the 708p, the whole package is tested and measured at the factory to generate the desired result.

Another error is lack of bass extension/flattening in my 780i DSP. I expected this to be resolved as well.

Anyway, moving on, here is our near-field response:

View attachment 254730

Compare this to the passive measurement:

Vemos que la zona alrededor de la resonancia de graves se reduce como debería ser, pero hay un aumento adicional alrededor de 5 a 6 kHz que no debería estar allí.

Lamentablemente, tanto la ventana temprana como la respuesta prevista parecen poco refinadas:
View attachment 254731

View attachment 254732

La distorsión sigue siendo excelente a 86 dBSPL, pero el tweeter no funciona bien a 96 dBSPL:
View attachment 254733

View attachment 254734

La direccionalidad general y el control del haz en el eje horizontal siguen siendo excelentes:
View attachment 254735
View attachment 254736

Vertical no lo es, pero es de esperar en un diseño bidireccional:
View attachment 254737

Finalmente aquí están las respuestas CSD y escalonadas:
View attachment 254738
View attachment 254739

Aún no he escuchado al orador. Cuando lo haga, añadiré una sección a esta reseña.

Conclusiones
En un nivel alto, el 708i ofrece más flexibilidad en comparación con el 708p integrado. En la práctica, al menos en la configuración que probé, resultó complicado y bastante difícil de optimizar. Lo peor es que parece que los perfiles de ecualización que proporciona Harman no son precisos ni representativos de las muestras de altavoces reales. Me pregunto si la producción del altavoz tiene en cuenta sus variaciones de respuesta y si coinciden con lo que intenta hacer la ecualización. Si no es así, es básicamente una tarea imposible de optimizar, ya que no veo cómo los usuarios finales son capaces de crear mediciones anecoicas para cada muestra.

Otro error es no tener un funcionamiento verdaderamente activo con filtros de cruce en el amplificador en lugar de en el altavoz. Se puede lograr una mayor eficiencia haciendo eso.

Dejo abierta la posibilidad de que haya un error del piloto o una muestra extraña, pero con el 708p listo para funcionar, no estoy seguro de que valga la pena seguir probando y probando otras configuraciones.

Tal como está, no puedo recomendar el altavoz DSP activo JBL 708i. Realmente disfruté del 708p, que produjo mediciones objetivas más correctas.

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Como siempre, preguntas, comentarios, recomendaciones, etc. son bienvenidos.

Agradeceremos cualquier donación mediante: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Dice Harman que cuando fue creado el sistema de goteo del M2, la serie 700 tiene una forma de enrutamiento para los de sonido instalados y los 708 power qué es muy fácil de centralizar todos los altavoces y con gestión de grabes y optimizacion de sala .
Se llama Entonato 24 .
Aparentemente sirve con cualquier monitor de estudio.
con preferencia serie 7 y corona.
alguien tiene conocimiento como funciona ?
Si fuera cierto me serviría mucho con los 708i, los 4329 y 4309 de jbl para emparejarlos a todos.
muchas gracias de antemano.
Gracias me gusta mucho el foro.
saludos!!