JBL 708i vs ????

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JDUBS

JBL 708i vs ????
« on: 23 Jul 2020, 02:14 am »
Hey guys, I'm pretty set on the idea of the JBL 708i speakers as my next set of speakers and will be running them via a minidsp SHD and an undecided amp (so, single-wire mode for the JBLs)

Is there anything else out there that I should be considering?  Same-ish form factor?

Thanks!
Jim

JLM

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Re: JBL 708i vs ????
« Reply #1 on: 23 Jul 2020, 11:56 am »
The JBL 708 is a wonderful speaker.  I owned a pair of the 708P's and thought they were among the very best overall home speaker available.  Sold them due to substandard ADC and DAC circuits used that is typical of virtually all "digital" active speakers which renders external DAC's all but useless and right or wrong drove me nuts.  Others in my small audio club thought I made a big mistake selling them on.  Have since looked into the 708i but installation is complex and expensive.  Have you read:  https://jblpro.com/en-US/site_elements/7-series-set-up-guide

The recommended Crown Dci 4/600 amp is NOT the ones that came out years ago (cheap/plastic), it cost $4300 to handle a pair of 708i.  Also seemingly required is a Windows computer to load the Harmon speaker tuning files.  Since many JBL engineers have left after the Samsung acquisition don't know how good factory support would be.  Not sure how the Crown would connect to the minds SHD.  Don't know what you mean by "single-wire mode".  Don't know what the alternatives to the Crown/Harmon software would be.  Seems like a lot just to loose the lackluster ADC/DAC from $4000/pair 708P. 

Unfortunately "analog" (no on-board digital conversions) controlled directivity active monitors is pretty rare.  Genelec has a series of 2-ways and Neumann is the only other option I'm aware of. 

JDUBS

Re: JBL 708i vs ????
« Reply #2 on: 23 Jul 2020, 07:04 pm »
Thanks JLM, was hoping you would chime in.

Luckily the tuning files for the 708i have been hacked and you can actually load them into any DSP that has enough EQ bands.  Soooo, that gives the flexibility of using hardware other than the Crown!  I could use the minidsp SHD Studio and output to the DAC of my choice and then to the amp of my choice.

Here's a thread on minidsp.com:

https://www.minidsp.com/forum/minidsp-for-newbies/12769-jbl-lsr708i-dsp

The 708i can be biamped or it can be run from a single amp (they call this single-wire). 

Seems like the 708i has all of the advantages of the 708p but with additional flexibility in terms of being able to choose the hardware you use.

-Jim


JLM

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Re: JBL 708i vs ????
« Reply #3 on: 24 Jul 2020, 12:14 pm »
Link is interesting, but as a big fan of active loudspeaker design, can't recommend the single-wire approach.  Much of the dynamics, imaging, and bass performance would be lost.  Best if each channel of amplification is dedicated to each individual driver load to allow each to better "see" and react.  Would the minidsp SHD still be available for room EQ? 

From Floyd Toole: "Active speakers have a huge advantage over passives.  Consumers in general have not caught on.  Merging good speakers with dedicated crossovers and amplifiers designed for those specific components in a specific enclosure can yield better sound."

Again from Toole: Properly designed EQ can address specific resonances making active loudspeakers distinctly advantageous, but speaker directivity (which influences the listening window and room curve) cannot be changed via EQ.

The ADC in the JBL 708P can be bypassed via use of AES/EBU digital inputs.  But it wouldn't allow for use of subwoofers without adding DAC's to each sub. 

JDUBS

Re: JBL 708i vs ????
« Reply #4 on: 24 Jul 2020, 08:49 pm »
Ahh, yes, great point about the need to bi-amp here to really get the full active loudspeaker effect.  No problem, though, as that's easily accomplished with the minidsp SHD.

You can drop in the filers specified in that link (the ones for the biamp setu) and then use the dual outputs from the minidsp  into whatever 4 channels of amplifications you want. 

Yep, the minidsp can still run Dirac (room correction) after the EQ filters have been applied.  Plus, its ADC is supposed to be very good should one want to run vinyl.

-Jim


andy_c

Re: JBL 708i vs ????
« Reply #5 on: 24 Jul 2020, 09:43 pm »
I've got a pair of the 708i that I use in "single-wire" mode in conjunction with the filters specified by the poster "nyt" in that miniDSP thread.  I'm using an HTPC and Equalizer APO to implement the filters, so there's no A/D in the path.

If you examine the biamp filters for the 708i, you'll see an active low-pass filter for the woofer, but no active high-pass filter for the high-frequency driver.  That's because the passive high-pass filter is retained in the 708i even when biamping.  Only the passive low-pass filter for the woofer is bypassed in biamp mode.

JDUBS

Re: JBL 708i vs ????
« Reply #6 on: 24 Jul 2020, 09:55 pm »
Very interesting, andy_c!  Do you see this as limiting the advantage of bi-amping?  I.e., single wire should be close / as-good in this case?

How are you liking 708i's btw?

-Jim

andy_c

Re: JBL 708i vs ????
« Reply #7 on: 24 Jul 2020, 10:26 pm »
Very interesting, andy_c!  Do you see this as limiting the advantage of bi-amping?  I.e., single wire should be close / as-good in this case?

How are you liking 708i's btw?

There's probably still some advantages to biamping.  One such theoretical advantage is being able to use a lower-power amp on the high-frequency driver than on the woofer.  There's probably about a 10 dB attenuator in the passive high-pass of the 708i, since it uses a waveguide and compression driver.  But such advantages mainly accrue to the manufacturer in the form of lower cost.  As it is, identical amps are supposed to be used for LF and HF sections when biamping.  I don't see it as a big deal.

I like the speakers quite a lot!  They play quite loud for such a small speaker, and have a clean, effortless sound.  I"m not big on subjective descriptions  :).

There was a big brouhaha over at AVS about the 708i filtering.  When nyt first revealed the filters, it was by digging into the software for the Crown amps.  They were shown to only be IIR filters at low frequencies.  Some claimed there were missing high-frequency filters, which turned out to be true.  It turns out that the Crown amps use a combination of IIR filters for the low-frequencies of the 708i and FIR for the high frequencies.  nyt then found and posted the FIR filter coefficients for the Crown amps.  In addition, he obtained a BLU processor and revealed the 708i filter information for them.  The BLU processors use IIR for all the 708i filters, so there's an implementation difference there.  I think that's where the final filter info came from in those later posts in the miniDSP forum thread.