JBL 705i/708i (7 Series Master Reference Monitors) & 725G/728G (subwoofers): Jan 2015 - Page 69 - AVS Forum | Home Theater Discussions And Reviews
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post #2041 of 2918 Old 01-25-2018, 08:09 AM
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Originally Posted by Zzzzz... View Post
I'm trying to understand this. How did you conclude that the heat was mainly from the display/processing board? Also, wouldn't the heat from the amps ultimately exit via the rear panel as well?
IR thermometer and fingers. There is some convection from the amp stage heatsink but it is significantly less than the heat generated by the processing/display board. Class D amps usually run pretty cool. For instance, the amp chip in the LSR305 doesn't even use a heatsink.
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post #2042 of 2918 Old 02-02-2018, 03:18 AM
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Is there any difference in SPL capabilities between using the 708i with the 300 watt Crown amps vs. the 708P?
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post #2043 of 2918 Old 02-02-2018, 06:59 AM
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Anyone using speaker stands for 705P's? Moving to a new house and might use them for surrounds.

I want good quality heavy duty stands. Haven't needed or used them for years, so looking for suggestions.
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post #2044 of 2918 Old 02-02-2018, 11:39 AM
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One more question...

With the DCi 8|600N, can I power, say, five 708i speakers and use the rest of the available channels to power some SCS 8 speakers? Basically, when you load the tuning file(s) for the 708i onto the amp, does it apply it to all channels or only the ones you select?
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post #2045 of 2918 Old 02-02-2018, 12:30 PM
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Quote:
Originally Posted by Kain View Post
Is there any difference in SPL capabilities between using the 708i with the 300 watt Crown amps vs. the 708P?
My guess is no. Even though the 708p uses a 250W amp on the woofer and 250W on the CD, I assume the CD is a lot more sensitive than the woofer and will use up only a little amount of the available power resulting in the same approximate overall SPL capability.
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post #2046 of 2918 Old 02-03-2018, 04:24 AM
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Not to bring this topic back from the dead, but will it be possible for someone who owns (or has access to) to the 708i/708P to do some frequency compression sweeps like Gooddoc did? If someone can replicate the same results it will confirm what Gooddoc produced. Maybe @COACH2369 or @John Schuermann can give it a try? No worries if it is not possible but would be awesome if we can get some results other than Gooddoc's (not that I don't trust them).
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post #2047 of 2918 Old 02-03-2018, 09:41 AM
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Quote:
Originally Posted by Kain View Post
Not to bring this topic back from the dead, but will it be possible for someone who owns (or has access to) to the 708i/708P to do some frequency compression sweeps like Gooddoc did? If someone can replicate the same results it will confirm what Gooddoc produced. Maybe @COACH2369 or @John Schuermann can give it a try? No worries if it is not possible but would be awesome if we can get some results other than Gooddoc's (not that I don't trust them).
I almost hate to admit this, but I don't know how to run what you are talking about. Are you referring to when I use the ARC in my Anthem? As much as I love this hobby, I am very uneducated in the technical end of things. I just hook everything up, have it calibrated and then it is tweaked until my ears enjoy what I hear.
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post #2048 of 2918 Old 02-03-2018, 10:27 AM
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Quote:
Originally Posted by COACH2369 View Post
I almost hate to admit this, but I don't know how to run what you are talking about. Are you referring to when I use the ARC in my Anthem? As much as I love this hobby, I am very uneducated in the technical end of things. I just hook everything up, have it calibrated and then it is tweaked until my ears enjoy what I hear.
No worries. I don't know how to do it either, I only know how to read the results.

However, I am pretty sure you cannot use your ARC mic for it. You need to get an external mic, attach it to your computer/laptop via USB, run REW on the computer/laptop, and then play some frequency sweeps through one of your 708P speakers at 75 dB. Then, increase the volume by 5 dB and do it again. Finally, plot the results in a graph. This will show when the speaker starts to compress and at what frequencies. @Gooddoc or @notnyt will be able to explain this much better than me. I know notnyt was interested in getting John to do this so we'd have a comparison to Gooddoc's results.

However, no worries if you can't do this.
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post #2049 of 2918 Old 02-03-2018, 10:50 AM
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Quote:
Originally Posted by Kain View Post
No worries. I don't know how to do it either, I only know how to read the results.

However, I am pretty sure you cannot use your ARC mic for it. You need to get an external mic, attach it to your computer/laptop via USB, run REW on the computer/laptop, and then play some frequency sweeps through one of your 708P speakers at 75 dB. Then, increase the volume by 5 dB and do it again. Finally, plot the results in a graph. This will show when the speaker starts to compress and at what frequencies. @Gooddoc or @notnyt will be able to explain this much better than me. I know notnyt was interested in getting John to do this so we'd have a comparison to Gooddoc's results.

However, no worries if you can't do this.
I have a calibrated mic but have never done the sweeps. My 708s have been moved to side duties and I'm now using the JBL SCL2 as LCRs.

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post #2050 of 2918 Old 02-03-2018, 11:10 AM
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to measure, just need to use REW or something with a calibrated mic. Start at like 75db sweeps of at least 5 seconds and keep increasing by 3db until you get to like 110 or so, or hit significant compression, whichever happens first.

Distance from the speaker needs to be measured as well. Measurements should be run with a frequency dependent window of 1/20 octave
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post #2051 of 2918 Old 02-21-2018, 07:08 AM
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It's too bad Jbl does not come out with a 708I for horizontal mounting as it makes the perfect ceiling pair with the M2. The length is just problematic for this function if mounting down vertically facing MLP.
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post #2052 of 2918 Old 02-22-2018, 04:09 AM
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Quote:
Originally Posted by notnyt View Post
to measure, just need to use REW or something with a calibrated mic. Start at like 75db sweeps of at least 5 seconds and keep increasing by 3db until you get to like 110 or so, or hit significant compression, whichever happens first.



Distance from the speaker needs to be measured as well. Measurements should be run with a frequency dependent window of 1/20 octave


Why does the mike need to be calibrated, really? All you’re looking for is relative information. So as long as you keep levels low enough to avoid clipping on either side it should be fine.

IMO, an ARC mike or even an Audyssey towerlet is adequate to the task. The tricky part is having time to set up and run the measurements when environmental conditions allow one to do so.

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post #2053 of 2918 Old 02-22-2018, 08:59 AM
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Originally Posted by DS-21 View Post
Why does the mike need to be calibrated, really? All you’re looking for is relative information. So as long as you keep levels low enough to avoid clipping on either side it should be fine.

IMO, an ARC mike or even an Audyssey towerlet is adequate to the task. The tricky part is having time to set up and run the measurements when environmental conditions allow one to do so.
It needs to be calibrated so you know what levels it's actually compressing at.
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post #2054 of 2918 Old 02-22-2018, 09:55 AM
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Often mike calibrations are done without absolute SPL. The Cross Spectrum ones for example. To get close enough to absolut-ish SPL for this purpose, you can use the NIOSH SPL meter app with your phone next to the mike and run your measurement software’s absolute SPL cal routine.

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post #2055 of 2918 Old 02-22-2018, 09:56 AM
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Often mike calibrations are done without absolute SPL. The Cross Spectrum ones for example. To get close enough to absolut-ish SPL for this purpose, you can use the NIOSH SPL meter app with your phone next to the mike and run your measurement software’s absolute SPL cal routine.
Then you're assuming your phone is accurate
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post #2056 of 2918 Old 02-22-2018, 10:13 AM
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It's too bad Jbl does not come out with a 708I for horizontal mounting as it makes the perfect ceiling pair with the M2. The length is just problematic for this function if mounting down vertically facing MLP.

MULTIPLE MOUNTING OPTIONS
JBL 7 Series monitors provide construction and mounting features that make installation simple. Constructed from rugged birch plywood, the cabinets are specially braced and reinforced to allow safe mounting. Top and bottom mounting points in a two-hole mounting pattern facilitate effortless wall and ceiling installations using readily available brackets. Both vertical and horizontal orientations are supported. Integrated handles aid in speaker positioning.

  • Compact enclosures minimize interference with sight lines to video monitors
  • Front-ported enclosures allow shelf and soft mounting without degradation in performance
  • Rear and bottom mounting points allow wall and ceiling mounting in either vertical or horizontal orientation using standard hardware
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post #2057 of 2918 Old 02-22-2018, 10:27 AM
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MULTIPLE MOUNTING OPTIONS
JBL 7 Series monitors provide construction and mounting features that make installation simple. Constructed from rugged birch plywood, the cabinets are specially braced and reinforced to allow safe mounting. Top and bottom mounting points in a two-hole mounting pattern facilitate effortless wall and ceiling installations using readily available brackets. Both vertical and horizontal orientations are supported. Integrated handles aid in speaker positioning.

  • Compact enclosures minimize interference with sight lines to video monitors
  • Front-ported enclosures allow shelf and soft mounting without degradation in performance
  • Rear and bottom mounting points allow wall and ceiling mounting in either vertical or horizontal orientation using standard hardware
I don't think 708's are made to turn horizontally due to their vertical pattern, they can be mounted that way but not designed for horizontal placement. It would be great if they could design a 708H - for horizontal placement.
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post #2058 of 2918 Old 02-22-2018, 10:40 AM
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It seems like a non-issue for ceiling mounting if you're aiming in the general direction of the MLP. I'm also not sure why the 705 would work just as well for ceiling speakers vs. 708 since the tweeters are the same on both speakers and trying to squeeze every last bit of sub ~80Hz loudness has little utility at that location.

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post #2059 of 2918 Old 02-22-2018, 11:01 AM
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JBL knows horizontal orientation is not ideal for studio monitors which is what they are designed to be. A horizontally oriented 708 type of speaker would have to be an entirely different cabinet design, just rotating the horn in the existing model would not be a good design.

I'm sure somewhere there are still recording engineers who are laying their 708's horizontally so they can be on the mixing console bridge or behind it on stands. But, most of those guys learned that doesn't work well because it screws up the dispersion pattern.

If size is your concern, the 705i/p has very similar specs and is much smaller. It could be hung vertically with the horn on top or bottom. Subs are going to handle the low end anyway, right?
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post #2060 of 2918 Old 02-22-2018, 11:36 AM
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Agreed on all points.
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post #2061 of 2918 Old 02-22-2018, 11:37 AM
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Then you're assuming your phone is accurate

See https://blogs.cdc.gov/niosh-science-...01/17/slm-app/

Perhaps phone mike accuracy is more of an issue with generics than with iPhones. I don’t know.

Regardless, for this kind of measurement by a hobbyist, in the ballpark is good enough as far as absolute levels go.

If one really wants to be anal about it, one could measure absolutes using voltage out from the amp rather than SPL at the capsule.

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post #2062 of 2918 Old 02-24-2018, 02:26 PM
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When we were discussing the SPL capabilities of the 708i, people stated you can only expect so much out of a 8" driver. However, Alcons Audio gets 130 dB out of a speaker with a 2" pro-ribbon tweeter and a 6.5" woofer and 134 dB out of a speaker with a 4" pro-ribbon tweeter and a 8" driver. And these are surround speakers.

Link to 2" pro-ribbon tweeter + 6.5" woofer: http://www.alconsaudio.com/product/crmsc-sr/
Link to 4" pro-ribbon tweeter + 8" woofer: http://www.alconsaudio.com/product/crms-sr/
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post #2063 of 2918 Old 02-24-2018, 04:53 PM
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Completely different price brackets. There's also a little bit of Hoffman's Iron Law involved when comparing the low frequency reach of the Alcons' vs. the 708.

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post #2064 of 2918 Old 02-24-2018, 05:16 PM
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Nominal SPL peak 129 dB (Sentinel3 200 Hz - 10 kHz)
134 dB (Sentinel10 200 Hz - 10 kHz)

Important to note where it can reach these levels
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post #2065 of 2918 Old 02-24-2018, 06:59 PM
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They're also claiming 103dbspl sensitivty out of an 8" woofer. I don't know about that claim :/
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post #2066 of 2918 Old 02-24-2018, 07:21 PM
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This info is from a JBL booth at a trade show:


JBL 708P
Distance from Speaker / Output:

3ft (1 meters) / 110dB

5ft (1.5 meters) / 107dB

7ft (2 meters) / 105dB

9ft (3 meters) / 104dB

17ft (5 meters) / 102dB



JBL 705P
Distance from Speaker / Output:

3ft (1 meters) / 104dB

5ft (1.5 meters) / 101dB

7ft (2 meters) / 99dB

9ft (3 meters) / 98dB

17ft (5 meters) / 96dB


(Room Size: 75 cubic meters. Measured in half space.)

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post #2067 of 2918 Old 03-01-2018, 08:52 AM
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Quote:
Originally Posted by LJG View Post
It's too bad Jbl does not come out with a 708I for horizontal mounting as it makes the perfect ceiling pair with the M2. The length is just problematic for this function if mounting down vertically facing MLP.
You would want to use the in wall or incelings from the synthesis line from JBL to accompany the m2 or 7XX line. They are designed to be integrated with one another sharing lots of characteristics. They however are more expensive than 705's. IM looking into changing over to some 708s and 705 still awaiting to hear back if I need to use the JBL amps for them or if I can use my existing DSI crowns and mimic the settings.

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post #2068 of 2918 Old 03-01-2018, 10:59 AM
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The amps that will allow you to load in the tunings for the M2 and LSR7 series:

Synthesis SDA
Crown DCi-n
Crown iTech

One can also add a BSS BLU box to the equation.

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post #2069 of 2918 Old 03-01-2018, 11:57 AM
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If I'm driving 708's from the balanced outs of a Marantz 7702mkII, which has an output rating of 2.4V, I assume I should be using the +4dBu input sensitivity on the JBLs, yes?
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post #2070 of 2918 Old 03-01-2018, 12:20 PM
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Quote:
Originally Posted by lemonslush View Post
You would want to use the in wall or incelings from the synthesis line from JBL to accompany the m2 or 7XX line. They are designed to be integrated with one another sharing lots of characteristics. They however are more expensive than 705's. IM looking into changing over to some 708s and 705 still awaiting to hear back if I need to use the JBL amps for them or if I can use my existing DSI crowns and mimic the settings.
The in ceilings cannot be aimed directly at MLP, the 705's and 708's can be mounted vertically and aimed. That is one of the advantages over in ceiling. The in walls can be aimed to an extent at MLP.
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