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JBL Control 28-1-WH - Teardown, inside pics, personal thoughts

trl

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Hello, I'm welcoming you with a new teardown: JBL Control 28-1 passive speakers meant to be used indoor and outdoor. Given that it's an outdoor speaker too, I do not expect it to sound as good as an indoor speaker, given rougher and water-proof drivers membranes, anti UV exterior plastic etc. Specs can be read here: Control 28-1 Spec Sheet.​
  • Components:
    • 8” woofer with woven fiberglass cone
    • 1” PEI diaphragm tweeter with fluid cooling​
  • Contemporary, high-design appearance​
  • Built-in InvisiBall® mounting hardware*, plus available U-bracket​
  • Weather resistant enclosure and transducers​
  • Wide 100° x 100° coverage​
  • 120 Watt power handling (240 Watt program) in direct 8Ω setting, plus built-in 60 Watt 70V/100V multi-tap transformer.​
  • High fidelity sound character with broad frequency response of 45 Hz – 20 kHz.​
The previous version of JBL Control 28 has been teared down here and I really enjoyed the short movie presentation. The author disassembles almost every single part of these nice speakers.

Speakers are rated IP55 if the front MTC-28WMG-1-WH WEATHERMAX GRILLE and the back MTC-PC2 or MTC-PC3 panel cover are properly installed. I'll copy-paste here from its datasheet: "Exceeds MilSpec 810 for humidity, salt-spray, temperature & UV. Passes MilStd-202F for salt spray and ASTM G85 for acid-air plus salt spray. Optional MTC- 28WMG-1 WeatherMaxTM grille for breaking up driving rain and for especially difficult environments".​

IMG_3848.jpg

Front picture with the grill On
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Front picture with the grill Off

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Backside line/power level selector

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Backside wires connectors

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Inside picture with both drivers
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8" Woofer - front close up

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8" Woofer - UTC1733

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DC resistance of the woofer

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1" Tweeter - front close up


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1" Tweeter - UTC1739

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DC resistance of the tweeter
I see in the specs the term "fluid cooling" for the tweeter and I have no idea where the fluid cooling (perhaps ferrofluid?) is located, given that the tweeter has a big visible regular magnet attached on the backside. I suppose the tweeter is covered in ferrofluid and on top of that a big magnet surrounds it.
IMG_3859.jpg

The inside stuffing

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The line voltage transformer and the selector on top

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Top of the crossover filter

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Bottom of the crossover filter

I do hope that the above images are self-explanatory for most and based on these and on the specs provided by the manufacturer we can see a great nice looking piece of indoor/outdoor speakers. I personally use them as rear speakers in my home setup and the sound is very clear, a bit on the bright side perhaps, with female voice accents, somehow contrasting with my front speakers CANTON GLE 496 that are having a more neutral sound (perhaps a bit on the dark side). Given the increased level of clarity, the JLB Control 28-1 could be used as monitor speakers for home or studio use, especially if paired with a subwoofer. These speakers are rough and built to last, so using them outside might not be an issue as well, especially if the backside connectors are properly sealed, as per specifications and JBL recommendations.

However, some other things I've noticed as well, that I can not fully understand. First one is related to the wire thickness inside, same issue seen in the Mackie MR10SMK3 subwoofer: the wires are simply too thin.​

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Aluminum wire coming from the 8" woofer

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22 AWG aluminum powers the 8" woofer

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18 AWG aluminum wires the line voltage/power selector

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Wires "upgraded" and bypass

I wanted to get rid of those thin wires and install 0.75mm2 copper ones, but I've also got rid of the line voltage/power selector as well by bypassing it with a couple of wires, although this is usually not necessary on this model because the selector itself has a THRU setting that already does that.

I also found that the passing inside is somehow lacking in depth and volume, at least comparing with the previous model from the Youtube movie review from the beginning of this article, so I've added a bit more of "stuffing" inside.
IMG_3870.jpg

A bit more stuffing added inside to get rid of any possible inner standing waves

In the end I've compared a couple of rough in-home measurements pre vs. post the above so called "modding" (rewire and stuffing).
IMG_4245.JPG

ECM999 + Motu M4 + REW

JBL_Control_28-1_Original2-Distortion.jpg

SPL and THD for the original speaker

JBL_Control_28-1_Original2-RT60_Decay.jpg

RT60 Decay for the original speaker

JBL_Control_28-1_Original2-Spectogram.jpg

Spectogram for the original speaker

JBL_Control_28-1_Rewired-Distortion.jpg

SPL and THD for the modded speaker

JBL_Control_28-1_Rewired-RT60_Decay.jpg

RT60 Decay for the original speaker

JBL_Control_28-1_Rewired-Spectogram.jpg

Spectogram for the modded speaker

As we all can see, the so called "modding" by rewiring and a bit of stuffing added is not making any real difference, at least I can't measure any, but still those thin wires should be upgraded by JBL in their future Control 28 revision of these speakers.​
 
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trl

trl

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The 22 AWG wires are about 30 cm each, the 18 AWG ones are shorter...perhaps 10-15 cm or so.
 
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trl

trl

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A screenshot done from JBL's specs page shows that frequency response is pretty similar with the one from my measurements, tough mine are a bit more bright after 10 kHz. These speakers are bright indeed, but for some this might be a good thing.

Screenshot 2023-12-03 at 15.46.46.png

Source: JBL's website.​

However, having a crossover frequency of 2.8 kHz it's basically impossible to adjust the internal filters to notch down only the frequencies between 5.5-9.0 kHz to make it sound less bright, so for whoever has issues with this brightness will probably need to get a new filter build and installed instead. Still, if someone has any ideas of a simple modification of the existing filter then please do comment here. I'll try to do a reverse engineering of the existing filter soon, to clear things up a bit.
 
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