JBL Cabaret 4698B Speaker - BWC alert!

Discussion in 'Speakers' started by purr1n, Jan 30, 2019.

  1. purr1n

    purr1n Desire for betterer is endless.

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    Finally, here is a measurement with the microphone shoved in front of the mouth of one of the four huge ports. I wanted to see what frequency the ports were tuned at.

    JBL 4698B port tuned to approximately 44Hz.
    upload_2019-4-28_0-31-53.png
     
  2. purr1n

    purr1n Desire for betterer is endless.

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    So one thing that always puzzled me with JBL's approach with the 4698b was using the woofer without a crossover and letting it naturally roll-off. In reality, this almost always means some unevenness and an eventual peak around 1-2kHz (for an 18" woofer) just before roll-off (example shown below). How the heck did JBL pull this off? Since after all, we did not see anything major sticking out in the mids for the overall frequency response seen here: https://www.superbestaudiofriends.o...98b-speaker-bwc-alert.7412/page-2#post-254866

    Here is an example of the Eminence Omega Pro 18" driver's frequency response. I'd hesitate to run this without a crossover because I would be concerned that the 1.2kHz bump would show up in the overall frequency response.

    Eminence Omega Pro 18" FR
    [​IMG]

    Out of curiosity, I decided to take a measurement of the JBL E155, with the microphone shoved up right next to the driver like this to isolate the behavior of the woofer. I could have put the darn speaker into biamp mode to isolate just the woofer, but I was too lazy. There's no crossover in front of the woofer, so this should get me a pretty good idea of what the woofer is doing. The output of midrange and tweeter should be attenuated significantly.
    upload_2019-4-28_11-24-6.png

    JBL 4698b E155 woofer measurement via microphone shoved close. Note peak before rolloff marked in red.
    upload_2019-4-28_11-11-35.png

    As we can see, the E155 isn't different from any other woofer. It doesn't have any magical properties. There a 5db peak at 600db, and the typical associated shallow dip just before that peak at 400Hz. However, there is one very important distinction that makes the E155 work. The peak is much lower in frequency than is usually seen with many other big woofers. The 600Hz does need to be addressed, but how is this done without a network circuit?
     
    Last edited: Apr 28, 2019
  3. purr1n

    purr1n Desire for betterer is endless.

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    The answer lies in the mids. I took a similar close mic'd measurement of the midrange driver.
    upload_2019-4-28_11-26-34.png

    JBL 4698b. E1110 midrange measurement with microphone shoved close. Note that the woofer output will still be in this plot, but highly attenuated. It would appear that the E110 might have a dip around 700Hz, just where the woofer has a peak. I would be an awesome coincidence huh, where the summed output of the woofer and midrange come out to nearly flat. Perhaps this is why the woofer can be run the way it is without a crossover network.

    JBL 4698b E1110 midrange frequency response via microphone shoved close.
    upload_2019-4-28_11-31-42.png

    To confirm, I found this JBL E110 frequency response graph on the Internet. Yup, it looks like that 700Hz dip is there and inherent to the driver. The E110 midrange, like any other driver in the world, also has issues with rising response and a 2.5-3kHz peak before rolloff, but this is addressed by the crossover circuit. The E110 has a coil for high-pass and a cap for low-pass. Note that we can still see the 2.5-3kHz peak in the ARTA measurement above, but highly attenuated by the coil.

    JBL E110 frequency response.
    upload_2019-4-28_11-34-11.png

    I am pretty sure the E155 and E110 drivers were designed way before the the 4698b speaker was conceived so this was likely a good coincidence. This is the kind of stuff I love, when engineers find elegant solutions, finding ways to make things work with less complexity rather than more complexity.
     
    Last edited: Apr 28, 2019
  4. msommers

    msommers High on Epipens

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    Marv what mic and software did you use for this? I'd be curious to try this at the speaker and listening position as well.
     
  5. purr1n

    purr1n Desire for betterer is endless.

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    One more thought: the benefits of not shoving a coil in front of a woofer driver are significant, especially in this case were the nominal impedance of the E155 is 4-ohms. A typical big-ass air core 1.4mH inductor (400Hz low pass for 4-ohms) using 18-gauge wire is going to have a DCR of about 0.65-ohms. Think how much energy loss there is with the inductor being 16% of the load.

    However, there is always a good argument for using crossovers or higher slope crossovers. We get the drivers working in their prime spots and we push their bad behavior down in amplitude. The cost, as explained above, is more "crap" in the way. More power robbing coils and to a lesser extent caps. It's about priorities, balance, and trade-offs. There's no free lunch anywhere. One problem of course is that it is difficult or impossible to measure subjectively observed dynamics.

    (One thing I won't do anymore is work with exotic material drivers that ring like hell. We need steep crossovers. This is really the realm of active networks, amps for each driver, maybe DSP, and wholly another topic.)

    The good news is that for those who want a little bit more accuracy, JBL has the 43* series.

    Here are some photos of the JBL 4345.
    upload_2019-4-28_12-10-20.png
    upload_2019-4-28_12-11-55.png

    The JBL 4345 is a 4-way speaker from the 70s: 18" woofer, 10" low-midrange, midrange-high horn (with fancy lens), and slot supertweeter. More crossover parts, but the approach is still minimalist. The polar response is better too. Overall efficiency is less than the 4698b, but we can argue that the 4698 cheats via the use of a 4-ohm woofer.

    JBL did some cool stuff for the 43* series, like biased capacitors for the networks.

    I'd love the build something like this. Some of the drivers are unobtainable now. However, it might be a neat idea to do a modern interpretation. Maybe I should quit my job and see if Schiit would be willing go in on it (to keep parts cost down).
     
  6. purr1n

    purr1n Desire for betterer is endless.

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    Dayton Audio UMM-6 USB microphone. ARTA software.
     
  7. Cspirou

    Cspirou They call me Sparky

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    I've mentioned this a few times but I am not sure if you are familiar with it

    http://www.troelsgravesen.dk/The-Loudspeaker.htm
     
  8. purr1n

    purr1n Desire for betterer is endless.

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    I know, but when Troels comes up, I tend to close my eyes and plug my ears and go la la la la. He likes to pick the most expensive drivers possible and then takes a surgical approach to crossover design to make everything work. I'm a cheapskate who likes to identify high value drivers and minimize crossover parts count.

    Troels design needs to be priced at $15k or more to be commercially viable.
     
  9. dmckean44

    dmckean44 In a Sherwood S6040CP relationship

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    If you thought you could sell a lot of them, you could probably keep costs down by doing the injection molded speaker cabinet thing like with PA speakers.
     
  10. dBel84

    dBel84 Friend

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  11. Philimon

    Philimon Friend

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    JBL 4628B

    [​IMG]
    [​IMG]
    (Will be getting a new media shelf to fit.) (For scale reference thats a 65” plasma tv.)

    From same line of Cabaret speakers but these were a step down. Same tweeter, smaller mid at 8”, smaller woofer at 15”. Same minimalist approach to “crossover” network. Biggest difference is reduced cabinet size which reduces LF extension which is fine since I live in a townhouse with shared walls.

    Will add some impressions and measurements from main listening position using Umik-1 mic.
     
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  12. aamefford

    aamefford Nothing like chamberpot coffee

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    Sweet mother of Music Boxes! My lovely wife would probably bury me in those. After dismemberment of course. All this after the intro to “Lazy” off “Made in Japan” was played loud enough to structurally damage the house. Might be worth it though….
     
  13. Philimon

    Philimon Friend

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    Here is some info by Zilch. Warning: those RIP titles are sad.
    [​IMG]
    [​IMG]

    The 4628B woofer (E145) was used in the Everest DD55000.

    Here is a company that rebuilds these with proper driver alignment and different crossovers.

    I wonder how much these JBLs would be worth today if they came from factory with a home stereo standard enclosure and crossovers.

    I dont plan to mod. Dude I bought these from had another pair but with custom enclosures and crossovers. He seemed to like both equally for different reasons but the customs he was asking twice the price. Good deals. He had lots more stuff too. These appeared to be the smallest speakers in his collection… :cool:
     
    Last edited: Nov 16, 2021
  14. Philimon

    Philimon Friend

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    [​IMG]

    JBL 4628B - stereo.jpg

    Not optimal in every way. Just for entertainment. The room is open to kitchen, dining room, and stairway, a little wider too than is shown but my kid was sitting on side sofa and didn't want to be in pic.

    iPhone > usb > cheap Pioneer avr (D class amp). Pink noise. Umik-1 mic. Full stereo. From main listening position. 1/6 smoothing. Turned up as loud as I thought my neighbors would tolerate for a few minutes. AND IMPORTANTLY the tweeter attenuator is set to 9-10 o'clock. I calibrated tweeter setting by ear while watching a movie last night. Setting the attenuator all the way to minimum (6'oclock) is like OFF. Tweeter attenuator at 12 o'clock (midway) is bright. The tweeter diaphragm condition I've no idea but they sound great. Seller said he was second owner and owned for a long time.

    Behringer 2031p crossovered to a pair of 15"subs for comparison in a different room (a relatively huge room - previous dwelling). Also from main listening position.:
    [​IMG]

    I've also played with new cheap pa speakers for home theater before (setup well in big room with very high ceilings). And custom car stereo (spent by far the most on this setup because used to commute a lot). I've also heard a few vintage flagships from JBL, Infinity, Klipsch, Acoustats, and others from meetups when buying stuff off Craigslist.

    What stands out on the JBLs is the dynamics and speed in comparison to my other speakers (Manzanita Ultra and Cambridge Audio Aero2). Gun shots from movies or FPS games never sounded this explosive / realistic (minus bottom). That woofer is amazing with music (minus extension), micro/macro in bass to upper bass is wow. Mids are fast and detailed and mostly rich/natural. Highs are smooth, fast, and also great off-axis.

    Its weird turning the avr volume setting all the way down to "1" and it still be too loud... But the little music listening I've done has been sublime. Small stage (current placement) and less linear but totally fun and exciting. Cambridge Audio Aero2 with BMR driver is totally boring. JBL mids not as smooth as Manzanita, but again there is a visceral-ness and speed that makes the JBLs demand attention from bottom to top. The Manzanita Ultras I used for background music... The Aero2's I used for television... Headphones I use for critical listening (which is least often of the three). I think I will be using the JBLs more often for music, or atleast until honeymoon period is over.

    These do lack in the bottom end but it not an issue for most music (mostly electronic that suffers), but townhouse life means I cant have anyway. Imaging is meh / smeared but my positioning is terrible. My biggest concern (for television use) was the intelligibility and clearness of vocals. I have this concern with stereo speakers for music too which is why I was drawn to widebanders crossed low-ish to big woofers in my other recent speakers. These work great for vocals.
     

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