JBLpro 4645C sub?

[porsche911]

I've always been curious as to why the frequency range for the 4645C subwoofer was 22 hz - 500 hz (-10) . I decided to read the 4645C subwoofer pdf and it states lower frequency limits:

without EQ: -3db@35hz
-10db@22
with EQ: -3db@22hz
-10db@20


I'm curious about why EQ would have such a big effect on output? Why the really sharp drop off from 22hz and 20hz? Also does this mean that the 4645C sub, or all movie subwoofers for that matter, are designed to play loud (ie high SPL output) but not to play low?

I've read it a couple places that movie subs really only play down to the 30-35hz range. I'm just trying to compare this output to say a Velodyne or Klipsch, Genelec or Kleiss subwoofers (all thx) which seemed to be tuned to much lower frequencies. The velodyne DD18 thx ultra2 is -3db@14

The real reason I'm curious is that the JBL Sythesis subwoofer S1S-EX has a freq resp. of -3db@30 hz(from the pdf) If the freq response is lower then why does is need the be EQ'd at all?


I thought it would be a nice to topic discuss.

Thanks

[4313B]

The 2242H is designed to play very loud, very low, with minimal distortion. The specifications you are reading are based on note 8 in that PDF.

THX subwoofer specification is 80 Hz cutoff. Using a typical 80 Hz 24 dB/octave low pass filter the 4645C without EQ is ~ 3 dB down at 26 Hz, ~ 6 dB down at 22 Hz and has usable response (-10 dB) to ~ 18 Hz. Maximum SPL at rated input in this configuration is ~ 125 dB. That's for one, and they never use just one. My point is, the Pros know exactly what these things do and aren't stymied by specifications.

As for dropping off so quickly - the 2242H in the 4645C is roughly a quasi-third order system with a roll-off of ~ 22 dB/octave below the knee, not quite a classic fourth order Butterworth with a roll-off of 24 dB/octave. When you EQ it with a typical 2nd order high pass filter (Q = 2, which means ~ +6 dB boost) set to the resonance of the system, in this case 25 Hz, the system becomes ~ 5th order and roll-off below the knee becomes ~ 34 dB/octave. For all intent and purpose the 4645C is 4th order without EQ and 6th order with EQ.

If you don't like those kinds of drops below the knee then use transducers built to operate in sealed enclosures that have a roll-off below the knee of 12 dB/octave. Incidentally, room rise usually occurs at 12 dB/octave so I'll leave it to you to figure out the ramifications of that. So why doesn't everyone simply build sealed box subs? Because they don't offer the biggest bang for the buck. They also require significantly robust, very expensive transducers for long term viability. They are often quite fine for HT but I can't see them surviving a large public venue unless you used a whole bunch of them and that's BIG bucks.

The velodyne DD18 thx ultra2 is -3db@14

Even the ancient B212 from ~ 30 years ago is flat into the midteens in certain rooms... no biggie.

I'm just trying to compare this output to say a Velodyne or Klipsch, Genelec or Kleiss subwoofers (all thx) which seemed to be tuned to much lower frequencies.

Unfortunately you would have to give them all dedicated listening sessions. Specifications aren't going to tell the whole story. What amps are you using? Do those amps have a healthy bottom end? Do you really need a +6 dB high pass bump filter or will +2 or +3 dB do in your particular situation? Are you placing the subs at the junction of three planes or just two? Will room rise give you all the extension you need without EQ? How many are you going to use? Are you going to space them for mutual coupling and at what frequency? What kind of low pass filter are you going to use and at what frequency? etc., etc., etc.

Basically what you have with the 4645C is a flexible subwoofer solution with a ton of power handling, ultra-low distortion, and high acoustic output. They also sound very nice.

[Don Mascali]

Yep, they kick ass!

[porsche911]

Giskard << dude with all the answers! I'm printing your answer now. Thanks.

[spkrman57]

Since my home is small and the room size is limited to 12' x 16' with 8' ceilings, I need no EQ at all with 9 cu' tuned to 28hz.

Biggest reason for that is the room loading happens quick and EQ brings on overkill and is unpleasant to the ears.

Kind of like listening in your car, the same drivers in a large room would sound bass-shy!

In fact, my biggest problem is getting the sub at the right level so it does not attract attention to itself.

But for my crazy rock and roll concert nights I know my neighbors hear it too. My (non-audiophile) friend came over one night and he had his lighter out during "Talking Heads live" cd! He forgot about going home until his wife called him up to remind him that he had his own home!

Ron

[JBL 4645]

Very interesting thread, I have a JBL 4645, set-up in front of my small but very loud home cinema, and having worked briefly for two cinema chains hear in the United Kingdom, I have to say the 4645, and 4645-C is darn good in every respect.

The first time I got a tasty, a thirsty tasty for the low end, was at the top cinema in the UK, the CIC Empire Leicester Square, screen #1, back in 1989, and played via the Lucasfilm THX /3417 crossover system, darn was it great or what.

70mm Dolby Stereo, and Indiana Jones and the Last Crusade” belting out lots of low end, when called for via the “Baby Boom track” it was from that moment I wanted a JBL 4645 in the home, but it wasn’t till late of 1997 when I installed this huge beast.

It surely put the little 12” sub bass unit that I was using at the time, in it’s place, and films like “Star Trek First Contact” thou it was only been played back in Dolby Stereo via a Pioneer Laserdisc CLD-1750, and a Yamaha DSR-70, for the decoding.

The only amplifier, on hand to run the JBL 4645, was Marantz 1050, which is a bit under powering, and I know about the dangers of running under powered, but there was no problems running it this way, even my friends said it “Sounds a whole lot better.”

since 1997, and at the present time the JBL 4645 is running via a slightly high power output, from a sub bass amplifier, with X-over set at 40Hz and a total output of only 350watts, but in a small room, huge power or less, really isn’t needed.

PS, I'm running a newer JBL driver in the enclsoer the JBL 2240H

Less is more.

Room Size

14 feet length
9 feet 6" width
8 feet height


Ashley

[spkrman57]

I am using Parts Express 250w plate amp. But with only a single 2242 at 8 ohms it puts out only 150 watts.

Previously with Titanic 12 setup(same plate amp with 4 ohm 12" sealed driver), I used that with my previous Edgarhorn setup powered by 45 SET(1.8 watts/chnl) and shut it down on a regular basis. With the 2242, the heat sinks are just barely warm at cranking levels!


Happy 2242 owner!

Ron

[JBL 4645]

That’s high numbers Ron’ positive thought, I like that in JBL owner.

Ashley

[spkrman57]

After being exposed to the likes of the 123A1/2226/2225/2242, I have come to the conclusion that after listening to JBL drivers with foam/rubber and pleated surrounds that I find myself generally avoiding the foam surrounded drivers.

It's probably just in my mind , but I find the pleated surrounds to sound quicker to me. Now I've been told that I am "half-baked" in the noggin so you have to make your own decisions.


I also like high efficiency horns and little SET tube amps, so I am in the minority as far as the trend goes!

Ron

[mikebake]

I also like high efficiency horns and little SET tube amps, so I am in the minority as far as the trend goes!

Ron

Time for a new avatar, Ron! No more 4430!

[JBL 4645]

After being exposed to the likes of the 123A1/2226/2225/2242, I have come to the conclusion that after listening to JBL drivers with foam/rubber and pleated surrounds that I find myself generally avoiding the foam surrounded drivers.

It's probably just in my mind , but I find the pleated surrounds to sound quicker to me. Now I've been told that I am "half-baked" in the noggin so you have to make your own decisions.


I also like high efficiency horns and little SET tube amps, so I am in the minority as far as the trend goes!

Ron

Ron

That’s why my newer JBL driver as edge ribbing surround, nothing like edge foam surround to Bugger your “Baby Boom” up is there,

Ashley

[JBL 4645]

Time for a new avatar, Ron! No more 4430!

Mikebake

He can always re-edge it with ribbing surround, a bit messy, hell I should know, I had to re-edge on of my JBL control 5’s three-screen channels, with rubber edge surround , foam sucks, and like I said it will really bugger your day up.

Ashley

[Zilch]

Lessee, where was I readin' just yesterday about the linearity, compliance, reduced distortion, and other virtues of foam surrounds that might induce a design engineer to employ them for a specific purpose in a particular driver?

'Course, if the designer's intent don't matter, then....

[spkrman57]

You are right Mike, but I need to find a photoshop pgm I can download for free. The Dell version was only good for 90 days and I did not know until it was too late.

Now that I am retired I hope to find the time to get that done along with the other things I have to do. Biggest is cleaning out the house!

Ron

Time for a new avatar, Ron! No more 4430!

[Lutz]

Could someone (maybe Giskard) shed some light on the differences between the 4645C and 4645B? (they both share the 2242H transducer)

I see in the specs. that the 4645B is -10db @ 18hz. (no Eq) where the 4645C is -10db @ 20hz. (no Eq.) Is this the only difference. Has any one compared the 2 sound wise?

Thanks for your input.

David