JBL L212/B212 Ultrabass - replacement amplifer - bass boost or not?

[Zonker92]

I'm shopping a replacement amp for my B212 subwoofer, and according to some product literature (see first image below), the original amplifier ("Bass Energizer") has a 25Hz, 10 dB boost. Yet according to the service manual (linked here (http://www.audioheritage.org/vbulletin/showthread.php?10058-L212-ultrabase-amp&p=103347&viewfull=1#post103347) and "screenshotted" below), there appears to be no such boost.

Can anyone confirm or refute the presence of such boost? (Of the plate amps I'm shopping, the most boost I have found is 6 dB at 25 Hz; see here (https://www.parts-express.com/yung-sd500-6-500w-class-d-subwoofer-plate-amplifier-module-with-6-db-at-25-hz--301-514).)

Thanks!

Eric

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1977-l212/page07.jpg

[Don C]

Take note of the passive equalizer shown as part of figure 7 in the manual.

[Zonker92]

Thanks, Don! I did see that, but page 5 of the manual (bottom-left corner) describes that EQ as being for the low-pass filter rolloff (of about 10dB/octave). It never mentions any bass boost EQ that I could find.

So anyway, regardless of the answer to my question, I'm thinking that this plate amp would offer the flexibility to custom-tailor the boost to suit my room, albeit up to only 6 dB of boost:

https://www.parts-express.com/dayton-audio-spa500-500w-subwoofer-plate-amplifier--300-807

Or just use a mini-DSP I guess.

Maybe there is boost (and the service manual is wrong), or possibly JBL made a running design change and omitted the bass boost because of excursion problems. Dunno. The upper illustration is certainly inaccurate in its absence of the low-pass roll-off curve.

[dprice]

I use a similar amp (SPA1000) to drive a B460 subwoofer. 10 years, no problems so far. It lives in a box alone away from the sub.

The description of the Ultrabass amp/EQ sounds a lot like the language used to describe the BX63 crossover/EQ used with the B380 and B460. I would bet lunch the same design philosophy was used.

[Zonker92]

Cool; good to know. The B212 has a largish cavity underneath for the OEM amplifier: there should be room for a decent-sized plate amp under there. I'm mentally designing a sort of embedded compartment for same.

[Zonker92]

OK, I've now ordered this Dayton SA230 subwoofer amp, which has bass boost adjustable up to 12 dB at 25 Hz (or higher) and an adjustable 18 dB/octave HPF (OEM amp is 10 dB/octave at what looks like around 45 Hz (though the literature suggests 70 Hz). At 156 watts it should have just over 3 dB more headroom than the factory amp, I reckon.

I guess I'll try it at various bass boost settings with an eye toward what appears to be the factory boost of 10 dB:

http://www.parts-express.com/dayton-audio-sa230-230w-subwoofer-amplifier--300-813

[Zonker92]

OK, I've now ordered this Dayton SA230 subwoofer amp, which has bass boost adjustable up to 12 dB at 25 Hz (or higher) and an adjustable 18 dB/octave HPF (OEM amp is 10 dB/octave at what looks like around 45 Hz (though the literature suggests 70 Hz). At 156 watts it should have just over 3 dB more headroom than the factory amp, I reckon.

I guess I'll try it at various bass boost settings with an eye toward what appears to be the factory boost of 10 dB:

http://www.parts-express.com/dayton-audio-sa230-230w-subwoofer-amplifier--300-813

OK, to my ears, flat is a hundred times better than boosted, which just kills the upper bass and maxes out the bottom-end excursion. I'll try some testing later.

72024

[speakerdave]

You've discovered the secret of the B212--almost! You have to kind of read between the lines in that promotional piece you posted. As Don C. hinted, equalization in the unit is achieved with staggered poles in the low pass circuit acting as cut eq. Notice the emphasis on the fact that having its own amp obviates concern about efficiency relative to the side panels. That means that the woofer response can be cut in its most efficient region and run naturally in the VLF. To do it the other way, with actual boost, would have required more amp and more woofer excursion. This has been discussed in considerable detail by 4313B in archived threads.

By the way, corner placement may not be best for the B212. Try it between the side panels.

[bldozier]

Subscribe, might be cool underwater?
Brian

[Zonker92]

You've discovered the secret of the B212--almost! You have to kind of read between the lines in that promotional piece you posted. As Don C. hinted, equalization in the unit is achieved with staggered poles in the low pass circuit acting as cut eq. Notice the emphasis on the fact that having its own amp obviates concern about efficiency relative to the side panels. That means that the woofer response can be cut in its most efficient region and run naturally in the VLF. To do it the other way, with actual boost, would have required more amp and more woofer excursion. This has been discussed in considerable detail by 4313B in archived threads.

By the way, corner placement may not be best for the B212. Try it between the side panels.

Thanks for the insights, Dave. But now I'm corn-fused: You're saying that rather than boosting the bottom end, the factory EQ lowered the middle bass range? I understand that concept, but mechanically and electrically speaking, how does that differ from boosting the bottom end? To my unsophisticated mind at least, that sounds like two different descriptions of the same thing. Can you please elucidate?

I'll also try try to hunt down those older threads to which you allude.

[speakerdave]

. . . . I'll also try try to hunt down those older threads to which you allude.

:thmbsup: