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Thread: Power Amps for JBL LSR6332

  1. #1
    Senior Member stevem's Avatar
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    Power Amps for JBL LSR6332

    Hi all. Several months ago I acquired a pair of JBL LSR6332 (12" 3-way) monitors. I have been experimenting with different amps with various output powers and configurations (single amp and passive bi-amp). I have a question that google hasn't helped me answer: Does anyone know, or can they tell me how to estimate, the amount of power the woofer will use vs the mid/tweeter? The crossover frequency is 250Hz. I had read somewhere that roughly 200Hz represents the point at which half an amplifier's power will be used for frequencies above it, and half will be used for frequencies below it. Is this correct? If I use a subwoofer crossed over at 60Hz (@ 24 db/octave) how would that change the woofer's power requirement?

    Also, I'd appreciate any opinions/suggestions regarding which amplifiers sound best with this speaker. Thanks!

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    Senior Member pos's Avatar
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    Did you notice an improvement with the passive biamp configuration?
    I have never tried this with mine but I have read that the results were positive with the LSR(63)32.
    If this is the case then you might want to try a single amp with a very low output impedance such as an Hypex nc400 or purifi 1et400a, bi-wired directly from the module (ie two sets of outputs on the amp enclosure connected to the same output on the module). That was deemed to be practically equivalent in terms of back EMF to using two independent amps by Bruno Putzeys.

    Another option would be to go all out and use an active crossover, in which case using current amps (transconductance) on the mid and tweeter would significantly reduce distortion.
    I cannot find my detailed measurements right now, but here is one for the mid: https://www.diyaudio.com/forums/mult...ml#post4410302
    That is an average 15dB reduction of 3th order distortion throughout the intended frequency range, and this could probably be improved further with a "real" current drive (ie higher output impedance).
    Of course the frequency response is altered, but that can be accounted for when designing the active crossover...

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    Senior Member stevem's Avatar
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    Yes I do notice quite a difference with passive bi-amp. Some people claim that there is little benefit with this approach, because the woofer uses most of the power and a separate amp for the HF is a waste. I was wondering if the low crossover point used for the midrange in the 6332 meant the MF/HF is actually using significant power, which would account for the difference I heard with passive biamping. That's why I was asking the question about power distribution between the woofer and tweeter/mid.

    I have no experience with class D amps, but I will check it out.

    Regarding active crossovers, are you suggesting bypassing the passive crossovers? I hesitate to try that because it is a large part of the engineering that went into designing this speaker, and I'm not sure that I can improve upon it.

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    Regarding your question about power vs frequency, it all depends on the sound you are listening to. But you knew that already...

    I look at it as a flexibility thing. When I listen to solo classical guitar, the woofer is not going to get that much work. But when I was testing a pair of Van Alstine amps against each other, they were sooo identical I wanted to cry (hybrid tube vs solid state), and then I listened to a tympani rumble towards the end of the first movement of Mahler's 4th and sure enough, the finickier pricier hybrid amp rumbled a teeny tiny microscopically bit better.

    So...if I'm going to be that picky, then the difference will eventually manifest itself, but it's likely that both scenarios will power these wonderful speakers adequately enough. They were even efficient enough for a 30-watt tube amp that I was using back in the day.

    Sometimes I look at foobar's spectrum display as I listen to a song and then it is all clear. If it's a Mozart piano sonata, the power bars are somewhere in the middle; if it's Supperclub or Goldfrapp etc. it stays very big well under 100 hz for most of the tune.

    So maybe horizontal bi-amping is first and foremost an insurance policy, so that Joni Mitchell is just as effortless as Saturday Night Fever and nobody has to answer any questions.

    btw I totally heart my LSR32's and I'm thinking about starting a new thread demanding an answer to the question of why JBL discontinued these (aka LSR6332's). We're lucky to still be able to score replacement drivers, these things are fantastic, endgame speakers in the analytical vein for a modest-sized room afaik. I suppose one can always stuff an L100 cabinet, but these rounded edge cabinets with no grills (yesssss), the 252G with tight tight tight bass, c500G miracle driver, ruler-flat FR, ah...

    Really, this speaker being so good, so serviceable, so inexpensive, it should not even exist (it even looks too inexpensive to tempt thievery). So yeah, horizontally biamp The Dude just to show respect, I do it myself and I tell myself that it sounds better and leave it at that.

    Oh and as far as that 250hz crossover point, that may have been done so as to keep human voices on the same driver, and fortunately that c500g exists. BUT...the 252G has an amazing FR response, so a higher crossover point (eg L100) is probably an option, but I stopped thinking about that experiment long ago.

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    Dang. Amateur speakerdave's Avatar
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    Quote Originally Posted by trebejo View Post
    . . . . btw I totally heart my LSR32's and I'm thinking about starting a new thread demanding an answer to the question of why JBL discontinued these (aka LSR6332's). We're lucky to still be able to score replacement drivers, these things are fantastic, endgame speakers in the analytical vein for a modest-sized room afaik. . . . .
    Good luck.

    I like the speakers, too, their accuracy, and agree with you about that midrange driver. I think the tonality/voicing leaves somewhat to be desired. It's objectively a better speaker than the Manley Tannoy ML 10, also meant for mid-distance monitoring, which I've also used, but I like the latter better for music. I use the LSR's for watching movies and TV, with a Revel C32 center. I drive them full range with a Bryston multichannel; at 4 ohms, I think it is about 180 watts, which I never need. Not real focused on dinosaur footfalls, earthquakes, low-frequency soundtracks for dread, explosions, or annoying the neighbors, so we get along fine without a subwoofer. Since my pre-pro is a Marantz 8802, we're not talking marvelous fidelity for music, which I play elsewhere.

    I think the low crossover for the woofer-midrange handoff is about leaving the voice range with a minimum of crossover intrusion, that and matching dispersion patterns in the crossover region. My Revel C32 uses the same points.

    There are other good monitors out there, some from JBL. These days, innovation changes the options pretty quickly. I think the LSR's had a pretty good run. Like you, I'm glad they are still being supported.

    Just enjoy them while you can. Maybe stock up on some parts, if you think it's advisable.
    "Audio is filled with dangerous amateurs." --- Tim de Paravicini

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    Quote Originally Posted by speakerdave View Post
    ...Just enjoy them while you can. Maybe stock up on some parts, if you think it's advisable.
    Thank you, it's a pleasure to read your reply. I have learned a lot from your posts over the years, and they helped me to understand better what I was hearing from these speakers.

    In a bigger room, I preferred a pair of Tannoy DMT II 15 (funny how we ended up comparing the same brands). The room was about 5000 ft^3 and the LSR32's were not able to energize the room in the same way...and that dual-concentric at a good distance is special. But I still managed to get the JBLs into the mix for a month or two every year, they were that good.

    I'd be curious to hear about what competes from JBL nowadays in the near-midfield, hopefully still in the reasonable price category.

    Something I really like about these LSR's is that the thing is totally serviceable even by someone like me. Taking the drivers out and replacing them is a piece of cake. So, indeed, I have at least two of everything, it's very reassuring to know that I'll never have to listen to anything "worse".

    I guess their sound is not necessarily relaxing, definitely analytical. That bass, though...oh, so tight. A little underpowered in the first octave, but digital EQ allows me to dial that in (that 252G responds well in that scenario). As for vinyl, that requires a sub, but I've been getting away with using an extra pair of LSR32s low-passed around 60hz and it sounds sooo good.

    Sometimes I bring in a pair of Ohm Walsh just to mellow out and enjoy the music, but darn it, that finely-etched detailing always ends up bringing the LSR's. It's a nice problem to have.

    Thank you JBL, you did good!

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