Chris,
Audiokinesis brings up a very important issue, i.e., the bias pots on the backplates. I got careless several weeks ago and tweaked one of these pots too much and messed up the level balance between the two speakers.
A suggested approach would be to turn up the bias pot on each speaker, one speaker at a time, until the "spitting" noise occurs and then ease back the adjustment just until the noise is gone. Then with a test LP or CD with test tones, and a SPL meter, match the levels of the speakers by reducing the bias pot of the speaker that has the higher level. This removes the problem as described by Audiokinesis and brings on as much speaker efficiency as possible.
Also, rather than still wonder if your ARC amp will work or not, take it with you once the speakers are working correctly. And taking your own speaker cables might be of value too.
John |
Chris, I hesitate to say this for fear of offending someone, but I'll say it anyway: the Crown Macro Reference is, in my opinion, a harsh sounding amplifier. And listening to only one speaker, quite possibly with the bias set too low, is hardly a meaningful way to judge the sound. Doubling the number of speakers (acoustic sources) played at the same SPL as one (and obviously using twice the power since two amps are working at the same level as one was) results in a 3 dB increase in SPL, not a large increase but audible. On the other hand having a stereo image will greatly benefit the presentation. John's (Jafox) suggested approach is good. While your VT-200 may not be the last word in amplification it should be a nice improvement over the big Crown amp, so take it along for the followup listening session when the system is up and running fully. Recently I posted the following response to a thread elsewhere related to matching amplifiers, which I hope is of help: The sensitivity of Sound Lab speakers, up till last year, was published as being equivalent to 88 dB at 1 meter at 1 watt input, measured at 4 meters, but in terms of real world performance they're more in the range of low 80s at best, meaning they tend to work better with healthy amplification to spring to life. Those built since early last year are on the order of 3 dB more sensitive, which certainly helps, and they're livelier, more responsive, and cleaner sounding.
Because Sound Labs are mostly a capacitive load, the impedance is relatively high in the low bass, falling with increasing frequency to a dip to about 5 to 6 ohms in the 500 to 550 Hz region, above which the separate midrange/treble transformer sees the signal and raises the impedance some and then the impedance drops off gradually with increasing frequencies. The impedance at 20 kHz is 2 ohms or less depending upon the setting of the brilliance control, which poses a difficult load to an amplifier but thankfully there isn't a lot of energy up there. The panel is driven full range, fed by the two separate step up transformers in the backplate to smooth the impedance curve, although it's still a tough load.
I don't have any recommended current capability for amplifiers to use, but solid state amps reported to work well include Parasound Halo JC-1s as well as some larger models by Krell, Levinson, Pass, Boulder, Bryston, and Rowland, and I have some experience with some of them. I understand the Innersound ESL amps can drive Sound Labs to high levels and can be very price competitive, though they might not be as clean and grain-free in the treble as some of the others. For solid state, I recommend a good beefy amp of at least say 200 watts per channel, and more is better. Perhaps it won't always be the case. With tube amps there seems to be more variation in the amount of power needed. I've had a 100 watt per channel beast in my system that left little to the imagination, while 250 watt monoblocks from another manufacturer didn't fare so well. With Sound Labs, a hefty amplifier power supply is very important whether the amp is solid state or tube, as are output transformers if they're present - an amp that skimps on output tranformers probably won't drive the speakers as well as a less powerful one that gets 'em right.
If you have other questions or comments, please feel free to contact me offline. I should add a disclaimer that I'm an authorized Sound Lab dealer. Brian Walsh |
Chris,
You might want to take a look at diamonds system, and possibly contact him:
http://forum.audiogon.com/cgi-bin/fr.pl?vopin&1107813475&read&3&4&5
He thinks his new Summits are awsome. |
My research indicates that the speed of sound is about 1116 feet per second, but perhaps that assumes a different temperature or humidity or other variable than the 1127 feet per second cited by Nsgarch; but let's say either is in the ball park.
I'm not sure it it's necessary to push for a system that can reach all the way down to 20 Hz; personally, I'd be happy to get a clean 32 Hz. At 1116 feet per second, a 32 Hz wave will be just under 35 feet long. I've been under the impression that you'd like to have 35' between the speakers and the back wall (behind the listener) to avoid a wall reflection before the wave completes one cycle. Nsgarch suggest that maybe you only need to have enough room for the wave to complete half it's form, ie, 17.5 feet will get you 180 degrees of a sine wave for 32 Hz (assuming a 1116 feet per second speed of sound). I don't know if Nsgarch is right, but I'm rooting for him to be correct as that makes the challenge of finding a decent room only half as difficult as I had presumed. Further, if I understood Nsgarch, he says that that dimension will suffice even if it's from a wall/floor line to the diagonally opposite wall/ceiling line. My geometry isn't working, but someone should be able to compute how long the room needs to be for a given ceiling height to support such a 17.5' diagonal. That would in turn tell us the minimum length needed to support 32 Hz. Then from that length, we could use the Cardas formula to see what width would compliment the length (and height). Then we'd have a pretty good room identified, but to make it optimum we'd need to pie out the walls and the ceiling so those wouldn't be parallel surfaces. Then we'd just have some room treatments left to go to get the absorbtions and relflections dialed-in.
Again, I don't know if Nsgarch is right about the need for only half the length of the lowest desired frequency, but either way, I am highly confident that there is a minimum room length needed to get solid/accurate bass. And if the bass isn't right, it's going to be a struggle to get the midrange and highs right.
My main point is that you can buy all the world-class gear you want, but without a decent room, you aren't going to realize the potential of the gear. And the more capable the gear is the more the room is going to become the limiting factor. I'm pretty sure that spending 100k on a system wouldn't make as much sense as spending 50k on a system and 50k on a room (unless you already had a deluxe room). I've found that somewhere around $2500 to $10k for a system, the room can easily become the limiting factor. In fact, all the critiquing we share with each other on Agon about how speakers, amps, preamps, etc. have this or that tonal characteristic is often just a report on what our equipment plus our room sounded like. If people think ICs can act like mini "tone controls" (and no doubt they do), I think we would be surprised to hear how our rooms are mega tone controls if we could swap rooms as easily as we swap ICs.
I'm not against pursuing great equipment and great systems, I'm just advocating a recognition that the room is a huge variable that introduces a huge number subtle variables that add up to an almost random and often unpredictable result. Being aware of the causes and effects of room acoustics could save you a lot of time, money, and effort. |
Martin Logan hasn't made a worthwhile speakers since they stopped making the Monolith III. As an old ML owner, there is nothing desirable or competitive about the new line.
If you must go hybrid/ESL then investigate the Innersound Eros III in its active version a very worthy rival to the Sound Labs with a much more Dynamic (punchy) Presentation like your Prodigy's vs. Maggies. The Innersounds compete with Dynamic speakers in their output and maintain the ESL sound and coherency. They are IMO are on a much higher performance level from your Prodigy's despite costing less.
I bring them up based on your input (what you've written) in the discussion, this seems like a it might be a good speaker for you. Too many ifs (from what others have said) in your system to go buy used Sound Labs it seems. |
