Hi Cmo,
Something definitely was not right with that single speaker setup you heard. Hard to say from here, but it could have been a problem elsewhere in the signal path, or it could have been improperly set bias. I remember once for some reason I had the bias set way, way too low, and on loud passages there was a horrible "crunch" that terrified me until I figured it out. Maybe what you heard was amplifier clipping as you suspected - note that a second speaker + amp would add 6 dB more headroom, so if he was trying to replicate two-speaker SPL's with a single speaker then he'd be asking the amp to deliver four times as much power output as normal. |
Time for my 2 cents again:
Never attempt to audition a Sound Lab with transistor amps! You will come away with the mistaken impression that the speaker is harsh and has no bass. This is not the fault of the amplifier so much as it is bad physics to put a transistor amp on ESLs. Here is why:
Most transistor amps (like a Crown or Krell for example) will double power when going from an 8 ohm load down to four, and double again from 4 to 2 ohms. Conversely, the power is cut in half going the other way.
Now the maximum impedance of most of the newer Sound Labs is about 16 ohms in the bass region. Guess what? You have no power to make bass and about *8* times more power to make the highs. Yes, the feedback in the amp helps reduce some of this (adding to loudness cues along the way due to the nature of negative feedback), but: in a nutshell, harsh sound. ESLs in general require the amplifier to maintain constant power regardless of load, not constant voltage which is how most transistor amplifiers work.
Tube amplifiers, especially those with little or no feedback, provide this constant power characteristic. Insist on it if you want to hear the speaker perform properly. Otherwise it is a good idea to refrain from making an opinion of the speaker! |
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. |
