Overkill Posted November 22, 2004 Share Posted November 22, 2004 I'm using the reference series with a McIntosh MC206 (6 CH Amp). Today I experimented to see what impact biamping the RC7 would make. My intention was to get more power (headroom) from my amp for the RC7. First, I ran the RC7 off a single channel on the Amp, at -11Db on the Preamp, and the power meter on the Mac was hitting 40W. Then, I ran the RC7 using two channels off the Mac with the Preamp again set to -11Db. I looked at the meter readings for each the HF Channel, the LF Channel, and summed. I expected that each, the LF, and HF meter readings would be significantly less than 40W (especially the HF designated channel!). However, each was still reading almost 40W. Combined, the meter was reading > 40. So, it doesn't look like I'm going to gain any more headroom from biamping the RC7 in this configuration. Anyone have an explanation as to how a bridged RC7 (single amplification) could be drawing as much power at the same pre-amp volume level as the HF channel (biamp)?? Next I will have to use a SPL meter to measure actual output under each setup. It is possible that the total summed output of the biamp configuration at a set volume is actually greater. In which case, I guess I would have to recalibrate the center channel output in the preamp settings to adjust for a biamping configuration. One other question: Are there any negatives to using a Y-connector from the center channel output on the preamp if I decide to go with the biamp setup? Sorry about being long winded here. Thanks for any feedback / advice you might have Quote Link to comment Share on other sites More sharing options...
michael hurd Posted November 22, 2004 Share Posted November 22, 2004 First, the meters would read the same, as you had the same preamp volume setting. The speaker is receiving the same amount of voltage, as it would with one channel. Instead of having the crossover sections connected in parallel with jumpers, you now have one section of the crossover on one channel of the amplifier. You are confusing a few things as well. If you used an active crossover between the preamp and the amplifer/s, you might see a difference in the output level meters due to the source material ( bass notes vs. treble ). But, both channels of the power amp are getting the same signal from your preamp, so the meters will show the same readings. Doubling the input power would result in an increase of 3 db output, other factors staying the same. Since the crossover function in the speaker is to divide frequencies, each section would reject either low frequency information or high frequencies. With the crossover sections in parallel, it is still an 8 ohm nominal speaker. If you remove the jumpers, they become ( 2 ) 8 ohm loads. Power is voltage squared divided by resistance. 40 watts into an 8 ohm load is the square root of 320, or around 17.9 volts. Each amplifier channel is putting out the same voltage ( same preamp setting -11db ), so the spl produced with the setup you have would be the same as if you only had one channel hooked up to it, and utilized the jumpers. Quote Link to comment Share on other sites More sharing options...
Overkill Posted November 22, 2004 Author Share Posted November 22, 2004 "If you used an active crossover between the preamp and the amplifer/s, you might see a difference in the output level meters due to the source material ( bass notes vs. treble ). But, both channels of the power amp are getting the same signal from your preamp, so the meters will show the same readings." These meters read power output to the speaker (not the strength of the signal coming in from the preamp). In a biamp config, the low frequencies should not be channeling through the HF channel using the passive crossovers in the speaker. Therefore, I expected to see the power output from this indepenant channel to be less than 40W. Quote Link to comment Share on other sites More sharing options...
michael hurd Posted November 22, 2004 Share Posted November 22, 2004 You are misunderstanding. Unless a crossover is used to remove part of the audio spectrum BEFORE the power amplifier, both channels will amplify the full range signal from the preamp. The passive crossover in the speaker filters out what frequencies get to each section through capacitors, that reject low frequency information, and also inductors, which reject hf information. Quote Link to comment Share on other sites More sharing options...
Overkill Posted November 22, 2004 Author Share Posted November 22, 2004 Ok, so even though the capacitors are filtering out the LF in the HF designated channel, the LF channel is still pulling a full range load from the power amp. I think I get it now. So, without an active crossover a lot of energy is being unnecessarily wasted. Thanks for your help. Quote Link to comment Share on other sites More sharing options...
TBrennan Posted November 22, 2004 Share Posted November 22, 2004 Overkill---Without an active crossover you're not really bi-amping at all but practicing what many bi-amping enthusiasts call "fool's bi-amping". Quote Link to comment Share on other sites More sharing options...
jheis Posted November 22, 2004 Share Posted November 22, 2004 Is there any downside to "fool's bi-amping?" If you have an extra amp channel why not use it? James Quote Link to comment Share on other sites More sharing options...
Deang Posted November 22, 2004 Share Posted November 22, 2004 It's only "fool's biamping" if it sounds bad. Passive biamping isn't the ideal way to do it, but it can be better than one amp pushing all of the drivers. This isn't to say that it will sound better, but that it can. It really depends on the amps and setup. Mike, I believe Overkill's experiment actually netted about 3db of extra headroom -- even though he may not have been seeing it on the meters. Transients should have been cleaner with the dedicated amp section on each driver. "Are there any negatives to using a Y-connector from the center channel output on the preamp if I decide to go with the biamp setup?" Not really. It's basically doing on the outside what is usually done on the inside when you have two main outs -- the outputs are merely wired in parallel. You'll probably have slightly reduced gain, and will have to turn the volume knob a little further to get the same output -- no big deal. Quote Link to comment Share on other sites More sharing options...
TBrennan Posted November 23, 2004 Share Posted November 23, 2004 Dean---Passive bi-amping is the practice of crossing the signal BEFORE the amps but with passive networks instead of active. I've done this myself and the practice was described in Altec tech papers way back in the 1950s. So I reckon fool's bi-amping is still fool's bi-amping and not passive bi-amping. Reminds me of the jaspers who call all monopolar speakers "direct-radiators" and think dipole Magnapans aren't DRs and horns are. Quote Link to comment Share on other sites More sharing options...
Deang Posted November 23, 2004 Share Posted November 23, 2004 How bizarre. I'd actually never heard of that before. Well then, "fool's biamping" it is. Quote Link to comment Share on other sites More sharing options...
djk Posted November 24, 2004 Share Posted November 24, 2004 http://db.audioasylum.com/cgi/m.mpl?forum=speakers&n=138657&highlight=cornwall+djk&r=&session= Quote Link to comment Share on other sites More sharing options...
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