Biamping Dunlavy SC-V

I can't say for certain, but breaking the speaker load up into segments can surely alter the power transfer characteristics of how each amplifier in a multi-amp system responds. This is in comparison to how one of the same amps driving the entire speaker full-range would respond.

If one factors in that each amp will have differences due to production tolerances, and whether or not each amp is up to the task to begin with, only adds further variables to the equation. This is not to comment on Dazzdax's specific amps and / or installation, but to say that not all amps are created equally regardless of what the paper spec's say and that some simply aren't suited for driving specific types of loads.

Having large multi-driver acoustic suspension speakers with a similar crossover point ( appr 200 Hz ) that i've passively bi-amped, my experiences are probably not that far off from what Dazzdax experienced. The difference here is how we interpreted the changes in presentation and the type of gear being used.

The reduction in distortion that takes place with such an installation can sometimes be quite fooling. Not only does this alter our perceived level of volume, but also of dynamics. By increasing the headroom and reducing the demands on the amplifier, transient response is improved, distortion is reduced and in some cases, the audio spectrum shifts slightly.

The loss in volume is due to the way that our brain and ears process distortion. Distortion is "grating" to our ears, telling our brain "this is loud". Removal of that distortion removes that agitant, resulting in less perceived volume. This is why many folks find themselves playing their system louder than they used to prior to a component change, although it doesn't sound as loud to them at the time. Less distortion equals less "apparent volume". Extreme levels of distortion become more apparent for what they are, telling us "this is not necessarily loud, it is just extremely distorted".

This also factors into both the high frequency dynamics and the shift in the audible spectrum. Due to a reduction in distortion and improved transient response, there is less smearing involved. Smearing is a by-product of non-linear harmonic distortion ( THD ), slewing induced distortion ( SID ) and ringing ( poor transient response ), all of which manifest themselves in a more prominent fashion as frequency rises. If you doubt this, take a look at almost all distortion curves and figures in a Stereophile review. As frequency rises, the distortion by-products do too. The wider the bandwidth of the amp ( faster transient response ), the more level the distortion is across the audible frequency range.*

By removing these aspects of high frequency output that one would normally hear, the midrange and treble region becomes both more subdued and less of an "irritant". Our brain processes that as a lack of dynamics, even though the output is cleaner and ( theoretically ) more dynamic.

In terms of increased bass output, this can be contributed to several factors. The first is that the amp can now concentrate all of the available power that it can develop over a much narrower bandwidth. If the amp was current deficient and / or lacking in power supply reserve for reproduction of longer duration notes, we've now freed up more energy to deal with these problems. The end result as we perceive it would be greater output in the low frequency region than what was there before. This output didn't just show up somehow, it was always there. The deficiencies in the previous installation simply didn't allow it to shine through.

This is one of the biggest problems that i've found with "digital" or "switching" type amps. That is, the bass lacks both intensity and duration. What is there sounds very fast and articulate, but much of that has to do with the lack of duration due to the power supply "pooping out". By reducing the duration of the note, it sounds both "faster" and "sharper" but lacks weight ( duration ) and impact ( intensity ). I've commented on this before as it was something that i ran into with several different types of "new technology" amps, including my Sunfire Sig's.

In most speakers that suffer from poor damping ( aka vented designs ), this can actually sound more natural, even though it is a distortion of the original signal. In this case, one positive error ( excess bloated output from the speaker ) combined with a negative error ( reduced truncuated output from the amp ) sums to a relatively flat presentation. Some would call this "system synergy" whereas others would call it "complimentary colourations". In this specific case, they are basically one and the same.

In Dazzdax's specific case, his speakers don't lack damping ( highly damped low Q sealed design ), so this is not the case. Instead, the increased output capacity of the amp was directly translated into increased output at the speaker. Since this speaker is a relatively linear transducer of energy, more input equalled more output. Combine that with the simultaneous loss of "apparent" mid and high frequency energy and you end up with a completely different presentation.

Given that the electrical characteristics of the speaker remain the same on the whole i.e. separating the top from the bottom doesn't change the nominal impedance or transient capabilities of the speaker itself, the only thing that did change is how the amplifiers themselves would load up.

Bare in mind that this is kind of a "crash course" on this subject. It should help some to understand why they might have run into specific situations when trying to passively bi-amp, but in no means can i hope to cover all the variables involved. Not in one post or a hundred posts. Sean
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* Negative feedback can be used to try and flatten the distortion curve on an amp, but even then, the distortion will typically rise as frequency climbs. While a completely different subject, slewing induced distortion ( SID ) typically increases as more negative feedback is used due to a reduction in response time of the amp. In plain English, more negative feedback means a slower amp. This can result in increased glare and high frequency stridency i.e. "Solid State sterility". The spec's on paper look good in terms of distortion, but that's only because all of the spec's aren't available to fully interpret the performance of the circuit on the whole.

This is why i've always stressed high speed, wide bandwidth designs in every aspect of the system. This approach naturally combats distortion without the need for "band-aids" that only introduce other problems into the equation.

Hi Sean, thx for the thorough explanation. I'm not a technician, but wouldn't a well designed loudspeaker system comprise drivers with the same impedance? Otherwise the system would not sounding balanced through out the frequency spectrum. But it "sounds" like there is some impedance mismatch (as I stated earlier) between the two halves of the cross over networks. What I hear is an almost caricatural reproduction of music, with a far too loud bass and recessed and undynamic midrange/treble. Btw, I'm also using the same speaker cables and a pair of interconnects, splitted by an Y-splitter to provide both monoamps with the same signal (in biamp configuration).

The pairs of Dunlavy drivers are 8ohm wired in parallel except of course the tweeter which is a single 4ohm driver. When I biamped my SC4s I thought the mids and highs stuck out more than the bass. I never used an RTA to measure this perception. Sean is correct about the crossover freq..of 200 hz. it uses a 8.2mh inductor to roll the highs out of the woofer and a 200 mic cap to roll the lows out of the mids. Could there be a dropping resistor in the mid crossover that some how gets bypassed when bi-amped?..That would be wierd..Tom

Dazzdax: I can't tell you what's going on, but you have obviously changed the impedance that the preamp sees. That is, you're dividing the signal between two amps rather than just feeding one. This lowers the impedance that the preamp sees by 50%, effectively cutting it in half. This in turn will draw twice as much current from the output stage of the preamp, which could account for yet another reason that the system sounds loaded down or bass heavy. Most preamps are horribly under-designed in terms of their output stage, hence designers trying to keep the input impedance of the amp up. Your system is now making your preamp work twice as hard and it may not like it at all.

The way that you are splitting the signal also creates different nodes in terms of voltage to current distribution within the cabling itself. This too could be a factor in why things sound differently than they did with just one amp per speaker. Optimally, the signal should have been separated at the preamp. Not only does this introduce less line loss by increasing the surface area, the amps also receive the benefit of better electrical separation from one another.

By splitting the signal closer to the amps, the potential for crosstalk from one amp to another is drastically increased. Given that most all amps suffer from their output stage modulating their input stage to some degree, the woofer amp may be modulating what the tweeter amp sees. Using separate interconnects all the way back to the preamp would have provided better isolation between the amps with the longer pathway acting as a buffer.

You've got a lot of variables going on here with the electronics in the system, not so much with the speakers. While it is possible that the speakers have an internal wiring problem inside of them as Tom suggests, you would literally have to pull the speakers apart and make a diagram of the crossover network. While Dunlavy was a good engineer, that doesn't mean that some knucklehead in production couldn't have made a mistake.

As a side note, we ran into this with my Father's Legacy speakers a while back. Sometime during construction of the crossover of these speakers, one leg of the midrange circuit was tied to the woofer circuit. Given that my Dad had never bi-amped these speakers ( only bi-wired them ), this wouldn't have created a problem since the entire circuit was all driven by the same amp anyhow. Having said that, had he tried to bi-amp the speakers, this simple mistake in production could have severely damaged both of the amps. That's because the mis-wired midrange would have electrically tied the two channels of the individual woofer and tweeter amps together. Sean
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PS... For as much money as some of you guys are spending on gear, you really need to find a technically competent dealer to work with. Buying and assembling a few components to work together and produce sound is completely different than building a complex audio system at the cutting edge of music reproduction. From what i've seen though, this might be more difficult than i've thought.

Most of the high priced dealers are either lacking in technical chops and / or more interested in profit margins than anything else. Keeping the customers on the equipment carousel i.e. "flavour of the month club", whether on purpose or due to lack of technical understanding, surely isn't going to hurt their income levels. That is, until the customer has had enough and either gives up entirely or learns to do for themselves.

Once you learn to do for yourselves and can understand basic electronics, it makes it much easier to cut through the marketing hype and snake oil. This is why i encourage folks to learn on their own, but at the same ti me, it is also why finding and supporting a good dealer is important to the survival of high end audio. Without them, we have no visible means of entry into this hobby to the general public.

You can unscrew the rear terminal panel and the entire crossover will slide out a tract..In this way you could diagram and inspect the crossover..These babies are ripe for component crossover upgrades..What a suprise lurking..Tom