I'm a tad confused (as always), you are running full frequency info to both woofer and tweeter/mid bypassing the crossover? The wiring setup that the original poster describes is typical of loudspeakers designed for bi-wiring, and still keeps the passive crossover in place. Both pairs of loudspeaker binding posts see signal voltage of the full frequency range, but only draw significant current from the amplifier through their respective frequency ranges. |
Thanks, Kirk. Excellent points, as usual.
Best,
-- Al |
Although I suppose it is conceivable that there may be some rare exceptions for which doing that would provide results that are somewhat reasonable, perhaps such as certain older Apogee speakers, and the Infinity Kappa 9, that have extremely low impedances. I'd differ with you on this point and say that connecting a loudspeaker between two transformer taps that weren't designed to have a loudspeaker between is a categorically Bad Move. For most iron-coupled amps this means that you should ALWAYS use the ground terminal for the negative speaker lead, and in the case of the Mac amps that are balanced-bridged (i.e. the MC402) to use a PAIR of speaker leads to a given PAIR of output terminals, and not to mix 'n' match a given pair of cables between taps. The reason for this that if you don't use the assigned ground terminal, then part of the transformer secondary becomes unloaded, thus undampened . . . but is still in the feedback loop. The resulting change in the transformer's response (usually a HF peak and resulting phase lag) is then presented to the feedback loop at the opposite polarity of what was anticipated by the designer. In the case of the more recent autoformer-coupled Mac amps, there is no conventional series output inductor, and several "feedback" connections from the output autoformer. IIRC there are usually one or two Zobel networks across combinations of the windings to compensate for inductive loads (HF damping), and additional feedback taken from 2- or 4-ohm taps that forms and additional pole/zero pair above the audioband. So to connect a speaker to disparate terminals means that the open-loop amplifier response will definitely be quite different from what the designer were thinking. And while the amplifier probably won't break out in sustained oscillation, it will at least have quite an unwelcome effect on the amplifier's transient response, and easily wreck much of the hard work they did when they designed the output autoformer and its associated compensation network. |
Hi Bruce (Bifwynne),
In a word, "bad."
As was mentioned, the turns ratio of the transformer or autoformer (the number of turns on the secondary or output side divided by the number of turns on the primary side) can be presumed to be about 1.414 (which is the square root of 2) times as great on the 8 ohm tap as on the 4 ohm tap. Equivalently, the turns ratio of the 4 ohm tap can be presumed to be about 1/1.414 = 0.707 of what it is for the 8 ohm tap.
So if the speaker were connected between the 4 ohm and 8 ohm taps the turns ratio would be (1 - 0.707) = 0.293 of the ratio for the 8 ohm tap. Since impedance is transformed in proportion to the square of the turns ratio, from the perspective of the output tubes or transistors the optimal load impedance for a connection between the 4 and 8 ohm taps would be (0.293 squared) x 8 ohms = 0.69 ohms.
So if just about any real world speaker were connected between those terminals the transformer's step-down ratio would be much too great, the speaker would see too little voltage, and the amplifier would see a very mismatched load. Although I suppose it is conceivable that there may be some rare exceptions for which doing that would provide results that are somewhat reasonable, perhaps such as certain older Apogee speakers, and the Infinity Kappa 9, that have extremely low impedances.
Best regards,
-- Al |
Mchd1,
"I have a pair of Mirage M3si speakers and I do not intend to upgrade."
Those are really good speakers. I used to be a dealer and know them very well. They are much improved over the original M series. The si's have an excellent balance from top to bottom. The originals were laid back to a fault. No question the best speakers Mirage has ever made.
Bojack,
05-31-13: Bojack
"Good speakers use good wires."
Tell that to Spencer and Derek Hughes and legions of other speaker designers who have designed the world's finest speakers! The key to great sound is called "design," not "cable."
How on earth do you get all that from 1 line? To be honest, though, I would definitely tell them that. Why wouldn't good designers use good parts to design their speakers? I don't really keep track of such things but I can tell you that I do know of some speaker manufacturers who use brands like Cardas and Audioquest for the internal wiring of their speakers, and other components as well. It wouldn't suprise me if they all do, but like I said, I really don't keep track. |
Al, I'm almost afraid to ask this Q, but here goes. Would it be a good, bad or neutral thing to use the 8 ohm tap for one speaker lead and the 4 ohm tap for the other lead?
Regards,
Bruce |
Hi Al . . . good to be back as well. You are indeed correct, my bad. It's 6dB between the 8- and 2-ohm taps, and 3dB between the 8- and 4-ohm taps . . . same as a tube amp. |
I'm a tad confused (as always), you are running full frequency info to both woofer and tweeter/mid bypassing the crossover? |
Kirk, you beat me to it! And it's nice to see you posting again.
A minor point, though. Wouldn't the 8 ohm tap have 3 db more voltage gain than the 4 ohm tap, not 6 db? In other words a factor of 1.414, resulting in the output transistors seeing the same load when an 8 ohm load is connected to the 8 ohm tap, as when a 4 ohm load is connected to the 4 ohm tap, as when a 2 ohm load is connected to the 2 ohm tap (since the impedance transformation will be proportional to the square of the turns ratio, and hence to the square of the voltage ratio).
Beyond that, I second Kirk's statement that "if you like what you hear, that's great." And a good takeaway from the experience reported by the OP is that experimentation with how multiple output taps are utilized can pay off big-time.
A not so good takeaway, on the other hand, would be an expectation that a similar connection arrangement will necessarily, or even probably, be optimal in the case of other amplifiers and speakers (although it certainly MIGHT be). In contrast to most amps that provide multiple output taps (i.e., tube amps), the autoformer-based McIntosh designs have output impedances that are low enough to be essentially negligible, as they are with most solid state amplifiers. And the XR100 speakers are complex four-way affairs having 15 drivers per speaker, and who knows what kind of impedance vs. frequency characteristics (I couldn't find impedance curves for them). So the OP's system is considerably different in relevant respects than the majority of others.
To the OP, again, congratulations on some imaginative experimentation that has paid off. Enjoy.
Regards,
-- Al |
Not to take away anything from the enjoyment you're experiencing . . . but I thought I'd point out that the 8-ohm taps have about 6dB more voltage gain than the 4-ohm taps. There's no problem with doing this from the amplifier's standpoint, except with the possibility of somewhat increased distortion should the loudspeakers' high-frequency section present significantly less than an 8-ohm load through part of the frequency range.
But the sonic effects are overwhelmingly akin to simply cranking up the bass relative to the highs - very simply a tone control, that has frequency characteristics of the loudspeakers' crossover slope(s). The configuration of the cables themselves are unlikely to have anything except a miniscule effect when compared to this change in gain.
Again . . . if you like what you hear, that's great! For those that don't have multiple amplifier taps or loudspeaker bi-wire inputs, a very similar result could be had with a simple twist of a well-designed tone control. |
Hi Ranchomirage,
I just purchased some MC2301's and was faced with the exact same dilemma as you. My previous amps, Octave MRE130 had two pairs of speaker out for each mono amp and I was able to use two pairs of double shot guns, ala biwire to the B&W Nautilus 800's. Now, facing the same issue as you, I also did exactly the same thing, running the mid-highs to the 4 ohm taps and the bass to the 8 ohm taps, sounds great to me. I thought about swapping, but based on your experience, I think I will stick with the current configuration.
On audioaficionado there are lengthy discussions regarding bi-wiring macs and many more enthusiasts there than here or asylum.
Glad you are enjoying your new macs. I am in music heaven with mine.
Ciao,
Audioquest4life |
I reversed the leads last night and it was clear to me that I lost some bass only, with highs unaffected and mids just undecided. Listened most of today with same conclusion and that the swap was not that dramatic so I just switched everything back to my personal contentment. However, as originally stated the big gain with these loudspeakers and cables was wiring them separately from the 8ohm and 4ohm outputs dual shotgun - rather than my previous bi-wiring and also trying straight shotgun with jumper cables. Ah, now time to pour a whiskey, pull up Diane Schurr and listen to Louisiana Sunday Afternoon and other cuts from her COLLECTION album. Best to all AudioGoner's |
Very interested on the results.
Please let us know. |
Jjreman,
Have not reversed leads yet, but after a house full of guest depart next week I will have the quite time to experiment and listen. |
It seems to me that you (if the jumper wires are removed) you have changed the impedance of the mids/tweets as far as the amp is concerned. Have you tried swapping the leads between the 8 and 4 ohm taps to see what the diff is? |
"Good speakers use good wires."
Tell that to Spencer and Derek Hughes and legions of other speaker designers who have designed the world's finest speakers! The key to great sound is called "design," not "cable." |
Zd542, the amp. is a SS McIntosh MC452 autoformer and yes, I did consider tapping in both shotgun pairs to the 8ohm binding post but as the new Macintosh binding post are great for banana connecters they really, really suck for spades and I don't think they will stand the stress of double spades. I picked up one pair of cables used on AudioGon in a 9/10 condition and the 2nd pair new from Canuck Audio and paid about $1,200 for each pair. Cardas has replaced the Golden Reference with some crazy priced heavy weight new cable but thanks to AudioGon
and a little patience some great Golden Reference cable can be had. As Philjolet suggests I will try reversing the 8 & 4 ohm taps but only after a few more "cigarettes in the silky after glow of the experience"! |
"ZD542 I presume based on the OP's post that he has tried standard shotgun config"
Most likely he did. I was just interested as to what the differences were. |
first of all interesting speaker!
so the 8 ohm tap to woofer is a bit fuller and the 4 ohm tap to mid/tweeter is a little tighter
or do I have it backwards?
Autoformers can work wonders - I used to own a pair of Spelz autoformers with Maggies, you could just dial in the tightness or full sound as you liked...
have you tried switching it around?
but then why would you since you are so happy with the results
ZD542 I presume based on the OP's post that he has tried standard shotgun config
thanks for sharing
enjoy |
I have a pair of Mirage M3si speakers and I do not intend to upgrade. |
"I have often wondered about my use of $3000 speaker cables when the wire connecting the speaker binding posts to the drivers is basic hardware store wire."
Good speakers use good wires. Maybe its time to upgrade.
Ranchomirage,
That's an interesting setup. Not many people get to try something like that. I bet your results have a lot to do with the autoformers on your amp. (I assume you are using a SS amp). Have you ever tried connecting both pairs of speaker cables to the same tap on your amp and running each pair to one of the binding posts on your speaker (a basic double or shotgun biwire)? That may tell you if your results are due to biwiring, or possibly something else. |
I have often wondered about my use of $3000 speaker cables when the wire connecting the speaker binding posts to the drivers is basic hardware store wire. |
