Impedance question: McIntosh MC60's and ZU Audio DW II's

tuberadios69

tuberadios69

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I posted this on the Mac forum here and did get one response but I'm hoping a few more might lend their expertise:

Just got my Zu Audio Omen DW's this past weekend. LOVE them! Question for the brain trust on here. The speakers are rated as 12 ohm. They sound fine using the 8 ohm taps on the MC-60's and equally well on the 16 ohm taps. They might be a bit louder on the 16 ohm taps so I'm thinking that is where I should leave them. Any comments or experiences you can share?
 
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Vintage tube amps, almost always sound better with higher impedance speakers.
the louder volume on the 16 ohm tap is also telling you they are happier, together
 
tuberadios69 said:
I posted this on the Mac forum here and did get one response but I'm hoping a few more might lend their expertise:

Just got my Zu Audio Omen DW's this past weekend. LOVE them! Question for the brain trust on here. The speakers are rated as 12 ohm. They sound fine using the 8 ohm taps on the MC-60's and equally well on the 16 ohm taps. They might be a bit louder on the 16 ohm taps so I'm thinking that is where I should leave them. Any comments or experiences you can share?
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Did you get them with the clarity caps?
 
L speaker 7-2021.jpg Upstairs system 7-2021.jpg
MaxP said:
Did you get them with the clarity caps?
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I got the Jupiter Copper cap upgrade. The speakers sound great! Way better than I ever expected! The bass, imaging, air, snap/transients and overall flow of music is outstanding for the price which was about $1800 including shipping. I'll play around with which impedance connection (8 ohm or 16 ohm) to ultimately settle on as this week progresses. Currently have them attached to the 16ohm connections on the MC-60's barrier posts but they also sounded really good initially on 8 ohms.
 
The 16 ohm tap is going to sound louder all the time, because it provides more voltage than the 8 ohm tap. To make things equal in a comparison you need to increase the volume slightly to compensate when using the 8 ohm tap. The 8 ohm tap on the other hand, will have a better damping factor, so will have less of a peak at the speaker's resonant frequency, lower distortion at low levels, and will supply more current to any impedance dips. I almost always prefer using the lower of two taps, but there is no harm in trying both and drawing your own conclusions.
 
maxhifi said:
The 16 ohm tap is going to sound louder all the time, because it provides more voltage than the 8 ohm tap. To make things equal in a comparison you need to increase the volume slightly to compensate when using the 8 ohm tap. The 8 ohm tap on the other hand, will have a better damping factor, so will have less of a peak at the speaker's resonant frequency, lower distortion at low levels, and will supply more current to any impedance dips. I almost always prefer using the lower of two taps, but there is no harm in trying both and drawing your own conclusions.
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That was going to be my point, too. The 16 ohm tap may be louder, but the 8 ohm tap may have tighter bass and smoother frequency response.

But, as said- which ever sounds better, is better. The amp isn't going to care, from a reliability and durability standpoint, either way.

Regards,
Gordon.
 
GordonW said:
That was going to be my point, too. The 16 ohm tap may be louder, but the 8 ohm tap may have tighter bass and smoother frequency response.

But, as said- which ever sounds better, is better. The amp isn't going to care, from a reliability and durability standpoint, either way.

Regards,
Gordon.
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Thanks very much both Maxhifi and Gordon! Great info and yes, I think my initial listening sessions at the 8 ohm tap did sound a bit smoother than the 16 ohm. So this weekend I'll listen to the system at 8 ohms to make sure of that. I have a subwoofer in the system, too, so I'll need to re-adjust the gain since the Marantz 7 has two sets of outputs with one set going to the MC-60's and the other set to the subwoofer. Sounds like a fun (or perhaps a slightly neurotic, lol) weekend of listening to settle on a final output tap!
 
I have, for the moment, settled on the 8 ohm taps. As a few of you mentioned, they are smoother at this setting vs 16 ohms and they still have great dynamics, snap and an atmospheric presentation. I am way more impressed with these speakers than I ever expected when I jumped on the sale March 25th. The last issue of Stereophile had a column by Herb Reichert where he said one should try all the taps on a tube amp, including 4 ohm. That seems a bit odd to me in this instance (4 ohm load for 12 ohm speakers) but what the heck, it can't hurt to try as Gordon mentioned so perhaps this coming weekend I'll try it for kicks. I'm anticipating that 8 ohms will be the final choice but I'll keep an open mind (and open ears!).
 
If I were to mention the 25 ohm parallel resistors ZU offers to bring the resistance close to 8 ohms would it just show my ignorance of tube gear? (All my stuff is solid state.)
 
Guido57 said:
If I were to mention the 25 ohm parallel resistors ZU offers to bring the resistance close to 8 ohms would it just show my ignorance of tube gear? (All my stuff is solid state.)
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Those actually might be useful with some tube amps, because the parallel resistor would smooth the impedance curve of the speaker, which could help make the speaker sound smoother with an amplifier having a very low damping factor. The MC60 already has a decent damping factor for a tube amp though, so I'd just use them as is without adding any resistor.
 
maxhifi said:
Those actually might be useful with some tube amps, because the parallel resistor would smooth the impedance curve of the speaker, which could help make the speaker sound smoother with an amplifier having a very low damping factor. The MC60 already has a decent damping factor for a tube amp though, so I'd just use them as is without adding any resistor.
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DF is related to the global feedback inside the amp, newer Latino VTA amps have relatively low FB compared to a Dynaco tube amp for instance.
 
Pio1980 said:
DF is related to the global feedback inside the amp, newer Latino VTA amps have relatively low FB compared to a Dynaco tube amp for instance.
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Yes, that's right. Triode/pentode/ultralinear mode affects it too. The most common low damping factor amplifiers, are the single ended triode designs which do away with negative feedback completely. Second most common would be badly designed pentode amplifiers.


A low damping factor is essentially the same as putting a resistor with a fairly high value in series with the speaker load. This is a problem, because it causes the speaker to see a voltage which varies with frequency according to the speaker's impedance curve, and therefore creates frequency response irregularities. Adding a parallel resistor to the speaker won't eliminate this issue, but what it does do is smooth out the peaks, since the parallel resistor doesn't vary with frequency.
 
I guess its me again. I owned MC 60's when I owned Altecs 16 ohms but with more modern 240's in mono /275's when I went to Bozaks 8 ohms and 4 ohms speakers because I wanted a tighter bass and as little tube bloom as possible. That doesn't mean a MC 60 can't sound great for it can. But if your speakers dip much below 66% of the taps rating over any range at all you are in for unhappiness. The amp doesn't just have the current available even though the amp will put out close to 90 watts at 4 or 8 or 16 ohms. Symphonies and Grands sounded fuzzy and overly warm with a bloating sensation. While AR-3 and 3a and even Mac ML-1c sounded delight full with MC 60's. If speakers have great damping then a MC 60 will shine as long as the impedance doesn't get to low. The latest 275 MK VI and MC 1502 have better capabilities by far, with their bigger power supplies and higher bias on the tubes, but they are very pricy. I wish you many happy hours of enjoyment.
 
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Fortunately, according to Zu Audio's impedance graph for the Omen DW II's, the impedance never dips below about 9 ohms (at 250hz). I'm currently running the speakers connected to the 8 ohm taps on the MC60. The room (actually my bedroom) is only 12 x 14 feet so I'm not pushing them too hard. I'm using NOS GE/MPD 6550's in the amps.
 
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