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4-ohm speakers okay for an Arcam A85 integrated?

67.100.29.94
Posted on November 6, 2009 at 18:29:24
hesson11
Audiophile

Posts: 621
Location: Florida
Joined: December 8, 2005
 Throughout my more than 30 years doing the audio thing, I have managed to remain a total imbecile regarding electronics. I’m considering several new speakers that are rated at a nominal 4 ohms. While I suspect this will be okay with my Arcam A85 integrated amp, I’m not absolutely certain. If you guys can help me out, I’d appreciate it. Here is some relevant info (sorry if it gets a bit lengthy):

Arcam A85 ratings:
Continuous power output, both channels, 8 ohms, 20Hz-20kHz: 85W
Single channel, 4 ohms, 1kHz: 140W

From the owner’s manual:
“You can connect one or two pairs of loudspeakers to your amplifier, provided each pair is rated between 8-16 ohms. If one or both pairs have an impedance of less than 8 ohms, the combined load on the amplifier falls below 4 ohms and could cause an overload. If so, the overload protection circuit engages and the amplifier will not work.”

I find this kind of ambiguous in terms of offering guidance for a single pair of speakers (just to be clear, I’m NOT thinking of connecting two pair of speakers to the amp.)

From JA’s “Stereophile” measurements, some salient excerpts (link to full review below):

“The output impedance was a fairly low 0.21 ohm over most of the audioband, rising inconsequentially at 20kHz to 0.25 ohm. While this implies an 8 ohm damping factor of 32-40, this is sufficiently high to ensure that any modification of the A85's frequency response due to its interaction with the manner in which the loudspeaker's load impedance changes with frequency will be small…”

“…The level of distortion and noise remained below 0.015% across most of the audioband into both 8 and 4 ohm loads, rising slightly to around 0.025% at 40kHz (not shown). However, into 2 ohms with continuous drive, it rose to around 0.045%, which, while still low, suggests that the A85 has to work harder than it really likes into this demanding load. The waveform of the distortion (fig.4) is predominantly third-harmonic, which bodes well for sound quality. This can also be seen in fig.5, the spectrum of the amplifier's output while it drove a high-level low-frequency tone into 4 ohms. Even close to clipping into this load, the third harmonic lies at -70dB (0.03%), and all other harmonics are at -90dB or below…”

“…The innocuous nature of low-order harmonics present in an amplifier's output depends on there not being high levels of intermodulation distortion. This was true of the Arcam; fig.6 shows that, even close to the clipping point with the punishing 1:1 mix of 19kHz and 20kHz tones, the 1kHz difference product remained below -80dB (0.01%). However, the higher-order products at 18kHz and 21kHz did rise in level as the load impedance dropped, which suggests that those admittedly rare speakers that drop to 2 ohms and below at high frequencies are perhaps best avoided…”

“…Finally, I used the Miller Amplifier Profile to examine how the A85 behaves with a low-duty-cycle 1kHz toneburst signal more like music than a continuous sinewave. The results with one channel driven are shown in fig.8. Even more power is available at the 1% THD clipping point with this signal: 164.5W into 8 ohms (red trace, 22.2dBW), 290W into 4 ohms (black, 21.6dBW), 461W into 2 ohms (blue, 20.6dBW), and 586W into 1 ohm (green, 18.65dBW). The latter is equivalent to an RMS output current of 24.2A, maintained for the 10ms duration of the pulse. However, the fact that the DiVA again turned itself off at this maximum level into the low impedance, coupled with the higher levels of distortion, suggests that speakers that drop much below 4 ohms are probably best avoided with the relatively modest-priced Arcam.”

My uninformed conclusion is that while 4-ohm speakers may be okay, I should probably look at their impedance curves to make sure they don’t “drop much below 4 ohms.”

If it matters, I rarely listen louder than about 80 dB peaks.

Sorry for the length, but thanks for sticking with me!
-Bob
RE: I Still Think The Arcam Would Be Happiest With Good British Or Canadian Speakers:, posted on November 9, 2009 at 14:25:11
Vinylly
 I'm thinking, Monitor Audio, Spendor, Harbeth, Epos, PMC or Canadian PSB's or Paradimn. All are easy speakers to drive.

Since you already have pretty solid information about the Arcam, posted on November 7, 2009 at 10:19:25
keith_d
Audiophile

Posts: 931
Joined: June 15, 2002
 You might want to follow the advice therein and determine whether the 4 ohm nominal speakers drop much below 4 ohms and whether they have nasty phase angles where and if they might do so.

That's probably a speaker question and probably for the speaker manufacturer.

Of course, most people will tell you it should be fine as long as you're not pushing the amp too hard in too big a space.

RE: 4-ohm speakers okay for an Arcam A85 integrated?, posted on November 7, 2009 at 05:03:56
Pat D
Audiophile

Posts: 7558
Joined: June 20, 2000
 Your Arcam should handle a single pair of speakers just fine. The measurements (clips at 200 watts into 4 ohms) indicate it is quite conservatively rated and does quite well into fairly low impedance loads, so it should drive most speakers just fine. It's a pretty robust amplifier.

Just what sort of speakers are you planning to drive with it?

When you connect two pairs of speakers in parallel, that halves the impedance seen by the amplifier. Since you are not doing that, don't worry about it.

"Probability is the very guide to life."---Cicero
Thanks, Pat, posted on November 7, 2009 at 05:16:26
hesson11
Audiophile

Posts: 621
Location: Florida
Joined: December 8, 2005
 My list of candidates is a long one, and I haven't yet narrowed it down much. A few candidates include:

Vienna Mozart, PSB Synchrony, Epos M16i or M22i, Opera Seconda or Mezza Grand, Chario TBD, Sonus Faber TBD and perhaps a few others.

Thanks very much for the info.
-Bob

RE: Thanks, Pat, posted on November 7, 2009 at 13:09:30
Pat D
Audiophile

Posts: 7558
Joined: June 20, 2000
 I presume you have measured the levels at which you listen with something like the Radio Shack SPL meter.

Anyway, at our kind of levels, I think your amp will be more than adequate for almost any speaker. It's always a good idea to try out the speakers with your own amplifier to ensure that it can drive them to the levels you need.

The speakers brands you mention have good reputations. I have heard some Vienna Acoustics speakers and they pretty good if a little laid back for me. I was highly impressed with the PSB Synchrony One and the smaller tower, the Synchrony Two should be good, too. I'm not very familiar with Italian speakers, though Sonus Faber has a good reputation and I rather liked the little SF Cremona Auditor.


"Probability is the very guide to life."---Cicero
Yes, posted on November 8, 2009 at 08:37:05
hesson11
Audiophile

Posts: 621
Location: Florida
Joined: December 8, 2005
 Yes, I did measure the peak 80dB I mentioned with the Radio Shack meter.

Thanks again for your comments, Pat.

-Bob

RE: Best To Stick With 8 Ohm Speakers. *, posted on November 6, 2009 at 20:04:10
Vinylly
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