THE INFINITY PRIMUS 360 LOUDSPEAKER
As I wrote in “Loudspeakers, Listening Rooms, and Spongy Floors,” I purchased a pair
of Infinity Primus 360 loudspeakers. This purchase was driven pretty much entirely by
the good review in the June 2005 Stereophile and the fact that I found a pair of factory
refurbished speakers for $279 plus shipping on eBay. Since purchasing my speakers,
I have found new speakers being sold for as little as $400 a pair on the Internet,
shipping included.
My initial response to these speakers was positive based largely on their impressively
good bass performance. The more I listened to them, however, the more I felt the
bass was too good, in fact out of control at some frequencies, and the rest of the
performance was not good enough.
I used a JVC receiver from my garage system to break-in the 360s since I could leave
it running even when I wasn’t home, something I just won’t do with tubes*. The more
time I put on these speakers, the more evident it was that there was indeed something
wrong with them. The bass boomed, piano music had a “clinky” quality to it, and the
sound seemed to be stuck in the boxes rather then emanating from them. But these
problems varied somewhat from CD to CD. Some CDs actually sounded pretty good.
I listened to an FM opera broadcast one Saturday afternoon and the 360s did an
excellent job of reproducing the soundstage. The singers moved back and forth right
in front of me.
Inadvertently, I discovered the source of much of the problem with the bass. The JVC
receiver has connections for two pairs of speakers. I had used the Speaker 2
connections simply because they were easier to get at behind the unit. Evidently,
using the Speaker 2 connections presumes that speakers are already connected to
the Speaker 1 terminals. Funny things occur with the damping of the amp when only
Speaker 2 is used. Connecting the 360s to the Speaker 1 terminals removed the
majority of the boom. So far so good.
At this point, I had finished the Eico re-re-biasing and put it back into the system.
There was an immediate improvement in the sound. Imaging and low-level detail were
noticeably better compared to the JVC--no surprise there. But still not great. Not
nearly as great as I had hoped. Pianos still sounded wrong and the phasey quality
was still present.
I continued to run the system hoping that maybe it was just a break-in issue. During
this time, I searched out reviews and information on these speakers on the Internet
and found no mention of break-in time anywhere. Every review I found of these
speakers was overwhelmingly positive, which provided no help at all.
I had reached the point where there was only one thing left to do: take the 360s apart.
Inside the Infinity Primus 360s--A Guided Tour
The Boxes
The cabinets are made of approximately ¾-inch thick (18mm) MDF material on all
sides, which is covered with a wood-grained black plastic finish. The cabinet sides are
tapered toward the front of the cabinet to minimize diffraction. The front baffle is also
machined to accommodate the speaker drivers and the decorative silver plastic trim
rings that cover them. Click here for a photo. Each cabinet is approximately 39
inches tall, 12½ inches deep, and 8¼ inches wide. Infinity specifies the weight of each
speaker at 48.5 pounds.
Both woofers and the midrange have trim rings. The tweeter’s silver trim ring is also
its mounting plate. The trim rings use nice looking torx-head screws, which are
actually larger than the Philips-head screws that attach the drivers themselves! The
only negative I see to this set up is that the front baffle that supports the woofers and
midrange drivers ends up being only about ¼-inch thick after being machined. I would
prefer to see these drivers supported better.
The box itself has three inner braces that tie the front, sides, and back together. I was
impressed to see this. I have seen far more expensive speakers that lack any sort of
internal bracing.
There is a single pair of binding posts on the lower back of the cabinet. These are of
decent quality. They will take large gauge bare wire and would appear to be large
enough to accept banana plugs as well as spades. I made my connections via bare
wire.
I have talked about the problems presented by the stock feet in “Loudspeakers, Living
Rooms, and Spongy Floors so I won’t repeat that here. I will say that being able to
level the speakers side-to-side and front-to-back proved invaluable as I worked to find
the best position for them within my listening space.
Each cabinet is lined with some inch-thick damping material. It doesn’t look too
effective but, again, at least it’s there.
The Drivers
I’m impressed by the apparent quality of the woofer and midrange drivers considering
the price. They each appear to have a substantial magnet assembly. While magnet
weight doesn’t necessarily correlate with quality, lack of weight usually correlates
pretty well with cheapness. The midrange also has its own sub-enclosure, which I
would not have expected at this price. There does not appear to be any damping
material used in the sub-enclosure. All three drivers are shielded. There are no
gaskets between the drivers and the cabinet baffle. Fortunately, the drivers’ mounting
flanges fit against the machined surface of the cabinets pretty tightly.
The tweeter is what you would expect at this price, which is not to say that it’s in any
way bad, just what you would expect.
The two woofers appear to be running in parallel. I tried the speakers on both the
Eico HF-81’s 8 and 4-Ohm taps and they sounded noticeably louder and better with
the 8-Ohm connection so that’s how I have listened to them.
The Crossover
The crossover consists of three inductors (coils). The larger two are iron-cored and
the smallest, presumably the tweeter coil, is air-cored. There are five electrolytic
capacitors used along with two resistors. Typical 18 gauge stranded wire connects
everything together. It appears to be a second order crossover.
Again, this is better than I would have expected. Most cheap speaker crossovers
consist of a series cap on the tweeter and midrange.
Overall, I was impressed with how well these speakers are built in view of their low
cost. Some of the quality clearly comes from clever engineering and the rest from
being made in China.
Some mods to consider would be: upgrading the crossover capacitors, putting some
damping material in the midrange sub-enclosure, and upgrading the internal wiring.
Back to the Problem
Once disassembled, the problem was obvious enough. One of the tweeters was not
connected. Its ground wire was off. While I had the speakers apart, I also tightened
the drivers down. This eliminated the remaining bass boom.
So I got off easy. The phasey quality disappeared and the bass improved.
At this point in time, I also got the Eico finished (for now) and could finally spend some
time actually listening.
Set-up
I have played with speaker positioning in my living room and critical listening was done
with the speakers about 66 inches apart, center to center; about 36 inches from the
rear wall, measured at the front baffle; and about 84 inches from my ears. What is
interesting is that the speakers look a lot farther apart than they are. I guess it’s their
small size but my brain keeps saying they are as far apart as they are from me. My
brain is wrong but the setup seems to be working fine. In truth, I can’t get the
speakers a lot farther apart but it also doesn’t appear that I need to.
The speakers fire almost straight ahead. I have only about ¼-inch of toe-in at the
moment. This set-up delivers a strong center image with decent depth and good
width. I found the Infinities responded very positively to careful set-up including
getting them as perfectly vertical as possible. Click here for a picture.
Measurements
Perhaps the most impressive attribute of these speakers is their bass performance.
While I felt that it was very good subjectively, I wanted to see how it measured
objectively given the relatively small space the speakers operate in.
I made the following measurements at my listening position using the Stereophile Test
Disc and my Radio Shack meter. I felt the sound quality of the system was slightly
improved using DH Labs interconnects terminated with Eichmann RCA plugs. I also
listened using the same wire with Canare F-10 RCA plugs. I measured using both
types of cables just to see if there was any difference.
Frequency Canare Eichmann
1000Hz** 76dB 76dB
100 78 77+
80 82 81+
63 74 74
50 76 76+
40 75 76
31.5 Dropped like a rock
**reference level
These are really good measurements. I am assuming that the bump at 80 Hz is room-
related but even if it’s not; it’s not that far out of line. Perhaps it is related to the
woofers’ resonant frequency. Having no drop at 40 Hz is excellent performance and
probably explains why the bass is so subjectively satisfying. While the measurements
with the Eichmann plugs were essentially identical, these plugs again made small, but
discernable, improvements in soundstage width and low-level detail***.
Listening
I discussed a number of CDs I used for evaluating both these speakers and the Eico
amp in “Improving the Eico HF-81, Part Two.” Here are some additional notes I made
while listening to the following CDs.
Bill Frisell’s Nashville, Nonesuch 79415-2, is a great sounding album. Through the
Primus 360s, bass was deep and physical with excellent impact. Plucked strings
sounded fast and clean whether from Bill’s guitar or Jerry Douglas’ dobro.
There are a number of performers on each track and it was easy to locate them in the
soundstage. There was a nice spread speaker-to-speaker. Images were rock-solid
and it was easy to follow any given performer’s playing.
Brand New Dance, Reprise 26309-2, is my favorite Emmylou Harris album. I listened
here to how her voice was reproduced and this system did an excellent job. There
was never any hint of shrillness. There are harmony vocals sung at fairly low levels
on most tracks. These stayed clearly audible through the 360s and were never
overwhelmed by the lead vocal.
Jennifer Warnes’, The Hunter, is a very good sounding CD. I like about half the songs
on it really well and really don’t care much for the others. Again, the Primus 360s did
a very good job of keeping backing vocal tracks separate, reproducing low-level
detail, and providing deep, tuneful bass.
I listened to quite a few other CDs as well. The strengths I have listed here were in
evidence on all of them.
Summary
I feel really lucky that Stereophile reviewed the Primus 360s or I would never have
been aware of them. They are clearly aimed at the home theater market, which is
generally not a recommendation for stereo listening.
The sound quality of the Infinity Primus 360s is outstanding. Given their low price,
there is no reason for any living room, bedroom, office, or even main system to
tolerate having speakers with lower performance. They occupy no more floor space
than most bookshelf speakers on stands and yet provide genuinely deep bass. They
have done far more than I expected with the ten Watts (or less) that the Eico
provides. I would expect their performance to be even better with a more modern
amp. While more power might benefit them, happily, no more power is needed.
The Primus 360s have made it possible for me to have a living room system that is
musically very enjoyable, very high quality, and at a very reasonable price. What a
deal.
Kent Johnson
June 26, 2006
*The Eico HF-81 was also undergoing some alterations at this time.
***And I felt in timing. I wanted to get up and dance to the Gipsy Kings’ version of
“Hotel California” with the Eichmann plugs installed. The music did not affect me the
same way with the Canare cables.
As I wrote in “Loudspeakers, Listening Rooms, and Spongy Floors,” I purchased a pair
of Infinity Primus 360 loudspeakers. This purchase was driven pretty much entirely by
the good review in the June 2005 Stereophile and the fact that I found a pair of factory
refurbished speakers for $279 plus shipping on eBay. Since purchasing my speakers,
I have found new speakers being sold for as little as $400 a pair on the Internet,
shipping included.
My initial response to these speakers was positive based largely on their impressively
good bass performance. The more I listened to them, however, the more I felt the
bass was too good, in fact out of control at some frequencies, and the rest of the
performance was not good enough.
I used a JVC receiver from my garage system to break-in the 360s since I could leave
it running even when I wasn’t home, something I just won’t do with tubes*. The more
time I put on these speakers, the more evident it was that there was indeed something
wrong with them. The bass boomed, piano music had a “clinky” quality to it, and the
sound seemed to be stuck in the boxes rather then emanating from them. But these
problems varied somewhat from CD to CD. Some CDs actually sounded pretty good.
I listened to an FM opera broadcast one Saturday afternoon and the 360s did an
excellent job of reproducing the soundstage. The singers moved back and forth right
in front of me.
Inadvertently, I discovered the source of much of the problem with the bass. The JVC
receiver has connections for two pairs of speakers. I had used the Speaker 2
connections simply because they were easier to get at behind the unit. Evidently,
using the Speaker 2 connections presumes that speakers are already connected to
the Speaker 1 terminals. Funny things occur with the damping of the amp when only
Speaker 2 is used. Connecting the 360s to the Speaker 1 terminals removed the
majority of the boom. So far so good.
At this point, I had finished the Eico re-re-biasing and put it back into the system.
There was an immediate improvement in the sound. Imaging and low-level detail were
noticeably better compared to the JVC--no surprise there. But still not great. Not
nearly as great as I had hoped. Pianos still sounded wrong and the phasey quality
was still present.
I continued to run the system hoping that maybe it was just a break-in issue. During
this time, I searched out reviews and information on these speakers on the Internet
and found no mention of break-in time anywhere. Every review I found of these
speakers was overwhelmingly positive, which provided no help at all.
I had reached the point where there was only one thing left to do: take the 360s apart.
Inside the Infinity Primus 360s--A Guided Tour
The Boxes
The cabinets are made of approximately ¾-inch thick (18mm) MDF material on all
sides, which is covered with a wood-grained black plastic finish. The cabinet sides are
tapered toward the front of the cabinet to minimize diffraction. The front baffle is also
machined to accommodate the speaker drivers and the decorative silver plastic trim
rings that cover them. Click here for a photo. Each cabinet is approximately 39
inches tall, 12½ inches deep, and 8¼ inches wide. Infinity specifies the weight of each
speaker at 48.5 pounds.
Both woofers and the midrange have trim rings. The tweeter’s silver trim ring is also
its mounting plate. The trim rings use nice looking torx-head screws, which are
actually larger than the Philips-head screws that attach the drivers themselves! The
only negative I see to this set up is that the front baffle that supports the woofers and
midrange drivers ends up being only about ¼-inch thick after being machined. I would
prefer to see these drivers supported better.
The box itself has three inner braces that tie the front, sides, and back together. I was
impressed to see this. I have seen far more expensive speakers that lack any sort of
internal bracing.
There is a single pair of binding posts on the lower back of the cabinet. These are of
decent quality. They will take large gauge bare wire and would appear to be large
enough to accept banana plugs as well as spades. I made my connections via bare
wire.
I have talked about the problems presented by the stock feet in “Loudspeakers, Living
Rooms, and Spongy Floors so I won’t repeat that here. I will say that being able to
level the speakers side-to-side and front-to-back proved invaluable as I worked to find
the best position for them within my listening space.
Each cabinet is lined with some inch-thick damping material. It doesn’t look too
effective but, again, at least it’s there.
The Drivers
I’m impressed by the apparent quality of the woofer and midrange drivers considering
the price. They each appear to have a substantial magnet assembly. While magnet
weight doesn’t necessarily correlate with quality, lack of weight usually correlates
pretty well with cheapness. The midrange also has its own sub-enclosure, which I
would not have expected at this price. There does not appear to be any damping
material used in the sub-enclosure. All three drivers are shielded. There are no
gaskets between the drivers and the cabinet baffle. Fortunately, the drivers’ mounting
flanges fit against the machined surface of the cabinets pretty tightly.
The tweeter is what you would expect at this price, which is not to say that it’s in any
way bad, just what you would expect.
The two woofers appear to be running in parallel. I tried the speakers on both the
Eico HF-81’s 8 and 4-Ohm taps and they sounded noticeably louder and better with
the 8-Ohm connection so that’s how I have listened to them.
The Crossover
The crossover consists of three inductors (coils). The larger two are iron-cored and
the smallest, presumably the tweeter coil, is air-cored. There are five electrolytic
capacitors used along with two resistors. Typical 18 gauge stranded wire connects
everything together. It appears to be a second order crossover.
Again, this is better than I would have expected. Most cheap speaker crossovers
consist of a series cap on the tweeter and midrange.
Overall, I was impressed with how well these speakers are built in view of their low
cost. Some of the quality clearly comes from clever engineering and the rest from
being made in China.
Some mods to consider would be: upgrading the crossover capacitors, putting some
damping material in the midrange sub-enclosure, and upgrading the internal wiring.
Back to the Problem
Once disassembled, the problem was obvious enough. One of the tweeters was not
connected. Its ground wire was off. While I had the speakers apart, I also tightened
the drivers down. This eliminated the remaining bass boom.
So I got off easy. The phasey quality disappeared and the bass improved.
At this point in time, I also got the Eico finished (for now) and could finally spend some
time actually listening.
Set-up
I have played with speaker positioning in my living room and critical listening was done
with the speakers about 66 inches apart, center to center; about 36 inches from the
rear wall, measured at the front baffle; and about 84 inches from my ears. What is
interesting is that the speakers look a lot farther apart than they are. I guess it’s their
small size but my brain keeps saying they are as far apart as they are from me. My
brain is wrong but the setup seems to be working fine. In truth, I can’t get the
speakers a lot farther apart but it also doesn’t appear that I need to.
The speakers fire almost straight ahead. I have only about ¼-inch of toe-in at the
moment. This set-up delivers a strong center image with decent depth and good
width. I found the Infinities responded very positively to careful set-up including
getting them as perfectly vertical as possible. Click here for a picture.
Measurements
Perhaps the most impressive attribute of these speakers is their bass performance.
While I felt that it was very good subjectively, I wanted to see how it measured
objectively given the relatively small space the speakers operate in.
I made the following measurements at my listening position using the Stereophile Test
Disc and my Radio Shack meter. I felt the sound quality of the system was slightly
improved using DH Labs interconnects terminated with Eichmann RCA plugs. I also
listened using the same wire with Canare F-10 RCA plugs. I measured using both
types of cables just to see if there was any difference.
Frequency Canare Eichmann
1000Hz** 76dB 76dB
100 78 77+
80 82 81+
63 74 74
50 76 76+
40 75 76
31.5 Dropped like a rock
**reference level
These are really good measurements. I am assuming that the bump at 80 Hz is room-
related but even if it’s not; it’s not that far out of line. Perhaps it is related to the
woofers’ resonant frequency. Having no drop at 40 Hz is excellent performance and
probably explains why the bass is so subjectively satisfying. While the measurements
with the Eichmann plugs were essentially identical, these plugs again made small, but
discernable, improvements in soundstage width and low-level detail***.
Listening
I discussed a number of CDs I used for evaluating both these speakers and the Eico
amp in “Improving the Eico HF-81, Part Two.” Here are some additional notes I made
while listening to the following CDs.
Bill Frisell’s Nashville, Nonesuch 79415-2, is a great sounding album. Through the
Primus 360s, bass was deep and physical with excellent impact. Plucked strings
sounded fast and clean whether from Bill’s guitar or Jerry Douglas’ dobro.
There are a number of performers on each track and it was easy to locate them in the
soundstage. There was a nice spread speaker-to-speaker. Images were rock-solid
and it was easy to follow any given performer’s playing.
Brand New Dance, Reprise 26309-2, is my favorite Emmylou Harris album. I listened
here to how her voice was reproduced and this system did an excellent job. There
was never any hint of shrillness. There are harmony vocals sung at fairly low levels
on most tracks. These stayed clearly audible through the 360s and were never
overwhelmed by the lead vocal.
Jennifer Warnes’, The Hunter, is a very good sounding CD. I like about half the songs
on it really well and really don’t care much for the others. Again, the Primus 360s did
a very good job of keeping backing vocal tracks separate, reproducing low-level
detail, and providing deep, tuneful bass.
I listened to quite a few other CDs as well. The strengths I have listed here were in
evidence on all of them.
Summary
I feel really lucky that Stereophile reviewed the Primus 360s or I would never have
been aware of them. They are clearly aimed at the home theater market, which is
generally not a recommendation for stereo listening.
The sound quality of the Infinity Primus 360s is outstanding. Given their low price,
there is no reason for any living room, bedroom, office, or even main system to
tolerate having speakers with lower performance. They occupy no more floor space
than most bookshelf speakers on stands and yet provide genuinely deep bass. They
have done far more than I expected with the ten Watts (or less) that the Eico
provides. I would expect their performance to be even better with a more modern
amp. While more power might benefit them, happily, no more power is needed.
The Primus 360s have made it possible for me to have a living room system that is
musically very enjoyable, very high quality, and at a very reasonable price. What a
deal.
Kent Johnson
June 26, 2006
*The Eico HF-81 was also undergoing some alterations at this time.
***And I felt in timing. I wanted to get up and dance to the Gipsy Kings’ version of
“Hotel California” with the Eichmann plugs installed. The music did not affect me the
same way with the Canare cables.
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