Infinity Primus P363 Floorstanding Loudspeaker Measurements and Analysis

Impedance / Phase Measurements of the Infinity P363

Although Harman rates the Infinity Primus P363 as 8-ohm speakers, what I measured tells a much different story. These are clearly 4-ohm speakers. They appear to be tuned just below 50Hz, but the saddle points are quite asymmetric. This indicates a system tuning too low for the available box size needed to produce a more optimal response. The 4 ohm dip between 100Hz to 200Hz is a bit concerning for those wanting to use these speakers with budget A/V receivers. Even if bass managed, these speakers can present a rather strenuous load if the amplifiers in the A/V receiver don’t take kindly to 4-ohm loads. I found that Infinity employed a 4-ohm tweeter as evident by the impedance dip above 10kHz. I believe they did this in attempt to increase speaker sensitivity.

Impedance Measurement Comparison of the Infinity P363 Left/Right Speakers

I was a bit perplexed at how differently the two P363 samples I received measured, as can be seen in the magnitude of the impedance spikes 30Hz and 80Hz respectively. I believe this was a combination of loose driver tolerances possibly combined with a leaky transmission path in one of the cabinets. It’s not atypical for budget minded speakers to show variances in impedance measurements, though this example was a bit more extreme than I am used to seeing.

Harman’s marketing is not only taking liberty with impedance ratings with the P363, but they are also doing the same with sensitivity ratings too. I found the sensitivity of the P363’s was around 90dB at 2.83V at 1 meter which is 3dB less than what Infinity claims. If you want to scale this back to 1 watt (remember the P363 is a 4 ohm speaker) that means its real 1 watt / 1 meter sensitivity is 87dB.

All frequency response measurements were taken with the grilles removed unless otherwise noted.

Infinity P363 In-room 1/2 meter Listening Window Response Spliced 1 Meter GP at 1kHz

I took a total of seven measurements (on-axis +-15 & +-30 deg horizontal and +-15 deg vertical) at ½ meter on the midrange axis and averaged the response to more accurately represent what the listener will actually hear. I then spliced this data with a 1 meter outdoor groundplane measurement for 1kHz and below. The combined response tracks very closely with the anechoic data Harman sent me for comparative purposes. As you can see, the frequency response is fairly linear with a slight tilt in bass response below 500Hz and treble response above 5kHz. These results don’t surprise me as the P363’s have a lot of top end energy and a good deal of bass punch and depth for a speaker of its size.

Infinity P363 In-room 1/2 meter SPL vs Frequency Response (1/12^th octave smoothed)
orange trace: on-axis; red trace: 15 deg off-axis hor; blue trace: 30 deg off-axis hor
green trace: 15 deg off-axis vert up; purple trace: 15 deg off-axis vert down

The P363 maintained well behaved dispersion characteristics off-axis which is of no surprise since that is a design hallmark of all Harman based loudspeakers. Well-behaved horizontal dispersion is an agreeably-predictable result from vertically-aligned drivers operating well within their wide-dispersion bandwidths, while the good vertical response within the 15 degree window comes from closely-spaced drivers and well-chosen crossover points.

Infinity P363 On-Axis Frequency Response Comparison ( red: no grille, yellow: with grille)

The grille covers weren’t quite as transparent as we’d like to see, though no speaker we’ve ever measured produces exactly the same results with their grille covers installed. The fairly significant dip in the 5kHz area with the grille cover installed is an extremely audible frequency range. I recommend critical listening to be done without grilles installed and to reserve using them only in the presence of small children or disrespectful house guests.

Infinity P363 In-Room THD Distortion Measurement (1/2 meter)

Using the OmniMic system, I positioned the mic about ½ meter away from the P363’s midrange to do a frequency vs distortion sweep. This is a similar test to how the NRC does distortion. In my opinion this doesn’t come close to giving you the whole picture on actual audible distortion since it’s a single tone sweep and doesn’t account for modulation distortion, if for example, a midrange driver is running full-range without a HPF (like this speaker has). This measurement does tell you of any obvious flaws or problems with the speaker system. I drove the P363’s at fairly high output (more than my ears could take for any duration of time) and they produced nice clean results as you can see above. If you want to convert the THD to physical #’s, you can subtract the SPL sweep (black) from the distortion sweep (blue) at corresponding frequencies and convert the numerical # to a percentage as follows:

For example at 1kHz, the P363 SPL was roughly 90dB while the THD level was 35dB. 90dB – 35dB = 55dB or 0.178% THD.

The Downside

Like any budget-minded speaker, compromises are always made in order to hit a certain price point. The Infinity P363 tower speaker system is far from perfect, but it does many things right. For one, the almost unremovable plastic plugs on the binding posts were simply ridiculous. The overall fit and finish on these speakers is unremarkable. They certainly won’t win any beauty contests. I feel the P363’s were deliberately voiced a bit hot in the treble and upper bass regions to stand out on a noisy showroom floor. I wouldn’t characterize these speakers as being particularly neutral (expect maybe for the mids), but few if any speakers in this price class are. I would imagine the typical consumer shopping for a speaker system like this would actually appreciate the little tonal color these speakers add to the presentation however. Totally neutral speakers are unpalatable for most listeners, despite it sounding like a good design goal to aspire to.

Recommendations

The Infinity P363 floorstanding speaker system is not quite as sensitive or as easy of an amplifier load as Harman spec’d them to be. They are truly a 4-ohm speaker, so care must be taken when pairing them with modestly priced A/V receivers, especially when trying to achieve high output levels in medium to larger sized rooms. These speakers would greatly benefit from external amplification; Emotiva and Outlaw Audio come to mind as great performance/value solutions. You can run these speakers full-range but in a multi-channel setup, I’d recommend bass managing them and allowing a separate powered subwoofer to handle the bass notes below 80Hz. Only moderate toe-in is recommended on these speakers since they exhibit very uniform off-axis horizontal dispersion and produce a rather lively top end response as is.