Infinity Primus 150 spinorama measurements (CTA-2034)

[kemmler3D]

The spec frequency range is a total fantasy, but still, these are really not bad, a good example of budget hidden gems. Thanks for doing the measurements, maybe someone will be able to find a good thrift store / craigslist deal because of this!

 

[uwotm8]

The spec frequency range is a total fantasy, but still, these are really not bad, a good example of budget hidden gems. Thanks for doing the measurements, maybe someone will be able to find a good thrift store / craigslist deal because of this!

I'm still bothered by that very low used price because you'll have hard time finding even Wharfedale for that small.
And there's nothing new around $100-150 measuring even nearly as good.

 

[AnalogSteph]

View attachment 436945
This compression gonna be audible in not-large rooms, listening to music with plenty of bass? Maybe the driver's compressiom behavior is a significant shortcoming?

It's not exactly exciting for a speaker with twin 6.5"s, is it? I guess the progress made in the last 2 decades had to show somewhere. There's also some crossover shifting going around that indicates inductor core saturation, so I bet you'll find plenty of non-air-core types in the crossover - not a real surprise in this budget line. (Maybe those are even responsible for some of the compression?) An upgrade may be a worthwhile project for the enterprising DIYer equipped with an LCR meter.

 

[eric-c]

I recall watching a dr Floyd Toole (McGill university) lecture on youtube where he talks about testing methodologies and on blind testing. a small harmon bookshelf was constantly chosen over much more expensive (worse measuring) speakers. If I recall he stated / outted this speaker. This infinity speaker was one of the early ones that was designed based on dr tools research when he joined Harmon. Believe it was this video / lecture. At an airport now so can't verify. Excellent video nonetheless

 

[Ageve]

Here's a teardown:

24dB/octave crossover (according the the specs):

Tweeter:

Woofer (magnetically shielded):

No damping material at the bottom of the cabinet:

Short port (1 inch / 2.5 cm):

I added some extra damping material:

it improved the port response a bit:

(Heating pump running in the background. Please ignore the small peaks at ~45 Hz)

It didn't improve the woofer response though:

Port open vs closed (with the added damping material):

 

[kemmler3D]

Here's a teardown:

View attachment 436973


24dB/octave crossover (according the the specs):

View attachment 436974

Tweeter:

View attachment 436975

Woofer (magnetically shielded):

View attachment 436976

No damping material at the bottom of the cabinet:

View attachment 436977

Short port (1 inch / 2.5 cm):

View attachment 436978


I added some extra damping material:

View attachment 436985


it improved the port response a bit:

(Heating pump running in the background. Please ignore the small peaks at ~45 Hz)

View attachment 436986

It didn't improve the woofer response though:

View attachment 436987

Port open vs closed (with the added damping material):

View attachment 436994

Huh, based on that last graph I really wonder what the point of the port is?

 

[Ageve]

Huh, based on that last graph I really wonder what the point of the port is?

The near-field response of the woofer itself doesn't change much with the port open, but when combined with the port, you get deeper bass.

Red = Combined port+woofer (port level reduced by 20 Log (40 mm/110 mm) = ~8.8 dB).

Blue = Simulated far-field response, accurate up to ~800 Hz (port+woofer, corrected for baffle edge diffraction).

I recall watching a dr Floyd Toole (McGill university) lecture on youtube where he talks about testing methodologies and on blind testing. a small harmon bookshelf was constantly chosen over much more expensive (worse measuring) speakers. If I recall he stated / outted this speaker. This infinity speaker was one of the early ones that was designed based on dr tools research when he joined Harmon. Believe it was this video / lecture. At an airport now so can't verify. Excellent video nonetheless

It could be this speaker in his presentation. Looks very similar:

On-axis comparison:

 

[Maiky76]

Here are some measurements of the Infinity Primus 150 Bookshelf speaker.

The MSRP was $198/pair back in 2003.

View attachment 436659


Specifications:

Frequency range: 58Hz - 20000Hz (+/- 3dB)
Recommended Power: 10 - 100W
Sensitivity: 88 dB
Nominal impedance: 8 ohms
Crossover frequency: 3300 Hz; 24dB/octave
Low-frequency driver: 5-1/4" (130mm) MMD
High-frequency driver: 3/4" (19mm) MMD
Weight: 13.5 lb (6kg)


My measurements are quasi-anechoic, with near-field port+woofer, corrected for baffle edge diffraction, combined with gated measurements at 1m distance.

I have attached a 1m vs 2m comparison, pair matching and measurement axis comparison for those who are interested. I used the speaker with the smoothest response for the spin.

Recommended listening height is with the tweeter "approximately at ear level" according to the user manual. I got the flattest response ~40 mm below tweeter axis, so that's what I used for the spin.


Here's the CTA-2034 data:

View attachment 436660


It looks surprisingly good considering how inexpensive this speaker was. Most of the response errors should be fixable with EQ thanks to the smooth directivity.


Early reflections:

View attachment 436663


Horizontal, and total early reflections:

View attachment 436664


Estimated in-room response:

View attachment 436665


Quasi-anechoic response:

View attachment 436693


Horizontal directivity:

View attachment 436667

View attachment 436668

0-90 deg compared to measurement by John Atkinson:

View attachment 436669

View attachment 436670

Infinity Primus 150 loudspeaker Measurements

Sidebar 3: Measurements

www.stereophile.com

Vertical directivity:

View attachment 436671

View attachment 436672

View attachment 436673


Near-field response:

Steep roll-off thanks to the 24dB/octave crossover, but there are clear port and/or cabinet resonances, and a woofer resonance at ~8 kHz.

View attachment 436674


Distortion:

View attachment 436675

View attachment 436676


< 1% THD from 75 Hz and up. Very low tweeter distortion (less than 0.1%).


Comparison with Stereophile, 30 deg horizontal listening window:

View attachment 436677


Overall, I'm quite impressed by this speaker. It sounds better than most of the budget speakers I have measured so far. Sure, it's not perfect, but frequency response is ok, horizontal directivity is excellent, and distortion is quite low as well.

There's no deep bass though. A subwoofer is definitely needed.

Here is my take on the EQ.
Please report your findings, positive or negative!

For the score rational your journey starts here
Explanation for the sub score
The following EQs are “anechoic” EQs to get the speaker right before room integration.
If you able to implement these EQs you must add EQ at LF for room integration, that is usually not optional… see hints there.

The raw data with corrected ER and PIR:

Score no EQ: 4.2
With Sub: 7.1

Spinorama with no EQ:

• fairly good save for some 700-2500 Hz resonances
• Limited bass

EQ design:
I have generated two EQs. The APO config files are attached.

• The first one, labelled, LW is targeted at making the LW flat
• The second, labelled Score, starts with the first one and adds the score as an optimization variable.
• The EQs are designed in the context of regular stereo use i.e. domestic environment, no warranty is provided for a near field use in a studio environment although the LW might be better suited for this purpose.

Score EQ LW: 5.6
with sub: 8.4

Score EQ Score: 6.1
with sub: 8.9

Infinity Primus 150 APO EQ LW 96000Hz
March182025-121855

Preamp: -1.50 dB

Filter 1: ON HPQ Fc 49.6 Hz Gain 0.00 dB Q 1.30
Filter 2: ON PK Fc 108.5 Hz Gain -4.09 dB Q 0.90
Filter 3: ON PK Fc 665.5 Hz Gain 1.72 dB Q 2.30
Filter 4: ON PK Fc 871.4 Hz Gain -2.88 dB Q 4.12
Filter 5: ON PK Fc 1520.7 Hz Gain -1.05 dB Q 4.96
Filter 6: ON PK Fc 2026.6 Hz Gain 1.63 dB Q 4.71
Filter 7: ON PK Fc 2986.4 Hz Gain -1.31 dB Q 1.98
Filter 8: ON PK Fc 13137.2 Hz Gain -3.12 dB Q 3.23

Infinity Primus 150 APO EQ Score 96000Hz
March182025-121855

Preamp: -1.50 dB

Filter 1: ON HPQ Fc 49.1 Hz Gain 0.00 dB Q 1.35
Filter 2: ON PK Fc 105.6 Hz Gain -3.46 dB Q 0.90
Filter 3: ON PK Fc 679.5 Hz Gain 1.72 dB Q 1.70
Filter 4: ON PK Fc 867.4 Hz Gain -2.88 dB Q 4.12
Filter 5: ON PK Fc 1505.1 Hz Gain -1.38 dB Q 4.96
Filter 6: ON PK Fc 2036.1 Hz Gain 2.43 dB Q 4.96
Filter 7: ON PK Fc 3309.8 Hz Gain -1.10 dB Q 0.52
Filter 8: ON PK Fc 7399.6 Hz Gain -1.08 dB Q 2.92
Filter 9: ON PK Fc 13008.8 Hz Gain -4.12 dB Q 2.23

Spinorama EQ LW

Spinorama EQ Score

Zoom PIR-LW-ON

Regression - Tonal

Radar no EQ vs EQ score
Some improvements

The rest of the plots is attached.

 

[fragzone]

Very cool. I'm looking to get into measurements and was wondering how you determined the 40mm tweeter offset. Did you just take on axis measurements between the tweeter and woofer at varying increments and choose the most favourable ('smooth'/neutral) position?

 

[Ageve]

Very cool. I'm looking to get into measurements and was wondering how you determined the 40mm tweeter offset. Did you just take on axis measurements between the tweeter and woofer at varying increments and choose the most favourable ('smooth'/neutral) position?

Yes, I usually do a number of measurements within +/- 50 mm of the recommended listening height (unless there are instructions to stay exactly at tweeter height) and choose the one with the smoothest response.

Most of the time, tweeter-axis is ideal, but in this case there was a small improvement slightly below it.

 

[kemmler3D]

Wow, EQ with sub gets a pretty crazy high preference score for the money...

 

[tktran303]

I wonder if this speaker, paired with a sub, was what did so well in the blind testing, but when people saw it, reacted negatively:

 

[tktran303]

Are you able to reveal this @Floyd Toole

 

[rsc1]

Imagine if all of today's so-called audio "experts" would have to do blind tests of the speakers they review. Consumers would get a lot more useful buying advice...

Infinity seems to have been ahead of their time back in the day. I never knew they made stuff this good until recently people started posting measurements - thanks OP for your contribution. This is great news for us bargain hunters. There's a listing for a set of basically new Primus 363 towers close to me for $200 that I'm thinking about picking up.

 

[beagleman]

That is VERY interesting! What's your subjective opinion on their sound, what's good and what's not so?

The very interesting part is here: back in the days when Primus was current and selling, it was sort of despised and oftenly considered cheap junk. At the same time, a lot was sold and used price was - at least a few years ago - very low as well. According to this one would never think these can be even remotely good.

There were some concerns about enclosure

View attachment 436687

And AFAIR a lot of used are selling with dead/damaged/replaced tweeters (kinda a weak point).

View attachment 436688
Does it sound sligtly V-shaped? Some complains were about that, again, if mind serves me well.

Unfortunately I never heard them presonally.

I remember hearing them and thinking they were quite neutral for a low priced speaker.

I think that was before neutral was considered a good thing. Most speakers, HAD to have sizzle or really boomy loud bass.

 

[tktran303]

Imagine if all of today's so-called audio "experts" would have to do blind tests of the speakers they review. Consumers would get a lot more useful buying advice...

Some publications do. Eg. Wirecutter.com ; led by the fearless Brent Butterworth

“we conceal the contenders behind thin, black fabric that has a negligible effect on sound quality. Whenever possible, we use a switching device that allows the panelist to listen to each speaker for as long as they wish and then switch to the next speaker; the speakers are identified only by number, and we change those numbers for every panelist to minimize any advantage a contender might gain by going first or last.

Science shows that this type of unbiased evaluation is absolutely critical to a valid evaluation of sound quality. As detailed in the 1994 Audio Engineering Society paper “Hearing is Believing vs. Believing is Hearing: Blind vs. Sighted Listening Tests, and Other Interesting Things” by Floyd E. Toole and Sean Olive, “when listeners knew what they were listening to, the opinions were dictated more by the product identity than by the sound.”

Reference-

How Wirecutter Tests Audio Products (And You Can, Too!)

Here are the procedures Wirecutter uses to test audio devices, plus a few tips on how you can evaluate them yourself.

www.nytimes.com

One of their old favourites (Aug 2024) that I measured:

A directivity mismatch af the XO frequency, but otherwise not too shabby.

Here’s what they had to say:
“If you want more bass from powered speakers and don’t need lots of features: The Edifier S1000 mkII system, a former top pick, offers sound quality comparable to that of the ELAC Debut ConneX DCB41 speakers (our Upgrade pick for Best powered bookshelf speakers) but with considerably better bass performance (roughly 6 dB more bass output in our testing). However, the S1000MkII system lacks the HDMI and phono inputs found on both of our picks, and it’s comparatively bulky.”

Reference:

The Best Bookshelf Speakers for Stereo and Surround Sound

A great pair of bookshelf speakers should last for years and deliver better performance than you can get from a tabletop speaker.

www.nytimes.com

 

[thewas]

Also a good German audio magazine (Hifi-Stereophonie) did such blind comparisons in the 70s and early 80s as well till today the state financed kind of Consumer Report equivalent (Stiftung Warentest) does them for loudspeakers and headphones.

 

[Ron Texas]

With inflation it would cost about double today. Pretty good for an inexpensive speaker from 2 decades ago.

 

[xNORgate]

Thank you both - @Ageve and @Maiky76 - for providing such great measurements and vital information.
In a 2012 close-out sale, I impulse-bought a pair of Infinity Primus "P153" speakers. They have been in use with my desktop-PC systems ever since.
The Primus P153s are fed through FOSI ZA3/ZD3 combo, using USB-C, NAS music library, Dante I/Os, Streaming and SXM (XLR + RCA).

OT: History of Infinity speakers is well covered in this davidsaudio website.
I had a pair of Infinity POSII during college years and I once dropped a pair of Infinity InfiniTesimal in one of my old cars, when car speakers really sucked.

 

[tktran303]

Ah the good ol' days.

I’m a fan of Infinity speakers. A BIG fan. In my mind, during their heyday Infinity produced some of the finest speakers ever made. If the only Infinities you’ve heard are the mass-market junk at Circuit City, then you haven’t heard good Infinities. Here’s my collection of vintage Infinity speakers (this page is a work in process). I still have a few Infinities I really want to complete my collection, but here’s what I have right now.

Reference: https://www.davidsaudio.com/html/vintage_infinity__speakers_and.html