Saturday, 16 January 2021

RETRO-MEASURE: Radio Shack / Realistic / Tandy Minimus 7 speakers (early 1980s, Cat. No. 40-2030A)

While the "latest and greatest" gear is always nice to check out, read about and measure, over the years, I've also loved the opportunity to examine some of the vintage, "retro" stuff from back in the day. For example, today we have a pair of all-metal, black, Realistic (Radio Shack / Tandy Corp.) Minimus 7 speakers from the early 1980's.

These were "classics" back in the day, found in many college dorms, restaurants, doctors' offices and available for sale at your friendly neighborhood Radio Shack for >25 years. For some more history, check out this page.

My friend linnrd is a man with quite a collection of audio stuff over the decades. He told me that he got these back in 1987 used from someone in his college days. He had them in his car for awhile and in the last few decades it looks like they've been in safe storage.

Other than a few little scuffs and couple of minor dents on the metal grille, these are in good shape.


As you can see, they are "Realistic" branded, not the later "RCA" or "Optimus" models and are in all-black die-cast aluminum. This "metal cabinet" model was on sale from 1977-1993 with design variations. They're small, measuring about 4.5" wide x 7" tall x 4.25" deep and weigh 4.5lbs each. Here's the original ad back in 1977/78 with a retail price of US$50 each in the catalogue with yearly sales down to US$30 each usually in the spring time:


We can see these catalog specs reflected on the back of the boxes also:


Notice that these are in fact early-model Minimus 7s - catalogue number 40-2030A (which replaced the original unlettered ones in 1980). Rated at 8Ω, 40W power handling, and manufactured in Japan. Speaker wire connectors are "push-in-to-release" metal clips; Realistic recommended just using 18AWG "lamp cord". The holes are small so 12AWG wires are too thick but 14AWG can be squeezed in tight. The speakers are enclosed acoustic suspension speakers, no ports. I have been told that later models had a rear-firing port.

To protect the identity of the innocent, I blurred out the last 2 digits of the serial number. Notice that these were manufactured about 3-4 months apart with quite different serial numbers - the one on the right has a serial code of 011XX 11A0 (November 1980), and the left one 130XX 2A1 (February 1981). I see that there is a thread discussing different serial numbers on AudioKarma with very cool chart here.

It's important to be aware of the age of these speakers because the drivers were changed over the years. Apparently the tweeter was redesigned in 1983.

Specs from the manual which can be found on HifiEngine for the 40-2030B model. Hmmm... Somehow I think 50Hz on the low end seems a bit optimistic for 4" woofers!

The thin and light metal grille is easily removable, there's a small amount of sticky stuff holding them in place. The drivers are 1" (25mm) fabric dome tweeter and 4" (100mm) "high compliance" greyish cone mid/woofer with rubber surround:



The picture above was taken just after opening it up before some cleaning. A wee bit dusty in there but otherwise the speaker surround and cone look like they're in good shape. The tweeter mounting plate is metal, later versions apparently were made of plastic. It would not be difficult to replace the drivers as the screws are easily accessible. I see there are discussions on modifying these speakers (see here, here, Zilch crossover page, PZ-2.2 DIY Mod, and reviewed with upgraded crossover here). The stock crossover design left the woofer running unfiltered while applying a 2nd order filter for the tweeter (~2.5kHz crossover).

Before I measure the speakers, I usually have a listen first. Alas, one of them, the older 011XX 11A0 clearly was not functioning as well with the woofer cutting in and out at times. So I opened it up to have a peek at what's inside:


Yup, indeed, not difficult to open. There's what feels like yellow fiberglass damping material (left). And when you pull the stuff out, there's the crossover inside (right). Indeed, the yellow/black woofer wires are connected straight to the speaker terminals without any filtering network in the way. The tweeter crossover is a simple 0.4mH inductor with a 50V 4.7μF electrolytic capacitor that still looks good and measured fine. There was a poor solder joint causing the loss of connection to the woofer; I was able to revise it, used some Deoxit on the speaker terminals and checked the other solder points. Electronics of this vintage tend to be easy to fix unlike modern stuff. :-)

Let's get to it.

I. Measurements

As usual, I listened to both speakers before measuring. Listening closely with a mono signal to each speaker, I felt that the speaker above that I fixed up, and spent time cleaning out actually sounded a little better (less harsh) than the other one. As such, I'll call this the "Main" speaker, and I'll include some comparisons with the other one ("Secondary" speaker) below for stereo-pair comparison.

Since this is a passive speaker, let's have a peek at the impedance the speaker will present to your amplifier:


The minimum impedance dips down to 4Ω up around 17kHz but for much of the spectrum it's higher around 6.5+Ω. Notice the driver resonance peaks at 115Hz and 2kHz. There are "wrinkles" in phase and impedance at the red arrows particularly at 700-800Hz and 4kHz suggesting some resonance in those regions. The EPDR (Equivalent Peak Dissipation Resistance), which accounts for both impedance and phase, dips down to 2.5Ω up at 7kHz. At bass frequencies where we need higher current, EPDR dips down to 3.8Ω around 50 and 200Hz which isn't too bad.

Here's the sensitivity measurement with a 2.83V signal sweep at 1m, measured on tweeter axis. As per my standard, the Emotiva XPA-1L was used as the amplifier.


I obtained an average sensitivity value of 86.5dB/2.83V/m from 500Hz to 7kHz. As you can see, the frequency response is uneven and there's a significant accentuation around 4kHz and 6.4kHz that's pushing the average up.

Let's see how this fares with the "qSpin" and the derived CTA-2034A-inspired graphs using blended nearfield and 1m gated measurements. Note that measurements were done with the metal grille on. At this kind of price point, I think it's unlikely many end-users would purposely take the grilles off for regular listening.


Hmmm... Not pretty. I'm seeing a dip at the 2.5kHz crossover point. Then with the woofer running filterless (no low-pass filter), we're seeing cone breakup causing those 4kHz and 6.5kHz peaks. Nearfield measurements tell me that the output rolls off after 7kHz; beyond that, we have varying amounts of constructive and destructive interference between the woofer and tweeter. It's possible the metal grille has an effect (didn't check).

Those are rather rough looking directivity index graphs (DI and ERDI) suggesting that we're going to be seeing quite an uneven dispersion pattern on the polar maps:


As suspected, both horizontal and vertical unevenness evident. The colors look pretty though. :-) Be careful about listening to these speakers below the tweeter axis.


There's the step response above. Notice that both tweeter and woofer are arranged in positive acoustic polarity. Quite a bit of "rippling" in the woofer response rather than a smooth roll-off one sees with better speakers.


This cumulative spectral decay graph is an example of "temporal blur" I think ;-).

Transients will take a bit of time to settle and we see a number of areas of increased resonance, not the least of which around the 4kHz peak, again probably related to woofer cone breakup (note the wrinkle in the impedance graph above at this frequency).

I think this finding is not unexpected given the enclosure. The metal enclosure vibrates noticeably when playing music (you can easily feel this) and it stands to reason that this "ringing" takes a bit of time to dissipate.

With increasing signal amplitude, the speaker does reproduce the sound in a linear fashion loudness-wise. Excellent, very little error on the multitone burst.


Harmonic distortion does not look bad. Remember that -40dB is 1% harmonic distortion. For the most part, distortion stayed <1% except around 2kHz where there's a bit of the 3rd harmonic showing up.

Here is the IMD test using 300Hz and 1300Hz signals at varying amplitude levels from 60-90dB SPL:


Generally again we're seeing <1% IMD (-40dB) at 80dB SPL and below. Distortion increases significantly by 90dB SPL though, so don't drive these speakers too loud. We've seen in the past that a more expensive "reference" speaker like the KEF LS50 can maintain low IMD even with higher output levels.

Remember I said above that one of the speakers didn't sound as good as the other? Here's then the stereo comparison of the "Main" speaker which is the one I used for the measurements above, compared to the other one which seemed a little "thinner" in sound - the "Secondary" speaker:


No wonder there was a difference in sound between the 2 speakers. Notice that they're not very well matched and the "Secondary" speaker has a very pronounced 3.5kHz resonance.

And here's that "Secondary" speaker's cumulative spectral decay:


Yup, strong 3.5kHz resonance (woofer breakup?) with this unit!

I think this is a good reminder that there could be significant variation between different Minimus 7s. Of course, after 40 years, I can't know for sure if these differences are examples of speaker matching issues from the beginning or changes that have happened over time. That's always one of the uncertainties when measuring "vintage" gear even if the device looks good externally and otherwise does not sound damaged.

II. Subjective

Let's just start with a mono evaluation of the "Main" speaker which is the one I opened up and fixed. Remember that one can still evaluate sound quality quite well in mono; in fact, much of the (Canadian) National Research Council and Harman speaker evaluations were done with a single unit. 

This little speaker sounded alright. For a small transducer with 4" woofer, it's obviously quite frequency-limited. The Minimus 7 clearly is not capable of 50Hz frequency response on the low end like the specs sheet says with any reasonable output!

With the frequency limitations, the sound tilts to the "cool" side. Frequency irregularities were notable when I played the familiar Stevie Ray Vaughn "Tin Pan Alley" (Couldn't Stand The Weather). Accentuated upper-mids caused the electric guitar to sound "aggressive" in relation to Vaughn's more recessed male vocals at times. 

The cymbals on Pink Floyd's "The Happiest Days of Our Lives" (The Wall) stood out in a harsh way but otherwise, the layering of guitar, bass, percussion, and the children's choir on "Another Brick In the Wall Part II" was enjoyable.

Apart from the frequency anomalies, I felt the Minimus 7 was also lacking in detail compared to even the small AudioEngine A2 (another severely low-end limited speaker). Details within the seaside sonicscape at the start of Elton John's "The One" (The One) sounded mashed together, losing the nuances of the waves hitting the shore and sounds of the various birds through the Minimus 7. While the resolution of the drivers might have something to do with this, it was hard for me to discount the vibrating metal enclosure also playing a part especially as I pushed up the volume.

Little Realistic Minimus 7's in the room.

Placed in the usual stereo configuration above in my soundroom using the RME ADI-2 Pro FS R Black Edition as DAC, Emotiva XSP-1 preamp, driven by my DIY Hypex NC252MP Class D amplifier, let's listen in the main AV room.

Well, guys and gals, IMO this simply is not "high fidelity" sound (obviously!). The uneven tonality makes music sound "nervous" rather than properly "composed". Delicate details were not as noticeable compared to other small speakers I've tried. For example, the violin on Nicola Benedetti's "Spiegel Im Spiegel" on Fantasie (a sparse piece composed by Arvo Pärt) lacked subtle dynamics and tonal character, sounding at bit processed, artificial.

Perhaps a more concrete and familiar example of the irregular treble response can be heard in the pop song "Eternal Flame" (The Bangles, Everything) where there's that recurring high-pitched bell (probably synthesized?) that rings through most of the song. On my main system, the bell has a unique position, situating itself at a fixed location in the mid-right soundfield and can be heard clearly as a unique event with the same tonality and amplitude regardless of the vocals and other instruments around it. Through the Minimus 7s, that sound is accentuated, moved forward instead of mid-depth, somewhat unstable in the soundstage and doesn't decay as smoothly (not that it's perfectly smooth on the recording itself).

Overall, the right-left soundstaging is okay most of the time, and the centering of solo voices can be focused (despite the interchannel imbalances in certain frequencies) but the sound was flat with little sense of depth, a "small" sound that's simply lacking in a subjective sense of spatial "volume".

Enough said. Enough heard... Need to reconnect the wires back to my usual speakers now! ;-)

III. Summary

Well, these are inexpensive, almost-all-metal bookshelf speakers with limited frequency range. The woofer is connected full-range with no low-pass filtering, essentially guaranteeing treble irregularities. I would say the "realistic" (pun intended) frequency response is more like 85-20,000Hz allowing for -6dB on the bass end. Putting these speakers against room boundaries might help enforce the bass.

For the size and for the price, these speakers will do a good job in the office waiting room, for background music, and I think would be alright as surround speakers crossed over at 100Hz or thereabouts. "Good enough" for casual computer speakers also; certainly better than cheap plastic stuff. I would not be satisfied for more discerning music listening however. If one were a music producer, I guess these would be fine samples of inexpensive speakers to check how a mix might come across. Consider some of the crossover mods linked above and DSP correction if you want to improve the sound quality.

Remember the speakers measured here are a couple of early "Made in Japan" 40-2030A units so the sound would have evolved over the years depending on which variant you have. I believe there were "Made in Korea" and "Made in Malaysia" versions as well. I don't know if improvements were made over the decades but based on what I hear and see with these two units, I'm not sure if there's anything special about the early "Made in Japan" version. I've seen on forums how some people claim these earlier speakers supposedly sounded better. There's probably an inherent tendency to be sentimental thinking about the "good 'ol days". Another possibility I cannot rule out is whether these sounded much better when they were brand new 40 years ago - before years of "breaking in" :-)!

Like with many things, there will be those who really like the "classic" product (see here and here). These are definitely my idea of what a "work horse" speaker would be like with their tough metal exterior. And probably they will always have their place in history as one of the best-selling speaker models ever.

US$100 for a pair of these at full retail price in 1980 would have been equivalent to around US$300 today given inflation. Looking around, there are clearly many options at US$300 that would more than likely be much superior sounding. Although bigger speakers, consider the ELAC Debut 2.0 B6.2 at US$250, maybe the Paradigm Monitor SE Atom at US$240 as examples. In fact, a small powered JBL Pro 305P Mk II for only US$100 each looks like an excellent deal.

I was curious about others who have measured the Minimus 7 over the years. I can see that MurphyBlaster's and Zilch's measurements also show peaks around 3-4kHz along with higher-frequency irregularities. I see that Zilch's measurements were done with the later 40-2030C version. I can't tell which version was measured by MurphyBlaster. For completeness, here's what they found:

MurphyBlaster measurement.

Zilch measurement (including nearfield tracings and Optimus Pro 7 variant).

Thanks again to linnrd for letting me rummage through the audio gear for interesting items like this to evaluate. :-)

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The other day I ran into Lights' album Skin & Earth Acoustic from 2019 which is a stripped-down version of the original Skin & Earth album from 2017 although there's still a fair amount of processing in those songs (you might have already heard the song "We Were Here" on the radio). If you like female pop songs performed in a singer-songwriter style, this one sounds pretty good on a nice sound system.

As a Bee Gees fan, I was very disappointed by the recent Barry Gibb "& Friends" album Greenfields: The Gibb Brothers Songbook, Vol. 1 (2021, DR6). Seriously, Capitol Records... You have some great talents doing duets of classic songs without dense instrumentation. Instead of focusing on giving the listener clean vocals, we get this dynamically compressed, unnecessarily loud, uneven-sounding album! What were the audio engineers thinking with such incompetence on display?! Were they trying to compete with auto-tuned pop? Was this "Mastered for Amazon Echo Dot" speakers?

Some tracks like "Too Much Heaven" with Alison Krauss sound decent, but others like Brandi Carlile's "Run To Me" was embarrassingly distorted. Likewise, the Dolly Parton duet "Words" is simply unnecessarily muddy - unforgiveable! As much as I would love to listen to this album more and even recommend it to other Bee Gees fans who might be audiophiles, in all honesty I would have difficulty doing so.

With Maurice and Robin gone, and Barry at 74, a collaboration like this is rather unique I think. For 2020/2021, this should really be a pristine-sounding album. Rather, this is an unfortunate example of poor recording/mixing/mastering, and a terrible legacy of how the quality of recordings have fallen over the decades and probably also why consumers don't want to spend good money on music recordings any more. A shame. I hope the raw tracks can be remastered for a better sound, and good luck with Volume 2.

I hope you're enjoying the music, friends. As usual, stay safe...

13 comments:

  1. Interesting test…In the ’80’s I bought two of these along with a Realistic Optimus STA 20 Mini Stereo Receiver as a gift for my father who kept listening to a cheap radio table. That was a little bit better…When he passed away in 1987 I got them back and used them for a while as computer speakers. One of the receiver’s channel quit and I got rid of it, but those speakers were quite solid and without too much audible distortion although I found them distinctly colored. I gave them away finally after some time as handy speakers for various non-hifi purposes.

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    1. Hi Gilles,
      Nice hearing from you, hope you're doing well out East :-).

      I'm sure there are many people with similar stories with these little speakers as part of their life at some point. Given that they're "built like a tank", I'm sure there are still many of these floating around out there. I see at least 40 on eBay with a quick search today of various quality.

      Yup, they'll certainly be good "handy speakers"! In fact, I think the impedance curve would make these a nice "standard" speaker load for doing amplifier measurements as well.

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    2. I'm ok but the Covid threat lurks around of course. We have a 8 PM curfew here to try to bring numbers down...

      If you ever want to test another small vintage speaker, I could suggest the original Paradigm Atom Monitor V1. My girlfriend still has them, at an angle on the floor, hooked to a more recent NAD amplifier and they sound remarkably good. Not much bass of course but wide dispersion and room-filling sound. The room might help here: an L-shaped piece well furnished and with high ceiling and real plaster walls, some of them textured, giving natural sound treatment.

      You can see them here along with the specs:
      https://www.canuckaudiomart.com/details/649362851-paradigm-atom-v1-bookshelf-speakers/

      Too bad we're so far apart... ;-)

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    3. Oh yeah Gilles,
      Classic Canadian design for those Atom v.1 :-).

      Yeah, too bad too far away to have easy access. I think it's fun listening/measuring these old speakers for context around sound quality and for comparison with newer devices. So often we hear all kinds of things but very hard to know how to take comments seriously.

      Arguable, I think measuring the "imperfect" and listening to them teaches us more about audio than incessant reviews of the "state-of-the-art"; especially without any objective context, not even knowing if these very expensive things actually perform to expectation.

      Take care Gilles. Hope the numbers come down soon and the vaccine gets out to the population ASAP.

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  2. Still have mine, but I bought them as I remembered how good the similar models from ADS were. I had heard that some even mounted them in their cars.

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    1. Hi Jim,
      Yeah, I think mounting in the car was what linnrd did for awhile. Certainly with the metal enclosure this would be very protective as people get in and out, and also good against the elements with temperature fluctuations.

      Let me know what you think of the sound these days if you're still listening to them!

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  3. Let me chime in. I have SIX of the things, as switchable extension speakers--two in the kitchen in daily use, two on a porch for clement weather only. The last two are part of an unused surround system. They are ca. 40 years old, and completely trouble-free. They are driven by my main system (Meridian G92 digital preamp/CD player, Quad 405 amp, B&W 802F speakers), and while they certainly have significant limits the sound they produce is musical. If I want to hear the nuances, why I step out of the kitchen into the living room. ;-)

    Their durability is admirable in this age of the throw-away economy.

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    1. Yup Peter,

      Very true... While I would not hold these up as the paragon of fantastic hi-fi sound, there is definitely something to be said about devices that hold their own even 40 years after they were made. That amount of long term value is a rare commodity these days even I suspect with some of the high-priced products here in audiophile-land...

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  4. Soon you'll be able to send them into Erin's Audio Corner for the Klippel NFS measurement. ;)

    https://www.youtube.com/watch?v=hQvXbJJln-s

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    1. Awesome Jason,
      Another Klippel NFS in the wild with results targeted to audiophile hobbyists (Amir and Erin). $100k is quite an investment for measurement gear and the personal commitment that comes along! Somehow, I think there are more interesting speakers than these to measure out there! :-)

      Let the more objective audio revolution continue! The more educated the audiophile hobby can be, the better...

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    2. I totally agree! You might enjoy some of the other guests on the podcast too. ;)

      More coming!

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  5. Some years ago i used to collect small speakers as they are inexpensive and it was fun to hook them up to an A/B switch for blind listening tests. The metal minumus were ok but 'congested' and 'artificial' sounding and distorted terribly at volumes. The wood cabinet 7W model sounded better, possibly due to the lack of cabinet resonance? The little Akai SM studio monitors were incredibly dynamic but the most musical and accurate were the KLH a/v monitors. Solid wood cabs, removable foam grills and a very pleasurable sound. Rear port and amazing bass for a 4.5" woofer. This hobby can be fun without $40,000 turntables and $100,000 speakers, i like how your blog covers equipment for the rest of us. I bought the topping DAC based on your experience and couldn't be happier. thanks!

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    1. I got a pair in 1980, and mated them by chance with the NAD 3020. It blew everything costing several times more away. Vinyl was of course the only decent source back then. Either you ears are bad or your amplification were bad. Contrary to your opinion, the M7's sounded HUGE and loud, quick, and dynamic. And the imaging was magical. I shamelessly took them to a high end store and auditioned them with even more expensive amps. The M7's imaging made the big Magnepans sound bad. Even the salesman was impressed. Everyone in my dorm were amazed Perhaps the NAD 3020 had something to do with the magic, but fact is...the M7's are legends. Little did I know back then that I owned 2 future audio classics. I still have the M7's, but I stupidly traded my 3020 for a lousy microwave oven.

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