• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Minimus 7 Loudspeakers - Measurements

It is unfortunate that Zilch's old posts have images that no longer work, sure
would be nice to get them back, perhaps with the Wayback machine.
EDIT: Just noticed that they still work as attachments just the inline links are broken.
Sure would be nice to fix those inline images.

Here is Dennis Murphy's measurement of the stock M7 in case anyone wants to
try DSP EQ, add a shelf for about 3dB of baffle step also:
http://murphyblaster.com/content.php?f=minimus.html
 
Last edited:
Well I FINALLY ordered my BoM for the Optimus Pro77's I've had since 2019. Can't wait to hear the difference, as I listen to these speakers daily. I also have a pair of Realistic Minimus-77 that I have to re-foam the drivers on.
 
Pete B said:
I posted the woofer parameters in another thread where I compared it to the MCM woofer.
Also at CSP.
Here's the thread on AK where I measure the woofers in the box:
https://audiokarma.org/forums/index.php?threads/minimus-7-with-mcm-1853-woofer-bargain-mini.755200/
And here's the CSP thread where I measure the original M7 woofer in free air:
https://community.classicspeakerpages.net/topic/4679-radio-shack-minimus-7-measurements/

The woofer would not work well in an open baffle for full range bass due to the low volume
displacement (VD). A bunch of them for midrange should work. But the question is why the
M7 woofer? They are old and a cheap design, Zaph has measured many excellent drivers on
his page.
Click to expand...
Thank you Pete. I was just considering using the M7 woofer and tweeter on an open baffle for frequencies above 200Hz. Frequencies below that would be handled by my Optimus-21 10” woofer. So I was basically just going to build a 200Hz two way passive crossover to split between the 10” woofer and the M7. Any thoughts on this?
 
I continue to be stunned by the unbelievable amount of attention that these speakers garner. For camping trips, around a deck/patio and maybe in a cheap office system, they are fine at low volume. I've relegated my one pair to the attic, I'm afraid. I do use a Pro-x88 as a speaker for my Hallicrafters SX-110, with a Pro-x7 at the ready, in reserve. I do think it is fantastic so many of you are having fun with these!
 
There are two pair at my house. Both are the walnut version. One pair is the original series with the smooth metal tweeter baffle. I gave those to my son and they are powered by a Sansui G-3500 in his room. The other pair is the second series with the plastic tweeter baffle that has the rings. I use that pair as my rear surround speakers until I can refoam my ProLX5II. They’re good enough for what they are. No mods. I can’t justify spending a lot of time or money or effort to try and improve the sound of them in the original cabinets. I feel like improving them would require building bigger cabinets in order to have more internal volume to fit a more elaborate crossover or even a different design cabinet to make them more efficient. Once I refoam my ProLX5II and can use them as my rear surround speakers then I’ll experiment with the M7 drivers. I’ve always thought it would be cool to build some small back horn loaded speakers out of some M7. Like a “scoop” cabinet where the horn mouth is at the bottom. Probably horn load the tweeter too. Or maybe some transmission lines.
 
AudioGMan said:
Thank you Pete. I was just considering using the M7 woofer and tweeter on an open baffle for frequencies above 200Hz. Frequencies below that would be handled by my Optimus-21 10” woofer. So I was basically just going to build a 200Hz two way passive crossover to split between the 10” woofer and the M7. Any thoughts on this?
Click to expand...


Probably not a great idea for a few reasons. Dipole "Peaking" is one, where you have to account for a large boost in the lower mids and lack of excursion for the woofer.
 
kevintomb said:
Probably not a great idea for a few reasons. Dipole "Peaking" is one, where you have to account for a large boost in the lower mids and lack of excursion for the woofer.
Click to expand...
I don’t quite follow what you mean. If the 4”woofer from the M7 is passively crossed over with a high pass 12dB/octave slope I don’t think there would be much excursion. Currently using M7 as my rear surround speakers crossed over at 110Hz @12dB/octave there’s hardly any excursion.
 
AudioGMan said:
I don’t quite follow what you mean. If the 4”woofer from the M7 is passively crossed over with a high pass 12dB/octave slope I don’t think there would be much excursion. Currently using M7 as my rear surround speakers crossed over at 110Hz @12dB/octave there’s hardly any excursion.
Click to expand...


You are right of course. I misread part of what you said. ...

You still would have to contend with "Dipole Peaking", which is about a 6 db boost at the frequency where the front and back waves come together "In phase", and below that you would have the "Dipole Cancellation" where they go out of phase and lose most of the bass. (which would not matter at all in your case, with them being High passed)
 
kevintomb said:
You are right of course. I misread part of what you said. ...

You still would have to contend with "Dipole Peaking", which is about a 6 db boost at the frequency where the front and back waves come together "In phase", and below that you would have the "Dipole Cancellation" where they go out of phase and lose most of the bass. (which would not matter at all in your case, with them being High passed)
Click to expand...
Oh I gotcha. Thank you for pointing that out. I suppose I could remedy the peak using an equalizer. I’ve done the math regarding the width of the baffle so the 4” woofer can get down to 200Hz before cancellation. And it will be slightly off center to help smooth out the response.
 
Wow, that was quick. Ordered from Parts Express on Monday night using the cheapest shipping and the package came this morning already. Time to make the circuit board and warm up the soldering station.
 
Well now, I picked up a pair of Optimus Pro 77 off of Ebay. They looked good in the photos and the seller said they were in excellent condition. Sadly what arrived was very poorly packaged and one of the speakers was thrashed. The grill crushed in and even on of the edges was broken from a hard impact. Worse yet was that after pulling off the grill to put it back to normal I noticed that someone had done a surround on the woofer and the tweeter face plate had been so over tightened that an ear was broken. I payed little more than $40.00 for the pair with shipping so not a major loss. Contacted the seller and provided photos, he response was sorry and a full refund! So now I have a pair of the 77s that I intend to do the Zilch mod on. I did the mod on the pair of Optimus Pro 7 that I did the cross over on and the difference was nothing short of miraculous in terms of balance and imaging. Will report back soon when the parts come.
 
Didn't upload picks of the damaged speaker as I really see little value in it for the users here. I will take a pic or two and upload the finished Xovers in sitsu once they are done. No calibrated mic so will not be sweeping them. But comparing one of the modified Optimus pro 7 speakers to the stock was a stunning difference. Both in terms of clarity and imaging when the pair were completed. Besides that, they are POS radio shack speakers and an hour plus $35.00 in materials is about as much as I am gonna put into them. Will post up later.
 
Hello. So, i saw locally a pair of Optimus Pro-X44AV which are basically the same as Minimus-7, but ported set. I thought it would be a great "cat-proof" set of speakers so i bought them for almost nothing.
Listened to them and i don't quite understand the hype of those Minimus/Optimus/rca miniature bookshelf speakers. I thought they sound saturated in the mid-high/highs or that frequency range has too much presence overall. So i opened up the speakers and realized that only the tweeter was filtered. The Minimus-7 mod here on AK could have been an option, but i wanted a really cheap mod for what i think is a really cheap set of speakers anyway. Salvaging parts if possible.. and the minimum amount of components possible to fill-in that already very small box.. So i went 1st-order, here is what i've done :
x44av_crossover_shem.jpg
Only the coils that i needed to buy from Digikey. Here is the part list i used in case anyone is interested in trying the mod :
Per speaker :
-1x 680uH (226milli-ohm), digikey : https://www.digikey.ca/en/products/detail/murata-power-solutions-inc/1468422C/5798129
-1x 3.6uF non-polar capacitor
-1x 3.3ohm 5watt (ceramic) resistor

The 3.6uF cap i used is a salvaged 3.3uF NP axial electrolytic 50volt, that i treated/reformed and that are measuring exactly 3.6uF (both of them).
The 3.3ohm 5watt i already had them. The range of the resistor that i would recommend is 2.7ohm (for a bit more high-end presence) to 3.9ohm (for a bit less presence).

It all fits nicely on the plastic backplate itself :
x44av_example_install.jpg

How it sounds? Way better. Well, its still a tiny speaker and won't do miracles, but is not weird sounding and all over the place in the mid-highs as it was before. It sounds.. more believable. So to me that fixed it!
Just a reminder in case someone would be interested in that modding option, 1st-order crossover is not filtering as fast. So do not drive them too hard to not put the tweeter at risk.
 
A quick follow up of my previous post, I have been listening to the X44AVs for the week and there is 2 things that i said that i would like to revisit :

1st : i said that I thought the speakers were very cheap... Well in its stock form they do really sound weird and cheap (and was doubtful that i could ever like them), but once they have been modified they become fascinating and its a real pleasure listening to them, long term. Sure they wont shake the floor, but they got their own thing..

2nd : I recommended a resistor range for the tweeter that I am updating to :
-3.3ohm (more high-end presence)
-3.9ohm (moderate)
-4.7ohm (lesser high-end presence)

3.9ohm is my new default.
x44av_crossover_shem.jpg

Thats it. Going back to the X44AVs. Very sweet, surprising and fascinating speakers indeed!
 
Very excited here to add the PZ2.1 mod to these cute little M7W's! PE components in the mail! Should be fun and much less back breaking than the crossover refurb of the beasts behind them!

Mini7 QSL.jpg
 
SHK said:
Hello. So, i saw locally a pair of Optimus Pro-X44AV which are basically the same as Minimus-7, but ported set. I thought it would be a great "cat-proof" set of speakers so i bought them for almost nothing.
Listened to them and i don't quite understand the hype of those Minimus/Optimus/rca miniature bookshelf speakers. I thought they sound saturated in the mid-high/highs or that frequency range has too much presence overall. So i opened up the speakers and realized that only the tweeter was filtered. The Minimus-7 mod here on AK could have been an option, but i wanted a really cheap mod for what i think is a really cheap set of speakers anyway. Salvaging parts if possible.. and the minimum amount of components possible to fill-in that already very small box.. So i went 1st-order, here is what i've done :
View attachment 2832507
Only the coils that i needed to buy from Digikey. Here is the part list i used in case anyone is interested in trying the mod :
Per speaker :
-1x 680uH (226milli-ohm), digikey : https://www.digikey.ca/en/products/detail/murata-power-solutions-inc/1468422C/5798129
-1x 3.6uF non-polar capacitor
-1x 3.3ohm 5watt (ceramic) resistor

The 3.6uF cap i used is a salvaged 3.3uF NP axial electrolytic 50volt, that i treated/reformed and that are measuring exactly 3.6uF (both of them).
The 3.3ohm 5watt i already had them. The range of the resistor that i would recommend is 2.7ohm (for a bit more high-end presence) to 3.9ohm (for a bit less presence).

It all fits nicely on the plastic backplate itself :
View attachment 2832522

How it sounds? Way better. Well, its still a tiny speaker and won't do miracles, but is not weird sounding and all over the place in the mid-highs as it was before. It sounds.. more believable. So to me that fixed it!
Just a reminder in case someone would be interested in that modding option, 1st-order crossover is not filtering as fast. So do not drive them too hard to not put the tweeter at risk.
Click to expand...

So so you think your mods are applicable to the Minimus 7?
 
jimreeves said:
Very excited here to add the PZ2.1 mod to these cute little M7W's! PE components in the mail! Should be fun and much less back breaking than the crossover refurb of the beasts behind them!

View attachment 2848623
Click to expand...

@jimreeves
I offered some of these component holders for free (in pink, trying to use up pink PLA) on here and
now I can't find the thread. This is another thread with a picture of them but in black:
https://audiokarma.org/forums/index...hos-printing-what.857566/page-4#post-12565738

index.php



I wonder if a mod deleted it? Is there a rule that it has to be in Barter town even if for free?
I did ask for shipping

They fit the metal box, but should probably also work in the wood one. Everything fits perfectly
but some of the lead holes (maybe all) need to be opened up with a 1/16" bit - easy.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom