Minimus 7 Loudspeakers - Measurements

[Stuart Pedaso]

The stock woofer is 8Ω. That Dynavox is 6Ω.

Are you sure it actually played deeper, not just played louder due to the changes to impedance drop, and thus altered the crossover point?

Also has higher sensitivity at claimed 88dB (or 87.5dB -- also cited on the same MCM spec sheet). I think Pete measured 85.4dB for the stock woofer.

Still, it's an interesting looking driver at that price. Full-range design. Could be fun to mount one in an M-7 cabinet with tweeter and crossover disconnected. Then see if it performs close to what its FR chart suggests.

 

[kevintomb]

Welcome to AK @bknop . Interesting 1st post!

The stock woofer is 8Ω. That Dynavox is 6Ω.

Are you sure it actually played deeper, not just played louder due to the changes to impedance drop, and thus altered the crossover point?

Also, I don't like the idea of a whizzer cone on my mid/woofer if there is an actual tweeter.

Deeper......
It might....It has a much lower resonance frequency, but obviously a much larger Vas, but lower Qts.

I will model it when I wake up more, but just from a guess the box resonant frequency might be a decent bit lower. Just got a new comp and old one with all my programs is not hooked up yet....

The stock woofer is about 128 Hz Fs and this dynavox about 53 Hz

 

[djnagle]

Turns out I had some 2.7Ω resistors and figured that was close enough. So, I have managed to carry this project through.

Here's the crossover all assembled...
View attachment 1661062

Here's them all polished up....
View attachment 1661065

Here's the crossover installed....
View attachment 1661068

gasket installed and fiberglass bats stuffed in..
View attachment 1661066

Asslembled...
View attachment 1661061

With grills....
View attachment 1661063

Compared to a stock pair of white ones (Korean build)
View attachment 1661060

A/B'ing them...
View attachment 1661067

Beautiful job on the polish. After I did that to the 11s I plan on doing to the 7s but life got in the way.

 

[Stuart Pedaso]

The stock woofer is about 128 Hz Fs and this dynavox about 53 Hz

That's the highest FS I've seen reported for the stock Minimus-7 woofer. Do you recall the source?

Zilch measured 70.348 Hz, as reported in post #62 of this thread.

Pete B measured a Malaysian era 1218 woofer and reported 62.5 Hz in a post at classicspeakerpages.net

Member IG81 in diyaudio.com stated measuring "FS~49Hz" in "most" stock woofers.

These all reference the stock model 1218 woofer found in all die-cast cabinet Realistic brand Minimus-7. One could imagine some small manufacturing variance between even brand new woofers at the factory. And probably more so after years of different use and environmental exposures. But FS of 128 Hz is quite a departure from the grouping I'm finding from measurements in the field.

Is it possible this could be in reference to one of the Optimus/RCA variants from the post Realistic Minimus era?

 

[kevintomb]

That's the highest FS I've seen reported for the stock Minimus-7 woofer. Do you recall the source?

Zilch measured 70.348 Hz, as reported in post #62 of this thread.

Pete B measured a Malaysian era 1218 woofer and reported 62.5 Hz in a post at classicspeakerpages.net

Member IG81 in diyaudio.com stated measuring "FS~49Hz" in "most" stock woofers.

These all reference the stock model 1218 woofer found in all die-cast cabinet Realistic brand Minimus-7. One could imagine some small manufacturing variance between even brand new woofers at the factory. And probably more so after years of different use and environmental exposures. But FS of 128 Hz is quite a departure from the grouping I'm finding from measurements in the field.

Is it possible this could be in reference to one of the Optimus/RCA variants from the post Realistic Minimus era?

Now I am not sure...
I found it on this forum on one of the posts a bit further up....15 posts or so above this on.....Post #843..... SEPT 16..Member "Mazza" had posted T/S parameters...now im not sure....??

But you are correct I would imagine. 128 Hz Seems quite High, as in box it would raise even a bit more......

 

[Stuart Pedaso]

Now I am not sure...
I found it on this forum on one of the posts a bit further up....15 posts or so above this on.....Post #843.....

Thanks. Don't know how I missed that. Though I do vaguely recall the calibrated tape rolls for added mass. Must've been one of those nights I got off to bed with keyboard face ...

I do like this picture:


Now THAT'S added mass!

 

[bknop]

Deeper......
It might....It has a much lower resonance frequency, but obviously a much larger Vas, but lower Qts.

I will model it when I wake up more, but just from a guess the box resonant frequency might be a decent bit lower. Just got a new comp and old one with all my programs is not hooked up yet....

The stock woofer is about 128 Hz Fs and this dynavox about 53 Hz

There seems to be some variations of the minimus woofers on their ts parameters. I have an one from the A version that is around 60Hz, and another from a C version that's around 70Hz . Some people on the net found theirs to be fs 49Hz and Qts .31.

 

[Pete B]

Thanks. Don't know how I missed that. Though I do vaguely recall the calibrated tape rolls for added mass. Must've been one of those nights I got off to bed with keyboard face ...

I do like this picture:
View attachment 1745717

Now THAT'S added mass!

I hope that this is a joke, you really do not want to move the rest position
of the cone/voice coil in order to keep the soft parts in their nominal center
position. I don't add too much weight for this reason and I test in the
vertical position rather than as shown.

 

[Mazza]

I hope that this is a joke, you really do not want to move the rest position
of the cone/voice coil in order to keep the soft parts in their nominal center
position.

Hi Pete and fellow Minimus appreciators,
I use the DATS V2 that will prompt if the added mass is too little. That picture is of the Minimus 77 woofer under test.

I'll pull out both 7's and 77's woofers tonight and measure with as little added mass as DATS will allow. I only did one of each previously.

Will report back on measurements and actual added mass used.

If my previous measurements have been negatively affected by my amateurish over application of mass I do apologise for any inconvenience or confusion caused.

 

[Mazza]

Added mass...…

 

[Pete B]

I learned the hard way by experimenting, the more people who measure the better,
thanks for posting.

 

[Pete B]

But you are correct I would imagine. 128 Hz Seems quite High, as in box it would raise even a bit more......

128 Hz is high even for in box, I seem to remember 110 - 120 Hz in box.

 

[Mazza]

Thanks Pete,
That's very kind of you to say. Very much appreciate what you have done here for us as the P in the PZ.

I did refoam my 7's woofers - I wonder if the new foams substantially changed the Fs?

 

[Stuart Pedaso]

I hope that this is a joke, you really do not want to move the rest position
of the cone/voice coil in order to keep the soft parts in their nominal center position.

When I see that pic I imagine a voice coil pushed right down against the backplate.
Mazza's a braver man than I'll ever be ...

 

[Stuart Pedaso]

Seriously though. I've only taken measurements rarely and done it the hard way -- suspended the woofer with wire vertically in an open frame, and then use a 1cu.ft. box without added mass. So what is a good material to use for added mass that doesn't tend to bounce about?

 

[Mazza]

I like the roll of tape method - the tacky side against the cone helps avoid bounce and can be stacked to get a variety of weights.

Some other ideas include magnets that stick together either side of a larger woofer cone or play dough pressed in evenly around the dust cap cone junction.

 

[Pete B]

Seriously though. I've only taken measurements rarely and done it the hard way -- suspended the woofer with wire vertically in an open frame, and then use a 1cu.ft. box without added mass. So what is a good material to use for added mass that doesn't tend to bounce about?

I've used nickels and quarters for years.
I use 15 to 25g on 8 - 10" woofers, 10 - 15g on smaller woofers.
Don't remember what I used on the M7 woofer but I usually report it, probably about 5g.
I use Mortite or poster tack to stick them on but they usually fall off by the end of the run.
As long as you get to about 2X Fs with the weight still on the reading is good.

I just started using the black sealant from PE on larger woofers where I can put the
weights on the back just in case it leaves a small mark - it is very sticky.
The black stuff works perfectly.

 

[Mazza]

Actually the foams were for the 77's. the 7's are original!

First try at 10 grams DATS reports this....



second at 27 grams is a pass.





Attached are woofer reports from DATS - both of my 7's woofers have better that 100hz fs.

 

[Mazza]

A Comparison - Minimus 7 vs Teac LS-X8

So I picked up these Teac and have them in my stash to try the PZ 2.1 in them. If that doesn't work I figure I'll measure and tweak till they do.

These speakers are visually and in terms of construction very, very similar to the Minimus 7's.

The Teac have a 60-ish hz fs interestingly enough....

 

[rothwellaudio]

Seriously though. I've only taken measurements rarely and done it the hard way -- suspended the woofer with wire vertically in an open frame, and then use a 1cu.ft. box without added mass. So what is a good material to use for added mass that doesn't tend to bounce about?

The woodwork involved in making a box for test box method puts me off. Probably puts a lot of people off, but it's probably the best way to do it.

I like the roll of tape method - the tacky side against the cone helps avoid bounce and can be stacked to get a variety of weights. Some other ideas include magnets that stick together either side of a larger woofer cone or play dough pressed in evenly around the dust cap cone junction.

I've used nickels and quarters for years.
I use 15 to 25g on 8 - 10" woofers, 10 - 15g on smaller woofers.
Don't remember what I used on the M7 woofer but I usually report it, probably about 5g.
I use Mortite or poster tack to stick them on but they usually fall off by the end of the run.

I'm still trying to find a method of attaching weights that I'm happy with. Yes, bouncing around and falling off are the problems encountered. I've damaged (slightly) paper cones by using double-sided sticky tape that didn't peel off cleanly. The search continues.

Btw, I suspect that any "magic" about the sound of Minimus speakers is more to do with the very rigid cabinet than the drivers/crossovers. That's just speculation though.