Minimus 7 Loudspeakers - Measurements

[lolwtfbbq]

I think I figured out how to fit everything in the Optimus Pro x44av.

I mocked up the layout:

With this configuration the crossover fits perfectly on the top of the cabinet.
The big coil will go on the back of the cabinet perpendicular to the rest of the components, (note the coil layout.) Same orientation, just 90deg off axis from the other coil.

I have 2 more questions though;
How hot do those resistors get? I mean I know they can dissipate up to 10w before they begin to fail, but wouldn't the drivers blow before the resistors see that much power? I'm wondering if I can mount them on a plastic surface that will velcro to the top or if they should just be epoxied to the cabinet.
The other question is if the small inductor will affect the tweeter being so close to it. The tweeter magnet won't affect the coil, I know. But will the ferrous material in the tweeter significantly affect the inductance of the .4mh coil? I'm assuming if it does then it's negligible because it looks like in most of the builds in this thread, the crossovers coils go right behind unshielded woofers and that doesn't seem to be an issue.

 

[Pete B]

The 10W resistors are overkill for this small speaker, normally they should be
elevated for air flow but the aluminum makes a good heatsink. I'd glue them
with Goop because it is strong but can be removed if needed on the other
hand epoxy should last forever, so your choice. Epoxy is probably better for
the big heavy inductor.
If you are using stock drivers the tweeter is so shallow that there is probably
at least 2 inches to the inductor which is fine. The woofer probably has 1" or more
clearance which should also be fine.

The MCM woofer is deep and shielded so it does hit the large inductor in some
applications.

Drop your mock up in the box and mount the woofer then you can look in the tweeter
hole to check the clearance.

 

[lolwtfbbq]

The 10W resistors are overkill for this small speaker, normally they should be
elevated for air flow but the aluminum makes a good heatsink. I'd glue them
with Goop because it is strong but can be removed if needed on the other
hand epoxy should last forever, so your choice. Epoxy is probably better for
the big heavy inductor.
If you are using stock drivers the tweeter is so shallow that there is probably
at least 2 inches to the inductor which is fine. The woofer probably has 1" or more
clearance which should also be fine.

The MCM woofer is deep and shielded so it does hit the large inductor in some
applications.

Drop your mock up in the box and mount the woofer then you can look in the tweeter
hole to check the clearance.

I did before I mocked it up. The shielded woofer just barely clears the large inductor mounts.
The rest of the crossover will clear the tweeter with a bit of room to spare.

 

[lolwtfbbq]

I wired everything up and tested it out.

It sounded like crap. I didn't expect much with the drivers outside the enclosure but I was NOT expecting so much distortion.
...then I realized my poor SA-150 was turned up almost all the way, trying it's hardest to dump all 1.8w that it can muster into this speaker.
I tried again with my SMSL SA-50 and it seemed fine so I decided to do ahead and glue down the parts. Most of the components are glued to a cut out piece of CD jewel case and stuck to the top with Velcro. The 1.0mh coil is gorilla glued to the back of the enclosure.

I moved on to swapping the spring clips with banana jacks. I used pliers to pull the terminals through the plate (towards the in-side of the plate.) Then I pulled the spring clips out with pliers and they popped right out by pushing them down further towards the spring than they were meant to go. Finally I snapped off all the interior plastic posts. I drilled 2 holes for the banana jack posts, so I would have pilot holes for when I had to drill through the epoxy. Then covered every opening on the back side of the plate with sticky-tack; that gummy stuff you hang posters with.

I flipped the plate over and filled where the spring clips were with 5 minute epoxy.

That's all for now. I'll drill through the epoxy, install the banana jack and button it all up tomorrow.

 

[lolwtfbbq]

As promised, I installed the banana jacks.

I stuffed it with some polyfill. You can't have too much polyfill right? (I'm joking, of course you can)

and buttoned it all up

You can see in the last pic where someone had the bright idea of drilling a hole in the back of the cabinet. I assume it was to put a pot in to attenuate the tweeter but the rest of the circuitry was untouched, so who knows. I just taped the inside and filled it with epoxy.

Curiously, it's mate was completely untouched. It even had the original polyfill whereas the cabinet I just finished had all the polyfill wadded and wrapped up into a ball and just tossed into the cabinet.

Before pic of completed speaker for comparison:

 

[RTally]

As promised, I installed the banana jacks.

You can see in the last pic where someone had the bright idea of drilling a hole in the back of the cabinet. I assume it was to put a pot in to attenuate the tweeter but the rest of the circuitry was untouched, so who knows. I just taped the inside and filled it with epoxy.

That speaker is not a Minimus 7. The label on the back shows it is an Optimus PRO X44AV. I suspected as much when I saw the separate, screwed-on terminal plate and the port on the back. The Minimus 7 is a totally sealed speaker. The Optimus Pro you have has a ported cabinet. The hole in the back is supposed to be there.

I have no idea if it is a good idea to convert an Optimus Pro into a Minimus 7 as you did here. I have no doubt that a search of AK would produce information or a discussion on such a mod.

I look forward to hearing about your listening impressions.

 

[niles300z]

Ok, so tweeter change a cap. And for the bass what pull the choke? I can't read through 18 pages.

 

[lolwtfbbq]

That speaker is not a Minimus 7. The label on the back shows it is an Optimus PRO X44AV. I suspected as much when I saw the separate, screwed-on terminal plate and the port on the back. The Minimus 7 is a totally sealed speaker. The Optimus Pro you have has a ported cabinet. The hole in the back is supposed to be there.

I have no idea if it is a good idea to convert an Optimus Pro into a Minimus 7 as you did here. I have no doubt that a search of AK would produce information or a discussion on such a mod.

I look forward to hearing about your listening impressions.

I am aware and have mentioned a couple times that the speaker is a Pro X44AV (like at the top of this page). I purposely did this one first because I figured it would be a good thread contribution instead of just another Minimus 7 mod. I only wish that I had proper equipment to take measurements before and after.

Look above the port at that white/clear spot. That is the hole that I epoxied, and that is epoxy in the hole.
The mate to this speaker does not have that hole, because nobody drilled it out.
The port was untouched. I don't plan on converting it, but if I did I'm sure it would sound very much like a Minimus 7, since everything about the speaker is pretty much the same.

I did A/B the modified and unmodified Optimus and they're definitely different. Bass extension is surprisingly much lower than it was previously, but I suspect that probably has more to do with the polyfill I added than the crossover.
I know that originally Pete (i think) mentioned that the tweeter could sound more sibilant but I find it rolls off quite nicely now, and sounds very pleasant.

Overall the speakers don't sound any more clear or detailed than they did before. Maybe the bass is less wooly than it was, and that mid to high transition is much nicer but I'm not able to make out any more details than I was before. I'll post a bunch more about my listening impressions when I finish the other one and can give you a full stereo before and after.

 

[lolwtfbbq]

Both speakers done!
Second crossover went much faster now that I didn't have to figure out things like where/how to mount, and having soldered everything once already it was a breeze to do it again. One slight change I made was to move the speaker's negative wires from the binding post, directly to the negative of the 2uf cap in the middle of the front side of the crossover there.

Functionally the circuit is the same but the tweeter's negative wire was a little harder to connect with the woofer in the way. The new configuration made stuffing the cabinet easier too.

Now for listening opinions:
I listened for a couple hours to them just by themselves powered by my SMSL SA-50 at various volumes. Then I compared them to a stock pair of good condition Minimus 7, followed by a pair of Minimus 77's then back and forth again with the Minimus 7's while using my Hifiman HE4XX as a reference point.
I tried a couple other amps for giggles and it made a bit of a difference, but honestly the woofer starts to break up pretty badly when you turn it up on any amp.

The x44av definitely sounds different than it did before. Bass is not as boomy, and you can definitely tell that the woofer has been reigned in, as expected.
One interesting thing to note though is that the x44av have a considerable amount of bass extension over the Minimus 7's. So much so that I'm considering trying out porting a pair of Minimus 7 or 77's or maybe adding a passive radiator.
The tweeter is way more tame than it was too. I think there was a real harsh peak following a null right around the crossover frequency before but now it's completely gone and it's actually difficult to hear where they crossover.
The speaker takes a LOT more power to drive and this is especially obvious when A/B them with the Minimus 7's.
Overall they sound pretty flat, but not detailed / revealing like I hoped they would be. They almost sound veiled or muted. They're a little more boring now; lacking that "rock and roll scoop" / cheap speaker sound. Imaging is a little better but not considerably.
I was hoping for a little bit more out of them. They're definitely not as 'fun' as I was expecting them to be, but they're certainly not bad.
The crossover upgrade is absolutely an improvement and I plan to do it again, but the price/performance of the project wasn't quite the value-add I was expecting, considering I spent 3x on crossover parts compared to what I paid for the speakers. Still for $40ish all in for the pair they're tough to beat. I'd still recommend them to friends looking for an affordable of durable speakers.

They're great little speakers. They're going to be perfect for my desk at work and I'll toss another pair out on my deck this summer after it's built.

This was certainly a fun project and I definitely recommend it to anyone interested in modifying speakers. I think after this I'm going to pick up a Dayton DATS v2 and OmniMIC V2 and start playing around with driver upgrades for these speakers.

 

[Pete B]

I wish I had the ability to design a PCB with onboard banana plugs for the mod.

https://audiokarma.org/forums/index...2-mod-diy-circuit-board-by-pete-basel.750334/

 

[Pete B]

Here is a response of the Minimus 77 w/ PZ2.1 crossover with and without the perforated metal grille. Keep the grille on, no ill effect.

I don't own a pair of Minimus 77 s but this post is making me want to try the mod on a pair.

 

[dogwan]

First time posting in this thread. I've been intrigued with trying the modded 7's.

A while back I was in a thrift and found a cheap pair of 7's that looked to be a fairly desirable early Japan model w/ the flat plate tweeters ($30). Only when I got them home did I realize they had originally been silver and painted black. Also, the aluminum grills had been pushed in just enough to dent the tweeters and touch the woofer surrounds. Once I got that sorted I realized the surround on one woofer had a tear from vibrating against the grill (for how long?).

Then a couple weeks after picking those up I found another pair of later Japan 7's with the ring faced tweeters ($5) at a garage sale. Again in black. And again, when I got them home I realized they were originally white and had been rattle-canned black. When I played them one of the woofers had very bad output. Quickly realized it had been subjected to water damage that ruined the driver (tweeter was safe though) and rusted the now steel grill. But! I managed to peel the surruound off the rusted woofer and use it to repair the other one. Now I had an extra woofer and an extra pair of tweeters.

Then, another couple weeks after that I answered a CL add for a mint pair of white Korean made 7's ($10). Absolutely mint. The guy had only used them at a trade show for a couple of days for sound reinforcement at his booth. They had been boxed up ever since.

So now here I am with all these extra parts. I tossed the cabs for the 2nd pair as I didn't want to deal with the smelly insulation and the cabs for the 1st pair had the extra tapped mounting hole with the larger crossover plate and larger inductor. Keeping the 3rd pair (white) stock for comparison's sake and going to build the PZ2.1 mod. Will order enough parts to do the mod on the white pair later. For the first pair to mod I decided to strip the paint off and go for a polished aluminum look. The aluminum grills look pretty cool too. Here's pics of the cabs stripped. Haven't started polishing yet.

 

[TPettenati]

Well worth it but hard to find. Overall they were less popular, had a shorter product life, and many were tossed when the foam deteriorated.
But can be picked up cheap in repairable condition. I paid $10 for a pair, needing refoamed.

I'll see if I can find some measurements I did, M7 versus M77. Both unmodded. The M77 definitely dug a little deeper. ISTR the M7 starting to roll off at 200Hz and the M77 at 150Hz.

I don't own a pair of Minimus 77 s but this post is making me want to try the mod on a pair.

 

[BAWSME]

First time posting in this thread. I've been intrigued with trying the modded 7's.

A while back I was in a thrift and found a cheap pair of 7's that looked to be a fairly desirable early Japan model w/ the flat plate tweeters ($30). Only when I got them home did I realize they had originally been silver and painted black. Also, the aluminum grills had been pushed in just enough to dent the tweeters and touch the woofer surrounds. Once I got that sorted I realized the surround on one woofer had a tear from vibrating against the grill (for how long?).

Then a couple weeks after picking those up I found another pair of later Japan 7's with the ring faced tweeters ($5) at a garage sale. Again in black. And again, when I got them home I realized they were originally white and had been rattle-canned black. When I played them one of the woofers had very bad output. Quickly realized it had been subjected to water damage that ruined the driver (tweeter was safe though) and rusted the now steel grill. But! I managed to peel the surruound off the rusted woofer and use it to repair the other one. Now I had an extra woofer and an extra pair of tweeters.

Then, another couple weeks after that I answered a CL add for a mint pair of white Korean made 7's ($10). Absolutely mint. The guy had only used them at a trade show for a couple of days for sound reinforcement at his booth. They had been boxed up ever since.

So now here I am with all these extra parts. I tossed the cabs for the 2nd pair as I didn't want to deal with the smelly insulation and the cabs for the 1st pair had the extra tapped mounting hole with the larger crossover plate and larger inductor. Keeping the 3rd pair (white) stock for comparison's sake and going to build the PZ2.1 mod. Will order enough parts to do the mod on the white pair later. For the first pair to mod I decided to strip the paint off and go for a polished aluminum look. The aluminum grills look pretty cool too. Here's pics of the cabs stripped. Haven't started polishing yet.

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Hi. Those look great! I just picked up a pair today and want to do the mod also. I would also like to strip the cabinets to the aluminum finish. How did you remove the paint?

 

[dogwan]

Hi. Those look great! I just picked up a pair today and want to do the mod also. I would also like to strip the cabinets to the aluminum finish. How did you remove the paint?

I used Citristrip.

 

[ericj]

That is an interesting way to do them.

Among my various 7's is a black one that has been severely weathered. Been procrastinating re-painting it. Blacks are a whole field of art, you know. Short of straining to tell the difference between Stuart Semple's Black 2.0 and Vantablack, there's a lot of variance in blacks.

 

[pliskin]

I wired everything up and tested it out.

It sounded like crap. I didn't expect much with the drivers outside the enclosure but I was NOT expecting so much distortion.
...then I realized my poor SA-150 was turned up almost all the way, trying it's hardest to dump all 1.8w that it can muster into this speaker.
I tried again with my SMSL SA-50 and it seemed fine so I decided to do ahead and glue down the parts. Most of the components are glued to a cut out piece of CD jewel case and stuck to the top with Velcro. The 1.0mh coil is gorilla glued to the back of the enclosure.

I moved on to swapping the spring clips with banana jacks. I used pliers to pull the terminals through the plate (towards the in-side of the plate.) Then I pulled the spring clips out with pliers and they popped right out by pushing them down further towards the spring than they were meant to go. Finally I snapped off all the interior plastic posts. I drilled 2 holes for the banana jack posts, so I would have pilot holes for when I had to drill through the epoxy. Then covered every opening on the back side of the plate with sticky-tack; that gummy stuff you hang posters with.

I flipped the plate over and filled where the spring clips were with 5 minute epoxy.

That's all for now. I'll drill through the epoxy, install the banana jack and button it all up tomorrow.

On a side note I think I have the exact same black steamer trunk you are working on there.

 

[Hofy]

I just picked up a pair of Optimus Pro 77 that are like new with woofer surrounds intact for $5. Will this crosseover mod work for them too?

 

[Mazza]

I believe the Pro 77 are the same as the Minimus 77 by the look of their drivers.

If that is the case the 77 has had the PZ2.1 mod done earlier in this thread and measurements confirm it works well. I've done the Minimus 77 and really like them. Needed new foams.

 

[RickeyM]

First, since the PZ-2.1 x-o seems to work on the Minimus 77's as well, I'm going to try it on mine. Secondly, RS has a penchant for using enclosures too small and I wonder if this extends to the Minimus line as well? I just happen to have a pair of Minimus 11's and wonder if the larger enclosures would benefit?