I have a couple of pairs of stock Minimus 7's. I bought a pair of TDA something stereo amps on Ebay so that I can Bi-amp a pair of the M7's to use as computer/FT-817 speakers. I'd like to hear recommendations for the electronic crossover frequency and slope. My first guess is around 2kHz and 18-24db/octave. Would it be a good idea to Zobel either the woofer and or tweeter too? Thank you!
The tweeter is extremely fragile on the M7, the crossover should be more like 3Khz to that massive 3-1/2" woofer.
I guess I'm late but;
I have read several posts on here and other forums about upgrading the Realistic Minimus speakers from using a homemade kit purchased for $39 plus shipping on ebay (if I can use this word) to building your own 2-way crossover (which could be more $$ than expected), doping or the replacing the drivers and adding binding posts (easily done on the 7W due to its round hole in the back where the terminals are located).
I have a pair of both the metal cabinet Minimus 7's (made in Korea) and the Minimus 7W (made in Japan). The simple crossover in both differ only by the capacitor; a 4.7 uF 50v in the 7's and a 4.7 uF 100v in the 7W's. I had discovered that the voltage on the cap is its limit; if more than that voltage is sent to the cap they can pop or explode! So, does it help to change them out for a higher limit when the stored voltage is the same? I know most upgrades suggest a polypropylene cap replacement.
Anyway, I doped the woofers.
Onto what I found:
I looked at Amazon for 2-way crossover and found a pair for just under $13 and a pair of gold plated binding post terminals for about $8. The 2-way crossover had some very good reviews (2 especially) and a couple not so good. I was hesitant because of the brand and made in China but I did order them. The crossover is a circuit board with a choke coil for the woofer (fairly long) and for the tweeter there is a 2.2 ohm resistor, a 3.3 uF 250v polypropylene cap and a spool coil. Dimensions are Dimension: 8.5 x 6 x 2cm or 3.3 x 2.4 x 0.8 inches (L*W*H)
The post terminals fit perfectly, no problem. I salvaged the parts from the crossovers, wires for the speaker leads on the new circuit board and caps & coils.
I soldered the speaker leads and terminal leads to the board, hot glued the board into place and soldered the terminal leads from the board to the terminal contacts.
I tested the speakers and they really sounded much better to my surprise!
I ran the Audyssey setup with these upgraded Minimus 7W's as surround back speakers mounted on the wall. Before the upgrade the Audyssey setup would set the size as small speakers and the crossover frequencies at 90 to 100 Hz, but this time the crossover frequency is 40 Hz!
The sound from these upgraded speakers is great! I really couldn't believe that I could have done this improvement and spent under $21 for the whole thing!
I am sure the new crossover will fit the Minimus 7's but I would probably have to keep the spring clip terminals because of the metal cabinet.
If you're thinking of upgrading a pair or more of the Minimus 7's I think this is the way to go. This crossover would probably fit the Minimus 77's also.
I have read several posts on here and other forums about upgrading the Realistic Minimus speakers from using a homemade kit purchased for $39 plus shipping on ebay (if I can use this word) to building your own 2-way crossover (which could be more $$ than expected), doping or the replacing the drivers and adding binding posts (easily done on the 7W due to its round hole in the back where the terminals are located).
I have a pair of both the metal cabinet Minimus 7's (made in Korea) and the Minimus 7W (made in Japan). The simple crossover in both differ only by the capacitor; a 4.7 uF 50v in the 7's and a 4.7 uF 100v in the 7W's. I had discovered that the voltage on the cap is its limit; if more than that voltage is sent to the cap they can pop or explode! So, does it help to change them out for a higher limit when the stored voltage is the same? I know most upgrades suggest a polypropylene cap replacement.
Anyway, I doped the woofers.
Onto what I found:
I looked at Amazon for 2-way crossover and found a pair for just under $13 and a pair of gold plated binding post terminals for about $8. The 2-way crossover had some very good reviews (2 especially) and a couple not so good. I was hesitant because of the brand and made in China but I did order them. The crossover is a circuit board with a choke coil for the woofer (fairly long) and for the tweeter there is a 2.2 ohm resistor, a 3.3 uF 250v polypropylene cap and a spool coil. Dimensions are Dimension: 8.5 x 6 x 2cm or 3.3 x 2.4 x 0.8 inches (L*W*H)
The post terminals fit perfectly, no problem. I salvaged the parts from the crossovers, wires for the speaker leads on the new circuit board and caps & coils.
I soldered the speaker leads and terminal leads to the board, hot glued the board into place and soldered the terminal leads from the board to the terminal contacts.
I tested the speakers and they really sounded much better to my surprise!
I ran the Audyssey setup with these upgraded Minimus 7W's as surround back speakers mounted on the wall. Before the upgrade the Audyssey setup would set the size as small speakers and the crossover frequencies at 90 to 100 Hz, but this time the crossover frequency is 40 Hz!
The sound from these upgraded speakers is great! I really couldn't believe that I could have done this improvement and spent under $21 for the whole thing!
I am sure the new crossover will fit the Minimus 7's but I would probably have to keep the spring clip terminals because of the metal cabinet.
If you're thinking of upgrading a pair or more of the Minimus 7's I think this is the way to go. This crossover would probably fit the Minimus 77's also.
40 Hz
You might want to re-measure them since the crossover is not going to change the low end of the M7.
You might want to re-measure them since the crossover is not going to change the low end of the M7.
Well, before the new crossover the M7 was only filtering lows to the tweeter but now both drivers have filters, low filter to tweeter, high filter to woofer but then it also could be because I doped the paper cone on the driver. Go figure. Honestly, I do hear more lows than before the modifications.
I might try a big cap to extend the low end on my current pair - I always have a pair of 7s - after I remove them from tv duty. Can't remember what I did to these; probably a zobel after an inductor robbed from the tweeter and a raised xo on the tweeter, first order with a shunt resistor. Some kind of damping on the metal box...there isn't a lot of room in there for more stuff.
I think you are right about the low pass for the main driver. There are sizeable peaks in the unfiltered response. Reducing or eliminating these alters the balance of the whole speaker and makes the bass apparently louder, which it is, (relative to the higher frequencies)
I thought about what you said re: thecrossover not changing the low end of the 4" woofer; I can't find anythingregarding the woofer freq. response and the 1" dome tweeter freq. responsefor the M7w since they are older speakers but I looked up 4" woofers andsaw that the freq. response can be anywhere between 50 - 15K depending on thedriver ; the 1" dome tweeter can be from 2200 - 20K. The original M7wcrossover (see pic and diagram) just filtered the low freq. to the tweeter andthere was no filter on the woofer; to me that means that the woofer and thetweeter could duplicate hi frequencies at the same time (is that a correctassumption?). After doping the woofer (which I understand can change the lowfrequency response) and adding the new 2-way crossover ( see otherdiagram)wouldn't the Audyssey setup mic then "hear" less of the hi'sfrom those speakers and therefore reset the crossover frequency from 80 or 100to less? And since in the manual setup has only 40, 60, 80, 90, 100 ...... thatthe Audyssey freq config would set at 40 rather than a higher freq of 60?
I do have a vintage pair of hlx 3-way speakers from the 70's that have a10" woofer and their frequency response range is 23Hz to 20KHz; the lowend is equivalent or better than some subwoofers nowadays.
Attachments
Now I get what you meant, that the balance shifted in the right way, as did mine. The original 4" has a four layer voice coil, which rolls off the high end but not enough to suppress the usual peak, so we agree I think. Mine have been used as mid-high source above 10" Grundig (yep) in 10:1 TLs.
Thanks
I'm new to all this speaker upgrades; I probably didn't really explain myself in the first thread.
I am attaching some pics of the work I did since I already posted the original pic of the old crude crossover. I am starting to learn a lot more since I am a retiree and need to save $$.
I do need to check a wiring diagram on my BIC America DV32 to see what type of crossover they have; I needed their size to fit onto a stairway post (and opposite to that is a wall) to act as surrounds since the M7's were slightly larger than the post.
I do have a great pair of B & W CDM1-SE fronts, a CC6-S2 center and a Mirage BPS-10 sub all purchased at an estate sale for $130. I really like the B & W's. I had to replace the sub driver because the voice coil broke; replaced it with a Blue Octave Kevlar sub that was originally came with a in-wall/ceiling mount. The new sub driver has improved my sub response immensely (thus far)
I'm new to all this speaker upgrades; I probably didn't really explain myself in the first thread.
I am attaching some pics of the work I did since I already posted the original pic of the old crude crossover. I am starting to learn a lot more since I am a retiree and need to save $$.
I do need to check a wiring diagram on my BIC America DV32 to see what type of crossover they have; I needed their size to fit onto a stairway post (and opposite to that is a wall) to act as surrounds since the M7's were slightly larger than the post.
I do have a great pair of B & W CDM1-SE fronts, a CC6-S2 center and a Mirage BPS-10 sub all purchased at an estate sale for $130. I really like the B & W's. I had to replace the sub driver because the voice coil broke; replaced it with a Blue Octave Kevlar sub that was originally came with a in-wall/ceiling mount. The new sub driver has improved my sub response immensely (thus far)
Attachments
Followed your advice
So I took your advice and re-measured the Audyssey Setup on the Denon AVR which sets up speaker configuration (Large or small) Distance of each speaker, Channel Level of each speaker and Crossover frequency for each pair; Like I said the first crossover freq. after modification was 40 Hz, the second was 60 Hz and the third was 40 Hz. This may be due to the doping the paper cone but those are the measurements. Before the modifications I was getting around 100 + Hz for the same speakers.
So I took your advice and re-measured the Audyssey Setup on the Denon AVR which sets up speaker configuration (Large or small) Distance of each speaker, Channel Level of each speaker and Crossover frequency for each pair; Like I said the first crossover freq. after modification was 40 Hz, the second was 60 Hz and the third was 40 Hz. This may be due to the doping the paper cone but those are the measurements. Before the modifications I was getting around 100 + Hz for the same speakers.
This set up has too many variables to be able to interpret. What the M7s output on their own was before and after your mods would be more meaningful.
I have some conflicting info; some I copied from a Realistic site stating the M7W have a freq. response of 95 - 20K Hz while the M7 had an 80 - 20K Hz from the same page. I wish I saved the entire page but...; however I downloaded a spec and instruction sheet for the M7 that states 50 - 20K Hz. I believe that that it was closer to 95 on the low end before I doped the cone and changed the crossover. I could not attach the pdf file of the specs & instructions sheet.
As stated previously the Audyssey setup would set the xover freq before the mods to around 100 Hz but now it is setting it around 40.
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