Minimus 7 Loudspeakers - Measurements
- Thread starter Zilch
- Start date
Mazza
Active Member
Hi,
I picked up a very clean pair of white RS Minimus 77's but the woofer foams were rotten.
I've purchased these woofers as replacements and wonder if the crossover mod in this thread would also work for the 77's?
The stock crossover and tweeter in the 77's is the same as the 7's.
Cheers.
I picked up a very clean pair of white RS Minimus 77's but the woofer foams were rotten.
I've purchased these woofers as replacements and wonder if the crossover mod in this thread would also work for the 77's?
The stock crossover and tweeter in the 77's is the same as the 7's.
Cheers.
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Replacement foam surrounds are available for the 77's. Check on Ebay, seller is bootapest2. I've refoamed a couple pairs using these surrounds and they work well.
Geetarpicker
Member
I’ll I did the crossover mods described earlier to all 5 of my white Minimus 7s earlier this year, with all the parts coming from Parts Express. I mounted the large chokes with 2 aluminum rivets, and careful layout and a little Gorilla glue held the rest. I’m quite pleased with how they sound now in my 5.1 system though recently I started using my KEF LS50s for the front right and left speakers, keeping the 7s for center and rear duties. My Marantz NR1508 receiver tweaks the EQ with its built in analyzer and included microphone. That said I noticed that after running the analyzer the Marantz receiver didn’t apply much EQ at all to the modded 7s. I take that as confirmation that the 7s are fairly flat in response after the Xover mods, at least in the range over about 100hz. I do run a REL T5i sub for around 100hz and down.
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aspisa
New Member
Pete, and others,
Thank you and Zilch for all of the great work in creating the crossover mod. I have been reading these posts for 3-4 years now, and building up a nice collection of Minimus 7 and 77's. My wife thinks I have a problem. Well, I do.. I have finalized my Desktop 2.1 setup, with 4 Minimus 7w's set about 5' apart, siting on top of each other at about a 30 degree angle to one another. These are being powered by a Lepai LP-S60 4 channel T amp and a Yamaha YST-W40 subwoofer (single 8") (total investment of $88). I have been listening to this system non-stop whenever I am home! While I am no Audiophile, I definitely like the sound I get.
I have made a few recordings that I believe I can hear a brightness or harshness in the sound around 3-4 Khz. I will be embarking on the Crossover upgrade over the next few weeks and will re-record these songs. I am hoping that I can provide some additional A/B comparisons for people to hear.
Anyway, really enjoy the setup as it is now, and if the change is as dramatic as everyone says, my door will always be closed!
Thank you and Zilch for all of the great work in creating the crossover mod. I have been reading these posts for 3-4 years now, and building up a nice collection of Minimus 7 and 77's. My wife thinks I have a problem. Well, I do.. I have finalized my Desktop 2.1 setup, with 4 Minimus 7w's set about 5' apart, siting on top of each other at about a 30 degree angle to one another. These are being powered by a Lepai LP-S60 4 channel T amp and a Yamaha YST-W40 subwoofer (single 8") (total investment of $88). I have been listening to this system non-stop whenever I am home! While I am no Audiophile, I definitely like the sound I get.
I have made a few recordings that I believe I can hear a brightness or harshness in the sound around 3-4 Khz. I will be embarking on the Crossover upgrade over the next few weeks and will re-record these songs. I am hoping that I can provide some additional A/B comparisons for people to hear.
Anyway, really enjoy the setup as it is now, and if the change is as dramatic as everyone says, my door will always be closed!
The circuit board is intended to reuse the original inductor which would save you about $12.
I did not test fit the one from PE but there might be enough room if you stand it up and hold
it down with a zip tie or hot glue.
Thanks for the nice comments folks, great to hear!
Finally got around to it. I went clean-slate with a piece of thin plywood that fit through the woofer hole as I wanted to keep the stock binders for better shallow shelf placement.
-Drilling through the wall mount bracket holes and match-drilling the plywood for bolts gave me a solid non-conductive surface.
-Working the original inductor loose left me with short leads so I soldered on extensions.
-The ground side ended up to be six wires ganging together. I ran another bolt through the plywood, crimped four wires into a terminal between two nuts and soldered the 47ohm and 4.7 cap to the remainder.
The first one took me hours of doing,undoing, swearing and redoing, going from lines on a paper schematic to an actual layout proved harder than I thought. By the second one I had it down to about an hour. .
Remarkable improvement in the sound and it was fun.
Many thanks Pete, looking forward to doing another set better than I did these.
ericj
Well-Known Member
I've performed this mod on a pair of 7's, a pair of 7W's, and a pair of Optimus Pro-77's (which are a bit too boomy and this is maybe not an ideal xover for them)
I have an unpaired 7 floating around unmodded and just picked up another pair of 7W, so I'm about to do 3 more.
I have an unpaired 7 floating around unmodded and just picked up another pair of 7W, so I'm about to do 3 more.
Joshewah
Active Member
Found some Minimus 7Ws about 5 years ago for $5 at a thrift store. Last winter I finally got around to installing the PZ 2.1 crossover.
I’ve been listening to these speakers for about a year now and I’m beyond impressed with the price/performance out of these small modified speakers. Even the bass is enough to satisfy *most* casual listening sessions.
For a total investment of about $40 for the speakers and crossover parts I have no complaints. I currently have them wall mounted in a 2.0 setup with an Emotiva Mini X A100 amplifier.
Anyone have any suggestions for an affordable small subwoofer that compliments PZ Minimus 7s?
I’ve been listening to these speakers for about a year now and I’m beyond impressed with the price/performance out of these small modified speakers. Even the bass is enough to satisfy *most* casual listening sessions.
For a total investment of about $40 for the speakers and crossover parts I have no complaints. I currently have them wall mounted in a 2.0 setup with an Emotiva Mini X A100 amplifier.
Anyone have any suggestions for an affordable small subwoofer that compliments PZ Minimus 7s?
I have questions about minimus 7 cabinet stuffing/damping that I'm hoping others here have had experience with:
* I've seen a few suggestions out there about using modeling clay (oil based, never dries) to thinly line the inside of the cabinet. I've searched high and low for reasons as to exactly how this would affect the speaker but I can't find any solid answers/measurements/or a body of evidence so to speak to conclude that it actually helps. Is it actually/potentially a measurable improvement in resonance or just placebo? Would there be any potential bad effects to sound quality, such as a risk of overdamping or whatever consequence there may be to losing more cabinet air volume? Would love to know this before i'd attempt to line my minimus 7 cabinets with clay because that would seem impossible to clean up if I didn't like the results. Yet, it's so cheap to buy clay it seems like a no brainer to do if there was solid reasoning behind it potentially improving the speaker.
* Also - even if using standard damping materials like fiberglass, why do different versions of minimus 7's have different amounts (and types) of fiberglass or other sheets of damping material? For example, one 1980's c model I own has 1 small white sheet of what looks like a synthetic substitute for fiberglass. Most of my other C models have 1 identical sized sheet of fiberglass. Where as my original models from the 1978 run were all lined with two of those sized sheets - double the amount of the later models! This makes me wonder if there ever was an exact science to this and if there was, which is the right amount? To me generally the original models have the highest build quality and components so is two sheets the best amount for a minimus 7 cabinet volume? Or did they actually improve it by subtracting one sheet?
* Also cabinet stuffing/damping placement... I've seen suggested that it's best to stuff as much behind the tweeter as possible, but to leave a cavity for the woofer. I've already actually done this, but I'm curious why is this considered the best way to distribute the dampening materials? Why does the woofer need as much space as possible while the tweeter can basically be smothered?
* What about a combo of Clay and the fiberglass? Is this a one or the other thing, or should one conceivably do both? Can a cabinet have too much of all this damping stuff done to it?
I'm just trying to see if anyone has put as much time into documenting or noting improvements that can be done to the cabinet with strategic damping as others have done with these fantastic crossovers. Any input would be appreciated.
* I've seen a few suggestions out there about using modeling clay (oil based, never dries) to thinly line the inside of the cabinet. I've searched high and low for reasons as to exactly how this would affect the speaker but I can't find any solid answers/measurements/or a body of evidence so to speak to conclude that it actually helps. Is it actually/potentially a measurable improvement in resonance or just placebo? Would there be any potential bad effects to sound quality, such as a risk of overdamping or whatever consequence there may be to losing more cabinet air volume? Would love to know this before i'd attempt to line my minimus 7 cabinets with clay because that would seem impossible to clean up if I didn't like the results. Yet, it's so cheap to buy clay it seems like a no brainer to do if there was solid reasoning behind it potentially improving the speaker.
* Also - even if using standard damping materials like fiberglass, why do different versions of minimus 7's have different amounts (and types) of fiberglass or other sheets of damping material? For example, one 1980's c model I own has 1 small white sheet of what looks like a synthetic substitute for fiberglass. Most of my other C models have 1 identical sized sheet of fiberglass. Where as my original models from the 1978 run were all lined with two of those sized sheets - double the amount of the later models! This makes me wonder if there ever was an exact science to this and if there was, which is the right amount? To me generally the original models have the highest build quality and components so is two sheets the best amount for a minimus 7 cabinet volume? Or did they actually improve it by subtracting one sheet?
* Also cabinet stuffing/damping placement... I've seen suggested that it's best to stuff as much behind the tweeter as possible, but to leave a cavity for the woofer. I've already actually done this, but I'm curious why is this considered the best way to distribute the dampening materials? Why does the woofer need as much space as possible while the tweeter can basically be smothered?
* What about a combo of Clay and the fiberglass? Is this a one or the other thing, or should one conceivably do both? Can a cabinet have too much of all this damping stuff done to it?
I'm just trying to see if anyone has put as much time into documenting or noting improvements that can be done to the cabinet with strategic damping as others have done with these fantastic crossovers. Any input would be appreciated.
Mazza
Active Member
Dear all,
I finally got around to completing my Minimus 77 Upgrade. I'm extremely happy with the results. Thanks very much Zilch. I just need to be careful not to put too much juice into them now, as the cut to the top end really drops their overall perceived efficiency. As a result I had to dial back my subs a heap.
First I replaced the rotted foams with foams from Queensland Speaker Repairs:
Fitted not yet glued:
Sprayed the frames and cones with a light coat of some black paint then EVA glued the new foams on:
I used this crossover schematic:
Used some salvaged parts (not quite to specification) and built this:
Hot glued them to the back wall
Stuffed them losely with some very nice Bradford acoustic batts
Marked the tweeter before removal as it has no +ve -ve markings 1992!
Coming back together
Pertinent details for reference
In situ on the shelf in my shed sounding fine
For $10 for the pair, $20 for foams I'd say that's a pair of speakers hard to beat for the price, especially considering they are all of 26 years new!
Thanks to all for this inspiring thread.
I finally got around to completing my Minimus 77 Upgrade. I'm extremely happy with the results. Thanks very much Zilch. I just need to be careful not to put too much juice into them now, as the cut to the top end really drops their overall perceived efficiency. As a result I had to dial back my subs a heap.
First I replaced the rotted foams with foams from Queensland Speaker Repairs:
Fitted not yet glued:
Sprayed the frames and cones with a light coat of some black paint then EVA glued the new foams on:
I used this crossover schematic:
Used some salvaged parts (not quite to specification) and built this:
Hot glued them to the back wall
Stuffed them losely with some very nice Bradford acoustic batts
Marked the tweeter before removal as it has no +ve -ve markings 1992!
Coming back together
Pertinent details for reference
In situ on the shelf in my shed sounding fine
For $10 for the pair, $20 for foams I'd say that's a pair of speakers hard to beat for the price, especially considering they are all of 26 years new!
Thanks to all for this inspiring thread.
Attachments
MellowDios
New Member
I have two pairs of Minimus 7W's. Did the PZ-2.1 mod on the first pair a few years ago (I think I posted it somewhere here, but don't recall exactly where. Using the first pair, driven by an NAD C 316 BEE (35 W/ch) amp, the low end supported by a Paradigm 8" sub, in my piano room. I have the parts for the second pair, which are destined to go in my home studio, as small reference monitors, for testing mixes. They'll be perfect with their 50 Hz to 20 kHz FR. I've loved these speakers since I bought them in the late 70's (maybe early 80's).
A while ago, a friend who works in the local hi-fi shop, repairing and modding amplifiers, looked at the PZ-2.1 schematic I have pinned up above my electronics workbench, and told me it's wrong. I told him how much work went into the design (all of which I followed at the time) but he would not be dissuaded, and we agreed to disagree. Unfortunately, I know next to nothing about design. I build from kits and schematics, or refurbish amps by replacing existing parts. I'm learning, but it's a slow process. That said, I have seen crossovers built that way elsewhere online where the design was commented on but not criticized.
My friend seemed to think one of the filters was backwards. So, for the record - is the PZ-2.1 schematic posted above in this thread correct. And if someone could explain why the filters are mirror images of each other, I would very much appreciate it. 'Cause life is for learning.
Thanks.
A while ago, a friend who works in the local hi-fi shop, repairing and modding amplifiers, looked at the PZ-2.1 schematic I have pinned up above my electronics workbench, and told me it's wrong. I told him how much work went into the design (all of which I followed at the time) but he would not be dissuaded, and we agreed to disagree. Unfortunately, I know next to nothing about design. I build from kits and schematics, or refurbish amps by replacing existing parts. I'm learning, but it's a slow process. That said, I have seen crossovers built that way elsewhere online where the design was commented on but not criticized.
My friend seemed to think one of the filters was backwards. So, for the record - is the PZ-2.1 schematic posted above in this thread correct. And if someone could explain why the filters are mirror images of each other, I would very much appreciate it. 'Cause life is for learning.
Thanks.
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My friend seemed to think one of the filters was backwards. So, for the record - is the PZ-2.1 schematic posted above in this thread correct. And if someone could explain why the filters are mirror images of each other, I would very much appreciate it. 'Cause life is for learning.
Thanks.
Hi, MellowDios. I'll try to describe what I see in the schematic... a simplified description which misses a bunch of the details (for which you'd need to read the long discussion earlier in this topic). I believe it's definitely a workable crossover - I built a pair for my own Minimus 77 upgrade earlier this year and it works fine.
First: it's drawn "upside down" in a way, with the woofer on top and the tweeter below. That's entirely an artistic issue - you could just flip the whole tweeter section up to the top and move the two lines from the inputs, and it'd be the same circuit and would actually correspond to how the speaker is usually mounted.
Electrically: the woofer section is a single-pole low-pass (L1 inductor in series with the woofer), so the frequency response of the signal being fed to the woofer falls off above the crossover frequency. If the woofer had a constant and resistive impedance with frequency, the L1 inductor would be all that's necessary to create a smooth frequency rolloff. However, the woofer's impedance rises with increasing frequency (a very common phenomenon). The R1/C1 combination is connected in parallel with the woofer, and its impedance (which drops with increasing frequency) "flattens out" the effective impedance of the woofer so that the low-pass frequency response is as desired. Since the resistor R1 is a bit smaller than the resistance of the woofer's voice coil, this is actually "over-compensating" the woofer a bit, and making the roll-off a bit steeper and deeper than just a single-pole (I think).
The tweeter is fed by a somewhat different configuration. First, there's a resistive "pad" (R2 in series and R3 to ground) which slightly attenuates the treble signal. Then, there's a two-pole high-pass filter (C2 in series and L2 to ground).
So, the low- and high-pass filters aren't mirror images - the woofer low-pass is a single-pole-plus-a-bit, and the tweeter high-pass is a double-pole with a small amount of attenuation/padding. The combination of these rolloffs, added to the built-in frequency responses of the drivers, leads to a smooth combined frequency response.
Most of the classic "cookbook" crossover configurations are built around symmetrical designs (e.g. the low-pass and high-pass sections have the same number of poles and the same tuning alignment). Impedance-compensation networks are then added to flatten out the real-world driver impedances so that the "cookbook" crossover formulas work properly. Vance Dickason's "Loudspeaker Design Cookbook" has a whole chapter on this approach.
This isn't the only way to do it, though. In cases like the Minimus upgrade, where you're starting with a fixed set of drivers with known electrical and sonic characteristics, it can make sense to construct a sort of hybrid, which takes advantage of the existing drivers' rolloffs and other quirks. This approach can give very good results, with fewer components being required than for a "cookbook" approach. You can think of the PZ-2.1 as the reigning survivor of a Darwinian competition between a bunch of designs of this sort.
I'm currently running my Minimux 77s (with the PZ-2.1) from a Proton D940 receiver I refurbished... there's a refurbed Definitive Technology subwoofer handling the bass below 100 Hz. It's a nice combination - a great bedroom system. I've got another PZ-2.1 pair under construction, for a pair of Minimus 7s which will probably end up as the TV speakers in the living room.
Mazza
Active Member
DavePlatt, thanks for this very eloquent description of the wonderful crossover design work documented here.
All of this crossover design process was a dark art for me until recently.
Then I fell down the Econowave tread here on AK and by reading through much of that and a lot of Wayne Parnam's papers over at Pi Speakers it's all very accessible for me now.
In fact I'm feeling so confident now about it all I'm going to purchase an Omnimic and start using the Xsim crossover design software, a development of PCD famously used by Zilch for this and other projects.
My intention is to measure my very nice old Klipsch KG 5.5's just like Zilch did here with the Minimus and see if I can't improve these lovely old speakers too.
I'm thinking of creating my own MazLab.... ;-)
All of this crossover design process was a dark art for me until recently.
Then I fell down the Econowave tread here on AK and by reading through much of that and a lot of Wayne Parnam's papers over at Pi Speakers it's all very accessible for me now.
In fact I'm feeling so confident now about it all I'm going to purchase an Omnimic and start using the Xsim crossover design software, a development of PCD famously used by Zilch for this and other projects.
My intention is to measure my very nice old Klipsch KG 5.5's just like Zilch did here with the Minimus and see if I can't improve these lovely old speakers too.
I'm thinking of creating my own MazLab.... ;-)
DavePlatt is correct.
I designed the mod that was the basis for this design, I'm the P in PZ-2.1 see post #75 in
this thread: http://www.audiokarma.org/forums/in...akers-measurements.199790/page-4#post-2355102
I designed this based on looking at measurements previously made by others on
the Minimus 7 drivers. I always use a larger than text book woofing inductor in order
to provide some baffle step compensation.
I hooked up the woofer with a 1.6 mH inductor to my measurement system and tuned
the R and C for the lowest R value that did not cause peaking and a C value that
gave a -3dB point around 3 KHz. A pure 2nd order filter will not work on the woofer
due to the voice coil inductance which resonates with the C and causes peaking in
the response. It would be nothing like text book without the R in series.
I tuned the tweeter response in a similar way, wanting to reuse parts resulted in the
.4 mH for the shunt inductor, then I chose the R and C to provide roughly 3 dB of
attenuation and a -3 dB of about 3 KHz.
All of the values were ball park and would be tuned as necessary based on a the
measured system response and reverse null.
First thing I did was listen to it, and the initial impression was not bad, adjusted the
tweeter R for a reasonable balance to my ears.
Checked the reverse null with the drivers out of phase and it pointed up by about
10 degrees. It sounded so good that I made no further changes.
I commented that the woofer inductor could be reduced to 1 mH for less baffle step
and higher sensitivity which Zilch did and he made a few other minor tweaks.
R3 is deliberately in a somewhat odd position the value of 40 ohms is a bit lower than
the 47 that I suggested and that is why we put it "behind" R2. The only purpose for
that resistor is to flatten the input impedance. R3 also provides a bit more attenuation
on the tweeter but the value is so high that it is a very minor effect.
The electrical networks are both 2nd order that probably combine with the acoustical
response of the drivers to form very roughly 4th order rolloffs.
This was very much of a quicky design with as few measurements as possible.
I designed the mod that was the basis for this design, I'm the P in PZ-2.1 see post #75 in
this thread: http://www.audiokarma.org/forums/in...akers-measurements.199790/page-4#post-2355102
I designed this based on looking at measurements previously made by others on
the Minimus 7 drivers. I always use a larger than text book woofing inductor in order
to provide some baffle step compensation.
I hooked up the woofer with a 1.6 mH inductor to my measurement system and tuned
the R and C for the lowest R value that did not cause peaking and a C value that
gave a -3dB point around 3 KHz. A pure 2nd order filter will not work on the woofer
due to the voice coil inductance which resonates with the C and causes peaking in
the response. It would be nothing like text book without the R in series.
I tuned the tweeter response in a similar way, wanting to reuse parts resulted in the
.4 mH for the shunt inductor, then I chose the R and C to provide roughly 3 dB of
attenuation and a -3 dB of about 3 KHz.
All of the values were ball park and would be tuned as necessary based on a the
measured system response and reverse null.
First thing I did was listen to it, and the initial impression was not bad, adjusted the
tweeter R for a reasonable balance to my ears.
Checked the reverse null with the drivers out of phase and it pointed up by about
10 degrees. It sounded so good that I made no further changes.
I commented that the woofer inductor could be reduced to 1 mH for less baffle step
and higher sensitivity which Zilch did and he made a few other minor tweaks.
R3 is deliberately in a somewhat odd position the value of 40 ohms is a bit lower than
the 47 that I suggested and that is why we put it "behind" R2. The only purpose for
that resistor is to flatten the input impedance. R3 also provides a bit more attenuation
on the tweeter but the value is so high that it is a very minor effect.
The electrical networks are both 2nd order that probably combine with the acoustical
response of the drivers to form very roughly 4th order rolloffs.
This was very much of a quicky design with as few measurements as possible.
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Pete - thanks very much for describing your development process. And, thanks again for the work you've put into making this design available - a lot of people have been able to benefit!
I just finished rebuilding/upgrading a "salvage job" pair of Minimus AV units. One tweeter was badly damaged - the tweeter module had been broken backwards out of the mounting plate, cracking the plate into several fragments (I suspect the speaker was dropped on its back). I had to epoxy the plate back together, clean everything up, and remount the tweeter assembly... seems to work OK although I haven't yet measured its output level against the other.
The rubber woofer surrounds had deteriorated - one was not too bad but the other had stiffened up to the point of near-rigidity! Never saw that happen before. I suspect these speakers might have been "under the eaves" outdoor patio speakers and that the bad one had been baking in the hot sun for years. I replaced both surrounds.
The new crossover is a PZ-2 (I had some 47-ohm resistors handy, and used 'em) scratch-built on some insulating board with glued-on terminal posts. It didn't turn out to be significantly less effort than making a PC-board using a pad cutter, as I did last time. Electrically I don't think there's a significant difference; esthetically the PC board is much neater.
I've started playing with Scimpy, an open-source Python package for speaker measurement and modeling. I used it to do an impedance measurement of the one of the woofers after the bad surround was removed, then again after the new one was glued on, and then of the final installation. I found the results interesting. With no surround, the woofer resonates at about 50 Hz; this rises to just under 70 Hz with the new surround in place. Apparently the added restoring force of the surround raises the resonant frequency, more than the added mass lowers it. Without the surround there's also a small secondary impedance bump at 127 Hz - I suspect that the unsupported outer edge of the cone may be ringing just a bit. This goes away when the new surround is present.
Don't take either the magnitude or phase measurements on that one for gospel - it was an initial (and not quite correct) Scimpy hookup, and the phase reference is definitely wrong. I corrected that before taking the "with surround" measurements.
The final system measurement looks not too bad at all - the shunt resistor seems to have tamed the woofer's impedance peak somewhat. I don't know how significant this would be in practice... for speaker wires totalling no more than an ohm, the system impedance variations probably don't affect the frequency response in an audible way... but it certainly doesn't hurt! From the amp's point of view this should be an easy system to drive.
They sound quite respectable, and I think I'll go ahead as planned and install them as part of the living-room TV system.
I just finished rebuilding/upgrading a "salvage job" pair of Minimus AV units. One tweeter was badly damaged - the tweeter module had been broken backwards out of the mounting plate, cracking the plate into several fragments (I suspect the speaker was dropped on its back). I had to epoxy the plate back together, clean everything up, and remount the tweeter assembly... seems to work OK although I haven't yet measured its output level against the other.
The rubber woofer surrounds had deteriorated - one was not too bad but the other had stiffened up to the point of near-rigidity! Never saw that happen before. I suspect these speakers might have been "under the eaves" outdoor patio speakers and that the bad one had been baking in the hot sun for years. I replaced both surrounds.
The new crossover is a PZ-2 (I had some 47-ohm resistors handy, and used 'em) scratch-built on some insulating board with glued-on terminal posts. It didn't turn out to be significantly less effort than making a PC-board using a pad cutter, as I did last time. Electrically I don't think there's a significant difference; esthetically the PC board is much neater.
I've started playing with Scimpy, an open-source Python package for speaker measurement and modeling. I used it to do an impedance measurement of the one of the woofers after the bad surround was removed, then again after the new one was glued on, and then of the final installation. I found the results interesting. With no surround, the woofer resonates at about 50 Hz; this rises to just under 70 Hz with the new surround in place. Apparently the added restoring force of the surround raises the resonant frequency, more than the added mass lowers it. Without the surround there's also a small secondary impedance bump at 127 Hz - I suspect that the unsupported outer edge of the cone may be ringing just a bit. This goes away when the new surround is present.
Don't take either the magnitude or phase measurements on that one for gospel - it was an initial (and not quite correct) Scimpy hookup, and the phase reference is definitely wrong. I corrected that before taking the "with surround" measurements.
The final system measurement looks not too bad at all - the shunt resistor seems to have tamed the woofer's impedance peak somewhat. I don't know how significant this would be in practice... for speaker wires totalling no more than an ohm, the system impedance variations probably don't affect the frequency response in an audible way... but it certainly doesn't hurt! From the amp's point of view this should be an easy system to drive.
They sound quite respectable, and I think I'll go ahead as planned and install them as part of the living-room TV system.
lukiedog
Super Member
Attached are frequency response plots generated by REW with a UMIK-1 mic. The speaker is the Minimus 77 w/ the PZ2.1 mod. I must say that I was never impressed with the 7s or 77s, never understood what the fuss was about, though I did approve of the build quality. But these 77s with the crossover mod are very, very good. I drive them with a DIY amp based on the TPA3118 boards. They are inefficient and will need some power, but they sound nearly magical and have uncanny imaging given their low end pedigree. They were part of my garage system for years before being replaced by the Pioneers with the Dennis Murphy mod. They measure the same with and without the grille. This is one of the most worthwhile DIY projects I've completed, very satisfying.
