Pete B Posted August 8, 2008 Report Share Posted August 8, 2008 I purchased several pairs of these over the years when they would go on sale.Always thought that I'd install better drivers someday if they burnt out, andperhaps shoot for performance close if not better than the Visonic Davids. Iheard these many years ago but not recently. Would like to use a SEAS, Peerlessor Vifa woofer replacement but there are not many that will fit. The long throwAura's (NS3 note that this smaller and would have to be adapted) look like theymight work well when seeking improved performance.Anyway, came across a woofer out of one and measured it:Radio Shack Minimus 7 woofer UNIT SAMPLE: PLB #1 8-8-2008 UNIT MARKINGS: 1218 8 ohms MALAYSIA UNIT DATE: estimated 1993 not markedNotes: woofer has a raised back plateImpedance file: RSM7W1Z1.ZF2T&S Impedance file: RSM7WTS1.ZF2Effective cone diameter = 3.25" measuredRDC = 6.60 ohmsFs 62.5 HzVas 4.35 liters Qe .47Qm 2.13Mms 5.99 gramsno .219 %SPLref 85.4 dBBl 5.92 T-mQts .382Cms 1.08 mm/NZpeak 38.7 ohmsZmin 7.60Z1K 11.9Lvc1K 1.08 mHZ10K 20.6Lvc10K .51 mHDelta M 6.3 gramsFshift -30%This is an excellent match for the original driver. The mechanical dimensionsshould be checked before trying it:http://www.mcmelectronics.com/product/55-1853Zaph's tests show good performance and value for the MCM 55-1853:http://www.zaphaudio.com/smalltest/ Quote Link to comment Share on other sites More sharing options...
JKent Posted August 9, 2008 Report Share Posted August 9, 2008 Thanks for the info Pete. Do you (or any other member) have info on the mods that were recommended in Speaker Builder? I know there is a fellow on ebay selling kits, but I'd rather build my own. Looks like it involves some caps and an inductor. One Minimus 7 enthusiast recommended just replacing the 4.7uF cap and adding more stuffing, but I'm curious about the full-blown mod. Kent Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 10, 2008 Author Report Share Posted August 10, 2008 Hi Kent,I have the SB issue filed away. I never did anything with these except replacethe woofers with the stock RS units. I couldn't find a better one that would fit,and didn't have the time to design a mod anyway back 10-15 years ago.I'm not certain if this is the SB mod, and there are errors in these schematicsthe pos input should be on the other side of the 4.7 uF cap in the top and bottomschematics. Please note that the first schematic looks to be stock, I'm not certain, and the other two mods do not really pass a sanity check, the woofer inductor israther large. The tweeter crossover was 2nd order, it was reduced to first order:http://www.diyaudio.com/forums/showthread....936#post1280936Zaph design, should work sealed with less bass extension:http://www.zaphaudio.com/ZBM4.html Quote Link to comment Share on other sites More sharing options...
JKent Posted August 10, 2008 Report Share Posted August 10, 2008 Thanks PeteActually, I did see that thread but did not know if that was the SB mod, and I was wary of the schematics because some contributers had noted errors. Maybe I'll just replace the 4.7uF caps with some 5uF film caps I have on hand. If you ever dig up that SB article maybe you could post it here. I had some Mini 7s--used them as rear speakers for years, then sold them on ebay. Just bought another pair, with walnut cabs, so I'd like to play with them a bit.Kent Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 10, 2008 Author Report Share Posted August 10, 2008 Here's a link to a SB back issues page. Search on Minimus to find modissues:http://www.audioxpress.com/magsdirx/backissues/BISSBM.htmI'll try to look it up when I have a chance. Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 11, 2008 Author Report Share Posted August 11, 2008 Pulled out the article. Yes top schematic is stock with the Pos terminalmoved to the other side of C1:http://www.diyaudio.com/forums/showthread....936#post1280936Second is the SB 1988 modification, note that drivers are wiredin phase. Inductor DCR is 1.2 ohms. The article shows a muchimproved system frequency response. I believe that he's addedsignificant baffle step compensation which is good for realism,however I expect a significant loss in sensitivity and maxSPL.He does not pad the tweeter and it looks to be 2 to 3 dB too hotin his curves. I suggest a small low cost iron core inductor for the woofer since it should be as small as possible.The third schematic is from another SB Mod article (4 - 91) howeverthere are two errors. The Pos input terminal should be on the otherside of the 4.7 uF cap, and the inductor was not 3.5 mH but ratherit was the tweeter inductor reused, which he states as .4 mH. Healso shows a fairly good FR plot but it is half octave smoothed anddoes include a peak at about 1.7 kHz. This version I would expect tonot include any BSC.Zaph's woofer network looks to be more reasonable:http://www.zaphaudio.com/ZBM4.html 1.5 mH to provide some BSC and a 1.0 mH option for use in situationscloser to a boundary. The shunt woofer cap is 3.3 uF. The stock Minimus 7woofers are very similar so it should be reasonable to use his network ifone wanted to experiment. Quote Link to comment Share on other sites More sharing options...
JKent Posted August 11, 2008 Report Share Posted August 11, 2008 Thanks again PeteKent Quote Link to comment Share on other sites More sharing options...
JKent Posted August 12, 2008 Report Share Posted August 12, 2008 My ebay Mini 7s arrived today. Nice walnut veneer and the grilles are intact.I had a couple of Sprague 5uF film caps from a previous project, so I pulled the xovers, removed the 4.7uF NPEs and installed the Spragues, then shoehorned the things back together. The cap "just" fit thru the hole in the cabinet, then I pushed ti aside to clear the woofer.These little guys sound good! And for a real treat, I ran them AND my AR2ax's. Nice. The Mini 7s are temporarily on top of a stack of other speakers, so they happen to be at ear level. I think they enhance the ARs.I may leave them as is or perhaps later use the SB mod.Kent Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 14, 2008 Author Report Share Posted August 14, 2008 Good to hear that you're enjoying them.All the talk got me to pull out one of my pairs, mine are all stock, only replaced a few woofers at one point.Disconnected the tweeter and measured the woofer in system;here are the results. Note that it is not the same woofer asmeasured above:Fc = 117.0Qtc = .74Qe = .89Qm =4.5Interesting that the Qtc is so low, usually a smaller magnet wouldbe used to raise Qtc and provide a bump in the woofer LFresponse. Qm is high because there is not much stuffing in thesystem, this means that adding some series resistance will beeffective in raising Qtc. Adding one ohm raises Qtc to .845, twoohms to .94. Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 14, 2008 Author Report Share Posted August 14, 2008 Interesting: http://murphyblaster.com/content.php?f=minimus.html Quote Link to comment Share on other sites More sharing options...
JKent Posted August 15, 2008 Report Share Posted August 15, 2008 Pete,While you had the mini 7 apart, did you happen to measure the physical dimensions of the woof? The MCM 1853 is:Dimensions: •Overall frame diameter: 4.13" (pincushion) •Required cutout: 3.66" •Mounting depth: 2.80"Kent Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 15, 2008 Author Report Share Posted August 15, 2008 Just measured Dimensions: •Overall width available 4.2" •Hole cutout = 3.67I removed the crossover and don't have it handy.There is 3.4" to the XO mounting flange, and the XOmight hit and require parts to be moved to clear.XO depth is .85 so 3.4 - .85 = 2.55" looks like partswill have to move.Relocate the inductor, cap and bend over the terminalsshould provide .55" for the XO depth, yielding 2.85"should probably work like this if all the dimensions arecorrect. Dont forget to insultate the terminals if anyonetries this. Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 17, 2008 Author Report Share Posted August 17, 2008 Aura 4" looks like it will fit: http://www.madisound.com/catalog/product_i...roducts_id=8470 Quote Link to comment Share on other sites More sharing options...
JKent Posted August 17, 2008 Report Share Posted August 17, 2008 Aura 4" looks like it will fit: http://www.madisound.com/catalog/product_i...roducts_id=8470Thanks once again for all the info Pete. The Aura will fit, but it is 4 ohms while the RS original and the MCM are 8 ohms. The other specs seem to differ also, but I don't know if those differences are important. What's your advice here?Kentoops--I see there is an 8 ohm version of the Aura as well. Is that the one ou mean?http://www.madisound.com/catalog/PDF/ns4-255-8f.pdf Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 17, 2008 Author Report Share Posted August 17, 2008 Thanks once again for all the info Pete. The Aura will fit, but it is 4 ohms while the RS original and the MCM are 8 ohms. The other specs seem to differ also, but I don't know if those differences are important. What's your advice here?Kentoops--I see there is an 8 ohm version of the Aura as well. Is that the one ou mean?http://www.madisound.com/catalog/PDF/ns4-255-8f.pdfI prefer the 4 ohm because it is more sensitive and the tweeter is already toohot without the pad. There is no crossover to the woofer in stock form so itdoes not hurt to use this 4 ohm driver, of course then the input impedance would be 4 ohms. The 8 ohm version is less efficient than the original andtherefore the excessive tweeter output would be even worse.These Aura drivers have about twice the linear throw of the stock and MCMwoofers and therefore will provide more max SPL in the bass. The cone mass is higher which will result in a slightly lower Fc and slightly more bassextension. This is a very small box to be working with and the Aura willwork well here keeping that in mind.Forgot to mention that it looks like this driver will also hit the crossover inback, might have to move some parts. The large roll outer suspension might also hit the grille, so try them at your own risk. Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 23, 2008 Author Report Share Posted August 23, 2008 Zaph's woofer network looks to be more reasonable:http://www.zaphaudio.com/ZBM4.html 1.5 mH to provide some BSC and a 1.0 mH option for use in situationscloser to a boundary. The shunt woofer cap is 3.3 uF. The stock Minimus 7woofers are very similar so it should be reasonable to use his network ifone wanted to experiment.I tried this network, and I was mistaken this is not good as is for theMinimus 7 woofer. I found a significant peak in the electrical response, 3-5 dB due to resonance of the 3.3 uF with the voice coil inductance.I am surprised since the MCM woofer looks to have similar inductance,however I did not check closely.I don't like any of the modifications that I mentioned above for variousreasons. Quote Link to comment Share on other sites More sharing options...
Pete B Posted January 4, 2009 Author Report Share Posted January 4, 2009 Measured a 1992 SD-60 Minimus 7 Tweeter:Radio Shack Minimus 7 1" Dome Tweeter PLB#1 1/3/2009 UNIT MARKINGS: SD-60 MALAYSIA UNIT DATE: 13 NOV 1992Rvc = 7.14 ohmsFs = 2049 HzQt of 2.58Qm = 3.82Qe = 7.92Zmax = 10.9 ohmsZmin = 7.98 ohmsZ10K = 9.44 ohmsLvc10K = 52.9 uHQtc is rather high but is probably due to the high Fs, and somewhat weak motor.Removed the front plate and dome assembly to have a look. The edge suspensionis simply a flat continuation of the dome fabric without any roll. Linearity withexcursion might be a concern, however the high Fs of 2049 Hz should help reducethe max excursion.Lead in wires are tinsel, this is good, and the voice coil former is paper would rathersee aluminum or aluminized paper for better heat dissipation. There is no ferro-fluidin the gap.There is a soft iron lip that extends from the dome assembly into the gap that is notusually seen in modern tweeters and I would expect that there is some loss in efficiency due to the larger gap.There is a felt pad on top of the center pole, however this one was placed slightly offcenter. I was concerned that it might rub, and I trimmed a small amount off to avoid any issues.This appears to be a low cost copy of the classic 1" dome tweeter. Quote Link to comment Share on other sites More sharing options...
Pete B Posted March 17, 2009 Author Report Share Posted March 17, 2009 This was a double post ... Quote Link to comment Share on other sites More sharing options...
Pete B Posted March 17, 2009 Author Report Share Posted March 17, 2009 Aura 4" looks like it will fit: http://www.madisound.com/catalog/product_i...roducts_id=8470Tried the Aura 4" and it fits, have not yet worked out a crossover:http://baselaudiolabs.googlepages.com/RS-M7-AURA1.jpgThis driver has some impressive Xmax and looks like it will perform well.I do notice that it has a Kapton former and I'm concerned about the driver's thermal capacity. Quote Link to comment Share on other sites More sharing options...
Guest skywave-rider Posted March 17, 2009 Report Share Posted March 17, 2009 Price is not bad.... Quote Link to comment Share on other sites More sharing options...
Pete B Posted March 30, 2009 Author Report Share Posted March 30, 2009 Tried the Aura 4" and it fits, have not yet worked out a crossover:http://baselaudiolabs.googlepages.com/RS-M7-AURA1.jpgThis driver has some impressive Xmax and looks like it will perform well.I do notice that it has a Kapton former and I'm concerned about the driver's thermal capacity.The Aura 4" driver measured in a stock Minimus 7, with stock fiberglass and crossover:Fc = 125 HzQtc = .89Qe = 1.1Qm = 4.9Fs is slightly higher than the original woofer, however it is fairly insignificant on apercentage basis. The higher Qtc provides more peaking around and above Fcas compared to the original which should sound better and more than make up forthe higher Fc.These are the figures I provided in an earlier post for the original woofer:Fc = 117.0Qtc = .74Qe = .89Qm =4.5 Quote Link to comment Share on other sites More sharing options...
Pete B Posted April 27, 2014 Author Report Share Posted April 27, 2014 I never took the Aura woofer any further since it was discontinued, butit looks like the Dayton ND-105 is a near clone of it and will also drop inso I'll probably purchase a pair. Quick look at the parameters suggeststhat it will have better bass (lower Fc) than the Aura:http://www.parts-express.com/dayton-audio-nd105-4-4-aluminum-cone-midbass-driver-4-ohm--290-212The Minimus 7 internal volume is .0592 cu ft or 1.76 liters.ND-105 Vas is 4.5 in liters.Here is how the Aura 4" fit:http://baselaudiolab.com/RS-M7-AURA1.jpg Quote Link to comment Share on other sites More sharing options...
JKent Posted May 10, 2014 Report Share Posted May 10, 2014 How's the Dayton project coming along? Looks like the surround protrudes quite far. Does it hit the stock grille?What about xo? Does the PZ-2.1 xo design work?I have a pair of Mini 7s with one bad woofer. Had bought a pair of the MCM 55-1856 as replacements but it's a very tight fit.Kent Quote Link to comment Share on other sites More sharing options...
Pete B Posted January 9, 2017 Author Report Share Posted January 9, 2017 Designed a PC board for the Minimus 7 mod and finally finished mine. Â Details here, pic below: http://audiokarma.org/forums/index.php?threads/minimus-7-pz-2-2-mod-diy-circuit-board-by-pete-basel.750334/#post-10182495 Quote Link to comment Share on other sites More sharing options...
Colubrid Posted August 8, 2019 Report Share Posted August 8, 2019 Deleted post Quote Link to comment Share on other sites More sharing options...
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