Minimus 7 woofer tweak

[gotvinyl]

Pics of kit mod

Atwood, that is very nice looking. The black woofer complements the tweeter nicely. It sure fills the space. Does it interfere at all with the grills?

Here are some pics of my kit modification. The woofer is the MCM #55-1856. You can see some rubber gasket material I used because it is not a perfect fit, and I wanted to assure that the box was sealed. This is home depot rubber gasket material from the plumbing section. I will likely chamfer the hole better and get some speaker gasket material from PE.

I put a stock woofer back in one and have been comparing them. The MCM woofer has better bass.

I am going to post a table of the different parameters of the woofers I am considering using in the next set which will have the PZ 2.1 crossover mod.

 

[atwoodt]

Looking good-- you even matched the woofer to your receiver . Thanks for posting. I'd be interested in the tables. I still need to do the A/B comparisons. Still breaking things in, still like them.

The grills still fit believe it or not. However, I usually add Felt for the tweeters and leave the grills off.

 

[atwoodt]

To honor those that developed the x-over (not just Zilch)... i made up a vinyl sticker to go on the back of my modified Minimus 7.

 

[gotvinyl]

Woofer comparison table

Attached is a table on woofer specifications I put together for the woofers I am considering as replacements. I circled the parameters for each candidate that measured closest to the stock woofer. I noticed that considering the closest and second closest, the MCM #3856 was closer to stock in the most categories. That would be my front runner.

I would appreciate any comments from those who understand the measurements better than me. This is not my field, and though I have been reading about it, my understanding is limited.

The goal here is to find a repacement woofer that will sound good with the PZ 2.1 crossover modification.

I have been A/B'ing my auction site kit modification (MCM # 1856 woofer) against a stock woofer and a pair of Definitive Technology Procinema 800's. The MCM woofer is superior in mids and bass to the stock woofer. It is very clear and detailed. I am shocked to say that it is more clear and detailed than the Def Tech as well. The bass is better when boosted 4-5 db from 250 hz on down, too.

Here is some info on the candidates:

http://www.mcmelectronics.com/produ...commendation&utm_source=prod&utm_term=55-1853.

https://www.madisound.com/store/product_info.php?products_id=1607.

http://www.mcmelectronics.com/produ...commendation&utm_source=prod&utm_term=55-1856

http://www.mcmelectronics.com/produ...commendation&utm_source=prod&utm_term=55-3853

Any help on this would be greatly appreciated.

 

[gotvinyl]

Cool Sticker, atwood. Great idea.

 

[gotvinyl]

Generally speaking, if one were to seek out a replacement woofer and knew the Thiele/Small parameters of the woofer being replaced, which of those parameters would be most important in choosing the new woofer in order to achieve similar performance to the woofer being replaced?

 

[Copa1934]

Generally speaking, if one were to seek out a replacement woofer and knew the Thiele/Small parameters of the woofer being replaced, which of those parameters would be most important in choosing the new woofer in order to achieve similar performance to the woofer being replaced?

Just taking a stab but the Qt (I believe). The replacement should at the very least work within the constraints of the size of the cabinet, otherwise the replacement won't perform optimally and likely perform poorly compared to the original, I did say likely, not always.

 

[outlawmws]

Can someone post a link to the zilch, M-7 corssover mod? (I know a search will get me nowhere fast...)

 

[Copa1934]

Can someone post a link to the zilch, M-7 corssover mod? (I know a search will get me nowhere fast...)

ROFLOL. I know the feeling. It would be nice if more posts had more meaningful titles, making it easier to search.

Try advanced search, you can include zilch as the member and it will narrow things down a bit faster. Give it a try. Oh, you'll still use the minimus 7

 

[gotvinyl]

Outlawmws, here is the link yoiu wanted: http://www.audiokarma.org/forums/showthread.php?t=199790

 

[gotvinyl]

Thanks, Copa. That makes sense. I wonder if the re is also very important for matching woofers without having to make adjustments in the crossover network...

 

[DKirk]

I blew my Minimus 7 center channel speaker last night. We were watching "Unstoppable" and I had it cranked up pretty loud because my wife likes it when the subwoofers vibrate the couch. I replaced it with a Cambridge Soundworks center channel speaker I had on hand and went on with the show. I know that the three front speakers should be a sonic match, but it sounds good to me. I don't plan to replace the Minimus.

 

[RickeyM]

What setting for your speakers did you have your receiver on, small or large? If the Minimus 7's couldn't handle the small setting, it may be time to step up to the Minimus 77's

 

[EscapeVelo]

What sounds better, the higher volume of the 7w's or the greater mass of the 7's?

Where do you get these superior crossover replacements?

 

[mikeybc]

What sounds better, the higher volume of the 7w's or the greater mass of the 7's?

Where do you get these superior crossover replacements?

Hmmm, I have never heard this question asked before nor do I know the answer, You'd think there would have to be some small differences somewhere :scratch2:

 

[EscapeVelo]

Hmmm, I have never heard this question asked before nor do I know the answer, You'd think there would have to be some small differences somewhere :scratch2:

Seems like you might get more resonance/flex with the walnut veneered wood (what is it partical board underneath there?) than with the heavy metal enclosures. The high mass gives a solid base from which the drivers to do their thing. Ive heard people talk about the cloth grill covers vs metal, but never about this issue. The 7w's look like they may have greater interior space, and that volume might be helpful, and the flexing wood resonance might actually help the overall sound.

The 7w's are more aesthetically pleasing. I have the 7's and am thinking about getting some 7w's for possibly replacing them. When I get them both together I can A/B them.

Just curious.

 

[Pete B]

Generally speaking, if one were to seek out a replacement woofer and knew the Thiele/Small parameters of the woofer being replaced, which of those parameters would be most important in choosing the new woofer in order to achieve similar performance to the woofer being replaced?

This is a good question and something to consider is that the Minimus 7 is a very small acoustic suspension system where the box compliance dominates.
Generally if you want an exact match, then Fs, Vas, Qts, Le and Re should match. The odd thing is that what you really want to match is moving mass (this along with the box volume determine the closed box resonant frequency Fc) and motor strength which is indicated by Qts. However, the same motor strength yields a different Qts for different values of Fs. Qts is proportional to Fs so if you found a driver where Fs was 20% higher then ideally Qts should also be 20% higher. This all assumes you want to keep the system sensitivity the same, you can always adjust the tweeter R to rebalance the woofer/tweeter and then just live with the change in system sensitivity. Large changes in tweeter R will also shift the crossover point but minor changes are not a problem.

If you want better performance then Fs should be as low as possible, Vas as high as possible consistent with the moving mass and motor strength being the same so that the midband voltage sensitivity is the same. Moving mass could be increased for a lower Fc and then the motor strength increased and/or the impedance dropped to keep the voltage sensitivity the same. The moving mass is indicated through the T&S parameters by Vas and Fs. Xmax should be as large as possible. Re and Le should be the same if you want to use the same crossover. If a lower Re is used, the woofer XO inductor and resistor can be scaled down proportionately and the cap up.

You can also alter the stuffing to compensate for system Q differences.

 

[newguy1]

my wife likes it when the subwoofers vibrate

Lol

 

[gotvinyl]

Thanks for that response, Pete. I made a table to compare woofer candidates and ended up picking the MCM 55-3853. It works great. Re and QTS are close but Le is 20% off. Here is the table: http://www.audiokarma.org/forums/showthread.php?t=366524. Go to woofercompare. I hope I did that right - AK wouldn't let me upload it again. Anyway, it is on p. 2 of this thread.

I don't know how accurate the information about the original woofer is, as I got it from surfing around the internet, but the results are excellent with the PZ 2.1 crossover. I have it on my desk driven by a yamaha CA 800, which has a bass boost up to 5db at 250 Hz and below.

 

[Pete B]

Good to know that the MCM woofer works so well. The original RS woofer was far from the best or anything high tech. Here are my measurements on the stock woofer:
http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=4679&view=findpost&p=75096

Keep in mind that the woofer carries much of the midrange and therefore the cone break up modes and any response irregularities are not likely to match the original woofer especially when one has an aluminum cone. Still the design does not treat any of the irregularities so you get whatever the driver has to offer, if it is flatter you get a flatter response and vice versa. The roll off also matters in terms of working with the crossover but most drivers of this size roll off around 5K or so.