I theorize: 'Synchaeta'....a Minimus 7 revamp...

[Wolf]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

Here's the pic of the patch:
Sorry for the fuzz- I was also trying to get the picture of the rubber floor tile glued to the side walls. This adds mass and lowers the Fb of the panels since they are 3/16" thick.



Xover in position:
I did not solder the resistor to the tweeter, as the leads on my used 15 ohm were not long enough. The space between the terminals is long enough to fit the resistor though. 3" hole saw for the boards. I had to go 'off-board' to get it all on there.




Mounting hole yet to be drilled marked by the blue dot, will allow installation through the tweeter hole with a simple screw:



All poly'd up:



Wall mount included to keep true to the original:



I have yet to build the other and solder both xovers, install the terminals and stuffing, and then apply seals for the drivers and torque them into place.

I should have them playing this weekend,
Wolf

[Navy Guy]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

That's a pretty tidy little crossover board.

[Wolf]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

That's a pretty tidy little crossover board.

Thank you! Winding the coil around that cap was not the easiest thing I've ever done either....
Saved a LOT of space though,
Wolf

[Wolf]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

I buttoned them up about 1:30am Saturday. The woofer seal will be done now that I'm satisfied with the results. I used 1+ oz of fill in the cabs. 0.25 oz Ultratouch denim in the back, and 0.75 oz premium poly-fil in front of that (measured on my scale). I also had a very small amount of the single layer Sonic Barrier left over, so I cut it in half and used about a 2" square on the inner top panels.

Had them over at Matt's waaayyy early this morning before coming home to sleep, and they really do a nice job at most anything. Sweep from the IMM-6 on his phone into the DTA120 shows relatively flat response, if not just a touch polite on the very top end- when sitting on his computer desk. The close boundaries really do emphasize the lowest bass, and it does a relatively good job in that area. It even does better than the Rat Shack 40-1030- so the revamp is an upgrade for sure!
The bonus is the vocals never sound thick even when on the desk, so the dippy 500-900 Hz range did improve that aspect of the design for easier placement. Raising it on stands and evening the tweeter to ear level was also better. Tonality didn't change much standing at a distance either.

Oh- they get pretty loud pretty quick too!

I'd say the xover is good as it is, and I won't be changing it. I know most steel core coils don't go below 1.0mH due to core saturation and such, but unwinding one to 0.9mH isn't going to harm much at these levels.

I'll post the official schematic in the near future,
Wolf

[Wolf]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

Final pics and official xover schematic:







Thanks for looking!
Wolf

[6thplanet]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

Nice little build there Benny! Whats the 0.1mH coil in series with the 3.3 cap doing for the woofer?

[Wolf]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

It tanks the breakup.
Thanks!
Wolf

[6thplanet]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

Kinda what I thought, do you feel thats any better than the cap/res in parallel with the woofers coil? Personally I can't hear a difference, whats your take on the matter?

[Wolf]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

Kinda what I thought, do you feel thats any better than the cap/res in parallel with the woofers coil? Personally I can't hear a difference, whats your take on the matter?

There is a difference in what a CR and LC(R) filter does. A CR will cause a change in the impedance and level of the knee before rolloff, so it does attenuate the broader range a bit. The LC focuses a resonance to shunt a narrower freq range, dictated by the Q of the filter's resonance, to 0 ohms or whatever resistance used as the R. The inductive rise of the lowpass affects the impedance to raise it back to a healthier range.

When you have a breakup peak, there are 2 ways to get rid of it- Attenuation, or shorting it out. This usually involves a notch rather than a CR filter, or it will not be completely compensated. A CR would not have done what was required to minimize the breakup to negligible levels.

Later,
Wolf

[6thplanet]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

So essentially what your getting at is if the break up is a bunch of crap at the end of the FR of a driver you'd shoot for a CR shunt. If its more of a large peaky looking break up then using a L w/ CR notch would be the better choice.

[Wolf]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

So essentially what your getting at is if the break up is a bunch of crap at the end of the FR of a driver you'd shoot for a CR shunt. If its more of a large peaky looking break up then using a L w/ CR notch would be the better choice.

I have sufficiently rolled off a resonance in a driver with a 3rd order filter and no notch. As long as the peak is reduced to a decent level, notches aren't required. Typically when I use a CR, it's more to tweak the knee of the xover to rolloff the woofer as I want it to. Some drivers like the Seas L18 require an LC (no R) to suppress the breakup, as well as a 3rd order:


In the case of the Stance, the RS125-4 has a gnarsty breakup that is +5dB above reference, from 8-15k. I had to take it to -50dB for it to not affect the FR or be heard.

If it's a broader peak, and of low amplitude like in baffle step bump, and in-bandwidth, then a parallel notch placed in series with the driver is your best bet. This also will not affect the impedance detrimentally like a shunt/series notch will. If it's out of bandwidth, then an LC(R) is usually easier, and won't affect the impedance due to the LP's inductive rise.

Another thing to try is a broad LC that is out of bandwidth on a woofer. This can work like a tank cap does across the main LP coil in terms of breakup suppression, and works sometimes when the tank won't.

I guess- it really depends on the application,
Wolf

[Wolf]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

Apparently, I forgot to add the relative driver centers to the thread, and I never mentioned the actual built dimensions.
The depth on mine are different to compensate for using 1/2" back and 3/4" baffle. All edges are rounded with a 1/4" roundover.
I used 3/16" wood paneling for the sides top and bottom.
HWD on mine is 7" x 4 5/8" x 6", and the real actual Min7 dims are listed easily on google:



Driver positions:



There- all info is included in the build thread!
Later,
Wolf

[6thplanet]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

Cool, thanks for the explications.

[Kevin K.]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

I got to hear these little guys last night with a group of guys in Ben's room and then heard them again at the competition in a very large room. They sounded fantastic for their size. I was floored at how well they filled up the room in the competition. If you need to go small but don't want to give up much sound quality, these are going to be hard to beat. I'm ordering parts for a pair to put on my desk next week! I may add a small sub under the desk to compliment them only because my desk is out in the middle of the office.

[Kevin K.]

Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

Ben,

Told you I liked em! I pulled the trigger on the order today, should have the parts in time for the weekend. I am going to use Tom's new 2.1 plate amp that is in the new flyer and build it into these as desktops. Tom mentioned he had run the amp with 4ohm speakers and didn't notice any problems. I figured as efficient as these little guys are and being near field on a desk, it should probably work fine.

Question, you put a note on your crossover schematic "2-3 inches above". Would it be ok to build the enclosure 3" taller with a false bottom and place the crossovers down there upside down? I guess I could use some standoffs to suspend them right side up if it wont work. Thanks for posting the design, looking forward to building them.