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

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  • Wolf
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    For those interested, here attached is the measured T/S of the RS 40-1030, and it's now very clear why the bass is decent in the Min7 cabs from them....
    I'm keeping these off of the Bucket to prevent confusion. The Xmax is 3mm, and 94dB is tickling the 2mm spot all the way down. Vas is TINY!!!

    The sim with the PRV is not far from this one, so it should be pretty close.

    Later,
    Wolf
    Attached Files
    Last edited by Wolf; 04-30-2015, 03:39 AM. Reason: added box sim for RS

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  • dynamo
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Cool project Wolf, nice crossover work as always!

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  • Wolf
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Originally posted by datranz View Post
    Wolf, would you mind helping me with this project for my physics class. I would like to learn more about designing crossover, it would be great if I can use this design as my learning reference. Thank you.
    Nicktran909(at)gmail(dot)com
    You might want to remove your e-mail addy to prevent spam, or space it out and use (at) and (dot) instead of the actual characters so spambots can't latch onto it.

    Beside that point- xover design takes a lot of research to understand. What is it you want to learn? We can start a new thread with the direction of many in terms of your project, with or without this design as the basis for discussion.

    Let the group of forum members help you out,
    Wolf

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  • datranz
    replied
    I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Wolf, would you mind helping me with this project for my physics class. I would like to learn more about designing crossover, it would be great if I can use this design as my learning reference. Thank you
    Last edited by datranz; 04-29-2015, 04:28 PM.

    Leave a comment:


  • Wolf
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Went to Matt's, and the PRV's drop right into the Minimus7 cabs. No mods required. The ND25FA-4 I'm using is a touch big for the Minimus7 sized baffles I'm using to keep the design as true to the original I can. I am using 1/4" paneling for the top/btm/sides, and 1/2" for the rear and 3/4" for the baffles; so the depth will be different on mine, but all else the same as a Minimus7. The tweeter will have to be shaved a touch on the circumference in one spot to allow the woofer to set down into the recess/hole in my case. If you use the ND25FN-4 (faceless) instead, and use the radius on the edge of the installation hole, the FR should match the FA-4 and not be an issue for either wood boxes as I'm doing or for the original aluminum cabs.

    Also of note- I was going to use some 0.1mH chokes from Radio Shack as the coil across the woofer in the LC shunt, but I found out they were ferrite-rod cores, and the value changed to 0.01mH (measured) when in close proximity (read: attracted magnetically) to the PRV's magnet structure. I will have to use an air-core coil for this spot, and keep the main LP coil FAR away from the woofer if at all possible.

    When building speakers this small, Neodymium or shielded magnets can help avoid issues with interaction of xover components. If you are using the aluminum Minimus7 cabs, also be sure your coils measure the same once they are installed inside. Aluminum can actually lessen the inductor's value if in too close of a proximity.

    As to where I'm placing the xover...
    I'll attach the parallel resistor to the tweeter. All else will likely be on a removable panel in the upper back This will also retain the components to within the 1/2" rear wall, and hopefully retain more internal volume than expected.

    Hole sizes:
    The ND25 installs perfectly into a 1.75" hole, and has a 5/32" recess depth. I drilled the hole with a 1.75" Forstner bit, sanded lightly woth 80g so it is not so tight, and used a 3/8" rabbet bit with my next size smaller guide bearing. This would have given me a 2 11/16" rebate diameter, but that's a smidge large. I wrapped the inside of the through-hole with masking tape before I routed to take up the slack, and came out pretty close. The diameter is pretty much a solid 2 21/32".

    The PRV will drop into a basic 4" exact hole. Any larger and it will not seal properly. Like most/many stamped-frame 4" pin-cushion drivers, there is a small 'ledge' where the surround is glued into the frame, and that makes the step in the frame meet the 4" diameter spec. The Minimus7 cabs have a layer of sealing felt on the baffles, and the driver seals quite well this way. I drilled a through-hole of 3" with the drill press and a hole saw, and hit the front side hole with a 1/2" roundover bit. The roundover bit was used beading-style, so the edge had a lip on it very similar to that of the driver. I will soon route away a majority of the 3" - 4" region that was left after these 2 steps, so that the driver will drop in and retain the lip I made for it.
    WAIT........
    BEFORE I DO THAT- I have to glue the side panels onto the baffles and backs, and then route. This is because there will only be about 1/8" of material left around the mounting hole without the sides attached. This makes the perimeter strength a lot better, and won't jeopardize the integrity of the baffle. If someone builds these out of wood-style materials, I would advise increasing the baffle dimensions a half inch per, so you won't have these issues. I'm doing it this way to keep the dimensional integrity of the Minimus7 cabs for viability, and I totally understand why the manufacturers went with an aluminum cabinet for these reasons alone.

    I'll post more pictures as time allows, and to illustrate what's been said here.
    Later,
    Wolf

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  • Wolf
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Well- I guess the alignment changed the overall response profile, and made the tilt in the LP too much. I also measured the tweeters, and the impedance was considerably different. This made a change for a higher xover point. I will say, listening to the ND25, I prefer it above 4k, as that is where it noticeably cleans up, but it's not imperative to be xover'd that high.

    So- tweeter Z's, Sim2, and sectors....







    The reverse null is not as deep either, but the phase is still as before. Fewer turns of copper on the LP coil is a plus for size reasons.
    I will try both the 1.2mH and the 0.9mH and see how the balance is between them.

    Looks like I have to see if I have some stock 0.9's, as I think I might....
    Later,
    Wolf

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  • humphreyblowdart
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    If you ever make a smaller version you should call it "Forum-mini-for-ya".

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  • Wolf
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    The System Sim is the first after 'On to the Preliminary Xover....' that has 3 panes/windows in it, followed by the next attachment- the reverse null. That DEEP trough is the reverse null.

    Later,
    Wolf

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  • DanHine
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Originally posted by Wolf View Post
    As well as the plot below the system sim that I've attached above.

    Later,
    Wolf
    You've attached a LOT of things above. Which one is the "system sim." I apologize if I seem completely dense but it's like you're speaking a different language. :o

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  • Wolf
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Okay- the Box model looks a LOT better in that little box. Aperiodic really isn't necessary, and 8W yields Xmax that is reasonable all the way down at an output of 94dB. The best part- the F3 is 108Hz! That's almost a half-octave lower than prior. Sealed and stuffed!

    The grit:




    This is likely going to be better than I thought....

    I'll be revising the Xover sim for accuracy next.
    Later,
    Wolf

    Leave a comment:


  • Wolf
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Originally posted by isaeagle4031 View Post
    Dan look at the two orangeish and light blue lines in the pcd sim. That is the driver phase. They track each other very well especially at the crossover point. Then look at the reverse null (grey line in the pcd sim). Deep and narrow also identifies good phase tracking.
    As well as the plot below the system sim that I've attached above.

    Later,
    Wolf

    Leave a comment:


  • Wolf
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Originally posted by Mark65 View Post
    The very first one at the top. But honestly, looking at that plot, I wonder if Fred might not be right. Space considerations aside, it looks like the woofer, at least, might be happier crossing lower, even given the pretty reverse null. It seems that phase is tracking really nicely up to 1.5kHz, whereupon it diverges noticeably. I'm well aware that Ben has forgotten more than I'll ever know about this stuff, but I wonder, nonetheless.
    Another concern is the Qts of the tweeter being 1.5, and having a HUGE bump before rolloff. To tame that, this is where it fell. FWIW, I see good phase alignment from 200 Hz to about 7-8k before it spreads quite a bit. When you view the phase unwrapped, the departure you speak of at 1.5k is really very minor.

    Later,
    Wolf

    Leave a comment:


  • isaeagle4031
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Dan look at the two orangeish and light blue lines in the pcd sim. That is the driver phase. They track each other very well especially at the crossover point. Then look at the reverse null (grey line in the pcd sim). Deep and narrow also identifies good phase tracking.

    Leave a comment:


  • Mark65
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    The very first one at the top. But honestly, looking at that plot, I wonder if Fred might not be right. Space considerations aside, it looks like the woofer, at least, might be happier crossing lower, even given the pretty reverse null. It seems that phase is tracking really nicely up to 1.5kHz, whereupon it diverges noticeably. I'm well aware that Ben has forgotten more than I'll ever know about this stuff, but I wonder, nonetheless.

    Leave a comment:


  • DanHine
    replied
    Re: I theorize: 'Synchaeta'....a Minimus 7 revamp...

    Originally posted by isaeagle4031 View Post
    And really look at that phase! That is just where these 2 meet up really well.
    I want to but I'm not sure which graph shows this. :(

    Leave a comment:

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