The Schlafmutzes Mini MT’s design and progress

[JonW]

Final- and revised- crossover for the basic (ER15 woofer) speakers for in room placement

Earlier I had posted a “final” crossover for the basic speakers with in room placement. I was pretty happy with them but not wowed. There was a fair gap between the deluxe and basic speakers in my perceived sound quality. But it was as good as I could get them. That was for the in room placement. Then I went to work on the on wall placement. I took on wall measurements and made up a somewhat different crossover for the situation. Clipped it together for voicing and… it sounded much better than what I had before for the in room basic speakers. Better and closer to what the deluxes were yielding. So I also used this new on wall crossover and listened to the speakers with in room placement. Still excellent. Consequently, here is the new and final basics in room crossover. I will change this crossover on page 1 of this thread. This one is final. Really. I swear.

The basic, in room crossover:



R1 is a tweeter padding resistor. Adjust it to taste, to get more or less treble. I like it where it is at 3 Ohms.

The electric filters for the tweeter (C2, C3, L2) and woofer (L4, L5, C6) are electrical third-order. Acoustically, they came out right at LR4.

The Zobels (C7, R11 and R12, C8 ) and filters (L1, C1, R3 and R10, C9, L6) all helped bring things under control and sound good.

The resistors R2, R4, R8, and R9 are not real. Do not add them in. They are there to account for the high DC resistance created by using these small 18 and 20 gauge inductors, needed to fit the crossovers into the tiny cabinets.

Lots of parts but I think that they turned out sounding good.


Final frequency response. No smoothing was applied and it’s just about +/- 2 dB:



Phase. Looks like a good match to me:



Impedance. I’m pretty happy with it but some amps may need to watch out for that dip to ~4 Ohms in the middle:



Reverse tweeter null:



Measurements taken 30 degrees off axis and put into the in room crossover:

[5th element]

What's interesting to me with these is how much the 30 degrees off axis measurement changes vs the on axis.

Usually you would expect a bump up towards the low frequencies as the bafflestep compensation is now going to be too aggressive. Your on wall, on axis plots, do not show this, but I am wondering if the off axis plots are a little better?

How did you make the off axis plot? Moving the mic or the speaker?

[JonW]

What's interesting to me with these is how much the 30 degrees off axis measurement changes vs the on axis.

Usually you would expect a bump up towards the low frequencies as the bafflestep compensation is now going to be too aggressive. Your on wall, on axis plots, do not show this, but I am wondering if the off axis plots are a little better?

How did you make the off axis plot? Moving the mic or the speaker?

Hi Matt,

Yes, you are seeing some things that I also noticed. There were two related items here that crossed my tiny mind:

-For the off-axis plots, there is a bump in the ~15,000-20,000 Hz area. I did not expect that. I expected a gradual drop as frequencies rise. Which I pretty much have, except for that bump.

-The on wall versus in room measurements do not show much in the way of baffle step changes. I expected to see more. Maybe it is more visible in the longer gate time plots, with the wall bounce nulls, than the shorter gate time plots.

I moved the microphone off-axis for the 30 degree measurements, rather than rotating the speaker. A few years back, I actually built a rotating speaker thingy. Basically, it was two large, wood discs. The bottom one stayed on the floor and the top one rotated. And I marked off degrees. It was big enough that a speaker stand could go on it. Take a measurement, rotate the speaker on this thingy to a specific degree, take the measurement, rotate it back without any significant change in the setup, etc. But we had an unexpected flood in our basement. This rotating thing was amongst the soaked and moldy items that needed to be thrown away. So, for this project, I just moved the microphone after all other measurements were complete.


More plots in a moment...

[JonW]

Basics on wall crossover

Last up is the basic speakers with the on wall crossover. The method I just described, two posts above, for the deluxe on wall crossover was pretty much the same thing that I went through here. Let’s walk through it…

Here is our starting point of the in room measurements with the in room crossover:




On wall measurements placed into that in room crossover:


As was the case for the deluxes, it’s fine. But we will deal with the tipped up top end.


On wall measurements taken long enough to see the wall bounce, placed into the in room crossover:



Here are the on wall measurements placed into the new, on wall crossover. Note how it is a little flatter than when these same measurements were in the in room crossover (two plots above):



On wall measurements taken long enough (9 ms) to see the wall bounce and nulls, placed into the on wall crossover:



Circuit for the on wall crossover:


It is the same as the in room crossover except for the tweeter padding resistor (R1) going from 3 Ohms before to 4 Ohms here. Remember that R2, R4, R8, and R9 are not physical parts of the crossover. They are just accounting for the DC resistance of the inductors.


Phase of the on wall measurements in the on wall crossover:



Impedance of the on wall crossover:



Reverse tweeter null for on wall measurements in the on wall crossover:



30 degree off axis, on wall measurements in the on wall crossover:

[5th element]

The high frequency peak could quite easily be diffraction related, is it there when the speakers are in free space? When you move the mic for the off axis measurements does it move anywhere near anything? We're talking 2cm wave lengths at this frequency, so if you've got a lamp stand, or anything nearby it could be throwing things off.

What's interesting is that baffle step, with your cabinet width, starts around 1kHz, with a small diffraction bump more around 1.5k, even with the gated shots you'd expect to see some rise, in fact most of the compensation should be over by around 200Hz. One of the benefits of using narrow cabinets is that the transition frequency goes up so it makes it a lot easier to measure.

One thing that helps with this though is that the speakers don't have a lot of bass extension. Too much BSC can make speakers way too heavy handed if they have extension down to 30Hz or so, which means positioning them and designing in the right amount is a little more critical. Usually too much BSC only though the mids just makes things sound a bit too warm and on the lush side, certainly not a bad thing for non critical listening.

[JonW]

Hi Matt,

Yeah, I am seeing that 15,000-20,000 Hz off axis bump everywhere. Here it is in the Deluxe, in room speaker. This was a physically different speaker than the one from above:




I don’t think that I had anything coming close to the measurement rig. Photos of that setup are below.


But maybe here is the answer. Look at the Scanspeak off-axis measurements:

http://www.madisoundspeakerstore.com/scanspeak-soft-dome-tweeters/scanspeak-illuminator-d3004/6020-10-1-tweeter-deep-chamber/

Doesn’t that look *very* familiar? So I guess it’s in the tweeter. Maybe a product of the small flange and all that. And it helps me think that my own measurements are working out to be OK.



Thanks for the perspective on BSC and bass output for narrow versus wide cabinets. I still don’t quite understand the BSC matters with these specific speakers, but things are coming along nicely. I think that they sound great so I’m not complaining. I am building a sub to go along with these speakers. I can hardly wait to listen to the Deluxe speakers paired with the sub.



By the way, last week I was kind of close to your neighborhood- Ireland. I was only there for 50 hours, from when the plane landed to when it took off again. It was a work trip and I had a nice time. I’m not a beer guy, but I did have a pint of Guinness. And I have to say that it was one of the best beers (OK, stouts) that I have ever had.




Image not available

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[---k---]

Jon
Good stuff. I was surprised by the lack of baffle step adjustment too. I've heard a definite difference due to placement of my Khancenter out in the room vs flush under a tv. But maybe. Matt's theory of wide vs narrow and the overall lack of bass extension explains it.

Hopefully one of these days we'll be able to do another get together. I passed through Lafayette last week on my way to Indy. Just long enough to get gas and a sub.

[5th element]

I have to say they are very nice looking speakers! This has been said before, but it is worth repeating.

Pairing the Deluxe version up with some subs should offer a serious wallop of good sound.

[JonW]

Jon
Good stuff. I was surprised by the lack of baffle step adjustment too. I've heard a definite difference due to placement of my Khancenter out in the room vs flush under a tv. But maybe. Matt's theory of wide vs narrow and the overall lack of bass extension explains it.

Hopefully one of these days we'll be able to do another get together. I passed through Lafayette last week on my way to Indy. Just long enough to get gas and a sub.

Yeah, my current thought is that the speakers are so tiny that BSC is less of an issue. It’s maybe almost no baffle at all. Let’s see. The cabinet width is 6.5”. We could remove 1” for the facets. Then suppose that we have a full sized, normal flanged tweeter of ~4”. That only leaves ~1.5” of baffle left. Maybe that’s it? I know that I’m stretching things here.

Yes, of course it would be great to get together. I still have your Woofer Tester to return to you. Are you coming down for any fall football games? I hope to have these speakers done into the football season.

I have to say they are very nice looking speakers! This has been said before, but it is worth repeating.

Pairing the Deluxe version up with some subs should offer a serious wallop of good sound.

Thanks, Matt! Here is a photo of that sub. No finish in the photo but I do have the finish coats applied. Still need to add the driver and plate amp.

Image not available

[5th element]

Oh is that the Vifa NE sub?

[JonW]

Umm, I will be putting a Tempest-X 15" driver into that cabinet. To pair with these teeny speakers. :B

[---k---]

You're going to have the most thumping office on campus.

[cjd]

Down firing? That's a nice sub cabinet!

[5th element]

Someone else built a vifa NE into a cabinet very similar looking to that over on DIYA, which is what I was remembering. The Tempest is obviously going to blow that out of the water. You will not lack for bass once that is set up.

[JonW]

You're going to have the most thumping office on campus.

That would be the goal.

Down firing? That's a nice sub cabinet!

Thanks! Yup, it’s down firing. And will have a plate amp. You can see the holes in the photo, below.

My wife thinks that it looks like the ummm, business end of an outhouse. She calls it my plumpsklo, which is German for outhouse.

Someone else built a vifa NE into a cabinet very similar looking to that over on DIYA, which is what I was remembering. The Tempest is obviously going to blow that out of the water. You will not lack for bass once that is set up.

Ahh, I see. Didn’t know about that. Just tried to find out about it but my search didn’t turn up anything.

When this sub and the little speakers are all complete, I will write up a step-by-step build thread on the sub. I took lots of photos along the way. It was a fun woodworking project. It’s birch ply with cherry accents, which hide all the ply lines. And I tried to give it a certain look. This sub will be the table upon which I keep all the electronics to run the little speakers. (I have not yet decided on what electronics I will use.)

Here is the sub in its current state:

[JonMarsh]

Coming along very nicely- bonus points on finish quality! :T

[knowledgebass]

From that angle, it does appear to be in the outhouse family, although much fancier than the ones that I have seen
Nice detailing on the edges and panels!

[JonW]

From that angle, it does appear to be in the outhouse family,

Jeez, I’m getting it at home and here on the web! Everyone is mocking my projects! :B

although much fancier than the ones that I have seen
Nice detailing on the edges and panels!

Thanks!

Coming along very nicely- bonus points on finish quality! :T

Thanks, Jon! It looks like progress will slow down for a bit. In the next two weeks, I’ll be in Florida, then California, then Washington, DC, then come back to Indiana. Am I missing any states there?

[JonW]

I’m back from all my summer travels. I flew all over the world and to nearly every US state, it sure feels like. And boy are my arms tired. I have started a little bit of the speaker work here. Not too much to mention, mostly just putting little things together that need to be done. I’ve had 2 of the deluxe speakers and 2 of the basic speakers going. In the end, I’ll be running 4 of the deluxe speakers. I just made the basic flavor in case someone wants to build a cheaper version of these speakers. So I pulled out the 2 ER15 drivers. (Not sure what I'll do with them.) Then glued on felt to the 2 remaining W16’s. And also glued felt into all 4 of the cabinets. More progress to report as it happens.

[JonW]

Ummm, this is going to be quite the puzzle in three dimensions. All of these parts need to fit into this tiny cabinet, in a specific order. But they can’t be too close to the woofer magnet. And the inductors can’t be too close to each other. Between the driver sticking into the cabinet and the thick sonic barrier foam at the back of the cabinet, there is only about 3” of bottom space depth left. I’m making two small crossover boards, one for the tweeter and one for the woofer. And then mounting them on opposite sides of the cabinet. Then maybe put something like a piece of peg board between the two crossover boards in case they ever fall down. So they don’t short out or anything out. Not exactly sure how I’ll do all of this. But I’ll figure out something.

[---k---]

Looking good. ... you would have made a great engineer.

[JonW]

Looking good. ... you would have made a great engineer.

Aww, shucks, thanks. You know, on paper and officially, I am now a professor of a particular engineering discipline. I'm mentoring Ph.D. students and giving them degrees. But no one over there knows that I've never actually taken so much as a single engineering course. Shhhh, don't tell them. It's a crazy world, I tell ya.

[---k---]

I had to Google to see what that was about. But, Googling your name led me to the Sexy Scientist blog. Dr. Jon is "HABANERO!" :T

[JonW]

Oh boy. That thing is still up? Ummm, I spend years trying to establish myself as a competent scientist and that’s what Google has to say about me. Could be a lot worse, I guess. What’s this thing about “the right to be forgotten?”

[JonW]

OK, enough silly talk. It’s time to get back to business.

All four woofer crossovers are put together. The first one was a bit ugly and the next three came out a little bit cleaner. I cut peg board to 2.5” x 6” and squeezed all the parts on there. Trying to keep the inductors as far apart from each other as possible:

http://www.troelsgravesen.dk/coils.htm

When I have all the crossovers built, I will take better photos and mark which part is where, to help in case anyone wants to build these.

Making the tweeter circuits will be a little more challenging, with more parts in a similarly small space.

I’m no sparks and wires guy. But I have to say that, for as long as this project has been going on, it’s nice to actually be making crossovers.

(Edit: Earlier I gave the wrong dimensions of the crossover boards. It's corrected, above, now. They are 2.5" x 6".)

[5th element]

Wow those crossovers sure take up quite a lot of volume in and of themselves.

[JonW]

Yep. I don't think that the crossovers, themselves, are any bigger than typical. It's just that the cabinets are so small. Small is one of the big challenges here. At the same time, we also want bass down to 80 Hz for good crossing to a sub. And low distortion. I'm not sure how well it comes across in the photos, but the speakers are pretty small. Certainly not the smallest that are out there. But maybe the smallest able to hit 80 Hz and to do so with low distortion.

[JonW]

I’ve got one of the tweeter crossovers made. Three more to go. It’s on the right in the following photo. Notice how it’s more complex than the woofer crossover, on the left. It’s not as pretty, but making the next three will probably be a little neater. That’s how it went with the four woofer crossovers.





I tell ya, cramming all the parts onto so small of a board is a bit challenging. Especially trying to get sufficient distance between inductors. The tweeter circuit has three inductors. I put the two largest ones far apart and perpendicular to each other, as much as possible. Then there was the tiny 0.025 mH inductor, closest to the camera, that I did the best I could with.

When I have all the circuits made, I think that I’m going to clean off the flux from all the solder joints with rubbing alcohol. I hear that's a good thing to do.

I took this next photo to give an idea of the scale of things. There is a CD there for scale, against the side of one cabinet. Then there is another cabinet with a tweeter circuit and a woofer circuit. Oh, plus the woofer. We can’t forget the woofer. That’s a lot of stuff for these small cabinets.

[---k---]

Use NPE caps would make those crossovers a lot smaller and easier. :P
hahaha

[cjd]

You should see the Jantzen I put in the Nebbiolo. 5.6uF, red, and huge!

[5th element]

See I thought the first xover board was the entire crossover, not like less than half of it!

I think I would definitely use NPEs with those. At least if the crossover required a 30u cap, I'd use a 25 NPE in parallel with a 4.7u poly cap.

[JonW]

You should see the Jantzen I put in the Nebbiolo. 5.6uF, red, and huge!

I just took a look and those Nebbiolos are some seriously good looking speakers! Excellent job there. I hope that they sound just as nice. :T



Use NPE caps would make those crossovers a lot smaller and easier. :P
hahaha

I think I would definitely use NPEs with those. At least if the crossover required a 30u cap, I'd use a 25 NPE in parallel with a 4.7u poly cap.

Yeah, you guys are right in that the NPE caps would be a lot smaller. Not to mention a lot cheaper- maybe by ~$100/pair. But… I don’t know… I have so much time invested in this project that I just didn’t feel comfortable going that way. I don’t crank out 5 designs a year. My hobby time is so scarce that these speakers are kind of a ‘make them right and make them once’ kind of a deal for me. The drivers are expensive. But spread out over 5 years as my only speaker project, it’s OK. Heck, if I bought the NPE caps when this project started, by now they would be one third through their usable life already. :E

See I thought the first xover board was the entire crossover, not like less than half of it!

Yeah, it’s crazy, eh? The crossovers are not big, in general. They are just big relative to this cabinet.

A long time ago, when I was picking drivers for these speakers, I tried modeling woofers with rough guesses on bass response versus cabinet size. Like we all do. And I tried to guess how much the crossover would steal away volume and bass response. It was not much of an effect. A rough guess with poor volume estimates and based on a fuzzy memory, it was something like an F3 difference of 1 Hz. When I have all the crossovers built, I will try to measure an actual volume for them. Then put that into a modeling program see what happens to the bass output. I have real, near field woofer measurements that I took. (The bass reaches a tiny bit deeper than expected.) So I can get a decent idea of what happens. I’ll post these results when I get them.

[JonW]

Got a little more crossover building done. Nothing warranting a photo. And still more to do. I started on the remaining three tweeter crossovers. All the components are now glued into place on the boards. No solder yet. I went a little crazy with the hot glue, to really bond things together. In my past project, I used hot glue and then zip ties. (Kind of like belt + suspenders.) I might have to skip the zip ties this time. The crossover boards will have to be mounted on the cabinet sides, not the bottom. So I want as much of a smooth surface on the bottom of the boards as possible for good contact to the cabinet side- no bumps from the zip ties. I have not decided how I will affix the boards to the cabinet side. Velcro is what I used in the past, but those crossovers were on the bottom of the cabinet. I might use hot glue. I don't think that I can screw the boards to the cabinet. Probably not enough space to get in there with a screw driver and such. We will see. When all the crossovers are built, I'll play around with them in the cabinet and see what looks best.

[JonW]

Does anyone have any tips for how to attach the crossover boards to the inside of the cabinet?

Due to the size restrictions here, the crossover boards are going to have to be mounted on the sides of the cabinet, not the bottom. I want them to stay on the sides and not fall down, say, 10 years into the future. I figure that I could use velcro with adhesive backing. Or put some hot melt glue in there. Screwing down the crossover boards probably won’t happen because it will be tough to work all that together inside the restricted space plus there is not much space on the boards to hold the screws. Any other suggestions that I should be thinking about? Thanks.

[Steve Manning]

Jon,

A couple of ideas ..... I've used cable tie mounts that have the ability to be screwed down to the surface so you don't have to rely on just the sticky backing, which would never hold in your situation. You could mount those in place on the cabinet walls before the x-over boards go in and then zip tie the boards to the mounts through holes in the boards. I've used a short stubby screw driver to get into tight spaces for that, or you could use a 90 degree attachment for a drill that also works rather well, they can be had for ~$20. You could also use that setup to drive screws directly through the boards as well.

Steve

[Steve Manning]

Something like this .....

[JonW]

Hi Steve,

Thanks for the excellent idea!

I had not thought about cable tie mounts. Hmmm. Interesting. I wonder how I might screw them into the cabinet sides. I doubt that I could drill a pilot hole for the screws. Maybe a sheet metal or some other types of self tapping screw. The cabinet sides are only 3/4” thick, so the screw would have to be short. And once the mount is in place, putting in the crossover boards and then feathering the zip ties around the mounts will be tough. There will be almost no space to work in there. When one board is in there, putting zip ties on the second will be challenging.

If the mount was screwed into the cabinet side and then the crossover boards are zip tied to the mount, that would make for a nice, stable attachment. And also one that could be removed easily, if needed, by clipping the zip tie. I’m definitely going to look into this one. Thanks.

[---k---]

Probably not the best solution for your project, but the woofer and mid crossovers on my Khans slide into dado cuts on a pair of boards that project from the sides. Works well.

[cjd]

You definitely want wood screws if you go the screw route, and who can object to a little screwing in cramped quarters? The shortest drywall screw you can get may be the easiest, but you're after fewer threads per inch and as long a taper on the tip as you can find. A shorty screwdriver gets the job done. Of all the tricks I've tried, unless you just use glue (be sure to let it off gas a week or so if you use silicone or something, it can damage drivers for the first few days) I've found screws easiest, because you can get them done blind.

[JonW]

Probably not the best solution for your project, but the woofer and mid crossovers on my Khans slide into dado cuts on a pair of boards that project from the sides. Works well.

Yeah, that’s elegant. Probably best left for a much larger cabinet, with enough space to lay the crossovers down flat. But a good idea that I can keep in mind for my next project, whatever that is. But whatever it is, it won’t be as small as this one.

You definitely want wood screws if you go the screw route, and who can object to a little screwing in cramped quarters? The shortest drywall screw you can get may be the easiest, but you're after fewer threads per inch and as long a taper on the tip as you can find. A shorty screwdriver gets the job done. Of all the tricks I've tried, unless you just use glue (be sure to let it off gas a week or so if you use silicone or something, it can damage drivers for the first few days) I've found screws easiest, because you can get them done blind.

Good tips on the screws- thanks! I tried some test fittings (see below) and I may have to go the glue route. Even with a shorty screw driver, I don’t see how I could get it all to work in there.

For glue, any recommendations? I’m thinking hot melt glue, which has worked well for making the crossover boards. Maybe I should let that off-gas, too, although I don’t know. Thanks for that tip.

[JonW]

I played around with the crossover boards and the cabinets and here’s what I’ve got…

The tiny iPhone lens and flash are good for seeing inside. Not in focus (too close) but you can get the general layout idea. It’s a test fit. You can see the felt on the bottom and the tweeter on the top. In the top left is the woofer board. Then the tweeter board is in the bottom right. I then added in a piece of peg board (2.5 x 8”) diagonally, the separate the two boards to prevent contacts and shorting. Things are squished and squeezed in there very tightly. I had to press down some of the solder joints and wires to make everything fit.

It looks so tight that I don’t think that I can even spare the added distance from the cabinet sides that the cable tie mounts would add. And trying to screw those boards down…? The photo actually makes it look like there is more room than there really is. For now, I’m thinking about hot melt glue to hold everything in place. Add the glue to the left cabinet side and slide in the woofer board. Then add the diagonal peg board, with some glue on the bottom. Then add glue on the right side and push in the tweeter board.

[JonMarsh]

Wow, that's a sardine can in there, isn't it? :B

High grade hot melt glue is my friend... it could be yours, too! I think it's definitely needed, but be extra sure you don't want to change anything, and that it's fully tested before installing! :W

[JonW]

Hi Jon,

Yup, it’s pretty tight in there, alright. If it was too easy, who would be interested?

OK, yeah. Hot melt glue is looking like the way to go. Sure, I’ll test it with the meter before sealing things up, making sure the resistance looks OK. I have already tested each solder joint with the meter. And I have checked and rechecked the path of all the parts. Is there any other way to check things out before closing it up?

I am thinking there might be a middle ground with the glue. Perhaps. Use enough that things stay in place for the long haul. But little enough that I can pry it all out should the need arise. We’ll see...

[JonW]

I’ve got all the crossover boards soldered together. Next up is wiring them into the drivers and binding posts.

And arranging things to get a switchable speaker, to go between the in room and on wall crossovers without having to open the speakers up. My current thought it to take advantage of the two binding post pairs that are there. Amp cables go into the lower binding post pair. The negative binding post goes into the negative of both the tweeter and woofer circuits. The positive goes into the woofer. Then the positive of the other binding post pair goes to the tweeter circuit. Outside the cabinet, I connect the two positive binding posts with a jumper cable. That’s for the in room configuration. For on wall crossover, there is just 1 Ohm extra padding on the tweeter. For on wall, I can make a different jumper cable with a 1 Ohm resistor in the middle. Just switch jumper cables and I can switch between in room and on wall easily. That’s the idea for now.

After all that, I will hot melt glue in the crossover boards. Then I will keep them open for a week of off gassing before closing them up. I’m getting there...

The woofer circuits:



And the complete police line up of the usual suspects:

[kevinm]

It must feel good! They're looking great! I'm quite impressed with your crossover layout ingenuity. I'm terrible at figuring out where to put the pieces