SR71 Build

[---k---]

Normally, we use MDF and ply because it is more resistant to movement due to moisture and temperature change. Engineered wood is also less resonant. But, enough people have done all solid wood and made it work. But, then again a few have had them crack.

Butt joints are strong enough with MDF and ply. I believe that real wood is obviously different. Glueing end grain to face of real wood doesn't work well - especially with the denser woods like mahogany. So, if you're using real wood then rabbets might be advisable.

[schnottus]

Pics please!

The pictures don't do them justice, it is eerie looking at them in person cause they are so shiny it's kind of a mirror effect like you are looking through them.
I also added some aluminum trim around the outer edge of each zaph driver, made it look a lot nicer. Polishing was done by sanding up to 2000 grit paper and then using an electric auto buffer and a Pinnacle 4 part scratch and swirl removing kit. They were then waxed with Wolfgang synthetic auto paint sealer. And I know, my listening room is cluttered, however I am in college and nothing can be done about it for now.

edit: I forgot to mention that these are crossed with an 8" subwoofer.

Raw mdf:

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Primed:

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Painted:

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All three:

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A few more photos can be found here:

[oneplustwo]

Normally, we use MDF and ply because it is more resistant to movement due to moisture and temperature change. Engineered wood is also less resonant. But, enough people have done all solid wood and made it work. But, then again a few have had them crack.

Butt joints are strong enough with MDF and ply. I believe that real wood is obviously different. Glueing end grain to face of real wood doesn't work well - especially with the denser woods like mahogany. So, if you're using real wood then rabbets might be advisable.

Ok... I'll go ahead and rabbet all the joints. Might as well. Hopefully, since half is solid wood and half is plywood (no end grain glued to face either), I won't have any cracking. Also, it's not that big a cabinet relatively speaking and living in San Francisco hopefully means the relatively temperate and consistent weather will reduce the risk further.

[evilskillit]

Man those are some good looking black cabinets. Its too bad it takes so long to get that finish. I'd love to have speakers that look like that. I don't think I've got the time or patience tho.

[schnottus]

Yeah, i wouldn't do it again like that, maybe just the front panels if i ever paint again. The thing that sucked is when you are polishing the paint up and theres no wax or sealer on it something as simple as wiping a little dust off with a microfiber leaves noticeable scratches that have to be repolished. And since all of my speakers were that vulnerable i had a hard time moving them and polishing one side without scratching the other. I ended up leaving the backs with quite a few little scratches since i got tired of messing with it.

[oneplustwo]

ok... here's my plan for my panels:



And my first cut at the steps to build plus some questions. Let me know if you have any edits.

1. Cut ply pieces plus top mahogany piece first. Dado sides and top.
2. Assemble the shell and glue
3. Measure for the front and back mahogany pieces next to make sure. Cut and dado, cut holes and counter sink. (Do I cut the hole to the outer dimension minus the router bit diameter I need?)
4. Cut strut pieces and glue in place
5. Measure for holes in the baffle and then drill
6. Transfer holes into strut pieces and drill through holes
7. Install tnuts and seal
8. Install cross members
9. Install crossover
10. Wire speakers, crossover, td cup
11. Test speakers
12. Install foam
13. Glue rear panel (probably need to trim and round over at this point)
14. Install drivers
15. Install front baffle

[oneplustwo]

I ended up using half a sheet of 1/2" birch ply left over from another project and laminated myself some pieces for the side panels. They'll be 1" thick now instead of the 3/4" I was originally planning. Also, I found some scrap 3/4" birch ply for the bottom so that will be as the design above.

[oneplustwo]

Hey folks,

Quick question... since my sides are now 1" instead of 3/4", is it best to preserve the interior volume vs. the exterior width? That's what I was planning on but I didn't know if having the baffle be an extra .5" wide was going to make a bigger difference. Or will a difference of volume by maintaining the exterior width even make a difference?

[evilskillit]

Preserving the face width is the most important thing of all when making the box. Make sure the inside is still wide enough to accomodate the woofer with the outside being the right width. If not just make the walls 1/2" thick and add lots of bracing.

You can keep the width the same and still keep the volume the same too, just make it a hair taller or deeper. Deeper is usually the safest/easiest way to go as taller shouldn't be a problem but may cause you some issues in the long run.

[oneplustwo]

Gotcha, I can do that. Deeper it is! Thanks for the input. Just got my circle cutting jig today. Waiting for the plunge router to arrive!

Anyone have any perspective on grills? I don't really want to build one mostly because I'm lazy, but also because it's more money to spend. And I kinda want to let the Mahogany show. But is there a technical reason to have one?

[evilskillit]

Grills increase WAF and keep the probing hands of little child monsters off of the drivers. (tho mine just pushed in hard enough on the grills of my BR-1S to push in the dust cap of the woofer anyways, vaccum cleaner to the rescue)

Sonically, and in my opinion, if you think your drivers are safe then you're better off without em. Bare speakers look better and the grill frames introduce a small level of diffraction in the sound. Just beware of children, pets, randomly flying objects, drunk friends, friends kids and spousal disapproval.

[oneplustwo]

Ok... and as for speaker height, IIRC, I want the tweeter to be ear height, right? I should be able to place them about 2 feet from the back wall and 3 feet from the side wall on the right.

[evilskillit]

Yeah tweeters like to be right around ear height.

As for room placement that is probably fine. Zaph may mention specific room placement requirements in the speaker's article, if there are any. Also you may want to google and do some reading on speaker room placement if you're really interested. But that placement sounds just fine.

[oneplustwo]

I'm trying to decide if I want to just glue the baffles in place or screw them in. On one hand, I doubt I'll ever redo the speakers. On the other hand, if something goes wrong at some point, it would suck to have to break them. Maybe I'll just screw the back in but glue the front in? Or is the other way around better?

If I do screw them in, does anyone have a recommendation on what kinda of seal to use? I think somewhere in my reading, that the standard material was some sort of adhesive backed foam tape?

[---k---]

6 of 1, 1/2 dozen of another. If you're not planning on reusing the boxes for a future project, just glue the baffle on. More than likely, if there are issues, you can reach in through the woofer hole to get whatever you need. just use industrial velco to secure the crossover.

If you do go removalbe, use weather stripping. I like the Marine grade weather stripping from HD because it has stronger adhesive.

[oneplustwo]

Glue it is! I would prefer the cleaner look as well. Should be able to get some more done this weekend! Fun fun!

[oneplustwo]

Hey folks,

I got my kit from Madisound yesterday. Quick question though. I understand how to wire to the speakers themselves. But there are two inputs indicated labelled high pass and low pass respectively. I think I use both in parallel... is that right? It's just the high pass and low pass labelling confused me. (Also, the kit comes with a biwire cup which makes me think I should wire in parallel.)

Otherwise, I got some work done on the cabinets... the panels are all cut and rabbeted. Just have to get the holes cut for the drivers and cup, glue them in, and round over the edges. Should be close this weekend!

Oh... One more question. Any problems using scrap rectangular cross section pieces for the stiffening members? The design calls for round dowels, but I thought I might as well use the scrap that I have lying around vs buying round dowels.

EDIT: picture of progress so far:

[---k---]

I got my Zaph kit yesterday also...

Yes, wire the high pass and low pass in parallel.

Yes, square scrap wood is fine for bracing.

[oneplustwo]

Ryan - you got the ZA MTM kit? I was thinking about building the 2 channel or maybe the 2.5 just to compare to the SR71. But I guess I should finish this project first.

[chupalt]

Not trying to thread hijack...

I finished my ZA5.3c this week and subsequently ordered a pair of ZA5.3 MTM for fronts.

I have some pictures in my photo-bucket account. The finish isn't super fancy, but I'm happy with how it turned out.

[oneplustwo]

chupalt - looks pretty good! what was your finishing process? I might do MDF next time... this plywood/mahogany thing was kinda pricey.

[---k---]

chupalt - those look great.

oneplustwo- yes, I ordered the Zaph ZA MTM kit. I'll be picking up some hardwood for the baffles today or tomorrow. I'll be posting updates to my thread Zaph ZA in a Steel Tube after I get the wood.

[chupalt]

oneplustwo - I decided to go simple and follow the method that zaph recommends for the baffles in his design mantras section.

I applied 3 or 4 coats of sanding sealer, followed by 3 or 4 coats of rustoleum textured black paint, followed by a clear coat to make the dust easier to wipe off.

They look surprisingly good in person and it was really simple to apply.

[oneplustwo]

Got a little bit more done today. Made a couple small mistakes though.

1. I should have rabbeted the baffles vertically to insure flat surfaces to mate to the cases (my table saw is kinda so-so.) As it is, my glue job may have some small gaps. I'll have to take a look after I trim and roundover to see if there are indeed gaps and if so, fill in with some sawdust/wood glue.
2. My initial countersink for the woofers was a tiny bit too small. About 0.10" or so. I didn't realize this on the first one until after I cut out the thru hole. I was able to sort of kluge together the little circle I cut out back in place so I could use the jig again with some backyard engineering so that worked out ok I think.
3. I probably should have made the countersinks a little deeper. I haven't tried it yet, but I'm not sure I'm going to be able to get the drivers in flush after I put the gasket in. I figure I could always add more gasket to build up to flush if necessary.

Well, hopefully tomorrow I can get them trimmed and rounded over. Then sanded and tung oiled.

[evilskillit]

Looking very good for a first speaker. As you are finding out tho, firsts are a learning experience. I'm eventually going to build new cabinets for my first project, transplant the crossover and drivers and throw the old cabinets away The Microbes deserve better. But we all have to start somewhere, and you're starting off a lot better than I did.

[---k---]

I've done all three of those on almost every project.

I wouldn't worry too much yet about your recesses being too shallow. The foam gasket will compress down to paper thin over time.

[oneplustwo]

Ok, a couple questions (thanks for everyone's help so far actually)

1. So I was only planning on rounding over the front face. I could round over the top and rear as well (not the bottom) but that seems like it would be too round looking. I don't think there's a technical reason to round those over, is there?
2. Is there any issue with interal wire management? I know there will be lots of slack so wanted to see if there were any key thoughts to keep in mind.

[oneplustwo]

Got the edges trimmed and the front baffles rounded over. Probably repair any problems, sand, and tung oil tomorrow.

[---k---]

I guess you answered your roundover question.

Usually, it is just the sides to ease veneering. My Khans are painted and have the top rounded over.

As for internal wiring, I've never worried about it. I have lots of slack so that I can pull the drivers in and out easily. JonMarsh goes to some extremes with wire ties to take the weight of the wire off the tab.

[oneplustwo]

Ok... got the sanding and tung oil done. I'm pretty happy with the finish. The Mahogany turned out about as I expected. The birch turned out a little bit darker than I thought it would be.



I also got the foam in. double layer on top, single layer on sides. I think Zaph said double layer on the back too, but there seems to be so little interior space and so little area with the cup and the vent tube... another layer seemed like a bit much. So far, I just have one layer. Is that ok?

I have the wires soldered to the crossovers too. Just have to connect to the drivers for a test before mounting everything inside! Very excited!

[---k---]

The foam doesn't really reduce the volume, it in practical terms increase it. It is really there to absorb the back wave and keep it from reflecting back into the driver and producing extra sound. Listen to it the way you have it. Then add the foam and see which you like better - or if you can hear a difference.

[oneplustwo]

I got them done tonight! I ended up doubling up the rear foam. Not sure if I got the right amount of acoustistuff in there, but I think it's probably close.

I plugged them in and they sound pretty good. Still need to get them set up properly and figure out what I'm going to do about stands. They seem a bit... I dunno, veiled? Kinda like my Sennheiser HD650 headphones sounded before I got them broken in and got good amplification. I guess I have to break these in too. Once that happens, I'll have a more thorough review. I also hope to have my DIY class A amp done soon too so that should help.

Anyone here going to the Norcal meet? Would it be worth bringing these if I can make the trip?

[evilskillit]

Wow, lookin good. Hrm, you might just try playing them at a bit higher volume and see how they sound too. They have full BSC so they may be a touch less sensitive than whatever you had before. If that is the case at the same point on the dial that you're used to listening they might be a bit quieter which might make them sound a bit subdued. Also I'm sure they just need a bit of breaking in. They look fantastic tho, I'm sure they will make you happy for a long time.

[Dean100]

Nice work. Those are beautiful! :T

[numberoneoppa]

Oh, wow, those look very nice. Well done!

[---k---]

Very nice.
If after they've broken in a bit, if they still sound veiled try taking out a little of the Acousticstuff. Not saying you got too much or too little, but tastes vary and stuff. Placement will also have a big effect on the sound as noted above. So make sure you get that right. Parts also have tolerances.

[oneplustwo]

Thanks for the comments! I think they look pretty decent if I don't get too close and see the little mistakes that probably I would be able to see at first glance.

I think they may be a little less sensitive than my current speakers. Also, I didn't finish them till about midnight so I couldn't really crank them up. I'll continue to break them in and get them setup better today sometime.

Question about feet... if I put these on speaker stands, do they need spiked feet? Or just rubber feet? No feet? Not sure what the thinking is on that.

[evilskillit]

Are you asking if the speakers need feet or if the stands need feet. If the stands are on carpet then putting spikes on them helps you get em really level and snug to the floor. My current stands don't have spikes and getting them to sit really flat is tough.

As for the speakers themselves, just putting them on the stands should be fine. If you really want to get em snug to the stands some people use blue-tac, or you could use rubber feet, but its not required.

[oneplustwo]

Gotcha. They're on hardwood, so I guess I'll stick with rubber feet. Thanks.

Also, is there a way to change the title of the thread? This really turned into my SR71 built so I thought it might help change the title for folks doing searches.

[oneplustwo]

Grr... my three year old pushed in the woofer centers. I tried vacuuming them out to no avail. I used a little tape and pulled them out. There's a little crease in them still and the tape took a little along with it, but it seems ok. Is this my excuse to build another pair? Or are they ok? (I moved them downstairs till I can get the stands done so I haven't listened to them since.)

[numberoneoppa]

Oh my god, that's horrible. Build some grills.

[evilskillit]

That sucks. I have a 3 year old and I've been conditioning her to fear daddy's speakers since she's been old enough to get near them. Btw grills are not a guarantee of safety, she pushed the dust cap in on a woofer on one of my speakers simply by pushing hard on the grill when nobody was looking. Thank god it was just the BR-1S. Just try to keep em out of reach and get the kid to keep their distance. Grills provide a small safety net but tweeters and woofer dust caps can still be pushed in through them by accident, or with a bit of determination.

[oneplustwo]

Oh well... it's my own fault I guess. Sometimes I just expect too much of her I suppose. Need to remind myself she's only three and it's her job to get in trouble. Gotta get those stands done! I was thinking about making them out of aluminum scraps from the local metal shop. Anyone have any experience with finishing aluminum? I was just going to wet sand and leave a dull matte finish.

[john trials]

When my daughter was a little over 1 year old, she turned the volume of my stereo up to full (200 Watts!) when it was turned off...she didn't know what she was doing. She later asked me to play some music. The explosion of sound was VERY impressive. It ruined the aged surrounds on the woofers. She grasped onto my leg in intense panic and wouldn't let go for quite a while. After I got over the shock (it scared the hell out of me too) I thought it was pretty funny. She never touched the stereo after that! Give your daughter a little fear and she'll leave your stuff alone!

On finishing aluminum: I do it all the time at work (and I've done it on both of my speaker projects...outriggers). Use Scotchbrite pads to give a nice random matte finish. You can do it all in one direction, or random directions, or swirls (do the same pattern all over or the finish will be different in various spots). Sometimes I use a bit of rough sandpaper first to get rid of crud or larger scratches on the aluminum, then finish with Scotchbrite pads. Wash the aluminum residue off your parts with soap and water, and that's it. There is no need for a clear coat. I do it dry, because doing it wet doesn't do much. It's too subtle. Wet sanding would be good if you were going to try for a mirror finish.

[evilskillit]

Btw, keep in mind that speaker stands with speakers on top are generally top heavy devices. Having my daughter around mine scares the heck out of me, which is why I use stands in the closed music room and just have my speakers on a console in the living room. Just something to keep in mind.

Btw, if you want to look at the bright side of this, you've got a pair of speakers that sound awesome and if the kid does somehow manage to destroy a driver you only have to spend about $80 to replace it, you know what it is and where to get the replacement parts. Vs, having bought a comparable sounding speaker (probably well over $1000-$1500) and having a driver get damaged. You'd probably have to send it to the manufacturer for repair and pay a couple of hundred dollars for a new driver. DIY is a beautiful thing.