DIY Home Theater based around CSS Criton 3TD-X + 3TD-XC (a build thread)

[musicisair]

Hi! Complete noob to speaker design (and really the idea of "audio science" altogether) here. Ya'll have been amazing answering my (very naive) questions, so thank you!

After derailing CSS Criton 3TD-X Kit Speaker Review for a bit it @Rick Sykora suggested I start my own thread on building a CSS Criton-based home theater. So here I am.

First off: why DIY? Just because I like it. I have the funds to go out and buy a pretty great 7.2.4 home theater set up, but I found DIY to be a lot of fun.

The Room:

My room is about 16.5' deep, 15' wide, and 9' high (5m x 4.5m x 2.7m). Volume is about 2200ft³ (62m³). THX puts this somewhere between "medium" and "large" size (aka "Certified Select" at 2000ft³ and "Certified Ultra" at 3000ft³).

Below is a rough render of the planned space.

• The ideal listening position is in the back row, and isn't going to be all that "ideal". The back couch will be pretty close to the back wall, making rear and side surrounds quite tricky. The ILP being so far back poses issues for Atmos, so I plan on hanging the height channels (about 12" down) to get the the listening angles closer to an ideal range.
• I have young kids, so the front sound stage will be much closer to the front wall than ideal; I'll treat the room and the inside of the front wall as best I can to try to mitigate this.
  
  
  

I'll be using the 3TD-XC as a center channel, and maybe a slightly modified 3TD-X for front left and right (see questions below). A Denon X3800H AVR (105W per channel) will power things for now.

Important notes: I already have all the drivers and crossover components for the 3TD-X pair and a 3TD-XC. Crossover components can be changed, but I'd like to stick with the CSS (modified Wavecor) drivers.

Now for some actual questions... which might be all the wrong questions (I don't mind if you answer the questions I should have asked)

1. The CSS Criton 3TD-X is front ported. I'll have dedicated subwoofer(s), so I won't need an in-room response down to 20Hz from the towers. Should/could I:
   • it's fine; leave it ported as CSS designed it
   • stuff the port (can I put the port on the rear so I don't have to see it then?)
   • seal it up (my guess is the internal volume could cause issues so the mid/woofer crossover would need to be redesigned?)
   • add a passive radiator or two (my guess is the internal volume could cause issues so the mid/woofer crossover would need to be redesigned?)
2. I'd like to eventually build on-wall surround/height speakers (or maybe even in-wall!) utilizing the LDW6 (the same 6" mid woofer used in the towers/center) and same LD25X tweeter. The towers already integrate a smaller sealed enclosure for the mid and tweeter.
   • If the sealed enclosure were separated from the rest of the tower it would look like almost exactly like the crappy render I made below, except the drivers in my render are on the angled (15°) face, instead of the 90° baffle (in other words: I just spun things around).
   • at about 8" deep and 13" tall, it looks like a typical on-wall speaker already!
   • My naive idea is to use the same tweeter/mid crossover points as the 3TD-X tower, changing the mid's band-pass filter for something else.
   • Is this in the realm of possibility for a DIY noob?
     
     
     

Relevant documents:

3TD-X (tower) crossover and plans (pdf):

(ignore the z values)

3TX-XC (center) crossover and plans (pdf):

(ignore the z values)

Driver info:

LDW6 datasheet: https://drive.google.com/file/d/1UYvEY2rz7jyjwyxbir-xkB1TUFnJEroE/view?usp=sharing
LDW7 datasheet: https://www.css-audio.com/online-store/CSS-LDW7-7-Midwoofer-p110079914
LD25X datasheet: https://www.css-audio.com/online-store/CSS-LD25X-XBL^2-25-mm-Silk-Dome-Tweeter-p144557321

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Hopefully this thread turns into a fun build thread over the next 6 months to a year or so!

 

[Kerry Armes]

I'll be using the 3TD-XC as a center channel, and maybe a slightly modified 3TD-X for front left and right (see questions below). A Denon X3800H AVR (105W per channel) will power things for now.

Important notes: I already have all the drivers and crossover components for the 3TD-X pair and a 3TD-XC. Crossover components can be changed, but I'd like to stick with the CSS (modified Wavecor) drivers.

Now for some actual questions... which might be all the wrong questions (I don't mind if you answer the questions I should have asked)

1. The CSS Criton 3TD-X is front ported. I'll have dedicated subwoofer(s), so I won't need an in-room response down to 20Hz from the towers. Should/could I:
   • it's fine; leave it ported as CSS designed it
   • stuff the port (can I put the port on the rear so I don't have to see it then?)
   • seal it up (my guess is the internal volume could cause issues so the mid/woofer crossover would need to be redesigned?)
   • add a passive radiator or two (my guess is the internal volume could cause issues so the mid/woofer crossover would need to be redesigned?)
2. I'd like to eventually build on-wall surround/height speakers (or maybe even in-wall!) utilizing the LDW6 (the same 6" mid woofer used in the towers/center) and same LD25X tweeter. The towers already integrate a smaller sealed enclosure for the mid and tweeter.
   • If the sealed enclosure were separated from the rest of the tower it would look like almost exactly like the crappy render I made below, except the drivers in my render are on the angled (15°) face, instead of the 90° baffle (in other words: I just spun things around).
   • at about 8" deep and 13" tall, it looks like a typical on-wall speaker already!
   • My naive idea is to use the same tweeter/mid crossover points as the 3TD-X tower, changing the mid's band-pass filter for something else.
   • Is this in the realm of possibility for a DIY noob?
     
     

---

Hopefully this thread turns into a fun build thread over the next 6 months to a year or so!

1. All of those options can work. There are pros and cons to each. If you build it as a sealed enclosure, you won't ever be able to use them in a stand alone two channel system should your situation ever change (or if you just want to screw around to see how it sounds). None of these require a crossover change because the area they impact is all below 60-70 Hz.
   1. No changes
   2. You can move the port to the rear with no changes. If you stuff the port you will convert it to an over damped sealed enclosure with a Qtc below 0.7. This isn't necessarily a problem and many people prefer this alignment. It does increase the excursion demands on the woofers over a traditional 0.7 Qtc and possibly over the ported in some areas above tuning (I would need to sim it to check) but you will be crossing to a sub so you can limit that.
   3. Unless you want to make the cabinet smaller, I wouldn't go this route as it limits any future flexibility.
   4. You can add passives but would need to re-model the design and make accommodations for that. There is really no benefit to doing this other than eliminating all possibilities for port noise. A passive operations on the same basic principle as a port and extends the bass in a similar fashion but has higher losses so the output at tuning is going to be a little less than the port plus it is much more expensive. The other benefits passives provide is flexibility in tuning for different rollouts (it's hard to adjust ports repeatedly) and they due limit excursion some below tuning over a port. I don't see a reason to go this route since you don't plan to use the lower output of the ported design in the first place. I would just stuff the port, which prevents the port noise from being a potential concern.
2. There are two problems with this.
   1. Unfortunately it doesn't usually work out to be able to just eliminate the woofer low pass and mid high pass. The mid high pass section of the crossover typically interacts some with the low pass section to create a more complex band pass than just a standard low pass. I can try and model to see what it would look like sometime this week but it likely would need some modifications. I can probably give you something that will be a decent starting point.
   2. Putting the speakers on wall will significantly change the baffle step/diffraction interaction and will likely need less overall padding down of the high frequencies to match the low end.

 

[musicisair]

1. All of those options can work. There are pros and cons to each. If you build it as a sealed enclosure, you won't ever be able to use them in a stand alone two channel system should your situation ever change (or if you just want to screw around to see how it sounds). None of these require a crossover change because the area they impact is all below 60-70 Hz.
   1. No changes
   2. You can move the port to the rear with no changes. If you stuff the port you will convert it to an over damped sealed enclosure with a Qtc below 0.7. This isn't necessarily a problem and many people prefer this alignment. It does increase the excursion demands on the woofers over a traditional 0.7 Qtc and possibly over the ported in some areas above tuning (I would need to sim it to check) but you will be crossing to a sub so you can limit that.
   3. Unless you want to make the cabinet smaller, I wouldn't go this route as it limits any future flexibility.
   4. You can add passives but would need to re-model the design and make accommodations for that. There is really no benefit to doing this other than eliminating all possibilities for port noise. A passive operations on the same basic principle as a port and extends the bass in a similar fashion but has higher losses so the output at tuning is going to be a little less than the port plus it is much more expensive. The other benefits passives provide is flexibility in tuning for different rollouts (it's hard to adjust ports repeatedly) and they due limit excursion some below tuning over a port. I don't see a reason to go this route since you don't plan to use the lower output of the ported design in the first place. I would just stuff the port, which prevents the port noise from being a potential concern.
2. There are two problems with this.
   1. Unfortunately it doesn't usually work out to be able to just eliminate the woofer low pass and mid high pass. The mid high pass section of the crossover typically interacts some with the low pass section to create a more complex band pass than just a standard low pass. I can try and model to see what it would look like sometime this week but it likely would need some modifications. I can probably give you something that will be a decent starting point.
   2. Putting the speakers on wall will significantly change the baffle step/diffraction interaction and will likely need less overall padding down of the high frequencies to match the low end.

Amazing. Thank you for all this information!

1.3, I guess at that point I'd just be building another 3TD-XC with rearranged driver positions, plus an integrated stand to make it look like a tower. Tempting, but your point about never being able to repurpose them does give me pause.
1.4, For the passives my thinking was that passives have a "tighter" bass response, but also a lower output compared to ported, that it'd make for a slightly better speaker for pairing with a dedicated sub, especially if the speakers are close to the wall/corner of a room. My very wishful thinking was that it'd just result in a steeper, but still smooth, bass roll out with the existing enclosure and XO as designed, physics be damned!

2.*, I'd love to see what you figure out! I'm struggling to get reasonable results with VCAD simulation using the published DR and Impedance for these drivers. I think I'm just missing too much critical information (exact measuring params, z-offsets, off-axis FR, enclosure SPL, and i'm probably screwing other things up as well).

I made a better model of the mid+tweeter enclosure from the tower using FreeCAD, including the internal baffle and recesses. The internal volume should be about the same as on the tower, but the baffle is obviously taller now.

I tried using the model in AKABAK but can't convince it go beyond the BE-Mesh calculation. It doesn't error, it just stalls at 0% and doesn't consume any CPU -- I had never heard of AKABAK before today so I'm sure it's just something I need to figure out. Let me know if you (or anyone else) wants any of these models to play with!

FreeCAD model screenshot:

AKABAK project screenshot, with best-guess cone dimensions on the diaphragms:

 

[Ktacos]

I guess at that point I'd just be building another 3TD-XC with rearranged driver positions

That would require redoing the crossover, likely from the ground up. Unlikely that you could just modify the existing one.

I would stick to the designs as is because no offense but you don't sound like you're ready to be modifying anything.

1.4, For the passives my thinking was that passives have a "tighter" bass response, but also a lower output compared to ported, that it'd make for a slightly better speaker for pairing with a dedicated sub

Doesn't matter if you're using a sub, and bass "tightness" is more down to the room than anything.

2.*, I'd love to see what you figure out! I'm struggling to get reasonable results with VCAD simulation using the published DR and Impedance for these drivers. I think I'm just missing too much critical information (exact measuring params, z-offsets, off-axis FR, enclosure SPL, and i'm probably screwing other things up as well).

You definitely need the actual speaker constructed and measured to get any sort of accuracy for filter design.

 

[musicisair]

That would require redoing the crossover, likely from the ground up. Unlikely that you could just modify the existing one.

The XO of the 3TD-X and the 3TDX-C are nearly the same already. As long as the mid and tweeter stay close to one another, wouldn't the main considerations be baffle step compensation and diffraction effects? Correct me if I’m wrong, but wouldn’t that mean the capacitors and inductors might not necessarily need a major overhaul—mostly just tweaking the resistors for proper balance?

I would stick to the designs as is because no offense but you don't sound like you're ready to be modifying anything.

Regarding your comment about "not being ready to modify anything," I understand where you're coming from, but everyone has to start somewhere. By that logic, we wouldn't let kids play sports just because they aren’t performing at a professional level yet. Besides, I'm building speakers, not building passenger airplanes where screwing something up has real consequences.

My hobby is doing new things I don't know how to do. But honestly, I'm really not really considering "modifying anything" all on my own (yet!); I'm asking questions here and learning, and the people here have already been an amazing resource. Last week I couldn't even tell you what an inductor was, and now I can tell you that they usually come in red (kidding, silver and brown are pretty common, too )!

Anyway, this is highly relatable:

Doesn't matter if you're using a sub, and bass "tightness" is more down to the room than anything.

As for room acoustics: like I mentioned, I’ll treat the room as well as I can with the space I have. Since speakers don't change the resonant frequencies of the room improving the transient response of the low end (even at the cost of some attenuation) seems like it could be a net positive here. I know these 7" drivers are low-mass compared to a sub, so an improved transient response likely won't be significant if the subs are playing, but theoretically (I know, I know, measurement trumps theory 100% of the time), a sealed enclosure's characteristics would complement dedicated subs better than a ported design would, particularly in preventing bass overhang and helping ensure a smoother roll-off. Again, please correct me if I'm wrong.

Speaking of measurement... I haven't bought a mic yet. I'm thinking about Dayton Audio EMM-6 Electret Measurement Microphone since I already use a DAC with 48V phantom power, any idea if this mic is good enough for speaker building? It comes with calibration, but as I understand it, I wouldn't be able to measure absolute SPL accurately due to the unknown or variable gain introduced by my DAC.

You definitely need the actual speaker constructed and measured to get any sort of accuracy for filter design.

I understand that, but it's good to start with a best-guess XO, right? And simulations are the best way to get that. I've seen a couple of pretty accurate simulation vs actual measurements here on ASR. Like this one from: https://www.audiosciencereview.com/...orm-speaker-project.20407/page-27#post-812478
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rereading this I realized I might not be coming off as grateful for your feedback. I am. Thank you for taking some time to respond in the first place!

 

[Ktacos]

As for room acoustics: like I mentioned, I’ll treat the room as well as I can with the space I have. Since speakers don't change the resonant frequencies of the room improving the transient response of the low end (even at the cost of some attenuation) seems like it could be a net positive here. I know these 7" drivers are low-mass compared to a sub, so an improved transient response likely won't be significant if the subs are playing, but theoretically (I know, I know, measurement trumps theory 100% of the time), a sealed enclosure's characteristics would complement dedicated subs better than a ported design would, particularly in preventing bass overhang and helping ensure a smoother roll-off. Again, please correct me if I'm wrong.

The difference between ported and sealed bass is group delay in the lows, which the towers won't even be playing if you use subs. There will be effectively zero difference in the speakers transient response if you go ported or sealed. The room will absolutely mangle this group delay so the differences really don't matter, especially if you're using corrective EQ in the bass which you absolutely should.

Regarding your comment about "not being ready to modify anything," I understand where you're coming from, but everyone has to start somewhere. By that logic, we wouldn't let kids play sports just because they aren’t performing at a professional level yet. Besides, I'm building speakers, not building passenger airplanes where screwing something up has real consequences.

I'm just trying to provide some info on what one should expect when developing a speaker. Developing a measurement process that is accurate and consistent can take months in itself. It is a non-trivial task that largely requires a good bit of failure before you get it right. Some people never get it right, I would maybe focus on getting the towers and center done because that's going to be a lot of work by itself. Finishing can take a long time as well and messing that up can make you hate the whole project.

I can give you some tips on finishing later if you'd like. This is generally the result I get. I assume you'll be wanting to veneer them, it's actually really easy.

Speaking of measurement... I haven't bought a mic yet. I'm thinking about Dayton Audio EMM-6 Electret Measurement Microphone since I already use a DAC with 48V phantom power, any idea if this mic is good enough for speaker building? It comes with calibration, but as I understand it, I wouldn't be able to measure absolute SPL accurately due to the unknown or variable gain introduced by my DAC.

The lack of calibrated spl doesn't really matter, as long you're not changing the amplifiers output or mic gain when switching between drivers to measure you're fine. You want to be delivering a consistent voltage to each driver when you measure so that you appropriately pad down the drivers. I'd recommend grabbing an EMM6 from cross spectrum labs, it has calibrations that are better and more useful for speaker design and it doesn't cost much more.

I understand that, but it's good to start with a best-guess XO, right? And simulations are the best way to get that. I've seen a couple of pretty accurate simulation vs actual measurements here on ASR. Like this one from: https://www.audiosciencereview.com/...orm-speaker-project.20407/page-27#post-812478

Well the difference here is that Rick's stuff is ground up designs, where as all the work for the CSS towers has already been done and even verified on klippel so there isn't much need to "proof read" the speakers filtering. There's certainly some value in learning the ins and outs of vcad though through this process.

rereading this I realized I might not be coming off as grateful for your feedback. I am. Thank you for taking some time to respond in the first place!

You're fine, I understand I often come off as curmudgeonly.

 

[a4eaudio]

Speaking of measurement... I haven't bought a mic yet. I'm thinking about Dayton Audio EMM-6 Electret Measurement Microphone since I already use a DAC with 48V phantom power, any idea if this mic is good enough for speaker building? It comes with calibration, but as I understand it, I wouldn't be able to measure absolute SPL accurately due to the unknown or variable gain introduced by my DAC.

The Dayton is okay for crossover measurements and you don't need absolute SPL. Ktacos is correct to recommend getting it calibrated from Cross Spectrum Labs, unfortunately their website hasn't updated the status of Dayton mics since 2022.

Here is a study on the importance of a good calibration file.

 

[musicisair]

I can give you some tips on finishing later if you'd like. This is generally the result I get. I assume you'll be wanting to veneer them, it's actually really easy.

Thanks!

I've _thought_ about going with solid wood, despite the varying density, twisting, seasonal resonances, etc. But I've read horror stories about tall and well-braced solid wood speakers splitting, bowing, and even cracking woofer frames. Moisture sealing with a ceramic coating or impregnating with epoxy should help a bit; I'm in Florida so seasonal wood flexing issues are very real here.

I'm also considering adding edge treatments as described by Kerry here: https://audiosciencereview.com/foru...n-3td-x-kit-speaker-review.58467/post-2144829 , which will make veneering a bit trickier.

I do really like the look of speakers from Fleetwood Sound, Diapason, and another company I can't remember the name of that does solid wood bookshelves with dovetail joinery.

I'm not afraid of complex wood working, but veneering is still the most likely path I'll go, even though I haven't veneered anything in over a decade . I'd love someone to talk me into going with solid wood though! Realistically, it'll be a month or two before I get around to finishing. I'll be sure to post updates along the way!

 

[Ktacos]

Veneering a round over isn't hard, in fact a tower with 3/4" roundovers along the whole tower was the first speaker I ever veneered and it came out great.

 

[musicisair]

Veneering a round over isn't hard, in fact a tower with 3/4" roundovers along the whole tower was the first speaker I ever veneered and it came out great.

I haven't ever tried it, but veenering an offset corner chamfer at 30 degrees sounds like it won't be simple. Though now that I think about it, maybe it's actually easier than having to cut veneer for a corner roundover since there are actually hard edges to use?

 

[Ktacos]

I haven't ever tried it, but veenering an offset corner chamfer at 30 degrees sounds like it won't be simple. Though now that I think about it, maybe it's actually easier than having to cut veneer for a corner roundover since there are actually hard edges to use?

Chamfer is harder but a simple round over is probably sufficient for CSS's tweeter and baffle.

 

[Rick Sykora]

i would build the towers as designed. The fact that they have good bass is not a problem. It is actually an advantage and gives you more flexibility with bass management. If you find it is not better, would change the subwoofer crossover frequency rather than stuffing ports.

Another approach would be to reduce the volume of the tower while keeping its original dimensions. With the port in the lower part of the cabinet, incorporating a chamber to optionally seal it off could be done readily.

 

[musicisair]

i would build the towers as designed. The fact that they have good bass is not a problem. It is actually an advantage and gives you more flexibility with bass management. If you find it is not better, would change the subwoofer crossover frequency rather than stuffing ports.

Another approach would be to reduce the volume of the tower while keeping its original dimensions. With the port in the lower part of the cabinet, incorporating a chamber to optionally seal it off could be done readily.

Building it as designed is my plan right now, though I'd like to add some chamfers to the top and top corners of the front baffle (as discussed in Amir's review thread).

I'd like to also chamfer the center channel to somewhat match the towers, but the tweeter is too close to the edge in the 3TD-XC. I was thinking about extending the baffle by 3/4" on the top and maybe the bottom, but not changing internal volume or dimensions. And then chamfering everything. Obviously this will change the baffle step/diffraction: though I'm too naive to know how much this could alter the response. I think it may boost lower mid frequencies sightly and maybe attenuate and smooth 5k+ Hz slightly (vs the current baffle's top edge which is about 3/4" from the tweeter dome's top edge)? It might also narrow vertical off-axis response in the highs? Again, no idea how much this actually matters in actuality.

Hopefully I'll be able to find some weekends to build and measure these things soon.

I just realized I could build the center channel as planned, then just temporarily clamp on some pre-chamfered mdf on the top (and maybe additionally on the bottom) just to measure the effects without having to actually rebuild another enclosure. Corners and side diffraction changes are another story, though I don't think changes there will have as great an effect as the edges closest to the tweeter and mid?

 

[musicisair]

@Kerry Armes I'm moving our 3TD-X discussion here, as to not make so much noise in the review thread.

I modeled then raytraced the 3TD-X with a chamfered 1 3/4" front baffle (ignore the port, I just grabbed this NFR 0.5 Port model I found on DIY Audio - it's definitely not tuned appropriately).

The part that was tricky was ensuring the thicker baffle doesn't contribute to compression, as you mentioned in the review thread. I added a 1" pocket with a diameter equal to the enclosure's inner width to the backside of the baffle around each woofer, as the tower is as narrow as the woofers will reasonably allow already -- and I didn't think making the tower wider was a good idea.

These pockets add some additional volume I haven't accounted for, but it doesn't seem like it'd be very much (maybe the mid will "notice"?). I then ensured there were 45° chamfers on the backsides of the woofer cutouts as you suggested (added to the LDW-6 as well, even though it's not in the plans).

Do you think these pockets are a workable solution to the compression issue?

Notes:

* the chamfers angles are all 30° and are inset by 60.49 mm (about 2.38"). The corner chamfers are 11.5" down. So not exactly what you originally suggested, as 2.5" down from the top will "eat" into the top baffle a little bit. 2" down would work fine though.
* The 3TD-X plans are awesome! Though some of the Inch to Millimeter conversions are a bit wonky, like 5 5/8" [142.539mm] and 3 13/16" [96.599mm], and a handful of other places. They're off by fractions of a millimeter, so don't really matter in the real world, but they make things a bit trickier to re-model

 

[Kerry Armes]

Do you think these pockets are a workable solution to the compression issue?

Yes, that should work