Custom 2.1 computer speaker system. Need help with design.

**Undefinition** · 14 April 2010, 16:46 Wednesday

Looks like you've given this a lot of thought. And you have a pretty good plan.

That said, my first thought is that with those drivers, you'll end up spending more on a 3-way crossover than the drivers themselves. 3-ways are also pretty complicated in terms of XO design.

I'd recommend either the Scrappys or Overnight Sensation MTM for the desktop speakers. For the sub, the TB W5-1138 should be great. It gets the same extension as the W6-1139, but in a smaller box (can't handle quite as much SPL, though... but how much do you need when you're that close?)

**pcmofo** · 14 April 2010, 20:16 Wednesday

wow those are some great links you posted. I will have to read through those but it looks like a great place to start for both enclosure design/size and crossover design. Thanks!

**technodanvan** · 14 April 2010, 21:38 Wednesday

Man, you really have put a lot of thought into it - I like it!

Not much input on the speakers, but I'm not certain you would want a subwoofer built into the underside of the desk due to vibration and potential shielding issues. I.e...if you set some credit cards on your desk will they work next time you pick them up? Probably not a huge issue (in fact it's probably really unlikely) but I think the vibration right there would throw me off.

I would consider widening the back legs to the point your could get a 5-6" 'subwoofer' in them, and you could utilize the whole internal area of the legs as the enclosure if needed. They would be further from your ears so you would be less liekly to key in on them, and having them closer to the floor and back wall will give you a little bit of low-end gain.

Edit: That little amp looks cool! I've been trying to figure out what I could use at work that would be inexpensive and unobtrusive...thanks for showing that to me!

**mackintire** · 14 April 2010, 23:21 Wednesday

I 2nd the Overnight Sensations MTM.

**pcmofo** · 15 April 2010, 10:14 Thursday

Yeah it looks like you could use that amp as a headphone amp as well due to the in/out on the front face plate. I havent felt any real heat coming off of it. I plan on flush mounting it in the desk. And the LED is blue btw... which makes it about 2x cooler.

It looks like I might be able to take the Overnight sensations Ported design for the 4" driver (volume wise etc) and use that to figure out how big the ported enclosure needs to be.

The crossover design also looks very useful.

Does anyone have any thoughts on the total speaker wattage vs the amps 50w/ch and what combination of drivers I should use?

**Undefinition** · 15 April 2010, 10:42 Thursday

Originally posted by pcmofo

Does anyone have any thoughts on the total speaker wattage vs the amps 50w/ch and what combination of drivers I should use?

The T-amp is plenty to driver the Overnight Sensation MTM.

Now, as to the rest of your question... I think you're thinking of the whole "how many Ohms" situation too linearly. Car audio makes things seem simple (I have an X Ohm amp, therefore I should use such and such X Ohm speakers). Impedance of drivers is very complex--adding a crossover increases the complexity. This isn't a bad thing; it's the nature of speakers. But to understand it is to dive in to the black art of crossover design.

This explains what I'm getting at.

Paul Carmody's DIY Speaker Pages

http://sites.google.com/site/undefinition/diy-faqs-driverimpedances

Crossover design is not simple. It's not like matching up bus speeds for computer parts. You really should build the OS MTM design to spec. What people are going to tell you is to do a "proven design." Here's one more FAQ to explain why...

Paul Carmody's DIY Speaker Pages

http://sites.google.com/site/undefinition/diy-faqs-provendesigns

**pcmofo** · 15 April 2010, 14:51 Thursday

I read through most of your web site and the articles you just listed Undefinition. Your most likely correct, I should basically take your MTM design and modify the construction/outside to match my model. I will need to replace my 3" drivers with the 4" variety of course. I may just keep the 3" drivers to use in another project....

So assuming I am basically building a OS MTM with rounded corners and a plexiglass front I have a few questions...

How does the tweeter that I have compair to the tweeter you used? I paid less than $10 a piece so I would be OK with buying new ones.

How does the tweeter placement/driver placement effect the overall design? Can I center the tweeter and drivers so they are more symmetrical? I was thinking equal spacing between drivers and edges of the speakers. This also includes moving the tweeter to the center of the box as opposed to the left or right side.

I think that you have an excellent design and I am sure that it sounds great. I think I can successfully merge your design with the finished look I have envisioned for mine. If I have the measurements correct that should be 25w x2 + 10w tweeter for a total of 60w/ch which sounds like the T-amp can handle as you said. I'm going to take your dimensions and see if I can mock something up to get an idea of the overall size.

In regards to the general construction of the box, to create the rounded corners and square insides of the frame, I was thinking of having the box cut out of MDF in slices, rounded on the outside and square in the middle, then making a sandwich out of them and gluing them together into a hollow tube like shell the rest of the box would slide into. Unless their is an easier way to create the rounded corners with a router etc after building a square box...

Car audio is much easier, I have a 150w DVC sub @ 8ohms/coil and a 150w amp @4ohms so wiring and matching things is fairly strait forward. All of my speakers are component and have external crossovers premade. I have everything connected to a computer which I can eq each speaker individually. So I can correct for many mistakes. Clearly there is much more to this than I expected, even knowing I was not building super high end speakers. Thanks for your insite. A project log of my car audio build can be found Here

**pcmofo** · 15 April 2010, 15:39 Thursday

Want to know something really strange? My speaker box is nearly the exact dimensions as yours... weird. The face is the same size, 16"x6", The depth was 3" shallower than yours. I adjusted the depth, and added the 4" drivers and changed their placement to be centered. Here is what the finished product might look like. How do you think these would compair to the rest of your build considering the driver placement of the tweeter is centered? Also, the design takes into account using your exact tweeter. (driver frames shown in gray to show contrast)

**Undefinition** · 15 April 2010, 15:47 Thursday

Originally posted by pcmofo

How does the tweeter that I have compair to the tweeter you used? I paid less than $10 a piece so I would be OK with buying new ones.

Gotta use the same tweeter as spec'd. They differ mechanically, which means they'd react differently to the circuit, and it could either sound really bad, or cause a bad impedance load and shut down the amp.

How does the tweeter placement/driver placement effect the overall design? Can I center the tweeter and drivers so they are more symmetrical? I was thinking equal spacing between drivers and edges of the speakers. This also includes moving the tweeter to the center of the box as opposed to the left or right side.

While you will certainly find people who will argue that tweeter offset it vital, I'm going to go ahead and say that it'll be OK. It may cause a peak or dip of 1 dB or so up at 8 KHz or above, but would anyone know the difference?

If I have the measurements correct that should be 25w x2 + 10w tweeter for a total of 60w/ch which sounds like the T-amp can handle as you said.

You pretty much gotta forget about thinking of it that way in terms of home audio. The big limiting factor in a loudspeaker is almost always xmax of the woofer. Finding out where this happens is done in modeling (or you can do some old-fashioned SPL drag to find out when the woofer starts "popping"). I forget where you run out of excursion on the B4N in parallel, but I'm pretty sure it's under 50 Watts. A common tenet of hi fi is: "It's the first few watts that count the most."

In regards to the general construction of the box, to create the rounded corners and square insides of the frame, I was thinking of having the box cut out of MDF in slices, rounded on the outside and square in the middle, then making a sandwich out of them and gluing them together into a hollow tube like shell the rest of the box would slide into. Unless their is an easier way to create the rounded corners with a router etc after building a square box...

You're making it way harder than it needs to be, unless you're looking for a 1" or larger roundover. With anything less than that, a simple pass with a router and a roundover bit will accomplish rounded edges. LouC did a nice job with this look on his Rubys.

Car audio is much easier, I have a 150w DVC sub @ 8ohms/coil and a 150w amp @4ohms so wiring and matching things is fairly strait forward. All of my speakers are component and have external crossovers premade. I have everything connected to a computer which I can eq each speaker individually. So I can correct for many mistakes. Clearly there is much more to this than I expected, even knowing I was not building super high end speakers. Thanks for your insite. A project log of my car audio build can be found Here

Yeah, it's just a whole different world. Passive crossovers are a black art... but they're worth it when you hear a speaker that "gets it right."

**Undefinition** · 15 April 2010, 15:53 Thursday

Originally posted by pcmofo

Want to know something really strange? My speaker box is nearly the exact dimensions as yours... weird. The face is the same size, 16"x6", The depth was 3" shallower than yours. I adjusted the depth, and added the 4" drivers and changed their placement to be centered. Here is what the finished product might look like. How do you think these would compair to the rest of your build considering the driver placement of the tweeter is centered? Also, the design takes into account using your exact tweeter. (driver frames shown in gray to show contrast)

Mockup looks great!! You can keep the woofers spaced farther apart, however it will create a smaller "vertical sweet spot" due to comb filtering. But if you spend all your time with your ears pretty much on-axis with the tweeters, it's fine. However, if you move up and down vertically in front of the speaker, you will hear a dip in the midrange as you move off-axis from the tweeter (aka: "lobing").

...ain't this fun?!? Welcome to the dark side. :B

**pcmofo** · 15 April 2010, 16:40 Thursday

Wow. You have been a huge help. I understand what your saying with the amp. I will build exactly what you have electrically, I am ordering the same drivers and tweeters and crossover components etc. I assume you stuffed these inside the box and that they fit through the front driver openings. I will most likely put these on some kind of proto board or etch a board specifically for the crossovers.

I have a few general questions...
- is their a specific gauge of wire thats best to use for internal wiring?
- How is the box assembled? Is it screwed/glued etc. Its hard to tell from your pictures.
- Is their a way you attached your xover inside the box to not let it rattle?

I may adjust the position of the drivers slightly closer together or, closer together an offset up higher with dead space at the bottom ( or maybe the ports at the bottom as you suggest in your write up) I will have to play with the ascetics and see what catches my eye. The tweeter will definitely be centered if it's not going to be a huge effect on anything.

Here is a detail picture of how the front face might be done. 3/4" MDF, 1/8" deep border to inlay the plexiglass. ~1/8" to flush mount the drivers. Plexiglass will be secured with screws in the corners and maybe the middle as needed.

That picture of the rounded corners is exactly what I am looking to do. You seem to have some great resources. I am thinking I could use a sub design for the desk based on an "under the couch" design. Here is one that inspired me...

Page not found

http://www.parts-express.com/projectshowcase/indexn.cfm?project=Boogieman

I'm sure the sub box is more up my ally, do you know of any other similar designs. I want to use the same amp.

This is tons of fun. I get the feeling this is just the beginning....

**don9146** · 15 April 2010, 17:33 Thursday

There are 2 links on the Overnight Sensations web page that show pictures of the build process for that speaker. Both links go to extensive detail with pics of the cabinet build (both cabinet builds are slightly custom) and pics of their crossovers.

Hope that helps,
Don

**pcmofo** · 15 April 2010, 17:42 Thursday

I did a quick mock up of the fronts in 4 different configurations.

1. Equal spacing between drivers and edges
2. Closer together and centered
3. Closer together but offset up higher
4. Closer together, offset up higher, ports facing forward.

To some degree this is just visual, feel free to comment/vote on a layout you like best.

**Bear** · 15 April 2010, 23:17 Thursday

Tighter = Better (esp. nearfield and with higher XO point)
Offset to one side or the other with the tweeter = usually better (diffraction)

**Undefinition** · 16 April 2010, 01:50 Friday

Originally posted by pcmofo

I did a quick mock up of the fronts in 4 different configurations.

1. Equal spacing between drivers and edges
2. Closer together and centered
3. Closer together but offset up higher
4. Closer together, offset up higher, ports facing forward.

My vote's for 2 and 4.

I don't think you should abandon the "flat sub" idea. It's underutilized, in my opinion. No one says it has to be the desktop (though it is an original idea, and could actually work fine). It could just lay against the wall.
Again, my vote goes for the TB W5-1138. Vented, you can get an F3 in the low 30's in like 10 liters... :T You'll probably run out of excursion around 100 dB, which will require 80 watts--assuming normal program material.
The W6-1139 gets about the same F3, but will need a box around 15 Liters. I'd estimate you'll run out of xmax at 105 dB, which will take 150 watts

**pcmofo** · 16 April 2010, 10:18 Friday

I'm starting to like the 4th one with the ports facing forward more and more as I look at it.

The TB is a true Sub woofer not just a woofer, though they both go just about as low. So I can design a ported box that is about 10L in volume that fits the constraints of my desk. Kind of like a box inside a box. The sub boxe/s would be built with MDF first and tested etc then a desk made out of the selected wood would be wrapped around them.

Assuming I use the same amp, each is 4ohms, the amp is rated for 8ohm loads. I know I am rehashing here but should I be bridging the two outputs into a single series loop wiring two of the TB's together? Or should they be wired directly as if they were just a single speaker?

Because I am not using a mono sub amp I assume I need a simple low pass crossover. How should this crossover be set in relation to the speakers it will be paired with so that they will work well together? Are we talking a simple lowpass or do I need like a 2nd order, 3rd order etc.... anything else... I want to have the entire list of parts I need so I can place my Parts Express order asap!

So far... I need everything listed on your BOM on your site, inc some poly stuff, a second amp, two woofers, and sub xover stuff. Am I missing anything? As soon as I know what I need to make the sub xovers I can place my order

)

Looking forward to building these speakers and posting a build log.

**Undefinition** · 16 April 2010, 10:53 Friday

Originally posted by pcmofo

The TB is a true Sub woofer not just a woofer, though they both go just about as low.

I'm confused. Both what?

Assuming I use the same amp, each is 4ohms, the amp is rated for 8ohm loads. I know I am rehashing here but should I be bridging the two outputs into a single series loop wiring two of the TB's together? Or should they be wired directly as if they were just a single speaker?

Because I am not using a mono sub amp I assume I need a simple low pass crossover. How should this crossover be set in relation to the speakers it will be paired with so that they will work well together? Are we talking a simple lowpass or do I need like a 2nd order, 3rd order etc.... anything else... I want to have the entire list of parts I need so I can place my Parts Express order asap!

Really, all you need for the W5-1138 is this plate amp. 75 watts is a very good match for this driver, or two of them in series. The plate amp has a built-in adjustable low-pass filter. Which reminds me, you may want to find a way to plug the ports on the Overnight Sensations when running with a sub sometimes (I stuff a sock in them, but there are much more elegant methods...)
If you're going with the TB W6-1139, you may want to step up to a 100-150 watt plate amp to take advantage of the extra SPL.

**pcmofo** · 16 April 2010, 11:31 Friday

They both go as low freq wise. The TB looks better made with a more robust surround though as well.

The idea behind using the same amp was so that I could front mount it and retain control. The only place I could mount a plate amp would be under the desk and not very accessible to control volume etc.

Is their a way I can use the same amp + a low pass crossover? How would it be wired? each to its own L/R output on the amp or both in series/parallel with the outputs bridged on the amp.

A plate amp is a good solution but I want to control the subs still and having access to the controls is important.

**Undefinition** · 16 April 2010, 11:39 Friday

Originally posted by pcmofo

The idea behind using the same amp was so that I could front mount it and retain control. The only place I could mount a plate amp would be under the desk and not very accessible to control volume etc.

Is their a way I can use the same amp + a low pass crossover? How would it be wired? each to its own L/R output on the amp or both in series/parallel with the outputs bridged on the amp.

A plate amp is a good solution but I want to control the subs still and having access to the controls is important.

OK. I hear ya. Well, you could make a passive LP filter, but it could get pretty expensive; it will require a large inductor.

Alternatively... I looked at your site; you have the hacker spirit. Why not make a short wire run and move the pots from the plate amp and mount the pots onto a plate on the front of your desk? It'll cost you like 30 cents in wire and a bit of solder.

**pcmofo** · 16 April 2010, 12:31 Friday

From what I have seen a "plate" amp is really just a bunch of circuits that make up an amp, mounted to a plate, and covered on all sides to make it easier to install. I suppose I could open it up and move the pots etc to the front to make things easier. I was also considering doing this for the T-amp I have as it is basically a tube with a front and back plate... I could disassemble both, and rewire into one control pannel plate on the front of the desk, with a custom aluminum faceplate.

I can see how that could work. Its also about the same cost with better performance. OK so lets say that I want to run 2x TB subs... I want to spend ~$100 or less on the amp... which one to get?

Dayton SA70 70W Subwoofer Amplifier - $53
Dayton SA100 100W Subwoofer Amplifier - $109
Dayton SA240 240W Subwoofer Amplifier - $140
Dayton SA240-B 240W Subwoofer Amplifier with Boost - $140
Bash 300W Digital Subwoofer Amplifier - $150

The Bash 300w looks particularly interesting as it does not have a huge heat sink, which is going to be an issue with limited air flow after being installed into a desk. It also looks like the switches etc are a sub board already...

In this case, using a sub plate amp, I assume I want the amp wattage to be close to or greater than the subwoofer rms wattage.

The 70w dayton only does 45w total on an 8ohm load, which I could get by wiring the two subs together, but then they really want more like 120w rms... this eliminates the first two, the dayton 240 puts out 170w@8ohm which sound like it would work just fine, but has a rather large heat sink.

The Bash 300w has no heat sink, The project I linked to earlier used the 500w version to power 4x TB subs, same model I am looking at. The 300w has no listed 8ohm wattage but I can assume it is at least half, or 150w.

Is their any reason not to go with the Bash 300w? Wiring the TB in series will give me an 8ohm load.

**pcmofo** · 16 April 2010, 15:57 Friday

I went ahead and placed an order.

INTERNET ORDER DETAILS
-----------------------------------------------------------------------------------------------------------------------

QTY PartNumber Product Price Ext. Price
2 004-10 Dayton DNR-10 10 Ohm 10W Precision Audio Grade Resistor $1.25 $2.50
2 027-340 10uF 100V Non-Polarized Capacitor $0.58 $1.16
2 027-402 Dayton DMPC-0.22 0.22uF 250V Polypropylene Capacitor $0.75 $1.50
4 027-422 Dayton DMPC-4.7 4.7uF 250V Polypropylene Capacitor $2.41 $9.64
2 091-1260 Dayton BAGS-G Banana Speaker Plug 2 Pair $8.50 $17.00
4 091-1245 Dayton BPA-38G HD Binding Post Pair Gold $7.89 $31.56
2 004-1.5 Dayton DNR-1.5 1.5 Ohm 10W Precision Audio Grade Resistor $1.25 $2.50
2 255-022 Jantzen 0.15mH 20 AWG Air Core Inductor $3.27 $6.54
2 255-246 Jantzen 0.90mH 18 AWG Air Core Inductor $7.64 $15.28
4 297-429 HiVi B4N 4" Aluminum Midbass Round Frame $16.83 $67.32
2 264-832 Tang Band W6-1139SI 6-1/2" Subwoofer $49.74 $99.48
2 275-030 Dayton ND20FA-6 3/4" Neodymium Dome Tweeter $7.96 $15.92
1 300-750 Bash 300W Digital Subwoofer Amplifier $149.87 $149.87
2 260-779 Cast Frame #8-32 Speaker Mounting Kit $3.39 $6.78

I imagine I will be placing a second (well third now...) order for some odds and ends. I ordered some really nice banana plugs for the speakers and to make cables with. I am hoping to get some really interesting looking wire so that the bits that are exposed look nicer than standart brownish/gold flat speaker wire. Or just round black with internal wires. I can use up to 8ga with the plugs I have. I assume ~14 is good. Anyone have a recommendation?

I also ordered some bolts/ T-Nuts that I will either use to hold the drivers in or the plexi to the front of the drivers, I will have to see how things look when they arrive.

Thoughts, comments?

(I started a build log on Parts Express forums... http://techtalk.parts-express.com/sh....php?p=1639518)

**Not2Evil** · 16 April 2010, 23:08 Friday

Personally, I think I'd keep things off of the desk and go this route, especially since you're going with a sub. A simple 2-way, and built for not so optomistic (but defined) placement

Zaph|Audio

http://www.zaphaudio.com/audio-speaker20a.html

**Undefinition** · 17 April 2010, 00:43 Saturday

The BASH 300 is a great amp. It has adjustable EQ...which you have to swap out resistors to do it, but still, it goes a long way to add flexibility to box size.

Custom 2.1 computer speaker system. Need help with design.

Custom 2.1 computer speaker system. Need help with design.

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