Tweet
UPDATE: This project did finally get finished. However, it is not a low cost HT system. See : "Finally the AC54Alpha Has Life". To match the quality of the finished speakers I just upgraded my Yamaha RXV353 receiver to an Emotive surround processor plus bigger amplifier. The result is astounding but the cost may be prohibitive. That said, I like it.
I've seen several DIY home theater setups but nothing ready to go from parts easily obtainable sources. Since I'm in the process of building just such a setup I'll post what I have so far with the goal being an un assembled parts list that requires almost no cabinetry (you will have to route speaker holes either with a hole saw or a router) or measuring equipment, just a small place to work and some good DIY common sense. Since the intent is to produce a complete low cost home theater system, including sub woofer, any advice will be welcome.
Sub woofer goal:
Sub woofers abound and in HT use are basically a woofer in a box with a separate amplifier. Other than choosing the driver for the enclosure there is little additional real engineering since crossover is dealt with in the amplifier and receiver/processor. However, there is always the voice of experience. Knowing what you don't want is more than half the battle. Sub will be covered in separate posts, assuming this is more than my own personal meanderings. I currently am using a TC sounds EPIC 12" in 3 cu ft ported box tuned around 23 hz and it sounds fine. It's still settling but I do need to rebuild the enclosure to a different shape and reduce it to about 2.5 cu ft to reduce extension in my small room. This is an expensive woofer. A less expensive option would be a TUBA folded horn coffee table. A Fitzmaurice "TABLE TUBA" would be a great low cost 8" sub for HT use and it doubles as a coffee table or ottoman.
Satellite goal:
Satellites in a home theater need to be as large as possible to produce as much air movement as possible yet as small as possible to reduce space and wasted transducer size at the same time. The THX, DOLBY, SDDS and DTS are 5 and 7 speaker standards engineered for a multi speaker theater sound system with a crossover point of around 80hz and generally state that no program material lower than 120Hz should go to the satellites. While in the real world things seem to work best when we stay close to this standard there are notable exceptions such as older DVD's with only 2 or 4 channel soundtracks. Thankfully most decoders know how to either turn off the speaker without any input or mix down the side channels through a voice filter to produce a reasonable center channel. With this basic information in hand the goal is to build satellites, including a center channel, that will produce the best quality sound for the least amount of money.
Parts express has a small array of finished cabinets at reasonable prices. Since this will be a parts-list kit, I'll begin by choosing a suitable woofer and it's complementary enclosure. ... Oh look, I'm already done.
Woofer choice:
Visaton W130S 8 Ohm. Chosen for it's cost, reasonably smooth frequency response, power handling and f3 performance. In a quarter cu ft enclosure the visaton easily gets below 80 hz but not so far it's wasted to use a crossover. Measured f3 in a .23 cu ft knock-down cabinet is almost exactly 80hz. It will be slightly lower than that in any of the finished .25 cu ft Dayton Audio enclosures available on Parts Express. This woofer also comes in a 4 ohm version that has a slightly different mid-range profile but it's close enough we could use them in series for a center MTM arrangement with only slight changes to the crossover provided we find a tweeter that will cross low enough to prevent any mid-range issues. A center speaker with a dip at could be a disaster. The FR of each can be seen 8Ohm and 4Ohm
Tweeter choice:
The goal is to use a tweet that can be easily mounted with nothing more than a 2" hole saw so those are the options I've looked at so far. So far I've debuted 3 tweeters. A Beston RT003 round ribbon, a Vifa BC25SC06 and I'm currently waiting delivery of a Vifa XT25SC90-04 dual ring tweeter for testing. All 3 are below $25 making them ideal for en-masse speaker making. Tweeters are a little more difficult to choose for this duty. There is such a vast array or them available it would take years just to read all the specs. But since this is a low cost goal, cost becomes the initial guideline followed closely by FR extension and third by smooth response. After trying the Beston I gave up before I even mounted it. It requires extensive and tricky router gymnastics to make it fit and seal in 3/4" material and it won't cross low enough to make it usable with the 4 Ohm Visaton in an MTM arrangement so it's a gonner. I toyed with the idea of using it as a topper but gave up on that idea due to cost. I've listened to the BC25SC06 and although it's decent tweeter I think we can do better for the price. The ring tweeters are a new design that, so far, get rave reviews. With an fs below 1K this tweet will easily cross around 2.5K for low power applications assuming it doesn't sound gritty going that low. The BC25SC won't cross at 2K without sounding like it has a speck of dirt stuck in it so it's on the sideline for now. If the XT25SC90 lives up to it's rave reviews it will make an excellent low cost HF driver for this project. Also on the drawing board is one of the new ceramic dome tweets like the Tang Band 25-1719S or its bigger brother the 25-1744S 1" Ceramic Dome Tweeter. Both are near $30 but probably worth it. Anyone having direct experience with one of these in HT use? The comments on the Vifa page make the Vifa XT25 sound a little weak for this application. Generally speaking HT does not drive a speaker for very long at one time. Movies generally have loud passages and lots of dialogue so high power handling is not usually an issue. But, there's nothing worse than having a tweeter heat up and gag in the middle of a long gunfight.
Crossover:
As always with my philosophy I'll try a 1st order first and only if It won't work will I go to a more elaborate crossover. Generally speaking I also keep similar orders. If tweet gets second order, so does the woof. My experiments indicate that the more total capacitance and inductance used in a crossover the more phase shift and the less detail and stereo imaging one hears. The BC25 sounded OK with a first order crossover (7.5 mfd) around 4K (1 mh on woof) with an L-Pad to match output but I noticed more than a bit of sibilance. Phase was beautiful with less than 360 deg (270 or so) over the entire spectrum and no woopies except at woofer res. The BC25 also has a hot spot above 10k that is probably not the cause of the sibilance but it certainly adds to it. A second order didn't help and covering the tweet with my hand during voice removes the spitting so either it's an interaction between the tweet and the woof or it's the tweet itself. Those are the reasons I've chosen to try a newer, supposedly smoother tweet.
Cabinets:
Dayton Audio/Parts Express has a plethora of cabs of the correct size for this project. Choose a square or tapered .25 cu ft for the front/back and either a .38 or .50 or the MTM. The .38 has slightly less extension but modeling and my testing indicates it would not be overly thick near roll off. It would sound a bit fuller though. A square cab might be better for center channel unless it's going to hang on a wall but then the smaller enclosure will probably sound better due to wall gain. The Visaton W130 extends very flat from 4K down in .23 with a barely noticeable bump before roll off so the .25 finished cabs will be nearly perfect. Add a small single wrap of damping on back and one side of cab and you're set. The only thing I don't like about the finished cabs is the connectors. They come pre-drilled for through-back screw connectors but the connector cups (like PE#260-276) have spring clips and a crossover board mount built-in making them very easy to use. The only issue is the plastic back increasing box losses. I'd like to be able to provide a crossover board PN and components complete with spade connectors that slips neatly into the spring-clip cup. Makes crossover wiring a breeze.
Thumb is my current test box, comments are encouraged.
I've seen several DIY home theater setups but nothing ready to go from parts easily obtainable sources. Since I'm in the process of building just such a setup I'll post what I have so far with the goal being an un assembled parts list that requires almost no cabinetry (you will have to route speaker holes either with a hole saw or a router) or measuring equipment, just a small place to work and some good DIY common sense. Since the intent is to produce a complete low cost home theater system, including sub woofer, any advice will be welcome.
Sub woofer goal:
Sub woofers abound and in HT use are basically a woofer in a box with a separate amplifier. Other than choosing the driver for the enclosure there is little additional real engineering since crossover is dealt with in the amplifier and receiver/processor. However, there is always the voice of experience. Knowing what you don't want is more than half the battle. Sub will be covered in separate posts, assuming this is more than my own personal meanderings. I currently am using a TC sounds EPIC 12" in 3 cu ft ported box tuned around 23 hz and it sounds fine. It's still settling but I do need to rebuild the enclosure to a different shape and reduce it to about 2.5 cu ft to reduce extension in my small room. This is an expensive woofer. A less expensive option would be a TUBA folded horn coffee table. A Fitzmaurice "TABLE TUBA" would be a great low cost 8" sub for HT use and it doubles as a coffee table or ottoman.
Satellite goal:
Satellites in a home theater need to be as large as possible to produce as much air movement as possible yet as small as possible to reduce space and wasted transducer size at the same time. The THX, DOLBY, SDDS and DTS are 5 and 7 speaker standards engineered for a multi speaker theater sound system with a crossover point of around 80hz and generally state that no program material lower than 120Hz should go to the satellites. While in the real world things seem to work best when we stay close to this standard there are notable exceptions such as older DVD's with only 2 or 4 channel soundtracks. Thankfully most decoders know how to either turn off the speaker without any input or mix down the side channels through a voice filter to produce a reasonable center channel. With this basic information in hand the goal is to build satellites, including a center channel, that will produce the best quality sound for the least amount of money.
Parts express has a small array of finished cabinets at reasonable prices. Since this will be a parts-list kit, I'll begin by choosing a suitable woofer and it's complementary enclosure. ... Oh look, I'm already done.
Woofer choice:
Visaton W130S 8 Ohm. Chosen for it's cost, reasonably smooth frequency response, power handling and f3 performance. In a quarter cu ft enclosure the visaton easily gets below 80 hz but not so far it's wasted to use a crossover. Measured f3 in a .23 cu ft knock-down cabinet is almost exactly 80hz. It will be slightly lower than that in any of the finished .25 cu ft Dayton Audio enclosures available on Parts Express. This woofer also comes in a 4 ohm version that has a slightly different mid-range profile but it's close enough we could use them in series for a center MTM arrangement with only slight changes to the crossover provided we find a tweeter that will cross low enough to prevent any mid-range issues. A center speaker with a dip at could be a disaster. The FR of each can be seen 8Ohm and 4Ohm
Tweeter choice:
The goal is to use a tweet that can be easily mounted with nothing more than a 2" hole saw so those are the options I've looked at so far. So far I've debuted 3 tweeters. A Beston RT003 round ribbon, a Vifa BC25SC06 and I'm currently waiting delivery of a Vifa XT25SC90-04 dual ring tweeter for testing. All 3 are below $25 making them ideal for en-masse speaker making. Tweeters are a little more difficult to choose for this duty. There is such a vast array or them available it would take years just to read all the specs. But since this is a low cost goal, cost becomes the initial guideline followed closely by FR extension and third by smooth response. After trying the Beston I gave up before I even mounted it. It requires extensive and tricky router gymnastics to make it fit and seal in 3/4" material and it won't cross low enough to make it usable with the 4 Ohm Visaton in an MTM arrangement so it's a gonner. I toyed with the idea of using it as a topper but gave up on that idea due to cost. I've listened to the BC25SC06 and although it's decent tweeter I think we can do better for the price. The ring tweeters are a new design that, so far, get rave reviews. With an fs below 1K this tweet will easily cross around 2.5K for low power applications assuming it doesn't sound gritty going that low. The BC25SC won't cross at 2K without sounding like it has a speck of dirt stuck in it so it's on the sideline for now. If the XT25SC90 lives up to it's rave reviews it will make an excellent low cost HF driver for this project. Also on the drawing board is one of the new ceramic dome tweets like the Tang Band 25-1719S or its bigger brother the 25-1744S 1" Ceramic Dome Tweeter. Both are near $30 but probably worth it. Anyone having direct experience with one of these in HT use? The comments on the Vifa page make the Vifa XT25 sound a little weak for this application. Generally speaking HT does not drive a speaker for very long at one time. Movies generally have loud passages and lots of dialogue so high power handling is not usually an issue. But, there's nothing worse than having a tweeter heat up and gag in the middle of a long gunfight.
Crossover:
As always with my philosophy I'll try a 1st order first and only if It won't work will I go to a more elaborate crossover. Generally speaking I also keep similar orders. If tweet gets second order, so does the woof. My experiments indicate that the more total capacitance and inductance used in a crossover the more phase shift and the less detail and stereo imaging one hears. The BC25 sounded OK with a first order crossover (7.5 mfd) around 4K (1 mh on woof) with an L-Pad to match output but I noticed more than a bit of sibilance. Phase was beautiful with less than 360 deg (270 or so) over the entire spectrum and no woopies except at woofer res. The BC25 also has a hot spot above 10k that is probably not the cause of the sibilance but it certainly adds to it. A second order didn't help and covering the tweet with my hand during voice removes the spitting so either it's an interaction between the tweet and the woof or it's the tweet itself. Those are the reasons I've chosen to try a newer, supposedly smoother tweet.
Cabinets:
Dayton Audio/Parts Express has a plethora of cabs of the correct size for this project. Choose a square or tapered .25 cu ft for the front/back and either a .38 or .50 or the MTM. The .38 has slightly less extension but modeling and my testing indicates it would not be overly thick near roll off. It would sound a bit fuller though. A square cab might be better for center channel unless it's going to hang on a wall but then the smaller enclosure will probably sound better due to wall gain. The Visaton W130 extends very flat from 4K down in .23 with a barely noticeable bump before roll off so the .25 finished cabs will be nearly perfect. Add a small single wrap of damping on back and one side of cab and you're set. The only thing I don't like about the finished cabs is the connectors. They come pre-drilled for through-back screw connectors but the connector cups (like PE#260-276) have spring clips and a crossover board mount built-in making them very easy to use. The only issue is the plastic back increasing box losses. I'd like to be able to provide a crossover board PN and components complete with spade connectors that slips neatly into the spring-clip cup. Makes crossover wiring a breeze.
Thumb is my current test box, comments are encouraged.
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