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Questions on First DIY Sub Build


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14 replies to this topic

#1 of 15 hallb76

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Posted February 19 2007 - 03:03 PM

I would like to build a sub using a Quattro 15 and a rythmik 250w plate amp or a PE bash 300 for use in a 8.5x10 room. The room is completely closed on all sides. I will use it for 90% HT/gaming and 10% music. I would like it to hit 20 hz with some authority without being boomy. Since reading about "room gain" I can't decide on vented or sealed. I couldn't find any info on this setup in a very small room.

Because my room is so small does anyone think I would benefit from a sealed enclosure? With a 200w input at 2m WinISD shows 97db at 20hz and 109db at 80hz for a 2.5 ft^3 sealed enclosure. Would an LT correction circuit help my low end in this application? Could "room gain" boost my lower frequencies?

The response of a 5.5 ft^3 vented box looks much better: 109db at 80hz and 104db at 20 hz. But, I have been told that "room gain" could make the vented box sound boomy and loose which I don't want. Using 1130/(2*longest dimension) I got 56.5 hz. Does room gain affect frequencies above or below that value? Is room gain really a substantial factor?

Anyway, any opinions or insights as to which configuration would yield the best results in my room would be greatly appreciated. I know it's all a matter of personal taste that's why I asked for opinions. Thank you in advance for any information.

#2 of 15 Robert_J

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Posted February 20 2007 - 01:15 AM

Quote:
Originally Posted by hallb76
Would an LT correction circuit help my low end in this application?
The Quatro doesn't have enough excursion for an LT circuit.

Quote:
Originally Posted by hallb76
Could "room gain" boost my lower frequencies?
Is your room completely sealed? If yes, then it will definitely boost the low end.

Why don't you build a couple of different test enclosures of different sizes? Or build one big one that is ported. Stuff the ports to make it sealed. Fill it with wooden blocks, phone books, etc to simulate a smaller box. Find the combination that sounds best to you and build a final enclosure of that size. For a more scientific approach, you will need test tones and at least a Radio Shack SPL meter. Then you could plot the in-room frequency response.

Also, the Quatro is a fine sub but if you want something that moves just as much air but uses a smaller enclosure, the db500 from TC Sounds is on sale. You can also contact a guy named Supa_c on the TC forums and he has some b-stock TC2+ 12's (A TC-1000 with a different aluminum cone) for $60.

-Robert

#3 of 15 hallb76

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Posted February 20 2007 - 02:02 PM

Robert,

Thanks for your input. It is sealed to a degree, there is a 1/2" space under the entry door and a 1/2" space under the closet door, otherwise it is sealed. It wouldn't be a problem seal up the doors if it would have a positive affect. I'll have to check out the db500. Thanks again for your input, now I've got some other avenues to pursue.

#4 of 15 Robert_J

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Posted February 21 2007 - 01:44 AM

That would be considered sealed by all but the hardcore guys. These are the ones that use air-tight frames and thresholds.

That db500 is VERY similar to the SVS PC+ driver.

-Robert

#5 of 15 Brent_S

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Posted February 21 2007 - 03:26 AM

The Quattro15 in 3 ft^3 sealed with the SA240 amp is a tried and true budget DIY sub. It should have enough output for most sane people in a room that small. Searching here, avsforum, and PE's Tech Talk would probably turn up lots of posts on the combo.

However, I'm with Robert on the 12" DB-500 as the new budget leader. It models nearly indentical output in the same alignments as the PE Titanic 12-Mk3, which currently goes for $160...the power of buying direct from the OEM. Put the DB500 into 3 to 4 ft^3 tuned to 20hz driven by 300 to 500 watts and you should be quite happy. The only caveat is might be how fast you need the driver. From glancing through TC's forums, I get the impression they're in a build when ordered mode sometimes, so the driver you order may not be sitting in a box waiting for a shipping label. At $75 for that level of performance, it's probably worth the potential inconvencience.

-Brent

#6 of 15 hallb76

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Posted February 21 2007 - 10:05 AM

I ran the numbers for the db-500 and the response curve looks really strange. It has a dip around 35hz and a spike around 20hz. I have a feeling that I made a mistake somewhere. The Quattro is showing a considerable spl advantage with half the input power. (200w vs 400w)
Given the lower cost of a 240w amp and the simplicity of a sealed box I think at this point I'm leaning toward the quattro. I won't be building anything until early April so I've still got plenty of time to research. Thank you Brent and Robert for you input and suggestions.

#7 of 15 Brent_S

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Posted February 21 2007 - 01:52 PM

Sounds like you entered too large of a box volume for the DB-500, assuming you're using WinISD. I get something like you described if I use 6 ft^3 tuned to 20hz.

With the DB500, 3 ft^3 tuned to 20hz, gives a nice rolloff that's about -4db @ 20hz. With 300 watts, I get 106db @ 20hz, 109db @ 30hz and 110db @ 40hz. Remember, those numbers also assume no room gain.

For comparison. The Q15 in 3 ft^3 sealed with 240 watts. I get 99.5db @ 20hz, 106db @ 30hz, and 109.5 @ 40hz. That should still be plenty of output below 30hz in your room, depending on taste.

Even at regular price, the PE BASH 300 amp is only $20 more than the SA240. You get $10 of that back if you go with the DB500 instead fo the Q15. Just playing devil's advocate. You should be happy with either build.

-Brent

#8 of 15 hallb76

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Posted February 22 2007 - 12:12 PM

Brent,

I'm retarded, I never converted the x-max to meters for winISD. I am getting a very nice response curve for the db-500 now. I have to make the box nearly cubic, is there anyway I can extend the port using an elbow so it will fit in the box or can I use a port with a diameter of less than 4"?

#9 of 15 Robert_J

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Posted February 23 2007 - 12:51 AM

If you are using basic PVC pipe, there are elbows in the plumbing section of your local home improvement store. Also Parts Express has a line of ports with both flares and elbows.

I would not use a port with a diameter of less than 4". You are just asking for chuffing at high volumes.

-Robert

#10 of 15 Brent_S

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Posted February 23 2007 - 03:33 AM

You definitely don't want to go less than 4" with the DB500. Elbows are ok, but not ideal.

Depending on your aesthetic tastes, ports don't have to stay inside the box. Check out some of the art work here.

The other alternative is passive radiators. Adds cost and complexity, but functions essentially the same as a port without needing internal box volume. The rule of thumb is the PR needs to have double the displacement of your driver. Looks like one of TC's 12" PRs could do it, assuming it can carry the weight necessary to tune that low. Two of the PE DVC15 based PRs would probably do it as well.

Robert mentions the PE build-a-port system. I've also seen a few people claim to have luck finding thin wall PVC that matches the Precision Ports material, so that you could pick up one of their basic kits and then find appropriate connectors, couplers, etc. to shape to taste w/o the extra expense...and PSP doesn't offer elbows.

You didn't mention the cubic shape requirement earlier. What gives there? If you could do something that would be 13"x13"x36 internal, you'd easily be able to do the 3 ft^3 @ 20hz with a straight port either firing up or down.

-Brent

#11 of 15 hallb76

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Posted February 24 2007 - 03:18 PM

I don't have much room between my television stand and the wall. If the sub is too tall I won't have a spot for my front speakers. I can't put the sub in the back of the room because it will be blocking a door on either side of the room. I don't see any problem extending the port beyond the box if it comes down to it.

I'm thinking about replacing my mains and surrounds with bookshelf speakers using the plans from the Dayton Aluminum / Silk MTM kit. I could intergrate the front main into the sub enclosure. It only needs .8 ft^3. This would allow me to use a taller sub enclosure. I can get the drivers for $12.55 each and the tweeters for $13.80 each. I could probably construct six identical speakers for a little under $450 or even less if I do my own crossovers. The only problem is I'm not sure my reciever can drive a 4 ohm load. The manual shows power specs down to 3 ohms in stereo mode but nothing for 7 ch mode. The reciever is an onkyo htr540 which should be the same as a txsr504.

I could probably contact onkyo to find out for sure.

#12 of 15 Robert_J

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Posted February 26 2007 - 11:10 AM

Don't build the that Dayton kit. It does not get great reviews over at the PE Tech Talk Board. Build something designed by dB (http://users.d-web.c...rs/speakers.htm), Wayne J (http://www.speakerbuilder.net) or an improvement on Wayne's design (http://home.hawaii.r....JZ/DJZone.html).

I've heard the MT version of the DHT and it was great. I have all of the parts in for a MTM version but just not the time to build. I'll be building a full set of 6 along with a center channel.

-Robert

#13 of 15 hallb76

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Posted March 01 2007 - 11:06 AM

Great link Robert, I really like those speakers, but, I have come to the sad realization that this project is going to consume far more time and effort than I had anticipated. My receiver won't drive a 4 ohm load so I would have to replace my entire system or redesign an 8 ohm speaker and crossover which I have found is a very involved process. I would also have to buy a router, bits, and test equipment. If I thought I would use the tools beyond this project I would give it more consideration.

I can get a fluance AV-HTB 5.1 speaker package and an HSU stf-2 for less than the price of building a sub and buying the tools. I know they pale in comparison to the DIY setup I had in mind, but, in small room they should be fine for me. I am definitely not an audiophile. I'll have to put off my project for about another year or so.

Thanks to everyone for all the help and advice.

#14 of 15 Robert_J

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Posted March 01 2007 - 02:45 PM

Some people can't afford the time and/or money for a DIY setup and that's fine. I just enjoy building things. It gives me a reason to buy more tools.

-Robert

#15 of 15 MikeGee

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Posted April 05 2007 - 01:06 AM

I built a 15" Quatro with a PE240. Its in a 5.5cu. ft box. My room dimensions are 15x18' and it over powers the house. I would say you should put a port on it. I dont know if anyone else does this but with my port I somtimes will plug it wth a towel to give a sealed sound to it. I'd say put a port cause you can always stuff it if you wanna have a sealed sound. I often wonder if i should have gone with the Bash 300 but the way my sub is now.. its loud enough.





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