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Old 12th May 2006, 06:28 AM   #1
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Default Looking For Some Guidance

Hi Guys,

So my current setup is 4 Technics A70 3-Way Floorstanding Loudspeakers (really old but awesome quality) and 2 equally old Technics 225w Amps (each running a pair). About 4 years ago when I still didnt know much about home audio I purchased a Velodyne 8" 150w subwoofer, which did something in my small 10'x10' bedroom. Now I have moved down into my 25'x25' basement, and even when the little thing is cranked and begging for death, I hear absolutely nothing over the 4 12" drivers from the floorstanding speakers. Now I've got some money and I think I'd like to build a subwoofer instead of just handing Circuit City or Bestbuy 500 bucks. I've been doing lots of research lately and reading lots of posts in this forum, and it seems like theres a lot of very intelligent people posting here. I'm currently a sophmore Mechanical Engineering student so I'm always willing to learn, and the more I read about these things the more motivated I'm getting. Anyway, I was wondering if you guys could give me some tips on what size driver(s) I would need, and how much power I would need to get some good sound in my room. Also, if you guys could give some tips on box design/size and all that good stuff, it would be MUCH appreciated.

Thanks in advance,

CART
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Old 12th May 2006, 08:23 AM   #2
lndm is offline lndm  Australia
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Hi CARTRulz,
I've heard good things about Velodyne. I wonder, have you tried putting it in one corner of the room and listening from the other corner? (not permanently of course ) This may highlight their capabilities and help you to make your decision.

Anyway, making speakers is fun. If I were in your shoes (and I'm not), I would look at finding a nice 12" driver and put it in a closed box (for starters). This can sound very good, and is difficult to make a mess of.

There are many other options, some ambitious, some less so.

Maybe you could describe your needs in a little more detail?
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Old 12th May 2006, 09:16 AM   #3
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Given your current speakers are already large and you have four of the buggers, any sub is going to struggle a bit. I would go for at the very minimum a vented 12 inch design -- two would be better, and essential if you want to watch movies.

You could also consider simply extending the response of your existing speakers, if they are of a sealed box design. Even if they are vented you may be able to add a bit more.
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Old 12th May 2006, 06:11 PM   #4
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to keep up with 4 12s, and act as a sub i would want at LEAST a pair of high excursion 15s. but a pair of moderate excursion 18" pa drivers would prolly work better(more sensitivity). and 4 of them should be able to shake a 25'x25' room to bits.

when it comes to picking drivers, ive always kinda had my eye lingering over that mammoth 18" dayton pa driver at partsexpress, but ive never deisgned a box for it, so i dont know how feasable they are in a home enviroment.

But if you do decided to go the 18" pa driver route, you should tune for a 40hzf3, keep the f3 high, and run a subsonic filter to prevent excursion from getting too high.

thermal power is irrelivent in a case like this becuase chances are that the drivers will reach mechanichal limits before they reach theyre thermal limits.

to design speaker boxes accurately, search google for a prgoram called WinISD pro (alpha or beta, cant remember) this neat little windows program allows you to design a box with predicted charachtereistics before build time.
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Old 12th May 2006, 07:23 PM   #5
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Quote:
to keep up with 4 12s, and act as a sub i would want at LEAST a pair of high excursion 15s. but a pair of moderate excursion 18" pa drivers would prolly work better(more sensitivity)
In my opinion, this is almost dead on. You need the surface area of 2 15's to match the 4 12's(close enough), anything smaller and you'll be relying on excursion to match output.

I would personally go with one or two 18's I like 18's, as for pa it depends on how low the 12's play. If the 12's are putting out good sound down to 40 -50 hz then adding any speakers that cutout at 40hz might not benefit you much and would probably just cause a hump in the response with only mild increase in extension.

Pick up an analog Radio Shack spl meter calibration and using the signal generator(Winisd,as mentioned) and a spreadsheet you can measure and record the low frequency output of you current mains. You can also download Frequency Response Plotter and use it however it requires calibration which isnt that hard, and it will test 10-20000hz in room automatically.

I recommend doing this before choosing the subwoofer as it will let you know what you need to get the fr you want.
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Old 12th May 2006, 08:58 PM   #6
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There are no suitable 18" drivers available right now - the best driver at the moment is the SoundSplinter RLp15. Check out htguide.com's diy section for numerous projects using these drivers. If you want a sub that goes low, clean, and loud, a large, low tuned ported is the way to go - a pair would be even better, but you didn't mention a budget.
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Old 12th May 2006, 11:29 PM   #7
lndm is offline lndm  Australia
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Quote:
Originally posted by richie00boy
You could also consider simply extending the response of your existing speakers, if they are of a sealed box design.
I do not know the Technics A70, but many 12" floorstanders I have heard have a higher than expected f3. They may not be achieving what a sub using 12" drivers should achieve.
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Old 13th May 2006, 07:24 AM   #8
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Thanks guys,

Now I've got a few more questions for you. The SoundSplinter RLp15 looks awesome, and its a fairly reasonable price. I'd like to keep the price under $600 if possible, and it looks like this driver would fit the budget. Now, my next question is amplifier power and box size/specifications. Does anyone have reccomendations for a good amp for this driver thats about $250-$300? Also, does anyone have reccomendations on box dimensions? I know theres a program called WinISD Beta that I downloaded and played around with, but I'm not really sure what I'm doing. Also, I've heard a lot about a box tuned to "X"Hz. What does it mean to tune a box to a certain frequency and how do you go about accomplishing this? How does this affect driver performance? My current speakers have really great bass, so I'm basically looking for something thats gonna kick real hard and real low for movies and the hard rock/metal music that I listen to.

Thanks a bunch.
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Old 13th May 2006, 08:48 AM   #9
lndm is offline lndm  Australia
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You speak of tuning the box. This sounds like the vented variety of box. I think that this would suit your stated requirements well.

By adjusting the dimensions of the vent (or port), you create a box resonance which works in conjunction with the speaker's resonance to extend the bass.

Vented boxes need to be built to a formula. The wrong combinations will not sound right. The info required is the box size and the tuning frequency. With this info, you can calculate apropriate vent dimentions.

There are a few 'alignments', or kinds of rolloff available, giving you a trade off over quality, bass extension, and box size, for example. The needed info should be available in charts or a box sim program like the one you have.
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Old 13th May 2006, 11:50 PM   #10
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Using the dual 2ohm voice coil version, a proven performer is 260 effective liters with one 6" diameter port that is ~28" in length, giving you ~16.2hz tune. The dimensions of the enclosure aren't important as long as you make it end up totaling 260 effective liters, meaning that much is left after subtracting the volume of the driver, port, bracing, etc.

As for the amp, most have also been using the Behringer ep2500 with 750 watts at 4ohm for $300 from Parts Express, meaning the driver's dual 2ohm voice coils are wired in series. You don't have to use that one though, any good pro amp with 600-1000 watts should do.
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