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Help with subwoofer box and amp to use


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#1 of 12 OFFLINE   Jasonp31

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Posted August 28 2009 - 01:40 AM

Hello.  This is my first post here.    I have lingered for awhile, reading a lot, seeing how you guys do things and also attempting to obtain all of the necessary information before I posted this question.  Thanks in advance for any help you can give.  I apologize if this is long-winded.

I have a fairly cheap HT setup.  I recently upgraded the speakers, all Sony.  They aren't the best, but a huge step up from the tiny satellite speakers I previously used.  I have 3-way floor-standing towers for the front stage.  They have an 8" woofer, 3" (i believe) mid-range, and a 1" tweeter.  Center channel is two 5 1/4" woofers, with a tweeter.  Surrounds are typical bookshelf models, one 5 1/4" woofer with a 1" tweeter.  All are a voice matched set..  The surrounds are being connected using a RocketFish wireless device. (love it, wife loves it too, she hated me running wires under the carpet.  In the attic/walls is out of the question as we both love to rearrange the room frequently)  I have a Sony receiver running this, the original one that came with a cheap $300 Sony HTIB setup.  It seems to have decent power, running these speakers fairly well, though I know a newer receiver with more power would make a large difference.  For reference, the receiver (unsure of model, can't seem to pin it down using the internet either) has a single LFE output, this ties into my question.

The original subwoofer that came with the setup was an 8" anemic POS.  A year or so ago I sold a Firebird I had as we no longer wanted to dump money in it (I still miss her, smallblock V8, loved it, *sniff).  Part of the deal when I sold it was that I was going to keep the Earthquake amp and subwoofer (plus tiny box) that was in the car.  I am using the amp in my current car, driving a sweet setup.  I have Polk SR components and a Polk SR 10" subwoofer.  I realize the amp is not the greatest, but these speakers are so awesome!  Eclipse AVN6620 navigation HU driving)

The sub sat around awhile, and one day I decided to upgrade the HT subwoofer using it.  I spent a lot of hours searching the internet and using multiple programs in attempt to come up with a good box for the sub.  I don't know if I built it correctly or not.  It's ported, but I don't have the specs on me right now, but that's not really the point anyways.  I figure I need to build a new one or buy a new one after I talk with you more knowledgeable folks.  :)  

Here are all of the specs I can find on this sub.  I hope it's enough.  I have searched high and low attempting to find more specs, but this is it as far as I can tell.  This info comes from two different websites, and a couple things seem to conflict, but nothing of huge importance.

MODEL: DB-10 Street Pro 800 MAX (I cannot find an RMS rating anywhere, however I estimate it to be 300-350 watts.  I know it doesn't matter near as much in a HT setup)
Frequency Response = 26Hz - 1.3k
Sen = 87dB
50 Oz magnet
2" polymide coil (4-ohms)
Sandblasted pressed pulp fiber cone
High roll santoprene surround
Jet-black, textured basket
Stitched leads
MSRP: $165.00

- Fs = 29Hz
- Qts = 0.5584
- Vas = 1.30 cubic ft
- Sen = 87dB
- 2" polymide coil (4 - ohms)
- 50 Oz magnet
- Santoprene surround

My questions:

1.  Is this sub decent for HT?  I love low bass.  The current setup seems to be decent.  In the second Matrix movie (or third, always mix that up), when the Hammer flies over to pick up Neo and gang on the ground, it absolutely shakes the house.  However, I know the sub is not going very deep (maybe hits 30hz at a decent DB, I have used a test CD with test tones down to 20hz).  The sub also does not move very much, and I know I need a dedicated amp to really drive it correctly.  For as little as it moves however, it outputs quite a bit.  Shakes the crystal glasses of my wifes in the kitchen easily, vibrates stuff on the other side of the house :P

2.  What would be the ideal box for this sub?  Ported, sealed?  Size?

3.  What would be a good amplifier for this sub, bearing in mind the proper box?  What kind of power handling are we looking at, to reach mechanical / thermal limits at low frequencies?  Not looking to spend alot of money, I know the Behringer line of Pro amps look great, good power for a good price.

Any help you can give would be awesome!  Thank you so much!!


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#2 of 12 OFFLINE   Robert_J

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Posted August 28 2009 - 03:21 AM

1.  I can't answer this question without the full Theile/Small parameters and running them through WinISD or Unibox.  But from the look of the sub as well as the partial specs you have given, my answer is currently 'No'.  The Qts is already too high for me without a box.  I like my final Qtc of the system to be .500 or slightly lower.  The Qtc can never be lower than the Qts.  Most of the time the Qtc is double the Qts which would make this sub a boomy, one note wonder.

2.  See the first sentence of #1.

3.  The Behringer line would be complete overkill for a single 10" sub.  The amp is usually the last part of the equation after you have picked an enclosure design.

-Robert

#3 of 12 OFFLINE   Jasonp31

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Posted August 28 2009 - 04:11 AM

Ok, I fully respect your opinion based on spending hours reading other posts.

Would you say that, no matter what the rest of the specs are, that it's a waste of time doing anything with this sub?

If so, recommendations for a cheap sub and amp (I can build the box if you can help me with specs) that will go to at least 25-30hz with decent authority, and will match well with the sony setup I have?

Thanks for your time!

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#4 of 12 OFFLINE   Robert_J

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Posted August 28 2009 - 04:35 AM

What is your definition of cheap?  Start with a budget.  $300 is the lower limit for a DIY sub.  Anything lower and you can't compete with the inexpensive retail models.  How much space are you willing to give up?  Remember that the larger the sub, the more efficient it is.

Integration into your current system is the easy part.  It just takes careful calibration.

-Robert

#5 of 12 OFFLINE   Jasonp31

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Posted August 28 2009 - 08:05 AM

Ok, so what are some good "inexpensive retail models".  Space is not a concern. 

Calibration, well, my system currently doesn't have any.  I can reverse phase, and control volume.  Obviously an amplifier would allow x-over control on top of that.  My receiver is very basic.

Kinda bummed that the sub I am using now is not very good.  We just dumped money on a new 46" Samsung LCD, as our 720p Hitachi was on its last leg. (blue blob syndrome)  Also bought the new Sony speakers and Rocketfish surround device.  The wife is going to vote a big no on spending much money right now.  :P

EDIT:  Can you answer this question:  "Would you say that, no matter what the rest of the specs are, that it's a waste of time doing anything with this sub?"


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#6 of 12 OFFLINE   Robert_J

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Posted August 28 2009 - 02:51 PM

Since Earthquake isn't posting full T/S specs, I can't tell whether or not it will work well.  But to start you off with an idea, build a 1.2 cubic foot, sealed box and put the 10" sub in it.  Power it with the 240w plate amp from PE.  It may satisfy you for years.  But if it doesn't, then increase the driver opening and drop in the Dayton DVC 12" sub and you will definitely have a very good sub.

-Robert

#7 of 12 OFFLINE   Robert_J

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Posted August 28 2009 - 02:54 PM

Calibration requires a mic and a receiver with an auto calibration system.  My Pioneer uses the MCACC system.  But the first few times I went behind it with Video Essentials DVD and my trusty Radio Shack SPL meter.  Those two items have given me the biggest improvement in my system of anything I have purchased.  I've also used them to calibrate the sytems of friends and family as well.  The average person doesn't know about calibration but when I am through I have never had a person say it sounded worse.  In fact I have had nothing but praise from anyone I have helped.

-Robert

#8 of 12 OFFLINE   Jasonp31

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Posted August 28 2009 - 04:16 PM

Thanks for the additional info.  My receiver doesn't have a calibration solution.  I do want to upgrade to a Denon receiver later though, for multiple reasons.  One, to support the newer sound technologies for Blu-ray.  Two, to use MultEQ for calibration.  Three, just a better receiver in general with cleaner and additional power.  Thanks again for your help.  I will continue to search to see if I can stumble upon the thiele-small parameters so that you can give me an ideal box and opinion on whether its worth building a different box.  

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#9 of 12 OFFLINE   Jasonp31

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Posted September 01 2009 - 08:55 AM

FS = 29.95hz
RE = 4.21
BL = 12.5
QMS = 6.5977
QES = .61
QTS = .558
VAS = 1.3

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#10 of 12 OFFLINE   Robert_J

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Posted September 01 2009 - 10:23 AM

You found everything except xmax (maximum linear excursion of the cone).  I guessed and put it at 10mm based on the frame and magnet depth.

Unibox is recommending a sealed box of 88.7L or slightly more than 3 cubic feet to give you a final Qtc of .707.  Suff it will polyfil and it will push the Qtc down to .698.  You also have an Fb and an F3 (sub/box resonant frequency and the -3db point) of right around 35hz.  The F10 value is 20hz. Your driver will reach the 10mm xmax at 20hz with 49w of power.  If you are lucky and these drivers have an xmax of 15mm then you can double the input power to 100w.

Even though Unibox doesn't recommend it, 85L ported with the box tuned to 20hz looks very good.  You get an F3 of 19.97hz which is almost a full octave lower than the sealed sub.  Powered with  a 100w plate amp with an 18hz SSF, you barely touch 10mm of excursion.

-Robert

#11 of 12 OFFLINE   Jasonp31

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Posted September 02 2009 - 01:10 AM

So basically I modeled it correctly already and just need to get a decent 100w amp as the receiver currently is straining to push it.  Taking the sub load off the receiver should clean up the rest of the speakers as well I would think.  Later on I can get a better sub and build a smaller box if necessary.  Thanks for your help, appreciate it!

P.S.  Whats your suggested port length and width to obtain 20hz on the 85L box?

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#12 of 12 OFFLINE   Robert_J

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Posted September 02 2009 - 06:45 AM

Use the standard length of port that comes with the 3" PSP flared port from Parts Express.  DIY Cable has them on sale - http://www.diycable....products_id=582

-Robert