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Old 23rd July 2003, 01:10 AM   #1
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Default Sealed subwoofer system

Hi Guys

I have been tinkering with some designs with WINISD using the Lambda SB15. I have configured a system with 2 SB15s, sealed that is flat to 30Hz with a drop of 7 dB at 20Hz.

How much gain can I anticipate in the room? How much would the response pick up at 20Hz?

I love the sound of sealed systems and with all my playing around with different drivers and box sizes, this combo seems to work well as the group delay peaks at 10ms at 25Hz...lower than that everywhere else. The program is predicting sensitivity of 94dB also...which is nice and high.

What am I missing? Limits to max SPL? Distortion issues? Power Hungry? what?

Lastly, what is good source for 250-350W sub amps? I plan on using electronics for crossover.

Thanks!
Jim
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Old 23rd July 2003, 02:51 AM   #2
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Default Re: Sealed subwoofer system

Quote:
Originally posted by smithsonga:

What am I missing? Limits to max SPL? Distortion issues? Power Hungry? what?
Here is the answer, or an approximate guideline, to one of your questions anyway. Look up the displacement volume of the Strykes, and look at the corresponding place on the chart. Room gain goes on top of this.

PS: For 15 inchers, the approximate cone area is 132 inČ. Multiply that by your one-way excursion, and you have the displacement volume of the Stryke.

Volume Displacement For SPL Chart
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Old 23rd July 2003, 02:53 AM   #3
tcpip is offline tcpip  India
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Default High power amp for subs

You could try the high power designs by Randy Slone. You can buy his High Power Audio Amplifier Construction Manual and try building some of his designs. He used to sell PCBs of his amps, and even finished kits, on his Website, www.sealelectronics.com. But he appears to have decided to close down this business.
He still writes and answers email from readers, though. I can vouch for the fact that he has infinite patience, going by the number of stupid technical questions he has patiently answered for me.
His books include 400W amps (that's 400W/channel if you build a stereo amp), driven by L-MOSFET output stages. And performance for sub-woofers should be absolutely fine, because good transistor amps, even if they exhibit distortion, do so at high frequencies, which become irrelevant for subwoofer apps. In fact, Randy Slone's high power amps are good enough to be used for full-range applications, giving you 0.5% THD at those power levels.
Tarun
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Old 23rd July 2003, 02:57 AM   #4
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Here is a link to a chart of Room Gain. This is an approximation-other charts will differ slightly.

It's all guesswork because of the room and it's modes anyway, but at least you can get an idea.

http://www.speakerbuilding.com/content/1020/rge.gif
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Old 23rd July 2003, 03:02 AM   #5
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Quote:
Originally posted by smithsonga:
Lastly, what is good source for 250-350W sub amps? I plan on using electronics for crossover.


Here is a page with sub amps at pretty decent prices. Those power ratings are into 4 ohm speakers-they only put out half their power into 8 ohm speakers. Parts Express had other subwoofer amps, some with remote control, for similar prices. so does Madisound at www.madisound.com

http://www.partsexpress.com/pe/showd..._ID=9388&DID=7

Here is a somewhat more expensive 500 watt, (8 ohms), sub amp. It gives 720 watts into 4 ohms:

http://www.adireaudio.com/diy_audio/...iers/hs500.htm
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Old 23rd July 2003, 07:30 AM   #6
navin is offline navin  India
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funny i notice that drivers with big Xmax have low sensitivity. that means you are using a lot of power to produce high SPLs.

Ex: Driver with Xmax 27mm sens is 84db, Driver with Xmax 13mm Sens is 89db and Driver with Xmax 9mm Sens is 92db (all these 3 are well known 12" drivers).

What you should actually look at is what is max SPL the driver can produce. All things remaining equal, if a driver can produce 100db at 50hz using only 50W it is better than a driver that can produce 100db at 50Hz using 200W.

the driver that has a sens of 84db will need to thermally handle 100W to get to 104db but the driver that has a sens of 92db need only handle 10W to get to 102db. Again these are thermal handling capacities and are not directly realted to physical Xmax limitations but it vaguely illustrates what I am trying to say.

Does this make sense?
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Old 23rd July 2003, 08:28 AM   #7
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My opinion is that amplifier power is cheap for sub purposes it's
not like you need a Pass Labs X series to run a sub so I don't
generaly give much thought to the sensitivity of a sub woofer.

Rythmik audio makes a high power plate amp (350W RMS If I am
not mistaken) that would work well with the Lam or the Stryke
HE or AV series. I think the web site is http://www.rythmikaudio.com/ I
have no personal experiance with this company but John Janowitz
is working with Brian from Rhythmic and plans to carry the 350W
plate amp in the not so distant future.

Or the Parts Express 250W Plate Amp or you could always run
a Pro amp like something from Crown or QSC.

As far as X-Max, X-Sus and X-Mag is concerned. The drivers with
the smaller values are most likely higher sensitivity due to a less
stiff enclosure, they have far less displacement and travel and do
not need the heavy suspension that big excursion drivers require.

Low excursion drivers need some seriously large enclosures to
produce the same SPL as a large excursion driver will in a much
smaller enclosure. Plus they won't reach as low as most large
excursion drivers will.

I run an AV-12 in a sealed .5Q Enclosure fed 500W RMS and I can
bottom it out if I am not careful and that's with 23mm of linear
travel and more than 30mm of X-Sus.. Granted I am running that
driver in a 14" x 14" x 15" enclosure Read: Small
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Old 23rd July 2003, 12:52 PM   #8
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Actually, Brett, I think the way it works is this. The magnetic gap working on the voice coil is where the driving power comes from.

Two drivers both have a magnetic gap of 0.25" and equal magnets with equal magnetic power, (flux), in that gap. The driver with a 0.5" voice coil winding will have half it's voice coil in the magnetic gap at any given time. The driver with a 1" voice coil winding will have only one quarter of it's voice coil in the gap at any given time. The 1 inch voice coil driver has greater excursion and air moving ability, but the 0.5" will play louder on the same power input.
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Old 23rd July 2003, 12:58 PM   #9
navin is offline navin  India
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Quote:
Originally posted by Brett D.
My opinion is that amplifier power is cheap for sub purposes it's
not like you need a Pass Labs X series to run a sub so I don't
generaly give much thought to the sensitivity of a sub woofer.......Granted I am running that
driver in a 14" x 14" x 15" enclosure Read: Small
nice big amps are expensive.
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Old 23rd July 2003, 01:00 PM   #10
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Keltic,

Sorry I didn't go into detail about the magnetic gap I was just
speaking solely of the suspension. The suspension alone is never
the full measure of any driver obviously. It's highly unlikely that a
driver with a robust suspension will have a short voice coil as that
goes against what it was designed for.


That being said, give me the large excursion driver any day, no
matter what the sensitivity is.. I don't even consider sensitivity
unless I am looking at midrange and tweeters.
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