Madison Knight-12 Sealed Subwoofer - diyAudio
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Old 25th February 2007, 08:36 PM   #1
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Default Madison Knight-12 Sealed Subwoofer

Check out this driver: http://www.musicsupplycenter.com/Pro...Code=813%2D012

I was thinking of building a pair of subwoofers to enhance the bass of my Fostex 207Es. Main amp is a DIY se 2A3, preamp is the Bottlehead Extended Foreplay III (which has the separate sub outputs), Digital source is the Zhaolu d2.5 fed by Intel iMac (Apple lossless), and Phono source is a Hagerman all octal Cornet fed by a Stanton TT (I'll hopefully update this soon) w/Denon D103/Peerless 4722 stepUps.

I already bought the pair of the Madison Knight-12s and a pair of Cerwin Vega 150W plate amps (Crossover frequency 40-120Hz). My goal is to build a pair of subwoofers that are fast and musical. I chose the Knight-12s mainly for their efficiency and low-price. When I finally recieved them I was happy with their build quality - perfect for the price and my purpose.

My plan is to build the drivers into a pair of sealed 14(w)x18.5(h)x13.5(d) (internal dims) 3/4" Baltic Birch PlyWood enclosures. The plate amps will be built into their own separate enclosures. I've built a few DIY enclosures but never designed my own and just wanted to run this by the experts here at diyaudio before I buy and cut wood.

Am I on the right track?
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Old 25th February 2007, 09:58 PM   #2
ScottG is offline ScottG  United States
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Default Re: Madison Knight-12 Sealed Subwoofer

Quote:
Originally posted by maxdd_nj
Check out this driver: http://www.musicsupplycenter.com/Pro...Code=813%2D012

I was thinking of building a pair of subwoofers to enhance the bass of my Fostex 207Es. Main amp is a DIY se 2A3, preamp is the Bottlehead Extended Foreplay III (which has the separate sub outputs), Digital source is the Zhaolu d2.5 fed by Intel iMac (Apple lossless), and Phono source is a Hagerman all octal Cornet fed by a Stanton TT (I'll hopefully update this soon) w/Denon D103/Peerless 4722 stepUps.

I already bought the pair of the Madison Knight-12s and a pair of Cerwin Vega 150W plate amps (Crossover frequency 40-120Hz). My goal is to build a pair of subwoofers that are fast and musical. I chose the Knight-12s mainly for their efficiency and low-price. When I finally recieved them I was happy with their build quality - perfect for the price and my purpose.

My plan is to build the drivers into a pair of sealed 14(w)x18.5(h)x13.5(d) (internal dims) 3/4" Baltic Birch PlyWood enclosures. The plate amps will be built into their own separate enclosures. I've built a few DIY enclosures but never designed my own and just wanted to run this by the experts here at diyaudio before I buy and cut wood.

Am I on the right track?

I suspect your enclosure volume is to small. The params won't be as spec.ed either.. particularly fs and eff./sensitivity. If its anything like my 10's you are looking at a qts value of around .75 (and that requires a LARGE volume for moderate extension near the average sp-level)

IMO double your depth and utilize an appropriate aperiodic vent - that should get you there. (..google "aperiodic vent" for more info.) Its still won't have a lot of extension near the average, BUT it should make some pretty good bass.
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Old 25th February 2007, 10:41 PM   #3
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Default Buffer

I was thinking of using a "buffer" on the rear baffle.
A 5 to 6.5" driver with its terminals shorted (see the PDF).
This should create some resistance on the cone.

ScottG , Have you found the driver specs posted on Music Supply Center or other distributer web sites accurate? Thanks for the aperiodic vent suggestion. I never heard of anyone using an aperiodic vent in a bass enclosure but I'll def. consider it.

Does anyone know of an online calculator or an equation that will give the best internal volume by inputing the driver specs?

I'll try to post my first drawing. I don't have any fancy Cad or 3D software so I just used Adobe Illustrator. If the file doesn't post due to file-size restrictions, I'll upload the PDF to my server and post the link when I get home later tonight.
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Old 25th February 2007, 10:43 PM   #4
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...yeah, didn't work I'll post a link tonight.
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Old 26th February 2007, 02:49 AM   #5
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Default Diagram

Here's that link to the drawings: http://www.maxdd.com/_diyaudio/Maxdd_sub_v1.pdf

Knight-12 Specifications:
RMS Power Handling: 300 watts
Peak Power Handling: 600
Ohms: 8
Frequency Response: 45 to 4500hz
Sensitivity: 100 dB
Magnet: 50 oz.
Basket: Cast Aluminum
Voice Coil: 3" kapton
Cone: Paper
Surround: Accordian
Binding Posts: Clip Type
Pole Piece: .
Overall Diameter: 12 1/4"
Overall Depth: 5 1/8"
Mounting Diameter: 11 1/8"
Mounting Depth: 4 5/8"
Warranty: 1 year

Knight-12 TS Parameters:
FS: 50 hz
VAS: 2.25
SD: 95.033
Qts: 0.64
Qes: 0.665
Qms : 17.26
BL: 15.47
Re: 6.1
Nominal Ohms: 8
Le (uH): 511.32
Mms: 82.15
X max (inches): 0.25
X mech (inches): 0.5
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Old 26th February 2007, 03:05 AM   #6
ScottG is offline ScottG  United States
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Default Re: Buffer

Quote:
Originally posted by maxdd_nj
I was thinking of using a "buffer" on the rear baffle.
A 5 to 6.5" driver with its terminals shorted (see the PDF).
This should create some resistance on the cone.

ScottG , Have you found the driver specs posted on Music Supply Center or other distributer web sites accurate? Thanks for the aperiodic vent suggestion. I never heard of anyone using an aperiodic vent in a bass enclosure but I'll def. consider it.

Does anyone know of an online calculator or an equation that will give the best internal volume by inputing the driver specs?

I'll try to post my first drawing. I don't have any fancy Cad or 3D software so I just used Adobe Illustrator. If the file doesn't post due to file-size restrictions, I'll upload the PDF to my server and post the link when I get home later tonight.
..the buffer will turn out to be a VERY high tuned passive radiator - DO NOT DO THIS!

Not accurate. Not terribly off either though (except for eff.), AFTER its been "run-in". Notice that they no longer have the madison spec.s on MSC's website any longer? If I remember correctly my executioner 10's (fs in particular) were off more than my knight 10s.


Remember, a driver with a rather large Vas and a high compliance requires a large volume for a sealed (or "semi"-sealed for an aperiodic enclosure). This is not the case initially, early on the driver's spider is very stiff and you'll have little bass in either a large or small enclosure. Given some time though and things loosen up quite a bit.

Here is an 8" full range driver with somewhat similar attributes in an aperiodic enclosure:

http://www.6moons.com/audioreviews/redwine3/system.html

You would prob. need 3 scan speak variovents per cabinet. However, you can make your own single aperiodic vent with a similar surface area to 3 of the scan speaks.. In general, always position this vent directly behind the driver. The vent should have as little "length" as possible - which usually means routing the inside edges of the vent.
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Old 26th February 2007, 03:11 AM   #7
ScottG is offline ScottG  United States
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Default Re: Diagram

Quote:
Originally posted by maxdd_nj
Here's that link to the drawings: http://www.maxdd.com/_diyaudio/Maxdd_sub_v1.pdf

Knight-12 Specifications:
RMS Power Handling: 300 watts
Peak Power Handling: 600
Ohms: 8
Frequency Response: 45 to 4500hz
Sensitivity: 100 dB
Magnet: 50 oz.
Basket: Cast Aluminum
Voice Coil: 3" kapton
Cone: Paper
Surround: Accordian
Binding Posts: Clip Type
Pole Piece: .
Overall Diameter: 12 1/4"
Overall Depth: 5 1/8"
Mounting Diameter: 11 1/8"
Mounting Depth: 4 5/8"
Warranty: 1 year

Knight-12 TS Parameters:
FS: 50 hz
VAS: 2.25
SD: 95.033
Qts: 0.64
Qes: 0.665
Qms : 17.26
BL: 15.47
Re: 6.1
Nominal Ohms: 8
Le (uH): 511.32
Mms: 82.15
X max (inches): 0.25
X mech (inches): 0.5

Remember that Vas is cubic feet.

try doing some modeling in winisd pro (freeware alpha) and see what numbers it doesn't like. I'll guarantee its no 100 db eff.. If that confuses you then just try their non-"pro" version and simply use the numbers you have here to do some modeling.

The likely massive "peak" near in-box resonance will be reduced by the aperiodic vent. You may still need a filter though.

I personally use my knights as open baffle midbass drivers.
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Old 26th February 2007, 04:04 AM   #8
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Default Re: Diagram

Quote:
Originally posted by maxdd_nj
Here's that link to the drawings: http://www.maxdd.com/_diyaudio/Maxdd_sub_v1.pdf

Has this actually been built? I'm curious of the effects of the "closed loop coil" buffer driver when the active woofer is driven by just a low frequency signal.

I'm going to go try some experiments with drivers with coils open and closed. Still looks like a perfectly good driver wasted, but it just may be worth it.
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Old 26th February 2007, 04:23 AM   #9
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Is this the correct part (Parts Express #: 296-546)?
http://www.partsexpress.com/pe/showd...number=296-546

Can I still use my dimensions (about 2.025 cu. ft. before the fill and brace) if I line my rear baffle with the 3 Scan Speak resistance vents?

---or---

Should I increase the depth to 20" which gives me an internal area of about 2.998 cu. ft. (before adding fill and the center brace) & also use 3 flow resistance vents per enclosure?

ScottG - Thanks for your help!
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Old 26th February 2007, 04:40 AM   #10
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Hi Troy,

This design has not yet been built, it's my first sub and my first attempt at designing my own enclosure. But I've been jonsin' to try the "buffer" driver.

I heard one used in a small sealed enclosure with the smaller Fertlin field driver and a tweeter(don't remember which tweeter was used)...I was pretty amazed with the sound! On the rear baffle, the box had maybe 10 or 12 small 1/4" vent holes that allowed the little 5 or 6" driver mounted directly behind the holes to breath (like in my drawing).

I imagine that the little driver would not be very effective in the same box as a bass driver. It's probably better to use the "buffer" in a fullrange or mid-bass enclosure. I have a friend whose been DIYing & experimenting far longer then me that swears I should try it, that it'll work!
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