Complete newbie (I mean really new...!) looking for a simple project to learn from - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 19 Old 03-13-08, 03:34 PM
darrenh
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Complete newbie (I mean really new...!) looking for a simple project to learn from

Hi guys

I can only start to say what a wealth of information you post on here... if I only understood 10% of it! I have a fairly simple (oh I really hope it wont be too bad!) project building a modified M&K VX-1250 sub using the replacement M&K parts, but I would like to do something a little more inventive.

I have a 10 inch Alcone drive - BX10

250mm sub bass driver with coated paper cone, twin magnet, rubber surround, ventilated magnet system and sheet steel basket.

output (continuous/programme): 150/300 Watt
impedance: 4 Ohm
resonance frequency fs: 30 Hz
DC resistance Rdc: 3.5 Ohm
mechanical Q factor : 6.76
electrical Q factor Qes: 0.36
total Q factor Qts: 0.34
equivalent volume of compliance Vas: 50.07 L
voice coil inductance at 1 kHz: 3.12 mH
effective mechanical mass incl. air load Mms: 91.3 g
mechanical compliance Cms: 0.30 mm/N
effective piston radiating area Sd: 365 cm2
electromagnetic force factor BI: 13.11 N/A
sensitivity (2.83V /1m/1kHz): 87 dB
voice coil height: 23.5 mm
voice coil layers: 4
outside diameter: 258 mms
cut-out required: 229 mm
mounting depth: 133 mm
countersunk depth: 11 mm
cone diameter: 169 mm
mounting holes: 8x5 mm on 250 mm diameter circle

and would like to learn from installing it in different boxes, learn how to measure its performance, what the figures mean, and how that relates to subjective sound. Designing boxes to 'correct' shapes and volumes....

Questions:

Can I create a passive sub and use an external (inexpensive) stereo amp to drive it?
Do I need to use a crossover?

I love the look of those cylindrical subs!

So much to learn!!! Please be gentle with me!
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post #2 of 19 Old 03-13-08, 09:15 PM
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

Quote:
darrenh wrote: View Post
Questions:

Can I create a passive sub and use an external (inexpensive) stereo amp to drive it?
Do I need to use a crossover?

I love the look of those cylindrical subs!

So much to learn!!! Please be gentle with me!
1. Yes you can make a passive sub and run it with a leftover stereo amp. You can either use one channel or (if the stereo is capable) bridge the channels for a mono signal. I'm not sure if "twin magnet" is the same as dual voice coil. If so, you can run each VC off one channel. Make sure the stereo can deal with a 4 ohm impedence if you do that!

2. If your reciever has a sub out you don't need a crossover. If it doesn't then you do.


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post #3 of 19 Old 03-14-08, 03:40 AM
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

Thanks Boomie

It may sound stupid but I want to check these things before destroying any equipment. I was intrigued to read most people on here start with a 15 inch driver (or four). I just don't see this sort of thing in the UK that much. I guess we are restricted on space a little more and end up with massive 12 inch drivers!!!
 
post #4 of 19 Old 03-14-08, 06:13 AM
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

Here 12" is typically the biggest for a commercial sub with 10" being the most common. DIYers often use 15" because (when buying as parts) they don't cost that much more then a 12" and typically have higher efficiency and/or lower Fs. Also DIYers are often building much larger enclosures than what you'd find at Best Buy.

15" is not required though! I use two 12" subs in my HT which was an upgrade from a single 10".


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post #5 of 19 Old 03-14-08, 06:33 AM
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

Have you decided on the size of box yet?




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post #6 of 19 Old 03-14-08, 08:15 AM
darrenh
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

Quote:
Mike P. wrote: View Post
Have you decided on the size of box yet?
I wouldn't mind trying s sonotube style, or a flattened ported box (I read that by having the woofer up at ear level - could be a load of rubbish, but I'd like to give it a go!). I don't quite understand the figures that AJ Vented is giving me ....
post #7 of 19 Old 03-14-08, 08:48 AM
darrenh
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

Win ISD suggests a closed box of 11.5 litres and a vented port of 18.6 litres With a 10 cm dia vent 56 cm long.....
post #8 of 19 Old 03-14-08, 11:26 AM
darrenh
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

What am I looking for in the graphs Win ISD shows:

Gain
Phase plot
SPL
Group Delay?

I have been having a play and come up with these: (What do you think?)
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post #9 of 19 Old 03-14-08, 03:09 PM
darrenh
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

I think a new thread to take this in the direction and try to encourage some response as my title doesn't describe the help I need!!!
post #10 of 19 Old 03-14-08, 07:53 PM
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Re: Complete newbie (I mean really new...!) looking for a simple project to learn from

Hi Darren, I think your title is fine. Looking at your WinISD models and notice a couple of things: Are you looking to build a tiny box on purpose? Next, I notice all your vented boxes have tunes in the mid 30's. That is kinda high. Try a EBS3 vented and see how that looks. I think you need more volume and a lower tune - at least 30hz or less.

Warmon - "know what I mean Vern"
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