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Old 11th May 2011, 07:35 AM   #1
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Default 2X18 Bass Guitar Cabinet Help

Hello, I am new to this but I am attempting to make a 2x18 subwoofer cabinet that I can use for my guitar. I am going to use eminence sigma pro 18a-2 speakers.
power rating: 650watts rms; 1300watts music program
resonance frequency (fs): 28Hz
usable frequency range: 41Hz-2.4kHz
mechanical Q (qms): 8.28
Electromagnetic Q (qes): .30
Total Q (qts): .29
Compliance equivalent volume(Vas): 441.2 liters
peak diaphragm displacment: 695cc
Maximum linear excursion(Xmax): 6.1mm

I play alot of music that I want deep, booming, massive, loud, clear, Bass.
I have used a few online calculator for the enclosure and and came up with...
Height: 28.5 in.
Width: 46.1 in.
Depth: 17.6 in.
This makes the total volume of the enclosure 379.8 liters or 13.4 Ft cubed. the recommended enclosure volume is 3.3-7.5cu. ft for one so im guessing 6.6-15 cu ft. for 2?

My biggest trouble is tuning the ports. I have heard that the best balance between SPL (getting loud as possible) and SQ (sound quality) is about 32Hz so here are a few calcuation a i came upon on the web and said the minimum port diameter size should be 8.73 in. which seems a little big to me.....
but if i tried two 6inch ports the vent legths would have to be 6.71 in. in length. why is it the less quantity of ports & smaller diameter ports need to be shorter?

my questions are...
what kind of porst should i use?
how should I brace the inside for stability?
Will I need high pass or low pass filters? or crossovers?
should I have a fabric on the inside?
should i make the box the maximum manufacture recomended }volume(15 cu. ft.) to increase deepness?
should i consider bandpass?

i am looking for rediculously deep, clear, loud, massive booming bass, for reggae, hip-hop, rock music. any help or recomendations would be greatly appriciated. thank you.
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Old 11th May 2011, 10:15 AM   #2
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my neighbor loves his 4x10" ampeg. It goes deep and doesn't "fart out" as he says. It goes deeper than his ampeg 6x10" but the 6x10" gets louder (used in a larger room). His 4x10" box is tuned to 50hz if I remember.

This is more a question for the diy bass player forums.
Those guys do this stuff and try lots of drivers / boxes.

Norman
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Old 11th May 2011, 11:45 AM   #3
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Think I'd try modelling the driver in winISD.
420L tuned to 40Hz does well (127dB@1m, both drivers at Xmax), though it's a pretty big box.
What's the lowest tuning this cabinet is likely to see?
For a E-standard tuned 4 string, you don't need to go below 40Hz.
Drop C# requires ~35Hz. I'd expect B to be around 31Hz, so if you're using a 5-string, that'd be the target.

The lower you want it to go, the bigger the cabinet will need to be. Also, you lose a little SPL the lower you go.

How much power is available to you?
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Old 11th May 2011, 04:57 PM   #4
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the cabinet can be tuned down to 29Hz. but a program I used online showed 35Hz. I think It depends on what size I adjust the ports to? I have heard that an 8 inch port is ideal for 18 inch drivers, but dosnt semm right to me. some of the online port calculators seem kinda wack.

I dont have have a power amp right now but am planning on buying one soon.

what kind of power amp would i need to get max potental out of this? together 1300 rms watts 2600 peak watts. @ 8ohms.

so maybe a QSC RMX 2450: Stereo: 500W @ 8 ohms, 750W @ 4 ohms, and 1,200W @ 2 ohms. Bridge mono: 1,500W @ 8 ohms, 2,400W @ 4 ohms?

or Crown XLS 2500: 1550W, Stereo, 2 Ohms (per ch.); 775W, Stereo, 4 Ohms (per ch.); 440W, Stereo, 8 Ohms (per ch.); 1550W, Bridge-Mono, 8 Ohms; 2400W, Bridge-Mono, 4 Ohms?
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Old 11th May 2011, 05:50 PM   #5
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Looking at those, parallel the drivers to give 4 ohm, then bridge the amplifier.

You never said - what sort of bass or tuning will it see?

You needn't make it go to 29Hz if it'll never need to go past 40...
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Old 11th May 2011, 05:56 PM   #6
bjorno is offline bjorno  Sweden
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FYI:

b
Attached Images
File Type: gif eminence-sigma-pro-18a-2_ported.GIF (130.8 KB, 90 views)
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Old 11th May 2011, 06:07 PM   #7
wg_ski is offline wg_ski  United States
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Quote:
Originally Posted by chris661 View Post
Looking at those, parallel the drivers to give 4 ohm, then bridge the amplifier.
For an instrument application???? That's playing with fire. For both the loudspeakers and the amp.
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Old 11th May 2011, 06:13 PM   #8
jogi59 is offline jogi59  Germany
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Quote:
Originally Posted by crother316 View Post
I am attempting to make a 2x18 subwoofer cabinet
i am looking for rediculously deep, clear, loud, massive booming bass, for reggae, hip-hop, rock music. any help or recomendations would be greatly appriciated. thank you.
You will be the nightmare of every sound-man.

There is a reason, why most bass-players today use 4x10 cabinets.
On stage you have to hear, what you are playing. Too much LF below 100 Hz does more harm then good.
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Old 11th May 2011, 06:38 PM   #9
Stocker is offline Stocker  United States
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Default Freak what you heard!

32Hz is not a magic number, and 8" ports are also not magic. Go download yourself a copy of WinISD Beta and model the response of various sizes boxes and ports. It is one of the better FREE calculators available that runs on a modern computer, and you can change the setup to see what trade-offs you will make to get what result.

The free "calculators" you will find online range from decent-but-limited to plain nonfunctional. Give WinISD a try.
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Old 11th May 2011, 07:11 PM   #10
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why dont you use a 4x10" woofer box and a self amplified subwoofer ?
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