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Discussion Starter #1
Hi everyone!

I have a quick question. I am planing to build a pair of speakers for my fairly large room 16' (W) x 9' (H) x 40' (L). I wanted to know which would be a better choice to have the Bass fill out my fairly large room size.

(3) 8" Bass Drivers for Each Speaker

or

(3) 10" Bass Drivers for Each Speaker

or

(2) 12" Bass Drivers for Each Speaker


Right now, I am thinking of getting 2 of the 12" drivers because I think they will produce more air in the fairly large size room. So if I go with the 2 of the 12" bass drivers, that would be a total of 4 of the 12" bass drivers for both speakers. I would like to know which option would output a satisfying bass in my fairly large room.

Thanks for any advice!
 

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Discussion Starter #3 (Edited)
What is your intended use? 2 channel music? Home theater with a phantom center?

A blind recommendation without know more is the DIY Soundgroup, Fusion Tempest 12 as really great build for the price.

http://www.diysoundgroup.com/waveguide-speaker-kits/fusion-12.html

But realize that you will want a dedicated subwoofer or two for deep base.

For subwoofers, you'll likely find the best bang for the buck here:

http://www.avsforum.com/forum/155-diy-speakers-subs/1648673-martysub-faq.htm


Thanks for your reply.

I am using this pair for 2 channel music. I will not use them with a subwoofer even though I already have a pair of the latest SVS PB-12-Pluses with 800 watts sledge amp for each sub. However, I am using the dual subs for home theater use. I dislike listening to 2 channel music with a subwoofer because the bass is just too boomy and not tight enough or not enough detail for me. For some reasons, I have never like listening to 2 channel music with a powered subwoofer.
 

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JBL Selenium 12MB3P. Specs: http://www.jblpro.com/ProductAttachments/12MB3P_SpecSheet.pdf
140 USD a piece on ebay. As long as your amp can deliver 1000w peaks and 500w rms across all frequences (even to 20hz), then these can go down to respectable frequencies ( -3db 35hz) in large (300 liter) enclosures (2 of these in each enclosure). They're still able to bridge the gap to a 2khz crossover with some loud horns for the rest of the spectrum. Considering 4 of these drivers will have theoretical sustained 133db on open field, 120db with low THD in your room size should be very attainable. Room gain will make the bottom end frequency response higher, also. Just make sure you have a decent amp that don't drop off in juice at lower frequencies.
 

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You might find this helpful. It is a chart of Relative Speakers Sizes -

http://www.avsforum.com/forum/89-speakers/1654281-relative-speaker-size-these-vs-those.html

Here is a summary -

That resulted in this formula -

A = (pi) ((D - 1.5) / 2)²

Subtract 1.5" from the Rated Diameter to get the Piston Diameter, then divide by 2 to get the adjusted Radius. Then of course, Square the Radius and multiply by PI (3.14159).

This is the chart that resulted from this
-

Adjusted True Piston Size of the Driver
-

4.00" = 4.91 sq.in. = 1.00
5.00" = 9.62 sq.in. = 1.96
5.25" = 11.05 sq.in. = 2.25
6.00" = 15.90 sq.in. = 3.24
6.50" = 19.64 sq.in. = 4.00
7.00" = 23.76 sq.in. = 4.84
8.00" = 33.18 sq.in. = 6.76
10.0" = 56.75 sq.in. = 11.56
12.0" = 86.59 sq.in. = 17.64
15.0" = 143.14 sq.in. = 29.16

Let's redo the 3x6.5" vs 2x8" calculation and see if it made a difference.


3x6.5"
= 3 x 4 = 12

2x8" = 2 x 6.76 = 13.52

13.52 / 12 = 1.1266 = 1.13

The 1.5 in the formula above adjusts for the Surrounds. Take the rated size of the speaker, and subtract the distance from the outside of the frame to the center of the Surround. Subs typically have large Surrounds, so you may need to adjust the formula.

Next, how do you plan to wire THREE drivers in a way that results in an impedance compatible with most amps, or Sub Plate amps as the case may be?

I guess you could takeTHREE 2 ohms Subs, if you can find them, and wire them in Series for a total of 6 ohms.

But typical 4 ohms drivers are either going to be 1.333 ohms in parallel or 12 ohms in series.

There are only certain combinations of drives that allow you to have a uniform distribution of power among the drivers and have a resulting impedance in the working range of most amp.

If by some miracle you can find THREE 8 ohm Subwoofer drivers, the parallel combination of those three would be 2.6667 ohm. You might ...might... find some Sub Amp that can tolerate that load.

However, it can be done, but you need the confluence of a lot of events for it to work well.

Here is an example of someone who has figured out how to get it to work -

XTZ - Subwoofer - 3x12 Matt/Studio Black - $2,500 each -

http://www.xtzsound.us/shop-en/Speakers/sub-3x12-matt-studio-black



Though the specifics of how they managed it are unclear.

Steve/bluewizard
 

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The ohm isn't a problem, just measure the voltage and make sure you don't give it more voltage than the amp can handle through the given resistance load. If its only stable at 4 ohm at 1000w then the average voltage peak to peak is 63 volts, 63 volts over 2.666 ohm gives 63/2.666=23.63 amperes, 23.63*63=1488.69 watts. So you need to adjust the amplifier until it only gives just under 52 volts on average, because 52/2.666=19,5 amps, and 53*19,88=1014 watts.
We do it all the time in the car stereo world, no one buys another amp just because the subwoofer has lower ohm than what the amp is rated for.
 

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Thanks for your reply.
I dislike listening to 2 channel music with a subwoofer because the bass is just too boomy and not tight enough or not enough detail for me.
I doubt you've heard a good sub integrated with the mains properly if that is the case. Subs that are 'good enough' for home theater use often have glaring weaknesses when used for music.

I use a pair of DIY 12" sealed subs that are neither boomy or lacking in detail. I swear I can almost see the strings on a cello vibrating when I listen to some classical cuts. My otherwise 'ok' Elemental Designs A5-350 ported sub (15") lacks the detail the 12" subs have. It isn't even close! OTOH the 12" sealed subs cannot do what the ED sub can do - vibrate the whole house. Why would a 12" speaker built into a main speaker be more or less detailed than that in a sub? The only two reasons is because of improper integration - or you are using a sub that cannot play detailed sound. And there are more of them than you might think. A ported sub is (not always) often not up to the task of playing detailed notes. For that matter not all sealed subs can play detail well. A separate sub has one very good advantage over a sub built into the speaker - which is what you will be doing - you can move the sub around for best placement - which is what most sub owners do for best effect. Move the built in sub around and the rest of the drivers go with it. Where the low frequencies sound good often isn't where you want to place your L/R mains. I know - I've 'been there and done that' with a pair of Infinity IL-50s with built in subs years ago.
 
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