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# Recommendations for Subwoofer DIY, Budget \$700.00 - Page 2

"But being that they have about half the cone area of the 18, they don't need to have a motor of the same strength. Two drivers combined equals the same Sd as the td, so you can effectively add the bl."

that is an interesting way to think about it, but i'm not sure if that is right. the equations say its not.

"I forgot the specs, but isn't their cms under .5?"

cms is 183 um/N. qes which is probably what you meant is 0.69.

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You're right, it's not a 1+1=2 equation, but there is some summation. Two motors driving a cone of area equal to that of an 18. Anyone know the formula?

As for the cms, lackidaisically, I did not give my units. I meant .5 mm/N or 500um/N. Not that cms is the end-all, be-all to sound quality, but you already know it's one thing to consider.

Side note. Just saw someone on hts selling a pair of td18s shipped for 600. The wife would kill me ife I bought them... I have 4 mfw's still boxed up.
"Anyone know the formula?"

Qes = Re*Sqrt(Mms)/(BL^2*Sqrt(Cms))

NOTE: Re is in ohms, BL is in TM, mms is in kg (0.xxx), cms is in m/N (0.000xxx)

or

Qes=[Re/(Bl)^2]*(Mms/Cms)^1/2
Is Qes really what we want to be solving for? Just plugging in arbitrary numbers, Re doubles, BL doubles, Mms doubles, Cms remains the same. Going from one driver to two drops Qes by ~30% (or any other arbitrary number)...That doesn't seem right because Qes should remain the same. Cms must not be a constant, nevermind.

But what does that tell us about the relationship of using two motors vs. one when Sd remains the same? There must be a formula available that has BL and Sd as variables.

The way I see, I have driver A with 20BL and 1000sd and driver B (x2) with 15BL and 500Sd each. Together BB should have 30BL (or whatever the increase is) and 1000Sd, regardless what its Cms, Mms or Qts is. The formula to find the increase of the combined motor strength is what I'm looking for. Is it a 1:1?
Here is a generic example:
Quote:
Originally Posted by NEO Dan

Here is a generic example:

Cms halves? Didn't see that one coming. BL/Re doubles, so that's what I was guessing.

I would have to guess, sonically, two Alpines should be a good choice if compared to a single TD18 in similar alignments; Cms is pretty good, total BL product is good, xmax is ok, klippel results are good...
Hello,

My media room is about 2x of your space. I am building a LP THT sub (72" x 18" x 21"). It will serve as a bench along a wall or hide under the bar in the back. You may want to look into horn design and incorporate their size into the room furniture.
Quote:
Originally Posted by NK215

Hello,

My media room is about 2x of your space. I am building a LP THT sub (72" x 18" x 21"). It will serve as a bench along a wall or hide under the bar in the back. You may want to look into horn design and incorporate their size into the room furniture.

With my limited Wood working knowledge, large complex designs would not be feasible.

I am still investing in tools, that would blow up final costs ( I am going to live with that fact ).

But a Dual Alpine SWR-1243 + Behringer 4000s sound like reasonable choices, but I would still like to see if a single 18" ( fi ) would be sufficient.

Additionally, I want it for music too so I am leaning towards a sealed design ( tighter response v/s low extension )

But I greatly appreciate the thoughts that are coming in... gives me more power to decide.

Thanks,
Andrew
so did you go DIY or retail? I was itching to buy the LFM-1 EX but my taxes came the damned day after the \$549 shipped price sale!

Now I'm going nuts to find anything comperable for the same price... even DIY. I have all the basic stuff (table saw, band saw, circular saw, jig saw, clamps, brad nailer etc).... but I really don't have the full technical knowledge when it comes to speaker building to figure out a good design, that will match the sub I was looking at for the same price or less.
Quote:
Originally Posted by nintari

so did you go DIY or retail? I was itching to buy the LFM-1 EX but my taxes came the damned day after the \$549 shipped price sale!

Now I'm going nuts to find anything comperable for the same price... even DIY. I have all the basic stuff (table saw, band saw, circular saw, jig saw, clamps, brad nailer etc).... but I really don't have the full technical knowledge when it comes to speaker building to figure out a good design, that will match the sub I was looking at for the same price or less.

Well I went DIY, I got the Rythmic Audio DS1510 Kit. Still lying in my basement.. life has taken over right now.. and snatched me away from that dream land of Super Badass bass..
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