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Discussion Starter #1 (Edited)
I'm converting a ufw12 cabinet into an 18" Dayton um18. I don't know much about speaker building, especially the cabinet work but I thought this brace might be problematic. Can having the half of the back of the driver fire at a face 5" away (the brace) and he other half firing all the way to the back (16" with the amp installed) cause any kind of non linearities or acoustics problems? I believe the driver will just fit in with the magnet in the cutout. I could widen it up or cut some holes in it if necessary.
 

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SO is the opening in the picture for a 12?

If so the 18" is not going to fit properly. That 12" hole is very close to the edges. I dont think a 15" would fit in there either. Have you looked at buying a PE sealed flat pack?
 

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Discussion Starter #3 (Edited)
Nope, I already cut it out for the 18". There's not any room to spare but it fits.

Here is what it looks like with a fi 18" mounted. Looks lot nicer than a PE knock down box to me :D

That one was converted to an 18" by someone else. The brace was lower in that one but I'm not sure if that was just how it came from av123 or if the previous owner did
 

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Aw ok. So what are the outside dimensions of the cabinet?

Do you think you at least have 1" of spacing behind the magnet?

Which Fi speaker do you have? Q or SSD?
 

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Discussion Starter #6 (Edited)
Aw ok. So what are the outside dimensions of the cabinet?

Do you think you at least have 1" of spacing behind the magnet?

Which Fi speaker do you have? Q or SSD?
It's actually custom order based on the ib318. More or less a q18. The boxes are 3.45cu feet inside and roughly 18.5x17x17.5 Inside. The back of the cone is only 2-3" from the brace which is my main concern but there's a good 9-10" Behind the motor. At Least 6" with the amp Installed. The sides of the magnet will be within 1 cm of the brace cutout though.

I picked up the cabs for a really good price and it's looking like with the um18 it's going to work out very wel performance wise. PE told me to expect a qts of roughly .68 with the um18.
 

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I doubt somebody can answer your OP question precisely without some analysis or impedance measurements before/after adding a similar a brace (which someone would rarely do on purpose). So you might want to use a holesaw and drill 4-5 holes through it (in a circular array) and stop worrying about it. If you have REW you could measure before/after and learn whether it made a difference.
 

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2-3" is just fine behind the motor. Does your Fi even have a cooling vent?

I hope your custom woofer is based off of the Q/SSD and not the IB3. The IB3 are infinite baffle and need a LARGE box sealed. SO hopefully is based on a Q or SSD woofer. They also do make a FI SP4 home theater woofer also. Anyways.

Looks like you have a great looking finished cabinet. SO add some EQ a powerful amp and your set.
 

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Discussion Starter #9
2-3" is just fine behind the motor. Does your Fi even have a cooling vent?

I hope your custom woofer is based off of the Q/SSD and not the IB3. The IB3 are infinite baffle and need a LARGE box sealed. SO hopefully is based on a Q or SSD woofer. They also do make a FI SP4 home theater woofer also. Anyways.

Looks like you have a great looking finished cabinet. SO add some EQ a powerful amp and your set.
My understanding is that it was based off the ib318, but it was designed with a beefed motor and more venting to be able to work in a sealed cab. I'm not sure exactly what that means but I can say for sure that it does have venting that looking very much like the q18. The lack of specifics on the driver plus the fact that I can't exactly match it to another one is the main reason I'm switching to um18s. From what I gather the um18s are better drivers all round though.

With the fi driver the natural response had a pretty nasty peak at 45hz but I was able to tame that with just the 1 band peq on the amp. This resulted in a surprising decent close mic response. It's a little bowed instead of totally flat but it is +/-3 from 100hz to the mid 20s and to me sounds great. It has more punch and dynamics than my rythmik ds12 yet sounds tighter than my mfw15 and at least as tight as an epik empire. Once I get the second built in going to integrate a minidsp 2x4.

So back to my op, there are no major red flags with that brace being so close behind th cone? That's really what had me worried, not the space behind the motor. This isn't against best practice or anything in general?
 

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Discussion Starter #10 (Edited)
Just for the of it here is a pic of the mystery driver. And a close mic measurement before and after using the plat amp eq to address the main peak.
 

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That response shape is very typical of FI subwoofers. They have a very high inductance and thats what ends up happening to the response shape.

Regarding your brace being close to the speaker, as long as your brace is not loose you will be fine. I have had my older cabinets bracing rub on my drivers basket. Was a very tight fit and I sanded it back and there was only about 1mm of space. So your fine.
 

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Discussion Starter #13
That response shape is very typical of FI subwoofers. They have a very high inductance and thats what ends up happening to the response shape.

Regarding your brace being close to the speaker, as long as your brace is not loose you will be fine. I have had my older cabinets bracing rub on my drivers basket. Was a very tight fit and I sanded it back and there was only about 1mm of space. So your fine.
Cool, sounds like it should be fine. Did the brace you speak of only cover pert of the cone? I don't know if there's such a thing as back pressure in acoustics, can having an uneven surface right in front or behind the cone effect linearity?
 

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If this was a midrange chamber then I would be more worried. But 1m plus wave lengths I would not be too concerned with the brace. I had a similar brace in my ported cabinet. I had one above and one below touching it. Like yours but two parallel braces. I used the cabinet from 35hz-300hz just fine.
 

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Discussion Starter #16 (Edited)
Yeah, I wouldn't worry about that brace, unless it's actually making contact with something. You might want to add some bracing to the top half though, maybe even just some dowels.
Cool. I was kind of thinking the same thing about adding more bracing. The cab is suppose to be 1" thick throughout, and two 1" layers on the top and bottom. Does this thickness negate the need for bracing to some degree or not really? I was also considering adding some 1" half round trim pieces to all the corners to support and reinforce the corners . Partly because the other box already had it and I want them to be the same internal volume. Does putting 1" corners braces in all the corners really do much for stopping vibrations?

Also, is it possible to add dowels to a cab thats already built?
 

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Cool. I was kind of thinking the same thing about adding more bracing. The cab is suppose to be 1" thick throughout, and two 1" layers on the top and bottom. Does this thickness negate the need for bracing to some degree or not really? I was also considering adding some 1" half round trim pieces to all the corners to support and reinforce the corners . Partly because the other box already had it and walmartone I want them to be the same internal volume. Does putting 1" corners braces in all the corners really do much for stopping vibrations?

Also, is it possible to add dowels to a cab thats already built?
Cool and pretty awesome. Love this.
 
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