Monkey see, monkey do... two RL-P18s for me too! - Page 6 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #51 of 151 Old 10-14-07, 08:12 AM
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Re: Monkey see, monkey do... two RL-P18s for me too!

But I though the brace behind the driver should touch and hold the rear of the magnet. This applies some tension on the back of the magnet to physically couple it to the rear of the box? - (discussed in the SDX15 thread)

This design shows the magnet supported and braced. Could Bradley combine two birds with one stone and notch the back of his brace into the magnet and get support and bracing to the rear?

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post #52 of 151 Old 10-14-07, 11:10 AM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

DOH!

So, let me get this straight... the vent diameter is approximately 1.5" so I shouldn't have anything within 1.5" from that vent outlet? Of course that brace is only 3/4" thick MDF and will be radiused on the edges, so it's not like a solid wall or anything.

It's become apparent there is no way to make this design "ideal" (unless I returned to the dual six inch ports and tuned to a higher frequency... but let's not go there!) so the question is what is the lesser of the two evils? Am I better off with the port being 7 inches instead of 8 from the rear wall? Or am I better off with the port brace being 1 7/8 inches from the driver vent hole instead of 7/8?
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post #53 of 151 Old 10-14-07, 11:35 AM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

Quote:
brucek wrote: View Post
But I though the brace behind the driver should touch and hold the rear of the magnet. This applies some tension on the back of the magnet to physically couple it to the rear of the box? - (discussed in the SDX15 thread)

This design shows the magnet supported and braced. Could Bradley combine two birds with one stone and notch the back of his brace into the magnet and get support and bracing to the rear?
I'm pretty sure that SDX design does not couple the magnet structure to the rear of the box. Look at the horizontal brace behind the driver. It has a large arc that totally clears the magnet. The vertical brace on the other hand touches the magnet to support weight.

I guess I will just compromise and move the tube back half an inch. It's not the end of the world if the port outlet is 7.5" from the rear wall instead of 8. It has ample clearance in all other directions: 11.5" to side wall, 8" to top and bottom walls, 10.625 to front wall. Also, the MDF brace doesn't look like a "wall" to the magnet vent. Moving half an inch away will put it 1 3/8" from the vent hole instead of the ideal 1 1/2 inches. That isn't too bad considering a) the brace is only 3/4" thick and will have rounded edges, and b) the port tube outer wall (a much more significant "obstacle") will sit 2 5/8 inches from the rear of the magnet.

Bradley

P.S. On an unrelated note, cut my first piece of MDF on the table saw last night. Came out almost perfect. Smooth edge and accurate cut. The upgraded Biesemeyer rip fence kicks a$$.
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post #54 of 151 Old 10-14-07, 12:36 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

Sweet! Can't wait to see the build pics!


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post #55 of 151 Old 10-14-07, 01:12 PM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

OK. Moved the [email protected] port 1/2" back in the OTHER direction. If nothing else, I think I'm starting to get good at Google Sketchup. Here's the latest and greatest including a 3D representation of the driver!

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post #56 of 151 Old 10-14-07, 03:02 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

Would you be breaking any rules if you just decided to add 2" more to the 30" depth?


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post #57 of 151 Old 10-14-07, 03:21 PM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

No but I had the MDF cut for the major box dimensions when I bought it (at Lowes). So I cannot change the depth now without buying at least 2 more sheets of MDF. At this point I am not inclined to do so in order to solve what is a roughly 6 to 9% out of tolerance issue on dimensions that are based on "rule of thumb" best practices.

Here's a question for you: do you understand and can you explain why a slot port is exempt from a "one diameter" type of rule? Of course I know a slot is not round and therefore doesn't have a diameter. but it seems a slot port is as "biased" toward one side of the box as you can get. Granted it would be the full width of the panel it sits on, so maybe that helps compensate? Not trying to argue. Just thinking out loud and trying to understand it myself.

Thanks for the input, Steve. I appreciate it and the design has improved as a result.

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post #58 of 151 Old 10-14-07, 04:21 PM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

! Ran out of MDF! All the design changes totally ruined the way the pieces lay out on a sheet of MDF.

Off to Lowes I go...
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post #59 of 151 Old 10-14-07, 04:33 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

That's one of the reasons I don't recommend a slot port. The other is that a rectangular shape with corners will result in more air turbulence than a circle (cylinder) without any.


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post #60 of 151 Old 10-14-07, 07:51 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

Quote:
I'm pretty sure that SDX design does not couple the magnet structure to the rear of the box. Look at the horizontal brace behind the driver. It has a large arc that totally clears the magnet.
If you read a few pages of starting from here, you'll see were I ask specifically:

When I look at the designs for both sealed and ported boxes on the CreativeSound web site, they show an internal magnet brace that fits snuggly around the magnet and then another brace presses against the back of the magnet and the rear of the box. I've never seen this before?

and also in part:

it wasn't the vertical brace with the 'snuggly' fitting hole for the magnet that I found as strange as the horizontal brace that is so tight as to connect the magnet to the back wall of the box.

So, I am correct then, that the horizontal brace in your diagram places some tension on the back of the magnet to physically couple it to the back of the box?


The designer of the boxes on the CSS site says:

Yes it does. If you look at the designs on my websites you will see that i use this alot

and:

A driver can & does transmit a large amount of mechanical/newtonian energy into the box. Without a snug brace -- and by snug i mean as tight a fit as possible (with a woofer with as stout a frame as this you could get away with depressing the wood at the back and tension loading the front baffle) -- all of that energy gets transmitted directly to the weakest piece in the box (the baffle). These braces distribute that energy to as much of the box as possible so that the energy that any one panel has to dissipate/damp/deal with is dramatically lower.

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