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Old 28th October 2011, 03:49 AM   #201
djk is offline djk
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"Sorry to interrupt but it can work "

I don't recommend it.
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Old 28th October 2011, 04:10 AM   #202
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Old 28th October 2011, 08:20 PM   #203
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Default Some responses

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Originally Posted by Djim View Post
Sorry to interrupt but it can work Norman, as long the tolerances of the TS parameters between the two drivers are very close and the boxes behind the drivers have exact the same volume...

But realistically, only top (expensive) drivers have such small tolerances and Scott seems to have 'forgotten' to make up the volume differences made by the drivers...
If you mean because one driver is inverted... no, I didn't forget. I measured each driver by itself before i paralleled them, and amazingly enough- both
vent tunings were at 50 Hz. It's a moot point, because I intend to dis-assemble these failures. Even after 38 years of speaker building- it seems I am still very capable of a total blunder
As far as addressing the mid-bass- yes DJK, you are correct: I have been using a single PRO 15" driver in a sealed enclosure, and it sounds pretty good.
Pretty good, but not awesum sounding like Les'. Next summer, or when ever speaker building season starts up again, I'll seriously think about dual 15" ppsl's again. In a common enclosure, and everything as close to the design as what I can make out, without knowing any exact design details.
Next up- it's time to design/ build an awesum midrange section- which is beyond the scope of this thread. I better get on it soon, as it's getting colder and colder as the weeks pass by. Happy listening to everyone!
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Old 1st November 2011, 12:36 PM   #204
jea is offline jea  United States
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Well so far so good. I have one cabinet ready for the speakers which should be arriving any day. I have a question regarding mounting the speakers. I assume I will need to remove some wood so the speakers will mount flush. Is that called rabbeting? Anyway how wide? How deep? Just enough for the speakers or allow for a little space? What about rounding the corners? Anyone know a site which will give some pointers?
As for the mounting I am planning on using some kind of insert to screw into. I may have two studs on each speaker just to hold it in place while screw the rest in.
For wire I was planning on using some solid core cat wire. Good enough?

Thanks!
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Old 27th November 2011, 06:54 PM   #205
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I have a question regarding mounting the speakers. I assume I will need to remove some wood so the speakers will mount flush. Is that called rabbeting? Anyway how wide? How deep? Just enough for the speakers or allow for a little space?
This

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Originally Posted by djk View Post
I only make the plenum the total height of the inverted driver, add the frame thickness of the other, plus about 1/4" to spare.


Quote:
Originally Posted by jea View Post
As for the mounting I am planning on using some kind of insert to screw into. I may have two studs on each speaker just to hold it in place while screw the rest in.
These might be of help.

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Originally Posted by Don Snyder View Post
Two suggestions:

These work much better than T or Hurricane Nuts: McMaster-Carr

Rotating the inserts 1/8 turn gives you knuckle room
And instead of studs, why don't you flip the enclosure on its side so the inverted driver is facing down so gravity is helping you; and on the other side so the normal driver is facing up. That should help w/mounting.
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Old 29th November 2011, 09:46 PM   #206
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djk:

I'm going with the same layout concept as you posted:
Click the image to open in full size.

(This was designed for (2) Kappalite 3015LF w/an F3 of 31.86 Hz)

(A) 45 x 22.5
(B) 43.5 x 21
(C) 22.5 x 21
(D) 21 x 17.75
(E) 21 x 14.9125
(F) 21 x 9

With my layout, there is a 4" distance between the back (B) and (F). Is this acceptable?

Also, I was unaware that the wider a port is, the longer it would have to be - the opposite of what I was thinking. The inside height in my to-be enclosure is 21". I entered a 3" width and BB6 gave me a 9" length. If 4" width is entered, BB6 suggests 12.6" length. Just making sure this is correct. If so, I'm thinking of going with the 3" width option.

Any thoughts/suggestions before I start making saw dust? Also, any objections to Arauco (3/4")?

Last edited by CRESCENDO; 29th November 2011 at 09:50 PM. Reason: dimensions
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Old 29th November 2011, 10:13 PM   #207
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Originally Posted by CRESCENDO View Post
djk:

I'm going with the same layout concept as you posted:
Click the image to open in full size.

(This was designed for (2) Kappalite 3015LF w/an F3 of 31.86 Hz)

(A) 45 x 22.5
(B) 43.5 x 21
(C) 22.5 x 21
(D) 21 x 17.75
(E) 21 x 14.9125
(F) 21 x 9

With my layout, there is a 4" distance between the back (B) and (F). Is this acceptable?

Also, I was unaware that the wider a port is, the longer it would have to be - the opposite of what I was thinking. The inside height in my to-be enclosure is 21". I entered a 3" width and BB6 gave me a 9" length. If 4" width is entered, BB6 suggests 12.6" length. Just making sure this is correct. If so, I'm thinking of going with the 3" width option.

Any thoughts/suggestions before I start making saw dust? Also, any objections to Arauco (3/4")?
Four inch for the back area is a bit on the small side, you could make the D parts almost 4 inches smaller, reducing the plenum area (good) and expanding the cabinet volume, reducing the restriction between chambers, also good as it allows for a bigger port .

Longer ports tune lower, bigger volume ports require more depth to tune as low.

High aspect ratio (long, thin) ports have more surface area to enclosed volume by ratio, they will chuff at a lower volume than a more square or circular shape.
They also tune lower than the volume /length predictions of a circular duct.

Remember to deduct the port area from the cabinet volume, and round over all the port and plenum entrances and exits.

Arauco is a decent choice, the last birch plywood I purchased turned out to use a filler wood and was not as stiff (or heavy) as Arauco.

Art
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Old 29th November 2011, 11:42 PM   #208
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Thanks for the quick informative reply, Art!

"you could make the D parts almost 4 inches smaller"

With almost 15.5" overall diameter of the driver and taking the thickness of panel (F) into account, I only have .75" to work with inside the plenum (without screwing the drivers into panel E).


"also good as it allows for a bigger port"

Should I go wider than 3"?


"Remember to deduct the port area from the cabinet volume"

Do I just deduct the volume of panel G? Or the volume of panel G + the volume between G and C?


"and round over all the port and plenum entrances and exits"

I don't remember which test I read, but they compared a completely smooth enclosure to an enclosure w/sharp edges and the smooth enclosure didn't show any significant improvements. Thought it to be very interesting. I like how Bowers & Wilkins puts the "golf ball dimples" in their ports. I wonder how close one could get with drill bits & a steady hand.
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Old 30th November 2011, 12:39 AM   #209
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Quote:
Originally Posted by CRESCENDO View Post
Thanks for the quick informative reply, Art!

"you could make the D parts almost 4 inches smaller"

With almost 15.5" overall diameter of the driver and taking the thickness of panel (F) into account, I only have .75" to work with inside the plenum (without screwing the drivers into panel E).

"also good as it allows for a bigger port"
Should I go wider than 3"?
"Remember to deduct the port area from the cabinet volume"
Do I just deduct the volume of panel G? Or the volume of panel G + the volume between G and C?
"and round over all the port and plenum entrances and exits"

I don't remember which test I read, but they compared a completely smooth enclosure to an enclosure w/sharp edges and the smooth enclosure didn't show any significant improvements. Thought it to be very interesting. I like how Bowers & Wilkins puts the "golf ball dimples" in their ports. I wonder how close one could get with drill bits & a steady hand.
Diffraction effects (rounded corners) are different (and more subjective, and harder to test) than port chuffing. Rounding the ports reduces chuffing.

Make part D as small as you can and still fit the drivers in and still leave room for a grill, I'll leave you to figure out 3.5 or 4.25 or whatever :^).

The port volume (that slug of air that wiggles back and forth, and does not blow out if big enough) is not part of the cabinet volume, deduct it and panel G, and the volume of the speakers intruding in to the cabinet, and the plenum. And deduct handle volume, and jacks, and braces, and paint drips...

Other than the fact that big ports reduce cabinet volume, within reason it is hard to make them too big, seat of my pants says go 4", and put a brace in the middle of the port.

And make the port too long, do a dry fit and then cut it down after you confirm it tunes FB too low, easier than adding on.

P.S. Why are you planning to tune the cabinet more than 10 Hz below the driver FS ?

Art

Last edited by weltersys; 30th November 2011 at 12:50 AM.
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Old 30th November 2011, 06:40 AM   #210
djk is offline djk
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For a 9.6mm x-max driver the 4" port width would be the minimum, as far as I'm concerned.

I run a brace down the middle of the port, across the back, and up the other side.

I would also run a brace on part 'B', about 21" x 3". I don't normally brace this part, but I make mine smaller than this.

Tests of large-radius flared ports vs non-flared ports showed the large-radius port could play about 1.5dB louder before the onset of 'chuffing', I would just make the port a little bigger and don't worry about it. I always make the port as big as will fit in the box.
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