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Old 19th July 2012, 01:08 AM   #11
tb46 is offline tb46  United States
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Hi ShadyDave,

At least you're getting better wiht a new toy (Hornresp), just be careful it's addictive. :-) Good luck with your project.

Regards,
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Old 25th July 2012, 05:19 PM   #12
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Location: Appalachia, in the middle of nowhere.
Default Bottom Firing Port

I was wondering if anyone saw any major problems with my approach in making a floor firing port on a BR enclosure.
I had decided on making a sealed box but if I port the box it seems to have much better control over driver amplitude when close to Fb.
The boxes already exist and I am going to use 3/4" and 1/2" BB Ply glued together for the front panel, and also use the outside of the panel as a mount for a 1 x 3 frame with grill cloth stretched over it.
I will use both low pass and high pass filters (DCX 2496), but if the high pass filter stops working a sealed box has extreme over excursions.
Anyway, I was planning on making a base from 2 X 4 lumber so the port would have a 3-1/2" space between it's outlet and the floor.
Is this enough, or should I use 2 X 6 lumber (5-1/2").
It is a flared 4" port kit.

I was also a little concerned with the internal port flare ending up so close to the driver, I am not sure if that is an issue.

Any and all comments welcome.
A picture tells a........


Click the image to open in full size.

Thanks, Dave
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Old 25th July 2012, 05:32 PM   #13
ODougbo is offline ODougbo  United States
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Default Down Firing Ports

Didn't think I would like it, until I tried it - my subs never sounded better.

Isobaric - less then $20

post # 307 and 343.
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Old 27th July 2012, 12:54 AM   #14
tb46 is offline tb46  United States
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Hi Shadydave,

Post #12: "...a little concerned with the internal port flare ending up so close to the driver..."

It most likely will not be a problem, but maybe you can lower the driver a few inches to be on the safe side.

As to the ground clearance - assuming that the hatched, green pieces in the top view are the 2x4 pieces for the base - that looks fine (maybe a little overkill); you may be able to optimize the transition from tubular duct to 2x4 duct, and shave a bit of length of the tube. The last time I used a similar port was in a set of experiments with sonotubes; it worked just fine with a BR and a BP4. The ports worked just as predicted.

Regards,
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Old 24th August 2012, 04:59 PM   #15
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Cool In over my head...DOH..Newbie questions

This all started because a recent room mates cat sharpened her claws (the cat, not the room mate, I think) on the surrounds in my 3 ft.^3 boxes with old Pyle (15-400 I think) 15" drivers.
So I bought a set of Infinity 1262W woofers, then I found this forum and started to learn.
I still planned on using the boxes with the Infinity 12's for now, quick and dirty.
.
Well I removed the 3/4 ply baffle that was tacked onto the front of the boxes original baffles and found that the 30 year old particle board boxes are in worse shape than the surrounds on the speakers.
.
So, being in a hurry and working way too many hours right now I purchased a set of Knock down boxes from Parts Express.
These PA Knock-Down Trapezoid Birch Speaker Cabinet for 15" Driver 245-326
.
They are meant for 15's but I have 4 sheets of quality Baltic Birch that I was going to double baffle the old boxes with, so I will do the same.
Center the 12" woofer in the 14" cutout using another piece of 3/4" Baltic Birch.
.
I have several questions.
Should I use PL-400 or Titebond to glue up the cabinets?
.
If I need to fill small voids can I use waterputty?
.
I bought 4-4' sections of 1" diameter Oak dowel rod for bracing.
This should give me 3 or 4 braces in each box.
If I get one long #10 wood screw right in the middle of a tight fitting brace and also glue it, is that adequate?
Or should I add some 4" square end plates like one would use on a roll cage in a car, made from ply of course. (my wood welder is broken).
.
I am going to start with a sealed box, I can always port it later.
I have some egg crate foam sheets and was going to spray glue that to at least 3 walls.
I also have 3-1 lb. bags of Acousta-stuf Polyfill and was going to follow the directions of 1/2 lb. / ft.^3, or 1-1/2 lbs. per box.
Does this sound about right?
.
I would like to finish them with some sort of black very textured paint.
There is some pretty good stuff in spray cans but I would probably need allot of cans.
Any ideas what I could buy in gallon sizes for black texture finish?
.
The boxes are ~ 2-3/4 ft.^3 and seem to be just about right.
A Qtc of 0.707 needs 70 Liters and these will be 73 Liters after subtracting the speaker volume.
.
For some reason Photobucket does not seem to want to work, so a few hundred words sort of describe a picture, sort of.

And according to Jeff Bagby's Woofer Box and circuit designer 4.5 they will be 100 dB each at 30 Hz and if I add the Room Boundary Simulator they will be about 100 dB at 20 Hz and reach 113 dB by 40 Hz and 115 dB by 100 Hz.
This is at 300 watts, and although the amp is capable of 420 watts I would not be turning it up that high, so that is just headroom.
My old Radio Shack SPL meter tells me that I consider 80 dBA to be loud.
That is plenty for me, and that is using the 2nd order 40 Hz high pass in the Cerwin-Vega amps which should limit Xmax to 7.1 out of 13.0 mm.
Hornresp seems to agree fairly closely but I can not simulate the high pass filter to that to keep the Xmax down (or I don't know how).
.
Eventually I want to build a 15 or 18" PPSL and will relegate these to be mid basses, but for now at least I can have some sound.

Thank you for all your wisdom and patience.
Dave
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Old 25th August 2012, 02:30 AM   #16
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Default Photobucket is alive, it's alive.

Looks like Photobucket is working again.

This is with a 2nd order Butterworth at 40 Hz which is in the amplifier.
This gives a very safe 7.1 mm excursion out of a 13 mm Xmax.

Click the image to open in full size.

Dave
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