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Yet another sonosub newbie...


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10 replies to this topic

#1 of 11 OFFLINE   Kevin Golding

Kevin Golding

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Posted September 27 2001 - 04:44 PM

Hi all, long-time lurker, first-time poster. I've decided to take the plunge into sonosub Heaven, after pouring over Patrick Sun's site and many others. My Tempest arrived today, the PE 300-794 should be here Monday, 3/4" MDF is eagerly waiting in the garage, and I have a 6' piece of 24" sonotube gracing my dining room. I have come up with these numbers in LspCAD:

Volume327l
Ql 7
Qa 30
Fill 25%
Length 42.5 cm
Min Dia 15.2 cm
Res Freq 17 Hz
SAF Max Ht 4'-6"

(Okay, so the last number isn't in LspCad, but it should be Posted Image)

Edited to add airspeed in port is 16.39 m/s at 14.8 Hz, and down to 10 m/s at 20 Hz.

The size and tuning is very close to Pat's Sunosub II. My living room is 15' long x 19' wide with a 13' min. vaulted ceiling. You can see the see the 1 meter and in-room graph here . I have a few questions:

1. Aside from not being able to change it, is there any downside to rolling the fabric covering over into the sonotube at each end before I glue in the end caps?

2. I have a router, but it's not a plunge router. How do I start the hole to cut the endcaps?

3. Going to 50% fill flattens the response a little, but I've read large enclosures don't really benefit from that much fill. Is this correct?

4. Do I include the bottom layer of MDF in my overall port length? i.e. for a 17 1/8" port, I'd cut my PVC pipe to 16 3/8"

I'd like to thank everyone on this forum for sharing their ideas and wisdom. Posted Image

[Edited last by Kevin Golding on September 27, 2001 at 11:45 PM]

[Edited last by Kevin Golding on September 27, 2001 at 11:49 PM]

#2 of 11 OFFLINE   Brian Fellmeth

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Posted September 27 2001 - 07:14 PM

I can suggest something for #2. Put the pivot hole for the jig where the bit just hangs over one edge of the MDF. Leave the tiniest fraction of clearence since you don't want the bit contacting the MDF when the router starts up.

As for # 3, in a sealed sub the filling decreases the q. Not sure if it also does this in a ported alignment, but I don't think it does anything to the FR in any case.

#3 of 11 OFFLINE   Jeff Rosz

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Posted September 27 2001 - 07:28 PM

hello kevin,

1. the downside to this is you might not get a good air-tight fit. i wouldnt do it.
2. first off, dont try to cut the whole 3/4" in one pass. just set the bit depth to about 1/4" or so. start the router while holding it just above the panel. slowly lower the router until the bit "bores" its way into the mdf, then make a complete pass around. then reset the bit depth another 1/4" each pass until you have a nice pizza plate.
3. at least line the sides of the tube. experiment with the stuffing to your liking.
4. go ahead and use the complete length for your port and cut the hole to the outside diameter of the port for added strength. 5 minute 2 part epoxy works pretty good.

[Edited last by Jeff Rosz on September 28, 2001 at 02:30 AM]
why have one when you can have two for twice the price?

#4 of 11 OFFLINE   Patrick Sun

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Posted September 28 2001 - 12:59 AM

Just to expound on Jeff's suggestions:

1. It'll be a recipe for disaster if you fold the material inside the ends of the sonotube and then try to create an airtight seal on each perimeter of the endcap.

2. Practice on scrap MDF with your router and circle jig until you are comfortable with making the circular cutouts. Experiment with what works best for your situation. Some people like to recess the driver, but unless you have three layers of 3/4" MDF, I don't recess the driver because you give up strength for cosmetics that really don't benefit the performance of the driver/enclosure.

3. Since you already have quite a large enclosure (just about optimal for a Tempest, you should need to stuff the enclosure with polyfill. I lined the sides with batting, but compared to my Sunosub I (dual Shiva sub) with no batting, I can't really discern a quantifiable difference. Just be aware that if you do stuff it with over 25% stuffing, you will start to impact your tuning frequency (lowering Fb if you keep the port length the same).

4. I used the outer bottom layer for a ledge for the port to sit on. It's an added bit of "complexity" in the routing of the inner and outer bottom endcaps. But I like doing it because I didn't have to worry about the port falling out of endcap due to bad glue job. And I didn't have to worry about the air-tight seal once I caulked it up since I would have two chances to seal it up (caulk to seal the ledge, and caulk to seal the port on inside of the endcap vs. just one chance to just seal on the the inside. If you use my method, you will have to subtract width of MDF layer/ledge from the calculated port length.


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#5 of 11 OFFLINE   Jeff Rosz

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Posted September 28 2001 - 03:51 AM

hello again,
good points patrick. you really should do a FAQ. maybe there is a FAQ somewhere, but i havent seen one.

why have one when you can have two for twice the price?

#6 of 11 OFFLINE   MarkRS

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Posted September 28 2001 - 08:09 AM

One quick note on how I cut my driver and port holes without a plunge router. I first drilled a hole right by the edge of the traced circle of the driver cutout. This allowed me to place the router bit in the hole without having to drop the bit on the MDF while it was spinning. I was then able to do the cut in three passes, taking off a 1/4" with each pass. This worked fine for me.

Mark

#7 of 11 OFFLINE   Greg_R

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Posted September 28 2001 - 11:31 AM

Do NOT try to tilt the router bit into the wood while it is running (unless you like the hospital). Use either Mark's or Brian's method...

Greg

#8 of 11 OFFLINE   Jeremy Illingworth

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Posted September 28 2001 - 02:31 PM

Your Qa and Ql are changed from the defauly settings. Since I'm even newbie-er than you, what exactly are these settings and how did you reach them? I'm guessing they are for a piece of Sonotube. I put them in my .box and the curve really changed.

jeremy

#9 of 11 OFFLINE   Kevin Golding

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Posted September 28 2001 - 05:39 PM

Wow, I really appreciate all the responses. I was afraid I might have problems folding the material in. how bad does backless carpet ravel at cut edges, and is there a way to stop it?

I like the idea of drilling a pilot hole and starting very near one edge. I'm going to start practicing with scrap tomorrow. I'll only cut 1/4" at a time.

I think I'll stick with 25% fill -- that should be almost 3 pounds of polyfill. Going to 50% didn't make that much of a difference in the response curve.

Jeremy, every time I find a snippet of information I know I'll forget, I copy the text into a 'sonosub tips' Word doc. The down side is I cannot give proper credit to whomever originally posted the info. Those values are in my copied notes as:

Qa:
100% = no fill
30% = 25%
15% = 50%
7% = 100%
for 100% fill, the ratio is 16 ounces per 1 ft^3

Ql:
Sonotube = 7
Box = 10

My plans for tomorrow are to scout out fabric or carpet, and practice routing circles. If I can get organized, I'll post some pics of the project and my equipment and media flexy racks.

#10 of 11 OFFLINE   Jeff Rosz

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Posted September 29 2001 - 01:06 AM

hello again,
quote:
how bad does backless carpet ravel at cut edges, and is there a way to stop it?[/quote]

if its made of a synthetic fiber it can be melted. to see if this will work, use a scrap piece of carpet,sandwich the carpet between two pieces of scrap mdf so the frayed edge is just barely sticking out of the mdf. use a butane lighter to melt the fibers together. a little heat goes a long way. if you are the really really safety conscious type, make sure there is no mdf dust in the air or you could get a nice dust explosion Posted Image i guess you could hem the edge but that would take a pretty big sewing machine, check your local upholstery shop.

[Edited last by Jeff Rosz on September 29, 2001 at 08:07 AM]
why have one when you can have two for twice the price?

#11 of 11 OFFLINE   Vince Bray

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Posted September 30 2001 - 07:24 AM

A couple of suggestions,

Try finding some cardboard port tube instead of PVC. No glue but PVC cement *really* bonds PVC, including epoxy, liquid nails, etc. Try spreading some on and you will find that after curing it will peel off cleanly. You can get an excellent 6" diameter cardboard tube for this purpose free from carpet and upholstry shops. It is about 1/4" thick and very tough. If you use PVC, you should anchor it mechanically, at the end, and with a brace in the middle (this is a good idea anyway for such a long port).

Consider veneer for your sub. It does cost more, but the SAF is the highest of all, short of marble or something fru-fru. Instead of looking online, try your local cabinet supply shop. I get it for $56 a 4x8 sheet, paper backed in oak, hond mahogany, etc. Consider making the sub just under 4' and just wrap it around the tube. In the long run, the $$ spent give you an end product that you will love.

Vince





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