Need port recommendations

[subwoof]

Hello box buddies...

I am in the process of loading up a pair of massive double 15 cabs for my college rental living room ( ad hoc HT ) and need some port suggestions since I am nowhere near my shop / data...

The cabinets are stock UREI 813's that are about 11.75 ft3 internal volume and have a pair of 4.75 by 7.5 openings on the 1" thick front baffle.

I can easily make a pair of 1/2" plywood plates with 4" PVC stubs glued to them and use couplers to extend them later BUT A good starting point would help since a massive party is scheduled to begin at 7pm sat night.

The system:

(2) UREI 813 cabinets ( rescued from curb )
(4) 2225H woofers ( recycled / rebuilt pulls )
(2) 2360 horns ( Theater dumpster goldmine)
(2) 2445J drivers ( with coated dia of course)
(2) 2404H mounted in horn bell ( 4612 roadkill )
(1) 6290 amplifier ( one of 27 from aud )
(1) 6260 ( same pedigree )
(1) 5235 with the correct CD 800hz 18db cards ( 10 buck ebay special )

So who's up late with a program at hand?? I can use the "bump" feature in the 5235 to help the tune - I'm looking for a pretty deep response that won't have any massive imp spikes/troughs.

:cheers:

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[Robh3606]

Those cabinets are way to big and 2225's will not get you there as far as 20-40Hz. You need subs. Here is what Win Isd says. Simply load them up and block one port assuming they are only baffle thickness long ie 1 inch. That tunes it to 39Hz. I have no idea how much power you can push them with and not exceed the X-Max on the drivers. Don't try the bump in the 5235 use subs the bump will be below the box tunning.

Hope this helps if I get time I will load it into Bass Box to see what X-Max looks like.

Rob:)

[subwoof]

Yeah they are a little too big but they *are* exactly the same width as the horn (31") so it makes a cool stack.

I could install a pair of open-ended boxes inside to reduce the volume ( mount to the back wall behind each woofer ) but that will take some time.

I seem to remember that the generic cabaret box was about 4.5ft3 and tuned the 140 and 145 with various ports.

The HP filter WILL be engaged on the xover to keep out VLF and overall flatness is not the goal. Simply a tuning that keeps the woofers happy and the voice coils in the same zipcode as the frames.

75% of the music coming thru these will be crappy MP3 tunes off the web...sigh...

Simply blocking one "port" would be great and would save a lot of time.

-3db at 40 is better than most..:)

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[Robh3606]

Here is what BB comes up with. More accurate you loose 3 db at 40hz so figure -6 with no room gain. Still need subs to rock the house.

Rob:)

[subwoof]

I actually *could* install (4) 2235H's that are destined for another project but I have enough frames to replace them later...

So if the foamies were to be installed, what would porting be like?? If it's like the 4350 they are gonna be deep...

Not sure if I want that kind of response here BUT re-arranging furniture and bowels is an impressive thing..:)

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BTW - *thanks* bob for the comp time!

[Robh3606]

You would have to go with dual 4" ports but they would be impressive.

Rob:)

[subwoof]

Hmmm....an additional full octave down ( and then some ) looks very good.

The rectangular openings are each on a side panel so a 3/4 wood tube of a particular depth would be a very simple construct and that baffle opening would be 6.5 x 3.75 ( 24.375 ) which is almost the same as a pair of 4" tubes ( 26.12 )

The existing baffle opening would be stepped down to the new opening with 1 X 1/2 tapered trim molding to give them a nice modern flare look. Easy miterbox project for a living room football game.

What would *that* depth be since the so-called 10% depth reduction guideline for multiple ports isn't involved and the area is a bit less?

Back in the early 80's I made a number of the EV thiele boxes that had a closable center port and had runners inside the box to extend the side ports. Maybe I will just make these adaptable and install my first "depth" at 4"

sawdust time - kickoff is in 3 hours. I wish I had my big tablesaw here.

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[SMKSoundPro]

Well, How did everything work out?

Lisa and I are dying to know.

[subwoof]

a pair of snowstorms and a number of leaky window frames ( 1899 ) on the rental house took precedence. It's going to be below zero for at least 4 days this week and the poor grad students that are returning from india ( 90F ) to -10F on wed are in for a SHOCK. Time to lose the flip flops guys..

And The NAMM show flight is wed so it will be the weekend of the 24th before it's up and running.

But I hear it's -35 in fairbanks so all in all it's not too bad.

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[robertbartsch]

I'm currently building a similar set up that includes a 2225H, 2445H and bullet nose tweeter in a smallish box - 6 square feet - for the basement in my home.

I have not run these yet so I can't comment on the sound. I did note your compression drivers are 16 ohms, and you your other drivers are 8 ohms; right?

Did you consider the OHMs mis-match on the drivers or was this an oversight?

[subwoof]

Did you think that this was going to be a passive system?? For proper operation it *has* to be biamped ( look at the component list for 5235 and *multiple* amplifiers! ).

Ohms has nothing to do with it.

And it's not similar: the box is a dual cone and twice as big ( 4 ohms ! ) as yours. The tweeter is a different model / dispersion and if I remember from one of your many whatif posts ( 2380 ), a much larger horn.

And my 2445 diaphrams are original and are just fine. They do not fail under normal use but removing them and *cleaning* the gap with re-alignment before reuse is a prudent thing to do. You need a good oscillator, DVM and a distortion analyzer to be sure.

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[SMKSoundPro]

My mom's thermometer has been stuck at -46 for the past two weeks. We were supposed to go to Fairbanks for a drag show this past weekend, but no one goes out into the bush at -40. Its just not prudent.

Please send pictures and info from NAMM when you can.

I mailed the 3600 boat anchor last Monday.

Dear Robert,

In my 2x2225; 2445/2385; 2402 bullet boxes for the big ballroom, I triamped them. It is very simple to do! I know Zilch and some others will cry foul for not having any compensation filters, but all in all they are not too bad. In this manner, individual driver impedences are not a stumbling block. Just adjust the output gains of the crossover to flatten the speaker box out. Then use a graphic or parametric EQ to adjust for taste.

The really old pro guys have been doing it this way for a long time.

over and out.

scotty.