Large Cabinet Tuning

GM has kindly offered to look at my needs via this Forum. So, here we go.

I am looking for a starting point for port length for tuning the cabs.
I could work with Win ISD except it doesn't take into account the significant room gain in the corners of the room.

Cabinet internal dimensions: H=40.5 in., W=28.5 in., D=22.5 in. 3/4 in. braced MDF.

Nett Internal Volume with speaker mounted = 13.75 cu. ft.

Positioning difficult, Adjacent corners of 12 foot wide wall. Toe-ed in as needed. Otherwise no room to move them.

Driver: 416-8B the centre is 10.25 inches below the underside of the top.

Ports: 2x4 in. ID. the centres are 6 in. above the cab floor.

Castors raise cabs 4 in. off the floor.

Poly lining: light on back and sides, curtain between driver and back but clear of port area, heavier treatment under the top.

Room: Awkward. Basically an L-shape made up from 3 12 ft x 12 ft areas. Carpeted. Hard and soft furniture Various 1/2 height windows. Distance from wall behind cabs to the opposite wall(facing the cabs) is 28 ft.

Walls; bottom 1/2 height timber with plaster board above.

9 ft. ceilings.

House: Timber framed and clad, floor is timber on piers. Probably not good for too low of a tuning.

DEQ2496 for EQ.

Amplification: SS

GM, let me know if I have missed anything.

you're missing another 416 in each enclosure. Altec had a design that used 2 416s in a box about the same dimensions. Room gain can be your friend. Your journey will be something to enjoy. Sorry to mention it again, but if you look here altec scan | Flickr - Photo Sharing!

you might get another inspitation. who knows. weed through the photos, you'll see more relating pics, even a bar graph frequency sweep.

Greets!

Hmm, +12 dB is a lot of gain for corner loaded, especially considering the construction. At what frequency is it at? I have similar and only get around +7 dB/stereo corners down to ~25 Hz, then it flattens out as the house becomes a huge absorber.

Nifty electronics, lucky you :D, these have been on my wish list ever since they premiered.

Why didn?t you post the stuff in your PM? Anyway, referring back to it, a max flat alignment doesn?t have a better transient response than an EBS per se as the latter typically blends in-room better plus has as good or better a group delay above ~35 Hz where we begin to have some LF hearing acuity, which is why many folks [including me] prefer it.

Even better is to use an inverse tapered TQWT that once damped yields as good or better a transient response as a ~IB sealed except with more gain BW. Even my lightly damped ML-Voigt pipes have a perceived bass horn?s ?heart attack fast? response, though of course it?s in no small amount due to having dual ~20 Hz Fs, 0.2 Qts 15? drivers, but with more internal damping this type of loading will considerably ?tighten up? much less powerful drivers.

With MLTL loading, max flat will be a ~30Hz F3/Fb with dual 4? dia. x 0.75? vents, so you?ll need four of them to tune it up around 35 Hz. This gives you a good idea how much even a relatively modest aspect ratio can increase acoustical vent loading.
Regardless, when in doubt I always do/recommend a tuning at least as low as the speakers are likely to be required to reproduce or down in the BW where room gain is taking over, which in your case will be ~1130/2/28 = ~20 Hz [~7? long vent], so at least an ~Fs tuning [~2? long vent] seems a good place to start and use EQ to flatten its higher up BW if it sounds too ?lean? with whatever tuning you choose.

Of course all this is based on specs that?s probably off enough to make these predictions off enough to be audible, but they?re fine for comparisons, finding a starting point.

In my early days of building these types of cabs [they were much higher aspect ratio, so usually folded in half and still 50-60? H] I got so frustrated trying to figure out how much bigger to make the vent to get it within tuning range, finally giving up and leaving a huge, gaping hole way larger than the max recommended driver effective piston area [Sd] or even leaving the entire bottom off, which led me to experiment with bottom firing vents and removable baffle sections long before I ever saw any, so guess I can?t complain

Anyway, short answer is try ~baffle thickness to 7? with one at actual Fs, whatever that turns out to be. The 7? looks about right to me if the +12 dB is at/below 20 Hz.

GM

Quote:

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Originally Posted by gvasale

you're missing another 416 in each enclosure.

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LOL! Seems to me I said the same thing back at the beginning of this build.

GM

Quote:

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Originally Posted by GM

LOL! Seems to me I said the same thing back at the beginning of this build.

GM

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:biggrin2:

Edit. Add this preamble to OP.

I used WinISD and its 416-8B database parameters to come up with upper and lower ballpark tuning options for my cabs.
1. Optimally flat: -3dB @ 35Hz.
2. Extended bass: -8dB @ 25Hz.

However WinISD does not take into account the corner position room gain that will affect my speakers. I took this gain to be ~+12dB.
http://www.harmanaudio.com/all_about...kers_rooms.pdf

I mentioned that I could use EQ. and that I thought a higher tuning would give better transient response.

I ran this past GM and he suggested that I post it here for all to see. :)

GM, thank you for information. This has tied up the last impediment to completing my cabs.

Very kind regards,

Marshall

A little history. My project started life as an A7-500 build. After having all the panels cut I decided to go BR using the same parts. I pondered using 2 speakers per box, I have a pair of 421-8H I could have played around with but decided to stick with a single 416-8B. Also, the cost of shipping 416s Altecs to Australia is horrendous. This project has cost more than anticipated so I am comfortable with my choice. 2x416s would have been great, though.

One 416-8b is working well for me but two would, of course, be nicer ;):
http://www.hostboard.com/forums/hbmc...2011/11/22.jpg

Absolutely! In these large cabs, the second driver is really only needed for very high efficiency to get the most out of SET amps and/or high SPL and/or if tuned low enough [or sealed] for pipe organ symphonies, movie LFE tracks. Backed into a corner, it typically isn't needed, just as you say, nice to have.

Having someone over who's used to seeing a low efficiency [sub] woofer[s] work itself to death, go looking around my room for a sub because you can barely see the 515s move on most music, movies even at near 'Headbanger's Ball' SPLs.

GM