Altec 604s "built" into a Bookshelf?

[GM]

Is this what you had in mind GM?

Nothing so elaborate, but would be very nice if panel has an even fit. Me, I just normally make them full width as mah has done and as Altec did with the 846B and some others: http://www.lansingheritage.org/image...ign/page31.jpg

FWIW, here's one of my 'sub' woofers from '69: dual 515Bs in individual removable baffles, ditto the vent baffle, though not obvious since I haven't worn off the paint on the screws as I've done periodically rotating the woofers. Note that the big perimeter recess is for a heavy duty, flush fit grill frame, so not a good plan to have it otherwise if not filled with high density open cell foam.

The baffles are attached to a 2x6 frame with the two cross pieces being 2x6 on edge. This is way overkill, but wood was cheap and I didn't care how big/heavy the cabs turned out. 1x2 Fir or better with an added 1x3 on edge to form a 'T' cross bar[s] is sufficient.

GM

[vyju]

Hi,

GM what are the dimensions of your cabinet?

Would dual 416A's work in this cabinet?

Regards
Rajiv

[GM]

Greets!

60" H x 30" W x 24" D o.d. or ~ 20 ft^3 net and currently tuned to around 16 Hz, so require some corner loading. Note that my 515's specs are somewhat different from those published, ideally requiring somewhat larger cabs and that internally it's not just a simple reflex, but a single fold Voigt pipe horn with restricted vent [AKA ML-Voigt], so has a bit more usable gain BW and better damped than a reflex.

If the 416As are original spec and fairly closely matched, then would work OK in a corner, especially if tuned to Fs with a high output impedance, or up around 32 Hz otherwise. If they should be more like Pano-Mike's recent re-cones, then it would only be good for one driver.

Regardless, I never bothered to save any design details, so can?t easily provide dimensions plus ideally it would need to be designed for your driver?s specs, then manually fine tuned. Their construction has held up so well over the decades of moving and temperature/humidity abuse that I can?t even find the filled screw holes down the sides to measure from. Wish I could say the same for more recent builds using EPA approved fillers. I can?t even easily discern where I chain sawed a section out of them to fit a previous location.

GM

[GM]

Width = 20 in

Is there a rough formula for calculating the vent area needed based on dimensions alone?

You?re welcome!

OK, this shrinks the cab to ~11.7 ft^3, so allowing ~0.75 ft^3 for the driver and bracing, in a sim this equates to a longer vent for each alignment [ditto if the bracing takes up more volume] and ideally shifts the ~20.65? driver location up a bit to ~20.49? [or higher if more loss due to bracing] to maintain the ?ideal? tuning where the impedance peaks are equal amplitude for a 33 Hz Fs, which in turn means a slightly higher F3.

Bottom line, since we don?t know the cab?s actual net Vb or each driver?s Fs or much of a clue as to what tuning will work best in-room to the audience?s ears, in the scheme of things then; these types of sims are mostly for making sure the cab, vent starts out big enough to allow said manual tuning to achieve the desired performance or at least give some idea how much it will likely be compromised.

My only concern then is how accurate GPA?s published Fs is. If it?s lower, then all?s well as this just means a longer vent, but if higher, then the shortest simmed vent[s] may need to be larger in area. This in turn requires the vent to be wider to maintain the simmed driver/vent acoustical loading that becomes more vintage sounding as it shortens, rendering the extra effort to optimize vent acoustical loading [damping] moot.

All this is of course just theoretical and the room?s impact on a speaker?s LF performance often swamps it plus can be ameliorated with additional vent damping [AKA ?critical? system damping]. Still, many folks can subjectively perceive such minor variances, so I leave it to the reader to decide at what point ?good enough? is.

For a simple reflex or ducted port, the math is strictly cab net Vb and vent length dependent, i.e. Helmholtz plus ? WL resonant pipe theory math is all that?s required, but this assumes a cab with a ~uniform particle density, i.e. no eigenmodes within its audibly perceived BW and the vent is acoustically occupying the same space as the driver when used for vented speaker design.

This is why the original reflex patent uses an acoustically small cab with the vents ringed around the driver as close as physically possible, hence the reason behind all the vintage simple reflex/ducted port cab designs until Harry Olson?s late ?40s MLTL designed for his new LC1 15? ?full-range? driver, though he referred to it as a reflex, missing a major patent/marketing opportunity to enhance its promotion:
Sound translating device - US 1869178 A - IP.com

Anyway, the math is in WP?s PiAlign doc:
http://www.google.com/url?sa=t&rct=j...N7Mt5w&cad=rja

I don?t know the math for calculating the ? WL TL?s impact on vent design nor ever found a simple pattern to scale it, just that as the distance between the driver/vent increases, vent area increases due to vent length decreasing, which only AkAbak and MJK?s MathCad software can accurately enough calculate it including any added damping AFAIK:
http://www.google.com/url?sa=t&rct=j...1p7wdQ&cad=rja

http://www.google.com/url?sa=t&rct=j...VuH8Kg&cad=rja

GM

[Encyclopediabsh]

Thanks all. I'm going to order the GPA 604's and give the project a whirl. Will post update once completed...