Crossover is suggested no lower than 1500 Hz. A "K" crossover in very good operating condition works pretty good with the 704.

I agree - the 704 "likes" a little more power to get the low end working well, but mostly, I think, in order to handle transients in the modern digital media. They're the most efficient 2-way ever built in the Altec tradition, perhaps by anyone else, too, but they do like to have a big box and extra amplifier headroom.

As for box tuning, Jerry Hubbard tuned the Iconic Stonehenge V System we demonstrated at the GPAF at 40 Hz using a horizontal slot of 11" H x 2.5" v x .75" D.

• Iconic's Stonehenge Systems Page

I am surprised at the port size dimensions. I would think with the T/S parameters of the 704-8A that it would like a lower port frequency.

Why the 40hz tuning and not something like 28hz which would be close to the 6" x 10" x 14" deep I was considering???

Ron

I still have time to change up my vent size choice. But until I get info to change my mind, I still think that 6" x 10" x 14" deep sounds more like what the T/S paramters would call for.

I would be interested in what your techie has to say!

Ron

What you tune it to has to do with how much series resistance there is and the desired room/speaker placement, though some folks ignore these and tune them to a more personal taste, such as the 'West Coast Sound' championed by Altec, and now apparently by Iconic. Great party/DJ alignment, but no good for a more accurate reproduction in a typical wide BW HI-FI app of today.

One thing for sure though is that such a large vent you propose will have strong enough pipe harmonics that will audibly comb filter with the driver's response above ~250 Hz if not damped.

GM

You're welcome! Uh, no, not per se anyway. I mean you use whatever size vent that's required to keep vent speed low at whatever Fb you've chosen, and if it's big and/or long, then I recommend damping down its harmonics as required to smooth its response out.

WRT designs that use 3/4" long vents (baffle thickness only), it's my understanding that high cross sectional area (CSA):length vent ratios don't have enough acoustic inertance to work as well as when the ratio is reversed, so can be overdriven easier, allowing the driver to overexcurse since it needs a longer time period to 'pump up' (for lack of a better phrase). IOW the ducted port's much more rigid air mass 'piston' damps the driver better and is acoustically more efficient than the large, flimsy membrane of the shallow vent.

That said, I've compared them and found they both perform well and have designed/built many well received speakers using big CSA:length ratio vents rather than making/recommending multiple smaller, longer ones since learning of this, so I'm not going to lose any sleep over it.

As always though YMMV.

GM

With regard to the tuning port size/type, we looked at ducted ports, but Jerry pointed out that the speaker only "wants" to see a certain vent size, and doesn't really "care" how you achieve it as much as that it GETS the size it needs and can operate through it without having to work at it.

That said, we figured out it would take THREE large flared ports to accomplish the same thing we did with the horizontal vent, and the cost just didn't outweigh the advantages (if any).

When you listen to the 704-8A in the Stonehenge V enclosure, it performs almost effortlessly in the LF region (it does in the HF region too, but we're not talking about that right now), as does the "G" in the Model 17 and the "H" in the Model 18. So MANY speakers seem to have "work" hard to get the LF out to the listener - the 704-8A in the SH V box doesn't have this problem. In fact, the LF performance is very similar to listen to as the Model 19.

All I can say is that I'm very happy with a 40Hz tuned 9ft3 box for my G's. I don't know how much of a roll a wide baffle and dual side mounted vents of fairly large area (1 1/2" long) plays in the final product but I like the results.

Ron