Port Size for 620 Cabs

[ngccglp]

Hi,

I noticed my DIY 620 Cabs' port size measures about 11.3" x 2.6". When I looked at the available Altec plans for 620 type cabs, the port size specified is 11" x 2.5". May I know if the difference would be significant if I reduce the port size according to the Altec plans?

Also, is there a good way of reducing the port size without damaging the original cabs? Can I use foam to reduce the port size?

Thanks

[GM]

Your port raises the tuning < 1 Hz, so inaudible.

GM

[klausesser]

Hi,

I noticed my DIY 620 Cabs' port size measures about 11.3" x 2.6". When I looked at the available Altec plans for 620 type cabs, the port size specified is 11" x 2.5". May I know if the difference would be significant if I reduce the port size according to the Altec plans?

Also, is there a good way of reducing the port size without damaging the original cabs? Can I use foam to reduce the port size?

Thanks

The exact dimensions you should regard the driver?s Parameters for.

I use plates with different cut-outs which i attach behind the port and fix them with screws - that way i can alter the port-sizes until findig/measuring the correct one in combination with the driver.
I use 604E in the 620.

But as GM said: your differences don?t matter much.

best, Klaus

[ngccglp]

Thanks for the advice. While the bass articulation of the 604/620 is excellent, somehow I find the bass energy to be lacking when compared with say a JBL 4333/4343. Is this the limitation of the 604/620 combi?

[klausesser]

Thanks for the advice. While the bass articulation of the 604/620 is excellent, somehow I find the bass energy to be lacking when compared with say a JBL 4333/4343. Is this the limitation of the 604/620 combi?

It?s a matter of taste in the end - i know the 4333/4343 JBLs very well. I thinkt that the Altecs are light, swift compared to the JBLs which - again in MY opinion - are somewhat more "punchy" when listening to pop-music.

I like the bass of the Altecs - and especially the 604E - better because i prefer acoustical Jazz, voices and classic. The "lighter" bass results in more transparency and naturality opposed to the 4333/4343 - without missing anything even when listening to pipe-organs, which come rich, powerful without mudding low registers.

I also use an active Manger monitor-system - which goes very deep . . but doesn?t have the "taste", the swiftness i like so much with the 604E/620 but is on the very, very precise side of the road . . a system to do work with.

Of course the lack of deepest notes is what makes the Altecs that "light and swift" . . but as already said: i don?t miss a thing. And that?s very impressing for a system that?s more than 40 years old i?d say . . .

I wouldn?t prefer the JBLs at all.

best, Klaus

[GM]

Note that in theory the 620 can have the same bass 'weight' as the JBL by increasing the total output impedance and tuning it lower with a ducted port. Since the room dominates down low though, using a cheap 25 ohm pot in series to find how much extra is required is what I do/recommend (HF EQ required to re-balance the system) or use the simple expedient of an RTA/EQ to measure the JBL, then EQ the 620 to match and if any boost is required below its tuning, then re-tune the port to this boost frequency with the understanding that efficiency suffers, so more power is required for a given SPL.

GM

[ngccglp]

With my EQ ON, I turned the High Freq Lpad away from the Optimum position to the mid point. The sound is much more balanced now, the bass is now more pronounced, yet retaining a nice tight sound. However, the highs sounds a bit rolled off. Does anybody actually set the High Lpad at the Optimum position? Thanks