View Full Version : port position
07-16-2003, 03:02 PM
I am building a system more or less after the 4350/5's, but with 4 2245" woofers in 1400L enclosures per pair; What are the pros and cons of having the ports closer to the floor or higher up?
07-16-2003, 03:18 PM
1400 liters per pair of 2245H's?
Why so big?
What is the target tuning frequency?
07-16-2003, 04:51 PM
I know the size is overkill, I want to get 22Hz.
07-16-2003, 05:28 PM
Well you can do as you wish obviously but that's a whole bunch of volume and it will take an enormous amount of bracing to get the system losses down to an acceptable level.
Maybe you would prefer to place each 2245H in a decent B4 alignment and then give yourself the option to add an external 20 Hz second order high pass filter with a Q of 2 which effectively turns the system into a B6 alignment. The 3 dB downpoint will be roughly 20 Hz.
In other words, you build an enclosure of roughly 10 cubic feet per transducer (280 liters) and tune the box to 28 Hz. This is roughly a B4 alignment (4th order Butterworth). To turn it into a B6 alignment (6th order Butterworth) you simply retune the enclosure to 20 Hz and apply a 20 Hz high pass filter with Q = 2. This extends the VLF by roughly 10 to 15 Hz. We used to build the enclosure and then use two duct/port configurations. One port/duct would tune the volume to 28 Hz and the other port/duct would tune the same volume to 20 Hz. We would cover whichever port wasn't in use.
If you want further information on what I am talking about look up "A New Set of Sixth-Order Vented-Box Loudspeaker System Alignments" by D.B. Keele Jr. - Journal of the Audio Engineering Society June 1975, Volume 23, Number 5.
He and R.J. Newman worked on this concept while at Electro-Voice. Electro-Voice was a veritable powerhouse of talent during this time period with Keele, Newman, J.N. White and others on staff.
Incidentally, the JBL 5234A and 5235 electronic frequency dividing networks have the second order high pass options (Q = 2) built in. To use just the boost option, leave the unity gain cards in and run full range.
07-16-2003, 05:41 PM
Thanks a lot, I will look it up; for the enclosure You suggested, what port diameters and length should I use?
I already have a good M553 X-over, What can I do to it?
07-16-2003, 07:02 PM
Incidentally, the JBL 5234A and 5235 electronic frequency dividing networks have the second order high pass options (Q = 2) built in. To use just the boost option, leave the unity gain cards in and run full range
Should us 4345 caretakers be listening in? Per my post to Ken P sometime back, I'm aware of the option, and I'm always pleased with the results of implementing your "advice" (if this is that, or are you merely speaking fact...?), but personally cannot imagine the need for anything other than "factory flat".
I'm inclined to defer any EQ modifications until I get the transducers back in spec - it would seem to be games on an unlevel playing field. The 2122H's are done, but the 2245H's are in serious need, and I expect marvelous things on their resurround.
But, this is an easy enough test... :hmm:
07-16-2003, 08:10 PM
"for the enclosure You suggested, what port diameters and length should I use?"
For each 2245H use a 10 cubic foot volume with two 6" diameter ports each having a 12.5" duct. To extend the VLF simply block off one of the ports and add a 20 Hz second order high pass filter with a Q of 2.
The M553 doesn't have any VLF boost functionality that I know of. You would have to build your own to place between the M553 output and the VLF amp or simply put a 5234A or 5235 in the chain with the 20 Hz boost switched on and the unity gain cards in place. With the unity gain cards in place you are not using the dividing network functionality of the 5234A/5235.
"Should us 4345 caretakers be listening in?"
07-16-2003, 08:42 PM
Thanks again!, will do, and save some lumber and space.
To the original question, Where would You put the ports, up or down?
I will build it with the 2202H, 2445 and 2405H in a separate cabinet so I can endo the 2245H's and put the ports up or down, How about in the middle?
07-17-2003, 04:44 PM
"To the original question, Where would You put the ports, up or down?"
Depends on what kind of boundary reinforcement you're after. The further away from the floor you mount the driver/port(s) the less reinforcement you will get. Remember that a 2245H doesn't really like a whole bunch of boundary reinforcement when mounted in a vented-box of 8 to 10 cubic feet tuned to 28 to 30 Hz. A 2242H mounted in the same enclosure DOES prefer a bit of boundary reinforcement.
07-17-2003, 05:34 PM
... but with a 2245, you should be able to just tune it a bit lower (say 25-26 Hz), and then use a low-mounted port to utilize boundary reinforcement, right? (ie, trade off a little output at 30-40 Hz (which the boundary should restore), for a little in the 25-30 Hz range... )
07-17-2003, 08:31 PM
Thanks a lot for Your advice, I will be putting it on the forum in about a month and let You know.
08-14-2003, 01:35 AM
Have you built your subs yet?
I´m very interested in how the
play, if they turned up to be great.
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