The port numbers that don't make sense...

[turnitdown]

I'm not new to this and have built almost a dozen full-range projects. This one is just counter-intuitive. I built an exact copy of a B380 and put a 2235H in it with the correct port og 4" x ~9". I now want to mount Wayne P's waveguide with a B&C DE250 on the baffle and it does not leave room for the port on the front which, with no exceptions, is where I want it. So I went to WinIsd and ran the numbers for 2, 2" ports and their length for the same tuning came out to 2.21" each. It seems, somehow, counter-intuitive. Can someone check my back and validate or repudiate that? I want to preserve the tuning with smaller ports. Thank you in advance. (Great knowledge here in this forum)

[Mr. Widget]

I don't currently have any simulation software running so I can't verify the lengths, but you really do not want 2" ports, they will make audible noise. Try moving the ports to another surface.


Widget

[turnitdown]

Thanks Widget, Mr., that is. My thoughts exactly. I want the horn right above and touching the woofer (almost), but perhaps I can scooch each horn over a little, make a mirrored pair and still get the 4" port on the front. I need it on the front because of placement. Thanks. Anyone else?

[more10]

Often the placement of the ports are important. A vented enclosure will resonate at higher frequencies as well. These frequencies have to be damped and/or using clever port placement to avoid nodes inside the box. This is especially true for 2-way systems.

Place the horn on top of the box or build a new somewhat larger box.

[more10]

B380 is a sub. Not inteded for midrange. Get proper midrange drivers an put them in a new box with your horn.

[4313B]

B380 is a sub. Not inteded for midrange. Get proper midrange drivers an put them in a new box with your horn.JBL used it as a sub. They also used it in the 4430 two-way. The B380 is just a box tuned to 26 Hz for use with a bump filter at that frequency. The concept is no different than the 15-inch two-way M2 tuned to 24 Hz for use with a bump filter at that frequency. Now the W1500H or SUB1500 transducers are a different story, they can't fake it, they really are for subwoofer duty only.


I know a lot of people freak out when other people use a fifteen-inch transducer to 800 or 1000 Hz but just try to ignore them. People have also used the Citation 7.4 sub as the basis for two and three-way systems (just remember to pull that series inductor out of the circuit first).

One can use two three-inch ports in place of a single four-inch port. That has been done to fit ports on the baffle. In theory ports should be placed as near to the low frequency transducer as possible to maintain SPL and phase. That doesn't mean that people who place them wherever else are "doing it all wrong" it just means they'll have to live with the results.

[turnitdown]

One reason I asked for help from the brain trust is because I don't really care to do it wrong (driver combination opinions notwithstanding) - I can get two 3" on the front at ~ 8" each - - it also (WinIsd) suggests one 3" port @ ~ 3 inches will tune the box the same. Elementary questions these, but box size and port placement are non-negotiable. So go with two 3s or one? Thanks. I'll try to bring more challenging questions in the future. (Anticipating remarks of the kind - I did search and read - but, I trust this board a whole lot more than names I don't recognize. Thanks again.

[4313B]

Two 3-inch ports. I cannot imagine you liking the results of a single 3-inch port with the 2235H.

[turnitdown]

I appreciate your endorsement of the two 3 inch ports 4313B. That will be the config. Two three inch ports will fit in the lower corners on the front. I measured after seeing your reply. I knew I would receive good guidance here. I may have authored few posts, but read constantly and know the names to trust. My gratitude to you all for your knowledge and, sometimes "spirited" discussions.

[turnitdown]

I can't compromise on a proven design so I decided to make the 4" port on the front work by doing this...thank you all!!!

[4343]

I can't compromise on a proven design so I decided to make the 4" port on the front work by doing this...thank you all!!!

That works, how's it sound? What improvements does that horn have over the QSC?

If you felt like re-doing the baffle, you could slide the woofer over under the waveguide, that might get a (tiny) bit better, so probably not worth the effort...

[turnitdown]

Camera picture...ugh. Sorry. They sounded great with the horn on top, so no audible change once they were mounted inside. I did get c to c closer, obviously. I wanted the original port on the front baffle and the only place to put it was where you see it. By my (imprecise) measurements, the c to c spacing with the horn dead center over the 2235H would be 11.25 inches. Moved over to its current position the c to c spacing is 11.75 inches - still well within allowable distance. I'll be doing the second cabinet today and they will be mirror-imaged. As for the horn on the B & C DE 250, that is Wayne Parham's so it speaks for itself. I didn't want the extra c to c spacing of the large QSC...but I do daydream about building a 12" two-way with that. The SEOS 12" horn is lurking in the future plan mental file also.

[Ian Mackenzie]

The overall vent area is the key parameter.

2 e inch ports is closer to the area of a single 4 inch port.

Alternatively you could have a rectangular slot.

Moving the port closer to the box wall will alter the tuning.