Need help with 2235H enclosure design

[Doctor_Electron]

Nice CV.

Living in Ottawa, Canada which houses the National Research Council and as 'kid', was able to have home built speakers tested by Floyd Toole in the 70s for free there....

Ever heard of him?

No, but I will look him up on the web.

Speaking of some audio testing, I was once in a very large anechoic chamber on a military base where I worked. It was used for RF testing of transmiitters, receivers, antennas, etc. The steeply-sloped, pyramid shaped "cones" that covered all surfaces were made of "eccosorb", kind of a heavy foam rubber enfused with lots of a graphite compound of some sort. Although not specically designed for audio use, the chamber had the (non) audible effect of causing disorientation and dizziness, due to the lack of background noise on the inner ear. There was a twenty minute max. limit on occupation by personnel and a number of safety procedures to prevent over stays. I was not in there more than 15 min. but one could sense (not sense?) that there was something different going on, a disorienting quiet, of all things! To me it had a tecnologically pleasing creepiness.

[Fort Knox]

No, but I will look him up on the web.

Speaking of some audio testing, I was once in a very large anechoic chamber on a military base where I worked. It was used for RF testing of transmiitters, receivers, antennas, etc. The steeply-sloped, pyramid shaped "cones" that covered all surfaces were made of "eccosorb", kind of a heavy foam rubber enfused with lots of a graphite compound of some sort. Although not specically designed for audio use, the chamber had the (non) audible effect of causing disorientation and dizziness, due to the lack of background noise on the inner ear. There was a twenty minute max. limit on occupation by personnel and a number of safety procedures to prevent over stays. I was not in there more than 15 min. but one could sense (not sense?) that there was something different going on, a disorienting quiet, of all things! To me it had a tecnologically pleasing creepiness.

The only thing "pleasing" about that place .... was.....you new where the door was.......
I worked @ Goddard....it had a 170db horn set (room) to sumulate rocket invironment on satellites.....

[vanbeek]

Hello folks, I'm back again to finalize the JBL 2235H enclosure. I have winisd 0.44 to assist in the vent dimensions. With an internal volume of the enclosure of 5.5 cu.ft, win gives me a single duct of 4 inches at .070 m or 2.76 inches in length with a vent mach of .11. This seems short to me....or?

I would like to do a rectangular vent, because it just works visually with the design. I believe a 4 inch duct translates to 12.56 square inches, with the same length.

Would this be a correct assumption?

Help in this regard, would be much appreciated....

Have a great weekend

[vanbeek]

Hello folks, I'm back again to finalize the JBL 2235H enclosure. I have winisd 0.44 to assist in the vent dimensions. With an internal volume of the enclosure of 5.5 cu.ft, win gives me a single duct of 4 inches at .070 m or 2.76 inches in length with a vent mach of .11. This seems short to me....or?

I would like to do a rectangular vent, because it just works visually with the design. I believe a 4 inch duct translates to 12.56 square inches, with the same length.

Would this be a correct assumption?

Help in this regard, would be much appreciated....

Have a great weekend

Has everone had good success with the win calculations?

[Lee in Montreal]

You haven't mentionned to which frequency the cab was tuned...As you know it is a compromise. You can tune low, but you will be missing a bit of the octave above, or you could tune a bit higher but miss some extension. Check responses as well as excursions.

[vanbeek]

Thanks for responding Lee,

WIN ISD shows it tuned to 32.63 hz. for best overall response. My current vintage rig setup is crossed at 320 hz to a 2122H @12 or 18 db octave...with a Pioneer D-23 crossover.

This would be the Bottom section of a modular JBL 4 way using pretty much 4344 drivers.

The vent mouth area at the baffle of 12.56 sq. inches, works as well as does the overall duct length of 2.76 inches....visually and architecturally. This translates into 1) 4 inch round duct @ 2.76 inches long

I guess the question I'm asking, is the ISD program reliable? It just seems small to me....but quite frankly, I don't know.....

[fpitas]

My experience has been with WinISD Pro, designing (among other things) a 10 ft^3 cabinet tuned to 28Hz for a quad of 8" woofers. The design used two 4" diameter flared ports, each about 5.5" long. Its predictions were within one Hz of the measured results. Now, I accounted for finite box Q etc. etc., but I assume you are paying attention to details also.

[vanbeek]

I'm not anywhere near the level the designer as most if not all of the members are here. I've just taken the recommendations of folks in regards to enclosure volumes for the 2235H driver. Now I'm just looking at sizing the vent, which ideally would be a single rectangular vent or duct. The 12.56 square inch mouth size works....

So your experience says that WIN ISD is accurate for sizing ducts and vents, I'm guessing from your response..

[fpitas]

I'm not anywhere near the level the designer as most if not all of the members are here. I've just taken the recommendations of folks in regards to enclosure volumes for the 2235H driver. Now I'm just looking at sizing the vent, which ideally would be a single rectangular vent or duct. The 12.56 square inch mouth size works....

So your experience says that WIN ISD is accurate for sizing ducts and vents, I'm guessing from your response..

I haven't used the regular version, just the Pro, since that allowed me full flexibility in box size etc. as I designed for the response I wanted (more or less a Bessel high-pass at the low end for good transient response). Since the same guys wrote the regular WinISD though, it probably works just fine.

[vanbeek]

Thanks for your informed opinion....

[Lee in Montreal]

Using my Excel spreadsheet.

2235 driver in a 5.5cft enclosure. Tuned to 25 and 32Hz.



Excursion at 300W, comparing 25 and 32Hz tuning

[vanbeek]

Thanks Lee. I like the 32 hz tuning....I think?

I guess I'm looking for confirmation on my rectangular duct size and tuning.....and I'd rather not use electronic eq.

[Lee in Montreal]

Thanks Lee. I like the 32 hz tuning....I think?

I guess I'm looking for confirmation on my rectangular duct size and tuning.....and I'd rather not use electronic eq.

Yes. The 32Hz tuning is defintely the one to go for. Flat down to 40Hz and with some excursion margin. The common school of thought when going from square, round or triangular port sections, is to respect the area, whatever the shape.

[vanbeek]

Yes. The 32Hz tuning is defintely the one to go for. Flat down to 40Hz and with some excursion margin. The common school of thought when going from square, round or triangular port sections, is to respect the area, whatever the shape.

perfect, thats what I thought.....so the duct length appears to right? 2.76 inches? area 12.56?

[Lee in Montreal]

perfect, thats what I thought.....so the duct length appears to right? 2.76 inches? area 12.56?

Once you have established the tuning frequency, you can use some softwares to calculate your port dimensions. The bigger the area, the longer the port for the same tuning frequency. I personally prefer a large port to reduce noise.

You can use this online calculator

http://www.psp-inc.com/tools.html