Positioning of ports and driver?

[Greg_M]

I have been using a speaker design program for my up coming speaker enclosure build. Although I am happy with the tuning and response figures it really says nothing about where in the enclosure to place the ports and driver.

Does it make a difference?

Front firing speaker, front firing ports .

How far to separate the driver from the ports. The driver and ports from the ends and sides of the cabinet. That sort of thing.

Is there reference material somewhere?

Also a question of material thickness....

I lean towards 1" mdf, but on a ported enclosure that is internally braced will it make much difference, other than the weight?
Would 3/4" work as well?


I am using WinISD

one JBL 2235H
8.657 cu ft
26.85 hz tune

Internal dimensions
17" w (driver/ports mounted on this side)
40" h
22" d

2 ports 4" ID 7.71" long giving .04 mach

This design dimension ratio(s) are sort of like the Klipsch KLF-10s I am using now except bigger.
The horn will be external (another project)


The design looks great on paper....

[Robh3606]

You can put the ports where ever they make sense. I tend to put mine either on the back or on the side pointed away from where I sit. Helps keep any port noise inaudible. Just make sure the ports have room to breath.

Rob

[Woofer]

If you'd like to see an example of how inventive you can be, go here:

http://www.audioheritage.org/vbulletin/showthread.php?33697-JBL-4315A-with-custom-cabs-for-sale-UK

It's an ingeniously 'modernised' 4315.

[Mr. Widget]

You can put the ports where ever they make sense. I tend to put mine either on the back or on the side pointed away from where I sit. Helps keep any port noise inaudible. Just make sure the ports have room to breath.

Rob

True, but be aware that if you plan on pushing the speakers up against a side or rear wall you need a couple of times the port diameter distance to the walls.


Widget

[Mr. Widget]

Also a question of material thickness....

I lean towards 1" mdf, but on a ported enclosure that is internally braced will it make much difference, other than the weight?
Would 3/4" work as well?


I am using WinISD

one JBL 2235H
8.657 cu ft
26.85 hz tune

Materials and thickness...

Materials, thickness, and bracing do matter. MDF is a soft and soggy material. It is well damped and therefore will not ring which is very good, but it is also rather lossy. Baltic birch plywood is stiff as hell and will not flex... I like to use a hybrid of these two materials, say a half inch layer of MDF bonded to a half inch layer of birch ply. I typically use 2x4s or 3/4" birch ply for bracing depending on the size of the box.


I think you will find the 2235H is better suited to a 5 cu ft cabinet tuned to 30Hz.


Widget

[Greg_M]

If you'd like to see an example of how inventive you can be, go here:

http://www.audioheritage.org/vbulletin/showthread.php?33697-JBL-4315A-with-custom-cabs-for-sale-UK

It's an ingeniously 'modernised' 4315.

That's roughly the design I had in mind.
5 black bumpy sides and one "pretty wood" side. Haven't decided what "pretty wood" I will use, but I live a short way from "EdenSaw" which has a ton of exotic and domestic woods.

http://www.edensaw.com/MainSite/Stor...egoryHome/1092

The speakers will be in corners looking out at around 45° or so

Here's a couple screen dumps of the response curve. Not much difference in the two. The 8.657 cu ft has a very slight bump up (just above 40hz) before it starts to descend where the 8.245 cu ft does not.

I am leaning towards the 8.245?

Opinions?

[Greg_M]

Materials and thickness...

Materials, thickness, and bracing do matter. MDF is a soft and soggy material. It is well damped and therefore will not ring which is very good, but it is also rather lossy. Baltic birch plywood is stiff as hell and will not flex... I like to use a hybrid of these two materials, say a half inch layer of MDF bonded to a half inch layer of birch ply. I typically use 2x4s or 3/4" birch ply for bracing depending on the size of the box.


I think you will find the 2235H is better suited to a 5 cu ft cabinet tuned to 30Hz.


Widget

I used some Baltic Birch a while back when I made a Sunn 200S clone enclosure. It was good to work with but the piece I had was slightly curved which made making the enclosure square a bit of a challenge. The project took almost a year, but I was duplicating gathered measurements and back engineering the design plus gathering elusive parts.

[more10]

Driver and port placement is very important if you are using the speaker for midrange or building a large box. Since you are building a large box you will have standing waves between top and bottom, possibly ruining your response.

I built something very much like your box, Rebuilding a pair of srx. The box is basically a "-6 db bass shelf" as optimized by winisd. Placing the vent at the bottom allowed me to simulate in hornresp as an "offset driver". The box is a combination of BR and MLTL, the MLTL resonance filling in the dip in resonse curve around 100 Hz. Placing the driver in the middle of the box controls the first standing wave but the second at 300 Hz is impossible to avoid.

You can use Akabak if you have an old xp computer to simulate other driver and port placements.

If you want I can do a Hornresp simulation for you, since it is quite difficult to use before you learn it.

[Greg_M]

Driver and port placement is very important if you are using the speaker for midrange or building a large box. Since you are building a large box you will have standing waves between top and bottom, possibly ruining your response.

I built something very much like your box, Rebuilding a pair of srx. The box is basically a "-6 db bass shelf" as optimized by winisd. Placing the vent at the bottom allowed me to simulate in hornresp as an "offset driver". The box is a combination of BR and MLTL, the MLTL resonance filling in the dip in resonse curve around 100 Hz. Placing the driver in the middle of the box controls the first standing wave but the second at 300 Hz is impossible to avoid.

You can use Akabak if you have an old xp computer to simulate other driver and port placements.

If you want I can do a Hornresp simulation for you, since it is quite difficult to use before you learn it.

I do plan to do a cross over at 600hz.
It would be great to have your input using Akabak.

Thanks
G

[more10]

600 Hz will be difficult with such a large box.

I will make an Akabak script for you tonight, by exporting a Hornresp design. Then you can play around with the Akabak script placing the driver and port.

[more10]

Hornresp record (which you can import) and its simulation:

Input paramters (you will get this if importing the record)


Schematic view of box:



Port response:



The resonance at 180 Hz is minimized by changing length of L12 in loudspeaker wizard:



Combined response (driver and port):



Maximum spl:



Red color indicates maximum excursion, black maximum power.

Impulse response:



Simulation is done in corner (0.5 pi). The port peak at 350 Hz will be worse in real box, limiting this box configuration to about 200 Hz.

Hornresp cannot simulate other placements of the port, so I will make a simulation in Akabak later.

[Greg_M]

I'm totally lost

[more10]

Do you want me to remove the post or do some more explaining?

[Greg_M]

It's probably valuable to someone who knows the program, but I have no idea what all those boxes mean....

[Woofer]

Do you want me to remove the post or do some more explaining?

As someone that's just lurking in the shadows, please, don't remove it....
There's lots that I (for one), can learn from it.