vertical 4x8 build

[projectMalamute]

short version:

I want to take 4 speakers out of an SWR 8x8 and build a 4x8. I want the speakers to behave as closely to the way they do now as is possible.

I like the idea of an 8x8 sliced in half vertically (as opposed to horizontally like the Henry Jr). I figure I could still do tilt back casters and also get some free dispersion advantages that way.

This means I want precisely half the internal volume of the 8x8 and the same port tuning frequency, no?

Volume is easy but what do I want for ports? The 8x8 has 3 tubes, say of length x and diameter y.

longer version, or why someone would do such a thing:

I am addicted to first generation SWR Henry the 8x8 speaker cabinets. These are all I have used for well over a decade and for the purposes of this discussion you can assume I am medically unable to change.

I use about 1000 watts to drive the speakers well in to power compression and well past the region where things are behaving in a nice linear fashion. By 'about 1000 watts' I mean a Crest CA9 or CD2000 hitting the clip limiters when I really lay in to it(*). I'm also getting harmonic distortion from a Rusty Box preamp set to start getting hairy on the loud parts. In doing this I am absolutely playing the amp as much as the instrument. My rig is set up to allow a massive range of timbral variation from touch alone. This is good because my signal goes pickups (hardwired to the output jack, no preamp or volume knob or tone control) -> preamp(Rusty Box) -> power amp -> speaker box. No effects ever.

I've been using the same basic set up for a long time. Before there was such a thing as a Rusty Box the preamp was a Traynor TS50B, which is (don't tell anybody) the same thing. A couple different power amps have come and gone but all were for-real stuff in about the same range power-wise.

It sounds really good. At the levels where it is sounding it's best it's also pretty loud(**). Not Sunn O))) loud, but on the high side of average for your typical original aggressive type music sort of band. In the ballpark of an SVT rig turned up to where it starts acting like an SVT rig. Way louder than almost any cover band or 'my amp is just a monitor' type of situation.

I've got a project where I don't need that much volume.

I would like at least some of the same character at the quieter levels.

I have 8 or 16 extra speakers kicking around.

Also, as stated earlier, I am medically unable to use anything other than this setup.

Hence the project.

* - Yes the speakers can handle being run like this. At least if you know what you are doing and are paying attention. In 15 odd years of using the 8x8 I have damaged exactly two drivers. Both easily repaired minor tears at the surround and both when using an SM500 and it's stupid down to DC frequency response. The current setup has never damaged a driver.

** - Yes, some people play in and enjoy listening to loud bands. I've played a whole lot of shows and I've done a whole lot of live sound. I know what I want and I know what I'm doing, my bands sound good. Or, if you prefer, my bands sound exactly the way they are supposed to.

[Downunderwonder]

afaik, which is very little, you want the area of the combined ports to be exactly half but their length to be exactly the same.

Cross section area of a tube is 3.14 x (diameter squared) / 4
Area of shelf port is width x height.

Have at it.

[projectMalamute]

Originally Posted by Downunderwonder

afaik, which is very little, you want the area of the combined ports to be exactly half but their length to be exactly the same.

Cross section area of a tube is 3.14 x (diameter squared) / 4
Area of shelf port is width x height.

Have at it.

Using the calculator I found here:

Port Length Calculator

I am not getting this result. If I keep frequency the same and change internal volume and port diameters as you describe the port length changes.

[Munjibunga]

Originally Posted by projectMalamute

I want to take 4 speakers out of an SWR 8x8 and build a 4x8.

... I am medically unable to use anything other than this setup.

Let's see if I understand this. You are medically unable to use any speaker configuration other than a 4X8 vertically arranged?

[atrapp]

Originally Posted by Munjibunga

Let's see if I understand this. You are medically unable to use any speaker configuration other than a 4X8 vertically arranged?

nah, I think he meant he's medically unable .

[1n3]

Originally Posted by projectMalamute

The 8x8 has 3 tubes, say of length x and diameter y.

It would be more helpful to state the actual numbers. But let's assume for example that your ports have an internal diameter of 2.5". The length doesn't matter, since you want to leave that unchanged.

The radius is 1.25", so area (pi x R²) = 4.91 square inches. Since you have three ports, total area is 14.73 SI. Half of that (your new port area) is 7.36 SI.

To find the diameter with area = 7.36 SI, divide by pi, take the square root, then multiply by 2. (answer: 3.06")

If you want to use two tubes, you find the diameter with area = 7.36/2. (answer: 2.16")

This method should get you close, but your online calculator won't agree with these numbers. Why? I don't know, but my guess is, the program is taking port friction into account. Due to friction/turbulence, narrow ports tend to act longer than they are. I don't know how good this calculator is; perhaps someone else will.

To be really exact, you'd probably need to measure the tuning of your 8x8 cab, then measure the tuning of the 4x8 cab, adjusting port length to match.

[Downunderwonder]

Originally Posted by projectMalamute

Using the calculator I found here:

Port Length Calculator

I am not getting this result. If I keep frequency the same and change internal volume and port diameters as you describe the port length changes.

I plugged in a few numbers, halved the numer of ports and box volume and it spat out an identical port length every time. But changing numbers and diameters to match upsets length. Seems the port size does factor in so it's going to be a school day for me too!

[Peg_legs]

a one month later bump.. I'm quite interested in your project. I have been wanting to build a line array of 8s too.

For port sizes, you need the original volume of the SWR enclosure and ports and reverse calculate what the box is tuned to. My guess is 38hz since the adds for the cabinet state a roll off at that point. Take that tuning goal (hz) and plug it into your port calculator for the new box volume. Don't bother with any other method. I would try several diameters of ports too.
I use this calculator for port math:
Subwoofer Enclosure Calculators, Fraction to Decimal, Parallel, Series, Port Length and Volume Calculators

[sowegafly]

yes... please let us know how this turns out!!