Ports on KLF-30's

[dragonfyr]

Folks, I can appreciate all of your concern about many concerns...

But may I suggest that doing things by 'looks' and 'feelings' is not the best way to do it!!

If you are going to do anything other then simply relocate an identical port (the location of which generally should not matter), then much more is needed to 'do it right'. And you cannot generally simply build clones with different drivers and leave the enclosure & tuning the same - driver diameter is not a determining criteria...thus a better tool is needed...

If you do not wish to go the 'bigger' route and use LEAP, a rather simple answer is to get a copy of WinSpeakers, John Murphy's excellent speaker design software. This along with the measured (preferable) or the manufacturer provided Thiel Small parameters will allow you to look at all sorts of 'what if' scenarios and options. It is also a wonderful learning/tutorial product as well.

It is well worthwhile if you wish to design or modify a pair of speakers, and will pay for itself with the first pair! Good luck!

And BTW, if my defective memory serves me..., DiAppolito's MTM topology was intended to correct for an off axis polar tilt when using a 3rd order LR crossover, otherwise there are better topologies for close coupling drivers.

[STL]

On 8/16/2005 10:50:01 AM dragonfyr wrote:

If you are going to do anything other then simply relocate an identical port (the location of which

generally

should not matter), then much more is needed to 'do it right'.

I agree with one cavet. If one wants to use all the "stock" speakers but go to a smaller vented enclosure (from a larger vented one), this can be accomplised without needing any drivers specs. I've done this a couple times myself with good results. What I first do is determine the venting frequency of the stock enclsure. This can be do without woofer specs because the venting frequency is simply a function of the enclosure's internal volume, its port size, and its port length. I then design my new smaller enclosure so that it is vented to the same frequency as the stock enclosure. Be aware that there are limits and compromises re-sizing though. Smaller enclosures require:

1) longer ports if the using the same port diameter as stock, OR

2) smaller port diameters to keep the port length from getting too long.

Option #1 is sometimes impossible because it is often hard to put a longer port in a smaller enclosure. Option #2 can be a compromise because smaller ports are somewhat less effecient and going too small can induce port noise.

BTW, Unibox is a very useful and powerful program that is free. It's really just a macro that runs in Excel.

[STL]

On 8/10/2005 8:08:22 PM redtop wrote:

There are two circular ports (side by side)that taper as they extend into the speaker cabinet. On the cabinet surface they are 3 3/4" in diameter and taper down to 2 1/2". The port extends 2 1/2" into the cabinet.

Were you wanting me to come up with a new port setup for you or anything? If so, you need to tell me the internal dimensions of a KLF-30. Since it's known the the enclosure uses 3/4" MDF you can derive the measurements by measuring the outside -- but be sure to take into account the front baffle is recessed some. Since the KLF-30 already has two ports, I don't think you need to do anything special beyond moving them to the front baffle (and sealing the old holes).

[dragonfyr]

I would agree with STL above. Generally speaking, if no other changes are being made and there is nothing 'special' with the internal topology, you should be just fine moving the port(s) to the front baffle.

[redtop]

Thanks for the calc offer STL. I'll take some exact measurements tonight and let you know. I just hope this is not a lot of work for very little benefit...

[STL]

redtop,

So exactly what are you wanting to do...go with a smaller enclosure? Or go with four smaller ports (instead of the two stock ones)? Or what?

[HornEd]

Redtop... it's good to see so many Klipschers getting into the horizontal act.

KLF-30 woofers need to have their port area free to work properly. They are tuned ports and fire rearward to get the benefit of the wall for dispersion.

In my 30' yurt theater, the modified KLF-30's in the three rear positions have the motorboards with the woofers out as far as they will go... as in the first picture on this thread. The ports were not moved and have reflectors that shape the port exhaust toward the audience. This method preserved the best timbre match aspect with a non-modified KLF-30.

The Front Center KLF-30 has the two woofers as close to the mid-range and tweeter stack... as in the second picture. I do this because the front three speakers are closer together than the rear array speakers. Thus, the center speaker tends to remain in the center of your sound stage. Of course, since 80% or so of the sound comes from the front center... getting that speaker right is more important than any other in home theaters!

By placing the woofers as wide apart as possible in the cabinet, the rear array has a much wider angle of dispersion... and that relates to having more of your room in the "sweet spot."

Well, I must dash... I hope to read all of the entries on this thread at a later time. -HornEd

[redtop]

STL,

What I am considering, is moving the ports to the front so that I have more positioning options in my new HT. I am building a screen wall that is 28" into the 15' x 26' x 9' room from the front wall. With the KLF-30 being 16" deep I am concerned that the ports do not have enough room to breathe if left on the rear of the cabinet. It seems my two best option for positioning are above the screen (angled down) or behind an acoustically transparent screen.

If I do another mod, I would leave the cabinet unchanged except for taking out and changing the motorboard and plugging the rear port cutouts if I moved the ports to the front. Hope that makes my intentions clearer.

HornEd,

Thanks for joining this discussion. Any pics or diagrams of your rear port reflectors? I am all for not re-doing the motorboard, if I can accomplish the above goals with adding a component.

[STL]

redtop,

So you're saying you're going to have about 12" from the back your your KLF-30 to wall? If so, that is more than enough. Like I said in an earlier post, the rule oh thumb is to have at least the distance that equates to twice (exit) diameter of the port (but it's sometimes possible to get away with up to half that). With you're setup your distance is over three times the diameter of the port -- so you're fine!

[HornEd]

Redtop, I agree with STL, if you have 9" between the back of the '30 and a solid wall, keep some vent space around the cabinet... and you will have it made.

The reason I use port deflectors on my '30's is because I use porous walls to allow low end waves to pass through walls rather than rebounding into standing waves. Since you have solid walls, port deflectors are not necessary.

Venting the ports to the front will take away some of the slam inherent in the 30's. Enjoy! -HornEd

[redtop]

Thanks STL and HornEd. The wall behind the center is a double 1/2" drywall with Green Glue between the two layers, so that should be solid enough... I just wanted to be sure that I didn't do something to inhibit the performance of the speaker once I had gone to the trouble of HornEd-ing the thing. For some reason I just can't visualize the concept of what a port does and how it's position on a cabinet affects the speaker's performance.

Thanks to all who contributed to this thread.