"plugging" the port on RF-3's

[tpg]

Well, I have not gotten around to trying this yet, but I was wondering if maybe anyone else had tried it. Since the speakers don't need to play low (because of the sub crossover) maybe sealing the box up would improve clarity? I've always been a fan of sealed boxes over ported. Has anyone tried this? Any noticeable results?

[marksdad]

i havent exactly sealed the ports, but i did have in my sons room a set of rf 3's placed directly against a wall, this was because of room requirements, and to be honest they sounded like hell, once i moved them away from the wall they just opened up, i imagine where a speaker is designed to develope part of thier sound through ports it is best to not block or seal them

[Frzninvt]

The port would not be there if Klipsch felt they did not need it. The ports are there for a reason! They determine the speakers tuning frequency and need to be kept free from restriction for the speakers to perform the way they were designed to. You can try sealing them but you are changing the tuning of the speaker and quite possibly not for the better.

[DrWho]

Plugging the port would raise the resonant frequency of the box (I think they call it Fs). This would then in turn reduce the low frequency output of the RF-3 and then create a hump in the midbase. I would guess the hump would be around 100-300Hz which would now be in the audible range of your speaker. Nevertheless, there's really no harm in trying.

[D-MAN]

Theoretically, you would be increasing the intermodulation distortion by sealing the ports.

This would be the result of uneven cone excursion. The drivers are not selected for that type of operation, which takes a very soft compliance.

It will probably not have the results that you seek.

DM

[tpg]

Wow.. I didn't think it would cause any problems.

I have mainly been designing/building subwoofers... and you can use a woofer in sealed or vented pretty much interchangeably (given that the frequency response graph does change). Sealed boxes in subs generally are cleaner than ported designs, which is where I was basing my thought. I had never thought that sealing a box would increase distortion... If I get some time to try, I might go ahead and do this to see how bad it gets when sealed.

[sivadselim]

my speakers (not klipsch) came with foam bungs for blocking the ports. with my rsw15 to cover the bottom-end, i don't need the extra low-end output afforded by the port. my setup sounds much, much better to me with the ports blocked.

fyi, blocking a port will lower a speaker's extension yet decrease it's low-end output. blocking a port will also, generally, increase a speaker's accuracy.

[D-MAN]

Blocking or Unblocking ports in a given enclosure without changing the internal size of the enclosure will increase IM distortion, aka inter-modulation, frequency modulation disortion.

The enclosure size is quite a bit smaller in a tuned-port enclosure than the optimal size of a sealed enclosure.

That was the whole point of porting in the first place.

Now if you take a ported enclosure, sized for a specific driver and port-tuned, then it is as small of an enclosure that you can get, and by sealing the port, you are just using a too-small enclosure for the driver.

This will raise the low frequency response of the enclosure and driver combination. It will also cause the extenstion of the cone to be more out than in, where there is not enough compressable air to match the front of the cone. It therefore does not extend to the same degree as the frontward movement. This is MODULATION DISTORTION.

You can hear this, it also lowers efficiency as the driver is moving less air in one direction than the other, causing an unequal waveform.

DM

[sivadselim]

http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=418226&highlight=sealed

if i had no sub and/or was running my speakers full-range, instead of as SMALL, i probably would NOT use the bungs. but in my case, they were definitely the way to go.

whether the foam really "seals" the enclosure or not, i'm not certain. i suspect it does allow some air to escape.

i'm definitely not going to even pretend to understand all the theory (in fact, i don't!), but i do know what sounds best to my ears in my room with my particular setup.

whether blocking the port on an rf3 would be "wrong" or not, i have no idea. but it's easy enough to try it.

[D-MAN]

I checked out that thread, seems like lots of generalities and no specifics, here's some specifics:

1) OPTIMUM SIZE of an enclosure for the respective driver

and a specific lc (low frequency cutoff)

this is dependent on whether it is tune-ported or an

infinite baffle design.

2) Infinate baffle enclosures contain more volume than port-tuned enclosures.

3) Port-tuning allows for smaller enclosed air volumes per given enclosure and are more efficient as the reverse motion of the cone is phase inverted to match the front waveform via the port (on the negative stroke, if you will). Phase cancellation(s) at various points of the cycle is the major problem with port-tuned speakers unless timed correctly by accurate placement and length of said port.

4) The trade-off for ported speakers:

positive

reduced enclosure size

better IMD figures at or above fc

lower fc

negative

the port has a peak in response associated the tuned frequency

phase issues

If enclosure size and efficiency was not an issue, I would agree with the generalization that an infinate baffle enclosure gives better overall response, but again that depends on the driver employed and its specifications.

DM

[D-MAN]

See Gil's uploaded pdf post in this section called "Article: Eight Cardinal Points by PWK".

Somewhat fortuitously, PWK discussed this very subject.

DM

[michael hurd]

Assuming the driver is suited for both types, a ported enclosure for a given driver, will be larger in volume than a sealed enclosure, not smaller.

[WMcD]

Hey Mike,

You might want to upload that diagram I sent you. It shows the effect of plugging the port, on electical impedance.

= = = = =

There are some alternative merits to a well designed closed box system and a well designed ported box system. However, each design is optimized by selecting the proper driver with the correct TS parameters and choosing the box size and port.

In no case, to my understanding, can the port be blocked to get optimized closed box performance with the same box and driver.

Unless you've got a lot of data and design programs, I think most people are better off not tweeking in this way. Of course, everyone wants to tinker. It's the way of the tinkerer. Smile.

Gil

[Deang]

There's always "the drinking straws" tweak -- which actually works.