Question on Port placement ...Again!

[Rotorhead09]

JC

Yes, i stuck with the 4" ports (dia & 7" long) and they are flaired on both ends. I was telling Marvel in a early email that I notice a change in the way it sounded after I got them home. I think a lot of it had to do with the size and position that i have them in at my house.

The back panel where the ports are mounted is removable so I can go in and adjust my ports to my likings. Still playing with the ports.

There is more bass (deeper) coming from the ported ones than the factory ones. But I don't think the bass is as solid coming out of my speakers. I believe for the deeper bass one must give up on the solid bump! that's just my opion, Maybe some of the experts can chime in and explain. But over all I am satisfied with the project. Also, seems that at lower volume the bass really does not kick in.

Santa

[DrWho]

Have you tried the BEC woofers in your stock lascalas? They are not

identical drivers and will behave differently - especially when

hornloaded. I'd give the K-33's a try and see how it sounds.

I need to get off my butt and do some modelling of the lascala bass bin

with the K-33 driver and then make some comparisons with other off the

shelf drivers...

Also, the ported lascala mod works best when you have a peaking 2nd

order highpass filter...what it does is it takes advantage of the lack

of cone movement around the tuning point of the system and gives you

free SPL at the cost of a few extra watts (which is why the K-48? or

watever the pro woofer used in the lascalas is recommended for the

mod....higher power handling).

[Marvel]

DrWgo,

This has really about been done to death (I'll be building boxes to go unerneath my LS is the near future), but the following was from a post of Dennis' in Sept. '04.

The vented LaScala is a concept.

Execution is determined by what you have or are willing to build/buy.

The Industrial version of the LaScala comes with a woofer with a huge magnet (K43) and already has the top section closed off in back.

I replaced the existing back with another that had two ports, one on either side of the midrange driver magnet assembley.

The rear volume behind the woofer was opened up into the top volume by using a plunge router with a guide bearing.

The net volume was found to be correct for 6th order tuning for the K43 woofer (B6) or quasi 6th order tuning (C6) for the K33 woofer (in the stock LaScala). Vents are typically two 4" diameter by 7"~10" long. Longer is tuned lower, in general the larger magnet woofer can handle the lower tuning.

Boost is applied ahead of the amplifier and is usually Q=2 at Fb.

Fb is sort of experimental with the smaller magnet woofer liking the shorter ports.

Part of this has to do with room modes. The small sized bass horn does nothing below about 100hz, but floor to ceiling gives us boost in the 70hz~75hz region (7-1/2'~8'), and wall to wall (short wall) in the 47hz~51hz region (11'~12'). An Fb around 31hz~35hz seems to work best with these room sizes and speakers. If you have an actual wall for the third wall (most newer homes don't, they have a large opening into a 'dining' area) and it is around 16'~20', you may have to lower the Q of the boost. It should be pointed out that most recordings are rolled off in this area and a little extra boost is nice.

The same basic idea may be used with JBL or other drivers as long as the parameters are close. An Fs in the 30hz region, a Vas in the 10 cu ft region, with a Qts around 0.3 is what we are looking for.

The JBL 2205/K140 is good but the Qts is a bit low. You can try adding a series resistor in the 1 ohm to 2 ohm range to bring up the Q.

[DrWho]

Here's the active filter schenamatic Dennis sent me a couple months ago:

(just use the LF part of the filter...you don't need the whole thing)

[Marvel]

Gathering his notes, it becomes clearer that for the K-33 you would use the shorter ports and longer for the K-43. Personally, I would even be happy with them going solid down to 40Hz. My JBLs are rated to 45Hz, and are nice and deep. If you could keep the quickness and punch of the horn and still be solid to 40 -- what a great day.

I have a copy of the filter as well, but thanks for posting it again.

[jwc]

I've seen that diagram before too. I typically feel pretty comfortable reading filter schematics but I will easily admit that I don't understand that one.

jc

[Rotorhead09]

Guys,

That was some great info But, way over my head.

Doc, I was wondering if the woofer that I am using was not hitting as solid as the K33. I got the woofer from Bob C. and he stated that this woofer would go much lower than the K33. You present a good ideal about changing woofers and giving that a try. Will Klipsch sell me one? $$$? Just returned the factory LS to the owner...

Santa

[jwc]

Roto. Bob sells the K33 also. $129/woofer. I have purchased 6 from him. I also have the CW1526 like yours.

jc

[Rotorhead09]

JC,

So what is your opion on either one of them? Have you compared the two?

I was just told the the CW 1526 went deep and was close to the same as the K33. I don't care about the cost difference. I want preformance and quality sound. If the K33's sound better I will be changing them out.

[jwc]

roto,

That would be hard for me to do. I didn't do an apples to apples comparison. I would have to put the CW1526 in the Cornscalas of mine and do some RTA between the two.

My intent with the CW1526 was for a DIY cabinet design instead of the K33 used in a copied Cornwall or Lascala bass bin.

I will say thet the CW1526 sounds fine for what I did in a larger, ported cabinet tuned lower that a K33 in a Cornwall cabinet. There is much more lowend not typical of a heritage style speaker. This would be more of a Forte or KG sound for a crude analogy.

I would have to agree with the above posts. You may find different results with putting the K33 in the scalas ported.

jc

[DrWho]

Assuming the horn didn't make a big difference between the drivers, the

design theory would dictate that a larger volume would be needed behind

the CW1526 woofer and a lower tuning point too. Tuning too high with

too small of a volume introduces a bump in the response (prob around

80Hz) and also introduces a steeper rolloff (prob around 60Hz). I've

not modelled the CW1526 so I'm just making up these numbers (you mind

emailing the driver file, jw?)

[jwc]

I can do that.

Will have to wait until i'm off work.

[BEC]

The CW1526 is meant to duplicate the performance of the pre-1985 K-33E. The K-33E was changed that year from a square magnet model to the current round magnet model. More important than the change in magnet shape was the the FS moved up from 26 hz to 34 hz in the "new style" K-33E. This change came about at the same time that the Cornwall I dropped from the line-up. The Cornwall II got a new woofer at that time, the K-34E.

Now this is guessing to some extent, but I think the new style K-33E was not considered to be right for the ported box Cornwall after the change.

To confuse me further, though, the new 2006 Cornwall will again share the K-33E with the rest of the Heritage line. Perhaps that is the reason for the driver relocation and porting differences in the new Cornwall III.

Bob Crites