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jason str

Anyone successfully slot port Lascala ?

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I would use some polyester batting and not fiberglass. Not sure just how much, maybe our friend from down under can put in a few words.

I asked Dennis about the slot port before, and he sent this to me:

The vented LaScala as I described runs to about 4.8 cu ft net. Two 4" ID by 7.25" long ports gives an Fb=35hz.

A 15" by 1" port would need to be about 5" long for a 35hz Fb.

A 13" by 2" port would need to be about 8-7/8" long for a 35hz Fb.

A 15" by 2" port would need to be about 10-5/8" long for a 35hz Fb

It helps to have a good software port model, the long narrow aspect ratio requires a different length than the same area in a square or round port. It also helps to start out a bit long, and trim it shorter to reach your target Fb.

I just think the slots look better tahn the round ports.

Bruce

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I too like the slots look nicer than the round ports. I am confused by the measurements he gave concerning the slot dimensions. What, exactly, is the construction of the rectangular port. Apparently it is not just a rectangular cutout in the front. When you say a 13" x 2" port, what are those dimensions referring to? Sorry to be so thick.

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Rudy,

"Does that box need fiberglass or anything in it? I notice you said ...light stuffing. Could you be more specific for us novices? "

I used polyester wadding...about 50mm thick...to line the box. I just used a single layer & stapled it to all surfaces slightly loosely...it should just remove any standing waves. I haven't lined the dog house as yet, but am going to do that with the same material & try that. If you used polyester house insulation that would be OK.

"I saw pictures of this mod with Cornwall 'like' rectangular ports. Any advantages or disadvantages of this type of port?"

The type of port won't affect the sound....it is simply loading the driver & enclosure to a particular frequency. I came across the design with the round ports & went with that...when you paint the insides black they are less obtrusive. but yes, the rectangular ports look cool...don't know what the dimensions of that would be to achieve low 30Hz.

Hope this helps,

John

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"When you say a 13" x 2" port, what are those dimensions referring to?"

If this is what the spec calls for, it would mean that the port is 13 inches wide & 2 inches high.

And from what Dennis says if you make it 8 7/8 inch deep it will tune the system to 35HZ

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"When you say a 13" x 2" port, what are those dimensions referring to?"

If this is what the spec calls for, it would mean that the port is 13 inches wide & 2 inches high.

And from what Dennis says if you make it 8 7/8 inch deep it will tune the system to 35HZ

post-7149-13819500119408_thumb.gif

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Thanks gents. I will take a look at my cornwalls and see which is the easiest way to go.

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Just a thought....

I know you like the look of the slot better, but one of the main reasons I used the round ports was it was much simpler to build.

I used 4 inch plastic downpipe which is available from any hardware store & then simply cut it to length & glued & siliconed it into holes cut in the baffle.

Good luck,

John

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Just a thought....

I know you like the look of the slot better, but one of the main reasons I used the round ports was it was much simpler to build.

I used 4 inch plastic downpipe which is available from any hardware store & then simply cut it to length & glued & siliconed it into holes cut in the baffle.

Good luck,

John

John: Thank you and the others for all your assistance. I decided to go with the rectangular port for two reasons. One, I like the look a little more. Two, in my case it was about $50 cheaper to build that way since I didn't need to buy a 4 1/2" hole saw. Those things are very expensive around here.

Anyway, I have just finished the build. Going to get something to eat and then I will try it out. I plan on taking some ETF readings with and without the mods. Pictures to follow.

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Ok, the results are in. I just need to paint the box and I'll be done with this mod. I took a set of measurements from my sitting position of the speaker's performance from 20hz to 500hz. I am attaching the graph with the results. The green line is the original lascala at the same height and position as the ported modification will produce. The red line is the LaS with the bottom removed and sitting on the ported enclosure. I have not had time to compare my results with the supposed improvements, so feel free to point out any issues.

I only have a single LaS since it is my center channel for my HT. With music, the mod sounded good and I did not notice any problems. However, since I don't normally listen to mono music, it is difficult for me to give a true opinion of how it sounds. For me it is a win-win situation since I get to raise the mid section and tweeter closer to the surrounding Khorns and I may have an improvement.

LaS Port results

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Rudy,

Those measurements look interesting & confirm what I hear on my set up. Bass is much stronger from 60Hz down. I found I had to attenuate the mids on my ALK though as I lost a bit of efficiency in the bottom end with the bass reflex set up. Just went back 2 more notches.....perfect balance now.

By the way....what bass driver are you running in your cab?

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John: I have the standard K33 in the bass bin. I use the ALK Universal and the Crites tweeter in all my main (front) speakers. I am waiting on a third Trachorn for my LaS....I received two for my Khorns but am waiting for a third from Al.

Remember, those results I plotted contain the room boundary 'effects' for my room. So, it is not a direct measurement of the speaker itself. I do, however, have a fairly flat room except for the 150-200hz region, which has a little bit of a boost at listening position. The nice thing is that I also use Audessey in my pre/pro to flatten any room aberrations. These graphs DO NOT have audyssey or any other processing working. I listened to Billy Cobham's "Warning" to test the results and like what I heard. Again, listening to a single speaker and making a judgement is difficult. That is why I am glad to be able to measure the results. I ran the measurements three times for each setup and they were all identical.

I am waiting to get the Trachorn and the JBL 2470's I want to put in there before I spend time messing with the mid range taps. Audessey, however will compensate for any frequency mismatch.

Tomorrow I hope to post a picture of the finished product.

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I have not done it. I have wondered how the various parameters for box volume and port tuning are chosen by those who have.

It seems to me that people are considering the project as an LS with a supplemental box in back and port.

Another way of considering the project could be as follows: Let's build a Cornwall as far as box volume and port dimensions. These are described someplace or other on the forum. Then we are gong to add an LS horn in front of the pseudo Cornwall.

In the case of any port loaded box, it is necessary to get the port-box to resonate fairly close to the diaphragm resonance. Sometimes exactly the same in one of the Butterworth alignments. Then we see the characteristic effect in the electrical impedance. It is a dip at diaphragm resonance with symetrical peaks on either side.

Wm McD

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I used one of the port sizes recommended here. I have no knowledge on how to calculate the port sizes, so I depended on the recommendations of others. I presume these are ok, since the results seem to be an improvement. This size I chose was: A 15" by 2" port would need to be about 10-5/8" long for a 35hz Fb

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I presume these are ok...

Dennis' ideas are usually pretty right on. Since he came up with the bass mod, I don't think you can go wrong.

With the round ports, he originally had them at 10 inches. Most shortened them to 7-7.5 inches, producing a little tighter and quicker bass, retaining more of the horn sound.

Bruce

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Curious for your opinion on the ALK Trachorn fitted with the stock driver. Do you like the change? I too have the ALK Universals & the Crites tweeters. The ALK's made a huge difference to the sound IMO...much better.

I think my pair are coming along with yours....although I ordered them way back in July...I'm beginning to wonder if they'll ever turn up.

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Curious for your opinion on the ALK Trachorn fitted with the stock driver. Do you like the change? I too have the ALK Universals & the Crites tweeters. The ALK's made a huge difference to the sound IMO...much better.

I think my pair are coming along with yours....although I ordered them way back in July...I'm beginning to wonder if they'll ever turn up.

I have made many changes to my system and my room environment over the years. My impressions are that the biggest improvement came from the ALK crossovers and then the room treatments I made. The next changes were differences in incremental 'quality' of sound. I like the eminence tweeter much more than the K77. It is more refined. The Trachorn is along the same lines...much more refined than the K400. The fit and finish for my Khorns was very nice and a breeze to install. Adding the K55 adaptors is easy and they screw right on.

The Trachorn smoothes out the sound and kicks thing up a notch. I know many have said that the Trachorn was the biggest change they made. Perhpas I am not as sensitive to the K400 aberrations as others. However, I did do a sort of A/B with the Khorn and the Trachorns and my stock La Scala with the K55 and K400. That is when I really noticed the difference. The K400 sounds like the music or vocals are coming from a 'tunnel'. The Trachorn I feel is much cleaner and does not color the sound. I would certainly not go back. I am looking forward to adding the Trachorn to my La Scala, but am dreading taking a saw to that cabinet.

Today I should finish my attempt at the bass bin mod and hope to have some pictures to post.

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My son was good enough to take a few pictures of the finished product. I know, it is not 'perfect', but in all black it is good enough for my needs.

post-10337-13819500155598_thumb.jpg

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