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4JaxJags

Chorus 1 Port mods / bracing / & TESTING

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Since joining this great site, I've been searching/reading/researching all of the info on here I could find on modifying the ports for better bass response in my mint condition oiled oak Chorus 1's. 

 

I purchased the Chorus 1's to replace my black La Scalas that were really too big for my listening room & looked like 80's concert speakers. I know some here prefer the Chorus ll, for the mid horn & bass, but for my "music room" I wanted a front firing speaker w/o a rear passive. (so I chose Chorus 1's on  purpose) Since the previous owner had already upgraded them with titanium tweeter diaphragms & re-capped the crossovers using Bob Crites stuff, I figured that if I tweaked the low bass response a little, these would be a pair of speakers I would keep forever (& also improve the WAF of my listening room)

 

I got finished this past weekend & figured it was my turn to "pay it forward" & share the results in a build thread so others can easily duplicate the project if so desired (including pix/part #'s/relevant info) I also decided since I was "going in" the cabinets, I might as well try some of Morey James bracing ideas I read up on too. 

 

To make the post modification info more objective (hopefully) & less of my "opinion" I purchased a CD online that had digital test tones for all of the mid & low bass frequencies. I tested them pre & post mods & was quite happy with the results (testing info coming up after a few pix 😎)

 

Dave

 

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This is the cardboard shipping "tube" I used. I searched forever to find one that was a precise (semi-precise😁) fit. I also had to trim it to fit with my chop saw (fine toothed blade) because of the flare I used on the end. I tried to keep the overall length including the "usable portion" of the flare to about 7" overall.

 

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Edited by 4JaxJags
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This is a closeup of the part I used. I bought it at "Michaels" a big chain craft store we have here in Florida. You may find it elsewhere, but I tried other mailing tubes, carpet roll inserts, etc. for weeks on end and NONE fit like I wanted except this one.

 

https://www.michaels.com/shipping-tube-by-celebrate-it-3.9x6.2/M10323357.html     <-- LINK to shipping tube that fit

 

I did have to wind between 1-3 layers of electrical tape on the end of each tube to make it fit tight (& each one was different/unique in the amount it took)

 

 

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Edited by 4JaxJags
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This is the flare I used. It might be a little overkill (? unnecessary) but I wanted to make sure I didn't get any port noise/chuffing sounds afterwards

 

https://www.parts-express.com/precision-port-psp-4ofh-4-outside-flare-for-port-tube--268-376    <-- LINK to parts express 4"  flare

 

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Edited by 4JaxJags
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After I cut the cardboard, I had to figure out a way to join the flare to the tube (btw, they are EXACTLY the same size diameter)

I used blue painters tape on the inside (temporary measure, removed later) and then TWO coats around the outside seam of this flexible black adhesive called "E-6000" that I bought at Ace Hardware. 

 

After both of the 2 adhesive coats dried, I wrapped the seam with two layers of electrical tape to give it more strength.

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You can see the electrical taped seam in this pic, & I'm test fitting the ports to each opening. After experimenting on a scrap of the tube I previously cut off , I decided the best way to get them TIGHT (pressed in fit) was this:

 

1.  Place tube in one at a time from the inside

2.  leave an extra 3-4 inches of port sticking out through the hole

3.  wrap as much electrical tape as needed on each one individually (some took 1 wrap, others took up to three complete wraps)

4.  wiggle & gently press it back in from the OUTSIDE to get a final "flush" fit & have it as tight fitting as possible

 

In This pic the ports were almost done but I did do two more things, one of which is hard to see.

 

a.  I glued a small piece of foam underneath each tube about 3/4 of the way to the flare for additional support. They were so tight fitting, it probably wasn't needed, but I figured it couldn't hurt...

b.  wrapped the seam one more time, this time with silver "metal foil" tape that is designed for use on A/C ducts. I plan on CRANKING these babies & I don't want the seam between the paper tube & plastic flare to ever fail (& it did add some extra stiffening I think). You can see the silver foil tape in a pic of the braces coming up later

 

 

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Ports are now fully installed, in their final positions. The bracing work is in progress.

 

I glued oak 1x1's  (purchased at home depot) on the front & rear walls & also 1x1's as front to rear braces. I test fit the ports prior to gluing the braces to make sure I could remove the ports if I ever need to/want to (hopefully not, but ya never know what cranking up the volume may do some day...)

 

There is also a 2' x 3/4" oak strip connecting the walls side to side as seen in this pic. The lower bracing is installed just barely below the woofer opening on the front wall. 

20190706_104512_resized_1[204].jpg

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Better view of the lower bracing (Thanks Morey for the Quartet bracing pics I used for ideas !)

 

I was able to use small wood clamps (& titebond lll wood glue) on most places, but I did have to use two small 5lb dumbells on the cleats beneath the side to side brace in this pic. Flipping a Chorus speaker top to bottom numerous times for brace work is like going to the gym... 😁

 

You can also barely see a small roll of "polyfill" I put up front, right beneath the the two paper tubes side to side. You can also see the silver "metal foil" A/C duct tape I used as the final layer to strengthen the seam between the plastic flare & the cardboard port

 

20190706_103327_resized_1[207].jpg

Edited by 4JaxJags
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One more view of the lower bracing & ports...

Time to work on the upper part next

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The upper bracing starts right above the opening of the woofer. (side to side oak 1"x1"). This is probably the weakest section of the entire speaker, because it's where the motorboard is thinnest, between the woofer opening & the mid-horn opening. Most of the bracing is 1"x1", with one piece of 2" x 3/4" & 2 cleats used in the middle as a side to side brace (same as I used on the bottom section)

 

I also used construction adhesive to glue on 3 sheets of sound deadening egg crate foam. One sheet is on the inner "roof" of the speaker and one one each upper side wall. These were 2" thick 1 foot squares I bought on Amazon. (In case you're wondering, no insulation was inside the cabinet originally)

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Here's one cool thing that was inside each speaker. A paper "buildsheet" from Hope 😍 showing the P.R.I.D.E. in their work !

Anyone know any of the names/initials listed on here? (HDR Builder ?)

 

When I reinstalled the woofer, I rotated it 180 degrees then used this gasket tape from parts express to reinstall it. (the factory gasket was THIN plastic & crushed down to about the thickness of two post-it notes...

https://www.parts-express.com/parts-express-speaker-gasketing-tape-1-8-x-1-2-x-50-ft-roll--260-542   <-- LINK to speaker gasket tape

 

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Edited by 4JaxJags
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OK, I know I promised "testing" & I would try to keep it as "Objective" as possible. 

 

Here's how I tried to do the best I could w/o measuring it like an engineer would 😁 I ordered this CD (picture below) online that has Digital test tones of all the mid & low bass frequencies. I played it a few different times both before I started any mods, and again a few different times after all the mods were completed.

 

PRE- RESULTS:

I could hear a noticeable dropoff in volume & sound "fullness" around the 45 Hz test tone prior to my modifications

 

POST-RESULTS:

After the ports/bracing/insulation was installed, I can now play a 40 to maybe 39 Hz test tone without any dropoff. They will play lower tones as well, but I can hear a progressive decrease in volume as it gets lower (volume is at a consistant level 39-40 Hz and above)

 

In addition (this is subjective/my opinion...) I think the bass is tighter & generally just sounds better than before. I am glad I did all the work, & EXTREMELY happy with the 5-6 Hz I gained on the lower end !!!  NO REGRETS 😎        (But if you just want to keep it simple, & don't have a chop saw, just put the ports in...)

 

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Dave

Edited by 4JaxJags
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My dedicated music listening room (& a TV for my kids that doesn't run through the speakers)

 

I vibrated about 1/2 of the CD's out of those wall racks above the left speaker by playing Dire Straits "six blade knife" at who knows how many decibels 😎 These Chorus 1's will THUMP & I don't miss my La Scala's AT ALL (*hard to believe....I know...but It's true....😁)

 

https://f072605def1c9a5ef179-a0bc3fbf1884fc0965506ae2b946e1cd.ssl.cf2.rackcdn.com/product-specsheets/Chorus-brochure.pdf

(this LINK is to the factory Chorus 1 specsheet / brochure) Enjoy 

 

 

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Edited by 4JaxJags
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Well I could not sleep until I read your results... no not shabby at all. More to say later yet, when getting some bass extension with volume, and your results of your ongoing(?)

tests, I think your method is somewhat close to maybe spot on. Sounds like worth the doing, and the bracing as well...one thing you can say is the K-48-K is no slouch.Wish I had done the ports at the least... enjoyed your review and testing of the mods.

Thanks...

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Nice job on the project.  Nothing wrong with having a specific goal that may not conform with others general thoughts at all.  I did a rear ported cornscala because it fit my needs and room. 

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4 hours ago, billybob said:

one thing you can say is the K-48-K is no slouch.

Thanks...

 

I'll second that opinion ! 

 

I know many here say the Chorus does best with high power, My big Yamaha amp is getting recapped so I'm currently pushing mine with @ "measly" 85 watt Luxman R-115. I can't get it up much past 1/4 volume & things start falling off shelves 😁

 

I can literally feel my chest cavity start to vibrate with the K-48 woofer movement too. (If needed, I think I could do "self-CPR" if I turned the Luxman 1/2 way !

 

 

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This was an interesting project. I congratulate you for doing the before and after comparisons. 

A couple of points or questions. Was the modification of the port just the adding the flare or was it lengthening the port also (lengthening the port will, of course, lower the tuning of the cabinet).

 

Second, another trick for lowering the tuning is to make the cabinet larger. That is not practical but you can mimic a larger cabinet volume by lining the interior with an inch or so of pressed fiberglas. Was that the idea behind the egg crate foam. I bring the point up since not all egg crate foam is the same. I assume this was the correct stuff?

 

You might also try moving the cabinets around a bit sometimes a half foot will alter the effects of one of the room modes. Sometimes the effect can be surprisingly large. A bit of experimentation is useful. 

 

Great project and thanks for sharing.

-Tom

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I worked on a pair of Chorus I with @Matthews a few years ago. He too added the port extensions.

I'll look up that thread, having just worked on a set, you would find parts of it interesting.

Photo of his ports:

port.jpg.184337885f086d9e32e20ec2e5e4f5d9.jpg

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