Chorus II - crossover, diaphragms, passive subs and more

[mikieboyblue]

Hahaha....thanks guys! Some of you have convinced me to forgo my receiver upgrade so I'll pick up the prs. Although cutting ports would be cheaper, it will be nice to see...err...hear how these things are when fully together.

[STL]

PRs are superior in that they don't have vent colorations or wind noise (but those can be eliminated when using properly sized ports and/or through the use of flared ports) and they are better in small enclosures where it is simply not possible to fit a properly sized port (because the port length would be too long). They negatives about PRs is that they have a steeper cutoff, less transient stability, usually a slightly higher cut-off frequency, and greater overall losses compared to ports. As long as I could determine the tuned frequency of the PR, then I guarantee that I could design a port replacement that would sound indifferentiable to 99% (or more) of the people here.

[mikieboyblue]

PRs are superior in that they don't have vent colorations or wind noise (but those can be eliminated when using properly sized ports and/or through the use of flared ports) and they are better in small enclosures where it is simply not possible to fit a properly sized port (because the port length would be too long). They negatives about PRs is that they have a steeper cutoff, less transient stability, usually a slightly higher cut-off frequency, and greater overall losses compared to ports. As long as I could determine the tuned frequency of the PR, then I guarantee that I could design a port replacement that would sound indifferentiable to 99% (or more) of the people here.

So then why use a PR? And I have no clue where to find any specs.

[STL]

I'm a but puzzled why Kilpsch went from ports in the original Chorus to a PRs in the Chorus II, when in the KG series they went from PRs (in the .2 models) to ports (in the next generation .5 models). I do see the Chorus II came out in 1990 and the KG-x.5 series came out in 1994 -- so maybe by the mid-90s Klipsch decided PRs weren't needed anymore. I don't believe any current models use PRs so that may (or may not) confirm that thinking.

Looking at exterior dimensions of the Chorus II, there looks to be is plenty of room to place a 4" port on the back and unless the tuning frequency is quite a bit less 40hz there shouldn't be a problem with the depth of the port. You could measure fron the back of the woofer to back of the cabinet (or where that would be if it wasn't open) and let me know that value.

As far as specs, I really only need the inside dimensions of the enclosure along with the tuning frequency of the PR. You should be able to give me the dimensions, but you'd have to ask around on the forum to get the tuning frequency of the PR (like maybe from one of the Klipsch moderators -- since they speakers are no longer in production sometimes they'll give out some of the specs). I guess I could determine what the original Chorus speakers were ported to and use that frequency too.

[crawbeaird1]

Hello STL, I was wondering why some speaker makers' ports are in the rear of their cabinet? Is there a diff , front or back? Cornwalls (front) Chorus's,Quartets, Forte's (rear).

by the way, how much Xmax does a HED CV 15" have? Thinking of making a pair of CV(corn)scalas...

Thanks Jeff... crawbeaird@yahoo.com

[DrWho]

PR's don't necessarily have steeper cutoffs or higher cut-off

frequencies. That is entirely dependant upon the Q the designer chooses

to go with.

I am curious what you mean by losses and transient stability though.

Every engineer I've talked to says PR's have way less losses than ports

(that's why they're lower distortion). I have a feeling the transient

stability you refer to is addressed by ensuring the total displacement

of the PR's is at least double that of the active driver. It kinda

makes sense though because lower frequencies require more displacement.

The same level of displacement is being achieved in the ports, just

that the air is moving further and thus faster (until it can't go

faster anymore).

The only downside to PR's is that they're more expensive and require

more baffle space. Rear PR's limit placement options and aesthetic

trends have been moving towards narrower speakers. Also, I don't think

the KG series was targetting the same price point as the Chorus II.

Wasn't the KLF-30 the replacement? I believe the earlier versions of

the KG line had PR's because Klipsch was actively researching and

developing PR's in the mid 80's early 90's...so naturally that development went into many of their

speakers. I don't know the full history, but I do know that they use

PR's in a lot of their subwoofers.

Properly designed ports do work quite well (which I think is your point

anyway), and it's not difficult to engineer a linear port with higher

tuning points. The advantages are arguably larger with subwoofers

(especially due to the size of the enclosures)...that's probably why

Klipsch is using PR's in all their top of the line subs (except the

Ultra2's that needed to be flushmountable).

Btw, I ran some numbers...you only need two 2" circles cut out of a

3/4" piece of wood. If you want to go with something a little better,

you could go with a single 6" diameter, 6" long port like this:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-401

(I went ahead and measured and the Chorus is a 5 cubic foot internal volume - both ports yield a ~40Hz tuning)

[mikieboyblue]

Ok, so if I am reading all of this correctly (and more understanding it), the only true difference between ports and PRs is the cost factor with ports being far far cheaper (as a piece of MDF is cheap as is the port tube you linked to). If this is the case, still, why ever use a PR? With respect to the Chorus IIs, there must be one that simply works better? If not, Klipsch could have pocketed a few hundred more in profit by using a port and selling at the same price.

[DrWho]

The PR has lower distortion and less power compression.

It also takes up less space too...in many cases, an equal performing port would be longer than the cabinet.

[Erik Mandaville]

Ports can work very well. I've built a number of speakers using them, both on the front and the back of the enclosure. They are also cheap, and can consist of not much more than a length of PVC pipe of the length and I.D. The cabinet shown below is actually a dual-chamber ported design, with ports for both on the front baffle (only one can be seen here). If I'm right up to the cabinet, several inches away, I can hear some very, very light chuffing, but it hasn't been a problem in the least. As mentioned, you can use a flared port, or also something like the one shown, but with the cutout routed ro break the 90 degree angle. I was going to do that, but port noise was not an issue.

[Erik Mandaville]

These two way monitors were built into a rectangular length of chimney flue tile. This went through 3 different designs, including one sealed application. The final was ported, with the port on the back. I can take a rear picture if you'd like to see what it looks like. These sound best pulled out from the wall a little bit, but again, port noise does nothing to interfere with music listening.

[STL]

crawbeaird,

Doing the rear instead of the front might mask out some port noise if any is present, and having the ports rear firing might reinforce the corner loading effect of bass frequencies (depending on speaker placement) but that might also make the bass a just bit more boomy. Rear firing ports could inhibit you from placing the speaker too close up against a wall so that might factor in too. Ive' also seen that you can get some good coupling effects (with the woofer) if you mount ports on the front fairly close to the woofers. All that said, I think most the differences would be subtle.

I don't believe I know the Xmax of the 15" woofer in the HED speaker (I'll have to go dig though my papers), but I do know how well it performs. The speakers were originally built in 1977, and I sent the woofers back to Simi Valley, CA (Cerwin Vega) to have the woofers reconed 1990. The midrage and tweeter horns are still the originals -- but they will be replaced with a K-57-K and either a K-75-K or K-79-K.

[STL]

DrWho,

Yes, I just wanted to make the point that "properly designed ports do work quite well". I just felt like some people -- who likely don't have much of a grasp of the concept of venting -- were steering the thread author away from the porting idea for no good/real reason. Having done this on two separate occasions (and having designed and built many ported enclosures) I knew it could be done with very positive results. I also believe the cost of the replacement PRs is bit crazy, but I do realize it is likely because the PRs are built is such low volume (because of the low demand). Maybe some people are seeing the high cost of the PRs and equating that to mean there is something special about it, but I doubt that's the case.

[STL]

The use of the chimney tile is a really neat idea. How did you attach front and rear baffles to the tile? So was the Qts of the woofer in the grey area (so that's why you tried both sealed and ported desgins)?

[mikieboyblue]

Haha, so, we have two solutions, one cheap and one expensive due to low demand. There is one problem with all of this. I don't really have the tools to cut a 15in MDF disc. Making the port hole isn't an issue because that's just a hole saw. Suggestions on tools? I don't want it look like an idiot did it....

[DrWho]

I do all my circle cuts with a jigsaw...and really taking my time. A plunge router with circle jig would work too, but I can never seem to get the circles to turn out as well as the jigsaw. I'm sure there's a knack to it that just I haven't figured out yet.

[STL]

I now use a non-plunge router (so I have to drill a starter hole) with a circle jig, but I used a jigsaw for years. Just may sure your jigsaw has a new sharp (quality) blade on it and take your time. Of course you'll need something to draw out a perfect circle first, but some string (that doesn't strech -- like some nylon stuff like Home Depot has for free outside for tying up loads) and a pencil should do the trick.

[mikieboyblue]

I'll have to see if I can find someone with a jig saw...because if I have to buy one it would make these just as pricey... I'm young, not many tools yet...not to mention nowhere to put them...If anyone would be interested in fabricating these for me PM me.

[STL]

Yes, it might become more pricey if you have to buy a jigsaw -- but at the end of the day you'll still have that jigsaw for any future endeavors (and they don't take up much space so storing it shouldn't be much of an issue). You might be able to find a millwork shop locally to fabricate them for you. When I made my custom center, sub, and rear speakers, I found a place that only charged me $60 to cut up two complete 97"x49" sheets of MDF -- and we're talking a lot of precision cuts. They even delivered it in that charge. I thought that was money well spent because handling large sheets of MDF is no fun at all.

[STL]

Here is a nice jigsaw that's less the half the cost of the PRs:

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?jspStoreDir=hdus&catalogId=10053&productId=100007442

In fact it's nicer than what I have, and the one I'd probably get if I didn't already have one. Keep in mind HD/Lowes will do a few (straight) rough cuts for free when you buy a sheet of MDF; that might make it easier to get home and to handle once it's there.

[mikieboyblue]

Does the position of a port matter?