Will porting LS decrease efficiency?

[rjbond3rd]

For a given woofer, porting always goes deeper than sealed. Always. A sealed box with a Q of .5 has tight bass but it's also very light in the bass. Put that woofer in a ported box with a Q of .707 , and it will always be deeper and flatter, then rolls off steeper. Always. A box modelling program will show this. Sealed is simpler, ported is potentially higher performing. It's a trade-off.

I feel that saying that one "heard Klipsch found a suck-out" is not fair. Everything offered against this reversible tweak has been based on speculation.

All ported boxes are undamped / unload below the ported tuning frequency -- always. The flip side is that the speaker is well-damped at the port tuning frequency (xmax is reduced to a minimum). The ingenuity of the mod is in the choice of tuning frequency.

In the end, this is something that should not be debated without actually trying, listening and ideally, measuring. Since it's completely reversible, maybe it's faster to just try it than to debate it []

[DrWho]

Will you be measuring your results when you do the mod?

[rjbond3rd]

Yes, absolutely. Please accept my apologies for my initially harsh tone. I was out of line and I edited the post.

At the moment, I'm doing a Khorn restoration (with lots of mods) but once the weather outside is nice, I will start on a pair of 1968 La Scalas which (though listenable and functioning) were converted to PA speakers. They are covered in green carpeting (glued down), all edges have metal brackets which are riveted, and they also cut into the sides to install plastic handles.

So it's a big project but after it's all stripped down and repaired, I will mod, measure and post. If they are past the point of recovery (which sadly, is possible), I have another set which was stripped of all parts by its previous owner, who also cut the tops off, so it's top-hats for those.

[DrWho]

Sweet deal, I look forward to your results. I think sometimes the writing comes off different than expected, as I'm totally interested in this mod too - I was just trying to throw out some of the potential compromises.

[Quiet_Hollow]

I suggest you mod just one LaScala, then A/B them directly playing some male voices talking and some jazz that has a lot of bass guitar going on. Do that before porting all four. The extra extension will be nice, but it'll come with a cost.

I'm trying to tell you the mod will mess up the speaker's transient response. The problem with this is that the bass bin is not exclusively a subwoofer, it runs well up into the mid range, to crossover to the squawker properly.

See: http://www.bksv.com/doc/17-198.pdf

Page 13 , Fig. 34 Shows the generic phase shift profile for the two alignments. Then check out how that effects an impulse and it's harmonics on Page 2, Fig. 2

Not entirely an issue in the sub-bass frequencies per say, but with the La Scala, this will also be happening in the very audible and tactile 300-700 Hz range.

I don't need to build it to prove it. If you've ever A/B'd Cornwalls right along side LaScalas you'd also hear exactly what I'm talking about. The Cornwall goes deeper, but with less accuracy in the hand-off region to it's squawker. No sense beating a dead horse though. Just trying to keep you from missing the forest for the trees. []

[Marvel]

I believe that Dennis originally designed this with two 10 inch ports, but said thatmaking them 7 inches preserves the snappiness/speed of the bass horn while still allowing some extension. I'm paraphrasing a bit, but it's what I remember. All those notes are on another PC right now.

Also, while still within the range, the Cornwall crosses substanially higher than the LS.

How accurate do you think this is when the upper range on the LS (100 - 400 Hz) is a horn, while below that is acts more like a DR? The B&K paper doesn't show anything with a ported horn.

Bruce

[sootshe]

Now to throw a cat among the pigeons......................Here's one for the techno heads out there to ponder over.................I've used the mod very successfully & have always used SS amps.........................I recently switched to a tube amp & found that the bottom end wasn't as tight or defined as before.................it was actually very soft .......................& merely put it down to the fact that the valve amp wasn't as tight in the bottom end as the SS amp...............it was sort of boomy & muddy & a lot lower in level..................so I thought I'd plug the ports up & see if it made any difference..................now it sounds just fine, as tight as always & punchiness is back................without the ability to measure, my assumption is that the ported version is amplifying some frequencies that the valve amp is producing that were perhaps not there in the SS amp?????

[DrWho]

Porting changes the electrical impedance, which in turn affects the frequency response of a high output impedance amplifier (ala most tube amps). Another way to think of it is just above the tuning frequency the impedance is higher because the active driver is less damped - when this couples with the reflected wave off the mouth of the horn (since the horn is undersized and too short), the amplifier is less able to fight the effects those reflections have on the driver. When you're reactance anulled, the pressure on each side of the cone stays the same because the reactance off the mouth matches the reactance of the rear wave in the sealed chamber.

[sootshe]

Porting changes the electrical impedance, which in turn affects the frequency response of a high output impedance amplifier (ala most tube amps). Another way to think of it is just above the tuning frequency the impedance is higher because the active driver is less damped - when this couples with the reflected wave off the mouth of the horn (since the horn is undersized and too short), the amplifier is less able to fight the effects those reflections have on the driver. When you're reactance anulled, the pressure on each side of the cone stays the same because the reactance off the mouth matches the reactance of the rear wave in the sealed chamber.

Say what!!!..................But good to know that my ears were on the right track.[]

[RRFL]

Putting in my 2 bobs worth, I reckon the only way to satisfy yourself with this mod is to give it a go other wise you will never ever know.

This mod can be done without damage to your LaScala.

The top panel of the ported chamber that fits under the doghouse with the doghouse opening cut into it can be omitted and a brace fitted around the inside of the top edge of the port chamber that connects to the LaScala and a seal placed around this braced edge. The original cover for the doghouse can then be screwed down, with the original screws and stored in the bottom of the port chamber for safe keeping and additional bracing of the chamber base. The thickness of the doghouse cover inside the chamber will be offset by the absence of the top panel.

Use a good quality SS amp with plenty of head room "10db" and a high damping factor.

Don't use a valve amp as explained above by the Doctor.

The efficiency will likely increase with this mod.

There is an increased chance of striking the motor board with the driver and a plywood ring spacer between your K33-34 and the motor board might be prudent. My K33's were replaced under my "Klipsch Original Owner Lifetime Warranty" back in 1977 after striking the motor board and turning into 6 inch woofers at a live band gig. There was a stern "don't do it again kid" issued with the replacement drivers,[8-)].

For myself, I would not do this mod as it is detrimental to the transient response of the LaScala as outlined above by the Doctor.

For myself, There is no ported bass unit that I have ever heard that cuts the mustard for adequate transient performance and this is only important for some people. That is why some people have the MWM as part of their system and why I want Jubilee so surpass my LaScala. I would prefer the Heresy over the Cornwall for tight Bass performance.

Each person has individual ear frequency/transient characteristics and hears things differently to all other people and therefore it's 100% individual personal preference. We live in a democracy also, []

For myself, I'm going to build a pair of Tuba HT LP 18"x18"x72" to stand vertical in the corners behind each LaScala mouth pointing down to the floor and 18" above the floor. IMO this will be the best "compact" match for the LaScala as the Tuba HT LP is the same "type" of horn design.

IMHO I reckon one of the most compact ultimate upgrades for the LaScala is to use the K510 as Islander does, the K409 with K69 or TAD4002 and then tri-amp the LaScala with the Tuba so the time alignment can be adjusted. I'm going to use the Ashly NE8800 to achieve this as it has extensive EQ functionality available.

These 2 Tuba HT LP that I build for my LaScala will be the 3rd and 4th. The 1st is underway at the moment. I have bought myself a nice "electric" table saw, router and planner to surpass my Grandfathers "carpenter by trade" hand tools I have always used until now, [8-)]

I have built a panel jig for the table saw and I'm currently building the router templates for the joints.

The 1st Tuba HT LP 26"x18"x72" is for a beautiful waterfront home on Sydney Harbour at Parsley Bay.

The 2nd Tuba HT LP 36"x18"x72" will be the LFE for my Jubilee.

[Marvel]

I have said I would build in this mod for years. I really trust Dennis for this, but I DO use a low power tube amp (3.5 watt 2A3 amps). Tube amps are voltage amps, while SS are current. Just makes me a little bit hesitant. Everyone who has done the mod has kept it, but they have all been SS amp users.

I still may give it a try.

Currently, I have no trouble down to 40 Hz on my Moondogs, with my LS. It is a good match up, and I've always been fortunate that way. Some things just work... [:^)]

Happy New Year and God Bless to everyone!

Bruce

[sootshe]

I have said I would build in this mod for years. I really trust Dennis for this, but I DO use a low power tube amp (3.5 watt 2A3 amps). Tube amps are voltage amps, while SS are current. Just makes me a little bit hesitant. Everyone who has done the mod has kept it, but they have all been SS amp users.

I still may give it a try.

Currently, I have no trouble down to 40 Hz on my Moondogs, with my LS. It is a good match up, and I've always been fortunate that way. Some things just work...

Happy New Year and God Bless to everyone!

Bruce

Bruce,

I used it successfully with SS amps & now have switched to a CJ valve set up...................it's still a night & day difference....................you won't be disappointed.................you may have to plug the ports though.

[Quiet_Hollow]

How Klipsch felt about it:

[sootshe]

How Klipsch felt about it:

That's merely a way of protecting your specification from the opposition!

[mustang guy]

How Klipsch felt about it:

That's merely a way of protecting your specification from the opposition!

It's a good argument, though.

[Marvel]

It's a good argument, though.

What's the argument? Porting the cabinet gets you lower bass, so how do they claim 'inherent bass loss'?

That's also from 1976, and the K-33 spec changed since this version of the LaScala was 'specified' by the enginers. As I had mentioned Dennis in another post, that his orginal prting was to ues two 4 x 10 inch ports, he changed it to 7 inch ports to clean up some of the sloppines. Still the snappy bass while maintaining the lower extension.

Bruce

[DizRotus]

Bruce-

There's no shortage of those who criticize the theory. The naysayers are not among those who've tried it.

There's a distinct shortage of those who've tried it who would go back to un-ported. No one is forced to try it.

People love to say that something with which they're unfamiliar is not as good as what they already know. That will never change.

[Guest " "]

but will it take off??????

[DrWho]

How Klipsch felt about it:

That's merely a way of protecting your specification from the opposition!

It's a good argument, though.

The quote is taken way outta context....straight horns always have less distortion for the same Fc, but the suggestion is that a folded horn fits in a smaller footprint. In other words, at low frequencies the folded horn has lower distortion since you can't get the same Fc in a straight horn within the lascala footprint. The reference to a port is related to a ported box in the same footprint versus the folded horn. That particular article has nothing to do with a ported horn, or at least I'm not reading it that way. Btw, critique of a design approach is different than being a naysayer.