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ClaudeJ1

Quarter Pie Bass Horn: Measured FR, How2Build, and Hornresp

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Here's the "new improved" model that I will call a "SUPER QUARTER PIE." Keeping up with the traditional naming conventions of my mods and designs!!

This will use full sheets of 5x5 foot Baltic Birch Plywood, instead of 4x8 sheets cut in half to make 4x4 foot raw materials. Adding an extra 10 Hz. below and making the horn about 4 inches taller will do the trick. I will not be as huge and unwieldy as a Super MWM that DaveA built, but it will come very close in performance while using every cubic inch of room corners with no air gaps there!!

 

SuperQuarterPie.jpg

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The Quarter Pie horn is really a wonderful design (thanks Claude!). I really don’t see much benefit in adding a foot to the original design just to get 10HZ. Regardless of size, you are going to want a good sub (I have a pair of  Cinema F20 subs) and if implemented correctly seamlessly hand off to the QPs. Bigger isn’t always better, just harder to move.

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2 hours ago, tromprof said:

Bigger isn’t always better, just harder to move.

 

Did you have some MWMs before? Mine pretty easily play back 35Hz and I can hear lower in my room. I know Claude had MWMs in the past... he's had about everything from Klipsch. Could be my room. I have 10.5 foot ceilings. 21x23 ft floor.

 

But I agree, they are harder to move... 😁

 

Bruce

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1 hour ago, Marvel said:

 

Did you have some MWMs before? Mine pretty easily play back 35Hz and I can hear lower in my room. I know Claude had MWMs in the past... he's had about everything from Klipsch. Could be my room. I have 10.5 foot ceilings. 21x23 ft floor.

 

But I agree, they are harder to move... 😁

 

Bruce


No, never had MWMs. I chose to build the QPs instead since they are essentially the same but in a somewhat smaller package. MWMs would have required a bit more floor space and still have needed a sub to get to 20HZ which is my personal definition of full range.

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@ClaudeJ1   Wouldn't an MWM have a lower response the a 5x5ft Super Qpie? Just thinking the overall size is nearing a full MWM single.

 

Bruce

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29 minutes ago, Marvel said:

@ClaudeJ1   Wouldn't an MWM have a lower response the a 5x5ft Super Qpie? Just thinking the overall size is nearing a full MWM single.

 

Bruce

The MWM is a 6 foot long horn, the Super Qpie is 6.88 ft., so it's a tad lower. The Super MWM is 9 feet long and lowest of all. It's the horn LENGTH at 1/4 wave that is the main determinant for low end cutoff. Also, the MWM had a 55 Hz. peak in my rooms, so there's that also. The Qpie is actually smoother than the MWM. Also, DaveA's SMWM gets down into the mid to high 20's in this room, but it is a monster horn!

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4 hours ago, tromprof said:

The Quarter Pie horn is really a wonderful design (thanks Claude!). I really don’t see much benefit in adding a foot to the original design just to get 10HZ. Regardless of size, you are going to want a good sub (I have a pair of  Cinema F20 subs) and if implemented correctly seamlessly hand off to the QPs. Bigger isn’t always better, just harder to move.

People seem to want different things. DaveA wanted 30 Hz. with NO Sub just for music, not HT, so he's happy with the Super MWM. This one is a "tween the two" design, of sorts. I'm not the one who has to build it, so my part, in this case, was pretty easy.

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46 minutes ago, tromprof said:


No, never had MWMs. I chose to build the QPs instead since they are essentially the same but in a somewhat smaller package. MWMs would have required a bit more floor space and still have needed a sub to get to 20HZ which is my personal definition of full range.

I agree wholeheartedly with your definition of full range. But hey, some people are fine with plain Old LaScalas, so who am I to put my preference onto someone else, eh?

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2 minutes ago, ClaudeJ1 said:

I agree wholeheartedly with your definition of full range. But hey, some people are fine with plain Old LaScalas, so who am I to put my preference onto someone else, eh?

 

I, for one, am generally satisfied with the LaScalas with ported bins, hell I was happy without the bass bins. There must be some nice room gain going on in here as it has never seemed light in the bass. Like I mentioned in my initial post one of my major reasons for wanting to build either the QPie or SQPie is aesthetic, the other being my curiosity with regards to a fully horn loaded system. Having them dig even deeper is definitely a bonus!  A subwoofer with the expenses and complexities involved, are out of my reach/interests right now.

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7 hours ago, Ray_pierrewit said:

Does anyone recall off hand how low the LaScala dig with the bass bin mod? I trust either the QPie or SQPie will trounce them, right?

 

I know this will probaby cause an argument...

 

IIRC, and I will find Dennis' notes... IF  you add a filter between the preamp and amp, they are good to 30Hz. But you have made them a reflex speaker. Dennis listed the different alignments with each part of his modification.

 

His aesthetic is better. If you enclosed the top to do the mod they look no different than a straight LS. The box underneath just makes them taller. Everything else is simply bigger and for some that's no problem. I like my plain LS... absolutely love the MWM cabs. Totally effortless bass, but they certainly are big. Claude had them for quite a while.

 

For the size of Dave's shop and staying 100% horn, his Super MWM would trnce them all.

 

The Qpie and SQpie stay 100% horn. Kudos for that. MWMs, if flat against a wall are only 45-46 inches deep. If, for example, on left side of a room you have the left edge flat against the wall, it only come into the room about 57 inches. To me, they look better that the arc of the Qpies, but if the Qpies perform better and you are good with it then go for it.

 

Bruce

 

 

 

 

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Notes from Dennis:

 

The taper rate of a LaScala is 100hz,The mouth area is good for 125hz. Below this it is a big woofer in a small sealed box. If we plug the T/S parameters for the K33E into a box program we will see that the Qtc=.85, the Fc=82.5hz, and the F3=70.9hz.  If we close in the back of the high frequency cabinet and open the woofer rear chamber up into this volume and fill with fiberglass we now have Qtc=. 577, Fc=58.2hz, F3=73.6hz. Bessel=Qtc.577=D2 gives the best transient response and the least group delay of all the sealed boxes. At 30hz the Qtc=.577 has 4. 5dB more output than the Qtc=.85.

Compared with sealed enclosures,the transient performance of the best vented enclosure is worse than the best sealed box enclosure. Since we have made great gains in performance some may elect to stop here. But please read on. The next step is to port it. The K33E is not the optimum woofer for this but it works pretty good. With the box size optimized for a D2 we can port the stock woofer to an SC4. The transient response of an SC4 while not as good as an SBB4(more on this later)is better than the more common QB3. Unequalized the F3=49hz and has 3dB more output at 30hz than the D2. The response curves are parallel with the D2 the only difference being the Fc being a half octave lower with the SC4 and the output being 3dB higher from 30~70hz. The output of the SC4 does not drop lower than the D2 until you go below 17hz.

 

Again this may be a stopping point for some. But by adding a simple two pole high pass filter ahead of the power amp we can now have a C6 with a -3dB point of 31hz. Since this is the Fb of the system there is no increase in cone excursion or distortion. The filter consists of a cap an inductor and a pot. The pot allows adjustment at Fb of +/- 3dB. This is similar to being able to change the Qtc of a sealed box from .5~1.0.

 

If you think about it we have the choice between a D2,SC4,and a C6 in the same box by plugging the port and/or bypassing the eq. If you have a SET amp or simply want to get the most out of the La Scala you will want to upgrade the woofer to something with a lower Qts. The Klipsch K43E does the trick,as do the EV DL15W and the JBL 2205. The EV and JBL drivers require some minor network changes. The lower Qts drivers allow for an SBB4 alignment which has the best transient response of the vented alignments.

 

With no eq they have 3dB more output at 30hz than the stock woofer. With eq we have a maximally flat B6 and the F3 of the system is 27~28hz. If using a solid state amp with the low Qts woofers a small resistor must be added in series with the driver to have the same Rg as the SET does.

This mod can be backed out of a stock LaScala with no externally visible changes if you don't like it. No one has ever gone back to stock after hearing this mod. Paul Klipsch was violently opposed to the venting of horn speakers based on his experience with venting the K-horn.  In retrospect it is easy to see why.  The 12" Jensen field coil woofer he was using had an Fs of 60hz and a quick calculation of the vent area vs the Vb based on the photographs of this experiment looks like an Fb of ~80hz. I am sure this sounded horrible. Paul Wilbur Klipsch is a giant in audio. If I appear to see farther than PWK it is only because I am standing on his shoulders.  

 

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1 hour ago, Marvel said:

If, for example, on left side of a room you have the left edge flat against the wall, it only come into the room about 57 inches.

 

Why has nobody proposed a bass horn that runs the full height of the room, floor to ceiling, finished the same as the room walls, so that it just looks like a part of the room itself? Or a horn that is only 14¼" wide, so that it fits between the wall studs and only occupies space in the adjacent (presumably unused) room?

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11 hours ago, Ray_pierrewit said:

 

I, for one, am generally satisfied with the LaScalas with ported bins, hell I was happy without the bass bins. There must be some nice room gain going on in here as it has never seemed light in the bass. Like I mentioned in my initial post one of my major reasons for wanting to build either the QPie or SQPie is aesthetic, the other being my curiosity with regards to a fully horn loaded system. Having them dig even deeper is definitely a bonus!  A subwoofer with the expenses and complexities involved, are out of my reach/interests right now.

 

I think you will be blown away by the quality of the bass produced by the QP horn. I have owned La Scalas and still have a pair of Klipschorns.

Once you listen to the QP you will begin to understand as good as Klipschorns are, they still have their share of distortion down low. With the QP its gone (again, mated to a good horn sub to take care of sub 60HZ material).

They are also not hard to make, I managed to cut and assemble my front three in two days.

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2 hours ago, Edgar said:

Why has nobody proposed a bass horn that runs the full height of the room, floor to ceiling, finished the same as the room walls, so that it just looks like a part of the room itself?

 

Klipsch has notes for mounting an MWM single  with the mouth facing down, so it can be flat against a wall. Then it would only protrude about 17-18 inches into the room. I can't remember offhand how far off the floor it is. I suppose, if one were to stand them up on end, it could fire into the corners the same way. Then you would still have to figure out the top end and where to mount them.

 

You could just use two 4x8 sheets for the regular top/bottom, instead of making them a trapezoid.Then they would be easy to stand up...

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Would the super pies work well with 402s for a two way system?  These (meaning the pies) look like something I might could pull off.

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49 minutes ago, tom1066 said:

Would the super pies work well with 402s for a two way system?

 

Yes

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16 hours ago, Ray_pierrewit said:

Does anyone recall off hand how low the LaScala dig with the bass bin mod? I trust either the QPie or SQPie will trounce them, right?

Trounce is an understatment. a 2.5 foot horn vs. a 6.88 foot one, no guess required as to which one wins with the same driver.

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5 hours ago, tromprof said:

 

I think you will be blown away by the quality of the bass produced by the QP horn. I have owned La Scalas and still have a pair of Klipschorns.

Once you listen to the QP you will begin to understand as good as Klipschorns are, they still have their share of distortion down low. With the QP its gone (again, mated to a good horn sub to take care of sub 60HZ material).

They are also not hard to make, I managed to cut and assemble my front three in two days.

I remember this "not hard to make" quote about you. For those late to this party, Tromprof owns my original pair as surround speakers for his HT! He's the king of the Quarter Pies, for sure. He and his wife are musicians so they have great ears for audio, since they are surrounded by acoustic instruments in their respective professions. I'd say their opinions are more qualified than most!

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