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ClaudeJ1

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

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So I finally found another pair of EVM 15L drivers, so I didn't have to rob my main system of one (see Avatar) and finished building my first prototype horn, which is, after several dozens of iterations in Hornresp, is finally here.

 

I'm happy to report that it measures very much as predicted. Put the microphone at the edge of horn mouth and ran Frequency Response plots, same as I did with the FH-1 bin a while back. The FH-1 is similar to a Belle Klipsch/LaScala bass bin, but larger, more ruggedly built (for PA) and ugly as sin.

 

Now keep in mind, in my case, both bass horn cabinet use EVM 15L woofer, which is the preferred woofer by Dr. Bruce Edgar. This woofer has fairly high resonance for a 15", but it's low Q and low mass paper cone with minimal coil inductance give it superior high frequency response in the 300-400 Hz. range where I'll be handing off to the K402/1133 combo at about 300-320 Hz. I strongly believe in bi-amping or -tri-amping with the the Mini DSP or some other active Xover for the Quarter Pie because any mid/tweeter treble section you use will have an efficiency that is 3-9 db higher, so you need a higher voltage drive to the bass to make up the difference. All Heritage Klipsch products use Autoformers to attenuate the mid/treble section down to the bass section, so this idea is not new. It's just that woofers use most of the power and having direct amplifier drive to the woofer voice coil with lots of control option with an active crossover is really the best way to go in modern times.

 

On 2/27/2014 at 5:07 PM, ClaudeJ1 said:

 

On 2/27/2014 at 3:46 PM, kg4guy said:

Claude great job on this and for sharing this build it's relatively easy to build as you have done all the foot work .Ron a fellow Forum member north of me is going to build a pair for his new theater room I'm sure he will be very happy. It's nice to see these DIY builds are going strong still I hope to see more in the future. :D

Thanks. I really had no choice since I had no room for a full MWM and the FH-1's fell way short of the 60 hz. mark by a whopping 40 hz.

 

My tops and bottoms were precut to 45" for a pair of LAB Horns I never built, so I ended up using those.I also want to add that the MEASURED curves, Red Quarter Pie vs. Green FH-1, were done with the 45" and NOT the 48" version, which goes lower by at least 5 Hz., so the curves are quite real and if you build version 2.2, your response will be even better than the curves!

 

If I were to build another pair from scratch, I would just cut 2 sheets of 4x8 lumber in half for a 48" square top and bottom before the big radius. It would eliminate a 3" sliver of wasted lumber and lengthen the horn just a wee bit to about 65" total instead of 60". This would also allow the "core section" to recess inside the horn by 3/4" so the cover could be cut at 15.5 x 15.5" to be flush instead of 17" square on the outside like I'm stuck with. This would eliminate the odd duck 17" dimension and allow all the rip cuts to be 15.5" to 15 3/4" long ways on the other 2 sheets........an even simpler solution vs. what I built.

 

It's a minor tweak, I know but the horn would go down to 56 Hz. instead of 60, roughly. But hey, what's a few Hertz among friends. LOL.

 

BTW, this horn really sounds good without the Danleys, FYI. But I do prefer adding their "bottomless bass" for music and everything else.

 

The plots shown in the image are 1/48th octave resolution from REW (no smoothing) was used. The FH-1 had a 2.5 Mh Klipsch choke on it at the time of the measurement, so it rolls off more in this plot than it would without it. Nonetheless, the main reasons for designing this new bass horn was to extend the bass to 60 Hz. with the same driver and keep the 300-400 Hz response intact.

 

As you can tell from the RAW curves, with the FH-1 (green) I had to do a 141 Hz, -5 db PEQ to knock down the peak in the FH-1 (or LaScala) as well as adding a +10 db boost at 61 Hz. to get any sort of bass below 100 Hz, down to 60 Hz.. Needed to this to mate up with my DTS-10 Tapped Horn Subwoofers, which are best below 60 hz.. The red Quarter Pie curve shows I don't need to do this anymore.

 

So far, it looks like I have succeeded at lowering the bass response acoustically by making a 5 1/2 ft. horn (which I'm calling "Quarter Pie") vs. a 2.8 foot long horn for the FH-1 (or LaScala). I will also be lowering the 6 ft. height of my horn "stack" down to about 5 ft. or so, bringing the tweeter much closer to my ears when seated in the sweet spot. It also looks like I got a MUCH smoother horn in the process also. The distortion should also be lower because I will NOT need any kind of bass boost at all, so 10 db less power should translate into at least 10-16 db less IM distortion.

 

The green is the FH-1, the RED is the new Quarter Pie Bass Horn. They are RAW Frequency Response Plots with NO smoothing and NO Equalization of any kind. An EVM15L driver was used in both. The smoother, flatter curve of the Q-Pie is pure acoustic response of a better horn on the same driver. Mission accomplished.

 

PS: Since this first post, I have changed the woofers to Eminence Kappa 15C's since I'm crossing low and didn't need such wide bandwidth the EVM 15L provides. A few other Quarter Pie builders needed to cross at active 500 Hz. to a 2-way and passive 400 Hz. respectively, so they are the new owners. The Midrange response of the EVM 15L is best for those guys. The 15C's got me a little lower/stronger bass, but not by much.

 

If you want the most bass out of this cabinet and are willing to sacrifice a little midrange to do it, the K-33 driver (shown in Black on Hornresp FR Plot) or Bob Crites 1526C will give you the most bass from 60-120 Hz. which is where the "big slam" occurs. The original EVM 15L is in gray.

 

For those of you who own LaScalas without Subs and want to invest about $250 in just plywood and use your existing K-33 woofers, I have included comparison curves of the Quarter Pie vs. LaScala with your woofers. You can see HUGE improvement in REAL HORN BASS. Just use your empty LaScala bass bins as "spacers" for your treble section and run the woofer output on your AA networks to the Quarter Pie instead. You won't believe the difference. There's also a little improvement in the midrange also, but not as much as the bass.

 

As of May, 2014, I traded my new Eminence 15C woofers for a pair of square magnet K-33's, simply because based on measurement, and, ESPECIALLY, lots of listening time to various CD's with discerning bass content. I would only recommend this for those who can cross their horns at around 300 Hz. like I can with Klipsch K-402-MF horns. I'm not using any PEQ since the natural mass roll-off of the K-33 "shakes hands" with the mid perfectly without it.

 

Those who need to geto 400-500 Hz. may get away with a K-33, but a 15C would be a better choice (passive or active). Active bi or tri amping gives the ability to do a slight PEQ boost in that band with horns that have a higher cutoff or with drivers suitable for 2-way. In the 2-way case, you will, more than likely, be using modern active driver control anyhow, so you can PEQ a K-33 or any other driver to match your top end anyhow, since you will need it for high frequency shelving on the treble horn.

 

It's your SOUP, and, you own the taste buds AND the salt shaker. Your ROOM is the main determinant of the bass sound, so it is the BOWL for the soup. Enjoy your meal.

 

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QP402QSC.jpg

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Basically this thing fits neatly into a corner, but comes with it's own corner, so it doens't have to have one. It is a derivative of the famous, but huge Klipsch Magnificent Woofing Machine single (MWMs). I made the "MWM single core" section with a slightly smaller back chamber to match the woofer.

It only takes 11 cut pieces of wood to build it. I have made it as simple as posible and could be made without the curved front (just a 45 degree) if you are willing to scrifice 4-5 Hz. at the bottom end. Plans will be forthcoming for those who want a good bass horn that's easy to make, but I want to make sure I give the pair a complete listen once it's part of the system. You will know when I update my Avatar! I may not get to this for a few weeks. The above measurements are VERY encouraging. I look forward to your comments.

It's only 17" tall, just like a single MWM bin but save a huge amount of floor space while only giving up 10 Hz. at the bottom end, which, all good boys and girls handle with a Spud or Super Spud Tapped Horn anyhow, right? The only missing part is the back chamber cover. You are looking at the right channel position.

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Edited by ClaudeJ1
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That's a cool design. Does the driver mount in that hole in front facing outward?

Yes, the driver enters the hole sideways/diagonally, then sits in an 8" deep chamber. The cover goes over the hole and sticks out 3/4". They were built from leftover lumber. The top and bottom pieces were radiused from 45x45 pieces from a LabHorn I decided not to build. These could be made from 4x8 sheets cut exactly in half to simplify things a bit and make s slightly longer horn from 48x48 pieces......not critical. I will know for sure when I publish plans and cut layouts, but I'm pretty sure a pair of these can be made from 3-4 sheets of 3/4 plywood or MDF. The drivers go for about $125 each on the used market so they can be built for about $400/pair or less if you can find drivers cheaper. Here's the Hornresp model for this horn vs. the FH-1. Overall, the measured values were pretty close to this. You can see from the model and the plots that this represents a huge amount of bass extension in a low profile horn that's easy to build.

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Edited by ClaudeJ1
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Very nice design... So will I have problems getting the most out of the Super SPUDS with my La Scalas?

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Very nice design... So will I have problems getting the most out of the Super SPUDS with my La Scalas?

Since LaScalas are so close to FH1's the answer is yes..............but, you can PEQ them too to reach down to the Super Spuds.

Right now, I have the GREATEST bass definition on 2.1 music I have ever had. Every bass note, even from 5, 6, and 7 String Basses, that easily get down to 31 Hz. (or lower if detuned or MIDI synthed), so having "bottomless" horn bass capability is very cool.

The response below is with my FH-1's PEQd, which I won't need to do once the new Quarter Pie horns are in service. Can't wait.

The source was a Pink Noise CD with the RTA measurement of REW right where I sit in my sweet spot about 12 feet away. The results are WITH the Amazing Audyssey XT room EQ applied with a 2.1 setting on my receiver.

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Edited by ClaudeJ1
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Very nice design... So will I have problems getting the most out of the Super SPUDS with my La Scalas?

Since LaScalas are so close to FH1's the answer is yes..............but, you can PEQ them too to reach down to the Super Spuds.

Right now, I have the GREATEST bass definition on 2.1 music I have ever had. Every bass note, even from 5, 6, and 7 String Basses, that easily get down to 31 Hz. (or lower if detuned or MIDI synthed), so having "bottomless" horn bass capability is very cool.

The response below is with my FH-1's PEQd, which I won't need to do once the new Quarter Pie horns are in service. Can't wait.

What is PEQ?

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So will I need an additional one or will my Denon take care of the La Scalas?

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So will I need an additional one or will my Denon take care of the La Scalas?

You can get a 2x4 mini DSP for $105, run it with a 12V Radio Schack Wall Wart, get their Umik for $70, software for $10, and REW 5.1 for free to run on a laptop.

Or you can get a used Behringer DCX 2496, which is what I'm using now until I get the Mini DSP's up and running.

All this is done AHEAD of Audyssey, which is a time domain DSP for ROOM correction.

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So is the minidsp better than the Behringer DCX 2496?

Now with the minidsp does everything have to go through the PC after it is setup? I ask this because I have i3NUC that is my Home PC and an i3NUC that is my media server which runs on Openelex/XBMC.

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Guest David H

Mini DSP is set it and forget it. Its a really great tool.

Dave

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Would I use the mini DSP for all my channels, just the front 3, and the subs or just the subs? I see most use the 2x4 which would only be good for 2 channels correct?

Edited by ellisr63

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Claude. ......excellent design..!

miketn

Thanks Mike. You are one of the most respected technical people here and I've learned a great deal from your posts, even the ones that have a "fork in the road" leading to Audio Nirvana, (where we differ slightly) LOL. So I truly appreciate your compliment. JC also gave me some encouragement via telephone so I hope he pops in here for a post or two at some point.

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That is a great design Claude. Looking forward to learning more about it. :emotion-21:

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I can draw a sketchup for you if you would like to provide the dimensions, etc.

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Claude. Nice to start a thread on this. This gonna be in a corner?

When u say Quarter Pie, is this referring to 1/4 space exponential flare or basically saying the shape is 1/4 of a circle?

Can you provide the following info on the picture if you have time.......

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Edited by jwc
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On 2/2/2014 at 8:52 PM, jwc said:

Claude. Nice to start a thread on this. This gonna be in a corner?

When u say Quarter Pie, is this referring to 1/4 space exponential flare or basically saying the shape is 1/4 of a circle?

Can you provide the following info on the picture if you have time.......

Yes, I named it for shape of cutting up a Pumkin Pie with two cuts, eh? Literally and figuratively speaking. It's an MWMs throat and expansion into an assymetrical single fold with a 90 degree mouth. The corner radius is offset by about 2 1/2 inches, for it to meet with the core sections, which is a smaller back air chamber version of an MWMs. I tried a bunch of other variables in HornRESP, but this MWMs throat was still the best performer. The lumber was precut square so I decided to do a radius instead of a diagonal line as you have drawn. I will actually be able to use the leftover lumber for a white background in my photo studio. Waste not, want not.

For less waste, someone could end up with 47 7/8 x 47 7/8 top/bottom dimensions and add more back chamber volume, which could be variable for different drivers. After a few year, of experience and thoughts, I'm changing this to read: "To add more length to the horn (about  1/2 ft. total), which would lower the cutoff frquency from 56 Hz. to 51 Hz. Back chamber volume has very little effect on perfomance, so it's better to add horn length to get the extra 5 Hz. down below for free, since you have less lumber waste and are adding only 3 inches to each dimension.Since I was working with leftover lumber that was pre-cut for an aborted LAB Horn project I was stuck with 45x45".

So what do you think of my measured curves?

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