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post #91 of 127 Old 03-15-2013, 05:32 AM
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Carl, you have a PM my friend!
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post #92 of 127 Old 03-16-2013, 10:24 PM - Thread Starter
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32Hz Ported Measurements ...

The first round of ported cabinet measurements are in and not what I expected. First here is the plot one more time for the legacy sealed (ie: classic Klipsch La Scala) cabinet. ...



Below are the results of the ported La SEOS cabinet. For this test the doghouse is closed on the bottom side and left open on it's top side. The upper cabinet (occupied by the crossover and upper range horn/ waveguide) has its' back closed off and two vents tuned to 32Hz. Those two vents measure 9.25 inch tall by 2 inches wide by 13 inches deep and extend along the sides of the cabinet (see the PICs in post #76)



At first you scratch your head and say, "By golly that looks just like the results for the legacy unported cabinet!", and you would be mostly right. However a closer examination shows a 3dB rise at 43Hz. Note the red circle in the PIC below. This is with 32Hz ports. I tried 40Hz ports as well. The difference was negligible.



The ports for the La SEOS are on the back of the cabinet and these measurements were taken one meter on axis in front. It could be argued that the benefits of the ports are simply not being measured because of that fact. So I slid the cabinet within 6 inches of a wall and moved the measurement mic to align with the edge of the cabinet and measured the results. When I did that the bump at 43Hz rose to 4dB, offering 1 more dB of gain.

That's a lot of work for a narrow 3 or 4dB bump at 43Hz. However studying the plot shows a couple more changes. The notch at 50Hz has been pulled up 3dB as well. But the most interesting change is not down low but up in the mid bass output of the short horn.



Note that the horn is now more controlled. The overall amplitude is flatter and that is something that I simply had not expected to happen. So the question that everybody wants to know the answer to is ...

"Does the ported version sound any better than the unported version?"

The answer is a qualified, "Yes" but the difference won't set your knickers on fire. the change is subtle. The bass sounds marginally fuller and the midbass sounds less 'crashy' for lack of better words.

And finally, "Is it worth the effort to add the ports? "

Again I say, "Yes", not because the bass is extended but because the midbass cleans up. Perhaps that is the improvement that people are hearing when they add volume and ports to the Klipsch La Scala. Both the ported and unported versions need to be supplemented by a subwoofer.

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post #93 of 127 Old 03-16-2013, 10:46 PM - Thread Starter
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Th Magic of EQ ...

Below is what Dirac Live suggested would be an 'in room optimized response' for the ported La SEOS cabinet. The red line is the suggested target curve. The target curve can of course be edited should you desire to make a change.



Note that Dirac Live will limit filter gain to 10dB. And here is the in room results that it expects to get ...



Altho I didn't take the time to verify the results using REW or OmniMIC, it is my experience that Dirac Live does a pretty good job of delivering what it promises.

It could be argued that after applying Dirac Live we would no longer have a Klipsch La Scala and I would have to agree. I suspect that a big part of the cherished 'La Scala sound' is that bump in amplitude between 100 and 300Hz.

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post #94 of 127 Old 03-17-2013, 03:55 AM
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that weird port behavior is predicted by hornresp and is what i was referring to earlier, so i don't think you have done anything wrong with your port construction. that just seems to be how it works porting the rear cab of this front loaded horn.

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post #95 of 127 Old 03-18-2013, 02:52 PM - Thread Starter
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A last Round of Bass Cabinet Measurements ...

My final set of measurements was to measure the legacy sealed cabinet but with a reduced internal volume. LTD02 used Hornresp to predict that the la Scala cabinet would offer up improved performance if the internal volume was less. I tested the cabinet with approximately 1/3rd less internal volume. I accomplished this in an impromptu manner by using a scrap piece of plywood cut to size and gaffer's tape to seal the edges and hold the board in place. And it worked! Below again for reference is the legacy La Scala sealed cabinet.



And here is the same cabinet but with a 3rd less internal volume.



LTD02 and Hornresp have been vindicated! Note that the amplitude response of the short horn flattens out, much like it did in the 32Hz ported version. Clearly the Klipsch La Scala can be improved by reducing the volume of the sealed enclosure.

So which is the better idea to improve an existing pair of Klipsch La Scalas, adding volume and ports or reducing the cabinet volume and leaving it sealed?

I'd have to say reducing the volume as it is the easiest improvement and offers similar results. Adding volume and ports is major surgery with only a minor improvement over reducing the cab volume.

In either case you need to add flanking subs per Wayne Parham's guidelines (Yes, I have been studying up ...)

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post #96 of 127 Old 03-18-2013, 03:17 PM - Thread Starter
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On Adding a Horn or Waveguide ....

My measurements over the recent weeks show us that the La Scala bass cabinet has a typical 'PA horn' service bandwidth. It reliably services the band from 120Hz to 900Hz. In fact it could be argued that for 'Hi Fi' purposes matching it with a 500Hz horn is the best idea. This points out why a popular mod to the La Scala is to replace the factory horn with an Altec 511 or Emilar EH500 horn (a 511 clone minus the vertical vanes and with a 2 inch throat).



In the case of the La SEOS I will be using an 18 in SEOS waveguide and GPA 902 compression driver. The GPA 902 is a modern day version of of the old Altec 902 that was intended to be bolted to a 511 horn.

CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), quality = 90

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post #97 of 127 Old 03-18-2013, 04:11 PM
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it will be interesting to see how much that upper bass increases once placed in room, particularly if corners are available. it doesn't look like 50hz is out of the question for this guy, even before dirac processing.

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post #98 of 127 Old 03-18-2013, 07:06 PM
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i cant wait to see this. im definitely a Heritage fan. i would love to see a SEOS Cornscala!!

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post #99 of 127 Old 03-18-2013, 07:32 PM
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Will the LF rear chamber be lined with absorption? It may be a good idea, in addition to the volume reduction.

JSS
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post #100 of 127 Old 03-18-2013, 09:30 PM - Thread Starter
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Quote:
Originally Posted by maxmercy View Post

Will the LF rear chamber be lined with absorption? It may be a good idea, in addition to the volume reduction.

JSS

It is interesting that you ask that! Late today in the course of my experiments I added a 1 inch thick layer poly foam to the inside of the doghouse and took some measurements. The poly foam that I used is the same stuff that is in your couch bumm cushions. Below are results when I added a 2 foot by 2 foot sheet of 1 inch foam to the legacy sealed cabinet. The notch at 200Hz is all but gone and the one at 575Hz is substantially reduced. And notice the new gain above 700Hz in the red circle.

* LEGACY CABINET UNPADDED *


* LEGACY CABINET PADDED *


And below is the cabinet opened up and vented at 32Hz. Adding the padding did reduce the notch (red circle) that was at 150Hz and the response at 1kHz is better

* 5.75 cu ft PORTED to 32Hz UNPADDED *


* 5.75 cu ft PORTED to 32Hz PADDED *


And finally here is what I measured when the cabinet volume was reduced by 1/3rd and sealed.The notch at 575Hz pulls up but we lose amplitude at 1kHz which may or may not be important dependent upon the upper horn or waveguide that you have in that cabinet.

* LEGACY 1/3rd REDUCED VOLUME UNPADDED *


* LEGACY 1/3rd REDUCED VOLUME PADDED *


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post #101 of 127 Old 03-18-2013, 09:50 PM
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Are these in room measurements? Is everything in the room including speakers and mic within half an inch between measurements? Measuring in the nearfield helps, but I'm curious if some of these changes are placement related?

Btw, super cool too see measurement correlating to theory. Do you have means to measure impedance?

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post #102 of 127 Old 03-18-2013, 10:39 PM - Thread Starter
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Quote:
Originally Posted by MBentz View Post

Are these in room measurements? Is everything in the room including speakers and mic within half an inch between measurements? Measuring in the nearfield helps, but I'm curious if some of these changes are placement related?

Btw, super cool too see measurement correlating to theory. Do you have means to measure impedance?

I think it unlikely that the differences are placement related. I have been diligent in my attempt to be consistent from session to session. I have been using the test setup as shown back in post #70. I have gaffers tape on the floor to mark where I put the mic stand between sessions and the loudspeaker cabinet is never moved. I am using an Earthworks M30 (with calibration file) and a USBPre microphone preamp for the measurements. The measurement mic is always pointed dead center of the cabinet at the same height, same distance.

These are not in 'living room' measurements. These are open space 'in garage' measurements. The cabinet is positioned near an open garage door so as to avoid room affects. The cabinet is sitting on a pile of 3/4 plywood raised roughly one foot off a concrete floor. I think that I'm pretty good and my results should be repeatable between sessions. Your thoughts??

Can I measure impedance? Yea, I have a DATS (Dayton Audio Test System) lying about somewhere.
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post #103 of 127 Old 03-19-2013, 07:11 AM
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LTD, do you have a screenshot of the Hornresp params? Before Carl chooses between sealed and ported, we could try sim'ing some different ported alignments. I'm not sure 32hz is the best tuning. There might be some opportunity to help out that super anemic response below 150hz.

I much prefer the response of a modified Altec A7 bass cab. I think it is bigger though.
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post #104 of 127 Old 03-19-2013, 08:09 AM
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mr. c., in post #22, the black line is the ported enclosure in hornresp model. the strange thing about porting the front loaded horn is that the tuning frequency does not seem to really change where you get the boost (completely unlike a standard ported design). across a reasonable range of various port tunings, the additional spl was always at or around the same frequency. the higher tuning frequency just made the spike more pronounced. i don't understand why. it just seems to work that way.

i can't imagine what a pain this stuff must have been for pwk 70 years ago.

while the a7 does appear to have a "horn" bass unit, that really isn't going to be doing anything for the bass frequencies. for bass purposes, the a7 is just a ported cab.

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post #105 of 127 Old 03-19-2013, 09:16 AM - Thread Starter
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Coctostan,

I tried both 32 and 40Hz cabinet tunings. The results were virtually identical, the delta being a 1dB gain at 43Hz. These results are in line with what LTD02 using Hornresp had predicted. I went with a 32Hz tuning because there was slightly less measured ripple overall.

I will finish out these cabinets ported at 32Hz. However that's because I am building these from scratch. If I were looking to improve a pair of factory La Scalas I would go the route of reducing the cabinet volume by 1/3rd.
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post #106 of 127 Old 03-19-2013, 09:46 AM
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Yes, rear porting a FLH is tricky. I'd guess that PWK did lots of trial and error.

The A7 is a midbass horn but so is the LaScala. The A7 doesn't give as much boost to the top end but has the benefits of not being folded and having a more even response. In room, an A7 is pretty flat. The Scala is tilted the wrong way even in room without cutting the top end significantly.

I was hoping to tweak the enclosure and tuning to see if it could be more effective. It could also be that this driver is far from optimal for this horn and rear port.
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post #107 of 127 Old 03-19-2013, 10:13 AM - Thread Starter
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Paul Klipsch was an amazing man that was well ahead of his time. I was lucky enough to meet him back in the 70's. It was at a CES show in Chicago. I was a young man totally fascinated, standing in front of a large Klipsch Pro Audio display. I must have had a smirky grin and dazed look about me. Paul walked up and just started talking. I remember him going into great detail as I asked question after question and he gave me thoughtful answers. I've been a 'PWK groupy' ever since.
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post #108 of 127 Old 03-19-2013, 11:57 AM
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interesting story carl.

"The A7 is a midbass horn..."

the horn is too short to load the bass. hoarn loading begins around 175hz and doesn't get to good loading (+6db) until around 275hz.

that is more of a midrange horn, but these are mostly semantics.

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post #109 of 127 Old 03-19-2013, 04:11 PM
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That is what makes the A7 great. I've modeled a modified version (150l tuned to 40-45hz) with a TD15M and its response has a nicely rounded hump response that should conjugate nicely in-room with a multi-sub or flanking sub configuration. It gives about a 6db boost over a similar vented TD15M until th lower end where it starts to converge. It is a happy medium between a direct radiating vented speaker and a more complete horn like the LaScala which is more efficient but only plays well down to 100-150hz causing you to either cross up in that range or give up all of the efficiency gained with EQ.

Ultimately, with today's drivers and amp power I see little reason to fold a horn that will play up to 800hz. I understand the nostalgia and it might be useful with a 2w SET amp but the fact is that, like most older things, it just doesn't stand up to modern technology.
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post #110 of 127 Old 03-19-2013, 04:50 PM
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i see what you are saying. not sure if i agree that the increase in sensitivity provided by folded horns is no longer useful though.

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post #111 of 127 Old 03-19-2013, 05:34 PM
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Quote:
Originally Posted by LTD02 View Post

i see what you are saying. not sure if i agree that the increase in sensitivity provided by folded horns is no longer useful though.

I may have overstated that it is useless but if I don't see how it is worth the downsides of a folded horn playing higher frequencies. There was a time when it was well worth it and that separated Klipsch from its competition. The fact is that it will probably be a waste of my time taking two TD15Ms per channel and putting them in small horns. It is already ridiculously sensitive. But I'm curious.
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post #112 of 127 Old 03-19-2013, 07:29 PM
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i know what you are saying mr. c.

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post #113 of 127 Old 03-20-2013, 04:35 AM
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I am still very curious to hear the differance between the Jubilee and direct radiator comparisons. Just curious on voicing mainly. I have always loved Klipsch designs but it has been sometime since I have heard one or the heritage products. I have plans for a bigger dual 15 heritage style but might try and build a La Scala for now. I prefer keeping wattage low if I can but maximum fun is still needed.

Either way great build and tests, thanks Carl.


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post #114 of 127 Old 03-20-2013, 08:29 AM
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Quote:
Originally Posted by Carl_Huff View Post

I think it unlikely that the differences are placement related. I have been diligent in my attempt to be consistent from session to session. I have been using the test setup as shown back in post #70. I have gaffers tape on the floor to mark where I put the mic stand between sessions and the loudspeaker cabinet is never moved. I am using an Earthworks M30 (with calibration file) and a USBPre microphone preamp for the measurements. The measurement mic is always pointed dead center of the cabinet at the same height, same distance.

These are not in 'living room' measurements. These are open space 'in garage' measurements. The cabinet is positioned near an open garage door so as to avoid room affects. The cabinet is sitting on a pile of 3/4 plywood raised roughly one foot off a concrete floor. I think that I'm pretty good and my results should be repeatable between sessions. Your thoughts??

Can I measure impedance? Yea, I have a DATS (Dayton Audio Test System) lying about somewhere.
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Interesting - somehow I missed that post.

There are a few things in the plots that don't correlate to the 1/2 space outdoor measurements I've performed on the Lascala bass bins over at Colter's place - namely the response below the ~100Hz horn cutoff is more of a plateau and doesn't have those dips at 35Hz and 50Hz. Basically a lot of the jaggedness seems to be coming from your measurement environment. You're also getting a floor bounce effect into the mic affecting stuff in the 100Hz to 200Hz region (where we see a peak and a dip it looks like).

That said, it sounds like you've done the due diligence in terms of comparative measures and the deltas you're seeing seem realistic. I'm just curious if you would draw the same conclusion if you saw those comparative measures in a more anechoic measurement? I don't know. I'm working from memory here and have never had the chance to play with the ported tricks. I personally put the microphone on the ground and tilt the speaker forward to bring the mic on-axis...and I usually measure at least 10ft away (to reduce the steepness of angle required). It looks like some of your garage is getting into the measurement is all.

Unfortunately I lost that old data to a harddrive that failed, otherwise I would totally post it.

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post #115 of 127 Old 03-20-2013, 09:09 AM - Thread Starter
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Mike,

So you think that I am getting some floor bounce that is causing some cancellation? Hmm ...

I've got some moving blankets that I could lay in front of the cab and take another set of measurements. If you and others think it to be worth my time I can do that this weekend. I invite feedback!

A few more details on the Dirac Live software that I have been using. A single Dirac Live plot is usually the result of taking 18 samples from 9 different positions. When I began this project I was moving the measurement microphone in a 3 x 3 pattern at a distance of 2 feet from the mouth of the cabinet. I called this my 'one meter measurement' because I was roughly taking into account the distance introduced by the fold of the horn. However after wearing myself out jumping up and down to move the measurement mic within an imaginary grid (I'm getting old ...) I took a set of 18 samples without moving the measurement mic, being careful to consistently place it dead center at that same 2 foot distance. Much to my surprise the resulting plot was essentially the same as when I laboriously moved about the microphone in an imaginary grid! The downside of my new technique is that normal passband ripple has the potential to become exaggerated as it will be found in every sample and might not have been if the microphone had been moved within a grid pattern. However my experience has shown that if this is happening the delta is typically not more than 1dB or so.

Another side affect of my new technique is to reduce the affects of the samples being normalized. Dirac Live normalizes the plot data to 1/12th octave resolution for readability purposes. If the data is exaggerated the ripple becomes 'less normalized' in the finish plot. You can see the affects of what I am describing by looking at the OmniMIC versus Dirac Live plots back in post #70.

Assuming that the participants here think it worth my time this weekend I will take two sets of measurements with moving blankets in place. Set #1 will be moving the measurement mic around in a 3 x 3 grid at the mouth of the cabinet and another set with the microphone in a fixed position centered as has been my habit as I have published on this thread.

The La SEOS cabinet is currently configured as 32Hz ported with a 2 x 2 foot by 1 inch thick poly foam sheet lining the inside of the dog house.
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post #116 of 127 Old 03-20-2013, 09:31 AM
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The moving blankets won't make any significant difference in the plot because the wavelengths are too big.

Why can't you fire out the garage and put the mic on the ground?

-Mike Bentz
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post #117 of 127 Old 03-20-2013, 09:51 AM - Thread Starter
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"Why can't you fire out the garage and put the mic on the ground?"

The idea of the moving blankets was about knocking down potential reflections 100Hz upwards since I repeatedly show notches in my plots.

The cabinet is firing out the front of the garage thru the open door. There is very little in front of the cab while being measured. The cab is in the front left corner and firing out into space at a 45 degree angle. Isn't putting the measurement microphone on a cement surface a bad idea? Are you saying that the boundary affect of the cement floor and driveway acting on the measurement microphone is a good thing? That's how Crown's boundary affect microphones work. Or am I missing something?

http://www.crownaudio.com/media/pdf/mics/127089.pdf

I need to think about this.
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post #118 of 127 Old 03-20-2013, 12:22 PM
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Carl, I believe Mike is referring to ground plane measurements: http://www.mh-audio.nl/Groundplane.asp

I'm not sure Dirac Live is going to give you what you want here. Typically you would splice a ground plane measurement for the bass with a gated measurement for the higher frequencies to get a good fullrange measurement when an anechoic chamber is not available.

It might be better to use OmniMic.
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post #119 of 127 Old 03-20-2013, 12:34 PM - Thread Starter
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Aah ...

Sometimes I can be very slow and thick headed. That makes more sense to me. Dirac Live has an automated gating mechanism built into it, altho I don't know enough about it to say that it would work reliably when used this way. As you point out Dirac Live was intended to be used to craft filters to optimize loudspeakers within a room. I'm already using the product in an unintended manner when I use it to measure the free field response of a loudspeaker.
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post #120 of 127 Old 03-21-2013, 11:35 AM
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I personally don't even bother with splicing two separate LF and HF measurements....you can get very good ground plane results all the way up to 20kHz if you're careful about the setup.

I've successfully performed all of the classic mic'ing techniques, but I find the ground plane to be by far the simplest and most consistent approach. The second you take the mic off the ground, now you've got a maximum gate window that is reflection free - and for good frequency resolution, we need the window to be as long as possible. Short windows are just as bad as smoothing filters when trying to implement EQ.

Btw, the reason I bring it up is two-fold. First, djk mentioned that everyone preferred the higher tune frequency - and you're going with the lower one. Second, those dips near the tune frequency could be due to the phase relationship between the port and the horn (since the sound isn't traveling the same distance for both paths). I'm also curious to see how much the damping material is affecting the Q of the tuning - PWK was adamantly against stuffing the inside of the cabinets because it lowers overall efficiency. I'm not saying I entirely agree with that blanket statement, but I do think there is some merit to understanding the potential tradeoffs. My experience is that the effect is small, but maybe horns are more sensitive? I dunno.

Anyways, just some thoughts to ponder - definitely not trying to criticize as I think the measurements thus far are very interesting to see. The magnitude of the difference is probably why Klipsch and Company never pursued the port (the extra complexity doesn't have a business justification).

Oh...the impedance plot will give us some insight as to the tuning of the driver too. The horn is playing a roll in the acoustic impedance seen by the driver, which is probably why changing the port frequency doesn't affect the resultant frequency response by that much. The benefit here would be in understanding where the cone excursion is at a minimum and trying to maximize that reduction with the EQ you employ...

-Mike Bentz
~It's all about compromise~
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