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Discussion Starter #81 (Edited)
Interesting graphs, wondering about how different wiring patterns might work, such as vertical vs horizontal pairs run as two separate channels. Then, if one were running two Devs (8 drivers) what happens with 2 lower & 2 upper drivers wired in parallel, then run in series with the second Dev. That would give all the drivers seeing the same relative position in the horn the same circuit. Wiring would be a little bit of fun, but honestly it wouldn't be that big of a deal, especially if they were located on the same wall.


Hmmm ... might need to get playing on a tuned PR box!


A funny observation from the pics: 2 pairs of drivers ordered at the same time ( I think) and yet 2 different "models"!


Lol, missed your post earlier. I see you had the same thought I did on splitting it into two channels.

As for wiring multiple cabs, run all drivers parallel for 1ohm. Then series two cabs, 2 ohm load. One channel of a nx3000d will run that nicely.
That leaves an open channel though, better add two more.
Four of these would be very serious output, might just give 8 VBSS a run for the $.

EDIT: As for the two different “models” of drivers, the CS1214’s were ordered from amazon, while the gx1200’s were sent by @gpmbc.

Chris
 

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WOW!! This is so cool! So far it seems it measured pretty well according to sim!
It defenitely need a comparison, so get it into your HT and compare to your mini dev ;)

Awsome work, thanks so much ;)
 

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Super impressive results so far Chris. I can't wait to hear and see more. I wish I could send you a virtual six pack.

When do you plan to bring it into your theater for a showdown with the mini's?
 

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Discussion Starter #86
Super impressive results so far Chris. I can't wait to hear and see more. I wish I could send you a virtual six pack.



When do you plan to bring it into your theater for a showdown with the mini's?

Thanks!

After the ground-plane measurements. So likely tomorrow.
It’ll be on 2500w in the theater, I don’t want to accidentally toast it before getting measurements. I have trouble resisting the urge to turn it up.

Chris
 

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How did you decide how much power to use in the measurements last night? If I am following the discussion, the different impedance produces different excursion levels, so there is risk in destroying the driver getting the most juice. So is it the total limit on power input (due to the variable load presented by each driver) the primary problem, and if so, how does one assess individual driver excursion? Simply, is there any way to assess how much output would be lost by running these as a single 4ohm load?


This issue has been quite interesting as I have tried to follow what Ricci has shared... things I had never pondered! I enjoy the intellectual stimulation as well as the practical enjoyment of these toys :)


And PLEASE, clarify if/when I am missing the boat. Horn subs = new ground for me!
 

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Discussion Starter #88 (Edited)
How did you decide how much power to use in the measurements last night? If I am following the discussion, the different impedance produces different excursion levels, so there is risk in destroying the driver getting the most juice. So is it the total limit on power input (due to the variable load presented by each driver) the primary problem, and if so, how does one assess individual driver excursion? Simply, is there any way to assess how much output would be lost by running these as a single 4ohm load?


This issue has been quite interesting as I have tried to follow what Ricci has shared... things I had never pondered! I enjoy the intellectual stimulation as well as the practical enjoyment of these toys :)


And PLEASE, clarify if/when I am missing the boat. Horn subs = new ground for me!


For close-mic measurements, its really irrelevant. I just turned it up until it was 10db under clipping the mic.
Close-mic takes so little power that its not possible to damage the drivers.

Now when I actually turned it up and demo’d it, there was full possibility of driver damage. I just slowly increased the level while listening for evidence of bottoming out.
This is in no way foolproof, but the BOSS crew has proven these drivers generally survive bottoming out. I decided to take the risk, and didn’t get burned THIS time.

My understanding is not that the drivers are taking additional power, but are exhibiting extra excursion due to the acoustic loading of the horn path. I could be completely off here, this is for @Ricci to answer.
I have detected no coil-smell. My fear is mechanical damage, not thermal.

The amp I’m using has no indication of power level. I’ll try to figure out voltage measurements during the ground-plane sweeps. I am worried about destroying the drivers during that process. And more so in the theater on 2500w.

Don’t get me wrong, I’m not trying to damage the drivers. I would greatly prefer them to survive. But the whole point of this experiment is to determine how this setup performs and if its worth building. I can’t claim to have proven anything without pushing it to the limits.

Horn subs are new ground for many people.
Multi driver horns are new for almost everyone. Tom Danley and Josh Ricci are the only two people I’m aware of that have significant real-world experience with these. This is why I’m grateful Josh is helping out with models and explanations on this one.

Chris
 

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Chris, thank you for your quick and thorough response. So what you are saying is localized low pressure areas that extend the driver beyond what the motor is actually driving. Okay, as Josh had talked about the impedance variance, I was thinking that one driver had lower impedance and therefore got more current.



When I graduated with my bachelors degree in ChE (again, back in the Fred & Barney days!) I went to work for Owens-Corning for about 8 months before I went off to med school. It was fascinating to see the interplay between physics & 'black magic' as so much about molten glass flow at 2500deg was purely learned by empiric observation. In one sense, that is how ALL engineering operates: observation => theory => application & measurement which gives us 'the science.' But real-world application never seems to play by the rules. I actually LOVE this as it points to our arrogance, as in each age man convinces himself he has got it all FIGURED OUT! Humility is in such short supply in this present narcissistic age. Ultimately many folks do realize the two basic rules of life: (1) There is a God, and (2) I am NOT Him ;)


So each year as I age I learn more, and recognize more of my own ignorance and shortcomings.
 

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Discussion Starter #90
Chris, thank you for your quick and thorough response. So what you are saying is localized low pressure areas that extend the driver beyond what the motor is actually driving. Okay, as Josh had talked about the impedance variance, I was thinking that one driver had lower impedance and therefore got more current.



When I graduated with my bachelors degree in ChE (again, back in the Fred & Barney days!) I went to work for Owens-Corning for about 8 months before I went off to med school. It was fascinating to see the interplay between physics & 'black magic' as so much about molten glass flow at 2500deg was purely learned by empiric observation. In one sense, that is how ALL engineering operates: observation => theory => application & measurement which gives us 'the science.' But real-world application never seems to play by the rules. I actually LOVE this as it points to our arrogance, as in each age man convinces himself he has got it all FIGURED OUT! Humility is in such short supply in this present narcissistic age. Ultimately many folks do realize the two basic rules of life: (1) There is a God, and (2) I am NOT Him ;)


So each year as I age I learn more, and recognize more of my own ignorance and shortcomings.


I hate to elaborate too much, as there is a good chance I have it totally wrong.
I believe that the acoustic loading of the horn path causes variable loading on the drivers at different points along the path, thus exhibiting as variable excursion.
The variable loading will show in the individual impedance curves, so It could well cause power delivery variation.
I don’t understand how parallel vs series wiring effects this, only thing that comes to mind is delay caused by the series connection.

So far, I have no evidence that this thing is playing by the model. I was definitely sending it enough power to bottom drivers. I also have no evidence that it ISN’T playing by the model, which is why I have visions of driver destruction.

I am a Mining Engineer by education, but did start out in EE. The highly theoretical nature of the program caused me to loose interest, my school had much less focus on Power Systems. Its been many years since I used any of it though, so I’m beyond rusty here.

Hey, I’m just supposed to be the buillder/tester here.

Chris
 

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I hate to elaborate too much, as there is a good chance I have it totally wrong.
I believe that the acoustic loading of the horn path causes variable loading on the drivers at different points along the path, thus exhibiting as variable excursion.
The variable loading will show in the individual impedance curves, so It could well cause power delivery variation.
I don’t understand how parallel vs series wiring effects this, only thing that comes to mind is delay caused by the series connection.

So far, I have no evidence that this thing is playing by the model. I was definitely sending it enough power to bottom drivers. I also have no evidence that it ISN’T playing by the model, which is why I have visions of driver destruction.

I am a Mining Engineer by education, but did start out in EE. The highly theoretical nature of the program caused me to loose interest, my school had much less focus on Power Systems. Its been many years since I used any of it though, so I’m beyond rusty here.

Hey, I’m just supposed to be the builder/tester here.

Chris

Interesting point about power in EE. I was in school during the 70s when they still had a lot of focus on that, but computers & solid state circuitry were taking on more importance. I hear that most EEs don't even understand what 3-phase power is!


This is really an interesting theoretical issue to understand, so I eagerly await the experts to show up (Josh, and perhaps TD himself. I poked around earlier, curious about Danley's educational background. Sounds to be OJT rather than university! Another Einstein, I suppose. Creative thinking and efforts to apply have yielded him a tremendous bit of knowledge. I would have loved watching the development and testing for the military sub (idea of using subsonics at high levels to induce significant anxiety; seems to work).


Okay, to the matter at hand: you mention using enough power to bottom the drivers. Is this just a seat-of-the-pants guestimate, or are there specific measurements you took? Can your measurement apparatus log voltage while measuring dB? Is there any capability to look at waveforms to measure distortion? Sorry, but you have stirred my intellectual curiosity! Perhaps you have built a bumblebee that flies despite what the design says :cool:


I eagerly await measurements, and would love to see max output along the frequency axis. Although I hope you can have long term use of this sub, feel free to blow up the drivers I bought if it furthers our knowledge:p.


As I have said, I am interested to see what these drivers could do in a PR box with HEAVY weights = low tuning. What are the ultimate performance levels we can get out of these cheap drivers with different designs, THAT is the question.
 

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Discussion Starter #92
Interesting point about power in EE. I was in school during the 70s when they still had a lot of focus on that, but computers & solid state circuitry were taking on more importance. I hear that most EEs don't even understand what 3-phase power is!


This is really an interesting theoretical issue to understand, so I eagerly await the experts to show up (Josh, and perhaps TD himself. I poked around earlier, curious about Danley's educational background. Sounds to be OJT rather than university! Another Einstein, I suppose. Creative thinking and efforts to apply have yielded him a tremendous bit of knowledge. I would have loved watching the development and testing for the military sub (idea of using subsonics at high levels to induce significant anxiety; seems to work).


Okay, to the matter at hand: you mention using enough power to bottom the drivers. Is this just a seat-of-the-pants guestimate, or are there specific measurements you took? Can your measurement apparatus log voltage while measuring dB? Is there any capability to look at waveforms to measure distortion? Sorry, but you have stirred my intellectual curiosity! Perhaps you have built a bumblebee that flies despite what the design says :cool:


I eagerly await measurements, and would love to see max output along the frequency axis. Although I hope you can have long term use of this sub, feel free to blow up the drivers I bought if it furthers our knowledge:p.


As I have said, I am interested to see what these drivers could do in a PR box with HEAVY weights = low tuning. What are the ultimate performance levels we can get out of these cheap drivers with different designs, THAT is the question.


I’ve been having a lazy day in the house. I’ll go get the ground plane measurements done as soon as I finish this post. Time to annoy the neighbors.

Enough power to bottom the drivers is just based on the output level shown in minidsp, and the input sensitivity and power ratings of the amp. I have no measurement data on that. I have no way to log voltage.

I have no idea how to measure distortion. I will look i to that one.

My plan for the ground plane is to make sweeps at increasing levels until something gives. If I hear mechanical noise from the drivers, output stops increasing, I run out of amp, or the drivers smoke.
I will be running a multimeter on the amp output, so that should give a good idea of wattage.

I certainly wouldn’t declare this thing a bumblebee yet. Josh’s models don’t indicate that it won’t work. They just indicate that maximum output will be less than the HR model, due to the undesirable excursion characteristics. Overall response shape remains generally unaffected. Thats why one of my questions to him is at what wattage the drivers should hit 15mm excursion. This should allow for a very good prediction of the cabinets output in this configuration.

At some point, buying more drivers becomes cheaper than trying to maximize output from a given number. With the jbl’s, that point is reached pretty quickly. The SLAPS are cheap enough themselves to be worth experimenting with though.

Chris
 

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Funny! I recall a few days ago when you were talking about 60s in SD and it was 40s in AL. Now we are back to NORMAL.


Thanks for the further info on measurements and such. So many interesting ideas start bouncing around, and KNOWLEDGE is always intriguing. As to your point about the cheap drivers simply being multiplied... yes, although the number of & size of necessary boxes becomes part of the equation. Complexity of build is the final variable, I suppose. What I am most curious about is the ultimate output and frequency response these cheap drivers can produce in different configurations. The first mention of the SLAPS was just one member here just randomly adding them to the box, and I don't think anybody loaded additional mass on them. I ordered 4 when Amazon had them for $40 (and they will drop the price when nobody buys them at $57!) and have 5kg of washers to play with.


Anyway, stay warm and entertain us! I would actually do well to STOP checking this thread ... I can spend far too much time reading and pondering :D
 

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Discussion Starter #96
Well, I have data. I’m not entirely sure what it means though.

Pretty pic:


The first sweeps were in 3db increments starting at 6v.
The final three sweeps are in 1db increments.
The final clean sweep showed 33v.
The final sweep showed 38v.

I will go back to the shop and get all the voltage numbers in a bit. I’m warming up inside now. Should have worn heavy boots.

The final sweep was a perfect storm of failures. The mic ran out of headroom and showed clipping. I heard mechanical distress from the drivers. I was unsure if the driver noises were indicative of bottoming out, or popping from signal/amplifier clipping.

It looks to me like the trouble area of the final sweep is below port tune. This also matched where I heard driver distress. I’m wondering if the protective HPF isn’t steep enough.
I would have adjusted the HPF and performed more sweeps, but it was starting to snow. This is bad for laptops and other electronics.

My multimeter reads RMS voltage. Should I use these readings to calculate input power, or do I need to multiply it by 1.414?

Chris
 

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Nice work!
 
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Discussion Starter #98
So, I spent some time analyzing the data. Something is not adding up. Either my voltage measurement and wattage calculation is way off, or I’m misinterpreting something in the models.

First off, a quick review of testing setup.

I wheeled the enclosure out in the driveway, about 20 feet from the shop. I placed the test cart 10ft or so behind it, due to mic and speaker wire lengths. This also put me close enough to listen for blatant driver distress. I set up my multimeter on the amplifier output, in 600v mode.

The microphone was placed 2m from the enclosure:


I ran 0-200hz sweeps in REW, and recorded the voltage to the nearest volt. I began running sweeps 3db apart, and switched to 1db as the levels got high. The final sweep had both audible driver distress or amp/signal clipping, and microphone clipping.

For calculations, I took the displayed voltage and multiplied by 1.414 for peak voltage. I then converted this number to wattage using the driver’s combined Re of 3.4.


Here is the result. Voltages are as-displayed by DMM, wattages are from above calculation.


The wattage on the final clean sweep is 640w, the problem sweep is 850w. These numbers seem low by HR model, but may match up with Josh’s AkAbak model.

For comparison purposes, I overlayed the final clean sweep with the HR 1000w simulation. I took 6db off the HR sim to convert from 1m to 2m mic distance.

Here is the sim using ChrisP and Josh’s Semi-Inductance data:


Here is the sim using JBL’s driver specs:


With those, It looks like this cab is performing right at the model.

Now the big question remaining: Which interpretation is correct? Is my crude voltage measurement technique heavily flawed? Am I missing something in how I compared the models?
@Ricci, or anyone else familiar with ground plane measurements, please help me out here. Or anyone in general who sees a flaw or error in my methodology or calculations.

Either way, I am quite pleased by the outcome of this experiment. This sub hits the simulated response very nicely. The remaining question is whether or not it is hindered by the undesirable variable excursion predicted by AkAbak.

I will incorporate this data into the original posts once the questions are resolved.

For those of you anxious for the head-to-head, sorry. I chose not to attempt to blow this sub, with a side-by-side showdown, until the ground-plane is officially complete. It will happen, but not yet.

Chris
 

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Discussion Starter #99
I was going to add a second terminal cup and retry the sweeps with the woofers wired parallel on two separate identical channels, but its still snowing today.

Chris
 

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Are you going to do sweeps indoors? I want to see if the response flattens out without any EQ or BEQ.
 
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