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post #151 of 446 Old 02-11-2020, 10:24 AM
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I think this thread has become one of my favourites in a long time Awsome work guys 🤓😜
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post #152 of 446 Old 02-11-2020, 11:11 AM - Thread Starter
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EXPERIMENTAL Quad JBL Devastator Build

Quote:
Originally Posted by Ricci View Post

Also you are nuts for dragging all this gear out in the snow and cold! I was being half sarcastic earlier when I asked if this was fun...It can also be very frustrating and a lot of work!
Gotta deal with the conditions I have. You’d think I’d be smart enough to unload the tools from the amp cart, gotta be an extra 75lbs on there, lol.

I was responding with sarcasm as well. Have to have some fun with the thread. Along with the fun in the cold

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The cold will tend to slow down the speed of sound, boost the SPL some and stiffen the speaker suspensions compared to normal room temps. Humidity and barometric pressure also will affect the measurements.
Yup. Again, just working with the conditions I’ve got.


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Originally Posted by Ricci View Post

I use the voltage corresponding to 100w nominal into the nominal impedance because it is well accepted as the standard voltages for sensitivity. I use 10X the voltage in order to get better SNR and also because subs get used harder than any other speaker usually so it's more representative of use than 1w nominal.



Don't worry about labeling things with power or testing at a certain power IMO. I never do. It's voltage that matters. Power is not constant at all and varies with impedance and frequency. Voltage on the other hand is constant from the amplifier. It takes a while to get this stuck in your head, since everything is marketed by power ratings and it's deeply ingrained in most of us. Power still matters of course but it's much more complicated than a single number.



If you want to calculate how much maximum power the speaker is receiving just use the dcr if you don't have an impedance measurement. It's close enough. If you have the impedance curve just use the in bandwidth minimum.
Yeah, my power fixation is just the way most people (myself included) think about this stuff. Plus, I know my amp is rated at 1000w, and power doubling every 3db makes the calc really easy.

Ok, back to using Re instead of nominal for power calcs.



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Originally Posted by Ricci View Post
Speaking of which an impedance curve would give a lot of additional information. You already seem to have a good grasp of REW and you seem to have everything you need. Just takes a bit of wire an amp and a resistor if you don't have something like a DATS. You do have to be careful with the level to not fry your soundcard with the amp. This is something that could be done inside at low volume with 1 volt or less into the sub.
I was reading on this one the other day, but got sidetracked with other measurements. I’ll have to order some resistors. Wait, does radioshack still sell components? Maybe I can grab some today. Apparently need 1% though.

Rew’s article talks about using diodes to protect sound card when using amp. Necessary? Or just use dmm to check voltage before hooking to soundcard?

Looks like a 33ohm resistor?

Article: https://www.roomeqwizard.com/help/he...asurement.html


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Originally Posted by Ricci View Post

Background noise is much higher in this set. Any time you see random bumps and dips in the measurements that do not repeat in other measurements it is noise. Sometimes it DOES repeat too like a 60Hz ground hum for example, but if it doesn't repeat between measurements that's a dead giveaway.
Right, it was getting windier on this set.



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Originally Posted by Ricci View Post

That is a BIG difference. Could be an imbalance in the amp channels, or the amp current limiting a lot more into the impedance minimums when it wasn't fully bridged. This'd be my guess. Other thoughts are some output compression going on due to drivers getting some heat buildup in the coils, mismatched excursion issue, etc but none of this would make that big of a difference.
Probably not thermal. The hatch was off between sweep sets in the cold while I rewired. Both sweep sets had an equal number of sweeps, at equal power (roughly)





Quote:
Originally Posted by Ricci View Post
I'm with you on this. I can see a bit extra from baffle effects and potentially a bit more from regular old variations in gear and the SPL calibration and another boost from the cold temperature and denser air. Parts of the graph show 6 to 8dB of difference though. That much of a difference is hard to account for.



How far away are you from buildings and other large objects?
At least 20ft from shop, there is a tractor on one side and some railroad ties on the other that are a bit closer.
I can push the mic down to the edge of the road and take the sub 10 feet or so farther away.

Pic kinda shows situation:


Tractor is farther away than it appears, about even with test cart and 10ft+ sideways.



Quote:
Originally Posted by Ricci View Post
Remember when MTG90 brought up the 90Hz peak in output and we were discussing it boosting the 2nd and 3rd harmonics? The orange bump at 30Hz is the 3rd harmonic getting boosted by the output at 90Hz and the large driver excursion in this range. The 2nd harmonic of 45Hz is being boosted by 90Hz, it is the red line. As expected.



Distortion is getting pretty high on these measurements. I don't think there's too much left in the tank.

Yup, I caught the boosted 3rd harmonic. Didn’t think about the second

Yeah, these measurements were at “1000w”, closer to 1200w by Re. So thats the end of this setup by model anyway.

Thanks again,
Chris

Last edited by a77cj7; 02-11-2020 at 11:19 AM.
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post #153 of 446 Old 02-11-2020, 11:11 AM - Thread Starter
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Quote:
Originally Posted by mtg90 View Post
For the distortion graphs in REW you can go into controls and check Plot Normalized to Fundamental and make sure Distortion Figures: Percentage and that will graph the distortion on a percentage scale which is much easier to interpret. Also be sure to make the Y axis limits something like 0.01 to 200%.


Will do, thanks.

Chris
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post #154 of 446 Old 02-11-2020, 11:16 AM - Thread Starter
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One additional point on the distortion sweeps I forgot:

During the high level sweeps, including the distortion sweeps, the enclosure rattled against the plywood at certain frequencies. Not sure if/how this affected results

I’ll get an old blanket or towel down in the future.

Chris
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post #155 of 446 Old 02-11-2020, 12:07 PM
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ACK! Edited as I can't even get my thoughts out right...


Chris, this is what I had suggested before: wiring the two drivers in series that were both seeing the same pressure gradient within the horn. Their impedance should track closely and so both should be similarly loaded. Now the other two drivers will likely have slightly more or less impedance at a given freq & spl, so there will be different current flowing from the other pair. Therefore (and this is simply from ZERO KNOWLEDGE, simply my hypothesis in thinking on electro-mechanical properties) slight differences in power consumption between upper and lower drivers.


As I type this, it further occurs that the pressure change inducing impedance change is going to either increase or decrease 'mechanical resistance to excursion'. So, for example, a higher pressure in one driver presents a higher load to the amplifier, yes? Using my utter lack of background in acoustical engineering principles, it might seem that this would induce differences in excursions, top-to-bottom... This is where drivers with a second vc (as used in servo drivers) would be interesting, monitoring what is happening mechanically.


So, to be silly for a moment we need a bunch of pressure transducers capable of VERY fast response times, a means of monitoring excursion of each driver, and realtime electrical data for each driver. Then we could really get a handle on it.


Such intellectual ... uh ... 'self-pleasuring' ... is quite appealing to me now. Back as an engineering undergrad, I never had any sort of interest in actually thinking through problems relating to my own interests. Girls & partying was the order of the day! Although I WAS into high end stereo gear, and for a time my roommate had what was probably the finest high end audio system on campus. I just didn't get "research" for the sake of FUN things ... other than perhaps a bit of experimentation in the chemistry lab. It is truly a blessing to have guys like you, RedFive, Ricci, LTD02, and others who like to think AND try stuff out.


At some point I will commit to doing a Quad JBL + 2xSLAPS-M12 box and measuring the results. What I am most interested in is adding mass to the PRs and reporting on the changing frequency response. I would appreciate some guidance when I get to the measuring side of things. I have a Umik and MiniDSP-HD, so I should be able to contribute something.


Okay, back to you guys who actually know what you are talking about, I will cease my speculations

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post #156 of 446 Old 02-11-2020, 12:08 PM
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Quote:
Originally Posted by a77cj7 View Post
One additional point on the distortion sweeps I forgot:

During the high level sweeps, including the distortion sweeps, the enclosure rattled against the plywood at certain frequencies. Not sure if/how this affected results

I’ll get an old blanket or towel down in the future.

Chris
I've noticed rattles often present themselves in the data as a narrow spike of a bunch of high order harmonics at the frequency the rattles occurs. I don't really see that in your measurements but it may be just low enough in level to be hiding out of view. Either way eliminating that rattle will give you cleaner data.
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post #157 of 446 Old 02-11-2020, 12:52 PM
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Quote:
Originally Posted by a77cj7 View Post
Can you verify this for me?
Confirmed.

Quote:
Originally Posted by a77cj7 View Post
First, lets make sure we are using the same terminology. I use top referring to how the cabinet sits. Closed end of horn is top.
Correct.

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Originally Posted by a77cj7 View Post
How I have it wired for series-parallel now: the top driver series to the one directly below it. The two resulting vertical pairs paralleled. I believe you’re saying this is Uneven.
Correct. According to Akabak this results in uneven excursion.

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Originally Posted by a77cj7 View Post
What you’re saying: Top two series, bottom two series, results parallel = Even.
Yup. According to Akabak this results in nearly equal excursion.

The reason I find this interesting is I modeled it in the MAUL when I was going to use 21Ipal's and since those are 1 ohm each you are pretty much forced to wire those in series. I may have been able to use them in parallel but I went another direction and never really thought about it further. I think the excursion difference was more exaggerated in that case because the spacing on 21" drivers is much larger. I'd sold my DTS-10's by then and I never investigated with those, but I've heard of a few people killing only one driver out of the cab. I think in the DTS-10 case it may not have been so bad due to a really tight spacing on the drivers. In the case of this 4X12 sub according to the model I'd advise against wiring in ways that cause it but it may be a total nothing burger anyway. I've never seen anybody investigate it really.

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Originally Posted by a77cj7 View Post
Standard compression sweep stuff, sure. Super easy since I know the db changes. Do you want me to use the 12.5w and 1000w sweeps, or start a little higher to avoid noise issues?
The lowest volume would be best but sometimes those are noisy so it's a judgment call.

The way I measure for output compression is I take multiple sweeps at the lowest 2 or 3 output levels. I'll usually do 5 or 6 at the starting level, 3 or 4 at the next highest and 2 or three at the next. I'll average these to get a clearer measurement out of the background noise. It helps particularly below 20Hz. I'll remove any measurements that are clearly "bad" if there are outliers that don't match the general trend of the rest and are contaminated with noise. There isn't enough power at these levels to cause any real heating in the drivers so it doesn't hurt to run a bunch in a row. I usually consider the point where real heating can occur to be at the nominal 100w level. Past that it is single measurements but the level is usually high enough to get a good SNR anyway. Also I'll keep the mic at 2 meters up to the point that it runs out of headroom. This is also for SNR purposes. I'll move back to a further 4 or 8m distance only if required for mic headroom and use the inverse square law to scale it back to match the other measurements from a shorter distance if required. I always use a 1M length measurement in REW or whatever is longest in the software I'm using. This helps out with noise rejection too.

It takes longer to do it like this with the long measurements and many redundant low volume measurements but it is worth it later on. In a quieter environment like a house, or building this is overkill usually but outside with wind, road noise and the like it really helps clean things up.


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Originally Posted by a77cj7 View Post
Sure, I’ll try.
I’ve had issues with trying to use REW delay before. Don’t you need a timing reference to properly measure this? I was trying to use it to integrate sealed and ported in my theater, didn’t work out.
Hmm. I always have a loopback timing reference. You can try to estimate IR delay.
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Last edited by Ricci; 02-11-2020 at 01:01 PM.
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post #158 of 446 Old 02-11-2020, 01:04 PM - Thread Starter
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Originally Posted by MTBDOC View Post
ACK! Edited as I can't even get my thoughts out right...
Nice timing, you fixed it after I read it, but before I quoted it.

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Originally Posted by MTBDOC View Post
Chris, this is what I had suggested before: wiring the two drivers in series that were both seeing the same pressure gradient within the horn. Their impedance should track closely and so both should be similarly loaded. Now the other two drivers will likely have slightly more or less impedance at a given freq & spl, so there will be different current flowing from the other pair. Therefore (and this is simply from ZERO KNOWLEDGE, simply my hypothesis in thinking on electro-mechanical properties) slight differences in power consumption between upper and lower drivers.
I believe you’re correct here.

My original thinking on the wiring involved making series pairs that would act identically, thus drawing the same power.

I missed a key point though, that all drivers parallel removed the variable distortion problem.
This tells us that having drivers at different points of the horn in parallel is not a problem.

So what happens if we series the drivers at the same point in the path? Since they are experiencing the same acoustic loading, they will act as one driver with twice the impedance.

Then, they can be paralleled without experiencing the variable excursion problem. You end up with the same situation as the narrow 2-driver version discussed earlier. Problem solved, at a nice 4ohm final load.

I do believe drivers at different points in the path will be demonstrating different impedance curves, and therefor absorbing different amounts of power. The difference shouldn’t be enough to put us anywhere near thermal failure, these are robust drivers and relatively low powers.

Looks like we just opened up the “magic square” version of horn design. @Red Five , better get the 3x3 BMD design rolling.


Quote:
Originally Posted by MTBDOC View Post
As I type this, it further occurs that the pressure change inducing impedance change is going to either increase or decrease 'mechanical resistance to excursion'. So, for example, a higher pressure in one driver presents a higher load to the amplifier, yes? Using my utter lack of background in acoustical engineering principles, it might seem that this would induce differences in excursions, top-to-bottom... This is where drivers with a second vc (as used in servo drivers) would be interesting, monitoring what is happening mechanically.
Remember, the amp supplies constant voltage at a certain frequency. The acoustic loading if the drivers will affect their impedance curves, causing them to absorb variable amounts of power. This is way above my ability to visualize to get any more specific.

Quote:
Originally Posted by MTBDOC View Post
So, to be silly for a moment we need a bunch of pressure transducers capable of VERY fast response times, a means of monitoring excursion of each driver, and realtime electrical data for each driver. Then we could really get a handle on it.
Yup, high speed cameras and scales should work nicely for excursion measurements. Lets go all myth-busters on this one and use a ridiculous amount and cost of equipment to measure a $300 subwoofer

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Originally Posted by MTBDOC View Post
Such intellectual ... uh ... 'self-pleasuring' ... is quite appealing to me now. Back as an engineering undergrad, I never had any sort of interest in actually thinking through problems relating to my own interests. Girls & partying was the order of the day! Although I WAS into high end stereo gear, and for a time my roommate had what was probably the finest high end audio system on campus. I just didn't get "research" for the sake of FUN things ... other than perhaps a bit of experimentation in the chemistry lab. It is truly a blessing to have guys like you, RedFive, Ricci, LTD02, and others who like to think AND try stuff out.
I got tired of partying after my first two years of college. (Really after the first one) I enjoyed audio, but didn’t have the budget to play with it much.
I mostly got into junkyard hotrodding instead. We rented a house with a decent sized detached garage. This caused me to just miss having a 3.5 GPA, but I had plenty more fun in the process. Was pushing 350hp from a NA ford 302 with no aftermarket parts besides valve springs. Was trying to mess with boost, but thats very hard to do without aftermarket controls.

Quote:
Originally Posted by MTBDOC View Post
At some point I will commit to doing a Quad JBL + 2xSLAPS-M12 box and measuring the results. What I am most interested in is adding mass to the PRs and reporting on the changing frequency response. I would appreciate some guidance when I get to the measuring side of things. I have a Umik and MiniDSP-HD, so I should be able to contribute something.
This thread has a bit of measurement information, lol. I’ve certainly learned way more than expected.
Feel free to pm me questions, or just start a thread when you get there.


Quote:
Originally Posted by MTBDOC View Post
Okay, back to you guys who actually know what you are talking about, I will cease my speculations
I’m not sure that anyone here “knows what they’re talking about” with multi driver horns, other than Josh anyway. And judging by the variable excursion modeling, even he doesn’t deal with it much. Gotta love playing with abstract designs.

Chris
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post #159 of 446 Old 02-11-2020, 01:18 PM - Thread Starter
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EXPERIMENTAL Quad JBL Devastator Build

Quote:
Originally Posted by Ricci View Post

The reason I find this interesting is I modeled it in the MAUL when I was going to use 21Ipal's and since those are 1 ohm each you are pretty much forced to wire those in series. I may have been able to use them in parallel but I went another direction and never really thought about it further. I think the excursion difference was more exaggerated in that case because the spacing on 21" drivers is much larger. I'd sold my DTS-10's by then and I never investigated with those, but I've heard of a few people killing only one driver out of the cab. I think in the DTS-10 case it may not have been so bad due to a really tight spacing on the drivers. In the case of this 4X12 sub according to the model I'd advise against wiring in ways that cause it but it may be a total nothing burger anyway. I've never seen anybody investigate it really.
Hey, even you might learn something out of this one, lol.
Time for a NSW6021 MAUL?

I will do my best to investigate by performing sweeps at the corrected wiring and comparing.




Quote:
Originally Posted by Ricci View Post
The lowest volume would be best but sometimes those are noisy so it's a judgment call.



The way I measure for output compression is I take multiple sweeps at the lowest 2 or 3 output levels. I'll usually do 5 or 6 at the starting level, 3 or 4 at the next highest and 2 or three at the next. I'll average these to get a clearer measurement out of the background noise. It helps particularly below 20Hz. I'll remove any measurements that are clearly "bad" if there are outliers that don't match the general trend of the rest and are contaminated with noise. There isn't enough power at these levels to cause any real heating in the drivers so it doesn't hurt to run a bunch in a row. I usually consider the point where real heating can occur to be at the nominal 100w level. Past that it is single measurements but the level is usually high enough to get a good SNR anyway. Also I'll keep the mic at 2 meters up to the point that it runs out of headroom. This is also for SNR purposes. I'll move back to a further 4 or 8m distance only if required for mic headroom and use the inverse square law to scale it back to match the other measurements from a shorter distance if required. I always use a 1M length measurement in REW or whatever is longest in the software I'm using. This helps out with noise rejection too.



It takes longer to do it like this with the long measurements and many redundant low volume measurements but it is worth it later on. In a quieter environment like a house, or building this is overkill usually but outside with wind, road noise and the like it really helps clean things up.
Ok, will do. Sweeps at 2m until clip, then move back and adjust.







Quote:
Originally Posted by Ricci View Post

Hmm. I always have a loopback timing reference. You can try to estimate IR delay.
I got lost last time I tried digging in to this one. Then again, I was also looking at rePhase and FIR filters and other things over my head.

Thanks,
Chris

Last edited by a77cj7; 02-11-2020 at 02:18 PM.
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post #160 of 446 Old 02-11-2020, 01:30 PM
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Do not even bring up the magic square, that thing would get so wide and completely impossible to handle
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This is the way...
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post #161 of 446 Old 02-11-2020, 01:31 PM
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You can measure cone excursion rather easy and cheap using Viberry

https://www.avsforum.com/forum/113-s...l#post58615278
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post #162 of 446 Old 02-11-2020, 07:13 PM
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That's a beautiful pic! My lazy butt would place that unpainted enclosure in my mancave as is.

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post #163 of 446 Old 02-11-2020, 07:59 PM
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Ohh, BTW: when all the serious stuff is done, could you try plugging a port and measure again ?

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post #164 of 446 Old 02-11-2020, 09:28 PM
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Guys... remember the level of effort required to haul all that sh...tuff outside and do the testing. I'm all for data, just remember it's easier to ask someone else to do it than to do it yourself so....

Keep up the good work Chris.

Any subjective input on how she sounds?

Chris
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EXPERIMENTAL Quad JBL Devastator Build

Sorry if the writeup is rambling tonight, I’m really tired.

Popped the hatch and rewired to Josh’s instructions:


Deja vu all over again:


I set it up as far from the shop as possible:


I used the Re of 3.4ohm to calculate wattages today. For the baseline 100w, that is 18.44v.


I measured at 2m until mic clipping, then switched to 4m. The 4m isn’t as clean.

Sweeps:

EDIT: Corrected graph added.


Here’s the compression comparison. I followed Josh’s advice and averaged 5 sweeps at 12.5w.


I did take distortion sweeps, but haven’t even looked at that data yet.

For comparison purposes, I rewired the cabinet incorrectly, as I had it before, and reran all measurements.

The wind picked up on me, so these measurements aren’t quite as clean.

Compression:


Now, lets compare the two wiring configurations at 1000w, along with the simulations.

The two wiring configurations show a very close match, with the correct configuration gaining about 1db in the high excursion area. Its also up about the same at the peak.
The models are still way low, though the shape looks pretty good.

Lets take a look at the 100w data next. While making this comparison, I made hornresp models at 18.44v for consistency with my measurements. Once I imported them, I got a surprise:

Now there’s a pretty match to the models.
It looks like I have a 6db discrepancy.
Either A. My mic calibration is 6db high, which doesn’t explain why it clips at about the right level.
B. My mic is set down 6db, I’ll open it up and check the dip switches.
Or C. My hornresp is calculating at 2m. I don’t even know if this is possible, I didn’t see a distance setting while looking around quickly.

The two sweeps match nicely again, with the correct wiring configuration gaining a decibel at high excursion, and at the peak.

I will redo the 1000w comparison with the 6db offset.

I still need to look at the distortion sweeps.
@Ricci , I have all the sweeps saved. Pm me your email if you want me to send them to you.

Chris
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post #166 of 446 Old 02-11-2020, 10:04 PM - Thread Starter
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Originally Posted by Chris Popovich View Post
Guys... remember the level of effort required to haul all that sh...tuff outside and do the testing. I'm all for data, just remember it's easier to ask someone else to do it than to do it yourself so....



Keep up the good work Chris.



Any subjective input on how she sounds?



Chris
Ehh, I volunteered to test this concept, I’m trying to get it done right. It would have gone much faster if I had any idea how to do ground-plane correctly. A huge thanks to Josh for getting me on-track with minimal revisions.

As for the subjective... I’ve been having too much “fun” with the ground plane data struggle. I think I got it tonight though, I’m hoping that I can call it.

Its looking like blizzard conditions tomorrow, so good timing.

I’ll try to move it in to the theater tomorrow and do some comparison sweeps with my 18ds mini, and some subjective testing. That testing sounds much more enjoyable.

Chris
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post #167 of 446 Old 02-11-2020, 10:09 PM - Thread Starter
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Originally Posted by BP1Fanatic View Post
That's a beautiful pic! My lazy butt would place that unpainted enclosure in my mancave as is.

It looks better from a distance like that, lol. It was a quick build, I didn’t get overly careful on the cosmetic details. One of the horn rails has a decent warp to it, drives me nuts every time I look that close.
Its starting to show some wear from being carted around and opened constantly too. This is why I can’t have nice things.

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post #168 of 446 Old 02-11-2020, 10:12 PM - Thread Starter
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Ohh, BTW: when all the serious stuff is done, could you try plugging a port and measure again ?


Yeah, I can do that. Its already dropping like a rock on the low end though. I’m not sure this one wants a lower tune.

Chris
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post #169 of 446 Old 02-12-2020, 07:34 AM
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Ehh, I volunteered to test this concept, I’m trying to get it done right. It would have gone much faster if I had any idea how to do ground-plane correctly. A huge thanks to Josh for getting me on-track with minimal revisions.

As for the subjective... I’ve been having too much “fun” with the ground plane data struggle. I think I got it tonight though, I’m hoping that I can call it.

Its looking like blizzard conditions tomorrow, so good timing.

I’ll try to move it in to the theater tomorrow and do some comparison sweeps with my 18ds mini, and some subjective testing. That testing sounds much more enjoyable.

Chris
I'd say you're good man. Take a break. You're starting to make me feel like I'm lazy and that never happens.
The newest measurements look clean to me. Anything else like: Impedance, plugging ports, maybe listening to the damn thing, could be done inside at a later date.
I'll PM my email.

I keep meaning to bring this up and forgetting to...How close in performance are the 2 different JBL drivers supposed to be? I thought they were cosmetically different but otherwise the same. In that last picture it looks like the motors are different.
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post #170 of 446 Old 02-12-2020, 07:41 AM
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^^^ Same specs, just different labels and dustcaps:


Dual AVR 13.1.8 SWAtmos - Atmos 13.1.8/DTS X 9.1.8/Auro 3D 13.1 - Denon AVCX8500H+AVRX7200WA - Klipsch+KEF - 4xSI18" - 12x12" w/6xSLAPS M12 VNF - 4x12"HB+2x18"CLHB - 6x Crowsons - 4xBK-LFE - 2x12"BB - 2x "4DX" fans- 6xNU6K - Minidsp 10x10HD-Vertex2-Oppo UDP203-XB1X-ATV4K-JVC RS600-Dreamscreen V2 120"-Samsung QE82Q60.
>>>>Nalleh’s HT<<<<
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post #171 of 446 Old 02-12-2020, 07:48 AM - Thread Starter
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Originally Posted by Ricci View Post
I'd say you're good man. Take a break. You're starting to make me feel like I'm lazy and that never happens.

The newest measurements look clean to me. Anything else like: Impedance, plugging ports, maybe listening to the damn thing, could be done inside at a later date.

I'll PM my email.
Lol, but I’ve got a submax v3 and an Alpha Devastator I want to build this weekend, so I can try out my NSW6021’s. I’m trying to get this wrapped up first

Any thoughts on the 6db discrepancy?


Quote:
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I keep meaning to bring this up and forgetting to...How close in performance are the 2 different JBL drivers supposed to be? I thought they were cosmetically different but otherwise the same. In that last picture it looks like the motors are different.

They are the same driver with some different cosmetics. In the pic, the stickers are different colors, and one motor has black paint, the other is bright metal.
@Chris Popovich has tested all three variations and reports that they test the same.

Chris
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post #172 of 446 Old 02-12-2020, 07:54 AM
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Lol, but I’ve got a submax v3 and an Alpha Devastator I want to build this weekend, so I can try out my NSW6021’s. I’m trying to get this wrapped up first

Any thoughts on the 6db discrepancy?

I'm supposed to be working on the print for another sub I've been putting off for months but I keep ending up here. Haha.

Not yet. Maybe looking at the measurements will give me ideas. The 18.4v sweeps lined up correctly but everything else was 6dB too high? Do I have that right? Not sure why one would lineup correctly and yet the rest don't.



Quote:
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They are the same driver with some different cosmetics. In the pic, the stickers are different colors, and one motor has black paint, the other is bright metal.
@Chris Popovich has tested all three variations and reports that they test the same.

Chris
Ok just checking.
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post #173 of 446 Old 02-12-2020, 08:13 AM - Thread Starter
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EXPERIMENTAL Quad JBL Devastator Build

Quote:
Originally Posted by Ricci View Post
I'm supposed to be working on the print for another sub I've been putting off for months but I keep ending up here. Haha.



Not yet. Maybe looking at the measurements will give me ideas. The 18.4v sweeps lined up correctly but everything else was 6dB too high? Do I have that right? Not sure why one would lineup correctly and yet the rest don't.


Again, thanks for all the help. Its greatly appreciated.

No, the 18.4v sweep is just where I caught it, by bringing in HR sims also made at 18.4v.

To match the data up, I should have to reduce the hornresp model by 6db to match the 2m measurement distance used for the sweeps.
However, the graph I posted shows the data with no offsets. I believe this indicates a 6db discrepancy.

I plan to bump the sims +6db on the 1000w sweeps, again that should match up. I was just past-tired when I discovered it last night.

Do you know if it’s possible that hr is calculating at 2m, and/or whether the distance can be changed?

Chris
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post #174 of 446 Old 02-12-2020, 10:15 AM
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Hey Josh, are you going to add this build to the data-bass?

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At the risk of continuing a tangent...

Quote:
Originally Posted by MTBDOC View Post
A few decades ago when generic drugs were first being allowed into the US market, I was absolutely STUNNED when I learned the standard - that for a generic to "pass" then:


  • 70% of the pills sampled had to have ...
  • 70-130% of the potency of the branded drug
Think about that, 30% didn't even have to meet ANY sort of standard, and the remaining 70% only had to be in a tremendously broad range! You see, my friends, this is what happens with an ever expanding bureaucracy. It becomes far more cost-effective for pharmaceutical manufacturers to spend money lobbying for poor standards rather than for R&D and manufacturing optimization . I was an engineer before going to med school (in the days when Fred & Barney were still babysitting Pebbles & Bam-Bam) and worked in process control. There is no excuse for such lax standards for human meds, but that's the state of it!
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Wow, those do seem to be very loose specifications.

From my very limited knowledge of medications, don’t many work based on continuous dosing and latent level in the system?
In a word, yes.

Speaking generally, the key factor in medication efficacy is maintaining the proper levels of the drug in your system, which is only peripherally related to the amount of the drug in the drug itself. Things like differences in bodyweight, absorption, (for lack of a better word) "tolerance", and etc. are all involved factors. It's why they tell you that it's important to remember to take each dose of a medication, and to take them on a regular schedule.

While there are of course exceptions, most medications are not prescribed at levels where an amount as small as a double dose would result in an overdose, or where missing a single dose would result in dangerously low levels of the medication in the patient's system. Both missing doses and accidentally doubling doses (e.g. forgetting that you already took today's pill, and taking it again) are frequent occurrences in drug regimens.

I mean, think about it — for a headache you can take two (200mg) Ibuprofen... or three, or four, for a dosing range of 600mg ±33%. And you can safely take them "every 4-6 hours", for a consumption rate of 600mg / 5h ±20%. That same recommended dosage holds for all adults, whether their body weight is 120# or 300#, although it will generally result in measurably higher levels of medication in the 120# patient's system.

Safety information for ibuprofen only recommends against exceeding 3200mg/DAY. How you get there isn't really a concern, you'll be fine if you stay under those levels. (Or even if you exceed them, realistically, as long as it's not by too much or too frequently — the safety standards are of course established with an abundance of caution.)

All of which is to say, though it doesn't seem like it, ±30% potency per individual pill is pretty insignificant in the grand scheme of things. Medication standards are based on of human biological, not mechanical, tolerances, and we're pretty infinitely varied.

Now, you want to hear something really unsettling? As I learned from a friend who works in the food safety industry, the FDA maintains a set of cleanliness standards for food products in which they set contamination levels that require, for instance:
  • An average of less than 400 insect fragments per 50 grams of ground cinnamon
  • An average of less than 11 rodent hairs per 50 grams of ground cinnamon
  • No more than 20 whole insects per 100-pound bag of shelled peanuts
  • An average of no more than 5 mg of rodent poop per pound of sesame seeds

etc, etc, etc. ad nauseam, all codified in the FDA's gross "Food Defect Levels Handbook"

While we'd of course like to think that the standard should be "ABSOLUTELY NO MOUSE TURDS AT ALL IN MY FOOD!!!!", realistically our food comes from nature, and into every life a little feces will fall. Eating the stray bug part or rodent dropping won't do you any harm, especially if you don't know about it, whereas standards that required food be 100% free of contaminants would be completely unrealistic and impossible to meet.

Armed with this knowledge, I have decided that my personal take on it is: The less I know, the better.
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post #176 of 446 Old 02-12-2020, 03:30 PM
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People would freak if they knew what was all in their packaged hotdogs, hamburgers, and sausages!

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EXPERIMENTAL Quad JBL Devastator Build

Teaser pic: The Quad heads inside.

Glad I finished the ground-plane testing last night. Current conditions are... unfavorable.

On another note, I have discovered the capacity of my door:


Chris
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post #178 of 446 Old 02-12-2020, 05:33 PM
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On another note, I have discovered the capacity of my door:


Chris



Time for a door upgrade!



https://www.homedepot.com/p/Steves-S...4ILH/205486625

Ask your doctor if DIY is right for you. Side effects of DIY may include anxiety, elevated blood pressure, lightheadedness, rapid heartbeat, skeletal muscle flaccidity, euphoria, psychological dependence, insomnia, confusion, blurred vision, impulsivity, uncontrolled or repeated movements.
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post #179 of 446 Old 02-12-2020, 05:42 PM - Thread Starter
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Wouldn’t help, that entryway is too narrow and has a 90* corner.

Luckily I have a sliding glass door with a straight shot in. Submax will have to come in that way.

Chris
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post #180 of 446 Old 02-12-2020, 07:26 PM - Thread Starter
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@Ricci

I’ve been trying to diagnose/verify my mic calibration.

Popped the umik apart, verified dip switches are set for 0db.

Got out my old dayton imm-6 iphone mic. Levels displayed are WAY off.

Tried some iphone spl apps, waste of time as expected.

Gave up, and ordered a cross-spectrum calibrated cm-140 spl meter. I probably should have one anyway.

Chris
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