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post #391 of 448 Old 06-13-2011, 05:28 PM
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That is an interesting moving aberration. One of the joys of measurements.

The same area is still off, if is just off to a different degree. The "N" shape is still there, it has just moved around a little.

Were the first measurements done on virgin drivers? Did you pull the parameters on them first?


I'm looking forward to seeing the full workup on these, and the other horns.
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post #392 of 448 Old 06-13-2011, 05:56 PM
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How about higher Qe because of VC temp?

Quote:
Originally Posted by Ricci View Post

After testing a DTS10 a couple of times and switching to totally different much beefier drivers and testing that and now testing this tapped horn I have noted that the usual peaks that are seen at low volumes and in simulation get heavily compressed and squashed at the highest playback levels... It appears that there is either severe compression occuring in the drivers or that there is some sort of acoustic limiting or compression occuring inside the horn itself. i am leaning towards some of the later. Thoughts?


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post #393 of 448 Old 06-13-2011, 06:34 PM
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Quote:
Originally Posted by noah katz View Post

How about higher Qe because of VC temp?

Increase in Rdc has no significant effect in simulations.
(Sim I am sitting with now is for a different system, but we can assume that it is the same mechanisms that comes in to effect.)

Same goes for Bl - reduced Bl has no significant effect, and, seeing as this occurs at a relative high frequency, Bl reduction due to excursion should not be an issue.

Impedance curve shows a very narrow peak at the same freq as the peak in the (low level) freq response, indicating a very high q.
Excursion also shows a smaller increase.

This leads me to believe that non-linear damping occurs in the horn, so that the resonance that creates the peak in the freq response is dampened sufficiently at a higher sound pressure level to have a measurable effect.

Other suspects might be mechanical resonances in the walls.

But, what we do know is that when the pressure differences over a small enough distance gets too high, or the air velocity gets too high, then the small-signal model of the propagation of the sound through the horn is not valid any more.
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post #394 of 448 Old 06-13-2011, 09:38 PM
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Quote:
Originally Posted by Okv View Post
Increase in Rdc has no significant effect in simulations.
Does that account for the attendant increase in Qe?

Everything I've read about horns says they're sensitive to driver parameters, and I'd think Qe is one of the more important ones.

But I agree that given the high freq your analysis seems more likely.

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post #395 of 448 Old 06-14-2011, 10:19 AM
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Quote:
Originally Posted by noah katz View Post

Does that account for the attendant increase in Qe?

Everything I've read about horns says they're sensitive to driver parameters, and I'd think Qe is one of the more important ones.

But I agree that given the high freq your analysis seems more likely.

Qe depends on Re and Bl, given that the moving mass does not change.
(A horn is generally not that sensitive to changes in suspension compliance, and thus changes in Qe due to changes in driver fc will not have much effect.)

Changes in Qe will also affect the response lower down in frequency, often more than in the upper range.

Would be interesting to see some distortion figures as well.
The SPL in these measurements are, well, quite high, and many mics will have problems when the spl exceeds 120dB.
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post #396 of 448 Old 06-14-2011, 03:17 PM - Thread Starter
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Yes the drivers were "virgin" when dropped in. These are some of the most linear and highest power handling drivers around with plenty of test data to back that up, so I do not think it is non linearity on their part causing it. Perhaps break in had something to do with it. Seems like an aweful big change. Could very well be a combo of driver non linearity, air pressure non linearity and cabinet vibration or flex. I am suspecting that at high volume levels there is some sort of point where the loading at the throat is changing or the air pressure itself undergoes some sort of change. If you take the simulation data I provided a few pages back and look at it in Akabak there may be some clues looking at the pressure, velocity, acceleration, etc... Maybe this is the dreaded throat distortion kicked into overdrive? Perhaps we can entice Tom D. to comment since he probably has some good insight. One thing to note is after the response changed it is a lot closer to the simulation now. I have attached a comparison graph. At least all of the peaks are in the right place. I have already completed the full test work-up on these but it will be a while before I get everything put together and up for consumption. I did have to move the microphone back to 4 meters to get accurate results for CEA-2010 burst testing. The results of that test are...Strong... Shall we say...







Attachment 214901
LL
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post #397 of 448 Old 06-14-2011, 03:37 PM
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Amazing work, Josh.

Wish I had something to input here but I'm really just ignorant to the whole subject. So I'm just sitting back with some popcorn and lovin' the results.

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post #398 of 448 Old 06-14-2011, 03:38 PM
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My vote is break-in...

That is a pretty graph....

JSS
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post #399 of 448 Old 06-14-2011, 05:05 PM
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Ricci,

Sorry, you lost me there. What are you thinking throat compression had to do with the change, or are you talking the difference in the high low voltage testing again?

My question about their chasteness and if you had pulled any numbers on them first was hinting at a break-in scenario.

Drivers are a little tight sometimes from the factory. A normal use heat cycle or two can fix this right up however. It doesn't take days at resonance frequencies.

I'm not saying that this is the only answer either, but it is the simplest one other than a measurement snafu.

As long as the new stuff is repeatable I wouldn't worry about it too much. They were fine before, and are even better now. Actually, they are so good now that you need to stop posting here, and get to uploading the rest of the data. I am really interested is the rest of the info now. Where you able to get the high voltage impedance testing setup done?
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post #400 of 448 Old 06-14-2011, 08:36 PM - Thread Starter
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Sorry man I was jumbling a couple of different thoughts together. I am happy with the way things turned out broke in. I will leave it at that. Now I am curious about the large changes in the response shape that occur at high power this happens in the dts10 too. My guess is some sort of overload of the air mass in the throat or something.

About the high power impedance tests....I was messing with the VI box and I have been having some irregular results running it into rew. I was trying to determine why the results weren't matching what I thought they should be and ended up frying the high level input. Apparently I am the first to ever do that. I only had it on a single channel of an 8002 running into a nominal 5 ohm load. It is rated at 2500w. I am worried about it being able to handle the tests now. I have another on the way. I really want to see the results for the tapped horns because I feel like it will give us insight into the changes that happen at the limit.
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post #401 of 448 Old 06-14-2011, 09:42 PM
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You do a very good job measuring and publishing the results, thank you for that.

As for the compression/high-level freq response - impedance curves at high level may provide useful additional information that can be used to try to determine what causes this, and, more important - the distortion.

Might be that horn distortion due to acoustic overload may also be an issue in bass horns, not only for compression drivers.

Something is causing distortion in the bass horns, and it is not the driver itself, and observations of measurements indicate that it is caused by pressure changes that is large enough in amplitude to change the wave propagation speed significantly - because the distortion is most often low from the 1/4-frequency and up to about 1/2-wavelength, where the distortion often rises rapidly.

Without further objective investigation this is just guesswork, though.
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post #402 of 448 Old 06-15-2011, 10:24 AM - Thread Starter
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Yes. I think that a high power impedance measurement may be the best shot at determining the cause. I am expecting to see some very large changes in the impedance profile at high power. I really need to get to the same input voltages as used for the last 2 sweeps in my power compression test I just hope the box will handle that much power. I may have to cut the sweep duration down some.


Okv you seem to have a good amount of knowledge and are quite the lurker I see (4 posts in one year). Glad to see I've goaded you into posting.
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post #403 of 448 Old 06-15-2011, 02:16 PM
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Quote:
Originally Posted by Ricci View Post

...
Okv you seem to have a good amount of knowledge and are quite the lurker I see (4 posts in one year). Glad to see I've goaded you into posting.

Thank you for noticing, I have found lots of inspiring information here.

There are many knowledgeable people around here, and when you present measurements that indicate something similar to what I have measured myself, and can not yet explain exactly, then I feel it is a good idea to participate and try to find out what is going on - may be someone else knows something I don't.

If the mechanisms behind distortion and high-level changes in frequency response is fully understood, then it may be possible to either make improved designs, or, live with it and utilise the designs differently.
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post #404 of 448 Old 06-15-2011, 05:04 PM
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Ricci,

I see the thread you started elsewhere, and I understand your posts a little better now. It least it hasn't hit "Sound difference between horn and sealed/vented?" levels of absurdity yet.

I'm a little disappointed in the VI Box. Sorry, I ever brought it up in our emails. I was a little worried about it handling the loads you would be placing on it. From the details of it's circuit and components I could never figure out how it could handle 2500W at that price point without liquid immersion. A resistor that can handle that load (dry,) and stay in spec is not cheap.

Maybe you just got a bad box. Crossing my fingers.

They replaced this one for free, right?
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post #405 of 448 Old 06-15-2011, 07:09 PM - Thread Starter
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No it was not free...They didn't offer and I didn't ask. I actually never saw any mention of any warranty on the site at all so I didn't bother.Talked to Chris at LinearX. He says this has never happened. I do not have time to wait around for discussions of what might of happened whether it will be replaced etc. I recieved the new one that I bought the same night today. I will be sending the burnt unit back for them to look at. Not much to say, the 4 first resistors on the high level input are toast. I could not have put anywhere near 2500w into it. I was running a single channel into a 5ohm minimum load and the amp was on a $10 powerstrip at the time. That amp could maybe muster all of 1000w into that and it was nowhere near clipping. I asked about duration and didn't get an answer on that. I had done 3 or 4 sweeps in a row at a good level when I saw an orange glow and the magic smoke. If I smoke the second I will have to figure something else out. Vance D. has been using one for years quite successfully. Getting ready to mess with the replacement now. Fingers crossed.



"yet" No doubt.
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post #406 of 448 Old 06-17-2011, 08:46 AM
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How did the testing go with the new box?

Not hearing anything by now has me thinking things didn't go smoothly.
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post #407 of 448 Old 06-18-2011, 12:09 AM - Thread Starter
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Haven't tried the new box yet. I will let you know how it goes.
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post #408 of 448 Old 06-23-2011, 10:53 AM - Thread Starter
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Still haven't messed with the new box.

For future reference.










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post #409 of 448 Old 06-23-2011, 08:06 PM
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At 65Hz, Th S3, you have a particle velocity of 49m/s and the pressure equals >170dB.
Then it should not come as a surprise that the output is affected by nonlinear effects in the horn, this is a very high pressure and a very high velocity.

Considering these numbers, it is more surprising that it actually performs as well as it does.
Numbers from other horn designs show that very high pressures and high velocities are common, and a smaller horn may actually present numbers higher than a larger one.
Also, the area of the horn channel is important here, because a larger area can manage higher velocities (and obviously, higher volume velocities) before separation and turbulent flow occurs along the walls.

I find your Gjallerhorn very interesting; it is extremely loud and powerful, and the powerful driver really works the horn, so that it may be possible to actually measure and find physical limits for this kind of constructions.
Knowing that design of things, and perhaps loudspeakers in particular, are often based on experience and known good practices, one may find that what was valid for horns in the old days may not be true for this kind of design, because the driver is capable of producing a lot more low freq sound due to its displacement capacity.
PA horns can of course be even louder, but rarely goes as deep and the drivers usually have a lot less displacement.

Now it would have been very interesting to see some distortion plots of this one.
Most useful would be dist at different levels, and 2hd and 3hd separately plotted.
(I understand you are working on getting the impedance measurements.)

I have started to look at nonlinear effects in low frequency horns and distortion, and what I can see so far, is that it may not be a big concern, as the distortion from the driver itself will be quite large before the horn itself add significant levels of distortion.
That is, unless you make an unfavourable design - and that is a good reason to search for more knowledge about the subject, so that one can learn good design practices, to avoid building expensive piles of wood.
It also surprised me to see the actual numbers for pressures and velocities inside the horn - very high pressure, and velocities that also quickly enters the range where separation and turbulent flow occurs.

The kind of dist people are so afraid of in horns, often called throat distortion, is not a big problem in bass horns, as the bandwidth of the horn really is not wide enough to allow waves to propagate long enough (in wavelengths).

Talking about turbulence, one can imagine what happens through the horn bends..

I tend to believe some distortion at very high spl levels are not that important, as the speaker should only enter this kind of spl on top of transients, and then the dist will not be detectable as the time span is too short.
I am more concerned about compression.

I think that using practical designs and measurements of those are the way to go.
This makes it possible to verify theoretical hypotheses, and find out what actually works.

I shall not indulge in to this any more here, as the subject is rather comprehensive, and also I do not have much valuable information, at least not yet.
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post #410 of 448 Old 06-23-2011, 09:29 PM - Thread Starter
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I appreciate your comments Okv. I already have all of the data collected including distortion measurements. The only thing left is high power impedance. Anyway I had not planned to post the rest of the data until the site update was done but I will post some of the distortion and also power compression results tomorrow.

You note that the internal pressure is reaching 170db at 63hz. (Btw horn segment 3 mouth is the end of the throat effectively and where all of the forces in the horn seem to be highest.) I am also interested in the area near 90hz as this is where the cabinet develops a notable buzz/ resonance at war volume giving the impression that the cabinet is in danger of popping a joint . It is hard to describe. I havent noted it with actual content but I dont normally dump >100v into cabs in real world use either. The charts indicate there is significant force involved at that area of response also.
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post #411 of 448 Old 06-24-2011, 01:05 PM
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wow, what a monstrous (in a good way) creation...

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post #412 of 448 Old 06-26-2011, 12:27 PM - Thread Starter
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1w/1m, 2 volts input.






Approximate input voltage for the following nominal levels.
90db 1.63v
95db 2.9v
100db 5.15v
105db 9.16v
110db 16.3v
115db 29v
120db 51.5v
125db 91.6v
128db 130v



Power compression sweeps.




THD and distortion by component measurements.












CEA2010 output. Measured at 2 meter, ground plane, rms.
10hz 90.2db
12.5hz 105.2db
16hz 118.3db
20hz 122db
25hz 124.9db
31.5hz 125.8db
40hz 128.4db
50hz 127.2db
63hz 130.2db
80hz 130.9db
100hz 131.1db
125hz 123.6db
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post #413 of 448 Old 06-26-2011, 01:07 PM
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Sorry if this was mentioned before - what proggy do you use to generate your distortion graphs? I tried using RTA in REW, but as far as I know, you can only do one frequency / gain at a time - no ability to do a sweep, which would sure save time.
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post #414 of 448 Old 06-26-2011, 01:14 PM - Thread Starter
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STEPS or ARTA or even HolmImpulse is what I use for distortion tests.
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post #415 of 448 Old 06-26-2011, 01:15 PM - Thread Starter
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post #416 of 448 Old 06-26-2011, 05:20 PM
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Excellent, these distortion plots add very valuable information.

Measurements (still) at 2m?
(Meaning - add 6dB to get to 1m.)

Distortion is overall sufficiently low, considering the SPL and frequency range at work, I would say very low.
I would not worry too much about distortion at the limit, and it can also be seen that distortion falls rapidly as spl is reduced from the 128 max level.

What is interesting, though, is to observe how the distortion develops.
It first increases at higher frequencies, relative to the passband, and then narrow bands with much higher distortion appear.

Measurements of other designs shows similar characteristics, which is interesting, because that may indicate that the mechanisms behind generation of the distortion are the same.
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post #417 of 448 Old 06-27-2011, 11:50 AM - Thread Starter
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Yes all output spl measurements are taken at 2 meters.


Some thoughts I have after looking at the data for a few days in different ways....
I think there are some trends apparent here if you consider the pressure, imp, velocity, current and acceleration data from Akabak in context with the actual compression and distortion measurements. The distortion performance I am pretty happy with really. The dramatic spikes up seen at high power seem to be inherent to TH's when driven hard. The DTS10 both in stock form and with alternate drivers exhibited similar spike in distortion. This cab is ridiculously clean from 15-45hz considering the power applied and the output. It gets rough above there but again given the levels used, I consider that it stays well under 15% THD from 15- 95hz even at the 130v level except for 2 up spikes at 50 and about 67hz to be great. The biggest spike in distortion near 100hz is also where I note that at the highest input levels the cab develops a buzz. Were I to build another pair I would beef up the internal bracing more. I plan to cross at 85hz or lower anyway.

Note that in the power compression test there is what appears to be an upper ceiling to how loud this sub will go at some frequencies no matter the increase in input power. There is a very large amount of compression of the 63hz responce peak and also the 85-110hz area where the sub also exhibits peaks in its response. Again this same type of compression behavior was noted with the DTS-10. A follow up test with EQ applied is planned. I have a feeling it will have some good effects on the distortion and high power compression performance in addition to giving the sub a smoother more linear response. For example the sub plateau's out at 63hz and ends up exhibiting nearly 12db of compression at the 130v input level. However looking at the basic response at the lowest 90db or 1.63v input level 63hz is boosted almost 11db relative to the surrounding frequencies to begin with. The same story is apparent at 85-110hz where the response is boosted up by 5 to 10db and again the compression and distortion performance is worst in this area. The output has already almost plateau'd at these frequency ranges by the 120db, 51.5v sweep. Further input does little more than add to the distortion. Once the response is EQ'd to be flatter at these frequencies by cutting some 5-12db of output, the compression performance, distortion and power demands on the amplifier should all improve quite a bit while the maximum output should be affected barely at all, plus the decay and response will be smoother. That's the theory anyway. Should be a win/win all around.

If you are running TH's I would consider EQing the major spikes in response down a must for better performance of the cabinet.
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post #418 of 448 Old 06-27-2011, 03:36 PM
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Quote:
Originally Posted by Ricci View Post

..
Some thoughts I have after looking at the data for a few days in different ways....
I think there are some trends apparent here if you consider the pressure, imp, velocity, current ...

Your excellent documentation is what makes it possible to study data that gives very useful information.

To actually come up with something theoretically valid for distortion in low-frequency horns may take some time and effort, though.
It might not even be worth the effort, seeing as distortion clearly is not that big an issue before the limits of the design is reached.
But even to come to that conclusion one needs measurement data from horns actually made.

To me it also seems very likely that the spl limit is actually set by the driver.

And, there are artifacts that seems to occur in many designs.
Like resonant spikes in the upper range of the passband (i.e. like your 100Hz-peak) with high distortion.

The distortion issue might perhaps deserve its own thread, where other as well could contribute with measurements and ideas.
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post #419 of 448 Old 07-01-2011, 06:06 AM
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Ricci could this cabinet design be used for live applications?

I always thought about having a PA style bass rig with a sub and top. The Top would probably be a pair of AE15's with some sort of horn to get up to atleast 16Khz. I would mainly just use the top for my standard tuned 6 string bass. Then when using the ERB bass I would use a sub like this one if it would work. 15hz is about as low as I would want to go myself. I figure a steep Hpas here would be perfect for me when using the Top/sub together.

Just a thought. I still liked your 24" cube, dual 21" B&C sealed sub also you did a while back when making your other pa subs.
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post #420 of 448 Old 07-01-2011, 06:18 AM
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Any estimations how one of these guys would perform in a ~3000 cube HT LPF @80Hz?
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