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post #361 of 448 Old 05-25-2011, 04:08 PM
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ricci, that 45 degree lip really gives it a finished look. little details sometimes really make the difference.

looney, compliance may not even be on the spec sheets, i don't recall. i've noticed that i often have to work backwards from the derived parameters to get to it (of course, i let winisd do the math).

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post #362 of 448 Old 05-26-2011, 08:56 AM - Thread Starter
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I managed to get one assembled and fired up last night.
















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post #363 of 448 Old 05-26-2011, 09:06 AM
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And!!!!!!!!!
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post #364 of 448 Old 05-26-2011, 09:30 AM
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And?????????
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post #365 of 448 Old 05-26-2011, 09:47 AM
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And?!?!?!???
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post #366 of 448 Old 05-26-2011, 09:55 AM
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so whats the result? Don't keep us waiting !!!!!!!!

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post #367 of 448 Old 05-26-2011, 09:59 AM
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Perhaps he caused seismic activity, and is currently explaining to the local officials how it's merely an honest mistake as he maintained < -10dB from reference...
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post #368 of 448 Old 05-26-2011, 11:19 AM
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Nice, that 4x10 aluminum Hartke cab is one of my faves....what preamp you driving that CE4000 with?

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post #369 of 448 Old 05-26-2011, 11:34 AM
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Josh Ricci ... like a boss!


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post #370 of 448 Old 05-26-2011, 11:35 AM - Thread Starter
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It's a Sansamp RBI. The CE4K does a real good job on beating up some bass guitar cabs and working on crap power due to PFC. Makes for some huge dynamics. I have wanted to DIY a bass guitar cab for years now but I just never find the time.
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post #371 of 448 Old 05-26-2011, 12:16 PM - Thread Starter
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Scott...LOL! p


Guys I don't really have a whole lot on this yet. I got it buttoned up at about 11:30pm last night just in time for the nightly tornado warnings and lightning storms. I ran about 5 sine sweeps through it, some pink noise, played a couple of sines at specific frequencies and ran about 3 songs through it.

I did get a close mic FR. Here it is compared with the simulated response.






Well in some ways I am a little disappointed that the top end is not as good as hoped, which would've been merely rough to begin with instead of plain old beat up. I was hoping for it to be useful up to 110hz maybe with help from EQ. On the other hand I am quite happy that it is as close as it is. I've never designed a horn before and this is a big and complicated one. I had no rough draft so it might not have worked at all! I could've gotten much worse. Also I had to expect that the sheer amount of turns in the middle section would have a detrimental and somewhat unknown effect. I'd suspect that these plus the internal resonances formed inside by the cab geometry have some large part in it as well. On the other hand as I had suspected it would the actual cab tuning came in a little lower than designed. This measurement was really rough and quick and at a pretty hot level, so I have no idea how the actual 1W efficiency will stack up. After I measure the other cab and do an outdoor gp test with a known voltage input I will have a better picture.


Here is a quick measured impedance. This wasn't really calibrated so the exact impedance magnitude may be a bit off but it shows that the peaks are close to the simulation and that the actual loading is a little bit lower in frequency than as designed. I did not recalibrate and I was using much longer leads than usual. I will have to redo this later with a proper calibration as well.






Some other quick observations are that these will definitely need a good dose of eq applied as mandatory and /or crossed over low like 60hz or lower. The cab does not want to let go of some notes. I do not have any damping at all in the cab currently I think there is a need for some. I can only reach the throat and the final 2 corners but I will see if this helps out at all. Also the cab is solid as a rock except for the bottom by the access panel where it is quite resonant. I knew this would be the case since the nature of the design didn't really allow any bracing in there and it is right by the driver back wave. The positive about that is that it is the bottom of the cab and in my application will be sitting on the floor with the full 300lb? weight on it. It won't be a problem in that case. I didn't wring the thing out but I did give it a little juice and thus far it doesn't appear that there will be any broken cone from horn pressure shenanigans. Its an angry little beastie. It slappa da bass around like it just don't care mon! . I can't really say that I am surprised by much of this. Par for the course so far.
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post #372 of 448 Old 05-26-2011, 05:02 PM
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that doesn't look too bad to me. maybe try two bands of eq on it in order to knock down those nasty resonances and then report back? i bet it will actually do what you were hoping for.

i wonder what is causing the 100 hz suckout.

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post #373 of 448 Old 05-27-2011, 08:01 AM - Thread Starter
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I am not sure what the cause of the 100hz null is. 100hz is a roughly 11.25 ft long wavelength. This is a 22 ft long horn with many turns and sections. It is most likely some interaction with the cabinet dimensions causing a cancellation. Maybe it is the driver placement relative to a return reflection. Perhaps I can determine it later. That is actually the main thing that bugs me is the suck out at 100hz. Peaks can be cut heavily but nulls are not so easily dealt with.

I did throw some rough eq on it last night to beat down 63hz and 91hz and slapped an 80hz bw 4th order on. That made a big improvement in cleaning up the sound. Output is not a problem. I am starting to wish that I had a way to watch movies in there so I can give it LFE channel to sink its teeth into. Music just doesn't have much for it. Hopefully outdoor gp testing will be next weekend.
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post #374 of 448 Old 06-02-2011, 01:57 PM - Thread Starter
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Blah blah...


I tried out a few things to see if I could get some worthwhile improvement yesterday.

I tried adding a reflector panel at 45 degrees in the last corner before the driver to see if it would affect the upper end response and perhaps help out at 100hz...No dice. Negligible impact. Scratch that from the list.





While I was at it I tried some damping in the throat behind the driver and a generous amount in the last 2 corners before the driver. The throat damping did nothing of note really other than sapping about a db of efficiency. With all of the damping in both corners and in the horn throat it did clean up the response some and knock down the horn resonances at 63hz and 90hz quite a bit. However it also caused an efficiency loss of nearly 3db across much of the bandwidth! No thanks. I don't think the slight improvement is worth the hefty loss of output which is what these big guys are all about. I'd rather just use EQ to knock the edges off. It would be needed with or without the damping anyway. You can see the efficiency losses in this graph.





Here is the effect that all of the damping had on the decay of the horn. It did improve it somewhat but once you bring the level back up to match what it was prior to loseing the efficiency it isn't as much as hoped. Again not worth the efficiency sac IMHO.

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post #375 of 448 Old 06-02-2011, 02:12 PM
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Thanks for sharing your efforts. I saw similar results with the damping experiments I did while working on the Shiva. Nothing really helped without also resulting in a decrease in SPL.
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post #376 of 448 Old 06-02-2011, 02:12 PM
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That's a pretty large chunk of off the total output right there with the extra damping. Not much improvement and as you mentioned, could be easily fixed with some EQ. I would have done the same thing.

I bet this beast will get super scary loud. What are you amping this with?

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post #377 of 448 Old 06-02-2011, 06:32 PM
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I lose 3db damping my dual THTs with pillow stuffing in the mouths. But I gain no cavernous reverberations from the mains that are close by....Audyssey calibration is a nightmare of reverb. I run them with very little power anyway, so no big loss, I listen at around 10db below reference to preserve my hearing...

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post #378 of 448 Old 06-03-2011, 05:02 AM
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Where is your mic and speaker located when doing these quick measurements?

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post #379 of 448 Old 06-03-2011, 05:42 AM
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The glitches are phase sourced, and are inevitable with tapped horns. So long as they occur below the passband they're of no consequence, but as you've discovered if you want a wide bandwidth a tapped horn won't give it. The inability of tapped horns to run above 100Hz is why Danley's charts only go to 100Hz. When they first came out he used charts that went to 200Hz, but the ragged response above 100 Hz scared away some, so he changed them in short order.

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post #380 of 448 Old 06-03-2011, 06:35 AM - Thread Starter
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Scott,
Yes these have easily handled anything I have thrown at them yet. Right now one is placed under the right side of the pa stack. The other is still unused since it will be 2m gp tested soon. Right now I just have a single channel of a Crest 8002 on the one. Eventually something like a big itech,pl380, or something is in order. I have a 230v line available.

Bentz,
These quick and dirties are with the mic positioned middle of the mouth and coincident with the plane of the side. The cab is rotated tall with the mouth off of the floor and the whole thing is on a furniture dolly rolled outside onto a dock.


Bill,
Yes It is difficult to get useable top end out of a TH. Like other horns it seems that the fuller sized the horn is made the more you can smooth the peaks out. Too bad most bass horns have to be undersized from ideal. I had expected the top end roughness. Actually the fact that I use no smoothing and the graph range is zoomed in quite a bit makes it look a little worse than it is. I had originally thought that the 100hz notch was due to the cab construction and length of the last couple of parallel walls. Now I am leaning towards cancellation from the front and rear radiation of the driver or phase as you say. 22 ft path length and 100hz being about 11ft long roughly seems to have some correspondance. I never really intended these to be used up past 80-90hz after eq but I was trying to get as much extension as possible just because. I didn't do so well in that regard. Now I would like to find out where the real build diverted from the simulation and how to square the 2. Hopefully I can learn some lessons from that.
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post #381 of 448 Old 06-03-2011, 06:46 AM
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All of these parameters look really pro. I am impressed! Way over my head - I guess I will stick to store bought subs heh.

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post #382 of 448 Old 06-03-2011, 06:57 AM
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For what it's worth, if you manage to maintain the assumptions of a model, then you should expect to be able to exactly match the model. If anything, the dips in the model should 'usually' be a lot steeper and more dramatic than in real life. Have you gone back to adjust your model to match what was actually built? Or can you think of any assumptions that may not be valid?

At about 115Hz and 130Hz you can see 2 extra peaks in the response that aren't in the simulation....and i don't think it would be a waste of time to track those down. If nothing else, it could be something learned for next time.

Looking at your build, it appears that there isn't any horizontal expansion down the horn? I'm gonna guess that the dimensions are roughly 2ft, which is about a 1/4 wavelength at the frequencies in question. The general rule of thumb for maintaining a planar wave front is for the wavelengths to be 10x the dimension of the horn, so I'm wondering if you're not seeing the horn break down in the horizontal....in which case, those wavelengths are going to start reflecting back and forth down the horn instead of keeping a coherent wavefront. I've always wondered what would happen in horns if a vertical wall was placed in the middle of the walls for the length of the entire horn...then each channel would be effectively 8x the wavelength which may be close enough to achieve a planar wavefront - I dunno, but it's probably too late to add that now, and it wouldn't be worth the hunch on a guess.

As far as mic position, any chance that the speaker or mic is within ~2ft from a boundary? You might also want to double check that you don't have cabinet resonances at those frequencies - Have you done slow sine sweeps at high SPL looking for buzzes yet?

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post #383 of 448 Old 06-03-2011, 08:01 AM - Thread Starter
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Yes. I have done some sine sweeps. That is how the measurements were taken. I used a pretty hot drive level for them. Here was one resonance from the cab that was somewhere between 120-180hz. I haven't tracked it down specifically yet just heard it. It was from the access hatch. I may just put a brace in the center of the panel that is forced against the driver motor when the hatch is screwed down.

There is no possibility that boundaries are affecting the measurement really. Once I get some gp measurements from out in the field I suspect they will bear this out. You are right there is no expansion in the width direction. The internal width would be some 22.7" give or take. 100hz is about 11.3 ft or 135.6". That would place the width of the path at about a 5th of a wavelength. It makes sense that there would be an issue related to the width but 100hz seems a little low to me. There is quite a bit of vertical mid wall as you put it in the cab, the braces, but that only covers maybe 30% of the total length.

Going back and tweaking the simulation to match the real result is exactly what I was talking about. I can't get the cab construction related resonances in there but I can get it closer. I think that the biggest discrepancy is probably in the atc and vtc values that I guessed at.
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post #384 of 448 Old 06-03-2011, 08:47 AM
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Quote:
Originally Posted by Ricci View Post

Now I am leaning towards cancellation from the front and rear radiation of the driver or phase as you say. 22 ft path length and 100hz being about 11ft long roughly seems to have some correspondance.

That's exactly it, the front and rear waves are going to be 180 degrees out of phase at some point, and that's where you'll get the deepest notch. Part of the design process is to jockey the driver position to place that notch above the passband, and to minimize the less serious peaks and valleys that will occur within it.

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post #385 of 448 Old 06-03-2011, 09:08 AM
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Let's not get carried away here. There are 4 DSL subs with 100Hz charts, 3 with 150Hz, and 6 with 200Hz charts.


Quote:
Originally Posted by Ricci View Post

Going back and tweaking the simulation to match the real result is exactly what I was talking about. I can't get the cab construction related resonances in there but I can get it closer. I think that the biggest discrepancy is probably in the atc and vtc values that I guessed at.

I do not believe you will be able to find this there.

It is a compound issue from having so many bends. The "simple" way that was used to get a path length (and horn simulation) loses a little accuracy with every bend. This is compounded with a smaller volume horn per the bandwidth used. Once you get over around a half dozen bends, it doesn't account for the full amount of resistance to volume, and starts drifting away from the sim some with each new bend.

The distance from the horns throat to the rear tap is part of it as well in a TH. If the real acoustic distance is different from the simulation distance, the two will not mesh exactly as the phase is different.
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post #386 of 448 Old 06-03-2011, 09:14 AM - Thread Starter
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EDIT: In reply to Bill's out of phase suggestion.

Yep. Actually now that I think of it visually that explains it quite nicely. If you consider the radiation from the driver side near the mouth as a single complete 11ft wave cycle in your head and then place another driver 22ft back from the first radiation (the throat side) it will make 2 complete wave cycles until meeting up with the first wave radiation perfectly in sync with it. However the catch here is that the second radiation from 22ft back in the horn throat starts out 180deg opposite phase so when it completes 2 cycles and meets with the radiation from the driver near the mouth it is still reversed phase and creates a huge cancellation at 100hz. Duh. This is simple stuff but not readily apparent sometimes. See I had been thinking that hey 22ft is almost exactly 2 complete 100hz wavelengths so that should be reinforcing not creating a null. I had forgotten that the rear radiation starts out in completely opposite phase. This leads me to another question...If the above is what is causing the 100hz null should there not also be one at about 50hz?


Soho what do you think about the above. Certainly makes a lot of sense to me intuitively.



Bill,
I know you are a FLH guy but do you have any tips for determining the delay needed for tops to go with a TH? The majority of the output comes from incubating 22ft inside the path but the driver also radiates some from only 2ft inside the cab...Perhaps it should be 3/4's of the full length? Actually everything about a TH alignment screams phase and time domain issues to begin with, but in practice it doesn't seem to be that big of an issue with bass freq's.
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post #387 of 448 Old 06-03-2011, 09:44 AM
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Quote:
Originally Posted by Ricci View Post

Soho what do you think about the above. Certainly makes a lot of sense to me intuitively.

This is how TH's work. This is what causes the regular peaks and dips as you go up in frequency. I posted the math to determine the change over point somewhere. This is accounted for in the sims. You can see the in-phase and out of phase crossovers quite easily if you widen the graphs bandwidth.

In your situation the real horns acoustic path is slightly different from the simulations because of the amount bends present in the horn. All it would take is a couple of feet at 100Hz. It may be easier to think of it as friction.

If you really compare the sim and real plots you can see how the phase is off up top. This is what is causing the really deep dip lower in frequency than simed, and the new mini-peak along the way to the real harmonic peak. It is the classic backwards "n" shape. If you did a sweep over a larger bandwith you would see the pattern unfold. You can see the same thing in lilmike's high resolution measurements in all the dip (out-of-phase) sections. They are just magnitudes less noticeable, as the phase of the two sides are better matched, so the volatile transition area is smaller.
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post #388 of 448 Old 06-03-2011, 01:53 PM
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Quote:
Originally Posted by Ricci View Post



Bill,
I know you are a FLH guy but do you have any tips for determining the delay needed for tops to go with a TH? The majority of the output comes from incubating 22ft inside the path but the driver also radiates some from only 2ft inside the cab...Perhaps it should be 3/4's of the full length? Actually everything about a TH alignment screams phase and time domain issues to begin with, but in practice it doesn't seem to be that big of an issue with bass freq's.

That's part and parcel of the TH conundrum, you have the front wave and rear wave with different arrival times, so how do you set it? The answer is to the distance between the mains and the exposed cone. The lower you go the less you can hear delay, so there's no need to worry about the rear wave arrival time. The reason it's not a big issue as you note is the period of those low frequencies, which also allows the front and rear waves to combine constructively in the low end despite being sourced so far apart, but as those periods decrease things get hinky. The reason I don't do tapped is that hinkyness (as some users want to run their subs higher than 100 Hz), the higher displacement demands at Fc and the higher distortion of the TH due to the exposed cone. But TH is still a lot better than direct radiating.

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post #389 of 448 Old 06-13-2011, 01:03 PM - Thread Starter
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Update:

I have done some outdoor testing on one of the cabs. I have attached the maximum long term output available using a 10-120hz, 24 second long, ascending sine wave sweep recorded outdoors at 2 meters ground plane. Amplifier is a Powersoft K10 on 240v. There is a good deal of thermal compression in evidence so CEA2010 burst testing should show peak output numbers somewhat higher still. There is no lack of output here. The driver did not grenade, or shred the cone or develop coil rock or any of that. If anything the driver has a much harder time dealing with the power themally. The power compression sweeps are 9 24 second long ascending sweeps back to back with each having the level increased by 5db over the last. This is ended when the sub exhibits clear distress signals. This was immediately followed by 1/48 octave sine burst distortion testing using the STEPS program which takes about 5 min to complete the full measurement. There were 9 of these run back to back at the same input levels as used during the power compression sweep tests. By the end of this the motor was extremely hot and there was the smell of hot voice coil adhesive (Mmmmm.) and some darkening. This was on a visciously hot 95degree day in direct sunlight as well. I ended up running a greatly reduced power 20hz sine wave for a few minutes, which is at the in passband excursion maximum to help cool the motor down afterwards. This is far far more punishment than even the worst real world, long term duty it might ever be asked for.

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. I am ruling out amplifier clipping due to having plenty of power on hand to either fry or launch the cones at will. 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?

Also after taking this thing a little bit past the limit truthfully I wish that I had beefed the cabinet up a little more and used more bracing. At the very highest sweep levels the cab sounded as if it may blow a seam and developed a buzz in a few narrow frequency ranges near 63hz and about 85-90hz. This isn't evident if you knock the output back to sane levels. I doubt they would be notable with real broadband content either. Outdoor sine waves are pretty unforgiving on exposing rattle and buzz issues. There must be an enormous amount of power being developed inside of this cab. I think I may have underestimated how much.

Now this is a real curiosity. When I first put the cabs together and applied power I took some close mic graphs. These all show a 100hz dip that was not apparent in the simulation. I then ran the pair lightly in a pa set-up for a few days. Fast forward...I get one of them outside to test it and lo and behold the 100hz dip is gone and between 90-110hz the response has changed. The 100hz dip is no longer there. I freak out thinking perhaps I had damaged something in this cab, or the driver, or both, which wouldn't have been out of the realm of possibility considering the beating bestowed on it, so i run inside and take a measure on the other cab and it is now missing the 100hz dip too. That one hasn't been used very hard at all. I thought that perhaps I somehow had EQ engaged during the original measurements but there is no way. The drivers were brand new and had never been above about 2v so perhaps they had a major break in and this is responsible but I find that a hard pill to swallow. The cabs are 13ply BB with pocket screws and are PL'd together and built by a professional cabinet shop who's owner owns DTS-10's and is familiar with speakers so I have a hard time believing that a panel came loose and shifted enough to cause the response change either. I am at a loss to explain it really. I have attached a couple of measurements illustrating this as well. The 100hz notch is easily seen in the original measurement. The other one is the current response where there is no longer a 100hz dip. Very odd. Atleast it is a response improvement.







Attachment 214743
Attachment 214742
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post #390 of 448 Old 06-13-2011, 03:48 PM
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Quote:
Originally Posted by Ricci View Post

..
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?

It seems that horns, even bass-horns, are subject to nonlinearities due to the nonlinear nature of air.
This nonlinearity can cause nonlinear distortion (harmonic distortion).
In you case here, it may seem that it can also affect the frequency response of the system, in a non-linear way.

I found some odd behaviour during testing with acoustical damping, and in that case the distortion level was highly influenced by the amount of damping.
Type of damping did not show significant differences.
Since the design was a success, part from some distortion in a narrow frequency band, I did not pursue this any further.

Now, what is actually causing this, I do not know.
Maybe we can find out.
It may also be mechanisms of different origin, causing the same kind of measurable artifacts.

Changes in driver parameters as the power is increased could be worth investigating.

This may be worth some more investigation, seeing as it would be nice to be able to simulate or at least calculate the distortion level earlier in the design phase.
Also, it will be possible to reduce the distortion by making better designs, if one knows what causes it.
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