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post #121 of 190 Old 08-07-2013, 07:16 AM
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Thanks for posting this. It i very interesting.

I am not sure I read the charts right, but it looks to me as the distortion is mostly some 35db down. If I understand correctly, that means the distortion above 3kHz at the chosen drive level is approx 1.5%. Is this correct?.

I have read many places that distortion in CDs is much lower than in ordinary dome tweeters (at equal SPL). Is that correct, and if so how much difference is to be expected? I understand the answer to that question will be sort of "that depends", but maybe someone could elaborate a bit even if the question is not overly precise? For my understanding of the benefits af CD/waveguides I think it would be very beneficial if one or two well regarded dome tweeters was also measured to serve as sort a reference to the CDs in regard to both directivity and distortion. Not sure if that is the plan but i sure would appreciate it (Polite request ;-).
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post #122 of 190 Old 08-07-2013, 08:32 AM
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I had done a such a comparison. I compared the B&W 600 series with a JBL 2445 on a large tractrix horn. The CD/horn combo sounds huge, effortless, pure. The B&W sounds small and distorted. But when the distortion is compared, they are about the same.

CD/horns don't inherently have less distortion. In fact, a compression driver works on the principle of compressibility of air, which is a non-linear phenomenon. Mostly, this gives rise to high 2nd order distortion, which is inaudible unless it is very high.

So, how do you explain the perception of dynamics of CD/horn versus a conventional dome tweeter? Here's one hypothesis. Horns beam sound at you. The perceived level of direct sound over reflected sound (depends on amplitude and delay) is much higher in this case compared to a tweeter. And this provides more clarity. You hear things and can follow things more easily because the brain can more easily ignore the reflected component. And this gives rise to the perception of dynamics. Just a hypothesis, mind you smile.gif
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post #123 of 190 Old 08-07-2013, 08:38 AM
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Quote:
Originally Posted by splotten View Post

Thanks for posting this. It i very interesting.

I am not sure I read the charts right, but it looks to me as the distortion is mostly some 35db down. If I understand correctly, that means the distortion above 3kHz at the chosen drive level is approx 1.5%. Is this correct?.

I have read many places that distortion in CDs is much lower than in ordinary dome tweeters (at equal SPL). Is that correct, and if so how much difference is to be expected? I understand the answer to that question will be sort of "that depends", but maybe someone could elaborate a bit even if the question is not overly precise? For my understanding of the benefits af CD/waveguides I think it would be very beneficial if one or two well regarded dome tweeters was also measured to serve as sort a reference to the CDs in regard to both directivity and distortion. Not sure if that is the plan but i sure would appreciate it (Polite request ;-).

Just one thing to be aware of....there are different types of distortion, and it is possible for one to be low, but the other higher.

There have been several psychoacoustic tests showing that Intermodulation Distortion (IMD) is less pleasing than Harmonic Distortion (THD). The nature of IMD, however, is such that it is difficult to make an apples to apples comparison because it requires two drive tones, so typically we only see THD measurements.

The reason I bring it up is because it is entirely possible to find a driver with lower THD, but worse IMD...this happens when the doppler effect starts to dominate the mechanical linearity of the driver. To put it another way, there is commonly a close link between THD and IMD because the non-linearities creating THD will also create IMD products. However, the THD measurement plays one frequency at a time, so the doppler effects aren't included in that measurement.

Getting back to your point above...

The acoustic loading of a horn is such that it reduces driver motion for the same SPL. So let's say you find a 1" dome tweeter with let's say 94dB sensitivity and somehow it measures lower distortion than a 1" throat horn. The horn will probably be using a 10:1 compression ratio, which is going to net you 10 times less driver motion for the same SPL. At some point, you can't increase the linearity of the dome tweeter any further because the driver motion required for the SPL will dictate the IMD performance of the system due to the doppler effect.

Here is some interesting research on doppler distortion if you wanna crank through the math:
http://forums.klipsch.com/forums/storage/8/1925766/modulation-distortion-in-loudspeakers-1-3.pdf

Which came from this thread comparing horns and direct radiator subwoofers (the same math applies to tweeters really):
http://forums.klipsch.com/forums/t/171873.aspx

Ironically, in that thread I make an argument for direct radiators for the subwoofers, but those arguments don't work at the higher frequencies because it's easy to make an almost ideal horn, and an almost ideal horn will have way better polars than an array of direct radiators (although I am aware of Keele's CBT array, but the horn is going to win on distortion and you can use that array with horns too).

Sorry to get all theoretical on this thread....I'm really enjoying have a place for all these comparative measurements. Keep up the good work!
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post #124 of 190 Old 08-08-2013, 04:46 PM
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Quote:
Originally Posted by rahula7 View Post

CD/horns don't inherently have less distortion. In fact, a compression driver works on the principle of compressibility of air, which is a non-linear phenomenon. Mostly, this gives rise to high 2nd order distortion, which is inaudible unless it is very high.

I'm pretty sure they do have inherently lower distortion, not at the same drive level but at a given output level, because they do it with much lower excursion.

The nonlinearity of air doesn't come into play until extremely high levels, far beyond any we'd have in a home.

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post #125 of 190 Old 08-08-2013, 05:22 PM
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Got any data to show a comparison?

Compression drivers may have higher output, but they don't have lower distortion.

And CDs are always compressing the air. That's how they work. It's not like it comes into play at higher SPL only.

See post 794 and 800:
http://www.diyaudio.com/forums/multi-way/221643-active-vrs-passive-80.html

And here's the B&W and tractrix horn with JBL2445 comparison I was talking about earlier. It was measured at 90db at 2m outdoors. There is another measurement at 100db and it is about the same as well.



The horn/JBL combo has rising distortion below 500 Hz, because there is no woofer below it.
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post #126 of 190 Old 08-08-2013, 07:46 PM
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"Compression drivers may have higher output, but they don't have lower distortion."

are you sure that you are comparing apples to apples?

compression drivers tend to be measured at 1w and give 105-110db output at that level with 1% distortion or so, while that is about the point where a typical dome is going into critical failure and coming completely undone or melting down.

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post #127 of 190 Old 08-08-2013, 08:11 PM
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CD/Horns do not measure for spectral decay as well as dome or ribbon tweeters do. I am not sure if it makes any difference in practical terms though
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post #128 of 190 Old 08-08-2013, 08:39 PM
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Quote:
Originally Posted by LTD02 View Post

are you sure that you are comparing apples to apples?

compression drivers tend to be measured at 1w and give 105-110db output at that level with 1% distortion or so, while that is about the point where a typical dome is going into critical failure and coming completely undone or melting down.

The B&W v JBL2445/horn comparison was made in one go outdoors, with same everything. You be the judge. It startled me as well. But looking around the web, I found this is accurate. CDs don't in fact have lower distortion. High efficiency, yes. SPL capability, yes. Lower distortion than domes, no.

It doesn't matter how many Watts you are supplying the driver. Well, it does in a way, but not for distortion. You might burn a tweeter if you drive it hard continuously. But instantaneous peaks of 105 db should be no problem. In fact, Barleywater's testing shows they have an order of magnitude lower distortion than comparable CDs. He was pumping over 400W through a 2" peerless fullranger. No smoke, he claims. And lower distortion than a CD at over 120db.

A lot of folks here do home theatre in spaces that are quite large. Domes simply cannot handle that much power continuously. To fill rooms that large, you need horns and CDs. But in normal living rooms, at sane levels, they will easily equal a CD/horn, at least in terms of measured distortion.

Now, why do CD/horns still sound more dynamic than domes? I still haven't found an answer.

Sorry for the off topic stuff, Matt.
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post #129 of 190 Old 08-08-2013, 08:46 PM
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"Now, why do CD/horns still sound more dynamic than domes? I still haven't found an answer."

power compression.

a typical dome is 90db 1w1m if it is lucky. so 110db is 100 watts.

a typical cd on a horn is 105-110db 1w1m. so 110db is 1-3 watts.

"It doesn't matter how many Watts you are supplying the driver. Well, it does in a way, but not for distortion."

a large chunk of distortion is related to power, particularly intermodulation distortion. just something to be aware of.

....

actually, I see that mike wrote another great post back in #123 related to imd and harmonic distortion. that is a very big idea that gets virtually no play on any of the boards. harmonic distortion is, in a sense, fundamentally flawed. :-)

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post #130 of 190 Old 08-08-2013, 09:29 PM
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Power compression is a long term phenomenon. Voice coil heats up from the current because it cannot dissipate heat fast enough. There is a time constant and it is relatively long even for tweeters compared to normal music program.

Again, if you running near 100 or 105 db continuously, the domes will run into problems. At 85 db and 105 db peaks, there will be no power compression.

IMD is nothing but various harmonic components mingling with each other. If you have low THD, you will have low IMD. True, it is another useful tool, and THD is certainly not the final word. But you cannot have high IMD without high THD.
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post #131 of 190 Old 08-08-2013, 10:41 PM
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I once asked about how much time it takes for compression to become a serious factor here, that thread had some thoughtful answers.
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post #132 of 190 Old 08-09-2013, 05:25 AM
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Quote:
Originally Posted by rahula7 View Post

Power compression is a long term phenomenon. Voice coil heats up from the current because it cannot dissipate heat fast enough. There is a time constant and it is relatively long even for tweeters compared to normal music program.

Again, if you running near 100 or 105 db continuously, the domes will run into problems. At 85 db and 105 db peaks, there will be no power compression.

IMD is nothing but various harmonic components mingling with each other. If you have low THD, you will have low IMD. True, it is another useful tool, and THD is certainly not the final word. But you cannot have high IMD without high THD.

Did you read the article I linked? A single tone measurement will not provide the criteria to see Doppler distortion. A multitone measurement is required. It is absolutely possible to have IMD with no THD.

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post #133 of 190 Old 08-09-2013, 05:51 AM
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Quote:
Originally Posted by splotten View Post

I have read many places that distortion in CDs is much lower than in ordinary dome tweeters (at equal SPL). Is that correct,.
It is, for the same reasons that midranges, woofers and subwoofers have lower THD at equal SPL when horn loaded than when direct radiating.
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"Now, why do CD/horns still sound more dynamic than domes? I still haven't found an answer."
power compression.
To some extent power compression, but that falls under the umbrella of headroom. If a dome has a maximum displacement limited output of 105dB that doesn't leave a lot of headroom if your listening level is 100dB. if you listen at 100dB with a horn loaded tweeter that's displacement limited to 130dB the available headroom results in less power compression, lower THD, lower IMD, and for that matter lower THD from the amp as well.
http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_1.pdf

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post #134 of 190 Old 08-09-2013, 10:47 AM
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Quote:
Originally Posted by rahula7 View Post

Power compression is a long term phenomenon.

Flux modulation compression.

Yes, thermal modulation is important, but compression isn't only due to the thermal aspects of the heating of the voice coil. Granted, a great deal of the compression results from the thermal characteristics of the assembly to dissipate heat. However, another component is magnetic flux compression.

Although the typical thermal compression most discussed is more long term, the effects of magnetic compression are instantaneous. These magnetic compression distortions, can dull transients, and render reproduction as lifeless, dull and unrealistic. The issue is quite insidious because it's not an overly offensive distortion. It just seems to thins out the playback, stripping away the life and snap.

Here's more from another post I submitted on this issue;
"The magnetic issue lies in the fact that when the drummer hits the kick drum pedal, and the beater strikes the head, the signal path results in the voltage is impressed across the loudspeaker's terminals. This results in the current flow in the VC, and subsequently the driver attempts to track the signal accurately. The problem is that when current flow begins in the VC, there exists three separate, and entirely different sources of magnetic flux in the gap. The permanent magnet's flux, the signal voltage VC flux, and lastly the flux that's generated by the varying eddy currents in the pole pieces. This is the problem, the flux modulation compression.

Whereby the thermal compression effects are a function of time, the magnetic flux compression is instantaneous. Magnetic saturation of any of the motor elements needs to be entirely avoided, as it's effects instantly impact waveform shape, the peak, and peak capability."

That's my take on the issue ...

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post #135 of 190 Old 08-09-2013, 10:57 AM
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FOH, How would this be different in a compression driver?

@MBentz, no, I didn't read it. I will do so.

Many of us here have popular CDs and tweeters. It will not take long to do a quick comparison. I recently moved and my stuff is in boxes. Let me see if I can rig something up this weekend. A DNA360 on a SEOS 12 versus a Vifa XT25 or one of the Dayton tweeters should be an easy enough comparison. 90 db at 2m should be a good reference. Or maybe Matt can do it for us smile.gif

I wanted to believe as much as you guys that distortion is THE cause for the perceived dynamics of CDs compared to domes. So far, all the real data I've seen doesn't show it.
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post #136 of 190 Old 08-09-2013, 11:16 AM
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Quote:
Originally Posted by rahula7 View Post

FOH, How would this be different in a compression driver?

Dome tweeter, compression driver, LF driver, ... it wouldn't matter.

The determining factor would be the how magnetically robust the motor is. Read my above take on the topic? Do you disagree?

"magnetic flux compression is instantaneous. Magnetic saturation of any of the motor elements needs to be entirely avoided"


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Originally Posted by rahula7 View Post

I wanted to believe as much as you guys that distortion is THE cause for the perceived dynamics of CDs compared to domes. So far, all the real data I've seen doesn't show it.

It's the ability to track the signal, call it what you want.

Compression, be it primarily thermal modulation or magnetic non-linearity, I don't know. But when those two aspects are out of the way, you're a lot closer to the goal.

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post #137 of 190 Old 08-09-2013, 11:18 AM
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"IMD is nothing but various harmonic components mingling with each other. If you have low THD, you will have low IMD."

with harmonic distortion, you get harmonic distortion products.

with intermodulation distortion, you get sum and difference distortion products.

sum and difference products are far more annoying than odd order harmonic distortion because they are unnatural occurrences, whereas harmonics are something that is common to many sound sources, particularly even order harmonics.

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post #138 of 190 Old 08-15-2013, 07:50 PM
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Quote:
Originally Posted by rahula7 View Post

And CDs are always compressing the air. That's how they work. It's not like it comes into play at higher SPL only.

Nonlinearity of the air spring and attendant distortion increases with drive level; same reason it's recommended that a sub driver's Vd should not exceed 5% of the enclosure volume.

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post #139 of 190 Old 08-15-2013, 09:53 PM
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I once took a couple robust domes and ran a sweep at 2.83 V. I then ran the sweet at +3db and +6db and so on. I then adjusted the offset in the measurement program to overlay them back to 0db. Around +15 db there was considerable compression in the domes. These were short sine sweeps.

I didn't try a CD though. I can.
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post #140 of 190 Old 08-15-2013, 09:55 PM
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Oh ya that was with a 2500hz second order high pass in place. The compression happened all the way up into the top octave.
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post #141 of 190 Old 09-08-2013, 01:16 AM
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Will there be some more results on these sometime? I was looking at either the SEOS 12s or 15s and the H290c, was looking forward to seeing some measurements on those guys.
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post #142 of 190 Old 09-08-2013, 06:45 AM
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Quote:
Originally Posted by LTD02 View Post

"IMD is nothing but various harmonic components mingling with each other. If you have low THD, you will have low IMD."

with harmonic distortion, you get harmonic distortion products.

with intermodulation distortion, you get sum and difference distortion products.

Any nonlinearity will produce both harmonic distortion and IMD. It's in the math. IM and HD are not properties of equipment. Nonlinearity is.

I think you are saying that HD and IM are simply two different ways to characterize nonlinear response. THD is simpler to measure and analyze, but fails to give accurate results for systems with limited bandpass, which can include CD players and speakers, and really just about anything.

For example you can have a speaker or other system whose response rolls-off at 20 KHz. Test signals above 10 KHz will appear to have no or unrealistically low harmonic distortion because the harmonics are lost or at least attenuated by the 20 KHz roll off. If you do an IM test with say 18 and 19 KHz tones, the 1 KHz difference tone will not be affected by the 20 KHz roll off. Of course if this is a tweeter, their may be a low end roll off as high as 3 KHz or more, so you have to know what you are measuring to measure it in a representative way.
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sum and difference products are far more annoying than odd order harmonic distortion because they are unnatural occurrences, whereas harmonics are something that is common to many sound sources, particularly even order harmonics.

Another way to say this is that sum and difference products tend to be aharmonic or non harmonic and therefore are less likely to be masked by the harmonic structure of the music. Virtually all music contains many different tones so a carefully planned IM test can be far more representative.
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post #143 of 190 Old 09-08-2013, 08:27 PM
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"If you have low THD, you will have low IMD."

Not necessarily; you could have a driver with a perfect motor and high xmax giving zero THD, but there's no way around IMD because of the physical excursion and resultant Doppler effect.

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post #144 of 190 Old 09-08-2013, 08:37 PM
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"Any nonlinearity will produce both harmonic distortion and IMD. It's in the math."

so are you saying that just by knowing the harmonic distortion, you can back out the imd??

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post #145 of 190 Old 09-08-2013, 09:55 PM - Thread Starter
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Quote:
Originally Posted by shadyJ View Post

Will there be some more results on these sometime? I was looking at either the SEOS 12s or 15s and the H290c, was looking forward to seeing some measurements on those guys.

Don't worry they are coming, things got busier this past month then I expected so this was sidelined for a little while. After the first few waveguides were tested on the baffle I made I thought the frequency response of some those waveguides that I have already used looked a bit more lumpy then I remember. I was hoping that by making the baffle so large It would simulate a half space measurement and eliminate edge diffraction unfortunately that does not seem to be the case. Just today I took some more sets of measurements of the EOS-6 waveguide, one set mounted in a regular enclosure with a baffle 8" wide x 14" tall, another set without the waveguide mounted to a baffle. I still need to generate the polars for those so I can show all three setups side by side but right now it looks as if the measurement without the baffle shows the least amount of diffraction. Now obviously most will use these waveguides in enclosures but it is impractical for me to build an enclosure to fit each waveguide. So I will be looking to see whether the large baffle or no baffle more closely follows the response of the waveguide as mounted in a regular enclosure. If the baffle is closer I will continue testing the rest that way, if no baffle does better then I will switch to that method and retest the ones that have already been done as well.
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post #146 of 190 Old 09-08-2013, 10:21 PM
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Thanks for the heads up mtg, and don't feel as if I am trying to rush you, I was just wondering if this testing is still on, as I know it is a lot of work.
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post #147 of 190 Old 09-09-2013, 08:19 AM
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Isn't your test baffle 4'x8' ? Seems big enough to minimize diffraction...

I think either way it won't matter as long as it's all consistent.
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post #148 of 190 Old 09-09-2013, 08:55 AM
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I still vote for dropping the CDs into a small pit with the baffle ground level flush. Easy to do and provides pure CD & horn response by avoiding the equivalent of a large baffle close to a wall.
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post #149 of 190 Old 09-10-2013, 08:16 PM - Thread Starter
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OK as I thought the baffle was creating major diffraction bumps in the frequency response. It would be nice to have a hole dug in the backyard for a few months so I could drop the baffle in when needed but I still don't think it would go over too well tongue.gif

All three of these are adjusted the same settings, 6ms gating, 1/48th octave smoothing, and were taken at 1m (though I did not have drive level set the exact same). This is the DNA-150 on the EOS-6 waveguide.

First the original set 0-90 degrees (0, 10, 20, 30, 40, 50, 60, 75, 90) horizontal on the large baffle:


Now measured flush mounted to a speaker baffle (8"w x 14"h):


Now measured without a baffle:



Now the polars in same order:




I should mention that the large baffle polar was done with higher resolution having 5-15-25 degree measurements in there as well.

Now I have come to the conclusion that the polar on the large baffle may look slightly narrower because the diffraction bumps cause some spots on the 5 and 10 degree measurements to measure slightly higher in level then the 0 degree line which skews the 0dB reference point a little.

The measurements of native frequency response look cleanest without a baffle, while the large baffle does the directivity polars best.

Ahhhh what have I have gotten myself into. rolleyes.gif
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post #150 of 190 Old 09-11-2013, 07:26 AM
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Hey Matt, can you explain to us non-technical novices guys what those graphs are and how to interpret them?

That would be a huge help as I have been following this thread the entire time but honestly have no idea what these graphs are telling us.
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