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Old 18th July 2011, 05:31 PM   #11
keyser is offline keyser  Netherlands
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Quote:
Originally Posted by ScottG View Post
Very nice!

That 150-500 Hz increase in pressure is likely all baffle related.

Look at MBK's experiments (and the difference in baffle/pressure release) here:

Adventures in cardioid
Thanks. I've seen that topic before. Do you mean that somewhere in that topic 'baffle related' issues are discussed? I browsed the thread again but I couldn't find anything directly related.

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Originally Posted by dantheman View Post
Fantastic Keyser! Excellent job. Thank you for posting and having the insight to do this.

Dan
My pleasure. Thanks for the kind words.


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Originally Posted by c2cthomas View Post
Very Nice!!!!

Look up aperiodic enclosures - it is similar to the method you are using on your enclosure and might help out with the crossover.

There are several websites that discuss the theory - here is one that shows a practical application: WD25A Design Pg2

There are some similarities (like the free-air resonance of the woofer in my speaker is 58 hz, but when built into the enclosure it drops to 52 hz - and the impedance peak at resonance drops from about 40 ohms to about 20), but the design criteria are very different. The aperiodic enclosure is designed for bass, but I designed my speaker with primarily directivity in mind.

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Originally Posted by CLS View Post
Great job indeed!



As I saw the throat of the WG, there's still that old problem. Have you seen this:

3 way open baffle with Eminence and Skytronic

It's not entirely the same situation as yours. But the throat is worth investigating and some improvement.

The entrance of this Dayton WG is not exactly 1", it's slightly bigger. So there'd be a step from the driver to the WG.
You're right, the waveguide and the compression driver don't match perfectly. Do you think this is what causes the ripples in the frequency response? The irregularities are the same at every angle, therefore I reckoned it was the Selenium.


By the way, yesterday I set the entire system up in the garden. First I undid some roomEQ in the midrange and I made the response very flat. Then I decided to have a listen. It seems the harshness in the midrange seems to be due to faults in the frequency response. Outside it sounded very clean, also at higher levels. The biggest issue was the floor-bounce, which degrades the frequency response much more than it does indoors, where its effect is mitigated by other reflections.

After yesterdays corrections the speaker sounds a lot better. I've decided to optimize the speaker placement based on measurements taken at the listening position and not to do any roomEQ on the speakers anymore. The subs still do have some EQ. This sounds very good to my ears.

To me this simple plastic waveguide and inexpensive compression driver sound no less sweet than the best cone-dome combinations. I'm not sure if I'm supposed to hear horn honk or HOMs maybe. What do those of you with more experience with horns think?
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Old 19th July 2011, 12:15 AM   #12
ScottG is offline ScottG  United States
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Quote:
Originally Posted by keyser View Post
Thanks. I've seen that topic before. Do you mean that somewhere in that topic 'baffle related' issues are discussed? I browsed the thread again but I couldn't find anything directly related.
Adventures in cardioid

You only need to read posts 1, 2, 4, 5, 6, 7, 8, and 10 in context with the measurements and the pictures. (post 3 is exclusively concerning the horn and tweeter.)

1 & 2 is an open baffle with a decidedly non-dipole polar pattern in the midrange - because of the overall profile of the baffle.


4,5, 6, and 7 all make use of a larger baffle (though with the "muffler", and as a result the pattern becomes "wider" or less directive than seen in post 8. (..graph in post 7 vs. post 8.) The baffle looks smaller than yours - so the polars become more directive higher in freq.. (..in this case starting at about 250 Hz and up).



Post 8 starts off with a "title in bold" of:

"So let's eliminate the baffle"

It's there that you get to see where the directivity is fairly uniform - because he removed the baffle. (..or actually there is still the small mounting "ring" baffle for driver and muffler.)

You can see a picture of it resting on top of the old baffle in post 10.



I suppose this is all a long-winded way of suggesting that you try "spliting" the baffle up from the horn/CD and the midbass driver. (..two separate "Baffles" stacked but with a modest amount of air-space between them.)
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Last edited by ScottG; 19th July 2011 at 12:29 AM.
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Old 1st August 2011, 11:38 AM   #13
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Scott, thanks. I've looked at it some more, but it still isn't completely clear to me. Maybe someday I'll experiment some more with it to get a better grasp on what's really happening in the transition region between dipole with damped rear-wave and the more cardioid/closed-box like behavior at higher frequencies.

I was under the assumption that last week I uploaded these measurement graphs, but it appears I only uploaded the sonogram.

The measurements in the opening post show an excess of energy below about 500 hz and recessed high frequencies. Those issues have been dealt with, as well as some other small irregularities. I'm also showing the more smoothed, ungated responses to better show what's going on at lower frequencies. The final curve is the average response at the rear.
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Old 1st August 2011, 02:24 PM   #14
doug20 is offline doug20  United States
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Cool project...

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The first thing I noted was the ragged response above 5 khz. Let’s hope it doesn’t sound as ugly as it looks!
IMO, the Selenium to me is the worst sounding CD of them all, it could be just the screw on types though ( I never did get anything I liked out of the Dayton + Selenium CD). In that price range I would choose the Celestion 1745 over it.

Last edited by doug20; 1st August 2011 at 02:28 PM.
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Old 1st August 2011, 02:49 PM   #15
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Thanks for sharing.

The opinions of the Selenium vary almost as widely as its amplitude response above 6 khz! I think if you look at the response curve (or the CSD, for that matter) long enough, you just have to hear lousy high frequencies!

However, it is interesting that of the several audiophiles I've had over to listen to these speakers - most of them with limited technical knowledge of loudspeakers - nobody commented about the highs being sharp or lacking resolution! I myself don't hear it either.

I would like to know what others think of it too, though!
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Old 1st August 2011, 03:00 PM   #16
doug20 is offline doug20  United States
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No problem, could be true about staring at measurements and then 'hearing' it but I listened to 5 CDs I bought for my 2-way waveguide build before I measured any of them.

There are many that have enjoyed the Selenium driver in the econo waveguides. Im just not one of them.

Last edited by doug20; 1st August 2011 at 03:03 PM.
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Old 1st August 2011, 03:10 PM   #17
doug20 is offline doug20  United States
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The passive crossover was a bit more difficult to get right than I’m used to. The acoustic centre of the tweeter lies a bit behind that of the woofer. This causes some excess phase. To work around this, I had to cross steep and I had to do a few tricks to get the right amount of relative phase rotation.
There was a good discussion about this on HTguide.com when Augerpro was building a two. I will try and find it. We also rear mounted our woofers to try and get the AC closer together.
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Old 1st August 2011, 03:21 PM   #18
doug20 is offline doug20  United States
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I think this was the discussion

Quote:
John Kreskovsky brought up an interesting alignment that might be prefect to try with this design, for the passive version. Here is what he said:

"Additionally, a 3rd order, quasi Linkwitz type crossover is easily constructed by cascading a B2 with a B1 filter and delaying the high pass section by 0.25 wave lengths at the crossover frequency. The response error will be +0, -1.2dB max. This is easily constructed using passive elements.

For the HP,

C1 = 1/(4 Pi R F), C2 = 1.2 /(Pi R F), L = 1/(2.4 Pi R F)

For the LP

L1 = R/(Pi F), L2 = R/(4.8 Pi F), C = 0.6 /(Pi R F)

Offset tweeter by 0.25 wave lengths at the x-o frequency and connect with inverted phase. "

What caught my eye was that the AC offset (versus 1300hz crossover) of my No Quarter design is nearly identical to the above spec of .25 wavelength of crossover. I also like that this has a broader overlap than LR4, but won't be as demanding as LR2. And all the usual LR properties of symmetric lobing and in phase drivers.
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Old 1st August 2011, 05:07 PM   #19
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Default D220Ti crossover point

I'm also using the D220Ti + HW12 in a speaker that I am building so I read your thread with much interest.

I noticed that you cross over at 1k Hz. This is on the low side for the compression driver. I am wondering if you have done any listening or distortion tests yet, and if so what is going on around 1k Hz? Can you detect any strain, etc? Maybe this is why the midrange sounds "shouty" (per your initial post)?

Nice work, BTW!

-Charlie

Last edited by CharlieLaub; 1st August 2011 at 05:14 PM.
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Old 1st August 2011, 06:32 PM   #20
keyser is offline keyser  Netherlands
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Originally Posted by CharlieLaub View Post
I'm also using the D220Ti + HW12 in a speaker that I am building so I read your thread with much interest.

I noticed that you cross over at 1k Hz. This is on the low side for the compression driver. I am wondering if you have done any listening or distortion tests yet, and if so what is going on around 1k Hz? Can you detect any strain, etc?

Hi Charlie,

I haven't done distortion measurements yet (will do that during next measurement session), but I'm convinced the Selenium is used nowhere near its limits. If these speakers were to be used in a PA, I would probably have used a crossover closer to 1.5 khz, but for hifi this is not necessary. Horn-loading is still evident around 700 hz, under which frequency the response begins to roll off. The crossover at 1 khz is about 30 dB acoustically, which is significant, so I don't see any problem here.

Last saturday I threw a party to celebrate my birthday. Some friends were interested in my new speakers and we listened to Child in Time by Deep Purple, from their Made in Japan album. Right now the limiting factor is probably the power amp (but it might also be the output of the miniDSP), an NAD C370 integrated amp with some 150 watts at 8 ohms. Up to about 107 dB continous inroom SPL it remained very clean, but above that it began to clip. This is probably due to the significant boost at 100 hz (about 8 dB's), to compensate for the open-box roll-off. I'm okay with a 107 dB SPL maximum continuous level - those aren't levels I want to endure too often or too long, let alone even higher levels.

Quote:
Originally Posted by CharlieLaub View Post
Maybe this is why the midrange sounds "shouty" (per your initial post)?

Nice work, BTW!

-Charlie
The slightly shouty character I mentioned disappeared after I omitted the roomEQ in the midrange, improved the EQ of the speaker and changed the placement of the speakers a bit. Now they sound very good to me. I was really happy with the sound of the dipoles I had before (link in the opening post), but I think these sound even better.

EDIT: Do have topic about your own speakers. I saw a picture in the 3-way econowave thread. Now I'd like to see some more! Also I'd like to hear about your design choices.
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Last edited by keyser; 1st August 2011 at 06:35 PM.
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