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Multi-Way Conventional loudspeakers with crossovers

pattern control below 400Hz
pattern control below 400Hz
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Old 4th January 2019, 06:14 AM   #1
hollowboy is offline hollowboy  Australia
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Default pattern control below 400Hz

My current system is a horn >700Hz, dual 15" midbass, dual 15" sub. The main flaw seems to be uneven midbass (in a big open room with lots of glass + hard floors). Better pattern control would be nice.

I made a prototype horn based on the Syncalc spreadsheet:

Coverage angle 90 x 65.52
~60cm wide, horizontal pattern control to 400Hz

I picked an easy build (mostly 45 degree angles, no secondary flare), and easy components, so it worked out OK.

I'd like to maintain some directivity < 400Hz, rather than have an abrupt transition to omni, as a small woofer would do.

Hence I'm considering using the biggest drivers I have (a couple of 18"), in boxes like the "Resistance enclosure" on this site:
Cardioid bass

That seems to have good output and directivity to < 100Hz in a reasonable sized box that doesn't require heroic crafting skill or lots of iterations to build.

Is there a similar / better option I've missed? e.g. would 2 x 15" arranged like the woofers in the small syns work better?
Small Syns

Notes:

the mains won't have to go super low, because subs.
happy to multiamp and use DSP, but don't want it to get super complicated

Limitations:

width <80cm
I'd like to keep everything simple(ish) so I have a decent chance of making the final build look pretty.
I'd like to use up old drivers I already have rather than buy new (one pair 18" EV woofers, multiple pro 15").
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Last edited by hollowboy; 4th January 2019 at 06:15 AM. Reason: fixed a plural thing
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Old 11th January 2019, 07:57 AM   #2
hollowboy is offline hollowboy  Australia
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I've done some info hunting:

- there's more info on cardioid response / resistive enclosures than I thought. Some of it is on this site. Some of it is very pertinent.
- doing a Google search, then choosing results that take me to this forum seems to find better results than the forum’s own search function.

I've done some info experiments:

- I'm staying with a small cone driver at the apex. It sounds better to me than the couple of 1" compression drivers I tried.
- an 18" on OB gives plenty of midbass, and seems to go low enough to work with subs. Sweeps show high distortion ~100Hz, but that's probably because the baffle is cardboard and cable ties The raw driver is OK.

I'm now trying to minimax the design:

1) how can I lower diffraction without overly complicating the build?
2) how can I avoid "waistbanding" without overly complicating the build?
3) the test rig has the woofer at floor level. If I raise the system to get the horn to ear height, will I make the bass worse?
- would it be good to use two woofers (vertically) to prevent a floor bounce suckout?

Pix: the directivity image is a Yorkville Unity, taken from the Red Spade blog, to illustrate "waistbanding". The others are from my prototype.

My FR plot has the midbass crossed at 1kHz, no eq. The HF driver is also crossed at 1kHz + has simple eq to address the HF rolloff.
Attached Images
File Type: jpg small prototype.jpg (132.1 KB, 501 views)
File Type: jpg small proto in use.jpg (106.5 KB, 496 views)
File Type: jpg Syn mids and highs 1kHz cross.jpg (91.3 KB, 573 views)
File Type: jpg Directivity-Yorkville.jpg (76.8 KB, 493 views)
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Old 12th January 2019, 11:56 AM   #3
oohms is offline oohms  Australia
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Pattern control means a larger horn.. you can't rely on the woofer (even at 18 inches) to do that at the ~500hz region.

Since i built that K402 replica a while ago i have thought of ways to make it simpler to build - one way would be to use foam at the mouth to combat the waistbanding instead of a tractrix curve ala:
Click the image to open in full size.

Alternatively, i would just build an even larger conical horn

What driver are you using for your horn, and how sensitive do you estimate it being in the horn? I'm thinking of getting an sb65wbac25-4 for a K402 like horn

Last edited by oohms; 12th January 2019 at 11:58 AM.
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Old 12th January 2019, 12:17 PM   #4
Juhazi is offline Juhazi  Finland
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Radiation pattern control below 400Hz indoors is a real challenge. A dipole or cardiod woofer can do that in principle, and perhaps also practically down to 100hz. But when you put that under your synergy on the floor it doesn't work any more.

Best practice is to just move speakers andl listening spot around the room to find best compromise with reflections and modes.

Go to this page hunecke.de | Loudspeakers Calculator

Give diemnsions of your room and construction materials. Scroll down to the colourful image of a room. Grab a speaker or mic, drag it and see how measured response and modes change! works also vertically. The simulator supposes that loudspeakers have typical radiation pattern, you can change speaker dimensions.
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Old 13th January 2019, 04:38 AM   #5
ScottG is offline ScottG  United States
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Quote:
Originally Posted by hollowboy View Post

Pix: the directivity image is a Yorkville Unity, taken from the Red Spade blog, to illustrate "waistbanding".

That's pretty horrific at 20 degrees: a broad-band dip of almost 10 db.

"constant" these days seems to be at best hopeful.
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Old 13th January 2019, 05:11 AM   #6
ScottG is offline ScottG  United States
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This depends on listening distance..

-you can do a horizontally-opposed design with 2x 15" all playing in the same bandwidth.

Say a 40" wide baffle cardioid (resistive side-vent on both sides) with each 15" at either end of the baffle and side venting. You can adjust the upper freq. pattern with how the woofers are "tilted" on the baffle relative to each other as in the Everest below:
Attached Images
File Type: png 3.png (465.1 KB, 67 views)
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Old 13th January 2019, 05:14 AM   #7
ScottG is offline ScottG  United States
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..of course pattern control below 400 Hz often extends not much more than a few feet from the louspeaker. (..but there does seem to be an audible difference regardless.)
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Old 13th January 2019, 05:50 AM   #8
hollowboy is offline hollowboy  Australia
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Quote:
Originally Posted by oohms View Post
What driver are you using for your horn, and how sensitive do you estimate it being in the horn? I'm thinking of getting an sb65wbac25-4 for a K402 like horn
Cone driver NE65w-04.

I compared it to a JBL 2" earlier, to get a guesstimate of sensitivity:

paper cone open frame driver for front horn

Post 39 shows the horn the comparison was done on.

Quote:
Originally Posted by oohms View Post
Pattern control means a larger horn
But that's what I'm hoping a more directive midbass would help with. I don't wanna go wider than them horn in that other thread. And I want it to be nicer looking
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Old 13th January 2019, 09:32 AM   #9
TBTL is offline TBTL  Germany
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Quote:
Originally Posted by Juhazi View Post
A dipole or cardiod woofer can do that in principle, and perhaps also practically down to 100hz. But when you put that under your synergy on the floor it doesn't work any more.
It does if you design it with the floor and top mounted stuff as part of the system. A passive cardioid enclosure is difficult to design. A box with two woofers (separate air spaces) and DSP is quite easy. Just place the box + top mounted stuff on a parking lot, measure both woofers at a certain distance at the angle at which you want maximum cancellation, add processing to make their amplitude and phase responses equal, then flip the polarity of the rear woofer. Then you end up with a cardioid response up to some frequency that is determined by the physical dimensions. A smaller box works up to a higher frequency.

Last edited by TBTL; 13th January 2019 at 09:41 AM.
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Old 13th January 2019, 11:27 AM   #10
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by hollowboy View Post
- doing a Google search, then choosing results that take me to this forum seems to find better results than the forum’s own search function.
I add "diyaudio" to a Google search if I'm looking for something here, I have given up using the site's search function
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