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3-Way Open Baffle Straight Line Array (Floor to Ceiling)
3-Way Open Baffle Straight Line Array (Floor to Ceiling)
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Old 27th December 2019, 09:03 PM   #1
mlee is offline mlee  Canada
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Default 3-Way Open Baffle Straight Line Array (Floor to Ceiling)

Moving on from a sealed fullrange line array made with SB65WBAC25-4 times 36 floor to ceiling is my next project. I like the current line array system, but I also like my 3-way open baffle and horn system so what to do? Full length 3-way open baffle of course!

Goals:
- Single driver from 400hz to above 7khz. (I think) one the things I find pleasing from the horn and existing OB system is radiation pattern control in that range. See Geddes. Also Linkwitz took his system from about 1khz to 7khz with a single 4" driver with a focus on radiation pattern. I'd like to push that down a bit with the Line Array application.

- I like the sound of Open Baffle bass! In my room it works and I don't have space for multi subs. I've had 4 sealed sources in my room and it works to smooth out low frequency modes; however, I don't like the room pressurization with sealed subs. Something about the presentation is slightly different. Since I don't listen loud and prefer low volume listening I've found the presentation of OB from 30hz to 500hz more pleasing.

- Floor to ceiling straight array. Trying to follow Jim Griffins white paper but will not be implementing shading at this time.

- Minimal baffle width. Trying to follow Linkwitz and John K. philosophies for baffle width. Trying to stay below the baffle peak in all drivers is difficult. Some compromise are in order of course.

- One thing I wanted to try is a space between the midrange and woofer line in hopes to get some horizontal OB control with minimal baffle. Not sure how to perform accurate measurements for this in room. Would be nice to get some side cancellation so the midrange line doesn't "see" the woofer baffle as support. Not sure this will be feasible. According to Jim Griffin white paper spacing should be less than 1/2 a wavelength. I think we can get close to 1/4 wavelength at crossover but I'm oscillating on the woofer array right now.

Tweeter Array:
Dayton PTMini-6. 24 high.
Since they are sealed will have to make the array with front and rear facing units. That doubles the cost of the tweeter array so we will make a front firing array first and see about the full monty later. The nice thing about these drivers and this application is the driver width = 23mm. So a full dipole line array could be constructed in a 1" by 1.5" package including all wiring. That is mechanically very nice. This also allows a type of plug and play tweeter array to use with my existing LA for sport. Also in theory the radiation pattern should be nice, although since we are using side mounted midrange we might not be able to take full advantage of the radiation pattern .

Construction will be done using 1/2" baltic birch with tweeter mounted using double sided sticky tape from home depot. This worked out well on the test baffle. Simply drill holes for the wires/quick connects and go one your way. Allows for nice spacing with minimal effort. Also one can pre-assemble the wiring harness for 6 in parallel and 4 in series. Making roughly a 4 ohm load. Can gain a bit of sensitivity that way. Construction will not be as excruciating this way and might get some damping due to the tape soft mount. Ceiling mount so they don't fall over.

Midrange Array:
NEO8-PDR times 10.
I know not really exciting here but it really is one of the best choices for this application. Will have to go with 2 in parallel and 5 series. This looses some sensitivity but no choice here. Cannot fit 12 in my room.

Construction will be done with 1/2" by 1/2" aluminum square bars. This allows for minimal baffle and hopefully enough strength to stay somewhat straight! Foam damping behind the driver and routed out depressions for the NEO8 rivets in the back. This will be a lot of work for me but not too bad. Probably need a hole template. Ceiling mount so they don't fall over.

Woofer Array:
TBD.
Would be nice to stay with 1/4 wavelength at XOVER and use 10" drivers times 8. That said I haven't really liked the any 10" OB drivers I liked for bottom support. Thinking 15PR400 would be something but no minimal baffle then and CTC spacing is a bit much. Some thinking to do........taking suggestions. I like the low QTS professional woofers with EQ better than the high QTS drivers I've tried. That said the GW-1858 was nice but missing the clarity of the 15TBX100 I used. I was using the GW up to 500hz so in this application the lower QTS sounded better. If low bass under 100hz, probably no difference. Since we are looking at 350hz to 400hz XOVER we should be careful about this or perhaps some major disappointment and expense.

More to come later. Tweeter and Midrange drivers on order!
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Old 28th December 2019, 12:15 AM   #2
CraigSu is offline CraigSu  United States
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If you’re using the NEO8’s do you really need the PTmini’s? That would greatly simplify your design and would save you some money as well.
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Old 28th December 2019, 12:45 AM   #3
mlee is offline mlee  Canada
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If you’re using the NEO8’s do you really need the PTmini’s? That would greatly simplify your design and would save you some money as well.
Based on my prelim listening tests yes. Also I'd like to try them with my existing arrays so not a complete waste. Only half.
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Old 28th December 2019, 01:39 AM   #4
cspieker is offline cspieker  United States
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very interesting that I am fiddling with an open baffle line array with the sb65. supplemented below 500hz or so with sealed woofer is the plan. still just scratching my head, but I have some drivers coming. You find the sb65 lacking in the treble??
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Old 28th December 2019, 01:51 AM   #5
mlee is offline mlee  Canada
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Originally Posted by cspieker View Post
You find the sb65 lacking in the treble??
I guess I'll have to fess up. Yes mostly and a bit no. You can eq the extreme treble to satisfy (so no) but it ends up being a very non-efficient speaker because you don't get the same gains in the treble as the bass.

I like the treble presentation better with some of my other speakers. Perhaps the LA form is more picky about absolute eq but I have trouble with long term satisfaction of the SB drivers in a full range line array application and I can't stop fiddling with treble levels. I don't do this with a number of other designs. That said the midbass is pretty smooth, better than a large number of my other speakers. There is an ease about it that is not easily matched.

Perhaps I should try Jim Griffins suggested shading or implementing a CBT but the one thing I wanted with that build was to use them fullrange to 30hz and no crossover. This goal was met but there are other issues that require solving for my long-term satisfaction. Not sure how much further I want to go with that build. I like the cabs and it was a lot of work. I don't want to change the enclosure and I don't have facility to do the shading properly at this time.
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Old 28th December 2019, 02:51 AM   #6
CraigSu is offline CraigSu  United States
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Quote:
Originally Posted by mlee View Post
Based on my prelim listening tests yes. Also I'd like to try them with my existing arrays so not a complete waste. Only half.
If dipole tweetering is the route to your satisfaction then you may be able to use half or less than the front amount on the back side. After all, the rear radiation will be augmented by reflection off the wall they face.
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Old 28th December 2019, 05:33 PM   #7
mlee is offline mlee  Canada
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Not so much dipole tweeter but wide dispersion me thinks. It's tough to argue with tooles findings.
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Old 29th December 2019, 01:49 PM   #8
cspieker is offline cspieker  United States
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Thanks. Excited to see your project come along. My ob line array should have somewhat similar polars as yours above 500hz although mine won't be so wide at the very top treble. But in general, wider dispersion in the treble, narrowing up as you get lower, im very curious how this power response will sound since it is the opposite of most speakers. My hunch is that the very high perceived resolution of horns will be missing because the response will have to be reduced in the treble to counteract the rising power response in the treble.
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Old 30th December 2019, 06:51 PM   #9
mlee is offline mlee  Canada
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Originally Posted by cspieker View Post
...But in general, wider dispersion in the treble, narrowing up as you get lower, im very curious how this power response will sound since it is the opposite of most speakers....
Yes, that is actually one of the items I was going for. It is exactly opposite to what I'm running now. Will be a neat change. I'll give some subjective prose and rudimentary frequency measurements when they are up and running. Hard to measure fixed dipole arrays in room with any sort of accuracy but some will be better than non!
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Old 30th December 2019, 07:13 PM   #10
ErikdeBest is offline ErikdeBest  Switzerland
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