Help with due diligence on a line-array project

egert

Member
2013-05-22 7:18 am
Up to date I have done three speaker projects and have started another one which is … let’s say, very ambitious. I would like to ask your assistance to poke holes into my design, so I don’t fail miserably. The reason I am going forward with it is that my wife does not really stomach the baffle-less listening rig I am using. She loves the sound, but her sensibilities do not really enjoy the naked drivers just hanging there.

Current system

The current rig is a baffle-less setup with a Audio Nirvana 10” fullrange driver per side and a Ripole woofer crossed over at 120Hz. The fullrangers are pretty heavily equalized with a major bump up to 500 Hz (+~12db) managed at the digital source, a computer run ASUS STX II. I enjoy the “disappearing act” of these “speakers”. They are great for Jazz and anything vocal while they seem a little out of breath for loud rock. Before you mention the amount of beaming a 10” fullranger must exhibit anywhere above ~1500Hz, I have them hanging at a 25deg angle at head height. This gives wonderfully good dispersion and conveniently does away with the on-axis response elevation at high frequencies. The drop-away at 15kHz+ is again equalized similarly to the midrange.

The starting point

My wife has requested to integrate the speakers to a new wall section we are ordering. It is full room height (2450mm) and 3200mm wide. The speakers must fit into the 200mm wide sides with an option of up to 150L of space for two side-firing subwoofers encroaching on the storage space. Listening point is ~3m away from the face of the cupboard. Major weakness is that the wall is right behind the listening point, but I am not allowed to pivot the system to align with the long axis of the room.

The project

Type: open baffle line array
Mids and highs: 10x Neo8 planars per side
Lows: 13x 5.25” peerless drivers per side with a ~40Hz resonant frequency, slot loaded at 134mm slot depth (650Hz resonance).
Crossover: ~48db/oct, digital, ASUS STX II, 350 Hz, mid-woofer high pass at 40-50Hz
Amplification: 15W class A for Neo8-s, 10W class A for 5.25s, 100W class A/B for woofer (reusing from current system)

Design drivers:

1. Ability to play up to 100db at any frequency with the low class-A amplification available.
2. Have a single driver cover as much of the 300Hz-8000Hz range to avoid any crossing over in the most sensitive hearing area (and avoid the need for a new computer to be able to mount another STX II mainboard as the other 6 channels are good only for lower stuff).
3. Highest near/far field transition distance at least 1m behind the listening position to avoid the large output swings in the transition range (array will couple to wall and ceiling at above 780Hz, so line distance should not be more than 22cm from wall and ceiling, a 2m array gives a 4m transition distance for the same frequency).
4. Keep most or all the imaging capability of the current setup.
5. Dipole bass to 50Hz to avoid room-modes, sealed closed box monopole below that.
6. High range coverage should extend to most of the 2m wide listening area. (Neo8 is near-linear up to 15deg off axis, requiring 10deg of toe-in)
6. Should not look like speakers.

Concerns:

1. The back wall is just 40cm away from the drivers and on one side about 60cm from the side wall.
2. The concealing side-slats are at a right angle. Should they be angled to let the back-wave through also at frequencies above 10kHz?
3. Angled drivers in a cut baffle. I am not very knowledgeable whether and what problems this may cause.
4. Crossing the Neo8 at 350Hz. This should not be a problem since the sensitivity in a baffle is around 85db at that level, meaning the array response would be around 95db, and thus 100db at just 4 watts.

Disclaimers:

1. I still need to simplify the design to keep the CNC costs in check.
2. Midwoofers are lacking bracing for now.
3. The overall design for the shelves and the like is a quickie-stopgap to showcase the idea, don’t pay attention.

Let me know what you think. If possible, I would like to order the drivers and put in the order for all the CNC work within a month.

In case you want to be more involved, here is a link to the thing in the OnShape application. You may need to register as a user to gain access. Be gentle, this is my first work in any kind of CAD.

Onshape
 

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