2 way design proposal- would appreciate help

[johnbomb]

Hello,

Thanks for your interest. I've been reading all I can about speaker design, and I have a proposal for speakers that I'd like to use for the front 3 channels of my home theater, currently under construction.

My goals for this project:

1) Apply the design principles of the Zaph Audio ZD5 to the build- thanks John, for your effort and clarity!:

Zaph|Audio - ZD5 - Scan Speak 15W8530K00 and Vifa XT25

2) Low baffle diffraction, with a smooth baffle step.

3) Ability of each two way driver pair to hit 105 db max (reference level).

4) 2-ways will be crossed to a subwoofer at 120hz, likely LR4.

I'd like to build three two way speakers into a large MDF baffle that is attached to the under surface of my projector screen, spanning the width of the screen frame (about 7.5 feet). This baffle design is currently a work in progress, but I would like to make the front of it that houses the drivers flat, and then curve the entire lower portion as well as the distal aspects of the sides toward the back wall. The flat part will ideally form a continuous surface with the screen. I'll try to attach a sketch later for clarification.

I will use digital crossovers in the form of the MiniDSP with the stereo two-way advanced pluggin to allow for and LR2 crossover, FR shaping, time/phase alignment, etc. I'll use an ETC, probably in the form of Room EQ Wizard, for measurement.

As of now, I have selected the Zaph Audio ZA14 midwoofer and the SB Acoustics SB29RDC tweeter to flesh out the project. Based on John's work, I think a 2300-2500 XO might work for an LR2.

I would very much appreciate a thought check or some constructive criticism of this plan before I buy the components. I expect that the baffel design will evolve, and may go through a few prototypes before finalization.

Thanks very much,
John

[kbgl]

Since the speakers can't be tilted inward, you are going to be more off axis at some seats, and you also may have more reflections off the side walls.

[pedroskova]

few points:

If you want 105 dB at the listening position, this will mean that your speaker must be capable of ~108 - 112dB at 1 meter... a tall order for a single 5 1/2" midbass. Look at the Zaph HT kits at madisound - there's a reason he uses two MW's.

You might get away with an LR2 xover with a notch filter, but you wouldn't be taking advantage of the steep slopes offered by the minidsp. You need to stay away from the metal cone breakup region that starts showing up between 4-5kHz.

Your baffle sounds interesting , and with proper placement of drivers, baffle step compensation needs would be minimal. I don't know how large / wide it will be, but I think you could get a little more ambitious with driver sizing, maybe going with a 10" / waveguide combo like the econowave that some around here have built. That would meet your dynamics needs.

hope this helped and didn't put you off.

[johnbomb]

Thanks for the response.

Kbgl, hopefully the side reflections won't be an issue, as I plan to use an ETC to search and destroy those with absorption.

Pedroskova- good point about the 108-112 db. I'm not sure if "reference level" refers to the actual measured output at the speaker position or at the listening position. This article suggests that "reference" level refers to the system output- correct me if I'm wrong.

Either way, reference level is more a goal than an absolute requirement, as 105 db coming out of the speakers is still REALLY loud in a small room. I'd almost certainly never listen at that volume unless I wanted to impress some friends . I think I'll re-specify my goal as "105 db output at the speaker level." With the sensitivities of the drivers and a 120hz subwoofer XO, that could work, right?

As far as the breakup node of the woofer cone, do you understand how Zaph was able to pull of LR2 with his Scan Speak driver in the ZD5? I'm all ears, as I'm very new to all this.

Thanks,
John

Edit- forgot to add: I'm shooting for an LR2, based on Zaph's comment on his ZD5 page:

"In the end, an LR2 design has 180 degrees of phase wrap through the crossover while an LR4 has 360 degrees. The lower phase wrap directly equates to an improved midrange coherency. Honestly, most drivers and system designs require LR4 or greater slopes just to work properly. But when everything comes together for a LR2 system, it's the sweet spot in speaker design. Why is it the sweet spot? Because the next step is no crossover at all in a full range driver, which is a step backwards, introducing a whole different set of problems that detract from good sound."

As a complete beginner, I'll defer to his stance. However, I'm certainly open to considering other opinions.

[johnbomb]

Here's the sketch. Does this look like a good start? That speckly stuff on the bottom of the baffle (front view) is supposed to imply shading.

Thanks,
John