please help w/ the .5 woofer in 2.5 way design

[johnbomb]

I'd very much appreciate some help with my 2.5 way speaker dilemma. First, some background:

I'm designing an open baffle system to house the front left, center, and right channel speakers for a home theater. I'm using an SB acoustics SB29RDC tweeter mated to a modified parts express 8" waveguide and two Zaph Audio ZA14W08 mid woofers, whose specs are shown here:

Zaph|Audio - ZA14W08 Woofer

The baffle will be 87 inches wide by at least 13.5 inches tall, taller depending on the two midwoofer arrangement. The baffle will be mounted directly below a projector screen, approximately 1.5 to 2 feet in front of a fully damped front wall. The drivers of each speaker will be oriented vertically, tweeter on top. I will use miniDSP/Emotiva amplifiers to power the tweeters and full range woofers.

Here's my question: how do I deal with the .5 driver? I know I need it for baffle step compensation, and I have come up with three different power solutions:

1) Easiest and most expensive: add more miniDSPs/amp channels, dial in the baffle step compensation, call it a day... to the tune of another $800-$1000.

2) An active/passive hybrid: add an inline inductor to the .5 ZA14, run it and the full range ZA14 in parallel and control that limb of the speaker actively.

3) Build a 4th order bandpass enclosure for the .5 woofer to create an acoustic low pass, tuned to the baffle step. This could come in a few flavors: place the mouth of the port below the full range ZA14, or even build a two port box with the ports placed on either side of the concavity between the tweeter waveguide and the full range ZA14.

My goal for this project: maximize dialogue intelligibility and sound track articulation. I want to hear "the space between the notes". I have already decided that the polar response of a TM or TMM arrangement and that the maximum SPL are acceptable.

Regarding damping factor: how much difference might I hear between a fully active system and one which uses an inductor inline with the .5 woofer?

Thanks for your consideration,

John

[RockLeeEV]

Why not use the MiniDSP along with software to help you optimize a passive circuit for the tweeter/midrange crossover.

Then use the sameMiniDSP active for the .5 way. between the TM and M

Active is MOST useful with lower frequencies where costs of air core inductors is just too expensive.. I think passive is okay for a tweeter/midrange circuit since inductor values aren't super ultra high.

Especially if it's as high up as wherever the Zaph 5" starts to match the waveguide (won't that be up near 3khz or so?)! By keeping the .5 way part active, you can always change easily BSC based on placement etc. Component costs for a tweeter/midrange crossover will be low, and you won't have to even consider settling for nasty iron cores

I think what I suggested is the most cost effective way to do this.

You will still be perfectly able to apply any OB equalization yo have in mind... BTW, if it's an open baffle, then I don't think you will need BSC............also for an OB I would do rear tweeters... otherwise power response becomes unnatural. I also don't know if a pair of 5.25" speakers have the dynamics for soundtrack articulation BTW. You might as well swap one of the Zaph woofers with a third driver altogether, like the Seas ER18RNX perhaps.

[johnbomb]

Thanks, RockLeeEV.

Originally Posted by RockLeeEV

Why not use the MiniDSP along with software to help you optimize a passive circuit for the tweeter/midrange crossover.

Then use the sameMiniDSP active for the .5 way. between the TM and M

I had considered that, but I'll lose the ability to time align the T and M. Unless I'm lucky and don't need it, I'll have to build a ladder delay network, which is beyond me.

Originally Posted by RockLeeEV

....also for an OB I would do rear tweeters... otherwise power response becomes unnatural.

What do you mean by "rear tweeters"?

Originally Posted by RockLeeEV

I also don't know if a pair of 5.25" speakers have the dynamics for soundtrack articulation BTW. You might as well swap one of the Zaph woofers with a third driver altogether, like the Seas ER18RNX perhaps.

I forgot to add: I'm using a sub, and I'll cross somewhere between 120 and 200 Hz. Should a 5" cover the lows above that? If not, the third driver idea makes sense.

Thanks,
John

[RockLeeEV]

QUOTE]I had considered that, but I'll lose the ability to time align the T and M. Unless I'm lucky and don't need it, I'll have to build a ladder delay network, which is beyond me.[/QUOTE]

You honestly can hear phase/time coherency in what would likely be a 2nd or even 1st order crossover? Well, if you can that's good and all but... well.. I don't think I can at least. With that said, I'm pretty sure the MiniDSP Advanced 2-way crossover can be used for all-pass filters with the right biquad values.... I bet you can do it if you read up on it for a couple hours.

What do you mean by "rear tweeters"?

Are you even making an OB speaker? I mean tweeters (and matching waveguides I guess) that fire backwards in order to keep the power response consistent. Look at the NaO or later versions of the Orion...

Maybe I'm just not following what exactly you're making.

I forgot to add: I'm using a sub, and I'll cross somewhere between 120 and 200 Hz. Should a 5" cover the lows above that? If not, the third driver idea makes sense.

IMO even 6.5s start to struggle with the area near 120hz-300hz, where a lot of power is located. 5.25s will definitely have some dynamic limitations IMHO unless they're some ultra high end motor design (and I don't believe the zaphs are designed to handle a full 100 watts or anything). A pair of 6.5s, an 8, or even a high sensitivity 10 or 12 IMO is the best way to go, and plus with bigger and heavier drivers you can lower and lower before it crosses to a sub. You don't need to make a full range speaker, but bigger drivers make a big difference in that midbass area.

The advantages will be better thermal power handling (lower distortion) and lower excursion (lower distortion).

[jerome69]

Originally Posted by johnbomb

I'm using an SB acoustics SB29RDC tweeter mated to a modified parts express 8" waveguide

Very bad idea the 8" waveguide if you want a good polar response to mate with the 5". Use it without this.

If you are a beginner, you will have a lot of trouble to design the OB...
If you don't have any tools to measure what you are doing, forget the project.

It is possible to do .5 in OB but very advanced technique in filtering. Use a MTM instead.

To go as low as 120Hz, it is better to use a 8" + tweeter (Note, it will work nice with the 8" waveguide on the tweeter , the crossover will be more simple ).

Hope this helps.

[johnbomb]

Thanks, guys for your responses. I haven't 100% decided to go with the 8" waveguide, but the results that Zaph posted in his blog on Feb 5, 2010 look promising:

http://www.zaphaudio.com/blog.html
http://www.zaphaudio.com/temp/SB29RD...5-30-45-60.gif

My theater seating will place everyone off axis with respect to all 3 speakers, so the relatively even FR at 30 degrees (after EQing down the hump from about 800-8000hz) might work very well for me. Plus, I'll get lower distortion in that range after the EQ. I'm in the process of prototyping baffles now.

Since I plan to cross the T and M at between 1-1.3k, the ZA14 should stay pretty flat off axis up to that point.

RockLeeEV- I definitely don't claim to have "golden ears." I just want to keep time alignment as an option so that I can keep my XO as painless as possible. I would like to know if one can readily tell the difference between a .5 woofer rolled off actively vs. one that's rolled off w/ an inductor. Also, what do you guys think about the 4th order bandpass idea?

Jerome69- could you elaborate on the filtering difficulties associated w/ a 2.5 way OB design? I am using "the Edge" baffle designer and Room EQ Wizard for measuring.

Thanks,
John

[jerome69]

Originally Posted by johnbomb

Jerome69- could you elaborate on the filtering difficulties associated w/ a 2.5 way OB design? I am using "the Edge" baffle designer and Room EQ Wizard for measuring.

You have to deal with a virtual baffle step and the OB cancelation.
The 2 woofer have the same response... You don't have a baffle step !
You must recreate it in order to properly do the 0.5.

[johnbomb]

I have only built woofers thus far. I just finished up a dual ported 140 cubic foot "large and low tuned" (LLT) woofer using 4 15" drivers which is tuned to around 12 hz. I had to build a special closet behind this thing to house it!

Originally Posted by RockLeeEV

You might as well swap one of the Zaph woofers with a third driver altogether, like the Seas ER18RNX perhaps.

I am starting to lean in this direction, and I might go so far as to build a 3 way OB. I really liked the infinite baffle sound that I got from having two 15" woofers built into the wall of my last home theater, and I want to take a shot at an OB design.

I like the idea of crossing the sub at around 120hz if possible, and if I go 3 way, I'll just suck it up and buy the gear to keep the whole system active. If I go this route, I'll keep the ZA14 as the midrange, and cross it at around 300hz or so.

What woofer size/model would you recommend at this point? I don't mind going up to 12" if necessary. I'd like to keep the cost below $100 for each driver and the non linear distortion profile as low as possible.

Thanks,
John

[RockLeeEV]

[QUOTE=johnbomb;2581223]I have only built woofers thus far. I just finished up a dual ported 140 cubic foot "large and low tuned" (LLT) woofer using 4 15" drivers which is tuned to around 12 hz. I had to build a special closet behind this thing to house it!

I am starting to lean in this direction, and I might go so far as to build a 3 way OB. I really liked the infinite baffle sound that I got from having two 15" woofers built into the wall of my last home theater, and I want to take a shot at an OB design.

OB and IB have some huge differences.

Whereas in an IB setup the backwave is isolated from the front wave, in OB you must apply notable equalization and meticulous design to get the back wave and front wave working with each other for a coherent sound.

I honestly think it's probably destined to fail until you've made a couple normal speakers first.

A 3-way is also something that you might find very, very difficult to get right.

It sounds to me like you just want that non-resonant speaker sound, as is offered by infinite baffle installs.

I suggest building something like this:

OBL11

It`s from an extremely skilled designer, it`s still OB, and you know the end result won`t dissapoint. Especially if it`s your first build, you need to build a speaker which you can use for reference - a speaker you can use when designing other speakers to tell yourself exactly where you inevitibly "mess up"

Alternatively you can build this one:

NaO Note Details

And I believe he does have information to allow you to use your MiniDSP in the finished project (an active/passive hybrid speaker).

I honestly think an established design is the way to go, especially if you're not making a simple 2-way speaker.

I like the idea of crossing the sub at around 120hz if possible, and if I go 3 way, I'll just suck it up and buy the gear to keep the whole system active. If I go this route, I'll keep the ZA14 as the midrange, and cross it at around 300hz or so.

This is simply too high for crossing a sub unless it's stereo subs. 60hz is preferable as a crossover frequency.

What woofer size/model would you recommend at this point? I don't mind going up to 12" if necessary. I'd like to keep the cost below $100 for each driver and the non linear distortion profile as low as possible.

The two complete speaker builds I referenced are the definite way to go in my opinion.

[johnbomb]

I just ordered 3 of the Usher 8137A 8" woofers from PE, who has them for $49 each. Their distortion profile from about 100-600 hz looks really good, so use as a .5 woofer or bottom of a 3 way with the Zaph will hopefully work. At that price, I had to jump!

Also, I've decided that I'll most likely keep the system sealed, as such a design will better fit my home theater room aesthetic. I'll post some results when I get some testing underway.

Something I just thought of: both the Zaph and the Usher are 8ohm nominal drivers. Would the damping factor increase if these two are run parallel in a 2.5 way with an inductor on the Usher (4 ohms + the inductor resistance) vs if they were run separately in an active 3 way (two separate amp channels at 8 ohms each)? Which would likely have greater "transient response" and dynamics? Again, I'm trying to maximize dialogue intelligibility.

Thanks,
John

John