# Curved baffle centre channel - help with design



## EG92B16A

Hi All,

I'm thinking outside the box a little for my next project, a curved baffle centre channel.
After searching this forum for curved baffle speakers, the only thread that came anywhere near to what I want to do is the wine barrel subwoofer by Mark DN, but it's the barrel that's the common component only. 

I've read in many articles that a curved baffle has many advantages over a flat baffle, so I'm putting it out there for discussion.

I've attached a pic of where I want to go, but my main question is whether to go convex curve to aid dispersion, or concave curve do help with directivity?
My next issue is how I'm going to router the driver holes in a curved surface. Am I mad? probably.:bigsmile:


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## robbo266317

That certainly is a challenge. You will need to make a jig to route the level flat unless you have access to a friend with a CNC router. :bigsmile:
As for convex\concave If you had an MTM arrangement either should work ok.

It is going to be interesting to see how you progress.


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## fusseli

Awesome idea. It will be pretty awesome looking if you can pull it off. My vote is convex!


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## EG92B16A

Hi All,

Here's a pic of the first pieces being glued together. Six pieces will be used to make up the baffle.

I have a question about the drivers and placement. My current centre channel is MMTMM with the outer woofers crossed at approx. 800Hz for better low end. What I want to do with the new design is to have just an MTM on the front baffle and use the extra two mid woofers as rear firing. Will this work?


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## BD55

Definitely a challenging project! Kudos for taking it on. Not only do you have to deal with the curve in one direction but two (the bend along the axis of the barrel and the circumferential bend!) This is a really cool build :T


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## robbo266317

EG92B16A said:


> What I want to do with the new design is to have just an MTM on the front baffle and use the extra two mid woofers as rear firing. Will this work?


That shouldn't be an issue depending on the depth of the cabinet and the crossover frequency.


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## EG92B16A

Hi Everyone,

Here is the latest update. I have managed to assemble and glue the baffle, and have just sanded it smooth.
I've included a few pics to show progress. 
Now I need some help? I have a few options with regard to drivers for this project. I'd like to use the existing drivers out of my current centre channel in some sort of way, but I'd also like to really enhance the lower octaves. The drivers I have available are: 4 x CW2194 6.5" mid bass drivers and 2 x 10" infinity kappa KSC100BR drivers. What do you guys reckon? 
The front baffle is 90cm wide and 32cm high, the depth is only limited by entertainment unit but that's 50cm, so I could make a rather large box if necessary. I've added a pic of a design I was thinking about to aid in vertical dispersion. Comments please?


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## fusseli

If you want to enhance your low end, then sure build a sub with your Infinity drivers you have. That seems like a separate project from your center to me and I wouldn't suggest building a sub into your center.


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## Kiwilistener

fusseli said:


> If you want to enhance your low end, then sure build a sub with your Infinity drivers you have. That seems like a separate project from your center to me and I wouldn't suggest building a sub into your center.


I would agree also, use the 6.5 inch drivers. I would suggest you model the 6.5 as a MTM setup. Two of these drivers in parallel in a vented 40 liter enclosure will nett you a box tuning frequency around 42 Hz which is way lower than you need in a mid if you run a sub. 

I use these drivers in vented enclosures a a mid-range speaker in my HT mains. They work very well as the main driver or as a mid.

To fit them I would partial route the flange recess as the curve will be flush at the mid points and the flange exposed at the other points. Option two would be to bury the flange completely until the highest point is flush with the surface of the baffle, but to me that would look somewhat ugly in appearance, although if you intend to have a grill that's not such an issue.

That then leaves your 10inch drivers for a nice little sub project


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## Kiwilistener

*Meet the family*

*Aria HT's* at center with *Aria2* on the right and the *Aria Pettites* left.










And with their clothes on 










Some of you will recognize the Jaycar drivers. The HT's use the CW2194 for a mid and the CW2196 for the bass driver. With this setup I dont run a sub, it isn't necessary, in fact the family complains about there being too much bass at times. You can also see the CT2007 tweeter. Its a Vifa OEM clone and its a good unit, but it needs an L-Pap and a contour filter as it has a rising spl in the 15000 to 20000 kHz range of 5 dB that needs to be smoothed out before the L-pad is effective.


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## EG92B16A

*Re: Meet the family*



Kiwilistener said:


> *Aria HT's* at center with *Aria2* on the right and the *Aria Pettites* left.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> And with their clothes on
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Some of you will recognize the Jaycar drivers. The HT's use the CW2194 for a mid and the CW2196 for the bass driver. With this setup I dont run a sub, it isn't necessary, in fact the family complains about there being too much bass at times. You can also see the CT2007 tweeter. Its a Vifa OEM clone and its a good unit, but it needs an L-Pap and a contour filter as it has a rising spl in the 15000 to 20000 kHz range of 5 dB that needs to be smoothed out before the L-pad is effective.


What crossover frequency did you end up using for your centre channel?
I already have a sub. It's the frequencies in the 80-400 range that I want to enhance, the region of baffle step roll off.

As I already have my main towers with SB Acoustics drivers, I want to keep the tone similar. My current centre channel that is pictured above, uses the drivers out of a Todds Auditone centre channel and an extra pair of Vifa M13SG drivers. Sounds good already but it gets serious lobing when you sit off centre and the vertical dispersion is limited. I wanted to expand the vertical dispersion by using the configuration in the last pic. I want to see if a 3 way system will work, 4 x CW2194 drivers rear firing, 4 x mids and a tweeter on the front baffle. That being said, if I use the 5" drivers for mid range only, could I get away with an open baffle? and have a box behind the baffle for the mid bass drivers? I want to get around the excursion limits of the drivers by using multiple units.


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## Kiwilistener

*Re: Meet the family*

As my amp allows me to adjust crossover frequency for the sub from 40 to 120Hz I settled on 100Hz for the centre as its more important ( at least in my set-up ) that the vocal range and a little below it is well covered right through to 4000khz where the tweeter crosses over.

I used two 5 inch CW2192 in parallel for my centre speaker and used a KEF T-33 tweeter for the top end.
The CW2192 turned out to be good performer covering 70 Hz to 7000 kHz


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## mdocod

EG9, 

I really like the creative use of the barrel pieces for a front baffle. That is going to have some real character. Very neat idea indeed! Mounting is going to be a real trick!

----------------------------------


I'd like to take this opportunity to encourage anyone following along here to download a free simulation program called "edge." Edge is a simulation program that simulates the diffraction effects, as well as the effect of driver size, number of drivers, and listening position, on the response. 

With a little math on paper one could easily determine the lack of suitability of most horizontal MTM configurations by just considering the wavelength size as one approach's the crossover to the tweeter, and consider how little horizontal axis rotation is required to move the 2 midbass drivers out of phase. However, allowing "edge" to simulate the effect is much more stimulating and motivating because it produces a charted response revealing the magnitude of the problem with greater clarity. 


Use "edge" to make a baffle to work inside of. (doesn't need to be exactly like yours, just similar dimensions). 
Set driver quantity to "2."
Set the speaker "size" to the diaphragm diameter in the speakers used. 
Set the center to center distance to match a real world configuration, (make sure to actually calculate it, visually the speaker diaphragm size alone will appear smaller in the simulation than the entire speaker does in real life, which can lead to spacing that is guesstimated to be much closer than is possible. Set the actual center to center distance in the design intended or built.)
Set speaker source density to ~6-10
Set the microphone on the center axis. 
Adjust the mic distance to match the distance to ear position at the "center" seating position. 
observe response
Move microphone horizontally to positions representative of people sitting a seat over, then 2 seats over. 
observe response.
Note: the person sitting right NEXT to the "center" seating position is missing nearly an entire octave of response if the crossover is set in a traditional ~3K range.

--------------

For center channel designs with limited vertical space, I think it's hard to beat a WTMW configuration with the "TM" in the center arranged vertically. The Morel CAT 558 (MDM 55) comes to mind as a good midrange unit with the sensitivity and dynamic reach for a center channel. Crossed to one of the small flange neo tweeter options (like the little dayton/aura 3/4" rear-mounting units) ~4-5K, then flanked by a pair of midbass drivers and crossed ~500-750hz. 

An approach like I have described extends the usable horizontal axis to involve basically anyone in the room. Nobody will be missing entire octaves of response at their seating position. 

-------------


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## EG92B16A

Thanks mdocod.
Have you had a look at my pic with regard to my proposed design for this build. I think it will end up like a large coaxial speaker with the added advantage of better off axis response due to the curved baffle.
I will have a look at edge software. I have been using the excel spreadsheet programs to simulate baffle diffraction and step, along with response modelling and crossover design.
Nothing can really simulate a curved baffle. I'm going to have to make another baffle to use for testing purposes.
What does everyone think about my design with four drivers surrounding the tweeter?


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## mdocod

Hi EG92,

The curved baffle will help adjust the directivity of the baffle diffraction, which _may_ help breakup up the primary baffle response peaks to a slight degree. In reality it's not going to be a major player in solving off axis issues especially considering that center channel speakers are so often cluttered into a space with so many other diffraction boundaries that the shape of the center channel box is going to serve primarily as an aesthetic fulfillment, not an acoustic solution. 

Here's a simulation of some 6.5" drivers on a baffle in a configuration that would fit a traditional flange size dome in the center of them...

 

listening position is 22 degrees off axis. Total cancellation occurs at ~2300hz on midbass drivers. Crossover would have to be very low (~1600hz?) to maintain "usable" response even at just 22 degrees off axis. Move to 45 degrees off axis and the cancellation is centered at 1300hz. (there is no crossover point that can solve this to a traditional dome tweeter). 

A good center channel speaker should not "drop" any of the mid-range within a ~ +/-45 degree or better horizontal axis. Some designs shoot for +/-60 degrees of usable off axis response.

Regards,
Eric


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## EG92B16A

Thanks Eric.
Would a wide baffle be of any advantage? The current baffle width is 90cm, height is 32cm. I'm toying with different designs at the moment, trying to find the best one. My other option would be go three way and use 2x6.5" mid bass, 2x5" mid, and a good tweeter. Put the mids under the tweeter in the centre and find a good place for the mid bass drivers.

Cheers Jason


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## Kiwilistener

mdocod said:


> EG9,
> 
> I really like the creative use of the barrel pieces for a front baffle. That is going to have some real character. Very neat idea indeed! Mounting is going to be a real trick!
> 
> ----------------------------------
> 
> 
> I'd like to take this opportunity to encourage anyone following along here to download a free simulation program called "edge." Edge is a simulation program that simulates the diffraction effects, as well as the effect of driver size, number of drivers, and listening position, on the response.
> 
> With a little math on paper one could easily determine the lack of suitability of most horizontal MTM configurations by just considering the wavelength size as one approach's the crossover to the tweeter, and consider how little horizontal axis rotation is required to move the 2 midbass drivers out of phase. However, allowing "edge" to simulate the effect is much more stimulating and motivating because it produces a charted response revealing the magnitude of the problem with greater clarity.
> 
> 
> Use "edge" to make a baffle to work inside of. (doesn't need to be exactly like yours, just similar dimensions).
> Set driver quantity to "2."
> Set the speaker "size" to the diaphragm diameter in the speakers used.
> Set the center to center distance to match a real world configuration, (make sure to actually calculate it, visually the speaker diaphragm size alone will appear smaller in the simulation than the entire speaker does in real life, which can lead to spacing that is guesstimated to be much closer than is possible. Set the actual center to center distance in the design intended or built.)
> Set speaker source density to ~6-10
> Set the microphone on the center axis.
> Adjust the mic distance to match the distance to ear position at the "center" seating position.
> observe response
> Move microphone horizontally to positions representative of people sitting a seat over, then 2 seats over.
> observe response.


Could you post a link to that software, I'd be interested in having a look at it.


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## mdocod

Hi Kiwilistener,

I found this: http://www.tolvan.com/edge/help.htm
That should be the place. 

I use it primarily to see off axis effects, and to export design-axis diffraction response to later be used in crossover simulation. 

Awesome software!

Eric


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## Kiwilistener

Cheers and thanks Eric, I will have a look at it.


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## EG92B16A

Edge is a great program. Used it tonight. Thanks Eric
With my baffle dimensions I can manage 2 x 5" mid drivers in the lower centre of the baffle, tweeter mounted above directly in the centre, 2 x 6.5" mid bass at the outer edges of the baffle. 

My next issue will be how I'm going to mount the tweeter. Being a curved baffle and the tweeter mounted directly in the centre, it's going to require a waveguide or something to recess it to the same depth of the woofers. Acoustic response is important. It seems many things come to the surface when working with a curved baffle. 

Jason


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## mdocod

Hi Jason, 

I may be misunderstanding your concern regarding the tweeter mounting. Are you trying to get the origin of the tweeter recessed to match the origin of the mid-range drivers? (If I misunderstand this purpose, I apologize. Note: Phase alignment can be accounted for in crossover design, there is no up-front need to physically align the coils, only in rare circumstances will a designer be forced to make a physical adjustment to correct for phase). 

A wave guide for the sake of a wave guide as part of an up front design decision makes sense, especially on a center channel where a little bit of directivity control could go a long way to avoiding undesirable diffraction from nearby boundaries. 

Regards,
Eric


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## EG92B16A

Normally I wouldn't do it, match the tweeter origin to the woofers, but I think with the curved baffle it would make sense to time align the drivers. If I left the tweeter mounted at the surface, there's over a 10cm difference between alignment of drivers. The curve on the baffle is quite deceptive with the edges over 20deg off centre. It's something I'm going to have a serious look at. 

Jason


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## mdocod

Hi Jason, 

Drivers are not "zero" phase devices. Physically "aligning" the coil-to-listener distance does not necessarily work to your benefit come time to design a crossover. Before any crossover components are even considered, a midbass and a tweeter that are physically equidistant to the listener will not be acoustically in phase anyway (though it could be "close" in some cases). More importantly, the crossover is going to rotate phase significantly. 

I'm working on hashing out the details of 2 or 3 networks for a HT system right now. None of them will have "physically" aligned drivers and ALL of them will have in-phase acoustic response on the design axis. In my tinkering with these designs so far, actually turns out that the version of the front channel speaker with the GREATER physical difference in driver position (from the design axis), is EASIER to time align while meeting my other design goals. Point being, if I _had_ "planned" in an effort to physically align them, I may have wound up with a greater challenge and more tradeoffs in the crossover design that I have currently. 

Again, do a wave-guide for the sake of doing a wave-guide for its' *other* benefits, not because it solves any time alignment issues. 

Regards,
Eric


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## EG92B16A

Thanks Eric. :T

I've decided not to use the drivers out of my existing centre channel and keep it intact, so my next decision is the mid bass drivers and tweeter. As my main speakers are utilising SB Acoustics drivers, I thought it best to keep the tonal quality the same. Do I use 2 x 5" drivers that will be located below an SB29RDC tweeter or 2 x 4" drivers that I could do MTM with an SB29RNDC, which would be cool. The bass drivers are 2 x 6.5" 8 ohm in parallel, so the project will end up with a nominal 4 ohms impedance. As for the tweeter, do I use the SB29RNDC small footprint or the SB29RDC? Waveguide put in the too hard basket, not really suitable for the SB29 tweeter.

Jason


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## EG92B16A

Continuing on from my last post, my decisions are as follows: small footprint dome tweeter SB29RNDC flanked by 2 SB12MNRX25-4 mid range drivers in series, and 2 x CW2194 drivers on the outside for mid bass duties.
After spending a lot of time using Edge, the 4" drivers give the most flexibility with crossover frequency and off axis response.
The curved baffle is starting to take shape. I have managed to plane the driver surfaces flat so I can use the router and jig for the driver cut outs. 
I was about to rout out the holes for the mids and tweeter when the router and jig fell off the bench. Router is OK but the Jasper jig is cactus. My neighbour runs a metal work business and has offered to make me a new jig out of 5mm alloy plate, which should outlast me.
The pic says 1000 words, so here it is.


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## robbo266317

I applaud your perseverance!
This will be a unique centre channel.


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## mdocod

Hi Jason, 

Sorry I didn't get back to this sooner. Looks like some very nice headway on that baffle...

The more accurate way to describe speaker matching would be to say that you want your speakers to share similar deficiencies. The theoretical perfect speaker with no distortion is inherently a good match to any other "perfect" speakers. Try not to get too swept up in the "timbre" or "tonal" balance . What these people are sugar coating with audiophiliac words is "matching distortion profile." Becomes more critical in systems with shallow crossovers. If you design a proper crossover that firewalls out the breakup behavior of the midbass drivers then it's less of an issue.

------------------

The CW2194's in parallel will be [email protected] sensitive into 2pi space. 

A pair of SB12MNRX25-4's in series will be [email protected] sensitive into 2pi space. Too bad there aren't 8 ohm versions of this. Did you simulate your dynamic limits of the woofers in the intended pass-band to see if you even NEED 2 of these midbass drivers? An upright "TM" of a single of this driver and the SB29 between the woofers would probably have been fine with an appropriate crossover, resulting in even better horizontal axis response. 

Doesn't matter if you were to use 1 or 2 of the midbass drivers, since they are wired series when 2 are employed the sensitivity doesn't change, The result will probably sound a bit "heavy" on the bottom end when placed in a typical center channel location with flanking objects. Center channel applications generally require minimal step loss correction, so this driver selection is a bit lopsided but can be made to work. (maybe use some high DCR air cores on the low pass filter for the woofers to knock down the level a bit and you'll have to sacrifice some flatness to preserve sensitivity on the midrange drivers).

Eric


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## EG92B16A

Thanks Eric.
I had been looking at the numbers on the weekend and discovered this too. The CW2194 drivers were intended to be crossed at 200hz. The SB12 drivers look good on paper but there's no way to get better sensitivity out of them. My decision now is whether to find two more 8ohm 4" mid drivers to increase the sensitivity or use my existing vifa m13sg drivers out of my current centre channel, or go for two SB15nrxc30-8 drivers in parallel and make the system a nominal 4ohm design. The SB15 drivers have excellent distortion figures when used as mid range drivers. 
If I go with the 2xSB15 drivers and SB29RNDC tweeter I have a few options available for crossover frequency and roll off, but it comes down to how they sound on the baffle and what the mic tells me.

Jason


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## EG92B16A

Hi all.
I now have a new router jig made out of 5mm alloy plate, which is awesome. I'll be progressing more this weekend. The drivers will now be the sb15nrx-8 x 2 in parallel and the sb29rndc-4 tweeter.
Crossover frequency will be around 2k as with my other project.


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## EG92B16A

Hi All,

I have done a bit more with the front baffle. Pictures are below.
First pic includes my new router jig.
I picked up a rather nice piece of 19mm ply from the local recycle mart, which should match nicely with the oak baffle. 
Now on to the box details. Whichever way I look at it, the box is going to be a labour of love. Lots of curved panels, lots of trial and error.
I'm aiming for an overall internal volume of 60L. 16L sealed for the mids and tweeter, with the balance ported and tuned to 44Hz for the woofers. I've allowed a little extra for bracing as I think this one's going to need it. Crossover will be mounted on the back.


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## fusseli

Nice progress, this thing's going to look impressive.


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## NBPk402

I like the way it is turning out! I have been making use of wine barrel staves myself for projects in our home too. Looking forward to seeing how it turns out when you are done. Keep up the good work!


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## EG92B16A

Thanks for the kind words and encouragement guys.

I have made a little more progress. The mid box has been completed and shaped to fit the curved baffle. The top and bottom have also been fitted to the curved baffle. The only tricky bit left is the side panels, of which I have done one piece so far. I have never used a curved file/rasp so much in my life.


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## Owen Bartley

Jason, that's going to be a really cool looking speaker. I wasn't sure how you were going to flatten the speaker mounting points, but seeing the finished version makes sense. How is that baffle for stability/rigidity? Will you need to add anything to the back to make it more inert?

Great work, keep it up!


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## EG92B16A

I was planning on using a sealer of some description and then use some dynamat or something similar to improve the rigidity. I've also braced the box a lot more. I'll have some pics up soon.

Cheers


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## EG92B16A

As promised, some progress pictures.

The box is starting to take shape. Box picture is looking at the bottom. The baffle picture is with two coats of bitumen sealer.

The top of the box is white melamine to match the current entertainment unit. The sides and bottom are all 15mm ply but there's up to three layers in places.

Cheers
Jason


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## EG92B16A

Progress update.

I have glued all of the panels in place and have attached the front baffle to the box. I used a lot of liquid nails and a few L brackets. All interior corners of both boxes have been sealed with caulking compound. The insides of the boxes have been lined with closed cell foam and carpet underlay. The back panel has been cut and cleats just about to be installed so the back panel can be removable. I'll post pictures tonight. The drivers are on their way, and should be here today. SB Acoustics SB15NRXC30-8-UC x 2 and SB Acoustics SB29RNDC-C004 x 1. I like the sound of the uncoated papyrus cone drivers over the coated cone version.

cheers

Jason


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## EG92B16A

As promised, some progress pictures.
Got the blue card in the letterbox, so I have to go and collect the drivers from the Post office.

I've since cut and glued extra plywood panels for the sides. So many odd shapes!:doh:
It has almost done my head in.


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## EG92B16A

I'm progressing well.
The pictures below are of the box upside down when I was testing the speaker fitment.
Only the tweeter hole required a little work to make the driver fit.
I have now lightly sanded the baffle and added another coat of polyurethane lacquer. The sides weren't thick enough, so I ended up laminating two pieces of plywood together for rigidity. The bottom pictures shows where I had to add the timber putty to fill in the spaces behind the baffle where it was impossible to get the pieces of wood to match. I now have another decision to make, whether to leave the plywood grain on the sides and varnish, or paint black to match my other speakers.:dontknow:


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## EG92B16A

Progress update.

I have sanded the front baffle a few times with 800 grit and added a couple of coats of spray clear. It's looking good. I've installed the port tubes to the sides of the cabinet as there wasn't enough room for them to be rear firing. Each port is 85mm internal diameter storm water pipe x 370mm long. One for each woofer chamber.
I've painted and sanded the sides and top of the cabinet with gloss black paint and added a couple of coats of clear. The mid box is absolutely air tight. I installed the drivers again today and gave them a quick test. Initial sound is similar to my mains, which is a good thing.

Cheers


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## Mike Edwards

very nice. I was wondering how this experiment would sound


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## EG92B16A

I've pretty much finished the box. 
Last night I did some preliminary testing with the raw drivers, and with a basic mock up crossover.
Impedance plot looks OK. There's a couple of bumps that will have to be sorted out though. One at 200Hz from the mids and one at 3K from the tweeter, although the tweeter bump I think is from the single cap crossover I used for testing. I'll continue testing today and post more data as I get it. All data is taken in room (my shed), so I can get a feel for the room interaction. 

I have a question though? Is it possible to convert my holmimpulse data into something that can be used in Jeff Bagby's PCD?

Jason


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## EG92B16A

Here's some more data from today. I had a bit of a play with PCD using the data from my other project and some crossover values used in Zaphs SB12.3 design.

It seems that when using the SB15 drivers as mids, they really benefit from the LCR trap. The tweeter also seems to have a better response shape with the zobel and LCR trap. It just means more components in the crossover, and some large values too.

Comments please. Does this look OK?

Jason


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## EG92B16A

Hi,

I've been experimenting with the crossover design and currently have four versions down on paper.

I have a few questions though, 
1. is negative phase such a bad thing?
2. should I always try and get the phase positive?
3. should I sacrifice response for positive phase?

My latest version of the crossover is phase positive from 400Hz and maintains at least 4 ohms impedance for the entire frequency range. It actually increases up to 8 ohms from 1500Hz to 20KHz. The only points of -ve phase is at 250Hz, only -14 deg at 5 ohms, and the dreaded 50Hz at -45 deg but the impedance is high at about 8 ohms. Off axis response is quite good up to 15 deg, then it turns to mud. I'll be listening at a maximum of 10 deg off axis. 

Jason


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## EG92B16A

Progress update.

More data, more graphs, more experimenting with crossover values.
I've been measuring response data with holm impulse, and it seems that when in the acoustic domain, making a quite large change in some crossover component values may only make a small change in the overall response. 
Below is some data taken today. Real electrical, real acoustic in room and simulated. The simulated data is 10 degrees off axis horizontal.

The actual response isn't far from the simulated version.

Jason


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## fusseli

That's great that your measurements are relatively matching your model! It looks like your woofer and midrange overlap quite a bit. I'm wondering how much that's going to impact your polar response... What slopes and crossover points are you going for?

It depends on the specifics, but changing a component may not always be for altering FR. Acoustic phase, dictated largely by the order of the electrical crossover, is very important for a speaker. For example you might need a 2rd order LPF for a woofer to get the phase alignment you need but tweaking the C in the LPF may do little for FR.


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## EG92B16A

At the moment the woofer is 2nd order using 5mh coil and 100mf cap with LR contour to adjust slope. Mid HP is 1st order using 137mf cap, LP is 1st order with contour LR and quasi zobel to adjust slope. Tweeter is straight 2nd order with zobel.
I don't have access to software that will do polar response and only rely on PCD for the electrical phase and holm impulse for acoustic. Don't know what else I can do to make the phase track better.

Jason


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## EG92B16A

Hi All,

As always I have some more data. This time I'm unsure what to do with it. I've got frequency response and phase data for the individual drivers, together on one graph and an overall response. Can someone tell me what is happening and how I can go about changing things. Data is taken with my current crossover setup as per previous post. I'm still waiting on some more crossover components to arrive, so the data will more than likely change. There is a resonant peak that will be sorted out with an LCR trap on the mid drivers. Also, the data below 200Hz is more than likely unreliable anyway as my setup seems to roll off from about there. I'll try some nearfield responses soon for the bass drivers.

thanks

Jason


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## fusseli

If you are designing your filters from scratch you can ditch the Zobels. In my mind, Zobels are best applied only when implementing a textbook filter. Otherwise they don't serve much of a purpose you can't achieve with other means. Try adding series resistance to the parallel capacitors in each filter section, this will dampen the cap's contribution which will shift phase alignment and alter your slope.

The next time you post PCD, can you post the system response with the phase of each section also (not total)? I'm still worried your woofer and midrange are overlapping too much.


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## EG92B16A

Thanks fusseli.

I have done a bit more with PCD and have come up with the following frequency response. It's good for up to 30 deg off axis. Please tell me how the phase is tracking.

Jason


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## fusseli

When tracking phase alignment you want the slopes to match. For even order crossovers like LR, ideally you'd want the slopes to match each other perfectly, but in practice they can be offset by some margin (maybe 30-40 degrees?). I'm not sure on a hard "limit" there. For odd order Butterworth slopes of course you'd want them to be 90degress apart. No matter what the type of crossover, you want the phase slope to match. When designing a crossover, I think it's common compromise to sacrifice flat as possible FR with aligned as possible phase. I've read commentary from experts saying flat FR is arguably more important than perfect phase alignment. Phase alignment matters only in the crossover region(s), unless roll-off is really shallow.

It looks like your high to mid transition is nice. I think playing with some values could get them more aligned. However the woofer to midrange looks a bit off. Try increasing electrical order, or shifting the crossover point slightly. I would aim for the nearest octave dictated by your already nice high/mid transition, looks like 250Hz or so in your case assuming 2kHz up high. This is the hardest part of 3-ways, the midrange should cover a whole number of octaves (like 3, not 2.5). This will affect phase response also.

The speaker looks beautiful by the way! 


Are you using the measured FR and phase from the driver in-cabinet in your PCD model?


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## EG92B16A

I'm unable to use my measured data in PCD. The data that I have from holmimpulse is normalised to zero dB. I don't know how to change the data to dB SPL to read it in PCD. My microphone isn't calibrated either, and I don't have access to an SPL meter to check things.

Is there another software program I could use? would REW be suitable?

Jason


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## EG92B16A

Hi all,

I have made some more adjustments to the crossover using PCD and have come up with the following results.
This is now version 7 of the crossover.

All sections are 2nd order electrical, but the slopes are up to 4th order. Phase tracking is better than the previous picture from PCD. Off axis response is also good. It only starts to suck out at 2k when greater than 30 deg off axis horizontal.
Components so far: coils are Jantzen P core, larger caps are Jantzen cross caps, LCR caps are bipolar electrolytic, smaller caps are Jantzen superior Z caps, all resistors are MOX or Superes 10W.
woofer - 5mH coil + 115 uF cap with LR contour for slope adjustment 2.2mH + 7.5 ohm
mid - 2.2 ohm pad resistor, LP - 0.56mH coil + 27 uf cap with 1 ohm series resistance, HP - 115 uF cap + 4.7mH coil, LCR for high pass slope adjustment 7.1mH coil + 660 uF cap + 4.7 ohm
high - 4 ohm pad resistor, 7.8 uF cap + 0.18mH coil, zobel 2.7 uF cap + 4.7 ohm


I've got a program called sonic beacon that can do everything except make a cup of coffee. I now have to read the instruction manual on how to use it.

Jason


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## fusseli

That's looking promising! Phase response looks great. The only thing I see now is how your impedance phase is curiously capacitive >1kHz. I believe impedance phase should be under 40-60deg to keep the current demand safe for most amps. Is your tweeter pad before or after the crossover? It should be in front. If it needs to move, you'll also need to rework the HPF to get it back to where it was... Try saving off a PCD version and comparing the two. I'm not sure if capacitive loading is a problem, might be worth verifying. 

Did you build in any BSC into your .FRDs? The bass looks like it's suppressed a bit compared to the rest. If no BSC is worked in it's probably okay. Once it's built you'll still need to verify the crossover is correct with measurements, and some tweaking of component values may be necessary.

You might experiment in PCD to see if there's a way to get crossover components minimized. I've toiled away for hours doing this to save a component here and there, part of it is just because a more efficient design feels like a better design to me.

To use your driver measurements in PCD you'd really need them to be SPL calibrated, otherwise the level matching from varying drive sensitivity would be a wash.


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## EG92B16A

Thanks fusseli.

I do remember doing some BSC stuff in one of Jeff Bagbys spreadsheets. I can't remember if I saved the frd.
The holm impulse data shows it up from 500 hz to 1000 hz. The bass sounds pretty good to me, so the data might not be showing the whole story.
The pad resistor is the first component in the mid and tweeter circuits.
I have all of the crossover components so I will start assembly later this week.

I'm not sure what you mean about capacitive loading. Is that the negative phase below 250hz?
I can add an LCr trap to fix that up but the components are quite large.

Jason


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## fusseli

I wouldn't suggest adding anything to compensate the impedance. It looks good overall, I was just noting that it's capacitive from about 1kHz and up. This is observed by the positive impedance phase, negative would be inductive as seen in the woofer section near Fs.

If your bass sounds good then it's probably fine.

Can you post your .ZMA and .FRD files you used? It's important that they include phase data also, I don't think I asked before. An alternative would be posting the FR and impedance plots from each individual section, with phase shown in PCD.


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## EG92B16A

Thanks Fusseli, that's good to hear.

As for the .FRD and .ZMA files, I don't remember which ones I've loaded into PCD, but by looking at the data, it seems that they are from my SPL trace attempts. I didn't see phase data in the FRD files, but there's phase data in the ZMA files.

I've attached the individual plots from each section.

I've had a reasonable look at Sonic Beacon tonight and it seems to be quite good. The calibration of everything isn't described very well in the help file, so I'm winging it a bit there. We'll see how we go.

Jason


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## fusseli

If you process your FRDs though Response Modeler (another PCD-like spreadsheet by JB), you can include baffle effects as well as generate phase data. I would highly recommend this. I have had successful designs using traced data, then Response Modeler, then finally PCD.

In Response Modeler you can (and should, following tracing ZMA and FRD data!):

Generate phase for ZMA or FRDs without it
Model your bass response and splice it onto your woofer's FRD
Model your woofer's impedance based upon T/S
Model baffle effects
Apply BSC to your FRD data by subtracting partial baffle effects. Then aiming for a flat response in PCD will result in some partial BSC rather than a full 6dB.
Other features

If you simply re-process your data and then re-load it into your PCD session, you may only need minor tweaks to a couple components. you may not even need any tweaks. And as a benefit on-axis FR, phase responses, and off-axis predictions will be more accurate.


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## EG92B16A

Again thanks Fusseli.

I'll revisit response modeller. I did go into that program the other night to look at the baffle diffraction effects, but hard to know what will happen with the curved baffle. All I can do is create a couple of files to test the data and see if the response comes close to my holmimpulse data. If so, I'm on the right track.
I'll also add the phase data and then put the files back into PCD to recheck.

cheers

Jason


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## fusseli

Yeah you're right, the modeler is only able to do rectangular baffles. But yeah since you have measurements of the drivers on the cabinet you should be able to compensate in PCD to match whatever effects are in your measurements.

In response modeler, open it up and scroll down tot eh cabinet model section with the "Extract phase from FRD" button. Hit that, and pick your FRD you are using in PCD. Once it completes it will ask you to save the new FRD with phase generated. Load the new one in your PCD model, easy as that. 

While you are there you can also model your woofer based upon T/S and splice the bass response on to the FRD. You might also consider generating a ZMA there for the woofers to see if changing to a vented alignment (rather than raw impedance data) has any effect on the crossover. Usually it doesn't but sometimes it can.


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## EG92B16A

Hi All,

Well, here's the next update. The FRD and ZMA files have been through response modeller, so adjusted for baffle step and box responses. Crossover has been created for now. Now for a bit of time to check acoustic response.

Pictures below.

Jason


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## fusseli

Nice! Did any components need to be changed by much following the updated files?


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## EG92B16A

Hi,

I only had to unwind a couple of coils and change the midrange cap from 135mF to 115mF. Luckily I had 47 and 68mF caps to mix and match to get the correct capacitance. I'm now in the process of adjusting the series resistance of each section to match levels.

Jason


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## fusseli

Sounds promising, minimal change is a good sign. Let us know how it turns out and be sure and post final measurements and listening impressions. You're in the home stretch :bigsmile:


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## EG92B16A

Hi,
I've had a little time now to listen to this beast. The mid range and treble are just the same at my HT mains. The bass was still a little lacking, so I added some pillow stuffing to the main box, adjusted the LR contour resistor and added a small series resistance to the 135mF cap. Result, more bass and phase tracking still the same. I'll post more once I have this speaker in the listening room, which will be in a couple of weeks time, when I get my new tv and amp.

Jason


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## EG92B16A

Hi All,

I have my new TV and amp, so have placed this project where it can be on display.
Initial listening: when used in TD (theatre dimensional) mode on my amp (Onkyo TX-NR515) the dialogue is crystal clear, bass down to 50Hz, treble that is clean, soft and airy. (sounds like an advert for fabric softener).
Pictures are included.

What does everyone think, should I leave it with the natural wood grain, or paint pearl white to match my mains? Guess what my wife wants me to do?

Jason


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## Mike Edwards

wow, that looks really classy. personally I'd go with your wife and paint it to match the mains.. I'm kinda OCD about that stuff


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## Owen Bartley

I will literally cry if you have to paint that gorgeous wood finish. 

I can totally understand wanting to match across the front, but in this case I'd make an exception. It has so much character, it really is a beautiful piece.


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## fusseli

I agree, that thing looks too nice to paint. Save it for another day! It will be a lot easier to enjoy the grain for now and paint later, than to regret it and want to un-paint it later 

I'm glad that it sounds good too!


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## EG92B16A

Thanks to everyone for their input. 

After careful thought, I've decided to keep the centre channel as a standout statement piece and ditch the wife. :bigsmile: (By the way, she told me to put that last comment in)

cheers

Jason


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## EG92B16A

I thought I'd update with a pic of the overall HT setup. Centre, mains, and new sub project.

Jason


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## fusseli

Beautiful setup man!


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## robbo266317

Now you need to redo your other speakers with the rest of the barrel so they match. :whistling:


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## EG92B16A

After living with this setup for a while now, I've decided to stay with the timber finish for the centre channel. It really doesn't stand out that much anymore. Sounds great. Stays clean and crisp even at high volume levels. Never sounds harsh even at volumes where I would consider putting earplugs in.
My wife is ok with it now too.

Jason:bigsmile:


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## Mike Edwards

glad it worked out. I was honestly curious how well it would work .


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