Introducing Directiva - An ASR open source platform speaker project

[Lbstyling]

Rick S: When trying to get the tweeter and bass drivers as close together as possible, manufacturers have difficulty with the small slither of wood that is left between them breaking. I assume you would not be willing to machine into the waveguide to decrease center to center spacing, so you could instead laser cut a piece of acrylic (or better yet polycarbonate) to surround the drivers (a la revel style) that allows closer spacing.

We know the reason why 5 inch bass drivers give better spinoramas is that the C to C spacing combined with extension capabilities of 1 Inch tweeters are a more perfect match than 6.5 inch. You will need to get them as close as possible.

 

[Rick Sykora]

Thanks for the nice comments @sgoldwin. Our next chapter is a bit of a reality check. As I started doing layout of the drivers, I realized the last designs we posted (and simulated), had the tweeter closer to the top edge than would be practical. The last thing anyone (wants when doing a build) is to have to take extra time to address a design flaw.

In this case, the original tweeter position was only a few millimeters from the top edge. This recess was already a challenge for those using a hand router, but even if successfully completed, the thin MDF would not likely survive throughout building, testing and finishing the speaker. One of the striking aspects of the Denovo cabinet is that you might expect it is "big enough", yet when choosing the port location that allowed some room for altering the length, there was (realistically) only 2 locations (one on front and one one the back). Pics forthcoming...

 

[Rick Sykora]

Rick S: When trying to get the tweeter and bass drivers as close together as possible, manufacturers have difficulty with the small slither of wood that is left between them breaking. I assume you would not be willing to machine into the waveguide to decrease center to center spacing, so you could instead laser cut a piece of acrylic (or better yet polycarbonate) to surround the drivers (a la revel style) that allows closer spacing.

We know the reason why 5 inch bass drivers give better spinoramas is that the C to C spacing combined with extension capabilities of 1 Inch tweeters are a more perfect match than 6.5 inch. You will need to get them as close as possible.

Am open to ideas to optimize at some later time. The Seas DXT does not really have all that much room to try the mod you are suggesting and then would alter its (already small) waveguide behavior. As you know, am trying to keep the design relatively simple to build. When we start talking driver mods, you need a reasonable way to reproduce them repeatedly to be able to attain consistent results. Maybe we could simulate that first to test its value...

Maybe should just consider a coaxial driver too?

 

[Rick Sykora]

Was hoping to have more to show, but had a diversion today. A fancy hanging lamp needed soldering over at my folks. So here is the front baffle (actually backside) with the driver locations shown...

If you can imagine a 2 inch diameter port (about half the tweeter diameter) about halfway below the woofer and add a speakon jack a little above that, you will have a good idea of the back baffle layout.

 

[ctrl]

Sorry Rick, but this snowman is unlikely to win an art award

 

[Rick Sykora]

Sorry Rick, but this snowman is unlikely to win an art award

Yes, but it will grow up to be a snowman with good directivity!

 

[Rick Sykora]

Am a bit rusty, so after chiseling a bit deeper tweeter recess and sanding a larger woofer recess, it turned out just fine...

 

[tktran303]

I must say, that weird DXT faceplate complements the weird Mariana Trench surround...

 

[sgoldwin]

Snowman no more, the Directiva takes shape.

For those of us following along at home, is there a drawing or table of dimensions and locations of holes?

 

[Rick Sykora]

Snowman no more, the Directiva takes shape.

For those of us following along at home, is there a drawing or table of dimensions and locations of holes?

Yes there are dimensions. Here are the preliminary ones:

for version 12c:

Cabinet
width = 216mm
height = 406mm
depth = 260mm

driver location (from bottom edge)
Tweeter 346mm
Woofer 201mm

Since this is pre-fab cabinet, the drawing is posted on PE website. Click here

 

[Rick Sykora]

Back baffle is a lot easier as only need a couple of hole saws and a forstner bit...

 

[sgoldwin]

A little international perspective here:

• The denovo cabinet is $40 each from parts express. Very reasonable. Shipping 2 of them to the UK is ... $180! No longer reasonable
• Soundimports.Eu sells denovo but the price is €55 each, about $67. And they are out of stock. But shipping to UK is only £15. So total is about equal to $128. Roughly 50%more than in the US. Not unreasonable but not joy and flowers either.

From my own selfish and unique position as the owner of a bunch of SPK5 cabinets and little USD, what would be the impact on directivity from using a SPK5 cabinet? Ie, replacing the Mundorf with the DXT? I realise no one else reading this would share my interest in that approach, nonetheless, I wonder...

 

[Rick Sykora]

A little international perspective here:

• The denovo cabinet is $40 each from parts express. Very reasonable. Shipping 2 of them to the UK is ... $180! No longer reasonable
• Soundimports.Eu sells denovo but the price is €55 each, about $67. And they are out of stock. But shipping to UK is only £15. So total is about equal to $128. Roughly 50%more than in the US. Not unreasonable but not joy and flowers either.

From my own selfish and unique position as the owner of a bunch of SPK5 cabinets and little USD, what would be the impact on directivity from using a SPK5 cabinet? Ie, replacing the Mundorf with the DXT? I realise no one else reading this would share my interest in that approach, nonetheless, I wonder...

Thanks for sharing and the perspective. Being in Europe, @ctrl might have some better substitutes than I. OTOH, it is not a difficult cabinet to build either. PE is so close to me that it does not make sense for me to create a bunch of dust for a simple cabinet.

As we cannot readily simulate the offset tweeter in the SPK5, plan to build a comparable one eventually. If you have any precut front baffles to spare, would get me there sooner.

 

[sgoldwin]

Weirdly, I do happen to have about 10 spare precut SPK5 front baffles...

 

[BrokenEnglishGuy]

I think a relative big bookshelf with coaxial like Kefs for mids and tweeter but a woofer of 8'' would be awesome.. or 2x 6.5'' in dual opposing config

 

[Rick Sykora]

I think a relative big bookshelf with coaxial like Kefs for mids and tweeter but a woofer of 8'' would be awesome.. or 2x 6.5'' in dual opposing config

Maybe at some point later. One variation on the current design is a minitower with 2 Purifi woofers. I can add another woofer at a comparable cost to 2 passive radiators and stay closer to budget. The established co-axials are $150 USD or more. SB Acoustics has added some co-axials recently and may allow for some more options.

 

[Rick Sykora]

As I mentioned, these Denovo cabinets are cut differently than others I have used. So before I glue, it is worthwhile to walk through how to glue to ensure as much glue gets into joints as possible to ensure a good seal.

For this cabinet, it means starting with one of the sides sitting withe the inside up. I propped the front edge along my table saw fence to have a straight edge to use. Next I applied glue to the joints for the top, brace and bottom. No real need for clamps in this case as gravity will push the joints together. Notably placed the other side (without glue) on top to align and add some weight...

Once the glue sets, I removed the other side and will add the back next...

 

[Rick Sykora]

This is the tricky one as there are 4 mating surfaces to be glued and any 2 cannot not be horizontal at the same. Since the 2 of the edges are the brace and the bottom panel, placed them facing up as well as the long edge of the back panel. This way you can apply glue to 3 surfaces without it running. Once this is done, you can lightly smear the long edge of the back panel and apply glue to the edge that mates with the top panel. Before any glue can shift, quickly place the back panel on top. Check alignments and wipe excess glue. I lightly clamped, but a some masking tape to hold the vertical joints should work too...

At this stage, I would apply an extra bead of glue around all interior joints and let it set. Next, if all is well aligned, you should be able to readily slide the remaining side panel in place. If it fits nicely, set aside as some other options are worth considering before you glue it on. The first is that if you did not chamfer or round the backside of the woofer cutout, you should! If you want to use t-nuts for more secure driver mounting, drill some pilot holes for the woofer and leave enough material for the t-nuts to grab when chamfering/rounding.

Some other important options in my next post...

 

[BrokenEnglishGuy]

Maybe at some point later. One variation on the current design is a minitower with 2 Purifi woofers. I can add another woofer at a comparable cost to 2 passive radiators and stay closer to budget. The established co-axials are $150 USD or more. SB Acoustics has added some co-axials recently and may allow for some more options.

it's a bad idea put 2 opposite woofer in a separate box and the coaxial above to the bass box?
like this but nicer xD, if the woofer are opposite the box will be smaller

 

[Rick Sykora]

At this stage, there some key considerations:

1. The inside bottom (and optionally inside top) of the cabinet should be lined with some sheet foam or other damping material. Notably if you use something with adhesive backing or that is less flexible, it will be easier to do now. If you are like me and need to experiment a bit more and are not quite ready to glue the cabinet entirely, here is my tip...
2. If you carefully glue the remaining side to the front baffle along the long edge, once it sets, you will be able to mate the remaining 2 cabinet sections and seal nicely with wide masking tape. It is important to do precisely. While right angle clamps could be used, suggest you slightly offset with other boards to prevent unintentionally gluing and can do on cabinet.

Apply glue along the top edge and then place the front baffle and align along the long edge...

If you do not have clamps, helps to put another board on top of the baffle and some weight. Wipe off any excess glue and allow to set. Before glue completely dries, rotate the cabinet on its side and remove the boards. Remove any glue that may have squeezed out and leaked into unintended locations.

Please note: If you chose to delay final cabinet assembly and utilize #2 above, without further reinforcement, the glue joint between the front baffle and side panel is NOT sufficient to handle the weight of the woofer and tweeter when mounted.