DR build questions

[Keryn O'Shea]

Greetings all,
On page 14 of hifibobs T60 & DR280 build thread
https://billfitzmaurice.info/forum/view ... &start=195
He uses a bit in the drill press to create a pocket style relief in the module for the mounting screws, what type of bit is it? Is it the pocket guide bit, or a plunge router bit..? I can't make it out from the picture.

Can a single vertical routed hand hold be used on the front of the cab, at the front of the horn towards the bottom?

Would it be easier to paint the inner of the horn before the sides go on?

Who makes the best digital angle gauge? I borrowed one and then lost it..

How do I tell which DR is the left or right side cab?

Why does the driver wire need to enter the rear of the cab closest to the centre?

What is the effect of the Piezo array diffuser?

[Grant Bunter]

Greetings all,
On page 14 of hifibobs T60 & DR280 build thread
https://billfitzmaurice.info/forum/view ... &start=195
He uses a bit in the drill press to create a pocket style relief in the module for the mounting screws, what type of bit is it? Is it the pocket guide bit, or a plunge router bit..? I can't make it out from the picture.

Pocket screw bit. If you could find the correct size Forstner bit that would work too. Just remember Bob doubled up his braces to do his build that way.

Can a single vertical routed hand hold be used on the front of the cab, at the front of the horn towards the bottom?

I'll be interested in the answer to this, I can't see why not.

Would it be easier to paint the inner of the horn before the sides go on?

Sure would, you just need to use tape on the edges that will adhere to the sides, so they remain paint free.

Who makes the best digital angle gauge? I borrowed one and then lost it..

That's where it went!
Seriously, it's about making sure that cuts are made with some sort of accuracy. If the same angle guide/ruler is used for the entire build, then you should be good. But if you use a bunch of saws/jigsaws/table saws/ compound miter saws, and set angles based on each tools angle guides, there is an increased opportunity for error.
So it's not about the best. I think mine cost me $20.

How do I tell which DR is the left or right side cab?

It shouldn't matter.
Having said that, my ground stacking plates are just so slightly different that I have marked L or R on the speakon mounting plate, using white paint marker, and on the stacking plates.

Why does the driver wire need to enter the rear of the cab closest to the centre?

Most people will mount the speakon plate inbetween the butt cheeks. Either minimum ply or full back, the only space for wire is that area closest to the centre.

What is the effect of the Piezo array diffuser?

It increases horizontal dispersion.
The diffuser makes horizontal dispersion at least 120 degrees. Without it that figure would be more likely 90 to 100 degrees.
I'm always pretty amazed that adding a piece of dowel (or whatever) the correct size, has such an effect...

[Bill Fitzmaurice]

It's simple acoustics. The higher you go in frequency the narrower the dispersion and the shorter the wavelengths. The dowel doesn't do anything at the lower end of the tweeter pass band, as those frequencies are long enough to go around it. At the upper end of the pass band the wavelengths are too short to go around it, but they do reflect off it, widening dispersion at those shorter wavelengths.

Hand holds at the mouth are fine, they're too small to affect the long wavelengths of the woofer.

[Keryn O'Shea]

Ok awesome thank you, I was joking about L&R cabs! My Dad once convinced a young salesman at a golf pro shop he needed left and right socks.. he was out the back for a while

Most people will mount the speakon plate inbetween the butt cheeks. Either minimum ply or full back, the only space for wire is that area closest to the centre.

So central on the vertical plane?

It's simple acoustics.

I really need to educate myself on this topic

Hand holds at the mouth are fine, they're too small to affect the long wavelengths of the woofer.

Excellent! I'm really enjoying the challenge of building your DR design Bill, learning all the time. I also just like standing there looking at it! Thank you very much mate

[Tom Smit]

Can a single vertical routed hand hold be used on the front of the cab, at the front of the horn towards the bottom?

I did what Grant said about a partial fill in the back on my DR250s. That is where I put the Speakons, and where I put upper and lower handholds....I find it quite handy that way.

[Keryn O'Shea]

I did what Grant said about a partial fill in the back on my DR250s..

Do you have picture/link of how you did that Tom?

[Grant Bunter]

So central on the vertical plane?

Whatever blows your hair back really.
My first pair of 250's have the plate mounted centrally and horizontally.
My second set, the plate is mounted vertically and centred about 1/3 of the way up from the bottom.

Don't forget to add a couple of reinforcing strips to mount the plate on.
And get the wire through before you add whatever back cover you're going with...

[Tom Smit]

I did what Grant said about a partial fill in the back on my DR250s..

Do you have picture/link of how you did that Tom?

I will take a picture and share, but it will be a day or two.

[Keryn O'Shea]

Whatever blows your hair back really.
My first pair of 250's have the plate mounted centrally and horizontally.
My second set, the plate is mounted vertically and centred about 1/3 of the way up from the bottom.

Don't forget to add a couple of reinforcing strips to mount the plate on.
And get the wire through before you add whatever back cover you're going with...

Roger, thanks mate, it was more bringing the wires from the driver chamber through to the back, l was caught thinking l had to bring the wires through from the chamber through the horn throat closest to centre, not the case ay? I can run the wires wherever l like that way, just not out through the back halves at the peak of the radius, yea?

[Tom Smit]

Here is the photo, as promised. I like the handles on the back because it makes it easier to handle, and to put on a stand. The handles give more options in how to hold the cabinet. The Speakons are in parallel.

[Keryn O'Shea]

Ah yes, l see now, very nice job man

[Grant Bunter]

Roger, thanks mate, it was more bringing the wires from the driver chamber through to the back, l was caught thinking l had to bring the wires through from the chamber through the horn throat closest to centre, not the case ay? I can run the wires wherever l like that way, just not out through the back halves at the peak of the radius, yea?

Uh huh.
My first pair I struggled with this as well. It seemed counter intuitive to ensure a leak proof horn, then drill a big enough hole in it!
But that's what I did for that pair, then brought the wire out were it seemed to be appropriate (ie allowing for drill and angles) as close as possible to where the butt cheeks meet.

Did much the same for the second pair regards exit point near where the butt cheeks meet, but on one side drilled the hole as close as possible to where the sheath and baffle piece meet, and put wire through the sheath before the sides went on so I could seal it with hot melt glue...

[Grant Bunter]

Ah yes, l see now, very nice job man

+1

Here is the photo...

Tom, that looks fantastic!

[Tom Smit]

Thanks Keryn and Grant!
I made that pair of DR250s on the hood of a retired Volvo 240 in my backyard, probably 10 years ago or more, with a cruddy circular saw. The back filler panel has a bunch of Bondo to fill in the gaps.

[Keryn O'Shea]

..but on one side drilled the hole as close as possible to where the sheath and baffle piece meet, and put wire through the sheath before the sides went on so I could seal it with hot melt glue...

Nice tip man

I made that pair of DR250s on the hood of a retired Volvo 240 in my backyard, probably 10 years ago or more, with a cruddy circular saw...

Tom I tip my hat to you, Bill, Grant & anyone else who has built a DR with a circular saw, I couldn't see myself being able to make the mitre cuts accurately, I'm using a plunge/track saw for this project as the track sits on the cut line all the way from 0-45 degrees, and with two tracks bolted together, you can square/cut lengthways a whole sheet easily without clamps or screws, the track doesn't move, Grant loves it! I can also see driver access covers being a less sphincter clenching experience..