Simple DIYable Waveguide testing (dome tweeters)

[Saurav]

Can you route a circular groove into the back of the baffle, around the cutout? Would that help hold the o-ring in place while you position the tweeter?

[dlneubec]

Off the top of my head, I can't think of an easy process that would allow that, since the excess depth has to be routed out to get the shallower depth of the waveguide. This is done after the hole for the waveguide is cut and the roundover completed, so there is not center hole left at that point. I'm not sure any circle guide routes holes as small as 1-3/8". I'll give it some more thought.

[BobEllis]

You could use a template to rout a groove, but centering is an issue.

[JonW]

I considered felt rings. The concern I have with felt rings is getting them the exact size you need for the inside diameter, the correct thickness and the correct outside dia. I'm not sure you could cut them by hand accurate enough. The rings can't be much wider than 1/8"-1/4" and 1/8" thick or they will not compress enough to allow the faceplate to settle evenly. The 1/8" dia. O-ring should not have that problem. It may have others, however. I suspect that the 1-3/8" O-ring, slightly compressed, will fill the space adequately. Measurements will surely answer that question.

Another approach would be to do this. Remove the tweeter face plate. Add something to the surface so that nothing will stick to it. Mount the face plate only to the waveguide. Fill the space in by handwith silicone, caulk, wood filler, spackling compound, or something like that. Once dry, you would have to be able to remove the face plate so that the material could be finished and the tweeter body added before re-mounting it. If the O-ring does not work, I may try something like this.

Hi Dan,

This is a good, practical point. Easy for me to say it, but that’s from sitting in front of a computer. Now that you mention it, yeah, felt is a little bit of a pain to work with.

The only thing that comes to mind for cutting the felt might be a hole saw. If you can find one with a diameter exactly like what you need. Then use it to cut the hole in the felt by hand. Work the hole saw down into the felt by twisting by hand. Don’t use a power drill or anything. At any rate, I’ll be curious to see what you work up.

This is a nice thread. I’m learning a few things and it’s making me think about some things I would not have otherwise. Thanks. :T

[Preacher]

I've got a tip for cutting holes in felt and such like. This comes from cutting mat board circles.

Take a piece of steel pipe and bevel the edge. Tack down your paper, mat. and lay the pipe on it and give it a whack with a hammer. It slices through. If you can't do this yourself I've gotten them from machinist and plumbers.

All you need is a good arsenal of pipe sizes.

[dlneubec]

I can see where the initial cut might be done reasonably well using various methods, say the inside diameter of 1-3/8". But then you have to cut it into a ring at about 1/4" width maximum. Getting good circular cuts in felt at 1-3/8" ID and then 1-7/8" OD, in concentric circles, seems like a real chore, based on my experience with felt. Granted, I've only used 1/4" felt, which is a b!tch to cut accurately, so maybe 1/8" thick stock would be easier.

[madisonears]

Dan,

My first post here. I am interested in your experiments because I have a pair of these tweeters waiting to be put into a system. I have one comment and one suggestion.

Your basic premise is that this tweeter has a rising high end response. Have you considered what almost every raw driver measurement fails to take into account? How are most tweeters used in the real world? They have grille covers, which typically attenuate high frequencies. I don't know of anyone who measures tweeters this way, yet every commercial application and at least 90% of hobbyists use some sort of cover. I would like to know how much the upper response is affected by such an arrangement. It may very well smooth out that rising high end. Maybe the Peerless guys are one step ahead of us.

Secondly, a suggestion regarding filling the cavity between front of faceplate and back of baffle. Instead of a rubber O-ring, why not make your own O-ring out of clay? The ID could be formed into perfect shape even after the tweeter is attached to the baffle. If you want something more permanent, you would need to remove the faceplate initially and build a dam around the ID and OD of the faceplate by applying masking tape or something similar "on edge" around the ID and OD of the faceplate, and cover the holes with tape. Then simply fill the space with molten wax. This could be smoothed, flattened, and shaped quite easily after it hardens.

I am more interested in the ability to adjust acoustic offest by using a shallow waveguide. The alteration of response curves and power handling and other factors are not so important to me.

Please keep us advised of your progress.

Peace,
Tom E

[dlneubec]

Hi Tom,

Welcome to the forum!

My expereince has been a bit contrary. Most DIYers do not seem to use grills and speaker covers, based on what I have seen posted on forums and at DIY events. Most OEM's certainly do. I have not measured the effect of the grill, but I'm skeptical that it would attenuate the high end that much. I never use grills, so I will probably never do that test myself, but it would be interesting to see the results.

Thanks for the ideas on filling the gap. I may try them at some point. There is a chance that it can acutally be done during the construction of the waveguide. The idea would to route out the back (before you bore the through hole) to within 1/4", or maybe even closer, to the bored out hole diameter. You have to leave the entire depth of the wood intact around the bored out hole for doing the roundover. After the roundover was completed, you would route out the remaining lip to a depth so that it would fill the gap due to the face plate. To get a perfect match, you might have to hand sand the remainin lip to an angle to match the face plate angle. Anyway, I might experiment with this concept as well.

[Bill Schneider]

About cutting felt...

Image not available

I used a chassis punch to cut this 1" circle from a piece of 1/4" adhesive backed felt.

It wasn't as clean as in sheet metal, but it might be something to invesigate further.

Felt shears nicely, and that's why I tried this.

[sendler]

Coil alignment?

Great work on the waveguide concept. How difficult is it to line up the voice coil/ magnet/ waveguide, as you install the tweeter so that you don't get any coil rubbing?

[dlneubec]

So far, alignment has not been an issue. The tweeters I have used have either had fixed dome/vc's or in the case of the Peerless HDS, there are registration dimples and holes through the removable dome/VC assembly to keep it aligned (I simply scotch tape it in place registered to the dimples). Other tweeters may be problematic, depending on how they are constructed. Aligning with the WG is not really been problematic with how I've done it so far, that is, without the face plate/flange. You can visually align the dome and surround in the hole quite easily by tightening the back pressure screws slightly at first to allow small adjustments , before tightening the body in position.

One might also make the rear recess for the tweeter body a tight (driver rebate-like) fit, but route out areas for the terminals. In that case, as long as you get the rear, tweeter body recess and WG hole concentric, the dome will be centered. I did this on my Duo-S, with the Vifa D26NC55 (face plate and frame removed). This is probably how I would approach one with the tweeter face plate still intact.

Of course, you may also have to adjust the through hole size depending on the size of the dome/surround combination on the particular tweeter.

[sendler]

Dome mid wave guide?

It might be fun to try an RS52 in a 1.5 x 1.5 wave guide as well.

[dlneubec]

Yeah, I had that thought as well. I have two available that I will try it on sometime (probably not soon, however). I suspect that the WG would have to be much wider and deeper to have much beneficial effect.

[sendler]

1 foot

Yeah. I thought about that after my post and realized that to get any boost down below 1000hz you would need guides of a foot or more. The shallow guides look awesome with the Peerless though and I see Jed is digging the DXT also.

[dlneubec]

It looks like a 4º slope on the BaSSlines open baffle section is working out about perfectly. It allows me to do an even better job of phase alignment in the crossover and to rear mount the midrange, which should be much easier than creating that odd shaped flange opening in the Lexan.

Also, I plan to do the waveguide tweeter mount 9/16” deep with a ½” roundover, for a pretty flat 15º off axis response. The Lexan is 7/16” thick (though spec’d at ½”), so I’m using 1/8” of wood between it and the tweeter body, giving me 9/16” total depth (see plan attached). That way you don’t see any of the tweeters except the dome and surround from the front. I also figured out that I could use the tweeter face plate as a template to drill holes from the front, through the baffle. This allows me to mount it with button head cap screws from the front side, directly to the tweeter body. That way I don’t have to press mount the tweeter from the back and the open baffle is better preserved. With this mount you do not have to be concerned about the tweeter position slipping, etc. I have a wood cap shown over the tweeter at the back, which I may or may not do, but it is only to improve aesthetics.

I will also be mounting the midrange the same way, 1/8” of wood sandwiched between the Lexan and the driver flange, which keeps the odd shaped flange hidden from the front. In side by side testing, the recessed mount measures virtually identically as the front mount, at least within the useable area of the driver's frequency response. The differences that do show up are well down in the passband.

[dlneubec]

Oops, I meant to post this in the BaSSlines thread! I guess the part about the WG mount has applicability here. ops:

[dlneubec]

I posted this in my BaSSlines thread, but thought it would be appropraite to copy that post in this thread for anyone who is intested in DIY waveguides.



Here are some photo's of implementing the rear mounted Peerless HDS in my ptototype mdf baffle, with the front screw mounts. I used the removed tweeter face plate to mark holes for the screws to go through the baffle and into the tweeter body. Here are a series of photo's:

Double sided tape on the tweeter face plate to hold it in place. Disregard the circles drawn in pencil on the mdf. That was the old tweeter position, which has been moved 1.5" closer to the mid to improve vertical lobing.



The for holes for the tweeter mount were drilled, then the center hole was located by connecting lines through the holes and a center hole drilled for using the Jasper guide.



Jasper circle guide used, to recess a hole for the tweeter at the back of the baffle at a 1/16" depth for an 11/16" deep waveguide. The center of the recess is left intact at this point for the 3/4" roundover bit that will be used in a later step. A simple 1/4" width slot is cut at the tweeter body dia. to form the outside of the eventual full recess.



1-5/16" dia. hole drilled through the mdf, using the center hole as a guide to form the sides of the waveguide, using a forstner bit.



This is shown for the midrange hole, but the same process is used for the tweeter waveguide. The depth of a 3/4" roundover bit is deeper than 3/4" to the bearing, so you have to have a equivalent size hole in a dummy piece of mdf, mounted behind the finished piece to act as a guide for the bearing of the roundover bit to run along. I again used double sided tape to stick the two pieces of mdf together and provide the guide for the bearing. The same process was used on the tweeter hole, but with a 1-5/16" hole.



Next up is a shot of the front of the baffle after both the woofer hole and tweeter waveguide 3/4" roundovers were completed:



Here is a shot of the back of the bafle with the full recess removed for the mid and tweeter. The mid was roughly done here for the prototype. I would use a template in the finished version. Note the additional recesses drilled for the tweeter binding posts.



Drivers mounted:



Finished prototype baffle, tweeter moved 1-1/2" closer than previously, both drivers mounted from the rear at a depth of 11/16", with a 3/4" roundover. Counterbores were drilled for the screws to recess them below the baffle. In the finished version, this will allow for 7/16" of Lexan, backed by 1/4" of hardwood for an 11/16" depth on the drivers. That is the reason for the 11/16" deep mount in the mdf. The result will be that you will only see the driver opening from the baffle side and none of the tweeter or woofer flange will be visible through the Lexan. Also, as you can see, I'm thinking of doing a combination of 3/4" roundover and a chamfer at the baffle edge. I will also be testing a chamfer for the midrange hole, rather than the roundover.