Are there advantages to a waveguide tweeter in a typical 3 way?

[aarond]

When properly implemented a WG tweeter has a lot of advantages over the same driver conventionally mounted. I’m specifically thinking the RS28f in this case. Due to its diameter the RS28f may not normally be my first choice if conventionally mounted in a 3 way. And the advantage of a lower crossover point allowed by the WG also gets negated. But does a waveguide provide other advantages that would make it beneficial to a 3 way? I believe off axis response is also greatly improved by a WG correct? But is the off axis improvement that much better than a smaller dome (say 3/4”) or ribbon would have?

The reason I ask is because I’m considering a 3 way and am trying to figure out a choice for a nice tweeter. 3 ways open the door for a lot of options. Normally the RS28 wouldn’t be my first choice in such an application but if the benefits of the same driver in a WG make it worth considering then I might just do that. If the WG route is worth exploring I’m kind of committed to the RS28 since it’s the only tweeter I’m familiar with that has a WG profile specifically designed for it, unless someone knows different.

[GranteedEV]

First of all, the horn loading effect of a waveguide should be considered secondary. It's a nice little bonus if it's there, but it's not the goal.

The real goal of a waveguide is to control directivity. That is, increase directivity index so that it matches the driver it's being match to.

With most speakers, you'd probably need to go 4-way to get decently matched DI in every crossover region without sacrificing power handling. Even then a waveguide can help. The Revel Salon2, for example, is a 4-way speaker that uses a small elliptical waveguide to match a 1" dome tweeter to a 4" midrange.

The goal, thus, is to avoid sudden "splashes" of harmonic content.

A small 3/4" tweeter or ribbon will beam less, but it's not really the top of the passband that's the issue. The top of the passband is really content above 8khz. I'm not going to call it meaningless because it isn't, but it's less meaningful than the bottom of a tweeter's passband.

In general it's never a bad idea to have a matching DI. If you've got the means to make a well-designed waveguide, I don't see "why not".

As far as coverage angles, a flat baffle is a 180 deg waveguide until the baffle step. A 120 degree waveguide is probably a good idea for most acoustically small speakers. A 90 degree waveguide makes sense if you want to really reduce the room from the equation in the tweeter's passband. A 60 degree waveguide takes it a step even further but is probably not desirable for hi fi unless you're the type that really dislikes reflected sound.

as for drivers, you may want to strongly consider a 3/4" exit compression driver mounted on a SEOS-6 or SEOS-8 waveguide mated to a 5"/6.5" or 6.5"/8" midrange respectively. These are 90 degree waveguides btw.

I don't recall exactly which driver those waveguides were made for but I'd imagine it's a 3/4" B&C or Celestion unit.

[aarond]

Lots of good information (fast too). So what about applying this to an open baffle (but not exactly) oriented setup ? I didn't say it in the first post but that's really what I'm considering but I don't want to do the dipole thing w/ the tweeter so I'm just trying to find a good match for an open back mid that will play down to 350Hz to cross over to an OB(ish) woofer.

[GranteedEV]

Lots of good information (fast too). So what about applying this to an open baffle (but not exactly) oriented setup ? I didn't say it in the first post but that's really what I'm considering but I don't want to do the dipole thing w/ the tweeter so I'm just trying to find a good match for an open back mid that will play down to 350Hz to cross over to an OB(ish) woofer.

Well i'm not really sure what you're trying to do so for starters it'll help if you clarify.

As far as waveguides in OBs, they're not unheard of. Here's one example:

http://www.troelsgravesen.dk/OBL11.htm

I'm not really a fan of having only forward firing tweeter mated to a forward/rear firing mid, at least not without some serious attenuation of the mid's rear wave. I can't imagine it sounding all that great, not that i've tried.

[aarond]

Well i'm not really sure what you're trying to do so for starters it'll help if you clarify.

Fair enough... think Statements' mid and high section (mids are already mounted in a tunnel) but with a different (to be determined) tweeter. Woofers mounted in a U frame. I use the Statements as a reference mostly for driver layout, but the Tang Band mids would be a good choice I think.

Thanks for the input, gotta go to bed (it's late here)

[cjd]

First... heck yes they can be beneficial. If I were to do the WWMTM again I'd WG the tweeter without necessarily changing anything else. RS28A to RS180-8 to RS270-8.

Second... check out JonMarsh's Arvo Picante. 180mm dipole mids, dipole woofer (w) but monopole WG mounted tweeter.

[Pallas]

But does a waveguide provide other advantages that would make it beneficial to a 3 way?

Depends, I think. If you use a very compact tweeter and a small mid, you may not have much of a directivity mismatch.

Look at the new McIntosh speakers for example. They have most of the sound coming from an MTM with two Aura Whispers (2") and a compact tweeter between them.

http://www.mcintosh-club.ru/images/galery/preview/mcIntosh_lcr80-2.jpg

That's one of the few prefab speakers that looks interesting enough to merit seeking out and hearing.

Jamo something similar a while back.

Then again, David Smith makes some great points in his discussion of the MTM array he based many of his Snell products on in this review. (http://www.stereophile.com/floorloudspeakers/334) (I think those midranges are Vifa MD10's.) One may well say that a big difference between the two is that when Smith was designing the Snell speakers, there were no great 2" drivers like the Aura Whisper on the market.


The reason I ask is because I’m considering a 3 way and am trying to figure out a choice for a nice tweeter. 3 ways open the door for a lot of options.

I would look to a compact faceplate first, to get C-C spacing as close to concentric as possible.

If I were doing a wide-dispersion three-way, I'd be really tempted to make the mid-high section an MTM with 2 Aura Whispers and a compact rear-mount tweeter in a shallow waveguide such as the Aura NT1 or Dayton ND20. I honestly don't think the latest-greatest from ScanSpeak or Seas Excel or Accuton or whoever could come close, simply because their drivers don't allow that kind of C-C spacing. True, efficiency isn't great (maybe 87dB/W/m if one's lucky, and that only because of bandpass gain on the Whsipers) but for a compact closed box with an F3 somewhere between 60-80Hz might not be the worst compromise.

Actually, I am seriously mulling a speaker like that, since I saw the Macs and started reading about the Snells. (David Smith posts on DIYA, and talks an awful lot of sense.) I'd like to see if I can make a separate-driver speaker I like as much a coincident and Dual Concentric driver-speakers.

[aarond]

First... heck yes they can be beneficial. If I were to do the WWMTM again I'd WG the tweeter without necessarily changing anything else. RS28A to RS180-8 to RS270-8.

Any specifics on what WG you would use? Also, I'm under the impression you would also need to to tweek the xover in an existign design, are you mostly saying you wouldn't change the crossover point. I'm also assuming that you are would be primarily interested in the improved DI?

The RS28 to RS180 is a pretty common 2-way combo. When I asked my original question I assumed (not necessarily correctly) that one would be using a more midrange specific driver that would allow a higher xover point to the tweeter than a typical 2-way.

Good link too.

[benchtester]

My 2 cents: My favorite feature of a waveguide is that it recesses the tweeter and helps with the alignment of the acoustic centers of the tweeter and mid. This is particularly useful with low-order crossovers.

With a three-way, I would stick to 3" to 5 1/2" mids; larger drivers drop off too fast off-axis IMO.

[cjd]

Any specifics on what WG you would use? Also, I'm under the impression you would also need to to tweek the xover in an existign design, are you mostly saying you wouldn't change the crossover point. I'm also assuming that you are would be primarily interested in the improved DI?

The RS28 to RS180 is a pretty common 2-way combo. When I asked my original question I assumed (not necessarily correctly) that one would be using a more midrange specific driver that would allow a higher xover point to the tweeter than a typical 2-way.

Good link too.

Oh. It would require me to redo the crossover. And I might make some other changes to both slopes and crossover points. Directivity is somewhere down the list of benefits but is definitely nice.

Small mids mean woofers reach higher which adds other issues. Its not always aright answer.