Is a two way using the Dayton DA215-8 and a tweeter practical ?

[Drjay]

Hi guys,

I got my Zingers copy up and running yesterday and am really delighted with the sound. The bass is super satisfying and the rest of the frequency response very nice as well. So, having discovered the joys of good 8 inch sound, I started rumaging around through my inventory of drivers I've bought in the past few years when PE specials came up that I couldn't resist. Well, lo and behold, I found a pair of new, in the box, DA215-8s.
I know they won't go as low as the SD215-a DVCs, but thought that maybe they would have a lot of that 8 inch goodness. So yes, they are aluminum and won't go as deep. but in a 1CF box they will play plenty loud and might sound darn good overall. Maybe crossed super low ( 1500? ) the breakup could be supressed? I have the RST 28 A and F in stock as well as the Peerless XT25 BG30. I also am OK with buying a different tweeter if there is one which is affordable and would be better. I searched for 2 ways using the DA215-8 and found zero. Thoughts and suggestions about a possible build would be much apprediated.

Best,
Jay

[fpitas]

The usual way to do that (well, the modern way to do that) is to use a waveguided tweeter, so you can cross low (say, 1kHz) and better match the dispersion of the woofer and tweeter. In this case you will also be better dodging the nasty woofer cone breakup around 5.5kHz.

[billfitzmaurice]

Looking at the SPL chart I see no need to cross it over lower than 2.5-3kHz. Worst case you might need to use 3rd order low passing to tame the 5.8kHz break up mode peak.

[rpb]

It would work well sealed, if you have a system with a sub. My xo guess, at a glance would be 4th order electrical filter, and cross somewhere between 1.7k and 2.2k.

A third order with a tank cap added might work well.

[fpitas]

Dunno Bill. I think that 10dB peak might be audible unless you crush it really well. In any event a lower cross helps match the woofer dispersion better.

[billfitzmaurice]

I don't see the woofer dispersion being an issue, unless it's intended for near field listening. At usual living room distances you're well within +/-30 degrees. The peak can be tamed with a high Q filter.

[Chris Roemer]

P.Carmody used the -175 in his "Hitmakers".

The 8" rings nearly +6dB louder near 6kHz (opposed to >8k for the 7"), but it SEEMs to have quite a bit more sensitivity (5-6dB?).
It also looks solid down to 40Hz in 1.0cf w/a 3"x 9" long port tube (a 2" PrecisionPort, x 4" long could also work).

It should sound as "acceptable" as the Zingers (IMO). Like the 7", the 8" has some BSC built in to its FR.
Crossed near 2k w/a notch/tank on the woofer, shouldn't be too hard.
If you're not looking for a "precision" 2-way, I wouldn't worry (much) about the dispersion characteristics. Could be a fun project.

[fpitas]

You can get a dip in the power response if the woofer narrows a lot at the crossover. Kind of a purist thing, and frankly sometimes people like a slight dip in power in that frequency range.

[a4eaudio]

I think Bill F.'s point about woofer dispersion in a living room distance is probably right in practice, but the theoretical challenge often brought up around 8" two-ways is beaming, which requires crossing over below 2Khz. But the RST28A or F will go down to 1.4-1.5Khz anyways so that isn't really a problem for you.

A lot of 8" two-ways use a waveguide. This helps crossover lower, which isn't a big deal with the two RST tweeters, but will also improve off-axis dispersion. The RST28F is a perfect fit for the Visaton Waveguide WG 148 R (KEthredge used it in the Defiants). I have yet to find whether the aluminum version fits or not.

Is the Peerless a XT25BG30 or TG30? It appears it is a perfect fit in the Visaton waveguide also. (see here and here)

[LOUT]

It sounds like that tweeter already plays low enough since it was matched with the SD215 and the DA215 looks to have smoother mids....so I'm assuming the main concern is the woofer's spike up high.
How much better does that spike get when you add a notch filter onto the woofer's inductor (just a tiny cap with a series ~16ohm resistor added parallel to the woofer's inductor)?

Something like this:

[note, the "0.36ohm resistor" on the inductor is just for showing some DCR...not actually suggesting to put a small R there]

[billfitzmaurice]

You'd use a notch filter to reduce a hump within the driver pass band, not one that's an octave above it.

[wogg]

It sounds like that tweeter already plays low enough since it was matched with the SD215 and the DA215 looks to have smoother mids....so I'm assuming the main concern is the woofer's spike up high.
How much better does that spike get when you add a notch filter onto the woofer's inductor (just a tiny cap with a series ~16ohm resistor added parallel to the woofer's inductor)?

Something like this:

[note, the "0.36ohm resistor" on the inductor is just for showing some DCR...not actually suggesting to put a small R there]

Tank cap on the woofer low pass inductor is the way to go. The smaller the cap, the less you need to worry about the series resistance. I did a 0.1uF cap without any series resistance, the load will become purely capacitive but at a really high frequency way above 20k. That's worked out just fine for me, but I'm sure there may be amps that won't like it at all. It's best practice to put something in there. If the notch isn't deep enough I'd drop that down to as low as 4 ohms.

[Wolf]

You'd use a notch filter to reduce a hump within the driver pass band, not one that's an octave above it.

I would use a notch filter for either case, likely parallel (parallel, placed in series with driver) for the in-band, and series (series, placed in parallel to driver) for the out of band.
If you don't suppress it by at least -25dB from reference, it will be audible.

Later,
Wolf

[Wolf]

Jay-

I would do like I did in the Zingers, and make the tweeter rolloff a bit early as it approaches the woofer's response so you don't get the on-axis peak like a lot of non-waveguided 8" 2-ways have with flat response. It makes it a lot more livable.

Advice? I would not do an 8" metal-cone 2-way unless you are really well skilled at xover designs. They are projects that take that skill and put it to task. I would use a tank cap as suggested, but also target an LC across the woofer at the breakup frequency. This will kill it.

The only project I know of recently with the DA215 is the one Greg Rueff did with a 3-way. I think maybe Arlis used it in a big 3-way a few years back.

Later,
Wolf

[Drjay]

John H. recently showed me what a tank filter can do to suppress woofer breakup on a different build and I was very impressed. Since the consensus is that using this woofer in a 2 way is not a hopeless project like my Decware clone attempt, I plan on giving it a shot. I'm heading out of town for two weeks in a few days so nothing is going to happen soon, but since I got all the necessary drivers on sale and they were just gathering dust, why not?
Everybody's input is much appreciated and I'll probably be asking for more guidance once the cabinets are built and the drivers in cabinet response are measured. I am definitely not skilled at crossover design but the kind folks who offer suggestions keep me going in the right direction.

Jay