Seeking advice on a 4-way dipole

[Mazeroth]

I knew that would get your attention! :T

The PE Tent Sale is taking place Saturday and I need to figure out what I'm going to purchase in a hurry. Buying a house that needed work put all my speaker stuff on the back burner for the last year but I'm now ready to get building. All along I've been wanting to build a pair of 3-way dipoles but with my recent acquisition of a second DCX2496 for $35 (don't ask, long story!) I have plenty of amps to do a stereo 4-way speaker pair. This may sound like overkill, but not to Monte Kay:

http://www.mfk-projects.com/seas_4way_dipole.htm

After having the Seas 4-way for more than a year, I have concluded that a 3-way system simply is not adequate to cover the full bandwidth. I had for some time believed the addition of a small driver between the 8" and the tweeter would offer some improvement and this system has been my opportunity to explore this. I now believe that the improvement has been greater than my original expectations. I further believe that this concept should be taken farther. I am currently working on a six-way system that will include a 5-way panel plus separate dipole subwoofers.

I currently have six Dayton RS390s (4 for IB) and plan on using a single one per side, in a shallow H-frame, up to 100-150 hz. From there I'm planning on using dual Dayton RS225 4 ohm, which would be in a SWMTW format. I really want to have exceptional midrange and was thinking of going with a pair of Tang Band W4-1337s but then I got to thinking. The RS52 midrange has a flatter frequency response and much lower distortion in the range I'd be using it in:

(Thanks to Zaph for his measurements)

Tang Band W4-1337 Frequency Response




Dayton RS52 Frequency Response




Tang Band W4-1337 Distortion




Dayton RS52 Distortion



I would mount one RS52 on the front of the baffle and one on the rear so I could still maintain a dipole radiation pattern. Going with a single RS52, opposed to the MTM mounting the Tang Band would require, will also allow me to use pretty much whatever tweeter I want and not have to worry about it not being able to cross low enough. I was thinking of using the Vifa XT25, with its extremely smooth frequency response and good distortion above 2.5 khz. Or, I could use some of the six RS28s I have sitting here...

Just looking for input here since I'm still very new to speaker design and don't want to mess this up! If you think there are better options out there I'm all ears. I've been getting pretty good with measurements and have an ECM8000 mic, SoundEasy, ARTA, TrueRTA and am thinking of purchasing LspCAD Standard. Hopefully this will help me yield satisfactory results. In the future, when I get even more proficient with measuring, I can revisit these and tweak them even more.

Thanks.

[Paul Ebert]

This won't help you decide, but I believe Jed measured the 1337s following a change to the drivers and found the distortion to be improved. Maybe, he will chime in. I, personally, like the idea of front and rear RS52s, but that's just me. You might also consider the RS100.

Whatever you choose, it should be an awesome system.

[Jed]

I like the W4-1337s better than the RS52. The pair of my RS52 had a 3rd order distortion spike that was very audible. You can see these tests on my webpage along with before and after measurements of the W4 after TB changed the basket. It was improved, but could be within spec variation of manufacturing etc.

[Saurav]

Are you thinking of putting a tweeter on the back as well, like Linkwitz now does with the Orion++?

http://www.linkwitzlab.com/orion++.htm

[Paul W]

I like the RS52, but would probably go with the TB in this application. You have the potential to generate low distortion/high SPL and the TB should have more clean displacement and may be a better mate to the RS225. I'd also invest in a very robust tweeter, probably SEAS with higher xmax.

If you go a small step further, a SWMTMW placed far from the front wall, you should be rewarded with a very stable soundstage and excellent imaging.

[Paul H]

My 4-way dipole project completed a few years ago included over a year of testing and tinkering. I'm very happy with it, and would (will) build more dipoles.

But, my next project will be a relatively simpler 3-way ...

[Mazeroth]

First off, thanks for all the replies.

Jed, concerning the 3rd order harmonic distortion around 4.5 khz, where were you crossing them over? If I were to cross them around 2.5 khz I should be nearly 24db down at that point (if I use 4th order electricals on my DCX) and should be able to pretty much eliminate that distortion peak. At least, that's what my amateur mind thinks. Also, the Tang Band has a similar distortion peak right at 900 hz, with much higher accompanying distortion than the RS52. Again, I haven't listened to either but am taking all this from Zaph's measurements.

In my disposal I have four RS125s, four RS150s, four RS180s, two RS225s, and six RS28s. I could easily make this an all RS dipole and use a pair of RS125s or RS150s but figure if I'm going to take the time to build it I may as well spend a few extra bucks and do it right. Speaking of spending a few extra bucks, the RS52s are in stock and should be $28 at the tent sale. Unfortunately, the Tang Band is out of stock and will run me twice that when they come back in, upping the total over $100. Decisions...decisions...

Paul, any reason for doing a 3-way next time? I've been thinking 3-way for the longest time but after acquiring a second DCX2496 I'm going to have 12 channels at my disposal. 8 for the mains (or 10, if I do a 5-way, hehe) and the remainder for my IB sub(s). I'm sure there comes a point where trying to integrate too many drivers diminishes the SQ. You know, somewhere around 7 :B

EDIT: I forgot to mention, but I also have a pair of Peerless 831882s sitting here next to me.

[Jed]

First off, thanks for all the replies.

Jed, concerning the 3rd order harmonic distortion around 4.5 khz, where were you crossing them over? If I were to cross them around 2.5 khz I should be nearly 24db down at that point (if I use 4th order electricals on my DCX) and should be able to pretty much eliminate that distortion peak. At least, that's what my amateur mind thinks. Also, the Tang Band has a similar distortion peak right at 900 hz, with much higher accompanying distortion than the RS52. Again, I haven't listened to either but am taking all this from Zaph's measurements.

.

Here's my RS52 I tested. 3rd order spike at 2K AND 4K- but not bad at all.

Image not available

My W4-1337 tests look better than that to me though. Lower D4 and D5.

Image not available

[Mazeroth]

PE had a great deal on the RS52s for $28 each at the tent sale so that helped decide which midrange to use in this project. If I don't like it I can always switch out to another. Plus, the Tang Band wasn't in stock so that made the choice even easier.

As of right now I'm thinking of going with a deeper H-frame to get more extension out of the RS390 and crossing to the dual RS225s as high as I can before I encounter the cavity resonance. I'm banking on 100 hz. but am confident the two RS225s can handle 80 hz. on a flat baffle.

I got a little excited and laid the drivers out on my bench to see how big this is going to be. I had to put a case under the RS52 and RS28 to lift them up a bit so they weren't overshadowed by the big boys.

(sorry for the grainy pic)



I've never heard a design with an RS28 I didn't like so I'm thinking of using it in this design. I'd like to use the RS52 as high as possible so I get more dipole output in the rear (using a rear mounted RS52) but I'd like to suppress that 4.5 khz 3rd harmonic so maybe a 2-2.5 khz. crossover would be best. It's a shame, but that would only be using the RS52 for less than 2 octaves. I guess the only thing I can do is build it and test it out.

Thoughts?

[Mazeroth]

I had to share this steal I got at the tent sale and didn't feel like making a new thread for it. Plus, this may serve as the fifth speaker if I decide my dipoles need to cross to a sub.

If you look at the back of your PE catalog you'll see the dual RS315 sub with opposing drivers. Well, I got to the tent sale 10 minutes before it was supposed to begin and wouldn't you know it, people had already started shopping almost 30 minutes before I got there! The absolute first thing I saw when I walked up was this sub enclosure with a price of $20 on it and I was shocked that no one else had snagged it. It was literally the first thing you saw to the left side if you were walking from the parking lot. I immediately saw a PE worker and asked if they could put my name on it because I was going to go pay for it. Also, all things at the tent sale are 20% off so I got this beauty for $16. It has a satin finish to it, not like the high gloss in the photo, but nonetheless it looks great. I measured the internal volume and it's 2.006 ft3, with a brace with holes, so we'll call it 2 ft3 to keep things simple. The whole enclosure is doubled 1" MDF, and my my is it heavy. I frequent the gym and I would say it weighs about as much as the 100 lb. plates do near the leg press.

I threw my new DSLR camera on top (Sony A100) that I just snagged from Sears this morning for $200 for a size comparison. They just dropped the price on them drastically as the new A200 is out so it might be worth your time to see if you can find one locally.