Dipole speakers - are these suitable drivers for a project?

**cjd** · 12 January 2007, 11:26 Friday

RS125 is not a very good candidate by the way... very very much masked rearwave.

RS270 won't cross to that tweeter - max of maybe 800Hz if you really push the slopes. Someone did a dipole with a pair of RS270's and they maxed. You'd be better looking at the 10" RS subs for shis application. For a fun quick'n'dirty little project you may be able to get away with a single 10 + mid and tweet, though the RS125 still would be tough.

Consider RS180 over RS125.

If you're simply wanting to experiment, have at it and don't worry about whether it all really works out well. As long as you DO have a use for the drivers in the end, or don't mind starting a collection.

C

**fjhuerta** · 12 January 2007, 13:47 Friday

Hi C, thanks for your thoughts!

You are right, I have no clue as to whether this may work or not, so I may just assemble something (anything!) using what I have at hand, just to see how dipoles behave. I'm also left wondering how to measure a dipole speaker - is it on a completely open field, or should I place them a bit near a wall, as they will be operating?

Anyway, I just have one question... is the masked rearwave related to the size of the magnet vs. the size of the cone? If so, do drivers with smaller magnets behave better when used in a dipole?

Thanks for your thoughts!

Javier.

**joecarrow** · 12 January 2007, 14:12 Friday

I believe that when you're starting out with your own original speaker design for the first time, if you don't have a good measurement setup then it's important to have really forgiving drivers. To me, that means paper or poly cones, a tweeter than can play lower than you need it. Metal cone breakup must be dealt with correctly, or you'll want to rip your ears off.

Rear wave masking for dipoles, it's largely about how much exposure the rear of the cone has. You're mostly right about magnet size, but basket construction is also important. Most stamped baskets get in the way of air flow than most cast baskets. Cast baskets can also have the advantage of having smoothly flowing curves that will often reduce turbulence.

Read through Linkwitzlab.com on the Pheonix and Orion projects if you haven't already- I'd probably print it out and comb through it with a highlighter if I was going to design a dipole for myself.

**JonMarsh** · 12 January 2007, 14:19 Friday

Originally posted by fjhuerta

Hi C, thanks for your thoughts!

You are right, I have no clue as to whether this may work or not, so I may just assemble something (anything!) using what I have at hand, just to see how dipoles behave. I'm also left wondering how to measure a dipole speaker - is it on a completely open field, or should I place them a bit near a wall, as they will be operating?

Anyway, I just have one question... is the masked rearwave related to the size of the magnet vs. the size of the cone? If so, do drivers with smaller magnets behave better when used in a dipole?

Thanks for your thoughts!

Javier.

It's a good idea to plan to have a dipole 3 feet or more out from the rear wall- if you can't operate in that mode, you may want to reconsider. "nice sounding" installations are typically 4 ft or so... just like Magneplanars and other panel dipoles.

Even if tha'ts not practical for you long term, you might want to experiment with one placed optimally at least temporarily just to get a "feel" for the sound...

Be warned that the common baffle configurations are more problematic in LF response and smoothness, particularly with rising response above 100 Hz, and a notch in the response usually in the 200-250 Hz area depending on dimensions, so expect to have more to deal with crossover wise if you go with a U baffle or H baffle.

The flat baffle for the Isiris with it's current driver positioning worked out as simulated; don't be surprised if you measure somewhat near field (1 meter) at the typical listening distance by the null in the upper midrange due to path length differences between the woofers. It's of no consequence anyway, as you shouldn't be using them up to 1 kHz.

All the usual things still have to be dealt with in the crossovers if you use metal cone drivers- see the last posts on the Arvo Heavy Metal testing thread in Missions accomplished for some alternative ideas about crossover and EQ.

Rear wave masking for drivers is an important aspect for any system design, it becomes more obvioius in the case of dipoles, as does pole piece venting and freedome from chuffing noise at higher driver excursions. Unfortunately some of the better drivers with regards to rear masking are also some of the more expensive ones, but not in all cases. Contrast the RS180 and Peerless 830883.

**Doug Lockwood** · 12 January 2007, 14:35 Friday

Anyway, I just have one question... is the masked rearwave related to the size of the magnet vs. the size of the cone? If so, do drivers with smaller magnets behave better when used in a dipole?

That's what many people believe. My experience is that this is not a major problem and drivers that have large magnets relative to the cone can sound good in OB. An example of that is the NSB, which has a large magnet but works very well in OB.

1) Would a completely passive solution make any sense, or do I really need to go active on the woofer side?

Really, active vs passive is no different with OB vs other designs. Same trade-offs. As they say, YMMV.

2) How is bass cancellation handled? I guess this is part of question #1. If I need to go all active on every channel, I won't be able to continue with the project... according to what I've seen on Linkwitz's site, he does everything using active EQ.

Your really asking how to equalize the base. Depending on the driver used and the baffle size, and driver placement on the baffle, you may require many db of EQ, or very little. I only needed about 3 db of boost on my first design.

3) Would a Dayton RS270 per side be enough? What about the new Tang Band slim 10" subwoofer? (http://www.partsexpress.com/pe/show...tnumber=264-862)

The age old answer: It depends. I have 2 RS270 per side in a small room. I think I could get away nicely with one. The Qts is a bit lower on these than I would like. Put them in a small baffle, add massive eq, dog don't hunt. :E

4) Would I be better off with just the Dayton RS270 and the Seas tweeter, and forget about the RS125 for now?

I agree with cjd. Using the RS270 up to 1200 Hz would probably not work.
I cross mine out at about 400 Hz, LR4.

4) Is a dipole far too complex for a relative (2 years experience) noob?

Lets just say they have their own challenges.

My advice is to go for it. You may never go back to "Monkey coffins". :rofl:

Doug

**Dennis H** · 12 January 2007, 14:51 Friday

Go for it Javier!

You've got all the measuring gear and software you need and plenty of practice modifying your MTMs. It's so easy to try an open baffle compared to building a box that I'd just try it with whatever drivers you have on hand.

**cjd** · 12 January 2007, 15:33 Friday

Yeah, I have to agree, experimenting is definitely fun and you learn a LOT. So by all means, toss some stuff together! I think I may have been the first one to use the ultra-cheap NSB open baffle a few years ago, and that was exactly what you mention - a curiousity experiment. No woofer in mine, just that little 4" honky paper cone.

Digital crossover would be useful if you want to do a lot of crossover experimenting, just because you don't need the big big parts bin.

C

**fjhuerta** · 12 January 2007, 19:51 Friday

Wow, thanks for so much great information!

I'll surely be at least trying to see how dipoles work. I think I'll get a pair of RS225's and start from there - if I don't like the results, I can always build something like Mark K's TM design.

**cobbpa** · 13 January 2007, 03:02 Saturday

I know very little about open-baffle designs..but from what I understand here, excursion and openness behind the cone are important. While trying to come up with some worthwhile input to help encourage this project, I remembered the impressive test results Zaph found with the Ascendant Audio midrange. The back of the speaker is practically naked:

I know you have RS125s, but since it seems arguable that the large magnet (especially if it's the 8 ohm shielded model) may interact in some peculiar ways...I'm trying to provide another driver to toy with

. It's even budget friendly! Regardless, I'll be following the project & interested in hearing how you fare.

**fjhuerta** · 16 January 2007, 21:47 Tuesday

I've been giving a lot of thought to the subject.

I got a pair of Peerless Exclusive 8" drivers before I realised they had a 900 Hz dip, so they were unusable for a nice two way design. So now I've scratched that project.

So, I'm considering a dipole panel with two Dayton RS125's and the Seas 27TBFCG working from about 500 Hz and up, with a bass module below (using the Peerless driver) going from 500 Hz down.

I've been sketching a couple of ideas I had. Mostly, they either look like a MartinLogan or like Linkwitz' Orion. Coincidence? I think not

My concern is getting enough efficiency from the RS125's. I suppose I won't be getting more than 80db/W from a pair of those drivers on a dipole panel.

Attached Files

**cjd** · 16 January 2007, 22:04 Tuesday

When you make it that narrow at the top, you bet you'll have trouble getting output from small drivers.

You might also be surprised.

Mock. Measure. Test. Put together a simple baffle, play with shape using cardboard or taped on chunks or whatever. Just experiment. You'll learn ten times, and then have specific "what causes this behavior I noticed" questions and stuff.

C

**Dennis H** · 16 January 2007, 22:06 Tuesday

The Peerless Exclusive 5.5" doesn't have the dip and the sensitivity is about 88 dB for a single driver. Crossed high enough, you shouldn't lose much of that on an open baffle. A pair of the 12" SLS look like a natural for the woofers; two in parallel rolled off at 6 dB for the open baffle should match the sensitivity of of the single 5.5. Cross them at the 'knee' of the dipole roll-off to minimize components and ease the crossover design. Cross to a sub at 80 Hz or so and you've got plenty of SPL. Of course, that's just bench racing.

**fjhuerta** · 16 January 2007, 22:23 Tuesday

Originally posted by Dennis H

The Peerless Exclusive 5.5" doesn't have the dip and the sensitivity is about 88 dB for a single driver. Crossed high enough, you shouldn't lose much of that on an open baffle. A pair of the 12" SLS look like a natural for the woofers; two in parallel rolled off at 6 dB for the open baffle should match the sensitivity of of the single 5.5. Cross them at the 'knee' of the dipole roll-off to minimize components and ease the crossover design. Cross to a sub at 80 Hz or so and you've got plenty of SPL. Of course, that's just bench racing.

Rats, I knew I should have asked first

I already have all the drivers I'll be using, so it has to be the Exclusive 8" and the RS125's....

I never thought I'd regret getting the 8", but apparently, I will.

C, thanks for your comments! I hadn't thought about bass cancellation, and was thinking in terms of aesthetics alone. I'll try and keep the baffle width at least at 10" (or more) of width.

I'm also seriously thinking about "upgrading" from LSPCad to SoundEasy. I find myself very limited by JustMLS, and from what I've heard, SoundEasy allows the modeling of dipole speakers...

Argh, there goes my savings.

**joecarrow** · 16 January 2007, 22:46 Tuesday

Considering you're only taking the RS125 down to 500 hz, you shouldn't have too much trouble with lost efficiency due to dipole cancellation. If you're going to use the Peerless drivers ported, which I think is a reasonably good idea, then I don't think that dipole operation from 500hz to 2ish khz is going to do you much good.

I think a relatively slim and dynamic floorstander is possible with one or two Peerless exlcusive 8's per side, and the aforementioned RS125 and H1212. If ported, one peerless ought to do it. If sealed, two would be decent. If you want them to be especially dynamic, then two ported 8's per side should be very nice- though I haven't checked to see how large the box would need to be.

If you want to go dipole, I think the AA 6.5 is the new budget king for midrange. It looks like an easy cross to a tweeter, and will play a lot lower at volume than the RS125. Dipole bass is the biggest advantage of dipoles, and for that you'll want lots of displacement- more than 8's will give.

**thadman** · 16 January 2007, 23:29 Tuesday

If you go with a large enough baffle, you should have no problems crossing at 500hz (or even 250hz). 1 octave below the fundamental frequency of the baffle (12"=1000hz), the front and rear wave combine in phase and give a 6dB boost in that passband.

You can design your baffle around the drivers being used and optimize the frequency where the front and rear wave combine, thus alleviating the excursion requirements in that passband and allowing you to dig deeper with lower distortion :B

**fjhuerta** · 31 January 2007, 13:36 Wednesday

OK... here I go now.

I have the drivers. Two Peerless 8" Exclusives, two Dayton RS125's, and one 27TBFC per side.

I'm still wondering, though. There's an Adire Extremis design with two 7" drivers per side, which is said to be quite enough for dipole operation. I know the Peerless have half the excursion of the Extremii, so I'm not really sure I'd have enough bass out of 8" drivers. Sadly, S/H charges won't allow me to use a 12" or two in there.

I'm still wondering whether to try a dipole with these drivers or build a very nice, slim tower speaker with some very nice bass response...

Has anyone ever heard of a dipole using just two 8"? I'm thinking about something like the Isiris baffle, only a bit wider.

**cjd** · 31 January 2007, 14:00 Wednesday

You know, it's worth messing with to see what you get.

I'd add some 15" or 18" though.

Mostly, you're going to be more SPL limited the lower you look to push bass extension.

C

**fjhuerta** · 05 February 2007, 22:55 Monday

Hi all!

I've been thinking about my alternatives.

So far, it looks like a MTMWW with the RS125's, the 27TBFC, and the Peerless Exclusives.

As you may suspect, shipping drivers to Mexico isn't the cheapest thing out there. I can't afford to buy a pair of 15" subs here...

I've been thinking about an alternative, though. How about automotive subwoofer drivers? I've seen a Cerwin Vega HED 15" with 18mm linear displacement for about $90 here. Or a JBL GTO for $85 (15", too).

Would this work, too?

Also, would there be an advantage on using the RS125 mids, or should I just use the Peerless as bass-mid units? At this point, I'm starting to think the added complexity of a three way crossover may not be worth it, and the only con I find in not using the RS125s is a slight dip around 1 KHz.

**Paul H** · 05 February 2007, 23:50 Monday

Originally posted by fjhuerta

...
Has anyone ever heard of a dipole using just two 8"? I'm thinking about something like the Isiris baffle, only a bit wider.

You mean 2-8" crossed directly to the tweeter, like the "Arvos" Jon was working on last year?

**fjhuerta** · 06 February 2007, 12:20 Tuesday

Originally posted by Paul H

You mean 2-8" crossed directly to the tweeter, like the "Arvos" Jon was working on last year?

Yeah, that's it... I think I'll start looking for that thread... well, there are a couple of Arvo threads...

I'd assume I'd still need a big sub if going dipole.

**JonMarsh** · 06 February 2007, 12:48 Tuesday

Well, I think he means more like the HiVi M8a MTM like we did for a few folks, including Tibor in Denver.

Dipole speakers - are these suitable drivers for a project?

Dipole speakers - are these suitable drivers for a project?

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