dipoles for me? help me decide

[batdorf9]

Hello everyone. This is my first post here. I've been reading through the archives for the past couple weeks. It's been great. I'm really glad I stumbled onto this site.

After 5 or so years with my same diy speakers, I'm finally thinking about upgrading things. This all sort of started when watching dvd's and not being able to understand the dialogue!!! That was driving me nuts, so I want to do something about it.

I've done a bit of reading about dipoles, and I like the idea of less room interaction. Back when I was at school 5 years ago, we made a few open baffle speakers and they were great.

But just about the time I'm ready to start building an open baffle dipole, it dawns on me that lots of my listening is either off-axis or in another room. I really don't spend that much time "in the zone" doing serious listening so that makes me wonder if a dipole is a wise choice for me.

I guess here's a few requirements that I think might rule out a dipole. Note that these aren't the most important things to me, but they are nonetheless important.
1) I occasionally have movie nights where 4-8 friends come over and sprawl out on the couches to watch. for some of the people they're probably getting the 45 deg off-axis response from the speaker. With a dipole are things going to be really quiet? Granted this doesn't happen too often, but I'd like to things to not just be good in one small spot.
2) Lots of my listening is when I'm about the house doing things other than serious listening. Am I going to have to really really turn up the volume to hear things elsewhere in the house?

There's another part of me that figures if I did have some decent dipole speakers with excellent midrange, I might want to spend some more time "in the zone" doing serious listening.

Surely someone must have thought through this before or actually has dipoles now and can give their opinion.

If I did build a dipole I was thinking some sort of ribbon tweeter (aurum cantus probably), PHL mid, and Eminence 15 or 18 low, with two sealed box subs (15" titanics) for really low stuff.

Part of me wonders if I should just build some monopoles with decent off-axis responce, and then put some effort in to taming room acoustics. Perhaps purchasing Cara or something...

Hm, this is way too long already. Please give me some suggestions or share your dipole experience. Many thanks!

- Robert

[Volenti]

1) I occasionally have movie nights where 4-8 friends come over and sprawl out on the couches to watch. for some of the people they're probably getting the 45 deg off-axis response from the speaker. With a dipole are things going to be really quiet? Granted this doesn't happen too often, but I'd like to things to not just be good in one small spot.

all the off axis listener will miss is some low end response from the dipole, they'll be able to hear what's going on, they'll still get bass from the conventional subs, you don't get an absolute null in the sound at 90 degrees off axis.

2) Lots of my listening is when I'm about the house doing things other than serious listening. Am I going to have to really really turn up the volume to hear things elsewhere in the house?

I've found my dipole speakers to be more penetrating through the house than my conventional speakers were.

[paulspencer]

I'd be more concerned about placement than off axis response - ie. they are meant to be placed with space behind them, preferably 1m. Given their size, generally larger than conventional speakers of comparable output, they have more visual impact in a room - you can't simply put them against a wall out of the way. Also you have to consider protecting the rear of the speaker.

Perhaps the biggest impediment, however, is the difficulty in designing them. To do them properly, they really need a lot of electronics. The Linkwitz approach seems the best to me, but is out of reach of my DIY'ers as far as design goes - you may be better off following his Phoenix or Orion design.

I'd also consider making them full range dipole, not just the mids (although it's not necessary with the tweeter) - the naturalness of the bass and freedom of room effects in the bass is one of the main strong points of a dipole system. You should only need a monopole sub for the bottom octave 20-40 Hz and if it turns out that dipole is really your thing then I doubt you will use a sub much if at all for music, perhaps only for HT.

cheers,
Paul

[AndersZ]

With a dipole are things going to be really quiet?

In my experience the sweetspot get significantly larger with dipoles and the response is some 6dB down at 90 degrees. When moving towards one speaker the stereo collapses towards that speaker, but that one sounds right like it should.

2) Lots of my listening is when I'm about the house doing things other than serious listening. Am I going to have to really really turn up the volume to hear things elsewhere in the house?

I've come to the same conclusion as Robert concerning listening in other rooms. If you visit Audio Artistrys Beethoven pages they specifically list that feature as being superior to normal speakers.

/Anders

[ThorstenL]

Konnichiwa,

Originally posted by paulspencer
Given their size, generally larger than conventional speakers of comparable output, they have more visual impact in a room - you can't simply put them against a wall out of the way.

Well, design a dipole right (from the right materials) and the visual impact is small.

Originally posted by paulspencer
Also you have to consider protecting the rear of the speaker.

Why? The basket and magnet of the driver by far protects the rear better than the plain open cone on the front....

Originally posted by paulspencer
Perhaps the biggest impediment, however, is the difficulty in designing them.

Is it? I didn't notice when I designed mine....

Originally posted by paulspencer
To do them properly, they really need a lot of electronics.

How do you come up with that particular delusion? In my sytem I have exactly the following electronics:

1) Passive Preamp (Transformer based)
2) Balanced line cable
3) Push-Pull DHT Amplifier (works with 45, 2A3/300B between 4 and 10W output depending upon valves fitted)
4) Copperfoild speaker cable
5) Speakers

Sayonara

[batdorf9]

First off, major thanks to everyone who responded so far.

I'm starting to think that dipole may be the way to go for the L and R speakers at the least. It does look like maybe it's not the best way to go for the center speaker, since that's pretty much back right up against the rear wall.

The only major stumbling block may be the distance to the back wall. I can easily have about 2/3 meter to the back wall. 1 meter might not be too unreasonable. Does putting some sort of sound absorber or diffuser on the back wall seem like a reasonable idea?
I actually haven't seen anything saying they need ~1m or more behind them. Paul Spencer - where did you read this? Perhaps you could share a link with some further reading. I'm still reading through all of the linkwitz stuff - it's really great that he's written all of that down and shared it with everyone.

I think I can probably manage a ~.6 to 1.0 meter wide baffle with the space given. Looks like that should get me down to ~80 Hz or so without needing a boost (f=0.17v/D, right?). I imagine I can either xo to subs at that point, or boost a bit to get the mains down to 50 Hz or so and then xo to subs.

I think I'd prefer a flat baffle as opposed to the H pattern, as then I don't have to notch out the upper resonance. Right now I'm leaning towards all active crossovers. My reciever will XO to subs at anywhere between 50 and 100 Hz. From there I can split the mains with a 3-way active crossover (probably pro-sound equipment -- any suggestions?). Seems like active xo's avoid a major hassle in sorting out a decent passive xo, and will let me try different drivers easily w/o having to constantly re-work a passive xo. I have a fair number of adcom amps to use.

So current fuzzy concept for L and R speakers would be:
3-way
all active xo's
tweeter - not sure
mid - PHL 6.5" or 8"
woof - probably eminence 12, 15 or 18, high Q
I generally look for drivers with high BL / low Mms and high efficiency
baffle probably ~.8m on the bottom tapering up to ~.4m ? on the top

Any thoughts so far?

Going with an 18 for the woofer would probably allow me to try things out with a boosted lower response. I could then turn off the subs and be true dipole and compare all dipole vs. dipole from 50Hz up. I did play with the room responce calculator on FRD Consortium and found a sub location that gives a reasonable response w/o any nasty peaks or dips. So I think there's a decent chance I may be OK with monopole subs below 50 Hz.

Kuei Yang Wang -- that glass baffle is awesome! Not sure I want to attempt that with a 3-way though. Very nice.


- Robert

[paulspencer]

I haven't built an open baffle myself so a lot of information comes from Linkwitz site. I'm intersted in doing OB at a later date, but I'm held back at the moment by 2 things - placement issues and active filters.

1. Placement - 1m rear wall clearance recommended by Linkwitz
http://www.linkwitzlab.com/faq.htm#Q31

2. Active filters - personally I'm convinced that the Linkwitz approach is the way to go. Having read through all the filters that are required, I realised that I would have to either follow Linkwitz design for the Orion and buy the plans (over my current budget) or design my own, which I don't yet have the ability to do. I like to take on each projects without too many things I don't know how to do.

What I would like to do is first gain more mastery of conventional designs, then later go on to a modified version of the Phoenix, perhaps using different but similar drivers and making aesthetic changes.

Do you want the best open baffle you can afford or do you have an insatiable urge to design your own from scratch? I think it's important to ask that question, as for many, the best result usually doesn't come from your own design. (but that usually doesn't stop us anyway!!!)

I have a few links that you might find interesting:

Bob - phoenix with different drivers

Stephen Moore - phoenix dipoles and a budget version

Line array OB

Mini OB's

Anderz OB's

Roist OB FAQ with good diagrams

Technical Details on Carver's Line Source Dipole - interesting article

You say that you can live with a 1m wide baffle. With 1m behind it, your speakers will occupy 2 sq metres!!! Why do that when you don't need to? ... I suppose it comes down to what compromises you are willing to make and it is a personal decision.

I'd be interested to see what you come up with
cheers,
Paul

[king30]

Here's another link for ya:
NaO

[paulspencer]

Originally posted by Kuei Yang Wang
Well, design a dipole right (from the right materials) and the visual impact is small.

The glass idea is nice but it still occupies more space than a conventional speaker of comparable output, which was my point. For some this is not acceptable. I may well be building an open baffle with a glass baffle in the future, the transparency appeals and it mirrors the open baffle concept nicely.

Originally posted by Kuei Yang Wang
Why? The basket and magnet of the driver by far protects the rear better than the plain open cone on the front....

A conventional speaker would have a grille on the front and the rest is box - nothing that attracts the attention of children as something to touch. Without a grille, a speaker is likely to be fascinating to children, they will want to get their hands on them. Even worse if they have scissors or a knife - you know what some kids are like!!! ... my ideal of the glass baffle with no grille on front or rear may be hard to realise ....

Originally posted by Kuei Yang Wang
Is it? I didn't notice when I designed mine....

If you look at Linkwitz site and his description (if you haven't already) you will see that it's not for the faint of heart! Yes a simpler approach is possible, but it wouldn't be my preference.

Originally posted by Kuei Yang Wang
How do you come up with that particular delusion?

It isn't a delusion. Please be respectful of my views.

Granted, OB can be done without active filters. Implicit in my statement but not explicitly stated were a number of goals along similar lines as Linkwitz which make active filters virtually essential.

regards,
Paul

[ThorstenL]

Konnichiwa,

Originally posted by batdorf9
The only major stumbling block may be the distance to the back wall.

This is less critical than you think, as you can see with the placement of my own speakers. You can get awa y with less than 1m distance.

Originally posted by batdorf9
I think I can probably manage a ~.6 to 1.0 meter wide baffle with the space given. Looks like that should get me down to ~80 Hz or so without needing a boost (f=0.17v/D, right?).

A baffle of around 0.8m X 0.6m will show a -3db point in the 50Hz region, based on the Math present by Backmann in his AES Paper. Placing the baffle on the floor (with no or only a minimal carpet filled gap) will add the floor image boosting the LF SPL by around 6db for frequencies starting (+3db) at a frequency with a wavelength around 4 times the distance to the floor - so with 35cm driver distance to the floor you get around 250Hz as the point belkow which the floor boost becomes noticable.

Originally posted by batdorf9
I imagine I can either xo to subs at that point, or boost a bit to get the mains down to 50 Hz or so and then xo to subs.

I use a main driver (8" Fullrange) with Qt = 0.8 and Fs = 50Hz and cross over at 50Hz to my (sealed box) subwoofer. Even without subwoofers the speakers sound fine, broadly in line with a decent standmounting 6.5" 2Way speaker for general LF performance.

Originally posted by batdorf9
I think I'd prefer a flat baffle as opposed to the H pattern, as then I don't have to notch out the upper resonance.

Absolutely agreed.

Originally posted by batdorf9
Right now I'm leaning towards all active crossovers.

Get (a) digital one, like the Behringer DCX2496, modify this (Op-Amp's, Capacitors and added PSU filtering) and then build decent Chip-Amp's (say LM3875 Bridged for MF and Treble plus LM3886 Bridge/Parallel for the Woofer - select 4 Ohm or lower Z woofer).

With a digital X-Over you can easily eqaulise drivers etc in addition to the X-Over function.

Originally posted by batdorf9
tweeter - not sure

My choice would be likely Aurum Cantus R2S ribbon.

Originally posted by batdorf9
mid - PHL 6.5" or 8"

Use the 6.5" that is development on from the AUdax PR170M0 (ask Andre Perrrault - he will know), perhaps 2 of these in a MTM with the ribbon?

Originally posted by batdorf9
woof - probably eminence 12, 15 or 18, high Q

Have a look at the Eminence Kappa 18 - we used this one quite succesfully in a dipole woofer.

Originally posted by batdorf9
Kuei Yang Wang -- that glass baffle is awesome!

Thanks, it's based on ideas from this speaker



http://www.dietiker-humbel.ch/micromag.htm

I use the Supravox 215 Siganture Bicone Driver, giving around 50Hz-18KHz on this open baffle, 96db/2.83V/1m and an easy 8 Ohm nominal load.

Sayonara