Dipole with 2 10" drivers

Hello,
I'm very interested in building dipole speakers, but I have no experiences with them. Most designs I've found are 3 way, but I'd like to go 2 way with pro drivers (2x Beyma 10G40) because I don't want to use 6 amplifiers for it. There are many distcusions in this forum about pro drivers usage in home hifi speakers and I think that pro drivers will be best for this purpose. I've chosen Beymas because in last issue of Stereophile I've found one Canadian company named FAB Audio, which uses them and there are some good reviews on the web. And that idea is quite interesting for me.
As crossover/equaliser I'd like to use Behringer DCX2496

So, here are some questions for you, experienced guys:

Did someone build 2 way dipole equalised to nearly full range?

Using spl_max from mr. Linkwitz's website I ended with these results with effective path difference 300mm (maybe I'll get more, this is just my appreciation):
25Hz - 74dB
35Hz - 83dB
50Hz - 92dB
71Hz - 101dB
100Hz - 110dB
So, what you think, is it enough to go flat to 40Hz? I don't play too loud, mostly rock and metal music (sometimes classical).
 
I have the same plans, a 2 way dipole with a full ranger or maybe a passive XO for a tweet and use the behringer to XO and EQ the bottom, but my woofer section will only need to cover where the main driver falls off (below 150 or 200hz). I believe it's a cheap and easy path to Orion type sound.

Unless you are planning to use a sub, I believe those Beyma's are going to fall short of your 40hz goal. With their high Fs (55hz) and low Qts (.31), you are going to be really pushing them to make bass. If you look at the free air response of the Beyma, it starts to roll off at 150hz, so even flat down to 60hz is optimistic regardless of baffle size.

If you want to stick with the Beyma's , just go with 1 per side and add a more appropriate dipole woofer to get you easily down to 40hz.
 
Yes, you are right. I missed the fact that there is response on infinite baffle, which goes down at 150Hz.
My first plans were to build system like you wrote, full range + woofer. But in my country it is impossible to get some fostex drivers which I wanted to use. I can buy only Lowther drivers in Czech Republic, but they are too expensive for me.

So, I don't know what to do now. I'm tired of listening to my Cantons, so I have to make something new (and much better sounding).
 
I created a 3 way dipole and used 2 very inexpensive 12" woofers on a .5 meter OB.

QTS was .5, so the roll off was good. With very little eq (4 db) I had usable output to 20 Hz. Xmax is listed at 3.5 mm.

My observations are that for Pro drivers, xmec may be much higher than xmax. And in a perfect world, we wouldn't exceed xmax, but we all have to make compromises.

Also, placing the baffle on the floor and the driver(s) low will give you a 6db boost at low frequencies.

Also, remember that spl is independent of eq. It is only dependant on SD and excursion, and baffle width. However, if you
EQ, you do need additional power.

Check out my $50 Dipole @ http://www.diyaudio.com/forums/showthread.php?s=&threadid=47592

Doug
 
Doug is right about pro drivers having the advantage of not banging against the back plate when you drive them into over excursion. However pushing drivers to their limits especially below Fs is just begging for distortion and why would you want to do that using drivers that cost you close to $500 per side. You can save a lot of money, get deeper bass, more potential output down low, and less distortion with a single beyma and more suitable cheaper woofer(s) to handle the manual labor down low.

I've got 20 cheapie 12"s that sound quite nice despite paying only $285 locally for the lot. With a mid Q and Fs of 28hz I don't have to force them to make bass. I want high output down to 25-30hz and my plan is 8 per side. I'm going to experiment with a W baffle Ripole first to see if they'll reach up to 150hz or higher in the very compact space for 4 12's of 11"W x 13"D x 26"H . Push/pull alignment and vibration cancellation are key factors for me along with compact size. If that works out, then I'll build 4 and combined with the flexibility afforded by the 2496, I should be able to get great results using a wide variety of main drivers in OB in a variety of configurations.
 
DarkOne,

I am listening to a small two way system with dipole 10" woofers up to 200 Hz and 3" fullrange drivers in CB up from there. (Just stepping up to 5" FR and 15" woofers)

Two things I have learned:
First: You better not try to push a dipole woofer below its free air resonance. You need incredibly steep equalisation to overcame the natural roll-off of the driver and the needed excursion will rise exponential.

Second: Keep an eye on the lowest resonance mode of your room. My woofers have a free air resonance at 37 Hz and my electronic equalisation doesn´t stop there. Still SPL precipitates down from 37 Hz. But even with the dipoles toed in 45° they do excite a heavy longitudinal roommode at ~30 Hz :( (while the higher roommodes are nicely suppressed). I guess I should better quit at ~45 Hz and have the roommode as a "free boost" from there. You surely know that it is hopeless for a dipole to reach below the lowest roommode.

Just my 2c
 
Rudolph is right you do still have one room mode to take into consideration, but the 2496 should be able to handle that. My mode just happens to correspond with the Fs of my woofers at 28hz, so I should get a nice free ride at the bottom. Then below that I'll have a pair of Tempests take over down to the low teen's for HT. I'll have to see how it all really works out in room, but I should be able to steeply low pass my sub before any room modes kick in and have my OB's go right down to and benefit from the lowest room mode eliminating the need for any bass traps or digital room correction.
 
Open Baffle Dipole Bass is Ridiculous

It is ridiculous to use two dynamic drivers as an open baffle dipole for bass. Much better results, and I mean MUCH, will be obtained when you use the two drivers in a box back to back wired for dipole operation. All you need to do is crossover below the the driver spacing notch. You can also wire in a nice high current switch and switch to bipole on the fly.
 
Re: Open Baffle Dipole Bass is Ridiculous

Magnetar said:
It is ridiculous to use two dynamic drivers as an open baffle dipole for bass. Much better results, and I mean MUCH, will be obtained when you use the two drivers in a box back to back wired for dipole operation.

Magnetar,
How can you make a statement like that and leave it unexplained. You give up half of your displacement, but you gain a push/pull alignment (only if you weren't using it already). Please explain why it's "MUCH better".
 
Re: Re: Open Baffle Dipole Bass is Ridiculous

johninCR said:


Magnetar,
How can you make a statement like that and leave it unexplained. You give up half of your displacement, but you gain a push/pull alignment (only if you weren't using it already). Please explain why it's "MUCH better".

Why would I give up half my displacement? This is not true.

It really doesn't require much experimenting to know an open baffle bass system using typical dynamic bass drivers is a waste of time compared to the back to back box. It requires more power and eq for a open baffle to even approach a properly aligned 2 woofer system wired as a back to back dipole. There will be less excursion, lower distortion, and higher sensitivity this way with all the benefits of driving the room in a figure 8. A no brainer.
 
Magnetar,

I really need some help understanding this. Are you talking about back to back sealed boxes wired out of phase or one box with a loosely coupled isobarik alignment?

I'm about to start a high output dipole woofer setup and your proposal would be a big benefit. I hope you aren't talking about 2 sealed boxes because I believe the free air operation of the drivers is needed for the natural dipole bass sound, not just the room effects of dipole radiation. Also, I need the better extension of free air operation over sealed.

Assuming you are talking about a common airspace shared by the drivers, let's forget about the effects of the basket for this example. 2 drivers in a clamshell alignment on a flat baffle with a basket to edge distance of 2ft vs a 2ft deep box with out of phase drivers front and back, essentially a driver size baffle that is 2ft thick. Why would the box be any different from a sonic standpoint and how can it's performance greatly exceed putting the 2 drivers side by side, in phase, on the flat baffle ?
 
Hello,

I have tried it both ways - where the two bass drivers are wired with the opposite polarity in two separate boxes placed magnet to magnet and also with one box one mounted on the front and one on the back firing out wired with the opposite polarity (push - pull - lowers 2nd order distortion) and in either case you will get lower bass at higher sensitivity, less excursion, lower distortion than two drivers on a single baffle board (or U, M, W baffles) PLUS you get the benefit of dipole radiation PLUS you can easily switch to bipole (excite the room completely differently) for different room placement, low volume listening, BIGGER sound, whatever your preference may be.

Open air is NOT a criteria for a dipole - now that isn't to say that an open air midrange dipole (200 cycles up) may not sound better or be a better way to go - Without reflections within the baffle box you may get better sound - You will still benefit in the mids with two drivers used as above with higher power handling, lower excursion, distortion, and higher ultimate SPL -

My speaker system uses three 10" mids, two 15" woofers and a Heil dipole tweeter, and an extra rear firing super tweeter for 15K up - (plus three 18" horn loaded subs). Crossover is electronic (4th order -35, 200, 1000 cycles plus a passive on the back firing super tweeter)

One 15" woofer is in it's own enclosure firing forward, the second shares the enclosure with one front firing 10" mid but is mounted on the back of the mid (MTM enclosure sits on top of the bottom woofer enclosure) enclosure firing out the back, the Heils is in the center of the MTM (open back) and two 10" mids are above the Heil with one firing out the front and one out the back. They are all pro drivers (except the Heils) so the efficiency is very high (103 db/watt + 16 to 1000 cycles) with dynamics of my big horn system, being dipoles they really do the sound staging well. IE the soundstage is HUGE even with the rear surround system shut off. It's a pretty big system - around 68" tall and around 400 lbs a side- (sand filled walls, 4" thick walls on the bottom bass enclosure, ect.....

johninCR said:
Magnetar,

I really need some help understanding this. Are you talking about back to back sealed boxes wired out of phase or one box with a loosely coupled isobarik alignment?

I'm about to start a high output dipole woofer setup and your proposal would be a big benefit. I hope you aren't talking about 2 sealed boxes because I believe the free air operation of the drivers is needed for the natural dipole bass sound, not just the room effects of dipole radiation. Also, I need the better extension of free air operation over sealed.

Assuming you are talking about a common airspace shared by the drivers, let's forget about the effects of the basket for this example. 2 drivers in a clamshell alignment on a flat baffle with a basket to edge distance of 2ft vs a 2ft deep box with out of phase drivers front and back, essentially a driver size baffle that is 2ft thick. Why would the box be any different from a sonic standpoint and how can it's performance greatly exceed putting the 2 drivers side by side, in phase, on the flat baffle ?

The room is going to be excited the same but in boxes the bass will go lower (no eq needed) less excursion (means lower distortion) and higher SPL (with higher sensitivity) are among the benefits. IME open baffle bass is wrong, wrong, wrong.

The drawbacks? It may be harder to build and in a two way (like the originator of this thread mentioned) you will have cancelation from the driver spacing (a deep narrow notch) - no big deal when you crossover below the notch - this will be difficult with a two way.
 
Thanks Magnetar,

I can't get my brain around why you have gotten those results. In the loosely coupled isobarik (same airspace) box, I understand that it's similar to open air operation (actually less airmass load on the backside) in terms of a freely moving cone. Is the advantage maybe in the resulting Q of the system ?

I'm going to have to try it. I already have 2 of the drivers in a W-baffle, so 2 mounted front and back on a box of similar dimensions should be a fair comparison.

I hope it really works. If so, I can fit 8 12's using manifolds in a box 26"H x 13"W x 26"D and get more and deeper output than the same drivers on OB while retaining push/pull and vibration cancellation. I was afraid to go 2 drivers deep in a normal W-Baffle but with the isobarik, it won't be a problem. My "d" , distance differential for front and rear wave will be tremendous at about 30" or equal to about a 70" wide flat baffle. Maybe the benefit is in the system Q combined with a much larger effective baffle width than you were thinking.
 
johninCR said:
I can't get my brain around why you have gotten those results.
I´m very much interested in magnetars development, but his results are a brainer for me too. I can´t see, how he achieves a valid dipolar pattern in the room without sacrificing efficiency in the same way as an open baffle does. Magnetars advice to just do it seems simple enough. But I really would feel more comfortable, if he could give us deaf, dumb and blind boys some hint where our understanding of physics is lagging behind. :xeye:
 
It's really simple - put one driver in an open baffle and and one in a tuned box. The tuned box will go lower with no eq, have less excursion (lower distortion) be more sensitive and have higher spl in the bass. Now the open baffle will have dipole radiation and the single woofer will have monopole (bad in most circumstances) NOW, add a second woofer and produce a dipole radiation pattern and you now have the benefit of both PLUS the added benefits (higher sensitivity, lower distortion, higher spl) of using a pair of drivers over one. Add a second woofer to the open baffle? well it will give you the same BUT WITHOUT THE benefit of the tuned box. You will always have baffle step problems (less amplitude though with the tuned box and room re-enforcment will bring it up to flat if you plan correctly) with either - Now switch to BIPOLE and the baffle step problem disappears-

It does really work - open baffle bass is wrong - just use two drivers instead like above and the results can be stunning.

johninCR said:
Thanks Magnetar,

I can't get my brain around why you have gotten those results. In the loosely coupled isobarik (same airspace) box, I understand that it's similar to open air operation (actually less airmass load on the backside) in terms of a freely moving cone. Is the advantage maybe in the resulting Q of the system ?

I'm going to have to try it. I already have 2 of the drivers in a W-baffle, so 2 mounted front and back on a box of similar dimensions should be a fair comparison.

I hope it really works. If so, I can fit 8 12's using manifolds in a box 26"H x 13"W x 26"D and get more and deeper output than the same drivers on OB while retaining push/pull and vibration cancellation. I was afraid to go 2 drivers deep in a normal W-Baffle but with the isobarik, it won't be a problem. My "d" , distance differential for front and rear wave will be tremendous at about 30" or equal to about a 70" wide flat baffle. Maybe the benefit is in the system Q combined with a much larger effective baffle width than you were thinking.
 
Rudolf said:
I´m very much interested in magnetars development, but his results are a brainer for me too. I can´t see, how he achieves a valid dipolar pattern in the room without sacrificing efficiency in the same way as an open baffle does. Magnetars advice to just do it seems simple enough. But I really would feel more comfortable, if he could give us deaf, dumb and blind boys some hint where our understanding of physics is lagging behind. :xeye:

Dipolar radiation is the product of the two drivers working as one - one pushing out as the other pulls in - just like a single driver on a board -

An open baffle system looses efficiency in the bass much quicker than a tuned box! This is a well known fact - It really is simple - just combine a tuned box with a second woofer and dipole radiation and you have the best of both worlds. No need to eq, no need for massive power, no need to have high excursion woofers, ect..
 

al2002

Member
2003-12-15 6:41 am
USA
It won't work.

You will still have cancellation, just as in an open baffle dipole, between the out of phase radiation from the two woofers, even if they are in enclosures, due to the path length difference between the front and rear radiating woofers.

There's no free lunch.
 
Magnetar,

Now you're talking about tuned boxes again. How do you "tune" something that is essentially just an isobarik coupling chamber in the case of a shared airspace ? With the shared airspace it's kind of like 2 out of phase speakers in IB, but effectively with less air mass on the backside than IB. 2 boxes I understand, out of phase will result in a null where the waves have travelled the same distance. Boxes put out a different sound though and I'd rather have the IB sound, but with dipole radiation benefits making the shared airspace approach more appealing to me.

On the other hand, for someone who wants high output bass with less disturbance to others and less room effects, having 2 identical subs with one as far away from the listening position as possible wired out of phase and one close to your listening position may be a great idea.
 
Another possible cause of your experience is compression waves vs velocity waves. I don't understand the difference but an OB speaker produces a velocity wave that changes into a pressure wave as it strikes something, like your ear. A boxed speaker produces a pressure wave, so maybe creating 2 pressure waves out of phase makes it somehow more efficient.
 
Magnetar said:
NOW, add a second woofer and produce a dipole radiation pattern and you now have the benefit of both PLUS the added benefits (higher sensitivity, lower distortion, higher spl) of using a pair of drivers over one.
It´s here where my theoretical understanding can´t follow you. If you add a second woofer at the back of the box in a dipole manner, the second one should not add energy to the room, but subtract from the energy because both drivers are radiating 180° out of phase. This holds true for the lowest frequencies. As frequency rises the phase difference should decrease - eventually becoming an addition of radiated energy where the distance between both drivers is lambda/2.

I suspect that you have experimented with drivers, that were much more suitable for sealed box than for open air. So it may have been easier for you to get linear SPL in a box than equalize them for OB use.

Please do not understand me wrong: I have no reason to doubt your reported results. But I get disturbed when personal experience is contrary to the laws of physics. Makes life less controllable. :D