Dipole with 2 10" drivers

[DarkOne]

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).

[johninCR]

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.

[DarkOne]

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).

[DougL]

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 @ Wide-band Dipole Project

Doug

[johninCR]

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.

[Rudolf]

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

[johninCR]

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.

[Magnetar]

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.

[johninCR]

Originally posted by Magnetar
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".

[Magnetar]

Originally posted by johninCR


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.