BSC vs Bipolar speakers

[Salsero]

Thanks for those who have helped out with my previous two threads. As I understand, the merits of a bipolar full range driver based speaker is that they provide an active BSC thus enhancing bass response and secondly they improve vibration damping. What is the advantage (sonically speaking, of course an additional driver will make the project more expensive) of using a single driver with BSC?
Feel free to post your preferences.
Thanks
Salsero

[TerryO]

Originally posted by Salsero
Thanks for those who have helped out with my previous two threads. As I understand, the merits of a bipolar full range driver based speaker is that they provide an active BSC thus enhancing bass response and secondly they improve vibration damping. What is the advantage (sonically speaking, of course an additional driver will make the project more expensive) of using a single driver with BSC?
Feel free to post your preferences.
Thanks
Salsero

Salsero,

The advantages are several, depending on what you're looking for. One that comes to mind is that you'll have more headroom for dynamic contrast, and the bipolar will play louder with the same amount of power. Second, depending on your drivers, you avoid any additional devices in the signal path which quite often translates to a better sound. The bipolar setup also may lend itself to a better presentation of the music with a more lively, "you are there sound". It's simple and effective and... BTW: components for the BSC circuits aren't exactly cheap either.
I've heard a fair number of bipoles and they can be very, very good indeed. However, YMMV.

Best Regards,
TerryO

[planet10]

Originally posted by Salsero
What is the advantage (sonically speaking, of course an additional driver will make the project more expensive) of using a single driver with BSC?

less money, half as big a box....

After having various horns & other monopoles in my system, i recently re-inserted the FE127 diyRef FR bipole ML-TLs... there is definitly something appealing with bipoles. I was inspired to nail down the biFonken Mark II ... now in Chris' able hands (good thing to, as it is a complex box, with lots of fiddly bits.

dave

[chrisb]

Originally posted by planet10


less money, half as big a box....

A I was inspired to nail down the biFonken Mark II ... now in Chris' able hands (good thing to, as it is a complex box, with lots of fiddly bits.

dave

well .... near the top of the "to do" before July 30th pile.

[jzagaja]

If you want produce extremely transparent transducer a wide range bipole is a way to go:

http://www.diyaudio.com/forums/attac...amp=1169110241

Bi-di-poles require a space behind them and disc like enclosures became too big if you plan to use 1/4*Fs radius and wide band driver.

Just remember - adding just a second driver is insufficient. Enclosure must be a lens like because of diffraction.

[DSP_Geek]

Originally posted by Salsero
Thanks for those who have helped out with my previous two threads. As I understand, the merits of a bipolar full range driver based speaker is that they provide an active BSC thus enhancing bass response and secondly they improve vibration damping. What is the advantage (sonically speaking, of course an additional driver will make the project more expensive) of using a single driver with BSC?

BSC is not a given with bipolar designs because the rear wave does not add in exact phase with the front wave.

Consider the baffle step -3 db frequency occurs when the baffle is approximately one third its wavelength. With the driver at the center of the baffle [1], the distance from driver center to baffle edge is lambda / 6. Now consider a front-to-back depth one quarter the baffle width (really quite shallow), which will add another lambda / 12 to the rear wave delay, and you get lambda / 4 delay (90 degrees) from rear to front. Adding waves in quadrature means you don't get the in-phase amplitude. The rear wave is something like 0.3 of the front wave, so by doing phasor sums you get about 0.8 amplitude at the baffle step, or about 2 dB down.

[1] If it's to one side then the frequency increases, but doing the math shows the effect is substantially the same albeit shifted upwards.


The situation is worse at twice the baffle frequency, because the rear wave is in antiphase, so you end up with the rear wave reducing the front wave for a 3 dB dip (0.85 - 0.15 = 0.7) even though the diffracted wave is down in amplitude. The picture improves below the baffle step because the rear wave gets closer to being in phase and providing the desired result.


Phase is everything when working with more than one loudspeaker, and any multiple driver analysis must take time domain information into account.


If you really want to do BSC with another speaker, I'd recommend placing the BSC driver on the front panel and crossing it over with a fat inductor. Note that BS frequencies for tall cabinets are not necessarily what one might expect from the usual width/3 wavelength, since a considerable portion of the diffracted wave will travel along longer paths to reach the baffle edges. For example, a short 14" wide cabinet will show a baffle step around 300 Hz, but the same width at 6 feet tall shows baffle step at 150 Hz, a full octave lower. This explains why some baffle step compensated designs tend to sound lumpy in the low midrange. Use Tolvan's Edge simulator to explore this further: http://www.tolvan.com/edge/


Cheers,
Francois.

[planet10]

Ever since you 1st posted this (valid) thot experiment i have been working on bipoles that are wider than they are deep. This should push the majority of the antiphase area above the point where the driver is seeing 2 pi space ameriolating the problem.... but even on the bipoles we have built so far (deeper than wide) where there should be a dip around the BS point, the advantages seem to outweigh the disadvantages.

Placing the BSC driver on the front just introduces a different set of problems and you don't get the advantage of push-push (which can be significant).

dave

[3-LockBox]

Originally posted by DSP_Geek
If you really want to do BSC with another speaker, I'd recommend placing the BSC driver on the front panel and crossing it over with a fat inductor.

Sounds like you are just augmenting bass more than you are doing BSC. I've done this with regards to wide range designs. I have done a fullrange BR w/ a second 'bass only' driver in an asemetric pattern on the front baffle, and it works as far as increasing efficiency for bass output, but its just not the same as a bipole, which for me, gives a great depth of soundstage, as well as increased efficiency, with out any x-overs or contouring or anything.

My bipole is basically two drivers on opposite sides of the cabinet, although the front drivers are offset, not because I thought they should be, but the cabs I used were old Epicure 100 cabs and the FRs I use occupy the tweeter holes. The front/rear drivers aren't on the same axis either, not that it should matter. I was careful to put some batting between the two drivers, since both are running fullrange, I didn't want the out of phase mid info from the back of the rear driver bleeding through the front driver.

I like it. But of course, ymmv. A single driver is still better for point source imagery and detail. I think that bipole gives me a great sense of depth but its placement in the listening environment is critical. I don't recommend a bipole be set in or near a corner.

I've also experimented with dipole/OB widerange drivers with BR augmentation, which also gives an expended sense of depth. The best example of this I've heard was at the Puget Sound speaker contest, where a 6" driver was used as a low range mid (but not in the upper registers; a traditional range tweeter was used). The bass was handled by a 15" woofer x-over at 400hz, in a seperate sealed enclosure. The 6" mid was mounted in a transmition line/infinite baffle enclosure on the rear, with a wide front baffle. It was a hideous, ungainly looking thing, but boy did that huge speaker image like a bookshelf speaker. It sounded great and disappeared in the room, which was amazing, considering it took the concerted effort of two men to push it around the room.

I think the back loaded, transmittion line baffle, driver concept is the way to go as long as size and space isn't an issue. The bipole concept in my case makes for a very good 'bang for the buck' solution. The benefits far outweigh any detractors I can hear.

[DSP_Geek]

Originally posted by DSP_Geek

If you really want to do BSC with another speaker, I'd recommend placing the BSC driver on the front panel and crossing it over with a fat inductor.

Originally posted by 3-LockBox


Sounds like you are just augmenting bass more than you are doing BSC.

Actually, adding another driver with a 6 db/oct rolloff, of which the -3 dB point is 0.707 of the baffle step frequency, is exactly equal to a baffle step network. I did the math a couple of years ago:

http://www.diyaudio.com/forums/showt...752#post650752

You do want to be careful about the exact baffle step frequency, as previously mentioned, or the midbass gets kind of lumpy.


Cheers,
Francois.