below is measurements of two 12BR70 in apx 40W x 80H x 30D (cm) H frame, raw and equilazed
I have tested Holm Impulse, but still I don't know how it uses/sets gating and smoothing... What is causing extra ripples in the eq'd measurement?
Thanks for the input. How was the measurement done? Outside?
Have you've been able to listen to the assembled speakers?
40W x 80H is certainly within what I had in mind. 30cm-depth H frame seems like it would impact the sound if I want to get to 400Hz. Maybe a sloping U wing that's 0 up top and 30 at the bottom.
I'm thinking of getting 12BR70 and try them OB and if I don’t like the sound, build a sealed enclosure and use them in that fashion. A 100 liter box would have an F3 of 48Hz and Qtc of 0.707 while a 70 liter would have F3 of 50Hz and Qtc of 0.72 - more than enough with the subs.
that is maybe 8 years old measurement, so do not remember particulars. I think the equilazed is not smothed at all. Anyway those ripples are not audible.
measurement is done per, I think, Kreskowsky proposal. Measure box nearfield both side and back measurement delay for box dimension (30 cm in this case) and sum with front measurement.
Extension on any side is trade. If you want to go high, baffle or box should be smaller and you loose support for low freq ie. need much more gain on low freq and very soon coming to limitation. if you make box (baffle) bigger dipole peak and/or resonances of H box go lower so crossover should, as well.
OB bass has no physical (body) impact so if you like it you will miss it. Otherwise bass is precise and "fast".
It is already mentioned that is no point to use OB bass to lowest freq. Below freq, where Lambda= 2xL (L is longest room dimension), room mods do not exist, but only 6dB gain per octave so make heavy and sturdy close box for freqs below 40-80 Hz and above OB. Everything is much easier and smaller without any loss.
measurement is done per, I think, Kreskowsky proposal. Measure box nearfield both side and back measurement delay for box dimension (30 cm in this case) and sum with front measurement.
Extension on any side is trade. If you want to go high, baffle or box should be smaller and you loose support for low freq ie. need much more gain on low freq and very soon coming to limitation. if you make box (baffle) bigger dipole peak and/or resonances of H box go lower so crossover should, as well.
OB bass has no physical (body) impact so if you like it you will miss it. Otherwise bass is precise and "fast".
It is already mentioned that is no point to use OB bass to lowest freq. Below freq, where Lambda= 2xL (L is longest room dimension), room mods do not exist, but only 6dB gain per octave so make heavy and sturdy close box for freqs below 40-80 Hz and above OB. Everything is much easier and smaller without any loss.
@danibosn
12br70 seem to fit the bill and would be good performers in a sealed enclosure, should I conclude I don’t like them in OB.
At the same time it seems midbass impact must come from frequencies below 200Hz, maybe below 150Hz. Obviously with harmonics way higher, but those should be fine in OB.
Are you using these drivers in OB today?
This is exactly what I seem to be solving for. I like the precise bass in OB. And I like bass with impact. Up to 70Hz I have sealed subs. Looking to try drivers with "proven" subjective OB performance (meaning people like it) above those subs. Maybe it's not to my liking indeed.
12br70 seem to fit the bill and would be good performers in a sealed enclosure, should I conclude I don’t like them in OB.
At the same time it seems midbass impact must come from frequencies below 200Hz, maybe below 150Hz. Obviously with harmonics way higher, but those should be fine in OB.
Are you using these drivers in OB today?
Have you explore the SLOB option presented by Nelson Pass a while back?……he’s had pretty good success with it an member XRK has built a tower using 8 6.5” drivers per side that has an equivalent SD to greater than a 15. The nice thing about this approach in your case is the desired XO point to the 8pe21 ( worlds best midrange driver btw)…….with a lot depth of 7” you wind up with an acoustic 2nd order low pass around 420hz. All you need from DSP is some minor shaping and a notch for the peak.
You enjoy articulate midbass…..and who doesn’t? Multiple small drivers using motors instead of 1 large surface area will give you the precision you’re looking for. Dual opposed drivers in an array also employ force cancellation and the slot cuts harmonic distortion in half…..everything you‘ve asked for.
I’m building my own variation of this now using instead 4 12” drivers dual opposed slot loaded instead of the 6.5s. I don’t require high output midrange so my 8pe21 will be crossed at 250hz instead…..that works with the 12” slot acoustic LP. Footprint is a little larger than what you may be looking for using the 12’s……i‘m at 40cm square and 90cm tall including a very thick base.
SB have one more driver designed for OB: https://sbacoustics.com/product/12-sb34nrx75-16-norex/
I have made 60 cm depth U-frame speakers (bass part) with 2 of this drivers paralleled, in opposite directions, corrected flat in room in range 25-200 Hz with DSP and analog circuit, actually 2 of this OB bass per channel in different locations in room and with independent DSP corrections and amps.
I like it, probably more the OB generally than this driver specifically.
Measurements below in listening position with THD, SPL level is not calibrated and is actually more than 80 dB.
As can be seen distortion increase starts lower than 40 Hz at this moderate SPL level.
with
I have made 60 cm depth U-frame speakers (bass part) with 2 of this drivers paralleled, in opposite directions, corrected flat in room in range 25-200 Hz with DSP and analog circuit, actually 2 of this OB bass per channel in different locations in room and with independent DSP corrections and amps.
I like it, probably more the OB generally than this driver specifically.
Measurements below in listening position with THD, SPL level is not calibrated and is actually more than 80 dB.
As can be seen distortion increase starts lower than 40 Hz at this moderate SPL level.
with
100% spot-on ! My Summer 2024 project is optimizing a hybrid open baffle (mid) and ported bass. It's that never ending (and nagging) aspect of mixing mono-pole, with di-pole. This is an extension of something my good buddy, who is one of those "Open baffle only" type of guys, discovered in a trial run of mixing his OB MTM with just some boxed bass I happened to have on hand. We concluded that there is something "special" about that 250Hz crossover point. He was absolutely amazed at just how much of that "beauty" of open baffle is retained, all the while using nasty box (his words) bass. Well, since the nasty box [sound] is verbotten, I decided to go with dual-opposed. Next step in the research is to calculate how much "ballooning" of the enclosure can possibly contribute to the sound of a box. To me, this is the last frontier, as there can be no box vibration from magnet-to-magnet coupled bass. A salute to Sir Isaac Newton !
This is an excellent point. Thank you for bringing it up!
I did follow XRK´s development of that speaker (that he named XSD) and asked users a couple of times about bass sense of impact vs 12 & 15" top performing OB drivers but at the time (late 2022, early 2023) there was no feedback. Then I stopped following it and kind of forgot about it. So I´m glad you brought it up.
I believe the 8x6.5" woofers allowed for a cavity that crossed around 420Hz as you mentioned, and 6x8" woofers lead to 350Hz cutoff.
Can I ask you why you chose 4x12" instead of 6x or 8x8"?
Is your 8PE21, crossed at 250Hz, in open baffle? 40cm wide baffle?
40cm wide is not a bad footprint for me... my starting point is a 18" woofer so I´m at about 52cm.
Good food for thought!
Simply put, displacement…….4 12” drivers have nearly the displacement of nearly 2100cm2…..a single 15 is in the 820cm and an 18 is roughly 1200. The drivers I chose are only 13cm deep so 2 across firing into a 10cm slot gives me massive displacement with a comparatively narrow footprint.
Yes, the 8pe21 can be crossed at 250hz if it’s not asked to play at pro audio levels without problems. Open baffle with no heat build up in a box, the B&C when cool can really play.
The lower XO point allows me to use drivers designed for subwoofer duty as Linkwitz did. Displacement is only part of the equation……high xmax and long throw exponentially expands the LF capability in an OB application. These drivers have 11mm of throw and an Fs of 38z. The Fs will fall to around 35hz once slot loaded. Using DSP, I can add EQ to extend the LF response and not have to worry about bottoming out the drivers. 4 drivers at 4 ohms series parallel is very efficient too……won’t need but 300watts to get the job done In a SLOB
Yes, the 8pe21 can be crossed at 250hz if it’s not asked to play at pro audio levels without problems. Open baffle with no heat build up in a box, the B&C when cool can really play.
The lower XO point allows me to use drivers designed for subwoofer duty as Linkwitz did. Displacement is only part of the equation……high xmax and long throw exponentially expands the LF capability in an OB application. These drivers have 11mm of throw and an Fs of 38z. The Fs will fall to around 35hz once slot loaded. Using DSP, I can add EQ to extend the LF response and not have to worry about bottoming out the drivers. 4 drivers at 4 ohms series parallel is very efficient too……won’t need but 300watts to get the job done In a SLOB
"Displacement" is often times used incorrectly. Plus, it would be expressed in cubic terms. What I believe is meant, is the SD specification. Bargain basement drivers can sometimes be used in the SLOB type of installation. Take a look at the Parts Express site for either of these two:
GRS 12PF-8 /
Goldwood GW-212/8
IMO the XRK approach is superior to a face-to-face SLOB. The acronym would then be PPSLOB. Push-pull, Slot-Loaded, Open Baffle. Which is really not an "open Baffle" in the strictest sense. Open Baffle bass in the classic sense is really not very good. Not good at all. The (XRK) approach mops up the floor against plain jane OB. You can find plenty of posted information about the concept ,already on line. Not exactly dual-opposed either. At least NOT 100% dual opposed. More like the 1st cousin, thereof. You should still get adequate vibration-cancelling; it's just that it won't be 100%. Some of the folks discover they prefer the ppslob bass array by itself, as adding in a "theatre" style sub has problems in that, directivities are dissimilar. Music systems only, of course. If one is doing home theartre, there is very little value in even attempting any sort of OB scheme at all.
"Which is really not an "open Baffle" in the strictest sense. Open Baffle bass in the classic sense is really not very good. Not good at all. The (XRK) approach mops up the floor against plain jane OB."
SLOB working principle is exactly OB.
Difference is driver arrangement, by which, long source distance is possible on smallest footprint and force cancellation (in use already long time, for example Orion).
If not made as ripol ie to have a slot on both side it introduce different loading for driver membrane and suspension. Of course there is 1/4 resonance,as well (could be quite high in freq but still is there).
Pros are small footprint, decent appearance (read high WAF).
And nothing beat well executed (high Vd, lot of power and good DSP) OB
SLOB and RIPOL are actually compromised OB in favor of small(er) size, same as H and U frames.
SLOB working principle is exactly OB.
Difference is driver arrangement, by which, long source distance is possible on smallest footprint and force cancellation (in use already long time, for example Orion).
If not made as ripol ie to have a slot on both side it introduce different loading for driver membrane and suspension. Of course there is 1/4 resonance,as well (could be quite high in freq but still is there).
Pros are small footprint, decent appearance (read high WAF).
And nothing beat well executed (high Vd, lot of power and good DSP) OB
SLOB and RIPOL are actually compromised OB in favor of small(er) size, same as H and U frames.
The Dayton SD315-88. The specs I quoted are from my own measures……the Fs doesn’t measure as low as Dayton shows…..but my measures show Xmax at 11……