[Bob in St. Louis]

Next time you're two hours South, let me know.
Being a fellow home theater guy, audio guy, and gamer dude, I think we're on the same page.

Numbers and theory can be thrown around all day long. What counts is what you can feel.

.........and that's all I'll say about that. 

Bob

[Graham Maynard]

Hi Rudolph,

Stiff heavy coned subs need power to go low too !  (Unless resonant which is what open baffle reproduction can avoid.)

There might be a short path from the front to the rear of a cone at LF for an OB, and that means that the cone must displace more air to radiate compared to when an enclosure is being used, but with high VAS and light coned OB drivers the energy is transduced into wave motion differently, so does not need excessive power.

Also it is room pressurisation which ruins LF reproduction. 
It might be something we have grown up with, and it can thrill our senses, but it is not what real live audio sounds like !
When does any instrument on a stage pressurise a venue - they vibrate the air, and that is what he hear and feel.  If we pressurise our rooms we are grossly distorting the reproduction.
 
So in return I say get yourself some increased cone area and enjoy the clean bass which no monopole can emulate in a normal room because dipoles do not energise room modes at LF in the same way the monopoles so noticeably do.

Axial nulls.  I could not put any figure on it due to the room itself having a more significant influence within the room than does the baffle for its given type.


Hi Martin,

Presently I don't use my equaliser. 
I would probably get to 20Hz if I did, but that would mean an additional LF amplifier, which I have plenty of.  However I prefer to minimise electronics !

30Hz is a fair figure.
Also I don't accept that SPL is THE benchmark. 
I have tuned circuitry to increase/level SPL below driver Fs, but that ruins the coherent reproduction of drums etc., the sound being worse than when there was naturally non-resonantly generated SPL.

You have made assumptions about my 18" wide plain baffle which do not include the 'T'-bass circuit, for it is not possible to acheive the same LF SPL by using conventional crossovers without increasing amplifier power or increasing driver efficiency.
The 'T'-bass circuit will provide more LF gain below driver resonance with one low Q driver than could two higher Q drivers of equal Fs driven in parallel via a conventional crossover, and, also sound better due to the driver Q not parasitically inducing the SPL boost in a manner which impairs the articulation of dynamic waveform reproduction (drums).


Cheers ............. Graham.

[gainphile2]

For midrange I would look for high Qms drivers, perhaps in the range of 5-8. Size around 5-8"

For bass Qts > 0.7 and Fs as low as possible. Also the size has to be 15" minimum. Or perhams 2x 12" maybe.

[Bob in St. Louis]

Also it is room pressurisation which ruins LF reproduction. 
It might be something we have grown up with, and it can thrill our senses, but it is not what real live audio sounds like !
When does any instrument on a stage pressurise a venue - they vibrate the air, and that is what he hear and feel.  If we pressurise our rooms we are grossly distorting the reproduction.

Can you please expand on this thought Graham.
Maybe I'm missunderstanding, or we have a different definition of room pressurization. It is my understanding that you need a certain amount of "pressure" to give you the "feel" of certain instruments, kick drums, kettle drums, etc....

Thanks,
Bob

[dewar]

I'll chip in with a few points if I may.

I've got one 15" Hawthorne Augie per side in a 19'x12' room and get bass (-3db) to just bellow 30hz on an 18" baffle.

About this idea of pressurization, to me it feels unnatural, though nice for movies sometime. I was running a sealed box sub (critical Q design) bellow my Augies for movies but have now stopped using it entirely. To me the feeling of pressurization is felt on my face and ears, as something which exists completely apart from the instruments in front of me. I believe dipole bass can deliver the needed impact from kick drums without pressurizing the room. Think of live outdoor concerts, I remember outdoor trance parties where the bass had so much impact I could feel it's physical effect on my heart (like CPR when you dont need it, probably not too healthy), but no pressurization obviously as it was outdoors.

[lord_glum]

Next newb question...when you say 18" baffle what does that mean?  Its 3" larger than the speaker?

Jvo

[dewar]

Yip

[Rudolf]

At low frequencies bass is coming either from the source (loudspeaker location) or from the room. I´m sure we all want to listen to the source and not the room. But how much you get of the former and how much of the latter depends very much on the frequency with regard to the room size.
Above the modal region (upper limit roughly 100-200 Hz aka Schroeder frequency) bass performance is almost completely controlled by the source.
If you go lower in the modal region below the Schroeder frequency bass gets increasingly "trapped" at the room mode frequencies. The bass - generated by the source - will be exaggerated at the resonance peaks of the room modes and subdued at the nulls of those resonances. Since those room modes have their own peak and dip location in the room, the bass will no longer appear to come from the source only, but from the room mode peak locations in the room too.

There is a frequency were its wavelenght becomes longer than 2 times the room lenght. Down from that point you no longer find discrete room mode resonances. If you have a monopole sub the room as a whole is pressurised by that source. It´s like you where in a giant air-pump with the cone of the subwoofer driver pushing air in and out. At and below this point every point in the room is identical from an acoustics point of view. You even loose any hint regarding the room size.
If you have a dipole sub it no longer can store energy in any room mode resonance. The acoustic shortcut between front and back will be almost immediate. Apart from having your ear in the vicinity of the cone, the cone will be flapping without generating more sound.

For big venues most of the modal region and certainly the pressure-only region are well below any frequency normally used by musical instruments. The only time I experienced such pressure from everywhere was when "attending" an earthquake.

For the dimensions of normal homes the modal region and the pressure-only region start - roughly speaking - at 200 Hz and 20 Hz. So we can´t escape them totally. With dipoles we just dispense with the lowest frequencies. With monopoles we have to find the fine line between "nice" low tones and annoying pressurisation.

[Bob in St. Louis]

And then there's infinite baffle.  aa

[Graham Maynard]

Hi Bob,

Dewar and Rudolph got in before me.

It is possible to hear LF more clearly via a dipole when the room is not pressurised, as by a monopole/sub., because the pressure within the room and acting upon our ear drums degrades our ability to hear the reproduced waveform.

My opinion is that there is not any suitable crossover point from dipole to monopole, only a LF limit for the dipole, whereafter adding a monopole ruins the open-ness of dipole bass.

Cheers ...... Graham.

[Bob in St. Louis]

Highlights of what you just said, "there is not any suitable crossover point from dipole to monopole" and
"pressure within the room and acting upon our ear drums degrades our ability to hear ".

Understood now gentileman, Thank you! 

Bob

[lord_glum]

after reading all this crazy stuff I think I am just going to run w/both projects.  Depending how the auctions go i will snag a pair of SI's (if auctions go well augies and amps too) and a pair of FE167's.  Just build some OB's and some horns as well.

Thanks,
Jvo

[Bob in St. Louis]

  Perfect!

[lord_glum]

Bob I figured you would approve. 

I have been talking with Diana @hawthorne; I read up on the baffle design on their forum and browed some gallery photos.  From reading the forum I have allot better understanding of what goes on.  Baffle design makes more sense now.

Jvo

[Bob in St. Louis]

"Good on ya' mate"! 
Let me know if I can help.

Bob

[Rudolf]

My opinion is that there is not any suitable crossover point from dipole to monopole, only a LF limit for the dipole, whereafter adding a monopole ruins the open-ness of dipole bass.

Very well said, Graham.

I would like to comment on another statement of yours:
"Also it is room pressurisation which ruins LF reproduction.
It might be something we have grown up with, and it can thrill our senses, but it is not what real live audio sounds like !"

Lately I´m under the impression that those "pressurised" listening habits common in car audio or discos already have invaded real live audio. In old times a live drumset would sound "di di di, da da da, do do do, duumm!" to my ears. Nowadays when I attend even a renowned live event, it´s just "dum dum dum, dum dum dum, dum dum dum, duumm." And in such a way, that my intestines could stop their work - the beat is doing it for them.

One of those concerts had been recorded for TV. I listened to the broadcast a fortnight after the live event (could see myself on the screen too) and the quality of the broadcast was superb. I found myself listening to better music with my dipoles at home than live at the concert (albeit not at the same SPL )

So, even real live audio does not sound as live as it used to.

[Graham Maynard]

Seems there is a concensus here.

Yes about the drums, their dynamic impulse is one which causes substantial monopole/room 'dumming' of bass.

I recon there is a proviso though, in that it is necessary to get down to at least 30Hz to be satisfied with dipole bass and get rid of the feeling that a sub would add depth.
Once you get to 30Hz with a dipole you hear instrumentally based LFs you do not (cannot?) with a sub or vented or ABR !

I would say that finding the correct driver(s) is probably the most important requirement for dipole LF augmentation, which is what this thread is about anyway.

Must go for tonight,

Cheers .......... Graham.

[MJK]

I've got one 15" Hawthorne Augie per side in a 19'x12' room and get bass (-3db) to just bellow 30hz on an 18" baffle.

I believe you have a room mode providing the bass extension. If my calculations are correct, half wavelength at 30 Hz is approximately 19 ft. There is no way an Augie can produce bass that is only 3 dB down from flat at 30 Hz in an 18" wide baffle in a passive set-up, no bass EQ. If you put the Augie into an infinite baffle, and measure it radiating into free space, I do not believe it could provide this level of bass extension. I do not know of any bass driver mounted in an 18" wide baffle that can do this without EQ. If you model this geometry in the EDGE program, it will tell you the kind of gain required to be only 3 dB down at 30 Hz.

Martin

[dewar]

Yeah, that is true about the 19'/30hz room mode, but,

I have DEQ on the Augie and use it to bring down the 30hz peak (no boosts at all) and get upper 20's, I imagine without EQ the -3db would be even even lower.

I cant guess what -3db would be anechoic(and dont know how to calculate), but I cant imagine it being too far off 30. If you look at these measurements Dick Olsher published,he was getting down to 27hz (its Fs I believe), measured nearfield on a similar size baffle. Doesnt give room size though.

http://www.enjoythemusic.com/Magazine/equipment/0107/diy_loudspeaker_project.htm

I wont swear by anything but I seem to remember the figure 30 being bandied around the Hawthorne forum. A post there will give you an idea of what the Augie can get down to in most rooms.

cheers
B.

do EDGE calculations only work off baffle width and Qt and Fs? All drivers have there own idiosyncratic frequency responses that cant be quantified, couldnt this account for the discrepancy if the driver has an inherent peak at 30hz that cant be taken into the calculation? I'm speculating here, you guys know more than me.

[Magnetar]

.

So the operating range of any bass dipole is restricted to the dipol-loss-range below the lowest dipole peak. JohnK explains this in some of his Tech Studies: http://www.musicanddesign.com/tech.html

If you build a 21" wide H frame with a depth of 21" (front to back), the first dipole peak will be at ~320 Hz. This peak will in no way be "peaky" - just the upper end of the 6 dB/oct dipole roll off turning down to the first dipole null. This H frame will give you ~6 dB more efficiency than a 21" wide OB. Crossing over to your line array at 80-100 Hz you will be well away from that peak too, even with a low order x-over.

That´s what I would recommend for your 'bass' dipole array.

Thanks for the link - I need to read this --------- 6 db more efficient is almost unbelievable. You have built and measured this comparision?