room gain in case of dipole woofer?

[graaf]

Hi everyone!

is there any room gain in case of dipole woofer?

I have searched the forum and found nothing conclusive, just some quotes from Linkwitz suggesting that there is no room gain and a post from GM suggesting that there is and that it has been measured in case of actual speakers (Carver Amazing in a small room - "room-gain effect (...) like +8dB at 20 Hz.")
see:
http://www.diyaudio.com/forums/showthread.php?postid=1550689#post1550689

so I wonder how it is actually
can anyone help?

best!
graaf

 

[john k...]

It depends on what you mean by room gain. If you mean the room pressurization below the room fundamental then essentially there is none. If you mean in crease in efficiency do to proximity to wall, corners, etc, then yes there is.

 

[Rudolf]

"The room is so small that in order to get adequate stereo separation, Foster had to arrange the speakers with the ribbons on the outside, swapping left and right speakers. Moran found the bass overpowering and measured the room-gain effect as producing something like +8dB at 20 Hz. Moran thought it was bit too much of a good thing."

I don´t believe that those 8 dB really were room-gain. The Carver Amazing had a built-in middle-to-bass gain:

You should also consider that the Carver was 135 cm high and almost 70 cm wide. Most likely it had to be positioned near some walls in that "small room". In this case John Ks remark applies.

Anyway the forum seems to be one step ahead of you. The real question lately was: "Is there any room gain at all in normal rooms?"

 

[graaf]

It depends on what you mean by room gain. If you mean the room pressurization below the room fundamental then essentially there is none. If you mean in crease in efficiency do to proximity to wall, corners, etc, then yes there is.

I mean "increase in efficiency"
thank You very much for Your response 🙂

best!
graaf

 

[graaf]

You should also consider that the Carver was 135 cm high and almost 70 cm wide. Most likely it had to be positioned near some walls in that "small room". In this case John Ks remark applies.

Anyway the forum seems to be one step ahead of you. The real question lately was: "Is there any room gain at all in normal rooms?"

people questioned room gain as such? really? 😕

I don't think questioning room gain as such is "ahead" of anyone 😉

anyway if "John Ks remark applies" then there is room gain as I understand it and as it is commonly understood AFAIK
frankly I am surprised that people are confusing room gain with pressurization below Schroeder frequency

best!
graaf

 

[Pano]

I dunno... seems that when you reach a certain Sd that there starts to be room gain. 2 x15" driver per side seems to be about the threashold in a normal size listening room.

Could be wrong, but something seems to happen....

 

[gainphile]

I did measurement far field at listening position, approximately 3m from speakers, in room. Where in this graph is the "room gain" ?

Speakers are Eminence 15 based dipole with 45cm baffle, equalised at lower frequency. The room is a bit long (about 80-10m)

An externally hosted image should be here but it was not working when we last tested it.

is it around 100Hz? I forgot at what freq. it is being equalised (shelving lowpass) but if aroung 150Hz then shouldn't it look like s smooth transition instead of "hump"

 

[Graham Maynard]

When running my OB with 15"+18" LF drivers they become as susceptible to room positioning as do monopoles because the room itself remains capable of generating different levels of dimensionally tuned augmentation at different places/heights, it being similar for the listening position.

The main difference is that the room itself does not become LF pressurised, thus ceiling, floor and walls do not provide the same LF resonant gain at specific frequencies which are related to structural construction (as with boom-boom in a car!).

When you hear live music in open space you do not sense an explosive like LF pressure pulse the same as you do with monopoles within an enclosed room space, and the smaller the room the greater the abnormality of relative increase in sensed LF monopolar pressure for equal mid range level seems to become apparent.

Dipoles don't induce the enclosed room pressure pulse, thus I do not understand how there can be any room gain if the room itself is rigidly and solidly constructed, and I believe this is why dipole reproduction can seem so correctly articulated, even at LF.


Hi Michael,

When cone/baffle area increases maybe there is a greater chance of exciting a room mode due to the localised pressure differential at the LS position ?


Cheers ....... Graham.

 

[jason_watkins]

gainphile:

Is that measurement offset?

You're getting an equalized ~135dB from 30hz on up on an 18" baffle? Which driver? How many? What sort of room?

 

[gainphile]

Yes, ignore the dB. I did not calibrate the SPL.

Driver is Eminence Alpha which is 97dB.

 

[jason_watkins]

Ahh yes, offset measurement makes a lot more sense than the multiple drivers and killowatts I was picturing 😀

I'd be very interested to hear the details.

I'm working on a H frame Alpha 15 design based on John K and MJK's projects. The cardioid response is the goal, so I'm planning to size the line such that the effective dipole distance is an octave above where I'll high pass it. John K's graphs hint that the cardioid response is fairly stable an octave down. Baffle will be 18" square, and I plan to use at least 2 of them, possibly 4.

I could go ahead and guess and cut wood at this point, but I'm doing some more learning with the hopes of getting more exact simulations.

 

[Rudolf]

... anyway if "John Ks remark applies" then there is room gain as I understand it and as it is commonly understood AFAIK

Am I too narrow minded? Could you please lead me to those discussions where "room gain" is used as a synonym for wall/floor/border/etc. gain?

frankly I am surprised that people are confusing room gain with pressurization below Schroeder frequency.

I am surprised too 🙁 . (BTW: Schroeder frequency is defined as the boundary between reverberant room behavior above and discrete room modes below. But I know what you mean.) "Pressurization below the lowest room mode" was the definition of "room gain" I was aware of.

 

[graaf]

Schroeder frequency is defined as the boundary between reverberant room behavior above and discrete room modes below. But I know what you mean.) "

thanks for the correction, my stupid mistake with "Schroeder" 🙂

Pressurization below the lowest room mode" was the definition of "room gain" I was aware of.

where have You found such definition?

in my understanding of "room gain" as "low-frequency gain" due to "interactions with adjacent room boundaries" I just follow well-informed people like Floyd Toole:
http://www.harmanaudio.com/all_about_audio/loudspeakers_rooms.pdf

best regards!
graaf

 

[Rudolf]

Thanks graaf.

Toole clearly avoided the term "room gain"in that pdf. I simply followed john k...s first definition (he offered two, you choose the second one).
Please note that I did reply before you made clear that you tend to the second interpretation.
So I´m sticking with "room gain = cabin gain" and you stick with your definition. We don´t need to come to common terms, don´t we? 🙄

Cheers
Rudolf

 

[Pano]

When cone/baffle area increases maybe there is a greater chance of exciting a room mode due to the localised pressure differential at the LS position ?

Could be. What I hear is that at a certain point the woofers start to "take control" of the room. Hard to describe. It was actually my buddy JB how noticed this first, but I've heard it too. 4x15" in an average room will cetainly do it - and an 18" often will.

To me it seems similar to a big PA in a bad room. If you're stuck in a venue with bad acoustics you can sometimes "power thru it." The shear size and power of the system seems to overide room acoustics. Not the world's most elegant trick, but sometimes it's all you have...

 

[graaf]

We don´t need to come to common terms, don´t we? 🙄
Cheers
Rudolf

of course we don't 🙂

best!
graaf