What is this room gain stuff anyways?

[SY]

John, I think you've put a finger on it- dipoles are VERY room-dependent. The point sources, less so, assuming good control of dispersion.

[auplater]

Originally posted by SY
John, I think you've put a finger on it- dipoles are VERY room-dependent. The point sources, less so, assuming good control of dispersion.

No doubt ... they need space to realize their benefits. Unless you can place them out into the room, the rear wave image enhancement seems to collapse, and interfere rather than augment the soundfield. Most naive listeners who hear mine state they're the first speakers that sound as good from behind as in front.

As psuedo linesources, they also fill the entire house with convincing sound, much different from conventional boxes.

24 NHT zero's?? That's the Scan Speak 18W/8545, right? What are you going to use for the mids-treble range? I've got 2 more of the ATC 25" Neoplanars on the way to play with, since they worked so well in my mains. I may replace the cones in my old Infinities, or maybe use them for HT surrounds...

John L.

[SY]

No, those are some paper cone jobbies from China. Very smooth rolloff. Tweeters are still up in the air, though an ESL ribbon seems intriguing.

[graaf]

Originally posted by GordonNHT
I've read that room gain affects low frequencies. So what frequency is that?

http://www.trueaudio.com/st_spcs1.htm
http://www.stereophile.com/reference/39/index2.html

best,
graaf

[GordonNHT]

http://www.trueaudio.com/st_spcs1.htm

Thanks for the links. I guess it is generally agreed that so called "room gain" is due to boudary effects at low frequencies in our small spaces. But my measurements show that reflections in mid and high frequencies also cause in increase in measured SPL. Why is this not room gain? I suppose it's matter of who invented and defined the term.

[Inductor]

I am not sure of the true terms but I would define it more like at resonance levels, not so much at high frequencies, being it room size dependent. GordonNHT I don't know if this helps or not.

That's why we adjust BSC on xovers for PA outside work or for Hi-Fi home enjoyment.

[AndrewT]

Hi,
I'm not too sure, but I don't think boundary reflection and the humps and bumps these cause is anything to do with room gain.

Imagine a sealed box speaker in a room that is the same volume as the box.

The pressure changes inside the box will be the same as the pressure changes outside the box, provided the room and box are BOTH sealed to the same standard.

Now decrease the sealed box to 10% of the room volume.
The room pressure changes will be approximately 10% of the internal pressure changes inside the speaker box.
There comes a point in this box to room volume ratio where the gain of room pressure is no more than would be felt if the room were not sealed. I suspect that box to room volume or possibly cone area & Xmax (Vd) to room volume and room sealing effectiveness are all tied into this.

Reflections and their inherent subtractive/additive interference effects will add on to any room gain effect.

But, I could be (very) wrong.

[GordonNHT]

I built a monopole line array and performed the same test as before measuring frequency response at 1', 2', 4', 8' and 16'. The results are a big mess. Comb filtering along with unavoidable reflections off the floor and ceiling yeilds ugly curves. More smoothing. I have never designed a line array before but I would say it is a bit more difficult than a small 2-way. In any case this does show that the SPL does fall off much less than a point source. In fact at 2700hz the level changes by only about 3 db from 1ft to 16ft.

[SY]

Well, that's quite cool- I casually mention that a particular measurement would be interesting, then you actually go do it! For your next task, please have your payroll department direct deposit your paychecks into my account.

Seriously, thanks for that- this is another thing that "everyone knows" but it's rare to see real data.