Monster Quest: Room Gain

[Ricci]

I messed around yesterday and tried to determine the amount of room gain I've got below 30hz. It didn't turn out as well as I'd hoped because it is hard to get anything accurate in the single digits. The ambient noise floor, equipment roll off, low output there, etc. make it difficult to get good measurements. The louder that the bass is the better the acurracy seems to be down that low. You may be thinking that the single digits are a waste of time and that may be true, but some people with enough displacement, power and room gain may theoretically have enough output for perceptible effects down there. I've seen 30db+ single digit gain touted before.

I used a XXX 18 in a sealed and stuffed 10cu ft enclosure and powered with an AeTechron 7560 DC coupled amp that is basically flat to 2hz. I used a ECM8000, Xenyx 1202, CM140 and Turtle Beach SRM with REW for the measurements. I ran directly out of the SC into the amp. I took the sub out in my back yard and got some readings at a loud level. Then keeping all settings the same I took the sub inside and took another measurement to see what it would do to the FR.


This is the close mic FR outside at a loud volume level. BTW all of these have no smoothing or anything applied. I think big warts are sexy.









This is the 2 meter outside FR at the same level.










This is 2 meter outdoor versus in the room with the SW at the SW position and the ECM8000 at one of the listening positions. About 4.5m distance. Looks like about 13.5db gain at 9hz.







This is the same deal. Outdoor measure versus the same sweep done in my upstairs room where my SDX's usually reside. Roughly 11db gain at 9hz.



Just for fun I took the sub and threw it in my Jeep WJ cargo area with the cone facing the rear about 10" from the back glass, placed the ECM8000 where my head would be in the drivers seat and measured that... Just sickens me how easy it is to get massive bass in a vehicle. EASY. 36db gain at 9.5hz. This is a single sealed 18 that's way underpowered too since the 7560 can probably only do about 900w into it (4.5ohm min in the box).

[Ricci]

Strange the image code is being changed after I post it. Let me try again...What the . It is changing the name of my image after I post it to this.

[avaserfi]

There is a censored word in the image link that is being changed. Looks like the file names need to be changed for them to work here. Sorry for the inconvenience!

[Ricci]

Ummm rigght.

The name of the first file is downstairsromoo baby mooain and the other is upstairsromoo baby mooain. It will not let me post them no matter what I change the name to. I even tried "please work".

It won't let me post any pictures. Oh well.

WHAT! it just changed the title of the words i typed in! Do you see the title of this thread? the last 2 words are what it is combined with "up stairs" and "down stairs". That's it. Apparently it's so offensive that my words are changed before they even hit the screen? Yet I can type XXX 18 like my drivers all day?

[Ricci]

test

room gain

romoo baby mooain

downstairs

stairsroom

down stairs room gain

Up stairs room gain



(apparently if you put the word ROOM and GAIN together it is unacceptable. LOL!

[Mike P.]

Definitely a glitch that needs to be addressed. I'll report it.

[Sonnie]

roomgain

It is fixed. We a replacement variable setup to replace the three letter after 'ro' and before 'ain'. Who would have ever thought someone would put the words together.



moo baby moo

[Ricci]

Leave it to me to uncover some strangeness like that!


I think I have the graphs fixed now...

[Mike P.]

In the third graph there looks to be about 5-6 db gain between 15 and 20 hz. How big is the room?

[Ricci]

My main room where the 3rd graph was taken is about 21.5 x 15.5 x 11 or roughly 3500cu ft. It is also very oddly shaped and open with a staircase, stair landing, bay windows and 4 doors.


Graph 4 is for my room upstairs that has my Klipsch system with the SDX15's. It is 21.5 x 14 x 10 or about 3000 cu ft. It is much more regular shaped though.

My Jeep is maybe 260cu ft .

I seem to have about 4-6db of gain in my rooms at 20hz increasing to 9-13db at 9hz. I was hoping for a bit more. I don't know what I've got in the single digits which is what I was really interested in determining. Just can't really trust the measurements too much there due to not enough gain above the noise floor and microphone insensitivity among other things.

[brandonnash]

Sonnie wrote:

roomgain

It is fixed. We a replacement variable setup to replace the three letter after 'ro' and before 'ain'. Who would have ever thought someone would put the words together.



moo baby moo

good thing this is not a hair loss forum. rogaine!!

[ISLAND1000]

I just found this thread. I'm surprised the in-room gain becomes obvious at such a low HZ. I had it in my mind it would start somewhere around 70HZ. Just goes to show you how incorrect my experiences and perceptions are sometimes.

[Ricci]

I have fairly large rooms that are open so they may no be very representative of anyone else's. Also the outdoor measurement was at 2 meters. In my rooms I used the subwoofer position and placed the mic at the listening position with the same levels used, but the listening position is around 4meters or more from the sw in both rooms. I probably should have kept the mic the same 2 meter distance in room. I guess I would keep the mic on the floor as well? Maybe I should take a 4 meter outdoor measurement which would correspond better with listening position distance in room?

I'm probably going to redo this in the spring. I need to figure out the best way to do it.

[ISLAND1000]

Yeah, if you would. Us guys with sealed boxes can use the definitive information about room gain when we proceed to equalize the in-room response.
Keeping all parameters equal while you measure outdoor vs indoor has got to be a basic experiment requirement.

[Ricci]

Yes , but exactly how do I go about that? I mean do I place the mic 2m from the sw on my floor and do the same sweep? Or do I measure the distance to the listening position and take the outdoor measurements at the same distance and orientation from the cab?

What can be said is that since the measurements were all taken further away than the 2m outdoor tests, even the one in the Jeep, they should represent at least the amount of gain I have. Tests closer to the sw in room or vehicle should further increase the difference between outdoor and indoor.

Also whatever I determine won't really apply for anyone else's situation. Though we can say that you will have a ton of boost in a vehicle.

[ISLAND1000]

To keep all parameters the same you have to have microphone placement and distance equal.
Ilkka places his mic on the ground 2 meters from the center of the driver for a sealed box. If you have 2 meter space indoors use that placement for equal testing specs.
For car measurements if you can get the 2 meters distance then that test comparison will be unofficially valid too.
But in my opinion, I would use close mic comparison ( mic placed in the plane of the cone surround @ cone center). With close mic testing procedure you have a better chance of avoiding in-room modal differences affecting the spl response vs outdoor. Use same close mic procedure for outdoor test.

[Ricci]

I don't think that close micing will allow the room to do it's thing to the response though. I'll probably go to a 4 meter ground plane and then set the mic 4 meters away on the same axis in room. That should better tell how much gain is there.

[ISLAND1000]

All right . . . . I'm standing by for the results.