HT Sub levels

[fauzigarib]

Hey all,

Here's a question that just hit me while I was considering room corrections in my brand spanking new HT.

Just FYI, I have the following system:
- Lexicon MC-8 Processor
- Kef Q7 Mains
- Kef iq6c center
- Surrounds Kef iQ3 and q2's.
- Rotel 1095 powering the front 5 speakers
- Nad c270 powering the rears
- Rel Stampede Sub
- Denon DVD
- Panasonic AE 900 Projector
- Dalite 119" Motorized screen

When I set up the speaker levels on the above system, I use my SPL meter to get the mains at around 80 dB, and then do the remaining adjustments from there.

So the test tones in all the speakers have been very carefully adjusted with the right distances and levels, but I can't, for the life of me, seem to tame the sub's response. It seems to fluctuate almost 20-30 dB's between 70 - 95dB's... Is that normal? Or is it my room?

I'm quite sure I have my crossovers in my Lex set correctly.

My room, fyi, is 36' x 14' with my listening position at about 33' from the mains. The sub is right at the front in the corner behind the mains. It's connected via both LFE and High Level connections.

My room is very bright, with marble floors and concrete walls and ceiling. The reflections were a lot worse, but since the furniture has gone in, it's been tamed significantly. Further corrections are being worked on to absorb at the reflection points, but I wanted to get some input from you guys.

Is this bass issue normal or is it a factor of the room?

Fauzi

[dyazdani]

I normally see about 5-6dB fluctuation in the sub... By "high level" do you mean you also have the sub hooked up via speaker level connections, like from your power amp?

You might try just hooking up the LFE and making sure the sub is turned on in the Lex. See if it makes a difference anyway...

[Azeke]

Here are a few things I would try:

1) Place the Sub on a rug.
2) Check your phase and adjust in very small increments, remember even minute changes may have significant impact on your acoustics.
3) Set the sub at 100 MHz Xover.
4) Sub placement, this is the most difficult, it took over a year to get my sub right, and I can probably still make placement adjustments. Try using the crawl around method to find the correct sub placement.
5) Don't make your sub too hot, it make affect the blending with your speakers. If you sub is booming your level is probably too high, adjust accordingly.
6) Ensure your delay is properly set, you may even want to make adjusments up or down on the distance. My sub's proper distance is 14 ft, but I have the delay set at 18 feet.

Just my quick thoughts, hope this helps.

Peace and blessings,

Azeke

[SteveCallas]

33' from the mains? :E Yikes. That, combined with the marble floors and concrete walls means your in room FR is probably a roller coaster ride. This is prohibiting you from being able to set a solid level with wide band pink noise. Download RoomEQ Wizard (free) and take a FR measurement of your subwoofer at your seat. That will tell you how bad of shape you are in and help you figure out what sub level would be the best compromise.

I would highly recommend you move up closer to the front of the room if possible.

[kirknelson]

My room, fyi, is 36' x 14' with my listening position at about 33' from the mains. The sub is right at the front in the corner behind the mains. It's connected via both LFE and High Level connections.

That's pretty far. Both from your speaker and the screen. For a 120" screen you should be at more like 15-20 feet.

Also I'm guessing from those dimensions that your couch is right up against the back wall. This will greatly effect the quality of bass you are able to get.

I highly recommend moving your listening position. Generally speaking odd factors of room dimensions work best. E.g. 1/3, 1/5, 2/5, etc. Looking at your dimensions I'd try to move the listening position to around 14' 5" or 21' 7" from the front wall (that's 2/5s and 3/5s back). I think you'll find both the sound and picture more involving from this distance.

...remember to measure to the listener's head not the dimensions of the furniture.

[fauzigarib]

33' from the mains? :E Yikes. That, combined with the marble floors and concrete walls means your in room FR is probably a roller coaster ride. This is prohibiting you from being able to set a solid level with wide band pink noise. Download RoomEQ Wizard (free) and take a FR measurement of your subwoofer at your seat. That will tell you how bad of shape you are in and help you figure out what sub level would be the best compromise.

I would highly recommend you move up closer to the front of the room if possible.

Steve, and others,

Sorry for the delay in getting back to you guys. I've finally downloaded RoomEQ. FANTASTIC. Took me a while to get the cable made and get it set up. Calibration and setup took a while. And I just got my first measurements last night.

Rollercoaster ride is right. However, I think that there might be something wrong with my SPL meter, because once it's connected to the Line In of my soundcard, it just doesn't go down to zero. How do I calibrate it? It's a Nady (I forget the model number, but it's asm something... equivalent to the RS meter). It's got a "Cal" button on the side. The manual says that you need a technician to calibrate it. How does one do it without a technicial because I know I won't find someone in Pakistan.

Will post the graph either tonight or tomorrow.

Fauzi

[whoaru99]

Almost sounds like the Line In from the sound card is putting a small voltage to the meter. Are you sure it's Line In and not Mic In?

I was wondering too about the dual connection of LFE plus speaker-level connections to the sub. Could that be part of the issue? I've not heard of using both at the same time, but then I'm not familiar with that sub.

[fauzigarib]

whoaru99,

Yes, I'm sure it's line in... But I will try the mic in to see if that makes a difference.

About the sub, it doesn't make sense to me either about using both connections, but even the instructions state (on ALL Rel products, IIRC) to do this. They tell you to set the x-overs on the sub without the LFE connection, perfect it, and then just plug the LFE in. But man, do those connections make this sub musical, or what??!!?

Actually, I just thought of something and went and checked. Even when the SPL meter is off, it's resting on the "-8 dB" position and not -10 like (I think) it should. So I guess the meter does need calibrating. Any ideas?

-Fauzi

[whoaru99]

No real good ideas on the calibration except to say that the needle in my RS meter lies exactly on top of a small hash mark just a bit below -10.

I wouldn't plug it in to the Mic In, I think that is expressly not recommended in REQW instructions.

I'm not sure the absolute calibration is all that critical anyway, but I guess that depends on what you use it for. It's the relative measurement that is most important to me.

[Audiophiliac]

I always set sub levels by ear with a few familiar movies/albums. Most SPL meters arent accurate at sub bass frequencies. Even the Sencore kit doesnt do perfectly. Itll get you in the ballpark, but once you know what it is supposed to sound like, its easier to dial in.

[ThomasW]

Here's your meter just so people know what's being talked about.

http://www.nady.com/pdf_files/manuals_pdf/audio/ASM2_userguide.pdf

[fauzigarib]

Here's your meter just so people know what's being talked about.
http://www.nady.com/pdf_files/manual..._userguide.pdf

ThomasW,

Thanks! I should be posting the link up, but thanks for doing my work!

So, any ideas about how I can bring the zero level to read zero?

Fauzi