Bass Sweep of Room

Holydoc

Need some opinions. I have attached a full hertz sweep of my room using the SVS PB-12/plus. My question is if this sweep looks reasonable or should I make some more adjustments?

This is the full sweep...



This is where I zoomed in on the possible problem areas...



What are your opinions? Is it acceptable or should I look into something like the SMS-1?

Thanks everyone.

PolkThug

Looks like a substantial room null around 58Hz. Experiment with sub placement, its about all you can do with a null like that. I assume you crossover at 80 or less, so above that is a non-issue.

jakelm

What program is that Holydoc?

Holydoc

PolkThug wrote:

Looks like a substantial room null around 58Hz. Experiment with sub placement, its about all you can do with a null like that. I assume you crossover at 80 or less, so above that is a non-issue.

Polkthug,

You are correct. My crossover is at 80. I have attempted to move the sub around some, but with no luck. That is why I was wondering if an equalizer like a SMS-1 would benefit here or not. I am afraid that if I equalized it out at the seating position, then it may just exaggerate it at the other spots.

Holydoc

jakelm wrote:

What program is that Holydoc?

Excel with a few hours of sitting down infront of the sub with a SPL Meter.

Holydoc

BTW...if any are wondering if the PEQ on the PB-12/plus works, here are some graphic examples of it in action.

This is a total room sweep. Notice the hump at around 44-46hertz.




This is a zoom in of the hump area:




A dramatic difference the PEQ makes... this is that same picture with the PEQ in action:

Holydoc

Finally...just for fun, I placed the sub out of Phase. Instead of 0, I set the phase setting on 180. Pretty dramatic results.


Full room sweep.



A nice zoom in of the out-of-phase sub.



Now you have visual proof of what happens when a system goes out of phase!

jakelm

Its the Rocky's

PolkThug

Holydoc wrote:

Polkthug,

You are correct. My crossover is at 80. I have attempted to move the sub around some, but with no luck. That is why I was wondering if an equalizer like a SMS-1 would benefit here or not. I am afraid that if I equalized it out at the seating position, then it may just exaggerate it at the other spots.

Typically, EQ devices are mostly, only good at taming peaks and not raising up a null that much. Also, think of this, if you eq the heck out of it to get it to 85db's at your listening position, the sub is really working at 95+db to compensate, so the sub may kick its own **** when you play material in the 55Hz range.

I bet if you set your spl meter on the ground, 3 feet in front of the sub, it probably plays 55Hz at the same db level as the other tones.

Holydoc

Polkthug,

The amount of power needed to raise out of that null is something I did not think about. You are correct in saying that I could potentially hurt the sub by trying to get it out of that null.

May be something that I just have to live with because of the open air situation of my living room. Sure makes for an interesting afternoon though of sitting around by myself.

kingkip

Not sure what you already have in your room, but have you thought of treating it? Sound panels bass traps and the like? Works wonders for most, and though it won't completely tame the null it should make it a lot better.

Holydoc

kingkip wrote:

Not sure what you already have in your room, but have you thought of treating it? Sound panels bass traps and the like? Works wonders for most, and though it won't completely tame the null it should make it a lot better.

Kingkip,

Do you have any links to how to make a bass trap? Any type of discussions about them would be great since I have never did anything like that before.

As far as treating the room, I am very limited. It is an open floor plan (i.e., the living room is open to the dining room and foyer) with vaulted ceilings. There basically is no rear wall or left wall. The right wall is a 14' sliding glass door. This makes my room treatment possibilities very limited.

Thanks again for taking the time to at least address this issue for me. Not really sure if that null is considered major or minor, but would be nice to know my options.

[Deleted User]

Hello,
Keep in mind that is a bass cancellation caused by the room's dimensions. You could increase the output at that particular frequency and it will just be cancelled. There's not much you can do, that is the effect of the room's wall-to-wall or floor-to-ceiling dimensions. The only thing you can hope to do is position the sub-woofer and your listening position to not make things worse. There will always be cancellations and standing waves in rooms with parallel surfaces. Hopefully the room's three different dimensions, giving three different sets of peaks and dips are spread out to avoid serious problems. This is why there are the, so called, "golden ratio" of room dimensions to ameliorate the problem.
Regards, Ken

Holydoc

I really do appreciate all the input. It is definitely a room problem as far as the null goes. Not sure how or if I can fix it since it is in the main room and modifications to this room may not be aesthetically pleasing.

Just one more thing I wanted to show everyone and ask their opinion. I mean after all, I have gone graph happy here.

I set my sub's subsonic extension from 25Hz extension to a 16Hz extension. My thoughts here was that I would hate to miss "FEELING" that low bass for shows that have it. It did however change my tuning graph slightly. The 25Hz setting is a bit more level at the lower frequencies 19-41hz (just a 2Hz fluctuation). The 16Hz setting is a bit more level at the 67-82Hz.

I think these differences are negligible given that my sub will be able to dig a bit lower to enhance my HT enjoyment. What do you think?

25Hz Graph....



16Hz Graph... Notice the much lower extension into the 11Hz range.

kingkip

Yep, here you go. There is a ton of stuff out there other than this too.
http://www.audioholics.com/techtips/roomacoustics/index.php

Holydoc

kingkip wrote:

Yep, here you go. There is a ton of stuff out there other than this too.
http://www.audioholics.com/techtips/roomacoustics/index.php

Wow, Kingkip! Thanks so much! Now I will be reading for days.

John K.

Good work, doc. Yes, the PEQ certainly did level out that peak in the 45Hz area nicely. To try to get an idea of what the depression in the 60Hz area is(it may or may not be an actual room null), what are the dimensions of the room, exactly how far from the room walls was the center of the sub driver when you measured that depression and what was the position of the SPL meter?

Holydoc

John K.,

The room is 12'x20' with cathedral ceilings. It is an open floor plan which opens up to the dining room in the back, the foyer on the left, and a 14' sliding glass door on the right. The sub is currently against the front wall in the only corner in this room (front right). I measured the depression with my SPL from my seating position exactly 10' diagonal from the sub.

Hope some of that helps.

John K.

Doc, that positioning that you describe removes one of the possible explanations for the 60Hz depression. If the sub driver was about 5' from a room surface, that would be about a quarter wavelength at 60Hz and would cause a partial cancellation at that frequency when the sound bounced off the wall and returned to the driver. From your description though, the sub is right in the corner(generally the best location) and the driver cone is maybe just 1' from the walls, so this doesn't appear to be the controlling factor.

Holydoc

John,

It is almost touching the corner. I would say less than 3" from both the back wall and the right wall. Tomorrow, I may try positioning it in the middle of the room to use as an end table to see if that flattens out the curve. Since the end table will be right next to the sitting positions, it may actually work out.

We shall see.

Dr. Spec

The dips are due to room modes. It is extremely hard to find a combination of listening position and subwoofer location which completely eliminates peaks or nulls.

The correct approach is to first employ bass traps, then experiment with listening/subwoofer location, then optimize phase relative to the mains at/near the XO frequency, then use a PEQ as the last step to cut peaks.

If you buy an external PEQ with gain, don't try to boost a true null; it will only waste amp power and stress the woofer and result in a poor FR elsewhere in the room. True nulls are best addressed with bass traps.

A very good bass trap is two or three stacked panels of OC703 4'x2'x2" (4"-6" total thickness). Place them in across every corner in the room.

Here are a few useful links........

http://www.ethanwiner.com/acoustics.html

http://www.harman.com/wp/xls/Room%20Mode%20Calculator.xls

Lowell_M

This an extremely interesting thread. I never calibrated using an SPL meter, but plan to sometime. To graph all of those frequencies, what did you use as a source? Is there some CD out there with test tones at different frequencies or something?