My second attempt at measurements

**thewire** · **03-21-08, 03:31 AM**

I was reading some information about setting up the subwoofer and I came across this statement.

Quote:

In a THX® system, Front Left, Centre, Front Right and Rear Total should each give an SPL of 85dB with a 0dB input using pink noise.

I think that I will look into Johns observation.

**thewire** · **03-21-08, 01:40 PM**

The reason it may have looked +5 hot was since after calibrating the subwoofer to 85dB and then setting the mains to 75dB, I raised the volume on my receiver +5 and then checked the SPL on the meter in REW that it said 80dB with the pink noise generator, knowing this is where the speakers and my sub crossover close at.

In DVE I would like to set both my mains and my subwoofer to 75dB. Will I be able to do this after setting up REW with a 75dB target for both?

**brucek** · **03-21-08, 02:01 PM**

Quote:

In DVE I would like to set both my mains and my subwoofer to 75dB. Will I be able to do this after setting up REW with a 75dB target for both?

I feel you're somewhat confused about the role of REW. It's intent is to provide filter recommendations for equalizers to smooth the subwoofers response. It also allows you to obtain a smoother transition between the mains and sub by revealing a better sub phase adjustment.

Any levels that are used during the course of REW testing have little if nothing to do with the setting of system levels once you're finished using REW. They're completetly arbitrary and only adjusted as a means to an end - which is setting EQ filters.

Once you're finished with REW and equalization of a BFD, then use the receivers test tones or DVE or whatever you like to set the actual system levels.

brucek

**thewire** · **03-22-08, 06:04 PM**

Quote:

brucek wrote:

Once you're finished with REW and equalization of a BFD, then use the receivers test tones or DVE or whatever you like to set the actual system levels.

I am using the XA2 player directly to my amplifiers with the levels set to 75dB using DVE. My speaker settings are set to small, PCM, and the "Digital Out HDMI" is set to "AUTO".

Can I use REW directly to my amplifiers to determine speaker distance settings?

**thewire** · **03-23-08, 07:44 AM**

I tried a search here and appears that it may be an acceptable practice, even although my amplifiers as a single solid state amplifier (not sure about bridged) are not appropriate for running a full range sweep. I could at least get an idea by using a cutoff frequency at the XO, and do the subwoofer separate for setting filters.

I had one comment about the volume last night. While the previews are playing my father says "loud enough for you?".

We watched b movie. I will do another test later today to be sure my AVR was not causing a problem with the measurements.

**thewire** · **03-24-08, 08:31 AM**

My left and right walls are already offset by one foot. I have tried moving the subwoofer, testing different locations. I even tried playing reference through the other speakers. Every indication says that I have 85 target and that I am -5 dB away from reference which is very easily corrected by adding a second subwoofer and simply turning down the volume. The left and right surrounds + better left and right towers are what is missing. I don't know that a BFD can help my situation at this point in time.

I was recommended at another forum to try here last week. Could anyone explain what a BFD is going to help me with right now?

**JohnM** · **03-24-08, 09:21 AM**

I have to admit I'm losing track of what you are trying to do. The main problem with your sub, based on your original plot showing sub and mains, is that it is too loud relative to the mains. To fix that just turn it down so that when you play DVE or similar test tones through each speaker in turn and then the sub your SPL meter shows the same reading for all. If you then feel the low frequencies are a bit lacking increase the sub volume until the sound is how you like it.

**thewire** · **03-24-08, 09:59 AM**

My goal is getting the HT best sounding as I can in the present for movie watching and as close to reference as possible for later with the newer speakers to match the current sub or subs. I'm not so much concerned about the other speakers being softer or the subwoofer being louder at his point as long as I can get them sounding decent to watch the occasional movie on the weekend. The other speakers are being moved to a new media room or we would have to buy new speakers for there. I think it makes more since to buy new speakers for the HT to match the sub, and move these to the new media room. The problem I have is that boosting the subwoofer now causes problems because it becomes louder than my other speakers. I do however want to have the 15Hz to 20Hz be a flat response also which would require a second subwoofer. I explained to the lady of the house that adding the BFD was less expensive than treating my front wall with custom absorption panels from GIK and she would rather me spend my $$ on the BFD because it is going to lower the peak that I have after I get to the reference 75dB. I need the BFD eather way. I need the front wall treatment eather way. I don't know what to do.

Basically I am trying to explain everything to someone that is not familiar with the setup of a HT, trying to treat things in an orderly fashion and such while enjoying movies. I don't have complaints about it being to quiet.

**thewire** · **03-24-08, 10:16 AM**

I know how to build the GIK traps, but it is something that goes under my screen, I want it to be perfect, and I am worried I will have less than perfect results with my first attempt at making them. She suggested I make them myself, or buy the BFD.

**JohnM** · **03-24-08, 10:40 AM**

From your descriptions so far you have been evaluating alternative sub positions by ear, but if you do not adjust the sub level relative to the mains for each new position you are wasting your time. The graphs you have posted of your sub relative to the mains show it much too high in level compared to the main speakers. It will draw attention to itself because of that, leading you to reject positions because the levels are wrong rather than the performance is not right. The measurement in your first post shows a small resonance, adding about 4dB at around 48Hz, and several others above the crossover where they are not having much effect on the overall response. The bulk of the sub response in that plot is simply the natural performance of the sub in the position you have placed it when measured where you put your mic, it is NOT a room peak and it is high because the volume of the sub is turned up too much.

To properly evaluate an alternative position take REW measurements first, to see if the position is helping to increase the output below 25Hz where it currently rolls off. The only way to raise that will be to get the sub closer to a wall or into a corner. If the output at low frequencies looks better in a position go through the normal sub/mains level balancing first then listen to how it sounds. Getting closer to walls or into corners will probably result in some peaks in the response as room modes are driven into resonance. A BFD could help reduce those, if they are below 80Hz or so you would need enormous bass traps (several feet deep) to achieve a similar effect.

**Wayne A. Pflughaupt** · **03-24-08, 10:47 AM**

Quote:

I ended up moving the subwoofer to the center of the back wall where according to my folks, they were unable to localize the sound anymore and it did not sound "boomy" to them there.

I tried the right side of the room and also the left side like shown bellow after installing bass traps - the new 244 traps and prior to doing any new testing with REW more recently. It sounded excellent on the right side of the room but I was still able to localize it.

The closer I put it to a wall, the more I am able to localize bass there with the exception of placing it between my left tower and center channel as seen bellow. It sounded good there but I was able to localize higher frequency sounds there around the crossover.

Hopefully you’ve realized by now that you don’t have to rely on your ear to find the best location for your sub? REW can do that for you much more accurately. You don’t even really have to move the sub all around the room. You can plant it at the listening position and take the mic to prospective subwoofer locations. The REW reading will be the same as if you had the sub there and measured from the listening position.

Don’t worry about getting a REW reading that tracks the Target as close as possible. You’re looking for a location that will give the best extension with the fewest peaks and valleys, or one with peaks and valleys that can be easily equalized. As John noted, this will usually be at or near a corner. The Target in REW can easily be re-adjusted, as can your sub level, when it comes time to equalize with the BFD.

Quote:

I would mostly like a second subwoofer to extend the low frequency which I understand is possible.

I do however want to have the 15Hz to 20Hz be a flat response also which would require a second subwoofer.

Adding a second subwoofer is no guarantee that you’ll get improved extension. Adding a second identical sub gets you the same extension as the first, only at a higher SPL level. Adding a second sub that’s either better or worse than the first will get you no improvement over what you had with the one (you’d want to go with the better new sub and ditch the older one). If you’re looking for sub-20 Hz extension and you aren’t getting it now, a change in subs is in order.

Quote:

I think it makes more since to buy new speakers for the HT to match the sub, and move these to the new media room.

Any sub can be “matched” to any set of speakers. That is not an issue as it is say, with center-channel speakers vs. main L/R.

Quote:

The problem I have is that boosting the subwoofer now causes problems because it becomes louder than my other speakers.

Well, yeah...

Regards,
Wayne

**thewire** · **03-24-08, 11:36 AM**

A place with smoothest response is on the center of the left or right wall. This causes the response to suffer greatly bellow 50Hz, and to increase above that, but there are no large dips or peaks. Between the left and center channel there are two large dips. Placing the subwoofer into a corner is what got me into trouble in the first place, but I see no problem with putting one on each corner of the front wall. I will try testing that. I am less concerned about lower extension, more concerned about feeling where the LFE is originating from. I don't think we need a subwoofer in my bedroom or the new media room, so I hope that results look better there.

**thewire** · **03-24-08, 12:29 PM**

Here are the measurements of the subwoofer in the front corners. I moved the 244 traps to cover the entire corners this time also. What do you think? Could I eq two like this with the BFD for a nice response? I could have not as bad of a null at near 60Hz?

left and right.jpg

**Wayne A. Pflughaupt** · **03-24-08, 01:04 PM**

What’s your crossover frequency? The graph looks peculiar; I’m not used to seeing a big hole like that in a smallish enclosed shoebox room. Plus, there is no rollout at the upper end, as we should be seeing with the crossover engaged…

SVS’ Ed Mullen has noted in other threads that moving the sub a few feet down the wall from the corner can eliminate a null and retain the benefits of corner loading.

If you want the extension down to 20 Hz or below that you’ve been talking about, you’re going to need a different sub.

Regards,
Wayne

**thewire** · **03-24-08, 01:12 PM**

I have the soundcard directly hooked into the subwoofer. Crossover is at 80Hz. I set it to the SPL meter at 75dB and used the 75dB target. I have the subwoofer turned down allot. It has never been this low. The dial in the back is sitting at about 3 oclock. I have extention to 19Hz at the 85 target, but I don't think I'm supposed to post those results.

**JohnM** · **03-24-08, 01:32 PM**

It would be better to connect the soundcard to your av processor so that you see the effects of the processor's crossover, the sub's own crossover would then be disabled or set to its maximum. You should set your sub's volume control by using a 75dB test signal from your processor or test disc, setting the processor level trim to zero then adjusting the sub's volume control to get 75dB at your listening position.

**thewire** · **03-24-08, 01:38 PM**

I don't have a receiver anymore. It is gone. The subwoofer has no adjustable crossover on the back. It is 80Hz crossover.

**JohnM** · **03-24-08, 01:52 PM**

Looking at the manual of your sub it does not have a crossover filter, it relies on the processor/receiver to take care of that which is why your measurement does not show the roll-off of a crossover. That deep null is probably related to the mic position, was it on the centre-line of the room? If you move the mic off-centre does the null become shallower?

**thewire** · **03-24-08, 01:56 PM**

When I set the volume of the subwoofer using the test disk, playback from my subwoofer is extremely loud from the soundcard. I would not recommend anyone use the XA2 test tones. Something went horribly wrong there, and I refuse to touch it again.

**thewire** · **03-24-08, 02:04 PM**

The mic was located on the head rest of the center seat front row, inside a slinky pointing upwards. It is the center of the room. I will try moving the couch.

**thewire** · **03-24-08, 02:15 PM**

Moving the seating forward seems to make little difference. Placing the mic at the left or right seat does. This is with the subwoofer in the right corner again where the 50Hz peak is lower for the center seat. The couch was moved forward about one foot.
center and right.jpg

**Wayne A. Pflughaupt** · **03-24-08, 02:51 PM**

Quote:

JohnM wrote:

It would be better to connect the soundcard to your av processor so that you see the effects of the processor's crossover, the sub's own crossover would then be disabled or set to its maximum.

Quote:

thewire wrote:

I don't have a receiver anymore. It is gone. The subwoofer has no adjustable crossover on the back. It is 80Hz crossover.

Quote:

JohnM wrote:

Looking at the manual of your sub it does not have a crossover filter, it relies on the processor/receiver to take care of that which is why your measurement does not show the roll-off of a crossover.

That would sure explain why everyone’s been able to localize the sub so easily. I suggest getting an outboard crossover...

Quote:

thewire wrote:

Moving the seating forward seems to make little difference. Placing the mic at the left or right seat does. This is with the subwoofer in the right corner again where the 50Hz peak is lower for the center seat. The couch was moved forward about one foot.

Once again, try moving the sub down the wall away from the corner a few feet. Try it in 1-ft. increments in each direction and see if that null disappears.

Regards,
Wayne

Advertisement