I think I have a problem.

[Conrad.]

Hi all,

I've been reading this forum for a while now and I've found it hugely informative and excellently written by people who clearly know their stuff.

Between you all you've managed to convince me that my system could (and should) sound better. With this as my goal I've bought into the whole REW/BFD solution and I have some findings that I'd like your opinions on.

My set up is an HTPC which is passing a decoded signal out to my Yamaha RX-V1500's pre-ins. THe sub output from the multi-channel outputs on the Yamaha is being split to a pair of Velodyne SPL1000 subs. These subs aren't co-located, one is forward facing just inside the right main and the other is in a deep bay at the back of the room, firing diagonally across the back of the seating area. I've tried to illustate this in the attached plan. The room dimensions are about 22ft x 14ft at it's widest/longest. THe bay is just over 5ft deep by 8ft wide and the ceilings are about 11ft high.

My first pass with REW produced the attached results. Initially I thought that this was excellent and that REW couldn't change it much because it didn't need changing but that drop from 20-40Hz (or a huge hump at 40Hz, whichever way you want to look at it).

I was thinking of dropping my target level down to 64dB and seeing if I couldn't EQ the hump down rather than try and boost the low frequencies (a real no-no, apparently). Is that the right approach to take? Should I focus more on placing the subs differently? I don't have a lot of options on that front unfortunately. Or should I just sell both subs and buy a Monolith?

I know that 2 good subs don't equal 1 great sub and that I can't expect my house to shake with the pair that I have but they should go way below 40Hz, right?

Any help would be appreciated. I'm posting this on AVForums as well, and I'll try and transfer interesting points and comments between the two.

Thanks in advance.

Conrad

[Wayne A. Pflughaupt]

Welcome to the Forum, Conrad!

It’s going to be difficult to properly integrate separate subs in a non-symmetrical room like yours. As you can see, if you don’t do it right you can’t hope to achieve good response. I agree that these subs should be able to get below 40 Hz. It’s probably your placement that’s causing them to brick-wall at 40 Hz.

At this point I’d deem your current response as essentially unequalizable. Not even considering the narrow hole at ~95 Hz, you have a nearly 30 dB spread between your worst peaks and depressions. That needs to be narrowed to something like 15 dB or less if you hope to achieve smooth response.

I suggest experimenting with different locations, using only one sub, and find one that gets the best reading. Then you can add your second sub to the same location. The first place I’d try is that corner at the top right of your picture, followed by the one at the bottom right. We’ve seen this a lot here recently, people showing is an abysmal graph that’s beyond help, with subs placed in some weird location - center-wall, etc. They move it to a corner, and there’s a huge improvement – response we can work with. Here’s one – look what happened to his response when he moved the sub to the right (i.e. best) corner.

Regards,
Wayne

[Conrad.]

Hi Wayne, thanks for getting back to me so quickly. I'll try EQing just one of the subs first and I'll try it with it's phase setting in both the 0 and 180 positions. I could move the second sub into the bottom right corner of my layout diagram, if I can get one of them working first.

I do have another question though. Currently, when things are going through my BFD I'm barely getting one light lit up. Even on really heavy bass scenes I get the third green flickering at most. As that's the case would it be safe to add some boosting filters to bring that 30Hz dip up a bit?

Again, thanks for your time and knowledge.

[Wayne A. Pflughaupt]

Currently, when things are going through my BFD I'm barely getting one light lit up. Even on really heavy bass scenes I get the third green flickering at most. As that's the case would it be safe to add some boosting filters to bring that 30Hz dip up a bit?

I wouldn’t do it. “Some” boosting isn’t going to do much, since the drop-off is severe and deep. Go ahead and get some readings in those corners – I’m betting that will improve your extension considerably – for “free,” with no boosting required.

Re the BFD’s low meter reading, can you increase the sub output from your receiver? It would be good if you could get it up some more.

Regards,
Wayne

[Conrad.]

My subs are on +3.5 and the LFE setting is at 0 on a -10 to 0 range. I could crank it up a bit but, previously, It'd just mean turning down the gain on the subs themselves (at about 1 o'clock). Once I've got the BFD in the chain though I guess I'll be cutting frequencies and that are domainating or, probably, overpowering that nice, clean, defined bass.

Actually, hang on, I'm not sure if I know what I'm talking about! I'm putting the BFD into the HT chain, not the music chain. The HT chain is already decoded by the HTPC by the time it reaches the pre-ins. I can drop the volume of the other channels and increase the sub channel though, that'll just mean I need to turn the reciever up. It's odd, my reciever which has multi-channel ins and pre-outs is still able to affect the volume when it's, apparently, performing pass-through. But that's something for another day.

The short answer is that all channels are running at the same volumes from the soundcard.

[Conrad.]

Ok, some serious improvements have been made!

I started by turning sub2 (the one in the bay) off. This made an immediate improvement to the frequency response. That ~45Hz mountain almost disappeared. I tried one sub in various positions including the corners Wayne suggested and, surprisingly, the smoothest frequency response came from the position it was in originally.

I then decided to be a bit bold and hooked up the second sub, trying them together in different locations, co-locating and taking many measurements. The best I could get was with sub1 where it was and sub2 now sitting in the corner next to it. This produces a graph that looks like the uncorrected attached.

I think I should probably have gone through some recalibration at this stage as it's clearly running a bit hot. Instead I upped my target within REW and added some filters. I've managed to generate the attached corrected file which, I think, should sound pretty good.

Full range sweeps to ensure good integration are a bit beyond me at the moment. I ran a couple but couldn't decipher them so I'll use my ears for the moment. We're currently watching the LOTR trilogy; we did FOTR last night, it's Two Towers tonight and then ROTK on Saturday. That should give us a nice comparison.

Any comments or further suggestions? I'm going to play some of the scenes a couple of times tonight, with and without the BFD in place to see if it makes a noticable difference.

[brucek]

Any comments or further suggestions

You done a lot of aggressive cutting and have left quite a hump at ~150Hz. You need to back off on that cutting to keep a smooth drop. You need to add your mains and see what that 150Hz area looks like. Remember the mains will be overwhelming that area in their addition and you may have a noticeable peak.

I like the look of the pre BFD response better than the after. You're using way too many filters. Not neccessary. I would just lower some of the peaks and then take a stab at adding the mains and see if you can get a smooth transition...

brucek

[Conrad.]

Thanks Bruce.

I was kind of hoping someone would come back and say that I could EQ the subs by just dropping their volume, no real need for a BFD. What are your thoughts on that?

I've played some music I'm familiar with (Daft Punk's Aerodynamic) and the new location completely overwhelmed the mains. I've turned them down quite a lot (from about 1 o'clock to about 11 o'clock and they sound much smoother and more integrated. That kind of explains the shift in target level from 75 to 82dB I guess. I'm going to get another shot at running REW at the weekend and I'll try and involve the mains.

Now, to do that, I need to increase my sweep up to what, about 300Hz? I'm assuming that I don't need to go up to 10,000Hz or anything as the subs are well out of range by that point; right?

[Wayne A. Pflughaupt]

Great news there on your progress, Conrad, and happy to see the much improved results! Extension towards 25 Hz is much improved.

The best I could get was with sub1 where it was and sub2 now sitting in the corner next to it.

Actually, SVS’ Ed Mullen (who is also a fellow Shackster) has previously noted that a sub a few feet from a corner achieves the same coupling you’d get with it being in the corner (as for as output and extension goes) and that a second sub in the nearby corner can get smoother response than you’d get from putting them both in the corner. Naturally, every room is different, but once again it’s shown that Ed knows his stuff.

Yeah, and what’s up with that 150 Hz thing? Isn’t your crossover working?

I agree that you’re probably applying too many filters, and possibly cutting everything too much as well. I suggest raising your target level a few more dB; that’ll help the latter. Your proposed equalized curve looks too “perfect,” which you only get by equalizing out ever little nook and cranny. (That's one reason why I don't especially like our standard 45-105 dB window - it compels people to over-equalize.) As improved as your response is now, it shouldn’t take more than a few filters. It doesn’t have to look perfect to sound great. For instance, this is my in-room curve. Looks a bit ragged, as you can see, but sounds great.

I was kind of hoping someone would come back and say that I could EQ the subs by just dropping their volume, no real need for a BFD. What are your thoughts on that?

Mine are, you won’t get that house curve without the equalizer.

Regards,
Wayne

[brucek]

I was kind of hoping someone would come back and say that I could EQ the subs by just dropping their volume, no real need for a BFD. What are your thoughts on that?

Well, it certainly was my first thought. I really don't like these negative house curves that people use because they start at 75dB and then drop the upper end too much. To me, the standard target should rise unaltered until the crossover and then begin to raise down to about 30Hz and then flatten out. The simplest curve there is, is a (0db at 80Hz and 5dB at 30Hz). Yeah, some people like to make that rise linear , and that's fine if you like that - but stay away from negative house curves. If you take away your house curve completely, your response is actually quite good on its own and it would be fine if the mains integrated well. You'll have to take a look at that when you add the mains.

Now, to do that, I need to increase my sweep up to what, about 300Hz? I'm assuming that I don't need to go up to 10,000Hz or anything as the subs are well out of range by that point; right?

No, do nothing different than when you measure the sub alone - except readjust your Check Levels routine. The area of interest is at the crossover (80Hz) and then an octave above and below that, so 200Hz upper axis is fine. Try to get the transition around the crossover as smooth as possible with the sub phase and a bit of sub distance trim if needed. If the sub began to rise after and below the crossover a bit down to your lower end, then all the better...

brucek