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Hello Shacksters!

I finally got my PC, soundcard, SPL meter, HT system, and REW all happily working together. I took a "baseline" measurement, then spent half a day tweaking levels and the Parametric EQs on my mains, and another set of measurements. Here is the "baseline" & "better but still needs help" All SPL chart:

zachsht-baseline_vs_current.png

I've attached my full .mdat file with the baseline measurement and a fairly comprehensive set of additional measurements (whole system, sub only, mains only, etc.) after my initial tuning session. I would greatly appreciate any and all assistance with:

a) sanity checking my measurements for validity. i.e. Is there anything in my .mdat to suggest any crossed wires, either in my connections or REW configuration? Pretty sure I've got it right, but just want to be sure.

b) analysis/interpretation. I understand the SPL/Frequency Response Chart, but am completely lost on how to interpret the myriad other charts and displays and plots. In particular, do any of the other charts/displays/plots suggest probable (or pinpoint definite?) causes of my "40Hz hump", or 83Hz to 96Hz valley-peak-valley, or ~ 144Hz plunge?

c) sanity check on my planned connections and settings for integrating an FBQ2496 to separately EQ my dedicated sub, and the powered subs in my towers.

d) advice on approach/process/technique for setting levels in my Processor/PreAmp, on my dedicated Sub, and the powered subs in my towers, relative to one other.

My measurement rig: Windows 7 PC w/ SoundBlaster X-Fi Fatal1ty, RS 33-2050 SPL Meter, REW 5.10beta7 w/ Java drivers (could not for the life of me get the output/input levels even close to matched with ASIO drivers), input channel Left, output left to splitter, to Pre-Amp and loopback to input channel Right for timing ref. signal.

A brief (or as much so as possible) run-down of the relevant bits of kit and their respective tune-ables:

Pre-amp/Controller: Parasound AVC-2500u (THX-Ultra)

- 2x Subwoofer outputs, monaural, duplicated signal (no independent level controls)
- +/- 16 dB level adjustments and Distance (delays) for each channel
- Calibration mic. & auto-calibration routine for both delays and levels
- Configurable Crossover points (low/high pass): 80/80, 1K/80, 40/40, 1k/40
- "Reinforced Bass"​
Mains: Snell XA 90ps Towers

- dual 10" subs with 300w subwoofer amp in each tower
- internal mid-to-sub crossover point and slope unknown, Manual states "Below 100Hz, a pair of 10-inch bass units provides bass to 32Hz (-3dB)."
- bi-wired (from Parasound HCA-2205AT)
- LFE input
- 1x single-band Parametric EQ built into the sub-amp on each tower, +/- 10 dB, 0.2 to 1.5 Octaves bandwidth, 30Hz to 100Hz frequency
- Boundary/Freestanding Bass Loading switch
- "Overall Bass Level" knob (min/max, no stated dB range)
- "LFE Level" knob (-12 to +3 dB range)
- "Cinema" and "Reference" Base Shape switch (via remote)
- +/- 6 dB bass level adjustment in 2dB steps via remote control (don't know if this persists between amp. power cycles)​
Sub: REL Britannia B1

- 300mm (~ 12") front-firing driver, "Balanced ARM loaded" cabinet, 120mm down-firing port
- 400W RMS amp
- 0dB, +12dB, and Balanced (XLR socket) "Lo" Level inputs
- High Level input (Neutrik Speakon connector)
- 4-position Mode switch for Phase (0/180 degress) and crossover engage/bypass for Lo Level input(s). High Level inputs are always routed through the crossover.
- Separate High and Lo Level input Gain controls, 80 dB range as per Owner's Manual
- 24 selectable roll-off frequencies, 22 to 95 Hz (12dB/Octave) plus 24dB/Octave fixed at 120Hz​

Primary system usage is HT, very little 2-channel listening.

The Snells are sweet, and I've adored them since the day I got them right around a decade ago... but they've never had enough punch in the very low bass region to suit my tastes for HT usage. I became a REL believer when I experienced the opening scene of Toy Story 2 on a pair of Studio III's with Wilson Audio X-1 Grand SLAMM mains and WATCH center/surrounds driven by Classé Omegas... but that is a different story (yes, it was a religious experience.) Anyhow I added the B1 a few years ago, and it absolutely rocks... but I know I have never gotten it and the Snells totally dialed together, as proven by my "baseline" REW Measurement above.

FBQ2496 Integration Plan

I've read up on how to connect a BFD, and a thread or two specifically on using one with a REL, and done a lot of thinking through how I should integrate one into my system. The best I've come up with:

  1. set the Parasound's crossover at the 1k low-pass/80 Hz high-pass setting, so I can use the REL [mostly] as it was designed and the Manual suggests... filling in the "sub-bass" that the mains simply cannot do. i.e. run the REL with the crossover engaged on the Lo Level input, to bring the REL's roll-off up to match where the Snell's response starts to drop off:
    zachsht-snells-only.png
  2. Set all 5 channels to "Small/THX" in the Parasound Bass Management menu (no sub-80Hz signal to the power amp/Main's speaker-level inputs, put it all through the subwoofer-outs for massaging by the BFD.)
  3. Parasound sub-out #1 to BFD Left Input, sub-out #2 to BFD Right Input, custom-made RCA to XLR cables.)
  4. Left BFD channel EQ'ing the REL, Right BFD channel EQ'ing the Snells (or vice versa):
    • BFD Left Balanced Output to REL Lo Level Balanced input with off-the-shelf XLR-XLR cable (no High Level input.)
    • BFD Right Balanced Output to LFE inputs on the Snells (custom XLR to RCA "Y" cable?)
Does anyone see any fatal flaws with this signal path, or inherent risk of "the dreaded BFD hum"?

My 40Hz Hump, my suspended floor, and my lousy room layout...

I spent a good chunk of a recent weekend connecting as per above (but without the BFD) and tweaking the REL's crossover point, levels on the REL and Snells, and the Snell's Parametric EQs and got things looking at least a wee bit better (ref. first Chart in this post) but obviously still have quite a ways to go. Managed to bring up the 50Hz to ~93Hz plummet, but couldn't do anything about the ~ 40Hz bump. Setting the REL's crossover to its lowest 22Hz setting and full -10dB attenuation at 40Hz on both Parametric EQs had no tangible effect. The 40Hz hump is exhibited by both the REL and the Snells when measured by themselves:

zachsht-40hzhump.png
zachsht-22hz_vs_95hz-rolloff.png

I do not know what to make of this or what to do about it. Is it a "room mode", or an effect caused by my room's floor: 60s-vintage hardwood flooring on suspended (hung joist) plywood, likely with no padding between the floor and substrate. The REL Owner's Manual contains a section that reads: "If the floor is an older, very 'springy' floor, spikes can be useful in reducing the influence of the REL on the floor. But better yet, a heavy stone slab placed under the REL will work better." Anyone here have any direct experience with the stone slab idea? Lots of threads on it here and elsewhere, and apparently just as many opinions.

Here is a dimensioned floor plan for my family room/kitchen "Great Room":

zachsht-great_room_floor_plan.PNG

Level Setting: Parasound vs. REL vs. Snells

As to where to go from here and what more I can do with the myriad remaining tweakables... I must confess my head is spinning as to where to start! I'm a ~ 20 year veteran Oracle DBA and UNIX SA and am no stranger to "System Tuning", but... I find my aptitude for tuning disk IO and complex queries isn't of much use in the realm of Acoustics, Impulse Responses, Phase, Room Modes, etc. I'm not so ignorant that I don't know the FIRST place to start is with speaker positioning, but my room size and layout (and 'domestic situation') rules out major repositioning and/or obtrusive acoustic treatments. So, my goal is to do the best I can with my current layout.

Do I start at the signal end with auto (or manual) calibration of delays and levels in the Parasound pre/pro, with everything "flat" or neutral in everything else, then move forward along the signal path from there?

Or at the transducer end with the REL's Crossover point, and Gain/Level knobs on the REL and Snells, and everything "flat" in the Parasound, and work backwards from there?

I've read Wayne's 'Gain Structure' thread but since all my equipment is consumer, not mixed consumer/professional, I'm struggling to wrap my brain around how to apply it to my setup.

Apologies for the lengthy post!

aTdHvAaNnKcSe

Zach Romans
 

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Welcome to the Forum, Zach!

b) analysis/interpretation. I understand the SPL/Frequency Response Chart, but am completely lost on how to interpret the myriad other charts and displays and plots. In particular, do any of the other charts/displays/plots suggest probable (or pinpoint definite?) causes of my "40Hz hump", or 83Hz to 96Hz valley-peak-valley, or ~ 144Hz plunge?
It’s just your typical room interaction with the low freq soundwaves. Other charts (like waterfalls) will show you the relation of frequency / decay times, but nothing is going to tell you specifically what's causing the modes.


I've read up on how to connect a BFD, and a thread or two specifically on using one with a REL, and done a lot of thinking through how I should integrate one into my system. The best I've come up with:

• Left BFD channel EQ'ing the REL, Right BFD channel EQ'ing the Snells (or vice versa):
• BFD Left Balanced Output to REL Lo Level Balanced input with off-the-shelf XLR-XLR cable (no High Level input.)
• BFD Right Balanced Output to LFE inputs on the Snells (custom XLR to RCA "Y" cable?)
It sounds like your Snell’s “subs” are fully independent of the rest of the speaker? If so you’ll probably get the best results just EQing them right along with the REL with a single set of filters. The experiences of others here has shown that trying to EQ different low frequency generators independently is exceedingly difficult: You’ll get a nice EQ curve for each one, but then when you fire them all up together, combined response is totally whacked. When you think about it, you what you hear is being generated by all subs in tandem. You can't tell one from another. So it makes sense to equalize them the same way – as a single entity.

To facilitate EQing both the Snells and the REL with a single BFD channel: When you send a signal to the input of say, the left channel, both outputs for that channel are then active. So, you can use say, the XLR output to your REL sub, and the 1/4” output to your Snells, with a "y" splitter.

I spent a good chunk of a recent weekend connecting as per above (but without the BFD) and tweaking the REL's crossover point... Managed to bring up the 50Hz to ~93Hz plummet, but couldn't do anything about the ~ 40Hz bump.

I do not know what to make of this or what to do about it.
The problem is that both the Snells and the REL are generating the 40 Hz peak. Using the Snells’ EQ takes it out of the Snells, but not the REL. It’s still putting it out.


I've read Wayne's 'Gain Structure' thread but since all my equipment is consumer, not mixed consumer/professional, I'm struggling to wrap my brain around how to apply it to my setup.
Good news – it doesn’t really apply to you. :D Your main issue is merely getting all your subs flattened out and blending nicely with your mains.


Do I start at the signal end with auto (or manual) calibration of delays and levels in the Parasound pre/pro, with everything "flat" or neutral in everything else, then move forward along the signal path from there?
I think perhaps you’re over-analyzing this. The EQ issue for the subs had nothing to do with system level calibration or delay settings.

Since you have the BFD, I’d just let it do all the EQ and not fool with the Snells’. This includes the boundary setting, it’s merely an EQ of some kind. I would suggest first level-matching (SPL) the Snell and REL subs by using a 40 Hz sine wave signal. Then run REW and equalize all the subs with a single set of filters. As part of that, you might experiment with a house curve. Once you're happy with the equalizing you can run the Parasound’s sub/mains calibration routine and set the speaker delays. You should be in business then. :T

Regards,
Wayne
 

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Hello Shacksters!

b) analysis/interpretation. I understand the SPL/Frequency Response Chart, but am completely lost on how to interpret the myriad other charts and displays and plots. In particular, do any of the other charts/displays/plots suggest probable (or pinpoint definite?) causes of my "40Hz hump", or 83Hz to 96Hz valley-peak-valley, or ~ 144Hz plunge?
Generally, one would use the decay, waterfall, and spectrogram to understand at what frequencies the system has extended decay time (which is the same thing as saying there is stored energy). Then to verify if it is some sort of "mode" you would dwell the sine wave generator at that frequency and walk around with an SPL meter (or the mic with the REW SPL meter) to figure out if it is an acoustical mode issue or something else. You would probably be able to tell it is your floor resonating if you touch it while dwelling at that frequency. If the floor is vibrating at that frequency, then you can feel the top of the subwoofer cabinet and if it isn't vibrating, then it is probably not mechanical transfer but being acoustically excited.

Managed to bring up the 50Hz to ~93Hz plummet, but couldn't do anything about the ~ 40Hz bump. Setting the REL's crossover to its lowest 22Hz setting and full -10dB attenuation at 40Hz on both Parametric EQs had no tangible effect.
You are going to want to have a careful read of the "minimum phase" page in the REW help. Then read it again until you think you understand it, maybe run some tests and read it again. Maybe you won't need as much repetition as I did though. :scratch:

The REL Owner's Manual contains a section that reads: "If the floor is an older, very 'springy' floor, spikes can be useful in reducing the influence of the REL on the floor. But better yet, a heavy stone slab placed under the REL will work better." Anyone here have any direct experience with the stone slab idea?
Experience isn't necessarily valuable unless it was coupled with decent measurements or blind auditioning - and both are rare in audiophile circles. IMO, the manual is wrong. The spikes might reduce coupling of the sub cabinet to the floor by supporting it only at positions that don't move as much, but the subwoofer will be attached to the floor (coupled) even more firmly than before spiking so there are competing factors as far as whether the situation might be helped. Adding mass can shift the frequency of a resonance, but isn't really an actual solution. If you have mechanical energy transfer then what is really needed is to decouple the sub cabinet from the floor, by using something like sorbothane feet properly rated for the static weight - though placing these at the corners does help in the same fashion as that portion of the spiking.

If the sub is well constructed, there shouldn't be a significant problem with mechanical energy transfer. IMO, much of the audiophile fascination with spiking is misguided - not that they don't have their uses, they just don't do what many of the explanations claim.

Here is a dimensioned floor plan for my family room/kitchen "Great Room":
I presume there is no acoustical treatment in the space. Also, are you trying to optimize the sound at one location and don't care about other locations? The best way to address issues varies depending on the "great sound at one location" versus "good sound at lots of locations" goals to some extent.

I note that your diagram shows you sitting against the rear wall. Often seating positions at boundaries or halfway between are troublesome with modes. One common starting point is to move your listening position to 38% of the wall-to-wall distance. It's by no means a hard and fast rule or universally helpful but it can be a start.

You may want to look up the papers on the Harman website by Welti and Devantier on subwoofer placement. They aren't the be-all and end-all (what is) but they might kickstart your thinking and they are free.
 

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I would greatly appreciate any and all assistance with:
a) ...
b) ...
c) ...
d) ...
Not exactly what you ask for, but maybe this will also be helpful:
[There are lots of options for this type of setup and good results are probably possible with several approaches. ]

The process that I think is most likely to lead to good results would be:

> Set 80/80 in the AVR [The LP/HP XO filters will then be well aligned for sure.]
> Set the B1 “24dB/Octave fixed at 120Hz” [Optional - but will assure no leakage into the midrange. Also the B1 phase setting should be 0 deg.]
> Set the starting B1 level closer to the Snell SW level [about -8 or -8.5 lower than current measurement]
> Set the relative delays of the SWs so they are in phase. [You used the loopback timing reference in this measurement set so the current relative delay can be seen. The B1/Snell SW IRs shows the delay difference to be 2.69 ms or 3.0 ft. This is about 60 deg out of phase from 50-100 Hz; not too bad, but could be better. The B1 is actually arriving before the Snell SWs even though it is physically behind the Snells. Was there a delay in the Snell SW’s signal path that was bypassed when the B1 was measured? You can align the SW relative delay using the BFD if you like.]
> Measure the time aligned SWs together vs. the main speakers and time align them properly. [either the AVR distance settings or the BFD delays can be used. The SW to main speaker time alignment procedures are a larger subject that can be addressed when you’re ready, that is, if you are not already familiar with one of them. The auto distance system in the AVR may be fine for this purpose, but I suggest you confirm the result.]
> Measure SWs together, find the EQ filters to match to your house curve and send them into BFD. [If you decided to add a relative delay to B1 vs. Snell SWs to time align them using the BFD, you would then need to use 2 channels on the BFD. You would set the 2 sets of EQ filters alike.]
> Match the SWs and main speaker levels for a smooth transition.

B1 and Snell SW IRs:
[Both offset the same 37.4 ms to place them near 0 so the relative phase can also be seen.]:
impulse.jpg

B1 and Snell SW Phase Comparison: after offset:
[Both offset the same 37.4 ms to place them near 0 so the relative phase can also be seen.]:

phase.jpg

This degree of care may not be needed to reach satisfactory results, but it sounds like you want to go through this very carefully to learn and to have confidence that you have everything setup just right.
 
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