Active/Passive Bass Correction Dilema

Hey everyone!

I hope that a lot of you will share my feelings and hopefully some of you have been in my position before and can lend some advice for the situation.

I'm literally wringing my hands over active versus passive bass correction right now, and it's getting the old lady upset, saying such things as "Just buy the stuff and see what you think!" Now, she hasn't been told the cost of my proposed experiment, and I think she would change her tune if she were told.

The big picture: I'm set on buying a stereo pair of VMPS subwoofers to add to my current system (which you can check out by following the link to gain some perspective). I need some bass and sub-bass reinforcement, that much is certain. I'm currently an apartment dweller with limited choice of speaker placement and no dedicated room. In the modal frequencies (bass), I've always had issues with peaks and nulls, but it hasn't been too much of an issue. With the addition of these subwoofers, I know that's only going to increase, and there are a number of solutions that I'm rolling around in my head. Keep in mind I've passively treated the room as much as I can without tearing down the walls (the landlord wouldn't appreciate that).

Solution One: VMPS offers passive crossovers for their Dedicated Subwoofers. They offer a simple 90Hz low-pass filter at speaker level that gently rolls the main stereo speakers in. They also provide something of an L-Pad for adjusting main speaker level (I imagine to match the subs with the mains in terms of level). This solution would not require me to buy another amp(s), but offers no correction. This would be the cheapest solution.

Solution Two: Order the Dedicated Subs fully passive and use an active/external crossover such as the Behringer DCX2496 to route newly-crossed-over signals to the stereo and subwoofer amps. In this solution, I would have to use XLR-RCA cables, and basically convolute the desired "direct" approach I currently have of taking my analog signal direct from the DAC to the power amps. My biggest mental hurdle with this solution is that, while it seems like the best, I'm forced to re-sample either the analog source from the DAC (redundant), or downsample my 24/192 content via my transport and pass it digitally to the DCX. Outside of essentially downsampling expensive ($30/album), awesome, best-I've-heard 24/192 content to 24/96, the DCX has only XLR (AES/EBU) inputs for digital. My current setup supports only RCA digital. This solution seems to have no postivies, aside from it's best: infinite adjustability of crossover points/slopes to fine tune system balance. That part is attractive. Again, no correction here, but more granular crossover tuning is a plus.

Solution Three: This solution is somewhat of a compromise, but seems enticing on a few levels. Again, I start by ordering the Dedicated Subs fully passive. By using another Behringer product, the DEQ2496, I can daisy chain from my power amps at line level to the DEQ, and then to the sub amps. This is the only solution of the three that offers room correction, as the DEQ comes with an RTA/correction function that can be done with an external microphone. I would exclude anything above the modal frequencies from the correction (or anything below the sub's stated maximum frequenct range). This would take care of the sub's bass peaks/nulls at the listening position, but wouldn't take into account the main speaker's bass output. They would still be running full range, and if they are complicit in producing peaks/nulls, I wouldn't be able to correct them without routing the mains through the DEQ as well.

Keep in mind that my stereo speakers are -6db at around 38Hz in-room. I think it would be a bit different if I were dealing with a small monitor that lacked bass energy, but I think the fact that my towers are near full-range is what makes this complex for me.

I know that there are many more solutions to the problem (PARC, DSpeaker, etc.), but I'm trying to get out of this for under $2500.

Where are my bass gurus? I need a calming voice in my brainstorm; tell me you've been here before and it will all be OK!

Thanks all,
Ekwisnek, There are subs that do automatic correction with microphone. JL Audio Fathom is one of them. I found this on their website:

"When you add a subwoofer to a music system, you face two challenges: integrating the subwoofer into the room so it doesn’t excite standing waves, and integrating the outputs of your subwoofer and main speakers so the result sounds as if there’s a single speaker playing. Computers can help with both challenges. JLA subwoofers include Automatic Room Optimization (A.R.O.), a proprietary computer program that generates a series of tones that are picked up by a calibrated microphone (included). The software then adjusts the output of the subwoofer to best blend with the room, to minimize the most serious peak in the frequency response. Ideally, this gives the owner more flexibility in positioning the sub."

You could get used F113 for less than $2500.

Thanks for the response! I'm pretty set on having a stereo pair of subwoofers, but I do need to look deeper into on-board room correction...

First off, I urge you to visit the " Home Theater Shack " web site.
Go to the forum section and read up on all of the different sub woofers and bass management techniques.

Second, I highly recommend the Dayton Omni Mic Precision Measuring System to measure what is going on in your room while you make adjustments. ( was on sale for $250 )

Third, any corrections that you make will be cuts to the bass peaks, there is no filling in of nulls.
This is a manual operation, don't trust "Auto EQ".

The Behringer products are good bargains to experiment with, but you may notice a loss of dynamics.

You will want to use parametric EQ correction for the bass peaks.

There are 10 per channel in the DEQ2496
I think that the DCX2496 also offers parametric EQ depending on how much memory that is left after you set up the crossover points.
Another option is the DSP1124P and FBQ2496 feedback destroyers, they can each be manually set for parametric EQ but are A/D D/A, no straight digital.
If you need to convert from SPDIF (RCA) to AES/EBU (XLR) digital connections, the Behringer SRC2496 will convert the formats for you.

DEQ2496's go for around $250 used
SRC2496's are around $160 new on Ebay
FBQ2496's go for around $110 used
DSP1124P's go for around $80 used
DCX2496 I have never purchased

If you have never used any of the Behringer products before be prepaired for a learning curve.
IME, Audyssey Xt32 is hard to beat. This is full-range room correction and includes subwoofer x-over in the digital domain, so analog types may object. However, this system is very, very effective.

Refurb Integra 80.2 pre-pros, which are Xt32 equipped, are currently available for $1300.


PS. Your neighbors may object, too.
You could also approach the bass correction entirely in the analog domain.

Contact Marchand Electric about an active or passive analog 2 way crossover to insert before your amps.

Then use an analog 5 band parametric EQ for bass correction of the subs. ( Rane )

I can usually flatten out all peaks from 200Hz down to 20Hz with 3 - 4 parametric filters.

There is also free room measurement software available from Home Theater Shack if you become a member.

REW or Real EQ Wizard.

This software will interface with MIDI connections to the Behringer products.

Its a bit too much for me to digest and you do need some extra hardware to implement it.
I see an eviction and broken lease in your future.

Don't multiple subs, properly placed, actually help the standing wave issue?

Crossed over low enough, even a single sub, properly placed will simply disappear, unless you are in an authentically huge (cave or auditorium) space. Playing at the levels which would justify a PAIR of subs will get you evicted.....or hung in effigy by the neighbors.

You should immediately begin a campaign to convince them you are deaf.
I had an honest chuckle when I read your reply, Magfan!

The idea behind a pair of sub-woofers isn't output, but faithful reproduction of the source material. You wouldn't want to down-mix your stereo to mono and output it via one of your maggies, right? A lot of folks say that bass isn't directional (aka you can't verify direction, only amplitude), and to this point, I agree. What if, in mastering, the engineer mixes the kick drum heavy to the left channel? A mono sub won't give me the directional cues that a stereo pair might.

Thank you all for your suggestions, thus far. I literally have this cash burning a hole in my pocket; couple that with the need for bass, and we have a problem!
It's the Overtones and Harmonics which provide directional cues.

I doubt that with a single sub you'll be able to identify the direction from which the kick to the chest comes.

And speaking of downmixing, my understanding is that frequencies below about 80hz ARE mixed down...but that may be in error.

Sounds to me like you're gonna' need a decent attorney.

Again, if the space is large enough, some of the above goes on hold and double subs MAY provide some benefit...if only to mitigate standing wave issues and provide enough energy to excite a large vol.
Most pop recordings are mixed mono below 80 or 50 Hz. There's literally a switch for it on most mixing consoles. For minimally mic'd classical, that's not the case though. True stereo subs will give you an amazing increase in soundstage, low frequencies being one of the psychoacoustic triggers to clue our brains to venue/room size of the original space. Once you've heard that difference on a recording with true stereo bass you'll be an ardent believer! Not many recordings have stereo bass but when they do, oh baby!

The Behringer and other solutions are all valid so I'll let you compare the validity of those and suggest another possibility: Purchase the passive VMPS subs. Get a quality sub amp. Parts Express and many others offer them. Parts Express uses licensed technology "tracking downconverter" from Sunfire for $300 or $400. Get the dspeaker sub correction device from Highly reviewed in The Absolute Sound and many other places. Only $400 so you could get one for each sub if you have the budget. Corrects for time, phase, frequency, much more than even a parametric eq does, similar the Audyssey suggested by another, but only in the low frequencies and for much lower cost. You're not going to sacrifice any of your HDtracks 24/192 range at low frequencies with this device. When you're able to place the subs in the corners and then allow this to correct for time, phase, and frequency, the nulls become much less of a problem, especially at your prime listening position. You will essentially have near perfect bass response. Just adjust the crossover on the sub amp until there is no overlap. I'd start at 30 Hz with your speakers and inch up gradually until you have the right blend.