[jmprader]

James (or any of you other technically saavy people):

I have an SP1.7, PMC IB1s's and an older HSU 12va sub, soon to be replaced with HO turbos.  I plan to colocate the new subs to gain some additional headroom at the bottom end.  They will be about two feet behind the front PMC's.  I specify all 5 IB1's as large on the 1.7.

Though not technically adept, I think I understand the 24db/octave xover in the PMC's creates a timing difference in the woofer signal vesus the mid/tweeter.  

I'm not sure what, if any delay the 1.7 induces on the sub signal.

I am interested in understanding what phase/timing interactions issues I might have running my IB1's and the colocated subs.  

Without getting into specifics of my room and precise speaker locations, should there be general consideration given to the "distance to listening position" adjustment on the 1.7 to account for differences in the woofer/subwoofer timing due to the crossovers...or is my presumed issue much ado about nothing?

If there are further issues when tossing in a Behringer unit for eq'ing the subs, an additional general caveat would be great there, too.

Thanks for any help.

[jethro]

jmpreader,

FOr 5.1 channel listening, with all of your IB1's set to large, no signal will be going to your subs. I would just set the sub xover to around 120 hz. I think you enter a distance to each speaker including the sub to adjust for slight delays. I don't know what you do with two subs to account for distance. A lot of people don't recommend an even number of subs for the LFE channel due to cancellation.

If you plan to use the subs only to lower the bottom end of your L&R IB-1's then  there are a number of ways to set this up. Even without knowing your setup, I personally think that this type of setup will ruin the tight bass of the IB-1's. I have an SVS Passive Ultra sub (powered by an 4B-ST) as my LFE and it stands out like a sore thumb.

Perhaps you could give us a better idea on what you want to achieve with this setup so we can fill in some details.

[ec]

jmprader,

I run 2 pairs of colocated subs (4 passive SVS CS Ultras) behind my LR.  Although I use the smaller PMCs (TB2's) I did try running them large with the lower freqs crossed over using a Bryston 10B to a Velodyne Sub.  I went back with the 80Hz sub crossover for movies.  I don't think I ran into timing issues, the sound seemed blended very well.  I used freq sweeps and a good ol SPL meter.  There are devices that allow you to adjust phase externally when using passive subs like the SVS interface box.  I believe HSU makes something similar.

I am not sure what Behringer device you will be using but I am guessing it is the BFD 1124 or feedback destroyer.  Nice cheap and effective unit.  I used one for about a year.  I then moved to Symetrix 551E Parametric EQ and found it easier to dial in in real time because of the analog knobs.  I now do not use any external phase controls (ie SVS Interface box) and the sound still appears pretty seamless to myself and others.

[jmprader]

jmpreader,

FOr 5.1 channel listening, with all of your IB1's set to large, no signal will be going to your subs.

Jethro:

Thanks for your response and offer of more advice, I always have more questions!

A quick clarification based on your opening comment (above).  My 1.7 directs bass to the sub in 5.1 mode with mains/surrounds set to large.  I'm confused because I know you have significant knowledge and experience here...where is our gap?

I appreciate the clean, tight bottom of the IB1's for my 2 channel material and I wouldn't think of digital eq/bi-amping for anything other than the subs (working on some room treatments for room correction issues).

However, for 5.1 (HT, SACD and DVD-A) material, the LFE requirements are somewhat more than my IB1's are comfortable with.

I'm looking for educated hints on integration of the dual subs in a manner that they might augment the IB1's for 5.1 SACD and DVD-A reproduction (2 channel also=better).  If it's a can of worms, then I need to decide if it's better to designate the IB1's as small and let the subs handle SACD/DVD-A material vs running just the IB1's (unless its a gut-wrenching HT movie or "dance party" for my 40-50 something friends).

My purist side says be concerned about phase/timing relationships with the subs/IB1 woofers...worry about cancellations due to location and "muddying" things up...solve it with placement and sub-eq.  My practical side says it might just be trading off a bigger but muddier bottom to get more impact in the last half octave or so and tweaking til the cows come home.

Sorry for the long clarification and explanation, hope it's not too convoluted.

Cheers.

[jmprader]

jmprader,

I run 2 pairs of colocated subs (4 passive SVS CS Ultras) behind my LR.  Although I use the smaller PMCs (TB2's) I did try running them large with the lower freqs crossed over using a Bryston 10B to a Velodyne Sub.  I went back with the 80Hz sub crossover for movies.  I don't think I ran into timing issues, the sound seemed blended very well.  I used freq sweeps and a good ol SPL meter.  There are devices that allow you to adjust phase externally when using passive subs like the SVS interface b ...

EC:

Thank you for your response, too.  You've clearly got a lot of oomph in your bottom octaves and apparently little issue with FR overlap, which is probably my bigger issue...and...unfortunately, the new Hsu's will use a 0/180 phase switch, not a continuously variable control, hence my issue of looking at distance/colocation adjustments versus "another box" in an equipment ensemble I'd like to keep about where it is!  

Using my IB1's from 80-120hz up is an alternate solution if I don't get some positive feedback using the IB1's in an overlapping or very low xover configuration.  I'm hoping there might be some experience/advice  with integrating the great tight bass in the IB1's with some reasonably good quality subs that would result in some additives properties.

Thanks again for your input.

[ec]

However, for 5.1 (HT, SACD and DVD-A) material, the LFE requirements are somewhat more than my IB1's are comfortable with.

For HT material eg stuff that comes from the DVD player from a digital connection.  The SP 1.7 will handle the bass management.  For SACD and DVD-A, the SACD/DVD-A player has to handle the bass management.  There will be a set of similar settings on that player (eg large/small, xover, distance etc).

If I were you and I wish I were in your shoes (IB1's).  I would do the following:

DVD-A/SACD player: speakers set to large, sub yes, cross over 120
SP 1.7: speaker set to small, sub yes, cross over 80 Hz

IMHO, the music will be more seemless and you will get the bottom end for movies

The best way to determine if you have phasing issues etc is to get (or get someone) with the proper audio calibration equipment to do this.  Many use "ETF" which is a software based tool used on a notebook attached to a mic.  It would be difficult to give a "standard" answer since everybodys setup especially the room are quite different.

jmpreader,

FOr 5.1 channel listening, with all of your IB1's set to large, no signal will be going to your subs.

I don't want to put words in Jethro's mouth but what I think he means is that if you set all speakers to large (like in my DVD-A, SACD scenario above) and you are playing 5.0 material (ie no LFE recorded in the track) which is semi-common, the bass from any of the channels (eg LR) will not be redirected to the sub since the LR is running large ie full range.

[jmprader]

ec:

Thanks for your followup.  Of course you are correct on the DVD-A and SACD bass management, speaker size, distance and xover are adjusted at the source, not the 1.7, I should pay more attention to details to avoid creating my own confusion.  I do prefer the 1.7's HT slightly over the Denon 3910 for movies.

I'll give the higher x-overs a shot, although probably in a more comprehensive (translates to time consuming) effort using multiple x-overs/combinations/locations and calibration to see if I can get to a solution that addresses the various issues.  I don't have the full ETF program, but I think I can try several approaches with Eq Wizard, my Rat Shack meter and laptop/external soundcard...and probably learn a little in the process.  I know there are always compromises.

Hopefully I can do a couple of sets that narrow the field and avoid too much of a workout moving at least 4 75-100 lb boxes all over the place.

If I get desperate, I'll ask for some input on AVS and see if I can get some of the bassheads there to help without getting flamed in the process.

Thanks again for your response and input.

[jethro]

It was late when I wrote my response. My comment about no signal was referring to a 5.1 setup where only the LFE channel is physically fed into the sub(s). If you have all of your speakers set to large, then none of the signal going to the front left and right, center, and rears will go to the sub, however, the LFE channel will still go to the sub. Sorry I wasn't very clear.

I haven't experimented a whole lot with subs. I've never used more than one sub at a time.

I'm still not sure whether you want to use the subs to extend the frequency range of the front left and right IB-1's, boost the bass output of the front left and right IB-1's, boost the LFE channel (.1) alone, or to boost the low-end of all of your IB-1's, plus handle the LFE channel.

They all have problems. If you want to extend the reponse of your left and right fronts by collocating a sub with each IB-1 then you will need high quality crossover gear which actually has a flat response at low frequencies. A lot of crossovers only have a bandwidth of 15 Hz and higher (Bryston excepted).  You're not going to extend the frequency your system using in-expensive crossovers. You will also need a similar quality amplifier for your subs. If it's the amount of bass and not the extension, then perhaps an equalizer can be used to boost the signal going to the IB-1's, rather than adding a sub.

I think you would be more likely to have cancellation/re-inforcement problems if you use an even number of non-collocated subs to boost the LFE channel output.

I'm not sure how much the extra gear and subs will cost, but perhaps you should check to see how much the MB-2 would cost after selling your IB-1's to replace the front left and right. It would give you some more headroom in the bass regions and you would get the better midrange.

What amps are you using to drive your IB1's (just in case they are running out of gas) ? Are you using large gauge speaker cables ?

Hopefully I haven't confused you too much and made too many mistakes.

In my setup I run all of my speakers large (3 IB-1s, small B&W's for rears) and my passive svs ultra crossover at 120 Hz. My next sub will be a PMC XB-2 or an XB-3 if I win a lottery.

With all due respect to ec, I would never run my IB-1 crossed-over at 80 Hz. I've never heard any speaker come close to the IB-1 in the bass department, even at twice the cost. It would be a waste.

HTH

[jmprader]

Thanks for the clarification, we are on the same page in the 5.1 signal routing department.

Before the IB1's, I had dual subs (old mains lacked the IB-1's clean low bass output).  I had some success, with setting the lo pass in the sub to the 40-50 hz range and running the mains large.  It's conceptually more difficult with the IB1's because of their better bottom end, but I am hoping good integration can be accomplished with the new subs.  If two colocated subs don't cut it, one will head elsewhere.

In SACD/DVD-A and HT, the subs are going to do LFE duty.  The first two sources are where I expect to have more critical issues with distances/cancellations.  For CD's, if I detect degradation, I won't try to use the subs at all.

What I hope to find here at Audiocircle is not only anecdotal experience in a real world situation, but (and perhaps more important), some feedback from the Bryston/PMC gurus who can give some advice on the do's and dont's on sub/main integration with their products.  

For example, if the 24db/octave xover in the PMC's creates a time delay in the response of the woofer, and the subs are being fed with whatever slope filter the 1.7 applies, I'd want to make some adjustment for the subs in the distance setting to try and keep the timing of the arrival of sound from all bass drivers close to "equal" at my seating position.  Depending on induced delays, a sub collaocated with and IB1 woofer might have a different distance setting to compensate properly...or subs merely colocated with themselves might have an adjustment versus the IB1's depending on the xover characteristics and attendant "delay".  That's a mouthful, hope I explained it right.

As I noted to ec above, my other choice is to spend more time tinkering and "weight lifting", I'm just trying to get some educated hints on start point with what is know about the actual behavior of the electronic components involved in the Bryston PMC side (hence the post on this owner's circle!).
 
...and of course, if I'm way out in left field (and I'm beginning to think I just might be), I'll go concern myself with my room treatements project!

No problems on my mains amplification, Brystont 4&6B SST's and 12ga or better wire all around.  I can recall only a few cases where I saw the clip indicator flash...the wife was not home at those times.

Hey thanks again for helping drill down to the issue (or perceived issue).  Sorry for the tome and any typos!

[gaderson]

I've only got an SP1, and smallish speakers, so I run 'small' and enable the crossover in the 'bypass' mode to get nominal full range.  I have a sealed sub which are generally believed to be better/tighter for music.  Can you not do that with the 5.1 inputs on the SP1.7+?
 
To be surrounded by IB1s is also my dream, but, only if I first have a bigger room, and certainly a bigger budget.  I would think for DVD-A/SACD that all speakers 'to large' would be best; at least for those that actually use the '.1' channel for truly LFE.  And hopefully with acoustic music (aka Jazz, Classical, Bluegrass, etc), you shouldn't have to worry about them bottoming out.  The real question is for more 'modern' pop music (aka Pink Floyd, synth rock, techno, etc.)  The two to test this--ok what I would use to test--would be Pink Floyd "Dark Side of the Moon", and the Amon Tobin DVD-A for full range, full bandwidth surround sound.
 
Ultimately do to test, though I'd follow the other advice and for DD/DTS I'd go with the standard 'small' + sub, and adjust the cross-over to taste.  Since the IB1S is sold to studios I'd be interesting to see if JT can give us a few examples as to how these are set-up (the special cross-overs for the speakers are for big theaters so we'd want examples from mastering rooms for home play).

[ec]

JMprader.

Again it depends on your situation (namely environment room and listening preferences).  The first time I heard the IB1's was a friends house (Steven) about 2 years ago.  I was helping him dial in his SP 1.7, IB1s and Pioneer DV-47 (think that was the model) since he was not tech savy.  Because of WAF,  his single sub was located off to the side in a semi open room.  We tried the IB1s as large and at  sub xover of 120 Hz but he felt he wasn't getting enough bottom end "kick" for movies.  We then ran the IB1s as small with a cross over of 80Hz we used an SPL meter to get the right level.  He doesn't listen / watch movies at reference levels so the low bass is not as apparent.  I can't recall the scientific term for this.  They created loudness controls for this but I digress.   Still not enough kick for Steven. So we left the xover on the SP 1.7 at 80 Hz and the fronts set to small but boosted the sub about 4-6 db on the SP 1.7.  Steven was happy with this setup.  Some movies (Disney is notorious for this from my understanding) have a lot of bass extension recorded in the left and right channels.  When running the mains as large, you may lose some of this extension.  However, for the universal Pioneer player we set the speakers to large and sub xover at 120Hz.  Steven was pleased with the fidilety for MC music.

In terms of experimenting with the heavy lifting here is what I did based on my listening preferences.  My #1 priority is 2 ch audio, then HT then MC music.

So I placed my L & R in the most optimal place for 2 ch and then placed the remaining speakers in the most optimal spots for HT.  For the subs, I did experiement with two LFE's in each front corner with two more of the same subs (stereo) in front of the LFE ones.  After a while I went back to quad LFE's.  I wouldn't consider using an external xover unless it is of extreme high quality and has a very low crossover point so most of the bass is still handled by the IB1s and only anything below say 25-30 hz is directed to the subs.  The one benefit that many folks tout for redirected bass is that you can place your sub in an optimal position for bass whereas you can't do this for your L&R's.  I subscribe to this theory for HT but not for 2 ch.