Crossover settings for my home theater.... (1 Viewer)

[Aaron E. Smith]

Ok, those of you who have read my messages are probably familiar with some of my equipment choices and tinkering, but I'll go over the whole enchilada to try to be clear. I use a Lexicon DC-1 with four Adcom GFA-555's (200WPCx2 each). My speakers are a Vandersteen VCC-1 for my center, Vandy 3's for my fronts, the side and rear pairs are Vandy 2Ci's and I've recently received my SVS 16-46CS.
So what is my quandary? Well, I used to have my Lexicon all set for LARGE speakers (except the center) with a 40Hz crossover to my old sub (a Hsu). I had done this because the Vandy manuals claim response down to 30Hz for the Vandy 3's and 32Hz for the Vandy 2Ci's, so the LARGE setting and 40Hz crossover seemed well withing reason.
Now on to the problem. Last fall I had been doing a demo for my brother-in-law. I turned on the equipment, popped in a DVD and started to raise the volume to listening level. This is when I noticed my darling little doggy chewing on the couch. I shooed him away, only to realize that I had left my finger on the 'up volume' button. Unfortunately, the DVD I popped into the player had one of those studio promotion segments that boots up automatically and it came on at a very high volume (something like +6db on what was already a loudly mastered opening). Well, I immediately ruptured a woofer and, thinking this was the only problem, removed it and sent it to Vandersteen for a repair.
A few months later I noticed that there was something wrong with the sound. I began working to track down what it was (this is another story that I will relay sometime soon in a open letter to Vandersteen). Since I knew there was something wrong, probably related to the above incident, I decided I really needed to test out all of my speakers. Alas, I have sent three speakers back to Vandersteen and will be receiving these back soon.
So, I would like to minimize the chances of this happening again. I've changed the way the Lexicon is set for volume (and I'm a little more careful about just popping in a DVD), but I believe that reworking my crossover settings would help ensure nothing is damaged in the future.
I have considered leaving the speakers at LARGE and setting the sub to 80Hz, or I could set the speakers to SMALL with a 80Hz cutoff and also set the sub to 80Hz. I'm not sure if there is any technical difference between those two, does anyone know the DC-1 well enough to know? Also, what would you all recommend?
I'd like to strike a nice balance between reproducing accurate sound and making sure the speakers are not driven too hard. Thanks for any replies (and, of course, if you have any other questions, let me know)!
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- Aaron
"Some mornings, it's just not worth chewing through the leather straps"
-Emo Phillips

 

[Wayne A. Pflughaupt]

Aaron,
It is really not a good idea to use multiple full-range speakers in a home theater. Low frequencies coming from multiple sources causes a myriad of problems. It never gives smooth bass response, because the room modes are not excited in a linear fashion. Tom Nousaine has documented this in a number of articles for Audio magazine and other publications. Typically low frequency response is so bad with multiple full-range speakers that it cannot even be effectively equalized.
In addition, the half-way point between any two subs or other full-range speaker will behave like a boundary and cause cancellation at a specific distance-related frequency. A third sub or full-range speaker that is not exactly the same distance apart as the first two will display a null between the other two subs. Thus with three subs you will have cancellation at three specific frequencies. The problem compounds the more full-range speakers you add: Four subs positioned at unequal distances will deliver cancellation at six frequencies. Five subs will see cancellation at 10 separate frequencies. Six subs will display cancellation at an astounding 14 frequencies.
With corner placement a sub excites three room modes simultaneously and eliminates all nulls in response, which will result in the smoothest unequalized response. That’s why it is best to use only one sub, or if more than one, they should be in the same corner.
Setting your speakers to small, even if they can reproduce low frequencies, and letting the sub to the low-end work will give you the best sound, and will protect your Vandersteens from accidents at the same time. Win, win!
Regards,
Wayne A. Pflughaupt

 

[Aaron E. Smith]

Hi Wayne,
Thanks alot for the input, although I'm surprised by some of what you say. I've never heard of it being a disadvantage to have full-range speakers as surrounds, although I understand what you're saying about the bass information. I'd like to know more about this as well as get more feedback on my problem.
Anyone care to add?
Thanks again Wayne, very informative reply!
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- Aaron
"Some mornings, it's just not worth chewing through the leather straps"
-Emo Phillips

 

[Andrew Beacom]

Aaron,
I'm sure you'll get some Bass experts in here so I'll keep my answer simple. You have 2 SVS's in the house. They will take bass punishment better than a full range speaker. Try a higher crossover and use those dual 12" woof's.
If you wanted to pursue a flat room response and protect your SVS's from bottoming you might want to check out equalizers. I don't know the details but some equalizers let you protect your sub from bottoming on low frequecies at high SPL's.

 

[Bill Lucas]

While it is true that corner placement of a sub will excite 3 surfaces it is absolutely NOT true that corner placement will yield the smoothest response. The opposite is true. Corner placement guarantees that a serious hump will occur in bass response and will yield response that is not smooth. For smoothest response over the range of the sub, placement midway along a wall typically works best. Good luck.

 

[Wayne A. Pflughaupt]

Aaron,
There is nothing wrong with using full-range speakers for the rear. Just limit their low frequency output and let the sub do the work. As Andrew mentioned, the sub can take the punishment better. Actually, having full-range rears (and fronts, too) gives your speakers some extra headroom at those locations. The lows is many action movies is so intense it is the same as boosting an equalizer 15dB at 30Hz. In other words, if you filter the mains too high, the DVD’s high-level bass signal can effectively flatten out a crossover slope. In those instances, it helps to have a speaker that is rated to take some low frequency extension.
Bill,
In the June 1996 issue of Audio Tom Nousaine experimented using up to five subs in a home theater system, one at each main speaker location (which would put some of them midway between a corner and a wall like you recommend).
When the subs at main left, main right and center positions were measured individually, room response was abysmal. Response rose from the crossover point to 60-70Hz, then plunged 20dB to 40-50Hz, then rose 10dB to 30Hz, then fell rapidly. Response with this ragged curve was down 20dB at 20Hz from the 58Hz peak.
Numbers varied a little depending on which sub was being measured, but the basic large rise/huge hole/small rise/rapid roll-out response remained intact. Tests with combinations of two, three, four and five subs all yielded similar results. The ragged response was so bad not even an equalizer would have been able to correct it.
You are correct that corner placement will result in a serious hump. However, it is a single hump, therefore response is smooth, not ragged like the examples above. The hump generated by corner placement is easily corrected with a parametric equalizer, which will result in excellent response and extension. Taming the 40Hz hump in my two corner-placed subs resulted in smooth response to 25Hz, something I was never able to obtain when I had on sub in the corner and one somewhere else. Measured response of the "somewhere else" sub showed it fell like a brick below 40Hz.
Regards,
Wayne A. Pflughaupt
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My System
[Edited last by Wayne A. Pflughaupt on August 05, 2001 at 03:14 PM]

 

[John H]

Wayne,
I see a PCA on your equipment list. Do you use this on 5.1 movie material?
John
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Link Removed

 

[Wayne A. Pflughaupt]

I’m using at primarily as an electronic crossover. I guess you’re referring to the bass processing feature? I don’t use it for movies. Typically they have more than enough bass, and I don’t want to risk overdriving my subs.
It works good for bass-challenged material, like many rock CDs and TV programs. However, TV shows with badly EQ’d vocals (i.e., too much bass in them) can activate the processor and add an annoying rumble to the voice. So it’s a mixed bad. If it were remote controlled, I’d be a lot more inclined to use the bass processor.
Regards,
Wayne A. Pflughaupt
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[Chris PC]

Since I'm wandering through the area of bass management, I will poke my head in here. I want good bass response.
What about when you are using 2 stereo speakers like in the "OLD" days of regular full range stereo speakers? When I use speakers like that, one closer to a corner than the other, they seem ok. Does even using 2 full range speakers for stereo cause a similar ragged bass response (to a lesser degree I imagine)? I can understand how it might, as bass frequencies from different sources meet and cancel out or cause peaks due to their particular wavelengths, the room size and how and when they meet.
I have a pair of 2 way Boston Acoustics speakers. 1 inch tweeter and 8 inch woofer. on their own, even with a meager 50 watt per channel amplifier, the results are quite decent. Using a test tone generator on my PC, I heard down to 28 hz in my room. Thats pretty decent. my room of course, is anything but normal. In a concrete basement, 2 of the walls in this room are just cheap panelling. No concrete and no drywall. For this reason, i don't believe they act like true walls, in the sense of being boundaries which reflect all the bass. Go into an ajoining room, and you can hear bass quite well.
Anyways......my point is, I am experiencing horrible bass response right now. I was trying to use a new Mirage BPS-400 subwoofer with my system. Having no line-level outputs on the amp (NONE), I choose to borrow a Paradigm X-10. This accepts my speaker level output from my integrated amp and provides me with a line level bass signal to send to my subwoofer (the mirage has no speaker level inputs). The problem is, te X-10 has a 120 hz xover (high pass filter) with a shallow slope of 6 dB per octave. No matter what I do, the bass response is "Ragged". Thats the best way to describe it. I have used test tones and the amplitude (just what I hear, no conclusive measurements) goes UP and DOWN from 20 to 120 hz. I now have 4 drivers in the room producing bass and it just doesn't work right. I have tried to blend the subwoofer by playing with the level, the placement and the sub xover, but it doesn't help much at all. I can eliminate poor boomy sounds, but I'm left with HOLES. I can hear some great low end in there, but there is a lot that seems to be missing. I suspect that the 120hz high pass filter of 6dB per octave is causing the problem. Figure my Bostons are only down 6 dB at 60 hz! Even if I set the Mirage to 50hz, there is a HOLE or now, I realize its a bunch of holes.
Anyways. Thats my input in so far as ragged bass experience.
But what about regular full range stereo speakers? Can they be problematic in the same way as multiple subs or more than 2 full range speakers???
[Edited last by Chris PC on August 05, 2001 at 04:07 PM]

 

[Wayne A. Pflughaupt]

I was trying to use a new Mirage BPS-400 subwoofer with my system. Having no line-level outputs on the amp (NONE), I choose to borrow a Paradigm X-10. This accepts my speaker level output from my integrated amp and provides me with a line level bass signal to send to my subwoofer (the mirage has no speaker level inputs). The problem is, the X-10 has a 120 Hz x-over (high pass filter) with a shallow slope of 6 dB per octave. No matter what I do, the bass response is "Ragged".

So that’s what’s behind all those threads about rigging up out-board bass management!
Chris, I have the answer to your problems. What you need is an AudioControl Phase Coupled Activator III. Its primary function is a bass enhancement processor. However, it has a built-in programmable crossover with excellent 24dB/octave slopes and Linkwitz-Riley alignment. For your benefit, it can convert speaker level signals to line-level. You could send say, the “Speaker B” outputs from your integrated amp to the PCA III, and send its line-level sub out to your Mirage sub. (Of course, you would want to bypass the Mirage’s crossover, as the PCA-III’s is undoubtedly superior.) If that’s not possible, the PCA-III has a pass-through that will allow the L/R speakers to be connected directly to it. The stock crossover frequency setting is 90Hz, but you can buy or make a plug-in module for a frequency compatible with your Boston speakers.
I’ve been using a PCA-III for five or six years now. I got because I am using passive subs, and I wanted a better crossover than the 12dB/octave fare typical in most home theater gear.
The PCA-III lists for $299, but you can probably find one somewhere for $225-250. If you’re patient, you can occasionally find them on e-bay for no more than $150. Be sure and get the PCA-III, not the PCA-II or earlier model. I’m not sure if they have the crossover and line-level conversion.
Regards,
Wayne A. Pflughaupt
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My Equipment List

 

[Scott H]

Richard Vandersteen himself has said in an interview regarding home theater sound (Widescreen V5, N4, I21) that the ideal system would be made up of full range speakers for each channel. He also stated that he does not advocate the use of a single sub in any case, instead implementing two (stereo front L/R) to five (for 5 channel, re-directing the LF to those channels) if required. Like many others he is not a fan of the .1 channel.
Nonetheless, if I had the Vandy's you have, I would not use a sub.
Also, introducing equalization effects time and phase (in nearly every case).
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[Aaron E. Smith]

Well, this has been an interesting read, although I'm still sort of confused what I should do? I'm thinking at this point that the rear and sides will both be set to Small (80Hz), the sub will have an 80Hz crossover, and the center will be set to Small (120Hz). In re: to the fronts, I'm still not sure if they should be set to Large or Small. It is interesting to read the different philosophies of TN and RV. It seems that they differ markedly and I'm not sure which would be better for my system. To set my Vandy 3's to small seems like a waste--those speakers are capable of more. But to put too much oomph into them seems both ill-advised (as per Wayne's rec.) and, perhaps, a tad dangerous (for the speaker).
Andrew had mentioned using an external crossover (I've saved the link, thanks Andrew). I might go that route eventually, although at the moment money is tight.
Anyone have any other input? Am I on track with my thinking here?
About not using a sub with the Vandersteens, I would reply to that on two points:
1. Even the Vandy 3's are limited to something like 32Hz. That means that, even on paper, anything below that would either be eliminated or could damage the speaker. Unless I were to use Vandy 5's, I would really need a sub to reach down low.
2. While I admire the Vandy's (I should hope so since I own a bunch) I find Vandersteen's claim to go down to 32Hz to be very hard to believe. Having used these speakers in the "real world" (eg- my living room), I would argue that for these speakers to go down that low at anything more than infrequently at very light volume is asking to have a large repair bill. I simply don't see the Vandy's as handling the punishment that freqs. that low would dish out.
For those reasons above I think that a sub is really necessary. However, I would admit that a system of Vandy 5's really would not need a sub..... but I'll need to hit the lotto to get those!
Thanks again for any responses and info.!
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- Aaron
"Some mornings, it's just not worth chewing through the leather straps"
-Emo Phillips

 

[Scott H]

Well, to be honest with you, my preference would be not to have Vandys for HT, though I'm a big fan of them for two channel music systems. One of the reasons I wouldn't select them for HT is what you are dealing with now (and cost). They are full range speakers, and though I would likely never use a sub in a two channel system I would in an HT system, both because the program material calls for it and because it is economical to use one with affordable quality monitor speakers to great effect. I would also point out that both the 3A and 2Ci have frenquency response down to 26Hz (10" active acoustic coupler operates 26-35Hz). That will not produce the 'thump' of a sub, but it's presence it discernable. Without a sub in that room of yours, you sure have a lot of drivers, including four 10" ones (though of course a sub may perform much better in the 'thump' department).
I do not subscribe to two full range speakers negatively effecting bass in a properly configurated two channel system, and do strongly prefer full range speakers for that application. In twenty years of listening to many esoteric two channel setups I have never prefered the implementation of a sub in a music system to having great two full range speakers.
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My DVD Library
Runaway production? No thanks. Where I've filmed, benefiting local economies: AL, CA, ID, IL, IN, IA, KS, MN, MO, MT, NV, OH, OR, TX, WA, WY.

 

[Andrew Beacom]

>>While I admire the Vandy's (I should hope so since I own a bunch) I find Vandersteen's claim to go down to 32Hz to be very hard to believe. Having used these speakers in the "real world" (eg- my living room), I would argue that for these speakers to go down that low at anything more than infrequently at very light volume is asking to have a large repair bill.

 

[Drew Eckhardt]

I'm running a Lexicon DC-1 DTS v4, stack of 4 Adcom 545ii power amplifiers, Definitive BP8 front+side speakers, C1 center, BP1 rears, BFD, and a Citation 7.4 subwoofer.
That said,
1. The Lexicon processors do bass management differently. Perhaps most notable is that they send the .1 channel above the subwoofer cross-over to other speakers. I don't know how "other speakers" are determined, although historic belief that Bass Enhance increases bass and/or redirects to the side speakers is incorrect (the speakers getting the bass and levels are unchanged, BE merely applies a phase shift to monural low frequencies).
This can make the amplification/power handling/extension requirements for "full-range" (or Small 40Hz ) speakers somewhat higher than with other processors.
If you want to run your speakers full-range and just use the sub for LFE, set the sub cross-over to OFF and sub level to OFF in all of the PCM modes (where the low-pass sub cross over is applied to a full-range sumation of the left and right channels) although this still isn't a good idea because
2. Excursion increases as frequency decreases, especially in ported enclosures below the tuning frequency. While a speaker may be flat down to some frequency, it can (will) still be physically unable to move far enough to play low frequencies at high volumes.
This affects both main speakers and subwoofers, where you may need to set the peak limiter artificially low to avoid bottoming on subsonics if you don't run an external high pass filter on the sub-woofer (commercial powered subwoofers do this; generic power amplifiers with unpowered subs don't).
3. There's more to bass than volume and measurements. While I get deeper, louder, more musical bass with corner loading, I have more slam and articulate bass with the sub moved a couple feet in from the corner (even with the left main). On some recordings, I also get more natural bass (less inside-the-head seems to be an agreable description) with less slam and impact running a pair of speakers high passed at 40Hz (especially with Bass Enhance).
4. If you're not running sealed speakers with a natural roll-off frequency matching the cross-over, extension an octave below the cross-over frequency (40Hz for an 80Hz cross-over) gets smoother integration between mains and sub.
To go back to the original question:
Large/80 on a Lexicon will send full-range channels to the main speakers, duplicate bass below 80Hz on the sub output in PCM modes, and in discrete modes send bass below 80Hz to the sub and bass above to the main speakers.
Small/80 will send full-range channels down to 80Hz to the main speakers, LFE above 80Hz to the mains, and the rest to the sub.
I'd probably try small/40 on the fronts, small/40 and small/80 on the sides+rears, small/80 on the center, and 40 on the sub or 80 on the sub with it turned off in the PCM modes.
I'd also watch what I was doing with the volume control. With a normal input and anything but sound reinforcement or horn loaded speakers +12dB is likely to clip the amplifiers.
[Edited last by Drew Eckhardt on August 08, 2001 at 09:51 PM]
[Edited last by Drew Eckhardt on August 08, 2001 at 10:06 PM]

 

[Aaron E. Smith]

Andrew, thanks again for another slice 'o' help. I'll check that link right now!
Drew, thanks for the indepth and informative response. I'll try some of your suggestions and report back my findings. I just got back repaired speakers today, so this should be fun (and time consuming).
Thanks again!!!
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- Aaron
"Some mornings, it's just not worth chewing through the leather straps"
-Emo Phillips