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#7726 - 01/06/03 07:31 PM L/R subwoofers with M22ti
joearch Offline
frequent flier

Registered: 10/08/02
Posts: 14
I recently purchased a pair of (identical) third party subwoofers, intending to pair them up with my Axiom M22ti fronts.

Denon USA's home theater FAQ tells me that if I tell my AVR-3802 that I have no subwoofer, and set only my left and right mains to "large", that all bass below the receiver's crossover setting is sent to the mains, from all channels including the .1 LFE. (See http://www.usa.denon.com/support/faqs_ht.asp#Q1.)

After I make these settings, it seems that I have two options:
1. Hook up each sub and M22ti using speaker-level connections, and turn the sub's crossover to highest setting (bypass).
2. Use the RCA connection from the L/R pre-amp outs to each sub. Set the crossover on the subs to somewhere around 60Hz, the bottom end of output from the M22ti.

Option 2 would obviously introduce some opportunity for either a hole or an undesirably strong response near the crossover frequency.

But would there be any advantages to option 2? Is there any reason I should consider it over using the subs' crossovers via speaker-level inputs?

Thanks,

Joe

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#7727 - 01/06/03 09:29 PM Re: L/R subwoofers with M22ti
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10395
Joe, you haven't described your subs and their input and output provisions, so it isn't clear why you're suggesting those two options. The Denon FAQ you reference certainly doesn't suggest that; it gives the advice, which is generally best, to set all speakers "small".

It would seem that a "Y" connector to the 3802 sub out should feed a sub cable to the line-level input of each sub. All speakers should be set"small" and fed with regular speaker wire from their respective terminals on the 3802. The 3802 crossover should then be set at 80hz and the sub crossovers bypassed if they have that provision, or if not, turned up to the max to be as far out of the way as possible.
_________________________
-----------------------------------

Enjoy the music, not the equipment.



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#7728 - 01/06/03 09:35 PM Re: L/R subwoofers with M22ti
joearch Offline
frequent flier

Registered: 10/08/02
Posts: 14
Hmmmm.... guess I should have slept on this one. Please let me know if I am starting to understand this any better.

1. When using the speaker-level connections, I would not set the sub crossover to bypass, but to where I actually want it to be -- say 60-80 Hz. Oops. I'd only set to bypass if I were letting the receiver divide up my signal.

2. Whether I send the signal to the subwoofer by high- or low-level, my mains end up with the same signal (with the assumptions of my original post.) The sub's crossover is only telling the *sub* where to jump in. It does NOT cut off any signal passed thru to the mains. Which is why I would want to set my sub's crossover where my mains start to roll off (on their own).

Sorry for the conversation with myself.... Any other feedback on setting up stereo subs with M22ti fronts and a Denon AVR-3802 would be much appreciated.



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#7729 - 01/06/03 09:55 PM Re: L/R subwoofers with M22ti
joearch Offline
frequent flier

Registered: 10/08/02
Posts: 14
John,

The subs are Atlantic Technology T70PBMs. They have high and low level ins and outs, and these specs:

Type/Features: Sealed Acoustic-Suspension Enclosure, Powered Subwoofer
Driver: 10" long-throw woofer, 2", 4 layer vented aluminum voice coil, vented motor system
Typical In-room Response: 25Hz - 125Hz ± 3dB
Amplifier Power: 125WRMS discrete linear Class A/B power amplifier
Amplifier Distortion: <0.025%
Low Pass: Variable 60-125Hz, 12dB/octave low pass output
Peak SPL: 102dB
Magnetic Shielding: Yes
Dimensions (W x H x D): 11.375 x 16.5 x 14.9in
Weight: 37.5lbs.
Power requirements: 110V AC 50/60Hz; 240 AC 50/60Hz

The receiver has 80/100/120 crossover settings.

What I'm trying to get here is some reinforcement of the M22ti low end for music -- preferably in stereo -- and introduce LFE to my home theater.

Thanks for your help.

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#7730 - 01/07/03 12:16 AM Re: L/R subwoofers with M22ti
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10395
Joe,I found time to read the T70.1 manual. There's differences of opinion on all of this, but here's mine:forget the "stereo" aspect of the low bass(although if you insist,the sub manual includes stereo type connections for two subs);many recordings don't have stereo low bass and below about 80hz no difference is audible anyway. So, arrange the two subs right next to each other in the same corner. Connect them as shown in example 1. of your sub manual: single sub cable from 3802 sub out to line in on closer sub, then "daisy chain" to 2nd sub from sub line out on 1st sub. Again, set 3802 crossover at 80hz and speakers "small". Since the subs have a bypass provision, use it.
_________________________
-----------------------------------

Enjoy the music, not the equipment.



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#7731 - 01/07/03 03:07 AM Re: L/R subwoofers with M22ti
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10395
Commenting on your previous questions: 1. Yes, if for some reason the speaker-level connections were used, the sub crossover would have to be used, not bypassed, because the speaker terminal outputs from the receiver send out a full-range signal, rather than one limited to below 80hz which would be sent out by the receiver sub out; 2. That's about right; the sub crossover doesn't take any of the low bass off the mains, and that's one of the problems. It's better if the receiver amplifier and the speakers are relieved of part of the bass burden by introducing the bass crossover in the receiver.
_________________________
-----------------------------------

Enjoy the music, not the equipment.



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#7732 - 01/08/03 08:48 AM Re: L/R subwoofers with M22ti
joearch Offline
frequent flier

Registered: 10/08/02
Posts: 14
Thanks for the advice, John. Part of the reason I ordered two subs was the rumored stereo effect. The other is my strange room layout, an L-shaped custom entertainment unit, with TV centered in the corner, and the short side of the L opening up to another room. The area encompassed by surrounds will be about 22'x22', but the room opens to others on three of those sides. The long side of the L is the only solid wall in the encompassed area.

So it may be crazy, but I was planning to place a sub next to each M22 left/right on the countertop of the unit. I'm hoping I might make up some of the bass loss from the bad placement by having the 2nd sub. Floor placement in the room is probably not in the cards, unfortunately.

I guess I'll end up following your suggestion, but I really want to give the stereo thing a shot. So here's another way I thought I might try:


Set all speakers to "small" except "large" mains at receiver.
Set sub mode to "LFE only" at receiver -- meaning only LFE signal goes to sub preamp out.
Set receiver crossover to lowest setting, 80 Hz. All non-LFE bass below 80 Hz is now sent to the mains.
Connect the mains directly to the receiver as the already are.
Since the subs each have L/R RCA inputs, pipe the preamp L/R to each respective sub, and the preamp sub out to both subs (or just one, depending on results).
Set crossover on the subs to 60 Hz, the lowest setting.

I guess this isn't much different than using the speaker level connections to the left and right sub without the receiver knowing about them. I would still have the problem of blending in with the M22s at 60 Hz. The differences I see are:
* Now the M22s are never sent any LFE signal
* Depending on how the processor sends LFE to the left/right channels when no subwoofer is known to it, I might get a relative boost in this new setup from sending a full LFE signal to each sub. This might allow me to back off the output of each sub for good blending at 60 Hz, while still giving me an appropriately loud effect during movies.
* If any part of the LFE signal is above 60 Hz, it would be cutoff. Is this likely to happen?

Thanks in advance for any advice or feedback.

P.S. Has anyone else tried a subwoofer at counter-height in a bookshelf unit with satisfactory results?

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#7733 - 01/08/03 09:31 AM Re: L/R subwoofers with M22ti
alan Offline
connoisseur

Registered: 01/29/02
Posts: 3188
Loc: Toronto/New York/Dwight
Hi Joearch,

There's certainly merit in using two subwoofers to improve and even out low-bass coverage in a large and problematic space. But as to the "rumored" stereo effect: You DO NOT lose stereo cues for low bass by using a single subwoofer fed by the LFE signal from your processor.

What no-one understands is that the directional cues for bass frequencies are supplied by the initial transient sounds that are much higher in frequency and are preserved by the left/right mains and surrounds.

For example, when a jazz bassist plucks the the string, or a percussionist hits a tympani, the "pluck" sound and the mallet hitting the drum skin is the transient that gives the deep bass energy its directional component. And those sounds are almost all in the midrange. So don't be concerned about "losing" directionality with deep bass by using a mono subwoofer feed.

And crossovers don't "cut off" as if sounds of a certain frequency fall off a cliff. They gradually lessen in intensity, determined by the slope of the crossover. The two slopes overlap each other.

Regards,
_________________________
Alan Lofft,
Axiom Resident Expert

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#7734 - 01/08/03 12:14 PM Re: L/R subwoofers with M22ti
joearch Offline
frequent flier

Registered: 10/08/02
Posts: 14
Thank you, Alan -- and let me say thanks again for the help you gave me on the phone some months back when I first put my system together.

I think I understand the crossover better now. Makes a lot more sense than clipping a signal. That 24db/octave spec now actually means something to me.

As to bass cues, I should have said I was looking for them to be enhanced somewhat, after reading some articles indexed at ecoustics.com that mentioned *feeling* (vs. hearing) a side-to-side pan in the very low frequency range. This is starting to seem like a pretty insignificant effect in the grand scheme of things, but I'll probably check it out anyway.

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