To bi or not to bi?

[Hibernator69 47]

Bi-amp of course, lets keep it clean here now!

 

When I went from just my Denon AVR-3600 bi-wired to a setup where the Denon powered only the mid/upper dange and the TFM-15 handled the base I thought I was listening to the holy grail. Young kid, new dimension of sound, etc.

 

Now temporarily I've got my new VT-2 speakers hooked up to the new TFM-35. It feels like its not quite as nice, but it sure can play loud. Not as much base maybe, not sure exactly yet what it is.

 

The big question is:

 

If I bi-amp using the TFM-15 and the TFM-35 which should be for the bass and why?

 

In reality I'm also asking about this for when my M1.0s and M4.0 arrive.

 

I also have that BA A7200 available and have at times bi-amped the VT-2 speakers that way. This worked pretty well, but that takes away channels I need for my surrounds (and speaker building hobby/dreams, long story later ... Also kind of funny).

 

So, any though on whether to bi or not to bi with the big Carver monster amps and which ones should drive which range?

 

Hibernator

[cwad8505 102]

Bi-amp of course, lets keep it clean here now!When I went from just my Denon AVR-3600 bi-wired to a setup where the Denon powered only the mid/upper dange and the TFM-15 handled the base I thought I was listening to the holy grail. Young kid, new dimension of sound, etc.Now temporarily I've got my new VT-2 speakers hooked up to the new TFM-35. It feels like its not quite as nice, but it sure can play loud. Not as much base maybe, not sure exactly yet what it is.The big question is:If I bi-amp using the TFM-15 and the TFM-35 which should be for the bass and why?In reality I'm also asking about this for when my M1.0s and M4.0 arrive. I also have that BA A7200 available and have at times bi-amped the VT-2 speakers that way. This worked pretty well, but that takes away channels I need for my surrounds (and speaker building hobby/dreams, long story later ... Also kind of funny). So, any though on whether to bi or not to bi with the big Carver monster amps and which ones should drive which range?Hibernator

 

IMO, always go with the amp with more power on the lower frequency range.  Those frequencies require more power.  That being said, also, consideration should be placed on which amp you think sounds the best, for the fact that your mids and highs are what you can typically hear... My $.02.

Chris

[zumbini 6,150]

I wasn't familiar with the VT-2 so I read through the OWNER'S MANUAL.

Unfortunately NHT doesn't provide detailed driver specs so what follows is a best guess.

 

In general woofers need the most power (by a factor of 2), followed by mids, and then the tweeters. 

Of course there are exceptions, notably Carver AL's and AL-III's which are closer to 50/50 (ribbons/woofers).

 

I suggest you start with the TFM-35 driving the bass and the TFM-15 driving the mids/highs.

I suspect the TFM-15 will run out of gas 1st. If so perhaps a TFM-25 or 2nd 35 will be required.

Don't be afraid to try other amp/speaker combinations but be aware that the VT-2's are in the 4-6 ohm range

 

BTW - I use an M-500 for highs, and M-1.0t MKII opt002 for mids, and 2 M-500t's in mono for the subs.

I find them pretty well balanced when listening to blues or jazz but I could use more power to the subs for rock. 

[Hibernator69 47]

OK, more power for more air displacement generally speaking.

 

One thing I still can't get a straight answer on and NHT no longer supports this model for free (they said on phone we'd have to switch over to paid support if I wanted an answer) is this:

 

Crossover internally to sub is 125Hz, clear as day in the manual.

 

What happens when you biamp? Can you now send the sub something above that (say HT receiver set at 150 Hz for whatever reason)? Or will the sub signal still get "crossed" for anything over 125 Hz. Actually now that I think about it, thus probably affects the mud/high more as the surrounds (VS-2) which are identical to the mid/high section in the VT-2 can go down nicely to 80Hz.

 

This has pretty much always led me to set the Xover freq in the receiver as close to 125 Gz as it would let me. It just never passed my common sense test. P.s owner's manual? I thought that was just filing away somewhere, lol. NHT is pretty good with heritage info, but there very little inside info on any if their stuff unless you really scour the Internet and find a place like this forum. NHT used to run that forum, but it no longer exists sadly.

[DaveStL 85]

OK, more power for more air displacement generally speaking.

One thing I still can't get a straight answer on and NHT no longer supports this model for free (they said on phone we'd have to switch over to paid support if I wanted an answer) is this:

Crossover internally to sub is 125Hz, clear as day in the manual.

What happens when you biamp? Can you now send the sub something above that (say HT receiver set at 150 Hz for whatever reason)? Or will the sub signal still get "crossed" for anything over 125 Hz. Actually now that I think about it, thus probably affects the mud/high more as the surrounds (VS-2) which are identical to the mid/high section in the VT-2 can go down nicely to 80Hz.

 

From reading the manual, it appears that you can't defeat the crossover w/o opening up the speakers.  When you remove the jumper, the bass amp will be going through the low-pass filter to the subwoofer, and the mid-tweet amp will be going through the high pass.    The manual tells you to send an identical signal to both, because the internal crossover and drivers are matched for that.  So use amps w/ the same sensitivity on highs and lows, or you'll need to level-match w/ a volume control.  Somebody should have specs on the Carver amp sensitivities--they might well be the same.  The Sunfire theater amp channels all have the same sensitivity.

 

You can run the VT-2s full-range (on my Pioneer, I tell the receiver my front L/R are "Large") or you can unload some of the bass from your VT-2 by telling the receiver to cross over at whatever frequency it allows and send information below that to another sub on the LFE output.  If you do that, the power requirements of the VT-2 bass will be lower.

 

[zumbini 6,150]

....What happens when you biamp? Can you now send the sub something above that (say HT receiver set at 150 Hz for whatever reason)? Or will the sub signal still get "crossed" for anything over 125 Hz. Actually now that I think about it, thus probably affects the mud/high more as the surrounds (VS-2) which are identical to the mid/high section in the VT-2 can go down nicely to 80Hz ....

Hard to say with any certainty without seeing the passive crossover network or a schematic of it.

(My own 2-way Legacy Audio Super Satellites have 2 passive XO's tied together with jumpers.)

 

IIWY I'd use an active crossover between the bass and mids and keep the NHT mid/high passive intact.

That way any built-in passive EQ, peak limiting or frequency shelving engineered in by NHT stays intact. 

[Hibernator69 47]

I was trying to use the bass woofers as subwoofers, but now I think I understand.

 

If I want to use the bass section as subs I have to set the fronts to small and the crossover point to as close to 125 Hz as possible. Actually need to have the same 125 Hz for all speakers because of the internal circuits.

 

Will have to let the other stuff sink in for a bit before it all makes sense.

 

 

 

 

[DaveStL 85]

I was trying to use the bass woofers as subwoofers, but now I think I understand.

If I want to use the bass section as subs I have to set the fronts to small and the crossover point to as close to 125 Hz as possible. Actually need to have the same 125 Hz for all speakers because of the internal circuits.

Will have to let the other stuff sink in for a bit before it all makes sense.

 

Yeah, calling them woofers is probably more accurate, although 25 Hz is low for a full-range speaker.

 

A la zumbini, I pulled up the receiver manual:  http://data.manualslib.com/pdf/4/383/38289-denon/avr3600.pdf?3838aa56eab23eb7c66cbaf025c0141b

 

The AVR-3600 has a fixed crossover frequency for small speakers to a sub, at 80 Hz.  The manual mentions that Dolby AC-3 contains information in the LFE (the ".1") below 120 Hz, but that's not the most important thing here, esp. for stereo music.  If you run the fronts as small and split the the sub output to another amp and then to the two woofers, you'll be sending the mid/tweet a signal down to 80 Hz;  the speakers' internal high pass will block some of that, so you'll lose a lot between 80 Hz and 125 Hz.  If you want to biamp, the easiest solution is to run the fronts as large, split the front pre outs to separate power amps, and run a power amp channel to each of the speaker sections (a total of four), with the speaker jumpers removed.  This is called passive biamping (don't be confused by the reference in the NHT manual about making the sub active).  Then you would need a dedicated sub for the home-theater rumble. If you don't use a separate sub, set Subwoofer to "No"; I think in 5.1 mode this receiver will reroute the LFE to large fronts.

 

Actively biamping as zumbini describes (as I do) often gives a big improvement in detail.  You would need active line-level crossovers and would have to get into the speakers and bypass the woofer low-pass, and ideally part of the mid-tweet XO.  The mid-tweet could have been built a couple different ways, so that would require talking w/ NHT or figuring out the circuit.  I agree, it's probably better (and far easier) not to mess w/ the mid-tweet crossover.

 

Even if the receiver crossover frequency could be adjusted to 125 Hz, I think you'd still have a response dip because the crossovers aren't perfectly sharp--they have slopes, and you'd be stacking them.  The receiver XO could also cause more phase shift, which is beyond the scope of this discussion. 

 

There can be an issue running certain amps over a limited range.  There is a thread here somewhere on that; maybe someone else will chime in if it's going to be a problem w/ your amps.  I ran a pair of M1.5ts, and later a 1.5t and a 4.0t, in an active biamp configuration w/o any problems before moving to the Sunfire.

 

Stereo is so much simpler!  Unless we make it complicated.... 

[zumbini 6,150]

There can be an issue running certain amps over a limited range.  There is a thread here somewhere on that; maybe someone else will chime in if it's going to be a problem w/ your amps.

I think you are refering to locking an amp on the high rail. Here are a few quotes about the phenomenon:

 

....there is a frequency dependent phenomenon that is known to kill Carver amps in high demand ProSound applications.  Its an artifact of the commutation circuit failing to respond properly with HF bandwidth content.  When the Carvers rail hopping amps are used in bi-amped, tri-amped or quad-amped pro sound apps, the commutation circuits have been reported to get stuck on the high rails.  This runs the amp on the high voltage channels and induces rapid thermal wear.  The reports I've heard of have been primarily related to Carvers burning themselves out for no good reason while running the HF driver arrays in multi-amped setups.

 

OF course, the astute observer in you is going to ask, "Since there are so many of us bi-amping here, how come we never see this problem?"  Good question.  I think its related to the fact that in most of our bi-amping apps for the home, the amps just don't get driven as hard as pro sound amps that are pumping out high SPL for hours on end.   In an amp like the 1.5, it will produce over 100W @ 8R without ever commutating off of the low rail.  (P = V*V/R;  P = 35*35/8 = 150) 

 

When was the last time that you pumped over 100-150W into your tweeters?  Doesn't happen in the home but it happens all the time in pro sound applications.  In the home app there's rarely enough demand to force a HF amp to get off of the bottom rail.

 

 

Yes, Bob, we've discussed the commutator lockup problem previously.  IIRC, it happens when one amp only amplifies above 6.5kHz (I've actually seen the RC network on the board that does this).  Of course, you can change this by changing one of the components so the time constant is different, but I could cause some stability issues — I don't know.  Also, as you point out, pumping that much energy into your tweeter section is not something typically done in a home listening environment (my dogs would go crazy)....

[DaveStL 85]

 

 

 

There can be an issue running certain amps over a limited range.  There is a thread here somewhere on that; maybe someone else will chime in if it's going to be a problem w/ your amps.

I think you are refering to locking an amp on the high rail. Here are a few quotes about the phenomenon:

 

 

Yes, Bob, we've discussed the commutator lockup problem previously.  IIRC, it happens when one amp only amplifies above 6.5kHz (I've actually seen the RC network on the board that does this).

 

 

That's it!  Obviously not an issue here.