T-1030 bi-amp

[tvdantv]

I picked up a used T-1030 pair. I'd like to bi-amp them to make use of a 4-channel amp that I have availible. There is a sticker above the terminal cup that explains which terminals are for the mids/tweets, and which terminals are for the woofers. The sticker recommends that the operator's manual be referenced for bi-amping. I cannot find said manual online. I am currently running them w/ the shorting bars and all drivers function as they should.

The factory tag indicates that these are 8 ohm speakers.

I checked the impedence of the system w/ shorting bars in place. My multimeter reads 4 ohms. When I remove the shorting bars, the mid/tweet terminals read 'open', and the woofer terminals continue to read '4 ohms'. Can anyone expain why I have these readings?

I'm hesitant to attempt bi-amping when the mid-tweeter terminals read as 'open'.

Any advice out there?

Thanks.

[Gerry S]

The meter reads "open" because the signal being fed into the speakers is "dc" (or close to it). With the straps removed, the midrange/tweeter section has capacitors in the crossover to PREVENT low frequencies from reaching the drivers (or they will be easily fried). So, at LOW FREQUENCIES, it is "open". If you were to feed a musical signal, you will hear music (without bass)...obviously NOT "open".

The "nominal" impedance is 8 ohms (most of the frequency range), the "lowest" is 4 ohms in the bass section (the power hungry frequencies). "Bi-amping" permits using two "low-power" amps as opposed to a single humongous one before audible distortion sets in. When the woofer amp channel "clips" (runs out of power), any high-order/high frequency distortion generated by the clipped amp STAYS in the bass drivers, which by their very nature has trouble reproducing this distortion. If these same distortions were generated by a single amplifier, you would clearly hear them through the midrange/tweeter drivers...very unpleasant-sounding (and potentially dangerous to the midrange and tweeter)!

I personally would use a powered sub (I use a HSU product) to reproduce the power-hungry very low frequencies (80-100 hz) instead of bi-amping.

[tvdantv]

Thanks Gerry! I was on the phone w/ BA customer support when I noticed your reply. They were searching for an answer, but ended up forwarding my question to a guy in NJ. I'm curious to see his reply when he returns from lunch:)

If I can pick your brain one more time I'll ask "what would you do?"

This is for Home Theater. The listening position is 12ft from the TV, and my seat about 4 inches right-of-center. I watch a lot of concerts and musical performances. We also watch action/adventure movies. I do some critical listening, but not much anymore. The HT receiver is config'd so that the towers and center channel are crossed-over at 80Hz. The center is a modified T830. It is a custom cabinet that was made using a CNC router to perfectly match the face of a T830, but have the woofer enclosure fit into my TV stand. The main L/R are now T1030 and the surrounds are basic small Velodyne bookshelf speakers. The sub is an M&K MX-200 (dual push-pull 12" drivers). The HT receiver is config'd w/ gain settings to compensate for the differences in amplifier pwr.

Here are my amplifier options.

Option one: I can continue to drive the two towers w/ two channels of an Adcom GFA-2535 (no bi-amped). That gives me a very clean 60 wpc into 8 ohms. Channels three and four of the amp are bridged to provide 200 wpc to the center channel. The surrounds are driven by the HT receiver.

Option two: I can add a second GFA-2535 into the mix. Using the four channels to provide 60 wpc to each of the four inputs of the T1030 towers in bi-amp config. That's 60 wpc to each mid/tweet, and 60 wpc to each woofer set. Then use the other GFA-2535 with channels one and two driving the surrounds, and channels three and four bridged to provide 200 wpc to the center channel.

Option three: I also have a pair of Bryston 2B LP Pro amps that I can utilize. They are bridgeable to 200 wpc. If I do not bi-amp the T1030 set, I can put a bridged Bryston on each T1030 and use a GFA-2535 to drive the center (200 wpc) and surrounds (60 wpc).

Any input would be most helpful... I'm having a great time trying different options.

Thanks.

[Gerry S]

All seem very viable. Option two sounds ideal , if only because all amp channels are literally identical, and in phase with each other. And, there is sufficient power to drive everything even under "demanding" conditions.

In "home theater mode", the center channel is virtually "on" all the time, so a "large" speaker/amp configuration makes sense from a "clean acoustics" perspective. The T830 center-channel option is a good compromise between using a "small" speaker (which can distort at loud levels), and a third 1030 (which is overkill, IMO) !

In stereo mode, the 1030's do all the work, as they should. Bi-amping and subwoofer use is "optional"; audibly beneficial only under demanding circumstances. Bi-amping isn't "necessary" if you don't hear distortion at the playback levels you are comfortable with.

Normal -sized/conventionally configured amps are adequate for most program material. Virtually all "normal" listening is usually in the milli-watts/channel range, so even 60watts/ channel is a lot. Those "peaks" is where those extra watts come in handy. The use of a dedicated powered sub crossed over @ 80 Hz makes bi-amping less "necessary".

Adding bi-amping and subwoofers to a system that's "good" to start with is like adding turbocharging to a car under "performance conditions". In normal use, you don't need it. When needed, it's operation should be seamless (unnoticeable).

[tvdantv]

Thanks Gerry! This is very helpful.

To simplify follow-up posts I'll just concentrate on the L/C/R amplifier testing. Keep in mind that the MX-200 will always be 'in play'.

Here's what I tested last night:

Single 2-channel Bryston driving T1030 pair as L/R 60 wpc.

Bridged channels 3/4 of Adcom driving C 200 wpc.

Findings: The Bryston outperformed the Adcom in all aspects of musicality. It was hard to believe that I was listening to the same speakers (T1030) in the same room.

Next steps: Tonight I'll use a second Bryston to drive the center.

Question: Is is "better" to drive the center w/ one channel of the Bryston and leave the other channel not hooked up? When used w/ the other Bryston this provides 60 wpc to L/C/R. Or bridge the second Bryston to 200 wpc for the center which would result in 60/200/60 to L/C/R?

[Gerry S]

I've never been a big fan of bridging amplifiers. You do get more power, but at possible expense of higher distortion. A bridged amp is less tolerable of very low impedance loads; higher current requirements can limit what's "useable power" before audible distortion sets in.

In real world applications, the center channel loudspeaker is usually mostly dialog, and band-limited (no bass)...not all that demanding. Which is why the center channel speaker can be smaller than the main channels. The surround channels are rarely "on", and also usually band-limited . It's a rare movie where ALL channels are driven to "max" simultaneously. That's why those "auxiliary channels" can be smaller in output and still perform adequately.

It's been a while since I compared amps but remembered Adcom as a "good value" offering high instantaneous power briefly, while Bryston has high continuous power throughout the entire range, and at low impedances. The Bryston approach seems like a "no-compromise" approach, using "stiff" (heavier/costlier) power supplies.

200 watts seems a lot more powerful than 60 watts, but acoustically not THAT great...about 5-6 db?

[tvdantv]

I did extensive testing w/ movies today to see if bridging or bi-amping is warranted. A resounding NO!

The Brystons drive the T1030 set and the modified T830 center channel w/ ease and grace. During extended scenes w/ very demanding passages at high SPL there were no audible distoritions, no distortion warning lights, and no thermal issues.

During one especially demanding sequence all five of the 8" woofers appeared to approach max excursion (really cool to have an 8" woofer in a center channel do this). I increased the LFE x-over from 80Hz to 100Hz. This resulted in what I feel is a more exceptable margin for error. The MX-200 did not seem to mind the increase in duties.

I am extemely happy w/ the wide range of material that the T1030 excells at reproducing. Concerts sound like like I'm seated in front of the mixing board; Studio recordings, like I'm in front of the mixing console; and movies like I'm dead-center in a theater. I do find that sitting in my wife's seat is sub-optimal. They really do have a sweet spot (my seat). But this is really only an issue for material that does not utilize the center channel. The 'more forward' sound of the T830 pulls dialog straight to the screen.

I was a little concerned about not matching drivers across the entire front stage. But the two designs compliment each other very well in this application.