active crossovers to bi-amp Ascend CMT 340 SEs - AVS Forum
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Old 10-14-2011, 03:20 PM - Thread Starter
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My bedroom stereo system consists of a pair of Ascend Acoustics CMT-340SEs being driven by an Emotiva XDA-1 preamp/DAC and Emo UPA-2 power amp. (All sources are digital). I also have an Outlaw LFM-1 EX sub. The power amp is connected to the sub's speaker-level inputs, and the mains are connected to the sub's speaker-level outs. As you might guess, the system is used primarily for music, although I do use it occasionally for movies (I'd say 70/30).

For a long time I've been thinking about buying an active crossover for the sub so that I can avoid sending unnecessary low frequency signal to the mains, and I'm about to pull the trigger on a dbx 234. But I also have this nagging desire to bi-amp the speakers at some point in the future (either with another UPA-2, or more likely I'd get rid of the UPA-2 and upgrade to the XPA series which has balanced circuitry). Knowing that I'll probably bi-amp down the road, I'm thinking that I ought to buy an active cross-over that is good for more than just sending the low frequencies to a sub.

With this in mind, I'm wondering if the dbx 234, which uses 24 dB/octave L-R filters, is a poor choice? I don't know what the optimal slope is for the tweeter/woofer crossover in my Ascends, but my thinking is that it'd be good to get a crossover that can vary the slope in case 24 dB/octave is suboptimal.

Is this something that I should be concerned about and paying attention to, or am I allowing myself to get spun up over nothing? Has anyone out there ever bi-amped CMT-340 SEs, and if so what sort of filters worked best for you?

Thanks for any suggestions!

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Old 10-14-2011, 04:55 PM
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You should call or email Dave at Ascend and discuss this.

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Old 10-14-2011, 06:38 PM - Thread Starter
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Originally Posted by cschang View Post

You should call or email Dave at Ascend and discuss this.

Thanks Curtis -- I just sent an email to Ascend tech support (presumably it'll get to Dave).

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Old 10-19-2011, 10:14 AM - Thread Starter
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Originally Posted by cschang View Post

You should call or email Dave at Ascend and discuss this.

I got a reply from Dave at Ascend and thought I'd share it in case anyone out there has a similar question in the future.

------------

Thanks for the inquiry!

>For a long time I've been thinking about buying an active crossover for the sub so that I can avoid sending unnecessary low frequency signal to the mains, and I'm about to pull the trigger on a dbx 234

This would be beneficial and will improve the overall performance of the entire system.

>But I also have this nagging desire to bi-amp the Ascends at some point in the future (either with another UPA-2, or more likely I'd get rid of the UPA-2 and upgrade to the XPA series which has balanced circuitry). Knowing that I'll probably bi-amp down the road, I'm thinking that I ought to buy an active crossover that is good for more than just sending the low frequencies to a sub. With this in mind, I'm wondering if the dbx 234, which uses 24 dB/octave L-R filters, is a poor choice? Is there a better filter type or slope to crossover the tweeters and woofers in the CMT 340SEs? Besides the dbx 234, I've been looking at the Ashly xr-2001, which I believe has variable slope filters, but it costs $200 more, and I'd like to save that money if I can.

OK -- now this is not possible. The CMT-340 can indeed be passively bi-amped. This means that you can connect a power amp to the tweeter input and another amplifier to the woofer input. However, you CAN NOT bypass the internal crossover of the speaker. A crossover like the one in the CMT-340 is far more complex than high pass and low pass filters... It contains various impedance compensation networks, padding and shaping networks and baffle compensation. If it were possible to bypass the internal filters and simply run active filters to the tweeter and woofers, performance would be greatly compromised as you would not be able to replicate the precise transfer functions of the crossover.

Hope this helps and take care!

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Old 10-19-2011, 01:50 PM
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.............the mains are connected to the sub's speaker-level outs.

For a long time I've been thinking about buying an active crossover for the sub so that I can avoid sending unnecessary low frequency signal to the mains..........

I assume that you are certain that the sub's speaker-level outs are not high-passed, huh?

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Old 10-19-2011, 02:23 PM - Thread Starter
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Originally Posted by sivadselim View Post

I assume that you are certain that the sub's speaker-level outs are not high-passed, huh?

I'm not certain, but the following specs are from Outlaw's website, and specifically mention a "low pass network." (Also, sound appears to gradually roll off the mains as I play test tones, rather than any sharp break at the bass's crossover frequency.)



LFM-1 EX Specifications
Driver Type: Down Firing, 12" Long-throw Woofer
Ports: Dual
Amplifier Power Rating: 350WRMS; 1300W peak
Frequency Response:
one port plugged:
16Hz. -180Hz. +/- 2 dB
no ports plugged:
22Hz. -180Hz. +/- 2 dB
Crossover Type: Linkwitz-Reily 4th Order Low Pass Network
Crossover Frequency: 30Hz to 180Hz and Bypass
Phase: 0 to 180 Degrees
SPL: 118dB (subject to placement and room gain)
Dimensions: (HxWxD) 22.75" x 17" x 24 "
Weight: 80 lbs

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Old 10-19-2011, 03:06 PM
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Quote:
Originally Posted by Thunder240 View Post

I'm not certain, but the following specs are from Outlaw's website, and specifically mention a "low pass network." (Also, sound appears to gradually roll off the mains as I play test tones, rather than any sharp break at the bass's crossover frequency.)



LFM-1 EX Specifications
Driver Type: Down Firing, 12" Long-throw Woofer
Ports: Dual
Amplifier Power Rating: 350WRMS; 1300W peak
Frequency Response:
one port plugged:
16Hz. -180Hz. +/- 2 dB
no ports plugged:
22Hz. -180Hz. +/- 2 dB
Crossover Type: Linkwitz-Reily 4th Order Low Pass Network
Crossover Frequency: 30Hz to 180Hz and Bypass
Phase: 0 to 180 Degrees
SPL: 118dB (subject to placement and room gain)
Dimensions: (HxWxD) 22.75" x 17" x 24 "
Weight: 80 lbs

Yeah, I looked on the website and downloaded the manual. It's not clear whether the sub's speaker-level outputs are high-passed or not. This varies from manufacturer to manufacturer. Some are, some aren't.

Simply listening to the way test tones behave to try and discern the answer will be difficult if not impossible. Our ears'/mind's perception of output levels at different frequencies as well as the effect of the room upon those levels will complicate this sort of listening test. And even if there is a high-pass filter, the roll-off will still be gradual (not a "sharp break") as the high-pass filter will have an associated slope. And, if there is a high-pass filter, it is very likely that the roll-off and frequency at which that starts may well be very similar to the speakers' own natural roll-off.

At the very least you would want to measure (identically) and graph the behavior of the tones coming from the speakers when they are connected directly to your amplifier versus when connected to the sub to see if there is a clear and definitive difference. But I would just contact Outlaw if I were you, especially since this is particularly relevant to your setup and indicated intentions.

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Old 10-20-2011, 09:10 AM - Thread Starter
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Originally Posted by sivadselim View Post

But I would just contact Outlaw if I were you, especially since this is particularly relevant to your setup and indicated intentions.

I just heard back from Outlaw tech support -- no high pass filtering. Based on all of this, I think I'm going to buy a dbx 223. No need for a 3 way crossover since I can't disable the built-in crossover in the mains for active biamping.

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Old 10-20-2011, 10:41 AM
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Consider the miniDSP for about the same price. With REW and a mic, you could also EQ your sub with it.

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