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Author Topic: 2 ohm loads on bottom end  (Read 19776 times)

Kevin Conlon

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Re: 2 ohm loads on bottom end
« Reply #20 on: August 24, 2016, 10:07:12 pm »

I have the really old 1980's , non-modern , very antiquated QSC 3800 amps for woofers(I dont do subs). Each channel is rated for a 2 ohm load. I have run the 3800's in bridged mono for many many years driving 4ohm woofer loads. Each channel is seeing a 2 ohm load or somewhere in the 2 ohm range. I never had a problem. The punch is incredible and the sound is great. I have know of Crowns to explode when driving a 2 ohm load. A friend was using Phase Linears to drive 4 ohm loads and kabloom ! It all depends on the amp and the QSC series 3 was overbuilt. I have heard the QSC 4050HD is a heavy duty amp. If it has thermal protection it will go into protect mode if it gets too hot.
I like old 80's stuff, most of it was overbuilt. That's why my BGWs still work and sound good doing it. This brings up another question. Are the MTL2B cabs subs or woofers? I think of anything below 40hz a sub. I cut mine off at 40/24db-oct. so am i using them as woofers or subs? I think of them as solid bottom end and pass the tops at 100-120 depending on the tops we use that day. EV says you can cross them at 160, i think that is more than i want them to produce. Tried it and did not think it was very clean. What is the best use of these mtl's, and don't say the scrap yard unless you can get good money for 180lbs of wood.  Thanks.
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Jeff Bankston

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Re: 2 ohm loads on bottom end
« Reply #21 on: August 24, 2016, 10:40:35 pm »

I like old 80's stuff, most of it was overbuilt. That's why my BGWs still work and sound good doing it. This brings up another question. Are the MTL2B cabs subs or woofers? I think of anything below 40hz a sub. I cut mine off at 40/24db-oct. so am i using them as woofers or subs? I think of them as solid bottom end and pass the tops at 100-120 depending on the tops we use that day. EV says you can cross them at 160, i think that is more than i want them to produce. Tried it and did not think it was very clean. What is the best use of these mtl's, and don't say the scrap yard unless you can get good money for 180lbs of wood.  Thanks.
I cross my mids and woofers at 130hz with a an Ashly XR1001(My Ashly XR4001 blew up) 24db/oct crossover. I have done listening test with others involved and 130HZ just sounds right. I have a 24db/oct low cut and roll off at 40hz since we dont have a 88 key keyboard.
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Kevin Conlon

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Re: 2 ohm loads on bottom end
« Reply #22 on: August 25, 2016, 12:09:37 am »

I cross my mids and woofers at 130hz with a an Ashly XR1001(My Ashly XR4001 blew up) 24db/oct crossover. I have done listening test with others involved and 130HZ just sounds right. I have a 24db/oct low cut and roll off at 40hz since we dont have a 88 key keyboard.
I use an xr2001 on my personal setup. When we use the mtl's for larger stuff it is with powered tops and the first dbx dsp. My own setup I cross mine at 100- 120 to 15's to 250, then 12's then horns. The keyboard player is sol if he/she wants anything down that low. Have no complaints about it yet.
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Ivan Beaver

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Re: 2 ohm loads on bottom end
« Reply #23 on: August 25, 2016, 07:39:39 am »

I cross my mids and woofers at 130hz with a an Ashly XR1001(My Ashly XR4001 blew up) 24db/oct crossover. I have done listening test with others involved and 130HZ just sounds right. I have a 24db/oct low cut and roll off at 40hz since we dont have a 88 key keyboard.
In most cases the ACOUSTICAL crossover is different than the ELECTRICAL.

It is for that reason that most "modern" systems do not use the same freq for high pass and low pass, since the loudspeakers are not flat across the entire band.

I know that is how most of the old analog xovers were (except the Crown units which offered independent freq control) and it was simple and easy to understand, but often resulted in a freq response that was less than optimal.

Of course this varies A LOT.
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Keith Broughton

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Re: 2 ohm loads on bottom end
« Reply #24 on: August 25, 2016, 09:04:56 am »

In most cases the ACOUSTICAL crossover is different than the ELECTRICAL.

It is for that reason that most "modern" systems do not use the same freq for high pass and low pass, since the loudspeakers are not flat across the entire band.

I know that is how most of the old analog xovers were (except the Crown units which offered independent freq control) and it was simple and easy to understand, but often resulted in a freq response that was less than optimal.

Of course this varies A LOT.
While Ivan is correct, and accurate crossover settings require a clear understanding and proper test equipment, if it sounds OK, go with it.:)
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Art Welter

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Re: 2 ohm loads on bottom end
« Reply #25 on: August 25, 2016, 09:55:36 am »

Are the MTL2B cabs subs or woofers? I think of anything below 40hz a sub. I cut mine off at 40/24db-oct. so am i using them as woofers or subs?
What is the best use of these mtl's, and don't say the scrap yard unless you can get good money for 180lbs of wood.  Thanks.
Kevin,
The definition of a "sub-woofer" is a woofer that goes below (sub, as in sub-basement) another. The other woofer can be of any size- 2" for home stereo or computer speakers can have a 4" sub- woofer.

Whether your sub-woofer is capable of low frequency extension at a level adequate for your needs is a question only you can answer. The MTL2B were OK when they were released, and are still fine now if you are happy with their LF corner, and the speakers are still in decent shape.

If SPL is not the primary concern, and you wished to extend lower than the present 37 Hz Fb, you could do the classic EV "step down" mode, reducing the port size to a  lower Fb, then apply LF EQ to bring up the reduced output level to "flat". As the stock cabinet response is already -3dB at 45 Hz, it needs +8 dB boost to bring 40 Hz to "flat", so doing a "step down" would only be advisable for stuff like bluegrass or acoustic jazz that does not require pants leg flapping 30 Hz response ;^).

And as far as the 2 ohm question, I'd never go on a gig with one amp and no spare, regardless of the impedance it drives. I have been running two ohm capable amps at two ohms (nominal) since around 1985, though unlike you, have rotated my stock to class D amps with far more power, far less weight that draw 1/2 the power per watt than amps available 31 years ago.

Of course, back then the Crest 5001 seemed like huge power and lightweight compared to a Macintosh 2300 from 42 years ago...

Cheers,
Art
« Last Edit: August 25, 2016, 10:04:17 am by Art Welter »
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Riley Casey

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Re: 2 ohm loads on bottom end
« Reply #26 on: August 25, 2016, 10:50:25 am »

Many sub makers make a point of bringing every driver in the box out to it's own set of pins on the input connector and its good practice to bring every sub cabinet back to the amp rack on it's own cable.  Don't parallel sub cabinets so that the 2 ohm load exists only at the back panel of the amp rack and is only dropped over the two feet or so of cable to the amp output connector.  On the other hand I've seen at least a couple of speaker vendors bring a triple 18 box out to a single connector pin set. 

Cross rented a set of boxes like that along with an amp rack and had to go in and rewire the boxes and racks.  The rental guy was surprised at how much more low end I had on the system than he was used to when he used the subs on his rig.

Mark Wilkinson

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Re: 2 ohm loads on bottom end
« Reply #27 on: August 25, 2016, 04:36:06 pm »

As mentioned by others, it looks like the new switching amps, and flexible routing topologies, have an easier time with low z loads than yesteryear designs.

I noticed in a whitepaper for qsc's pld, that you can parallel 4 channels and it's 'safe' for a 1 ohm load.

Kinda ironic though, using the flexibility of a 4 channel amp, just to drive a bunch of parallel subs.....;)
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Jeff Bankston

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Re: 2 ohm loads on bottom end
« Reply #28 on: August 25, 2016, 05:08:53 pm »

As for multiple amps go I would never take one amp to a gig. My guitar players always take a spare head(the kind that you plug a guitar into). I take a spare snare drum and sticks. In my PA I use the FaitalPro 18XL 1600 and they go below 40hz but I roll them off at 40hz. The 18XL1600 is rated 1600 watts RMS/AES and are 4 ohm impedance. the QSC 3800 is rated 1700 watts RMS/AES in bridged mono at 4 ohms. I connect 1 18XL1600 woofer to 1 3800 amp. I have a lotta amps. The woman in the video has 
http://www.youtube.com/watch?v=J1NOiCDpPiE
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Ivan Beaver

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Re: 2 ohm loads on bottom end
« Reply #29 on: August 25, 2016, 05:15:08 pm »



I noticed in a whitepaper for qsc's pld, that you can parallel 4 channels and it's 'safe' for a 1 ohm load.

Crown was doing that in the Macro and Micro amps back in the 80s.  Except it was just 2 channels for a 1 ohm load.
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Ivan Beaver
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Re: 2 ohm loads on bottom end
« Reply #29 on: August 25, 2016, 05:15:08 pm »


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