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Old 14th August 2001, 04:44 PM   #11
Super is offline Super  United States
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Just found out that the amp will not be stable with a 2 ohm load. Would bridging the two channels give me more power than with a single channel? With a single channel driving it, I think I'd get about 180 watts, wired in series. Can you tell me how to bridge an amp?
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-Bryan
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Old 14th August 2001, 04:56 PM   #12
Eric is offline Eric  United States
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For mounting the drivers, t-nuts are the best because you can remove the driver to perform maintenance, then put it back in just as tightly as before without fear of stripping the hole. Wood screws into MDF will last once or twice, and if you over-tighten, you're done!

Some people put small pieces of plywood on the back of the baffle where the t-nuts go to give them something more solid to grab into.

Practically no amp is going to be happy with a 2 ohm load, so I would not suggest paralleling 4ohm drivers. Bridging two channels will definitely provide more power than a single channel (at a cost of higher distortion). However, an amp can only be bridged if it is designed to do so. Have a look through the manual for your amp. If it doesn't say anything about bridging, I wouldn't try it.
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Old 14th August 2001, 05:23 PM   #13
Super is offline Super  United States
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Ok. This sub is going to be connected to the subwoofer output of a receiver. There is only a single output jack. Would their be a way of maybe using two plate amplifiers? So that I could have one amp dedicated to each driver? One of the primary reasons I want to use plate amplifiers is because they have a built in active crossover. If there are any 250 watt 2 channel amps with a built in active crossover, that can support a 4 ohm load per channel for less than 3-400 dollars, please, by all means, let me know. I would wire it in series, but I really dont think that 180 watts will be enough to power these two NHT drivers. If not, could I possibly use two plate amplifiers from a single subwoofer out? Thanks for the help. I just dont want to have to sacrifice over 70 watts of power

-Bryan
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Old 14th August 2001, 05:35 PM   #14
Eric is offline Eric  United States
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Sure, there is nothing wrong with taking the line level sub out from your receiver and using a Y-cable to drive two plate amps. Just be sure to match the output level of the amps if there are any types of output controls present.

On the other hand, you might be surprised what 180 watts will do. A few suggestions here: When you build your box, get a 4 way binding post and wire each driver to its own set of binding posts. This way, you have maximum flexibility to drive it in parallel, series, whatever. Then, give your current amp a try, pushing each driver with one channel. Most amps can drive a 4 ohm load with no problem even if its not directly stated that it can. Just keep an eye on it to make sure it doesn't get too hot...

If this is not satisfactory performance for you, then get two plate amps and drive the sub that way. This way, you don't spend the money unless you really have to.
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Old 14th August 2001, 05:55 PM   #15
Super is offline Super  United States
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Default Just an idea

If I buy the plate amp, could I put it in its own separate enclosure? That way, I could just put binding posts/terminals on the subwoofer, and put the amp in a location where the airflow is better (The sub is likely to be place near a corner.) Also, I noticed that the subwoofer amplifier doesnt have a line in for the subwoofer output. Could I just use the left/right line level outs for the fronts and connect that to the subwoofer amp instead? Thanks

-Bryan
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Old 15th August 2001, 02:08 AM   #16
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Bryan,
The Shiva, NHT, and Dayton Titanic should all give roughly equal performance, along with other drivers in their class. I'm concerned that you were getting rolloffs in the 50's for the Titanic and 30's for the Shiva. There's something fishy there.
Eric is correct, all drivers in that class are generally going to give optimum performance in a sealed enclosure. Yes, people use them in ported enclosures, but that's likely to lead to bottoming of any of the drivers, not to mention pretty loose bass, no matter how you tune the enclosure.
I disagree with Eric on the topic of mono vs. stereo subs, as there are enough recordings that are stereo all the way down to make it worthwhile (used to be true that recordings were mono in the bass, but that hasn't been the case for a while), not to mention directionality is evident much lower in frequency than most people realize. That said, if you're running a 5.1 system, you're trapped as far as the .1 signal goes.
It's not difficult to run the left and right line outs into a crossover and have separate plates pushing individual drivers.
Placing a sub in a corner is going to make your life interesting--the corner will act as a rough horn and you'll get unpredictable response. Be prepared to tinker.

Grey
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Old 15th August 2001, 02:34 AM   #17
Super is offline Super  United States
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I may have some space to tinker, but it may be limited position-wise. After discussion with my dad, the o-holy provider of funding, he wouldn't detest too much to having to purchase a second plate amp. However, two amps in a single box may cause some resonance/cabinet strength problems, so we were still wondering, can the plate amps be put in a separate cabinet? I don't see why not. So, I would be using a separate amp to power each channel. I figure this way, I could hook it up to the stereo outs, or put in a Y cable for the LFE channel. This way, I wouldn't have impedance issues with the amp, either. One more quickie about wiring. My receiver only has a single jack for the outputs of the left and right channel, i.e no red and white rca jacks. The sub amps however, have both red and white input jacks. How could I make this connection work? Same problem for the LFE channel. Only a single output jack, but the signal must be sent to two separate amps, which have no input jack for this type of connection. Thanks again

(BTW, I would make a pair of subs, rather than two in one enclosure, but a pair is out of the question in terms of what I'm allowed to make)

Oh, if possible, could someone use a boxplot program and tell me what results they get using two, NHT 1259's, in a normal configuration in a sealed enclosure? I get an internal volume of about 278.9 liters, and a -3db rolloff of about 29 hz. I appreciate it.

-Bryan

[Edited by Super on 08-14-2001 at 10:18 PM]
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Old 15th August 2001, 07:11 AM   #18
Ignite is offline Ignite  Canada
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Default Re: Just an idea

Quote:
Originally posted by Super
If I buy the plate amp, could I put it in its own separate enclosure? That way, I could just put binding posts/terminals on the subwoofer, and put the amp in a location where the airflow is better (The sub is likely to be place near a corner.) Also, I noticed that the subwoofer amplifier doesnt have a line in for the subwoofer output. Could I just use the left/right line level outs for the fronts and connect that to the subwoofer amp instead? Thanks

-Bryan
You don't really need an enclosure for the amp at all. If you are worried about SAF, perhaps a low-profile mounting of some sort is in order. I also wouldn't be too worried about ventalation, but if you are, don't seal the enclosure. More ventalation is better. Usually an amp won't produce THAT much heat, and it's over a reasonably wide surface area. Still if you must separate the two, just make sure your amp-to-subwoofer wire is of a high power rating and not very long. From the experiences I've had with car audio subwoofers, you can almost never have wire that is too thick.
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Old 16th August 2001, 02:28 AM   #19
Super is offline Super  United States
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Unfortunately, these plate amps should be in some sort of enclosure, since the face of them is all exposed wiring and components. Having them in an enclosure also gives me a foundation to attach the binding posts. One of the Madisound employees verified that my approximate dimensions were correct. With bracing I should come out with about 8.2 ft^3, and the recommended volume is between 7 and 10 feet^3. Now it seems that my only "problem" will be the wiring. Hopefully I'll be able to get the full 250 watts per channel, if not, I'll settle for the 180 per channel. Can anyone suggest some freeware that I can use to perhaps make a CAD drawing of the cabinet? Also, does anyone have suggestions as to how the cabinet should be braced? I'd like to keep the added volume to a minimum due to size restraints. I'll probably line the seams with 1/4 inch round strips, and 3 or 4 one inch crossbraces from front to back, and the same from left to right, since it will be a fairly tall unit. Thanks once again

-Bryan
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Old 16th August 2001, 10:18 PM   #20
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I believe turbocad offer their latest version as a downloadable demo. I'm not sure what restrictions apply but I think its a 30 day period.

http://www.turbocad.com

hope this helps

Dan
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