Umm... so, help me figure out the best amplifier setup, and stuff (1 Viewer)

[RichardHOS]

I can't seem to come to any resolution by myself, so I would appreciate input from you guys on the pros and cons of each alternative.

I need an amp(s) to power my planned subwoofer setup. This will be an infinite baffle design, with 4 AV15's per side.

I'd like to keep it stereo, so that rules out a single amp driving a mono load. For now, I'll plan on using both voice coils of each driver. The low Qts should be just to my liking, but if I need to alter the Q I'll use a linkwitz transform (may use one anyway to flatten response). I'd also like to figure around 250W per driver as a target to shoot for. Any choice will have to be either standard shelf or rack-mount chassis types. No plate amps.

That leaves the following options:

(1) Single stereo amplifier, stereo mode, 4 AV15's per channel, either 4 ohm or 1 ohm per channel.
(2) Two stereo amplifiers, one per side, 2 AV15's per channel, either 2 ohm or 8 ohm per channel.
(3) Two four channel amplifiers, one per side, 1 AV15 per channel, either 4 ohm or 1 ohm per channel.

For some reason, I have the urge to use a separate amplifier per side. Not sure why... perhaps because I have an addiction to large numbers of separate components?! Perhaps it's the peace of mind of having a separate power supply for each channel, and the ability to use two electrical circuits to ensure adequate juice to the amps.

My concern though is that a stereo amp per side would either be running into an 8 ohm load per channel (not as efficient), or a 2 ohm load per channel (higher distortion figures). Would I notice an increase in distortion due to 2 ohm vs. 4 ohm loading of a typical prosound amp?

So... any thoughts you guys have on the pros and cons of each alternative, please do share them. Also, any specific amp recommendations for your preferred alternative would be great. From a quick look at some choices, it seems the two amplifier, stereo 2 ohm per channel alternative would be roughly the same price as a single large amplfier (due to the increase power output in 2 ohm vs. 4 ohm, thus two smaller amps could be used).

I'm suffering from overanalyzingitis. Help!

 

[RichardHOS]

Here's a price comparison based on QSC amplifiers:

option (1): PLX3402 - 1100wpc @ 4ohm, .05% THD 20-20k, 275Watts per driver, $1200

option (2): 2x PLX1202 - 600wpc @ 2 ohm, 1% THD 1kHz, 300Watts per driver, $600 x 2 = $1200

option (2): 2x CX254 - 250wpc @ 4 ohm, .05% THD 20-20k, 250Watts per driver, $??

Well, it looks like a single PLX3402 is the most logical choice, but for some reason that is unsettling. Don't know why. I need convincing!

 

[RichardHOS]

:frowning:

 

[Dave Milne]

4 AV15's per side.

You're kidding, right? 8 AV-15s in one room... with 2KW?? Is that legal in your state?

green with envy

What about a Crown K2?

Also, you'd probably get more feedback from the DIY forum on this particular topic...

 

[Greg_R]

The PLX3402 and the Crown K2 are excellent amps. Either will work given your application. I don't understand why you need to keep the stereo signals seperate (when they're being driven to the same driver).

Crown:
- No Fans
- slightly lower power consumption
- higher dampening factor (according to specs)

QSC:
- Speakon connectors
- variable clip limiter & subsonic filter
- less expensive

The fans in the QSC are very quiet under most load conditions. If fan noise is a major issue, consider the K2. Otherwise the QSC will work well. BTW, neither amp is rated for a 1 ohm load.

 

[RichardHOS]

I'm keeping the signal stereo because... I will have a stereo infinite baffle setup. One baffle outlet near each of the L/R mains, with 4 drivers per baffle. Since I haven't settled on all the XO points yet, I want to maintain stereo integrity just in case I wind up with a XO point high enough that it would be beneficial.

And, in reality, I would get the same power from a stereo amp running into 4 ohms per channel as I would the same amp bridged mono into an 8 ohm load (what I would have if I went with a single mono load).

Still... I'll have 16 channels of amplification for the 7 main channels. It just seems "wrong" somehow to only have 2 channels for 8 sub drivers. :frowning: I think I'm an amp addict.

But, after doing the price comparison above, I suppose it looks more reasonable to go with the single larger amp.

Unless someone can talk me out of it. There has to be a good reason to buy more amps... I know it. Out with it!

 

[RichardHOS]

originally posted by Dave:

You're kidding, right? 8 AV-15s in one room... with 2KW?? Is that legal in your state?

I'm not sure, and I'm not about to ask!

It's roughly 6000 cu.ft. of volume in the room. 4 AV15's seemed merely "adequate" and 6 just seemed like an odd number. So 8 it is...

 

[Chu Gai]

Check out the Carvins here. Made in the USA and priced very very reasonably.

 

[RichardHOS]

Hmm... a pair of DCM1204's looks interesting. I'll keep them on my favorites list.

 

[Greg_R]

One baffle outlet near each of the L/R mains, with 4 drivers per baffle.

Aren't you concerned about cancellations between the two units?

 

[RichardHOS]

Yes, and no. Cancellations... not really. No more so than anyone else who has experimented with multiple subs. Difficulty in obtaining a semi-flat in room response? Yep. As much as anyone else with a sub!

I know what you're saying. I've looked at this extensively, and I'm not sure there is really any "best" way to approach in room sub systems. There seem to be two "better" placements for multiple subs: four, with one in each corner; and four, with one dead center on each wall. The next most desireable is one in each front corner. After that it's a mixed bag.

In reality, the modal response of the room is going to be so unpredictable that it isn't worth wasting a lot of time fretting over modal peaks and nulls before the room is done. I have formed the opinion that it is best to first tackle directional and time alignment issues (by using stereo subs that are in the correct plane wrt the mains for decent time alignment), and then tackle room response with room treatment.

If you find the "perfect spot" for a sub(s) that gives a flat response, it will only be perfect for the listening position. Other positions will find themselves in peaks/nulls. On the other hand, if you adequately treat the room to absorb energy at peak/null frequencies, then you can get a decently flat response anywhere in the room, no matter where you place the sub.

Perhaps you're talking about comb filtering though? As for that, all I can say is that there should be no worse effect than is typically heard from full range floorstanders. In fact, since the signal will remain stereo, perhaps that cancellation is actually important in maintaining the proper stereo image. I don't really know... but what I do know is that using multiple subs in multiple locations is something a lot of people have done, and a lot of experts recommend (including Dennis Erskine), so I won't be any worse off than they!


If you have some specific thoughts though, I'd love to hear them. Nothing is absolutely permanent yet, and I'm always researching to find out if there is a better theoretical approach to take.