1kW MOSFET amplifier

[AudioFreak]

Yes for 450Wrms into 4ohms you'll want a supply voltage of about +/-75V... Of course, i would use seperate rails for the front end and the output stage.... +/-85V for the front end and +/-67V for the output stage. I also have access to switching power supplies that can supply these power levels

[Kilowatt]

Sweet! Where can I get switching supplies like that? Also, why ever would you use two voltages? I would much rather use one, as it would make it much simpler, and that's what everyone does.

[SteveG]

Kilowatt,
I think that EV speakers absolutely rule for PA work, but that, as I said before, is a whole different animal than hifi.
It sounds like you are well on the way to success, and I think you will have a lot of help from a lot of different people from here on out.
As far as the Eminence speakers go, where are you looking? Parts express titanics are nice subwoofers, as are the NHT1259 (I believe that's the model number- they're sold at madisound)but it is better in closed boxes (probably not ideal for you). Peerless also sells some kick butt high excursion woofers, available at parts express. I've heard some good things about the 10" Vifas. I really like the specs on the titanics. In my opinion, you want something that will handle max wattage, and have long excursion for low distortion and great bass extension, which the titanics fit nicely. Remember- those two woofers being driven by that 450 watt amp will share the power, so you don't necessarily need a 1000 watt driver. With a woofer like the titanic, which is meant for home theater and music, you will get outstanding bass quality, as compared to PA speakers, which are compromised for the sake of durability (excursion limited) and extending the high end. Bass extension and quantity could be amazing with a setup like this! Have you ever felt the 16hz fundamental of a pipe organ? I haven't yet, but I may have to travel to MT if you pull this off, ha ha.
As far as mids go, you have SO many options, and using an array (and quite a monster, according to your post) will let you share the power among many drivers, which will let you concentrate on audio quality- again, the pa speakers being a compromise. I like the vifas P17WJ's because they have a very natural rolloff with no bad upper resonances, and they should work well with an active xover. Plus, they are a great value, which matters to me, since I'm not made of $$$$ haha. You may also look into 5" drivers, as that will slightly extend your high end ability before lobing (close center-center spacing). If I remember right, it is not very much better, and you will probably be better off going with the 6.5's to get the midbass quantity you need. Remember that driver phase will play a part in the crossing over, and it may be necessary to get the mids out in front of the horn a little ways to get them to sum right, which is ok since you are using seperate cabinets, right?
If you look at the linus array design, and the paper published along with it (I can't remember who wrote it) there is a formula that uses the center to center spacing of the drivers and the speed of sound to calculate the frequency where the drivers stop looking like an array and start creating interference patterns (lobing). The upper limit will be around 2Khz with 6.5's if I remember right- at double this frequency you will start to see severe lobing (hot and dead spots in the frequency response). Keep the drivers spaced as closely together as possible, and keep this info in mind when choosing your crossover frequency to the horn. I will try to find the pdf of that paper, which has a lot of great info. Be very cautious about running the mids too high. Choose a very good horn that will allow you to cross over fairly low. I wouldn't skimp on that area. I think you may be amazed how little power it will take to get that horn to ear-shattering levels.
Man, would I like to be there when you turn this thing on! I think you will even be impressed. If you want me to help in any way, just let me know what I can do for you.
Steve

[SteveG]

You need a higher front end rail to compensate for the gate-source bias voltage of the output Mosfets. It will need to swing about 5 volts per rail more than you will need at the output. See the pass A75 for details on that one.
Also, you want the power stage to clip before the front end- you should have about 3db headroom in the front end over the output stage.
I wish I could help you with the switchers... That's getting WAY high tech. If you're going that far, why not use class D output stage for the woofers- 90% efficiency looks really good!
Steve

[AudioFreak]

Yes as SteveG stated, you need the higher front end voltage or the entire amp would need to run off this higher in order to get the required output swing. You dissipate far less power with separate rails.

[Kilowatt]

Not only does class D have bad distortion characteristics- even for woofers, but I'm not that high-tech. AudioFreak said he knew about some ready-made switchers that will suit my needs. I want all my channels to have full range capability even though they won't all be doing full range, just in case the need arises for them to do so.

Since I won't be dissapating as much heat with this dual voltage thing, can I get away with 10 output devices instead of 12 for each 450W channel?

I like the specs of those Dayton Titanics, but I don't get enough bass that way because I can only use 8 per side (unless I put some in series or drive 450W into 1ohm). I'll only reach 132dB. The Peerlesses, being 8 ohm drivers, would be a little better, I could reach about 134dB per side, they're each not quite as sensitive. That might be enough with a low xover freq. All these woofers are reasonable in price. I'm impressed, for a home hifi sub. Car subs, however, are far superior in Xmax and power handling, like the Audiobahn ALUM12X, with 31mm Xmax, they claim 1kW RMS power capability and 96.4dB sensitivity. They only cost $169. The JL 13W7 comes to mind also, with it's 1.25" Xmax and 1kW/2kW RMS/Peak power capability, but it's more like 87dB@1W@1m and costs about $750. I have heard that these would suck outside though. What do you guys think?

P.S. You meant 450W into 2 ohms right AudioFreak? That's what I'm doing here. 45V would do it in numbers, but it would clip off all the peaks, so I'd need 85/75V.

[AudioFreak]

Originally posted by Kilowatt
1. Since I won't be dissapating as much heat with this dual voltage thing, can I get away with 10 output devices instead of 12 for each 450W channel?

2. I have heard that these would suck outside though. What do you guys think?

3. You meant 450W into 2 ohms right AudioFreak? That's what I'm doing here. 45V would do it in numbers, but it would clip off all the peaks, so I'd need 85/75V.

1. NO!

2. Yeah badly!

3. My bad sorry. My calculations were indeed for 4 ohms ... for 2 ohms 50V/65V rails would be fine for 450Wrms continuous but its all a matter of a matter of how much headroom you want... just remember that higher voltage equals more dissipation.

[SteveG]

You might have to look at PA subs, if you are primarily running this thing outside. Keep in mind though that the bass will not be extremely deep- those woofers usually only work best down to 40 or 50 hz. Not the best way to go for quality, I would think.
As far as car audio goes, I have a feeling that a lot of the specs are a little on the optimistic side.
Maybe the eminence woofers are right for your ap... Where are you drawing the line between PA and home stereo? If you want a PA system, you will be better off with the really efficient PA drivers. You'll have to find the balance between quality and quantity.

[SteveG]

This looks like it would do really well for a large outdoor setup:
Parts Express
Technical Information
#295-085
Parameter
Specification
Sens. 1W/1m
97 dB
Impedance (nom.)
8 ohms
Power Handling (RMS/Max)
500/700
Fs
25
Qts
.34
Qms
6.74
Qes
.36
Vas (ft3)
16.12
Cms (mm/N)
.25
DCR (W )
6.01
Levc (mH) @ 1 KHz
2
BL (Tesla m)
20.62
Sd (cm2)
1140
Xmax; one way (linear mm)
6
P-Vd (cm3)
687.8
Mms (grams)
161.3
Magnet Weight (oz)
109
Coil diameter (in)
4
Net weight
29 lbs.
Dimensions
A: 18", B: 16-1/2", C: 8-1/4", D: 8-3/4"

[SteveG]

Here is what it can do: