Plate Amplifier Load...

[aceinc]

A rather odd question that I haven't considered before, but I'm sure somebody has the answer...

What load does a plate amplifier present to the system when attached via the high level (speaker, not RCA) input?

For the sake of argument, say I were to take an unpowered 4 ohm subwoofer, and a powered subwoofer and were to attach them in parallel to the output of an amplifier what would the load look like to my amplifier? What affect would this have on the output of the unpowered sub? I would not be passing any signal to a full range speaker.

Does anybody know the answer?

Paul

[F1 fan]

The speaker level input on a plate amp will probably have an input impedance on the order of 100k ohms or more so that it will not place a large load the source amp.

[aceinc]

If this is true, and I have a 4 ohm load in parallel, virtually all of the power will be sucked up by the 4 ohm load. This would mean that adding a powered sub to the same line that has an unpowered sub should have little affect on the output of the unpowered sub, as well as little change in the load to the amp. This all assumes that my concept of how these things work has some basis in reality!

Does this also mean that I can daisy chain the powered sub from the unpowered sub with a smaller guage wire, such as a 18-20 guage?

Paul

[F1 fan]

The source amp will have to deliver far more current to the 4ohm speaker load than to the input of the plate amp.
yes 18-20 gauge wire is fine for this purpose.

[brucek]

say I were to take an unpowered 4 ohm subwoofer, and a powered subwoofer and were to attach them in parallel to the output of an amplifier what would the load look like to my amplifier?

The showstopper isn't the load, it's the level. A standard line-level input to a powered sub expects just that - line level.

This is why some subs have two seperate inputs provided. High level and line level. The high level input has an attenuator ~20-30dB built in....

brucek

[F1 fan]

brucek wrote:

The showstopper isn't the load, it's the level. A standard line-level input to a powered sub expects just that - line level.

This is why some subs have two seperate inputs provided. High level and line level. The high level input has an attenuator ~20-30dB built in....

brucek

Yes or the input will be seriously overloaded.I ve seen the use of 680k resistors in series with the input to get the required attenuation.

[aceinc]

aceinc wrote:

What load does a plate amplifier present to the system when attached via the high level (speaker, not RCA) input?

My idea is to attach to the Hi-level in not the RCA (Low level) in. What load does the "high level in" present to the amplifier driving it?

Paul

[brucek]

What load does the "high level in" present to the amplifier driving it?

None to speak of....... brucek

[aceinc]

So what I posited earlier, that the unpowered 4 ohm sub would get all the power, and I can use a smaller guage wire to daisy chain the powered sub is reasonable iyo?

Paul

[F1 fan]

aceinc wrote:

So what I posited earlier, that the unpowered 4 ohm sub would get all the power, and I can use a smaller guage wire to daisy chain the powered sub is reasonable iyo?

Paul

I will give the same answer as in post #4 YES it is ok.

[aceinc]

Sorry F1 Fan, I was really asking brucek whether he agreed with your & my assesment of the situation. He expressed some doubts, but I believe he misunderstood how I intended to hook things up.

Just trying to get consensus, I guess...

This actually resolves my dilemma in my wiring question thread...

Paul

[F1 fan]

OOPS sorry.

[brucek]

I was really asking brucek whether he agreed with your & my assesment of the situation

Yep, I agree. I did misunderstand, I thought you were trying to use the line level inputs of the powered sub. With the high level inputs, you can just use speaker wire - any gauge...

brucek

[Chrisbee]

brucek wrote:

Yep, I agree. I did misunderstand, I thought you were trying to use the line level inputs of the powered sub. With the high level inputs, you can just use speaker wire - any gauge...

brucek

I often recommend ordinary lighting flex for high level sub connections. There is no need for speaker cable since the sub's plate amp can't see the capacitance or inductance of the cable due to the high impedance.

Having been a strong advocate of high level connections (when I had that option and no other) I changed my mind completely when I finally had access to low level connections. LFE, active crossovers and the BFD.

All of which are denied to you by high level connections. You also get a slow 6dB/octave inbuilt crossover with high level connections unless you use the sub with an AV receiver. In which case any claimed advantages for improved SQ with high level connections go out of the window anyway.

[aceinc]

Chrisbee, What I intend on building is a main/satellite sub system. The connections would be;

AV Receiver sub out -> BFD in -> BFD out-> NAD Amp in left & right -> NAD left & right out -> (2) 10" unpowered subs, and in parallel the Hi-level in left & right on a 15" Direct Servo plate amp.

Doing the tuning will be fun, but I believe I have methodology for that.

Paul

[Chrisbee]

aceinc wrote:

Chrisbee, What I intend on building is a main/satellite sub system. The connections would be;

AV Receiver sub out -> BFD in -> BFD out-> NAD Amp in left & right -> NAD left & right out -> (2) 10" unpowered subs, and in parallel the Hi-level in left & right on a 15" Direct Servo plate amp.

Doing the tuning will be fun, but I believe I have methodology for that.

Paul

The inclusion of more than one sub of different output abilities is almost bound to cause problems with cancellation and reinforcement due to phase and room-related issues. Perhaps you can arrange your three in a satisfactory geometry.

I don't think the BFD makes any sense controlling all three subwoofers simultaneously. Though I suppose in theory you are only equalising for one hot seat. So the response there is what matters even if you are equalising subwoofers that don't need those particular filters and not filtering frequencies for subwoofers that do.

From my own experience mismatched subwoofers produce one that completely drowns out the other(s).

[brucek]

From my own experience mismatched subwoofers produce one that completely drowns out the other

Yep, a mistake many people make when they get a new capable sub and think it would be a waste to get rid of their old challenged model. Unmatched subs with different frequency extension simply dumbs down the capable one....

brucek

[aceinc]

My unproven concept is as follows;

I will have a pair of 10" subs handling 30hz-80hz, 1.333 octaves, which should be about what they will naturally roll off at in the sealed enclosure with no bass boost, the 15" will handle 30 hz down to below 10 hz according to the rythmikaudio.com web site, another 1.5 octaves.

The BFD is to handle any room boost, which based on what I have read will appear well above 30 hz...

This is actually a completely new installation, and will be a proof of concept, or a miserable failure if brucek is right. In any case, it'll keep me off the streets for a few days building and testing. I received the 2 titanics, an ecm8000, a mixer/mic preamp and the bfd today, my wife brought home everything but the drivers which were too heavy for her to carry to her car.

Hopefully I will have time to work on this over the weekend.

Paul

[brucek]

and will be a proof of concept

Sounds like an interesting idea if you can pull it off. Certainly it doesn't match the losing scenario I implied in my post where each sub outputs 'like' frequencies. You are essentially creating a system with two crossovers as opposed to one. How will you cross the 15" sub to 30Hz?

brucek

[aceinc]

This presents one of the challenges. 40 hz may be more realistic, as I believe the plate amplifier on the Direct Servo has a variable 35-150hz crossover. When I order the system I can specify either a 12db or 24db slope. I'm not sure which will be best.

I plan on building the two 10's and see how they do and what their curves look like in the room before ordering the 15" DS. Brian Ding (of Rytmik Audio), while not loquacious, is knowledgable and helpful.

Paul