Setting up active monitors with a sub and no external processor/amp

Lyons

Active Member
Hi,

I have some audioengine A5's and have recently bought a Mordaunt Short 309w to give them some more low end grunt.

I have all the line inputs going to the A5's then the sub is connected by the pass through rca's. This means the A5's and the sub both receive a full range signal, no problem for the sub as I can set the crossover to cut the high frequencies, but the A5's are still trying to amplify the <50hz which they cannot reproduce in any volume.

Am I right in thinking that the <50hz is causing distortion and stopping the A5's from being as effective as they could be?

In other words, would it be best to have a separate crossover to send set signals to the A5's and sub separately?

Or does none of this matter?

Thanks in advance :smashin:
 

BlueWizard

Member
Are you implying that your Sub's high crossover is 50hz? Or is that merely the rated low response of the A5's?

At any rate, for the most part, you want the high cut frequency of the Sub to match the high pass frequency to the front speakers. So, if your sub is set to 80hz, everything should be at 80hz.

Making a high pass filter to the A5's might seem easy enough, but not as easy as you might think, since you are feeding the A5 AMPS and not the A5 speakers.

To make a proper crossover, you need to know the input impedance of the A5. Likely it is between 10k ohms and 47k ohms; though there is a slim chance it could be 600 ohms. If you want a 6db roll off at say 80hz, then you need to calculate it based on those number. The roll off will begin when the impedance of the capacitor equals the impedance of the A5 amp input.

Assuming 47k ohm input and a required 80hz roll-off, you need a .04228µf (or nearest standard value) capacitor in series with the A5 input.

Here is the crossover calculator that I used -

Crossover Design Chart and Inductance vs. Frequency Calculator(Low-pass)

All that said however, the A5 naturally rolls off at 50hz or whatever the rated low frequency is. It doesn't stop abruptly, nor is there likely to be any distortion down that low. Usually filtering the low end from the front speakers improve that speaker midrange because there is less interference between the lows and mids.

You can experiment with a capacitor in series as long as you remember that it is in series with the input to the amps and not in series with the speakers. This is very much to your advantage, if the capacitor was in series with the actual speaker you would need a 248µf capacitor which would be HUGE.

So, it all hinges on knowing the input impedance of the A5 amps.

Steve/bluewizard
 
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Lyons

Active Member
The crossover on the sub is about 60-70hz, 50hz roughly what i think the a5's go down to, although i've not tested them yet as i only got the sub a few weeks ago.

What i am asking is - would it be worth cutting the low frequencies that the A5's can't play, whether it be <40/50/60hz to lower distortion and improve the sound?

If it's worth it i'll find out the impedance of the monitors and look into it.

Thanks for the help Steve!
 

BlueWizard

Member
Is it worth it? I say no.

However, it might be worth it if you crossed to the front speakers at the same frequency that the sub crosses. So, if you are crossing OUT the sub at 70hz, then cross the front IN at 70 hz.

Just one man's opinion.

Steve/bluewizard
 

Lyons

Active Member
Well should I just find out what frequency the speakers stop producing voulme and cut the sub out then?
 

Member 96948

Distinguished Member
Steve, why does it always need to be so complicated?:)

Reckhorn F-1 at 29.95Euro here (plus shipping) would be more than adequate in this situation and a lot simpler too and you get to choose where the crossover happens which will have obvious benefits for the A5s.

Have a look at this thread for someone using a Reckhorn B-1 and cribeiro should be able to help with German translation issues!

Russell
 
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Lyons

Active Member
Problem with that is that it only has one input, whereas I need 3! I have my TV, remote ipod dock and a wireless reciever for my laptop etc. It's all getting a bit too complicated, am I going to notice much difference if I use a crossover to cut the lows on the a5's?
 

Member 96948

Distinguished Member
You may not notice much difference at moderate levels, but if you divert the lowest frequencies away from the A5s, then the power they do have will go a lot further, meaning louder, cleaner playback.

The problem here is that you need to gather all three line inputs into one cable that can be fed through the Reckhorn. Something like a line level switch box will be required. This means you could set up the A5s and sub with the active crossover and leave them set, and just switch between sources, relying on their individual volume controls.

Unfortunately, things like the A5s are designed to be a complete minamilist solution, not the basis for an expanding system, so treating it otherwise is going to be more complex than a cheap stereo amp and passive speakers.

Russell
 

BlueWizard

Member
In all honesty, I think you are making too big a deal of the whole thing. You seem to be worried about filtering out frequencies below the rated cut off of the Audioengine speaker, but those frequencies are already naturally rolling off.

I suggested you cut them off at same frequency as the sub is rolling off on the high end. For example, if the sub is set to 80hz (something of a standard) then cross the fronts at 80hz. But since you don't have an AV amp, that is not that easy to do.

You could add external capacitors as I suggested, but that can get complex and messy.

Or, you could just be satisfied with what you have. Which is what I recommend.

If you can control and match the sub and front crossovers, you can improve the quality of the sound from the fronts. But again, that works best with an AV amp.

If you try external crossover suggested by Russel, that would solve your problem at a reasonable cost, ASSUMING you use it right. Adding the also suggested switch box, would bring your total to roughly £46 (£26 + £20). If you are willing to spend that much money to gain this control of your system, that is up to you. If you think it is worth your while, then more power to you.

But, it is either Russel's suggestion or be satisfied with what you have.

The Reckhorn active crossover, has two inputs (left & right), those channels are merged to create two presumably identical Sub outputs (A & B), and then the two stereo channels are fed out in Left and Right.

That is enough to feed your system. But again, you want the sub setting to match the front speaker setting, for best results, and I think you need a crossover closer to 80hz. But taking the low end strain off the front speakers, you will clear up their sound.

If you are willing to spend the money, then I think this is about the best you can do.

Steve/bluewizard
 
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Lyons

Active Member
Anybody want to buy my setup? ;)

I think you're probably right steve, I need to spend more time setting up the sub and see if I can optimise it, I always just want a bit more, without trying a crossover I don't know what I'm missing out on! I belive you guys call it upgrade-itus.

I'm moving out of my flat into a detached house in a few months so I think I'll wait until then and play with the setup, see if I can content myself.

Thanks very much for all the help guys, muchos gracias! :thumbsup:

One more simple thing I was thinking of doing was making myself some stands, mdf and sand with spiked feet, quick answer - yay or nay?
 
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