Speaker switch boxes...

  • Thread starter Thread starter Slackmaster2K
  • Start date Start date
Slackmaster2K

Slackmaster2K

Gone
Some questions in regards to speaker A/B boxes:

1) Can switching between 8ohm and 4ohm speakers damage the amplifier, or can it instantly adjust without a problem? My amplifier is rated for load from 2 to 8 ohms. Should the amplifier bet turned off when I switch?

2) Quality. Can somebody recommend a brand?

Slackmaster 2000
 
Slack,

Turning the amp off isn't really necessary, provided you turn the volume all the way down when making the switch.

Your amp doesn't actually "adjust" itself per se, but it will deliver more current through a lower impedance at any given volume level (ohm's law).

Twist
 
Right, but is the sudden increased current flow hard on components? The amp was probably not designed with this sort of thing in mind, and it's got to last me a bit longer.

So far two people have told me that it should be fine, so I'll probably take your word for it unless somebody else pops in.

Any recommendations on switch boxes?

Slackmaster 2000
 
Slack,
I think you misunderstood me slightly
4 or 8 ohm speakers are within the specs of your amp. You said it was 2 - 8 ohms, so under normal conditions, no it won't harm your amp. My concern was for switching the speakers with the volume turned up, and that could possibly create a huge current spike.

If your inclined, home brew would be fine. It's a very simple matter of switching one lead per speaker, the commons could all stay connected.
Radio shack probably offers something that would work fine as well. This is not a critical piece of gear, so there's no need to spend a lot of money on it, though I'm sure you could if you wanted to.

Twist
 
i must respectfully disagree with virtually all of the advice given to date... :)

here's a quick an dirty...

i'm assuming you want to switch speakers while playing.

unless you design this switch correctly, you are going to shorten the life of both your amp and speakers. you need a Zero-Crossing Current detector so the switch only occurs when the current is zero. this is because speakers represent highly inductive loads and current cannot instantaneously go to zero (during switching). if you switch when current is flowing, the relay will arc (dump the excess current) and the amp and speakers will see significant transients. possibly causing component failure; definitely shortening component life. note that solid-state amps are less forgiving than tube amps.

this is very similar to switching a light switch. the relay in a light switch will arc when turning the light on and off. same thing with a speaker with a switch that's not designed correctly.

unless you're versed in Zero-Crossing Current load switching, you're going to be subjecting your equipment to transients that may shorten component life and that will finally lead to component failure.

if you must, consider a quality new or used used amp speaker switcher. these devices aren't cheap, and there's a reason for it. also, check out Aiken Amps. they have a Tech Info section and a DIY speaker switcher.

my recommendation is don't.

regards,
-kp-
 
Aha, thanks Sonixx.

I'm still going to get a passive switchbox, but I'm only going to use it when the amplifier is off. Really I just need something so that I don't have to keep moving wires between my monitors and the old speakers that I use for everything else.

Slackmaster 2000
 
Yeah, Sonixx is right.

There can be big current transients whenever you switch. Some amps have built in protection against this sort of thing, still it’s sensible insurance to shut down first.

In this case I’d build it myself. Just a high quality, high current, double-pole double-throw switch in a box or on a rack panel with one pair of input and two pair of output connectors. Very simple. No need for relays. Anyhow, relays have poorer connections, are more complicated and less reliable than switches.

I can get back to you with good sources for the components if you want to go this route.

barefoot
 
barefoot, if it's not too much trouble, a parts list would be excellent. I am very concerned about sound quality however. I know it sounds stupid, but after hearing the differences in my various cables I'm a firm believer that every little connection is important.

Any help would be appreciated...it's within my ability to build something like this....but what to build it out of is my concern!

Slackmaster 2000
 
Slackmaster 2000,

No Problem. Hope they're not too obvious, but I've attached schematics of some connection options. Only the left channels are shown. The right is identical.

Here is the switch I recommend http://www.electroswitch.com/ind-1/page7.html It's 8 position but there are adjustable stops to limit it to two.

Option 1 uses a 4 section switch (part# 24304B) where both the + and - terminals are switched.

Option 2 is simpler and quite fine if you're not hung up on 'symmetry'. It uses a 2 section switch (part# 24302B) where only the + terminals are switched. You could use a fancy car stereo power distribution block http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Product_ID=6234&CATID=35 to join the negative terminals if you want.

Option 3 is a switchless patch cord approach and would probably be considered more 'audiophile'.

The number of binding posts and banana plugs you'll need depends on which option you choose and how much you want to hard connect things. I won't make any recommendations here, since I don't really subscribe to many of the opinions relating to importance of wires and connectors. For line level and speaker level signals it's an expensive placebo effect IMHO.

Parts Express sells good quality inexpensive binding posts, banana plugs, wire, rack panels, etc. http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=29

If you want cost-no-object parts then have a look at the Parts Connection catalog http://www.partsconnection.on.ca/pages/catalog.html. Sorry to disappoint you, but it seems the $120/ft Kimber 4AG speaker wire is no longer available :)

barefoot
 

Attachments

  • spkr_switch.webp
    spkr_switch.webp
    14.5 KB · Views: 135
consider this:

build a box with four Female Neutrik Speakon Connectors. basically a signal through box with two circuits (one circuit per cabinet).

From Amp-> >Speakon Female>->Speakon Female>-> To Cabinet

Or From Amp-> >Speakon Female>->Speakon Female>-> To Another Cabinet

One of the two connectors is connected to the Amp output at any given time.

each of the two other Speakons are each connected to two different cabinets

then build three Cables each with one Neutrik Male Speakon and a Jumbo 1/4" Phono Plug. each 14/" connects to the amp or cabinet. the Speakons connect to the box.

with a bit of creativity, design the box so you can switch it easily by hand.

Neutrik Speakon connectors are solid and will withstand a lot of abuse.

if you only want to use three Speakons in the switcher box, you can switch the Cabinet side of the box and wire the three Female Speakons in parallel.

-kp-
 
Better connection

Here's a better layout of Option 1 which only requires a 2 section switch (part#24202B)

barefoot
 

Attachments

  • spkr_switch2.webp
    spkr_switch2.webp
    10.2 KB · Views: 60
Just use 4 ohm dummy loads in series with the 4 ohm speakers they are the cheapest thing in the world and the amp will see the 4 ohm speakers as 8ohms so minimal damage will be done.

dont use 8 ohm dummy loads in paralell with the 8 ohms speakers to make them look like 4ohm speakers because the heat generated will be bad on your amp.

by the way I havent heard of an amp that wont safely drive a 16ohm speaker.
 
darrin_h2000,

Putting resistors in series with your speakers is a bad idea.

Two main reasons:

1. Most every modern speaker design relies on electrical rather than mechanical damping to control cone excursion. Series resistors reduce electrical damping and hence degrade both frequency and transient response, especially in the bass.

2. Passive crossover networks are designed to be driven by low impedence amplifiers. These resistors would significantly increase the effective amplifier output impedence and cause the crossovers to not work properly.

barefoot
 
The output Impedence on the amp should be a constant. with the input impedence on the speakers being the variable here.

true you will get some loss with the resitor in series but better the loss than the loss of the amp.

maybe If you used the other monitors on a seperate amp that would be ideal. But you should match the input impedence of the monitor sets in the first place.
 
I only have a penny instead of two cents to pipe in..................

Check out the Adcom switcher.....................

and if you use a sub and want to be able to turn it on and off at will.........I had a guy modify an old single button Marshall foot switch for me and it works like a charm!!!!
 
The 'effective' impedence the speaker sees looking back towards the amp is the output impedence of the amp plus the series resistance.

darrin_h2000,

I'd like do what little I can to reduce the level of disinformation flying around this bbs. I'm not trying to be a jerk, but why are you arguing points you don't seem to understand very well? Any introductory electronics text should clarify the basic principles we're discussing here. I suggest Horowitz & Hill "The Art of Electronics". It's an outstanding and classic text which explains things from a more conceptual rather than mathematical perspective. My copy is completely dog eared because, even 10 years out of my undergrad studies, I still refer to it a couple times a week.

barefoot
 
My point is a transducer doesnt heat up and burn output caps. the speakers are just going to see a wave. the amp sees a changing load that can be dangerous.

And my bacholors degree is in electronics engineering thank you.

I can dig what you are saying though. But the method of using a dummy load has been used constantly for as long as this problem existed. If there was a new method that worked as well for the same ammount of money hell Id reccommend it.
 
I was originally planning on using a 4 ohm dummy load when I was thinking about buying my 20/20's, as they're 4ohm speakers and I thought my amp was only rated for 8ohms. I contacted an engineer at Event and he said:

"If you add the 4 ohm resister (inductive or not), it will be creating a damping factor of virtually 1. This is not recommended. The other downfall here, is half of the amplifier power will be heating the resister instead of powering the
speaker."

Later I found out that my amp is rated for 2 to 8ohms, so I didn't worry about this problem.

I think I'm set on just using a passive switch here. Thanks to barefoot for the schematics & links! When I get something built I'll be sure to post a pic.

Slackmaster 2000
 
My intention with my answer was to protect your equipment from overload. If a 99cent resistor gets hot and burns up like a fuse the amp and speakers are still unharmed. So I was under the impression that the safety of the Equipment was the big factor.
 
Protection of my equipment is important, and turning it all off before switching speakers is an acceptable solution for me. My biggest concern is sound quality. If I thought a switch would have a noticable effect on sound quality, I wouldn't use it.

Thanks!

Slackmaster 2000
 
You must log in or register to reply here.
Back
Top