Dual-ing speakers?

[Mark R.]

jwhitten

Mark R.:

Wire the two 8 ohm speakers in series for a 16 ohm load. This arrangement is actually better than a single 8 ohm speaker in that the increased load creates a smaller current draw on the amp which will let the amp run cooler and it will allow you to drive it a little harder - great for driving the lower frequencies.

 

the increased load RESISTANCE creates a smaller current draw

John

Ok - If you are after accurate terminology ....

the increased load RESISTANCE REACTANCE creates a smaller current draw

The term "load" is actually more accurate. The load rating for a speaker - while it is in "ohms" - is a different rating that a standard resistor in that frequency also plays a variable. The calculations for a resistor component use "R" where-as the ohm calculations for a speaker component use "Z". Reactance is not the same as resistance.

The term "load" is a generic terminology referencing any component that draws current / voltage, whether it's a resistor, speaker, motor, bulb, etc.

Mark. 

[jwhitten]

Mark R.

Wire the two 8 ohm speakers in series for a 16 ohm load. This arrangement is actually better than a single 8 ohm speaker in that the increased load creates a smaller current draw on the amp which will let the amp run cooler and it will allow you to drive it a little harder - great for driving the lower frequencies.

the increased load RESISTANCE creates a smaller current draw

John

[Mark R.]

It's just all that nasty theory stuff, right Jay ?  For our model train installations, we're dealing with a maximum of usually around 1 watt. If you absolutely have to use a resistor, a 1 to 2 watt resistor isn't that big and could easily be installed in an engine, but it will get warm - if not hot - so make sure it's isolated.

However, start talking a resistor for those mega-watt car / home stereos, you're talking a cement resistor that you'd be lucky to cram in a boxcar !  LOL

 

Mark.

[modelmaker51]

Mark R.

 sound quality will suffer, because the speaker impedance changes with frequency, but the same is not true for the resistor.

Mark.

Sorry, I mispoke, but that is what I was thinking.

[Mark R.]

modelmaker51

Do not add a resistor to the speaker(s). Resistance is not the same as Impedance. Adding a 4 ohm resistor will not give you 8 ohms impedance

Actually, you can do this. A four ohm speaker in series with a four ohm resistor = 8 ohm load.

Resistance will only have to deal with non-shifting phases of voltage and current which makes it simple. The same thing cannot be said of impedance as it is determined by another value, which is based on phase shifts, aside from resistance. That extra aspect is the reactance. A standard resistor is unaffected by reactance and will introduce the additional 4 ohm load.

This is simple in theory, but problematic in practice. You need to use a high power resistor (in the 4+4=8 example, the resistor will dissipate as much power as the speaker). Also, sound quality will suffer, because the speaker impedance changes with frequency, but the same is not true for the resistor.

Mark.

[modelmaker51]

Do not add a resistor to the speaker(s). Resistance is not the same as Impedance. Adding a 4 ohm resistor will not give you 8 ohms impedance

[mobilman44]

Hi!

I've built a number of speaker enclosures in my earlier days for home and auto systems.  The enclosure can and will have a major impact on the sound quality.  Yes, you can put the speakers in the same enclosure.  Make sure it is securely attached and no air can leak out.

I am not knowledgeable about the best ohm rating for model RR systems (home systems are typically 8), but the logic previously mentioned to go with the higher number makes sense.

[Mark R.]

Definitely DO NOT wire them in parallel, the 4 ohm load will fry the amp output.

Wire the two 8 ohm speakers in series for a 16 ohm load. This arrangement is actually better than a single 8 ohm speaker in that the increased load creates a smaller current draw on the amp which will let the amp run cooler and it will allow you to drive it a little harder - great for driving the lower frequencies.

You can place both speakers in the tender side by side, just be sure the face and rear of the speaker are separated from each other in the enclosure. The best set-up would be to mount the speakers to the floor with the face of the speaker ported out the bottom. The rear of the speaker will utilize the sealed tender shell as its enclosure.

QSI has an excellent resource for speaker accoustics and I highly recommend ANYone who is attempting sound speaker installations to read it ....

http://www.qsisolutions.com/pdf/loco_acoustics_design.pdf

 

Mark.

[fwright]

tbdanny

Laurie McLean, an MMR and fellow Australian who hangs out on the HOn3 Yahoo Group (http://groups.yahoo.com/group/HOn3), has done a lot of research into sound using Tsunami decoders and various speakers in HOn3 locomotives.  He generally prefers hi-bass speakers.  But it's worth joining the group and reading his files and information.

Speaking from an electronics point of view, the lower the impedance of the speaker set beyond the manufacturers rating, the greater the chance of damaging the decoder speaker output amplifier by drawing too much current and power.  Higher resistance than recommended is generally a good thing, but may reduce available volume below what is desired.

Fred W

[tbdanny]

Hi all,

After examining the speaker options available at my LHS for a sound install in a brass HOn3 C-25 locomotive, it seems that the large, perfect-for-the-install speakers are just slightly too large (2mm) to fit into the tender.  So I'm considering doing a dual-speaker install with the next size down.  They're rectangular speakers, 8 ohms each and the decoder is a Soundtraxx TSU-750.

I was wondering if:

- Each speaker needs its own enclosure, or if one enclosure will be alright for the both of them?

- Wiring the speakers in series will give 16 ohms of resistance, while putting them in paralell will give 4 ohms.  Would putting them in paralell with a 4 ohm resistor be the best option, or is there another way to ensure the resistance/output of the speaker will work with the decoder?

Thanks in advance,

tbdanny