# Speakers: ohm ratings?



## Cap'nBill (Dec 27, 2008)

I just got through hooking up a Dallee system in my Aristo Doodlebug. I had an old Bachmann..I guess...speaker, about 3" diameter, had 8 ohm stamped on the back. Sound and volume is actually pretty good, but I'd like a bit more volume. In the instructions they talk about running 8 ohm speakers in series, as many as 4. Can someone explain what exactly the ohm rating has to do with this? Bill


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## toddalin (Jan 4, 2008)

Posted By Cap'nBill on 21 Aug 2009 02:55 PM 
I just got through hooking up a Dallee system in my Aristo Doodlebug. I had an old Bachmann..I guess...speaker, about 3" diameter, had 8 ohm stamped on the back. Sound and volume is actually pretty good, but I'd like a bit more volume. In the instructions they talk about running 8 ohm speakers in series, as many as 4. Can someone explain what exactly the ohm rating has to do with this? Bill


Sounds like they screwed up. When speakers are combined in series, the impedience (ohms) are simply added together. Two in series is 16 ohms and while this would increase the cone area, it would cut the available power (watts) by half, so there is no net gain. Put three in series and you're at 24 ohms and cut the power to 1/3rd. Four in series is 32 ohms and power is down to 25%. In this last case, each speaker would receive 16th the power of a single speaker (i.e., 25% of 25%)

The proper way would be to use four speakers with each of the two pair connected in series and these two groups of two speakers connected in parallel. (This is called parallel-series.) This would still result in an 8 ohm load with four times the cone area. However, each speaker would still receive 25 percent of what a single speaker would have received.


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## Greg Elmassian (Jan 3, 2008)

You can't get something for nothing... what some people try is a lower impedence speaker, which will draw more current, and COULD give you more volume 

BUT !!!! 

If the system is not rated for 4 ohms, then you usually damage the amplifier, or increase distortion, or both. 

The best way to increase volume is to make the speaker more efficient. 

First, buy an efficient speaker... quality speakers are rated (usually) in how many db they put out for 1 watt... the more efficient it is, the more sound you get for 1 watt. 

Then you need a good enclosure. Unless you understand ported enclosures, and have the specs and the program to calculate the volume, port diameter and length... use a sealed enclosure.. 

That's all you can do without going to an additional amplifier. 

Oh, you can make sure there is nothing obstructing the speaker, I open up or remove grills in many cases. 

Regards, Greg


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## Cap'nBill (Dec 27, 2008)

I made a very 'high tech' enclosure for the speaker which gives a very nice ,deep, engine sound! I used a plastic drink cup! Hot glued the speaker in. I used the setup with a 9v battery supplying sound when track voltage is 'off', which gives a nice engine idle,bell, etc. I'm thinking the thin plastic allows enough vibration to deepen the sound.


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## lownote (Jan 3, 2008)

You could try two 4 ohm speaker wired in series--that would be 8 ohms. More speakers might equal better sound, if you have the room. I'd be inclined to just buy a better speaker


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## lownote (Jan 3, 2008)

Posted By Cap'nBill on 22 Aug 2009 07:27 AM 
I made a very 'high tech' enclosure for the speaker which gives a very nice ,deep, engine sound! I used a plastic drink cup! Hot glued the speaker in. I used the setup with a 9v battery supplying sound when track voltage is 'off', which gives a nice engine idle,bell, etc. I'm thinking the thin plastic allows enough vibration to deepen the sound.

You made a sealed enclosure. Speaker design is a art, although it's got lots of scientific parameters. Speaker designers typically carefully match the driver (the speaker) to the enclosure. They want to optimize bass response. The thing that is always missing from large scale is bass--a locomotive put sout a TON of bass freuencies. The rule with bass and speakers is that you can have any TWO of the following

small size
light weight
Deep bass response

The laws of physics make it so you can't have all three. But in large scale we are stuck--small size, low power. 


Sealed enclosures typically have good bass sound in a large cabinet. they depend on the physical size of the cabinet. And they are relatively low efficiency--i.e., they don't get very loud. What you heard was probably a strong improvement in the midrange frequencies, which are more or less the range of the human voice and the range where our hearing is most sensitive. But if you put a frequency analyzer on it you are probably hearing zero actual bass frequencies. Which is fine--if it sounds good, who cares about the theory? 



I've done some experimenting with "porting" enclosures--instead of a sealed box, you put the speaker in a box of a specific size with a hole in it, usually a tube of some kind. This lets you bump up the low frequencies in a small enclosure. You still don't get a lot of real bass, but you get a lot of low midrange, which people will often hear as bass. It's kind of a hit or miss proposition, because you can never find the specs for small drivers. I've also done what you did, put a plastic cap on the back of the speaker, and sometimes that makes it sound better.


Easiest way to imprive sound is a better speaker. I like the ones QSI offers a lot


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