Using two speakers versus one and sound improvements

The quality of speaker and the enclosure are much more important factors than the number of speakers.  Two cheap speakers will sound like one cheap speaker.  A single high-quality speaker in a good airtight enclosure will sound better than a larger speaker without an enclosure.

I've found that the sealed enclosure is at least as important as the speaker quality.  It makes a huge difference in both the volume and the bass response.

First +1 what Bob and John say about speaker quality and enclosure. As for parallel or series wiring it all depends the on speaker impedance and what you want to end up with. If you had two 8 ohms speakers and wanted to end up with 4 ohms looking back at the amplifier you would wire them + to + and - to -.

Pete

I have a history in professional audio equipment through my father. He has run recording studios all my life. I have spent years critically listening to different amps, speakers, etc... I spent some time discussing speaker theory with a PHD who designed his own line of home speakers a while back. I'll spare you the details, but understand that the enclosure is actually the most important part of the equation when it comes to speaker design. A cheap speaker in a properly sized/designed enclosure will sound better than an expensive speaker in a poorly sized/designed enclosure. It doesn't necessarily have to be a sealed enclosure. These are the easiest to size and design and work well. Don't be afraid to try Ported, Bandpass, or Infinite baffle designs though.

I will be experimenting with the new cell phone/tablet speakers soon. They give you a lot of surface area for their size and they seem to be good at reproducing the frequencies that we deal with in our engines. I plan to build out an array similar to what is in this video:

Fast forward to about 3:20 on this one. The TCS WoW sound decoder has much better sound quality than the first decoder he uses.

Only reasons to use 2 or more speakers would be

Sound separation (for stereo effect) impractical for a small engine.

To match impedance. Another speaker giving off sound is better than a series resistor producing heat and returning nothing.

Using different speakers for greater speaker response. A large diameter for bass response and a small diameter one for treble. This is also impractical in model railroading unless we used remote speakers not in the engine.

great videos by Johnnyspeed but I think the solution is larger remote speakers mounted under the layout,then we are not limited to the world of miniature electronics and 2 inch or less speakers. 

Of course baffling is always important to a good sound system .

Dale H

I appreciate the info, but the questions still has not been answered.  Assuming I have 2 high quality 8 ohms and 1 high quality 4 ohm all capable of being installed in the same enclosure (Large Brass Tender).  What sounds better.

I do need to use the 4 ohm equivalent since this maximizes the power out since this is a PS-2 audio amp.

I have seen lionel 2 speaker units wire in parallel + to - vice + to +, I thought it had to do with preventing cancellation.  So we have one for + to +.

I realize the best way is to go and do it and listen, but that is a lot of work and I was hoping someone tried this and could provide some feedback.  G

I am not an expert,  but I have heard it said that if you connect two speakers in parallel, they will be out of phase.  This would affect the sound.  I'll leave it to others to discuss this subject in detail.

From my time working at Rockford Fosgate, if you can fit two speakers in the enclosure, and it sized correctly for those speakers, IMHO it'll sound better.  As for any power issues, on small speakers it's really a non issue, unless you are cranking the volume up to 11.

As to the wiring of the speakers, since the system was set up for 4 ohm, you need to wire 2 8 ohm speakers in parallel (+ to +, - to -) to get 4 ohm, or 2 2 ohm speakers in series (+ to -) to get 4 ohm.  If possible find 2 ohm speakers and it'll sound better than 8 ohm speakers, again IMHO.

I also think sealed enclosures sound better than ported or bandpass.  Sealed gives you nice tight and quick responses but the bass will not be as hard hitting, while a ported enclosure will give you nice load hard hitting bass, but has a slower response so you can loose some of the "details" in the sound.

And I've never had any phase issues with multiple speakers.  But you can check that visually by seeing if they both go out and in at the same time.

So, I'd say go for the dual speaker.  But also keep in mind that they will be making the same sounds, where my understanding is that 2 or 3 speaker setup in other fancy locomotives is so the different speakers can do different sounds, and that will always sound better.

One experiment that I am eager to get around to is to install a Bluetooth transmitter in the loco that would send audio back to a Bluetooth receiver that would be connected to an under layout amp and woofer. Since Bass is non-directional the thought is that it would really "round out" the low end. The mid to high level frequencies (which are directional) would come from the engine while the low end would be supported by the woofer. If each engine had a TX you could use a mixing board to output to a single woofer.

I'm trying to get the importers to design the Bluetooth capability into their electronics ;-) So far no luck though.

I have to disagree a little on there only being two reasons for having multiple speakers... A speaker is an air pump. If multiple speakers give you more surface area, then all things being equal, you will be moving more air and typically have better low frequency response and a fuller sound in the case of our models.

 G, I put the two speakers in a G gauge diesel. One reason it works is because usually there's only one speaker in the fuel tank pointing down on the track. I put the second one pointing up towards where the user stands running outside.

 Overall I have to say even that was a wash. One great speaker at 4 ohms does just as good. SO the only benefit I could see happening, is increasing the low end thump coming from the tender with two drivers in a given space. It would be a simple test for you to try.

For me, after a lot of work, I found one good speaker does the job. I will try again with a steamer. However one speaker will be put in the boiler to distribute the sound where it should come from. I wish MTH boards had gone with sterio output by now.

 I believe that Lionel does the two speaker thing to get the absolute most bass response they can get out of those speakers. You would need to consider how many watts the MTH board puts out to see that it may not be beneficial to drive the extra speaker to better results. How much power comes out of a railsounds 5 board??

Ok, good stuff to ponder.

Sinclair, I would still wire in parallel, but you can go with one wire to the + of one speaker and the - of the other and still stay in parallel.

Jonny, so then the question becomes just one larger 4 ohm?

The premise of my question was based on the fact that a audio amp that looks for 4 ohm equivalent doesn't send the higher current that would flow through a single 4 ohm, through the 8 ohm speakers.  They would see half the current.  The overall current would be the same, but individually you would have each 8 ohm seeing a reduced output.  So the premise is... do the 2 lower outputs combined sound better then a single higher output considering everything else is equal?

So I can get more surface area, and this may make the difference, unless cancellation wash that out as Joe mentioned.

Joe, the problem is this is a top end Brass Engine.  Location for mounting boards and speakers  would be the issue, and I don't want to drill any unnecessary holes on just a trial basis.

So maybe I just need to rig a test board and power the 2 8 ohms without mounting.  I have to wait on a 2 stack smoke unit anyway.  Other problem is I am not sure my hearing is the best to judge this.  G

 I bet you'd be fine to test as most hearing goes in the upper registers? I sent emails about discussing this further and what I was told that should work. There's a guy here on the forum (CRH) that I'd bet has tried it. He has good knowledge and experience of using PS2 boards.

In our small models it is going to be close. I personally prefer two 8 ohm speakers wired in parallel which presents a 4 ohm load to the amp. In car audio as Sinclair pointed out, this is usually a preferable arrangement. Sound is subjective, but that is what I prefer.

In my cell phone speaker experiment I am going to try to use 16 speakers in a parallel/series combo. The idea is not to overdrive the amp by presenting it with the rated load, but moving as much speaker surface area as possible. It should be interesting.

G, If you wire them in parallel you do NOT want to connect the + on one speaker and the - on the other speaker to the + of the amp or the bass will cancel out. You connect + of one speaker to the - of the other only when you connect them is series, eg. two 4 ohm drivers to create an 8 ohm load. For PS2 4 ohm amps best use two 8 ohm driver connected in parallel.

The way to test any combination of speakers for proper phasing is to connect the combined connection that would go to the amp and place a 1.5 volt battery to the leads and verify all the cones move in the same direction either all in or all out. By convention connecting the positive battery terminal to the + on the speaker should move the cone outward, away from the magnet.

On some earlier models Lionel did connect 2 8 ohm drivers in series like in the Niagara Tender. Not sure why they did this other than they did not stock 16 ohm drivers at the time and connecting them in parallel would overload the audio driver board which is designed for an 8 ohm load. Later engines with dual speakers use 16 ohm drivers. Fatboys both 40mm and 50mm are now available in both 8 and 16 ohm versions.

Pete

 I almost would always go with two speakers over one.

I just don't think there's enough current being handled to get benefits from two here. If you were under-driving (power) one speaker, would two be better??

Joe makes an interesting point here. I typically turn the volume down to about half on my trains. Having the 2 speaker, you can turn up the power a bit without overloading the speaker and causing distortion.  This will compensate for the fact the speakers are being driven at half voltage. Look also at te sensitivity of the speaker.

some speakers produce more decibels at a given input than others. I suspect this is where the Fatboys excell.

Like Pete said, don't do parallel wiring with + and - of the speakers.  This will cause one to push out and the other pull in, and this will give a canceling effect some have spoken of.  Both speakers need to move in the same direction at the same time to give the correct sound.  And as long as both speakers are the same model and brand, they should fire in unison when wired + to + in parallel.

"I have to disagree a little on there only being two reasons for having multiple speakers... A speaker is an air pump. If multiple speakers give you more surface area, then all things being equal, you will be moving more air and typically have better low frequency response and a fuller sound in the case of our models."

I think you are right about that,I stand corrected. I just did not think it through.

Dale H

 Stuff in sound doesn't always add up.

What if you ran a pump at let's say 2000 gal per min.

What if you added a second pump that stole the power from the first so that each ran at 1000 gal. Would there be a benefit?

 Of course there would if you could run each pump up higher and get the combined results. If you didn't have the power to drive them higher, you may be just wasting money.

There is one more reason to use two speakers - adding sound to a dummy A or B unit.  I have a couple sets of Alco PA that are semi-permanently attached with a drawbar.  I replaced the standard 4 ohm MTH speaker with two 8 ohm units from Madison sound.  Put one in the powered A and one in the dummy.  Ran 4 wires from the A to the B unit.  Two for the speaker and 2 for the electro coupler.

They don't pull any better but the sounds coming from both units sure makes me think they are.

A couple more wires and you could have has some lights as well.

Great analogy! I don't have the specs handy for the PS2 3v audio amp but you're only talking about a power output of 3 watts! That ain't much power for driving a speaker let alone 2. I can't remember the exact formula but Joe may as SPL (sound pressure level) isn't linear when you get up in the 90db range...that is a increase of 1db will sound twice as loud. So if the PS2 audio chip has to drive 2 speakers then there will be a drop in SPL..even a drop of 1db may only sound half as loud as 1 speaker. 

Chuck

I do not think the problem is volume, rather it is frequency response. It is not about capacity like pumps,it is about moving air volume. In the pump analogy,it is more like taking a 2000 gallon pump and running it through a 2 inch line,then taking a 2000 gallon pump and running it through 2 parallel 2 inch lines. More places for water to go and less resistance.  I used to repair a lot of jukeboxes and witnessed development. Later mono high fidelity Seeburgs used paired woofers and paired tweeters to get better sound. These were 25 watt amplifiers driving 4 speakers in some models. Earlier single speaker models still used a somewhat similar 25 watt amp. There was no problem driving extra speakers,further remote ones can also be added as long as impedance is matched with a selector switch. Either of these boxes filled a room up with sound and could be heard from a long distance. The volume level is similar but boxes with multi speakers sounded better as far as clarity noticed when a record is switched from one box to the other. I have both type models in my collection and can hear the improvements made by the use of multi speakers. 

Dale H

Still a lot to ponder, I guess I am going to have to test it.  The AB makes some sense now that you have speakers separated and in there own enclosure.

Dale,  In your analogy it still is Volume related and is would be two 1 in pipes.  Since you have to keep the same equivalent impedance of 4 ohms, the 2 8 ohm speakers individually are smaller pipes.   G

This talk of audio theory is interesting and most would hold true but Joe's point about having only a one watt amplifier means a lot of this doesn't apply. If we had 10 watt amplifiers to play with and 3 of those watts were all that was needed to drive the speaker into distortion then more drivers would improve the sound quality and allow for higher volumes. Cone travel in a piston driver is linear for only about 2/3rds of its travel. More power only distorts the sound. Adding more drivers keeps the drivers in the linear range for the same volume. Adding more drivers does not increase the frequency range though. That is limited by the resonant frequency characteristic of that particular driver. When Bose developed the 9 driver 901s which used smaller drivers he had to use an equalizer to boost the bass. This worked because all of the drivers only had to move a fraction of what a single driver had to move for the same volume.

Unless you wanted to add a booster power amp with equalizer your best bet is still the largest, highest quality driver that will fit in a well sealed enclosure. Ducted ports and transmission line designs might work in a large freight car but not practical in an engine or tender filled with electronics.

Pete

G

You are right. The whole water analogy really does not apply,as good as it may sound. It is more about speaker and amplifier design. Pete brings up good points also.Audio engineering is a science to itself and very involved.  I think the reason in a small train to add a speaker really is to match impedance. I did that in this thread because I needed 16 ohms. I could not find a good 16 ohm  2 inch speaker so I used 2, 8 ohm ones in series. I could have used 1 speaker and a resistor. But a resistor uses power,and gives back nothing.

http://www.jcstudiosinc.com/BlogShowThread?id=621

BTW,the Bose 901 speakers Pete is talking about could literally shake a building. Used to drive 4 to 8 of them with multi Phase Linear amps and an equalizer in the disco era. Patrons were so drugged out in the 80s,they could tolerate it. Im sure many had permanent ear damage.  Funny it was not really much louder close to the speakers than away from them. Bose had unusual reflective baffling. Infinity speakers used a different tower approach. A lot of controversy as to which speakers replicated sound better. The science is not really settled but Bose could put a lot of sound out of small spaces. If you get a chance listen to one of their wave radios. 

Dale H

Agreed Dale. Bose are masters of tuned porting. They can get an amazing amount of sound from the smallest package.

I agree with Norton as well in that the electronics in the tenders are too big. They are eating up space that could be used to reproduce sound ;-)

I still hope someday one of them will experiment with adding Bluetooth to their electronics package so we can offload the bass to a stationary under table woofer setup.

I have to say though, that Lionel in particular does a pretty good job with sound quality though. I was listening to a Scale Polar Express Berkshire with a FatBoy setup and short of letting Bose design the tender enclosure, they are doing pretty darn good. The esoteric 2%er nuts like me will always tinker and try to improve on it, but I have a screw loose A good sealed enclosure and a speaker or two that is properly matched to the amp is going to be fine for 98% of people. It never hurts to experiment though.

 (I just realized I'm now describing diesel sounds only)

Sound is not quite like fluid. There is a sweet spot driving an amplifier just right where it sounds warmer (hotter) and not overdriven. If they idle at lower volume, not only aren't you using there capability efficiently, they actually can sound dry.

 Now if you drive an amp near or worse, past it's limit, it gets mushy sounding and even distorted if driven too far past. I always drove my sound system to the sweet spot where people were not blasted out of a room, but the system was warm and full.

 Using that in model trains is tougher. The big warm frequencies aren't even available on some soundsets. If you could get the diesel engines to lug down electrically and the sounds to match, we could work towards fuller diesel sounds. If they are recorded in the upper frequencies that irritate the senses, people will turn them down anyways, so not to get blasted.

 So with three watts coming out of a stock board, how do we get the most of it. A very important link is missing. The ability to tune the frequencies with an equalizer of some sort. Instead we are trying to make our sound enclosure tuned to eminate desired frequencies. Yes two speakers will be better than one. Unless we:

 1) overdrive the amps smooth range towards distortion

 2) simply don't have the physical room for them

 3) don't turn up the volume to fill the enclosure with sound to gain the usefulness of more drivers anyways

 I prefer JBL loudspeakers over Bose. I prefer live sound over studio. I don't like louder is better now that I'm older.

My ear is influenced by these choices.

I think mounting (an enclosure) will be critical for evaluation.  I suggest you cobble together a test enclosure of similar volume and shape.  In other words make a 5-sided box to represent the tender shell.  Then make two 6th sides, one with the 4-ohm, the other with the 2-8 ohms.  Here's a "box" I used to evaluate different speakers in a proxy enclosure before committing to modifying the actual item (a custom-built non-train scale model).  It was cobbled together with acrylic sheets. I used Tacky-glue (inexpensive at craft stores) to seal the speaker to the enclosure as Tacky-glue cleanly peels off.  Obviously, this is a crude proxy for your real brass shell with circuit boards etc., but in my experience this method will get you a good way down the road.

If you're using PS2 electronics and presumably an MTH-developed soundset, they surely tuned or equalized the stored sounds to match THEIR speaker-enclosure combination.  Hobby-grade speakers are typically highly resonant with a sharp peak in the frequency response.  So if YOUR speaker-enclosure combination has different resonant characteristics, it becomes a question of what sounds best to you when driven by the specific waveforms which you cannot change.  That is, while instrumenting a traditional frequency-response might be instructive, listening to the actual chuffing, bell, whistle, etc. is where the rubber meets the road.

 Stan, I may have asked you before and if I did, I apologize. Were you part of the development of these boards? You seem well above the average repair tech. I look for your replies when I can.

You may be assuming facts not in evidence, I wonder how much trouble they go to match the sounds to the speaker and the tender side.

Wouldn't you, at some point listen to what the end result is?

If I may be so bold as to muck up the subject a little more, in my previous post I mentioned using two 8 ohm speakers in an AB set, one installed in each unit.  What I failed to mention was that I am also using a sound set for an MTH G gauge Loco. 

To me it just sounded a little better than the "O" version.  I dunno, might be my old ears. 

John

No need for modern blue tooth technology, perhaps we can pick up a pair of these on Ebay and use a transmitter.

www.jukebox-world.de/Forum/Arc...burgSpeak-O-Gram.htm

Just love those speakers with field coils,they add heat to the room on a cold winters night

Dale H

I think there are some facts here since MTH has 2 speakers of the same size and ohms but different designs.  Same goes for the earlier speakers.  If there wasn't any thought, there would just be one speaker of each size.  G

No doubt some thought goes into speaker selection but its the bean counters not the engineers who make the decision.

I have found the speaker pictured by Stan above and found in nearly all of the early MTH engines in a bucket at my local electronics store selling for 25 cents retail. You could probably estimate what wholesale would be on a many thousand piece purchase.

Stan mentions high resonant peaks. Those paper cone speakers have a resonant peak above 450 hz (measured). Compare that with a Lionel Fatboy at about 225 hz. I think Dale has found some 50 mm speakers with a peak at 190 hz. Bass rolls off below that point in a closed box. Regardless of the frequency content of the sound set, lower is better.

Pete

Early MTH speakers found in all my MTH PS2 engines,along side some of the ones I replaced it with. 25 cent speakers at best. No serious audio engineer would use them. Eventually I will get them all changed when opening the engine,space allowing. Diesels are a problem sometimes unless you mount something in a dummy. All that room in a dummy and MTH mounts a 25 cent one in the power unit fuel tank. Click on photo to enlarge

Dale H

Pete, you only see the face, not the back side?  You can go to the distributor web sites where you have to buy speakers in the 1000 to 10000 lot, and I haven't seen them at $.25ea.

The speakers I have seen in Lionel, Weaver, Williams, Bachman, Brass engines etc... have looked very much the same.  Granted the Fatboys and some higher end speakers are better.

One thing I do know is the magnets on the MTH speakers are far stronger than any other manufacture. I assume that has some effect on the quality.

I still believe a significant difference is Lionel's 2 board set up for sounds, versus MTH integrated system, plus the quality of the recorded sounds.  G

These look interesting for replacing the early 16 ohm ones in MTH engines. Not sure if they would fit

http://www.ebay.com/itm/2-2-in...;hash=item485677527e

Dale H