2x speakers = halving of minimum reproducible frequency?

Dear Bruce,

A great article as always. However, I'd love to see the specific speaker driver, enclosure, and specs which achieves a full Octave frequency extension (halving of the minimum reproducible frequency, as measured by ??? under ??? conditions) by pairing 2 identical speakers together...

Unless what you're suggesting is that by raising the overall dB SPL at a lower frequency via the doubling of speaker drivers,

IE lifting the entire frequency plot by +6dB SPL

the apparent "low frequency response" is extended?

Happy Modelling,
Aim to Improve,
Prof Klyzlr

PS its worth noting that "Frequency Response" of a given speaker (driver + enclosure as a complete system) is often measured when the frequency plot hits -3dB below "average", -10dB is the "Frequency Range". Of the two measurements, "Frequency Response" is more closely aligned with what the human ear will percieve.
(-3dB SPL is "barely noticable" roll-off. -10dB SPL is "where did the sound go?" roll-off).

Check the specs on page 17 of this, one of my fave portable powered speaker units, the Mackie SRM450 http://www.mackie.com/products/srm450v2/pdf/srm450v2_om.pdf

Freq plot on Page 5  http ://www.mackie.com/products/srm450v2/pdf/SRM450v2_SS.pdf

 JBL EON 515 example
http://www.jblpro.com/BackOffice/ProductAttachments/DOC_1190.pdf

Illuminating!

I have been wondering how to determine how to use multiple speakers.

Now I have confidence how to wire multiple speakers.

Thomas, DeSoto TX

Driving 4 speakers

Bruce

Thanks for a very informative and helpful article.  However I am still unclear about the decoder speaker wattage rating and multiple speakers.   In the article you show four 8-ohm, 2-watt speakers in series/parallel with a combined impedance of 8-ohms.  The impedance part is logical.  What about the watts?  It will handle 8 watts?  Can you drive them adequately with a TCS WOW decoder rated for speakers with 8-ohms and 1-watt minimum?  Any issues?

Thanks again,

Dave

Bruce, I'd be interested in your.............

...............thoughts about the new QSI Titan with stereo sound.  I just installed one in a V & T 4-6-0 (O scale) and was able to cram a small oval with enclosure in the smoke box directing the sound out the hollow stack.  I'm impressed with the sounds of the Chuff seemingly coming out the stack.  Each individual sound can be balanced left to right (front to back) so the bell is more to the front than the whistle and the steam generator.  The water fill is all the way to the back.  It's really quite an impressive sound as it passes you on the layout.

Thanks and Happy New Year,

Peter

Wattage

QSI Titan

Titan Stereo

I have installed QSI Titans one in an HO E6 and two Titan for Large Scale in an AristoCraft SD-45 and an AristoCraft Pacific. For the E6 I mounted one speaker through the fuel tank and one forward in the chassis with the baffling directing the sound out of the grills. The only sound I have messed with in the HO install is the horn which I directed to the top front speaker. I like the results, and I am planning on installing Titans in four more locomotives as the cash becomes available.

I used three speakers in the SD-45 and four in the Pacific. A large oval speaker is mounted in the top rear of the SD-45 directing sound out of the rear cooling fan towers. Two 2" speakers wired in series with one mounted in the floor of the front high nose hood and the other ported to direct sound out of the high vents behind the cab. Again I like the sound of the horn coming from the front and other sounds distributed around the engine But the oval speaker is not great and I need to find a replacement before tuning the sounds on this engine.

For the Pacific I wanted to attempt to move the sounds closer to the points of origin. I disconnected the speaker in the tender then I mounted two speakers in the bottom of the smoke box and two in the bottom of the firebox. Installing speakers in these locations requires modifying the weight, moving the wiring and drilling holes in the bottom of the loc so it is definitely not for the timid. I have directed the bell and chuff sounds to the front speakers. Several sounds such as the generator are directed to the rear speakers. The whistle is distributed to both sets of speakers since the locomotive whistle was located near the center of the loc. Even with the smaller speakers I like the sound of this installation, but I it could still use the umph of larger speakers in the lower ranges. Note: to reduce the wiring hassles I also moved the decoder mount from the tender to the boiler. The only active wires to the tender are for power and rear light.

All three installations can generate enough sound to be annoying especially the SD-45, so none of the volumes are set to more than 50% and most are set in the 25 to 30% range. Even without much tuning of the motor CVs the operational performance out of the box has also been very good.

I am looking forward to hearing the experiences others have with these decoders.

Mistake in MRH January DCC Impluses Column?

I think if you look at the diagram and read the text for Diagram 10 you will see the error:

10: Four speakers in a series-parallel array – the final impedance will be the same as the speaker impedance – 8-ohm speakers will yield an 8-ohm load. 

The top two alone are 8 ohms as are two bottom ones alone so you have two 8 ohm loads in parallel for 4 ohms. At least that was the way it was when I went to school. Others may have already pointed this out (??).

LDBennett

LD

School

That is what I learned in my school may years ago.

Rich

I concur with Bruce

You are correct that two 8 ohm loads in parallel are 4 ohms but when you wire  a pair of 8 ohm speakers in series you get 16 ohms.  Then when you wire those two series wired pairs in parallel you are back to eight ohms. Years ago in a past life I used to build my own PA speakers for my rock n roll garage band......

Michael

Loksound Version 4

Thanks Bruce

I really enjoy reading your DCC stuff.

I tried to use 4 x 8 ohm sugar cube speakers as you described maintaining impedance of 8 ohms. All speakers are properly aligned (+) and fire up, but I now have a volume problem. With the Loksound volumes all set at max I cannot hear the speakers once the top is placed back on. I am trying to get the sound to play out of each of three carriages of a self propelled carriage set. Each carriage should run two Cummings units which are identical to the GENSET units trialing in the States.

The model is powered in one end only I have one speaker mounted in each end and two at each end of the middle car. Nothing worse than watching a Rail Motor set pass with only one carriage sounding as if it is powering

Would you have expected the volume to drop so far with 4 Loksound cube speakers?

Is my next step to add an amplifier, and have you ever thought  of doing this,  or better still done it?

Cheers

Rod Young

Rod

OH.....I missed something

OH.....I missed that you were using 8 ohm speakers not 4 ohm as you had in the previous diagram.

So the top and bottom two are 8 + 8 = 16 then when in parallel you get 8 ohms. YES!

Can you really get tiny speakers like this in 16 ohms?

Sorry,

LDBennett

TIMELY COLUMN

With the recent influx of affordable micro-speakers from cell phones, this article was right on target.  All of this information is out there but you summed it up in one place.  Great job Bruce.

Ed Robinson