Which is Better? Big Speaker or Big Enclosure?

[cbroughton67]

So, in batting-around ideas for creating an enclosure for a 9x16 speaker to fit an Atlas GP38/40-2, @Lemosteam and I began to wonder which is better - a big speaker with a small enclosure, or a small speaker with a big enclosure? By the time the 9x16 speaker is moved down enough in the enclosure to clear the decoder board, the chamber over the flywheel is cut-off, and the volume behind the speaker is reduced to the small area directly between the speaker and chassis. With an 8x12 speaker, the chamber over the flywheel remains open to the rest of the enclosure, and volume behind the speaker itself is much larger relative to the size of the speaker than with the 9x16. Since each arrangement is a trade-off in one way or another, which one will produce the best sound? @jdcolombo this is an area where I'm sure you'll have valuable insight. What are your thoughts?

Thanks,
Chris

[jdcolombo]

You need enough internal volume in the enclosure to allow the speaker, whatever its size, to sound its best, and in general the larger the speaker, the larger the enclosure size needed.  My own experiments have indicated that the following are the absolute minimum internal volume sizes for various speakers to sound "good":

8x12 - 500 cubic mm
9x16 and 11x16 - 750 cubic mm
13x18 - 1000 cubic mm

Speaker manufacturers generally test their speakers with a 1000 cubic mm (1 cubic cm) enclosure.  All of the speakers above will sound better with a larger enclosure (you can have an enclosure that's TOO big, but we're not in much danger of that given the space we have to work with}.

Here are a couple of videos that illustrate the point.  The first is a video of 8x12 mm speakers in three different-sized enclosures: the "double deep" enclosure from SBS4DCC, which is about 8mm high, producing an internal volume of 8x12x8 = 768 cu.mm; the "regular" enclosure, which is 4mm high and with an internal volume of 384 cu.mm, and two I built myself that are "in between" sizes.  You can pretty easily tell that the "regular" SBS enclosure gives a significantly "thinner" sound than any of the others, and that the 5.5mm custom enclosure sounds just about, but not quite, as good as the two bigger ones:

And here is a similar test with a 13x18mm, which starts with no enclosure at all (no sealed back, and then goes to a 6mm deep sealed enclosure at the 1:12 mark.  The 6mm enclosure has an internal volume of 5.5x13x18 = 1,287 cu.mm (the 5.5 comes from the fact that I included a .5mm base in the 6mm measurement).  But note that at the 2:25 mark, I test the 13x18 speaker in an "elongated" enclosure that has internal volume of 5.5x13x24.5 = 1,751 cu.mm and this one clearly sounds better than the plain 6mm box.

So, you get better performance from speakers as the internal volume of the enclosure increases, and each speaker needs a sort of minimum to sound good.  In general, therefore, you are better off with a smaller speaker in an enclosure that is larger than the "minimum" vs. a larger speaker that is barely at (or below) the minimum.  BUT, a larger speaker at its minimum will sound better than a smaller speaker at its minimum, and a larger speaker somewhat above the minimum will always sound better than the smaller speaker.

So I'd conclude the following.  If you can make your enclosure so that the 9x16 speaker has an internal volume of at least 750 cu.mm, go that route.  If the internal volume of the enclosure is going to be much less than 750 cu.mm, go with the 8x12.

John C.

[cbroughton67]

@jdcolombo  Thanks for the thorough and very informative response! It not only answered my question, it provides an great overall education on speaker and enclosure sizing. Thank you!
Chris

[Lemosteam]

Agree, thanks John for this and for the PM response of a similar nature.

[jdcolombo]

BTW, I should have noted that in the first video, my 5.5mm enclosure is really only 5mm of internal height, since the 5.5 includes a .5mm base.  So the internal volume of that enclosure is 5x12x8 = 480 cu.mm.  And you can tell if you listen closely that the sound is starting to thin out.  Not as thin as the SBS "regular" enclosure, but not quite as full as either the SBS double-deep or the larger custom enclosure.

John

[Bill H]

John et al;
Expanding on your thoughts, literally, if you had significantly larger space, such as an Bachmann EM-1 tender - would you go with a larger speaker, larger enclosure, two large speakers or?

Apologies in advance if my follow up will seem comparatively delayed by RW standards, I am in Asia at the moment on a tax mission and it will take 48 hours before I land back in the US.

Kind regards,
Bill

[jdcolombo]

John et al;
Expanding on your thoughts, literally, if you had significantly larger space, such as an Bachmann EM-1 tender - would you go with a larger speaker, larger enclosure, two large speakers or?

Apologies in advance if my follow up will seem comparatively delayed by RW standards, I am in Asia at the moment on a tax mission and it will take 48 hours before I land back in the US.

Kind regards,
Bill

Hi Bill.

In my EM-1, I used a 13x18mm speaker in a plain box that was 10mm high overall, firing up at the coal load from the tender floor.  The interior height of that enclosure is 9.5mm, which means that the interior volume is 9.5x13x18 = 2223 cu.mm   I think it sounds great (I stripped out all the Bachmann stuff and put in an ESU LokSound with the BigBoy sound file).  I am wary of multiple-speaker installations.  It seems like a good idea, but two speakers firing inside a tender can result in weird sound nodes - where some frequencies get suppressed because the sound waves bouncing around inside end up out-of-phase, and some get reinforced.  This is true even when they are properly wired in-phase.  A bigger SINGLE speaker might be an improvement, however, if coupled to a suitably large enclosure.  I just had a bunch of 13x18's on hand, so I used one of those.

John C.

[Bill H]

Hi John:
Finally back in the US. Thanks for your thoughts. That EM-1 tender has a lot of available space once cleared of Bachmann clutter. Your speaker recommendation was based on what you had in hand, the 13x18. Hypothetically, if you were going to procure an even larger speaker what would you have selected?

Pleased to hear that the Big Boy sound file was appropriate, but curious as to what whistle you choose?

Kind regards,
Bill

[jdcolombo]

Hi John:
Finally back in the US. Thanks for your thoughts. That EM-1 tender has a lot of available space once cleared of Bachmann clutter. Your speaker recommendation was based on what you had in hand, the 13x18. Hypothetically, if you were going to procure an even larger speaker what would you have selected?

Pleased to hear that the Big Boy sound file was appropriate, but curious as to what whistle you choose?

Kind regards,
Bill

Welcome back!

I don't know of any "cell-phone" type speakers that are bigger than 13x18, and I think a 13x18 cell phone speaker vastly outperforms other rectangular speakers available.   For example, CUI makes some conventional speakers as large as 20mm x 34mm, but I don't think they sound any better than a 13x18 cell-phone type. 

However, it might be worth TRYING two 13x18's in a specially-engineered enclosure, like the SBS Twin Double-Deep and seeing if the results are worth it.

https://store.sbs4dcc.com/SBS4DCCSugarCubeSpeaker13x18mmw/DoubleDeepTwinCoupledSoundCham.aspx

The fact that I've been wary of using twin speaker designs doesn't mean it's not worth an experiment.  Every installation will be somewhat different, and it might work great in the EM-1 tender.  You never really know until you try.

I used the "steamboat" whistle available on the Big Boy file.  If I had it to do over again, what I'd probably do is use a V.4 decoder (maybe now a V.5?), and edit the Big Boy V.4 sound file to substitute a more appropriate whistle.  The steamboat is really pretty much a UP thing, but there isn't any sound file that contains a whistle like the actual EM-1 (which you can hear on a couple of YouTube videos).

John C.