GP15 Loksound

[GM50 4164]

I seem to recall someone posting pics of a Atlas GP15 they had installed the 73100 into. Would you mind sharing the link please. Trying to figure something out.

[Steveruger45]

I didn’t see a write up on this and I don’t have one of these locos.  But, checking out the frame at spookshow it does appear putting a 73100 in would be a similar install to the Atlas GP38.
Space under the rear end of the decoder for the Speaker enclosure looks a little shallow even with some frame filing at the rear end, but it looks possible to get an 8x12 speaker in with a shallow but longer enclosure to boost up the cubic capacity.

[GM50 4164]

Steve, here is what I've been able to do so far. The first pic shows my first attempt. 9x16 speaker with a piece of styrene across the front. The second pic shows the space milled allowing a 8x12 speaker and enclosure to fit under the end of the board. I also added 2 caps to the engines.

[Steveruger45]

I like the second pic.  Deeper speaker enclosure is good and I see you lengthened it too. It should sound really good.
Yep, it looks to me a very similar install to the GP38/40.
Nicely done.

[jdcolombo]

Yep, second pic is the way to go.

John C.

[peteski]

I wonder if gm50 4164 can hear the difference in sound quality between them? 

[tehachapifan]

I wonder if gm50 4164 can hear the difference in sound quality between them? 

Curious about this too as I've been surprised with how good a small enclosure can sound sometimes.

[GM50 4164]

I wonder if gm50 4164 can hear the difference in sound quality between them? 

There is absolutely a notable difference. Now since there was room after milling I took advantage of but if there wasn't enough room I could live with the other as well. The second pic does sound fuller.

[Steveruger45]

Yep, a flat piece of styrene applied like your photo 1 does work ok. In fact that’s exactly what I did with some MRC decoders a long while ago and they indeed sounded better than the original onboard MRC speaker.  Like you, I find if I had to live with that design I would but with a higher capacity enclosure the sound is indeed fuller to my ear too.  I have found around 500mm3 for and 8x12 and 800mm3 for a 9x16, seems to be the sweet spot to my ear at least.  I’ve put bigger capacity on an 8x12 up to about 930mm3 with an odd shaped stepped enclosure, it for sure is no worse sounding but at best only marginally better than around 500mm3. 

[jdcolombo]

Basically any enclosure is better than none at all, but there will be a sweet spot in terms of internal enclosure volume.  Like Steve, I've found 500 cubic mm to be a good choice for the 8x12, while 750 or so (close to Steve's 800) seems optimal with a 9x16 or 11x15.  The 13x18's I use in larger steam tenders seem to need a full cubic centimeter to be their best.

I've harped on this before, but as GM50's install shows, the enclosure doesn't have to be a simple box around the speaker.  A longer, thinner enclosure with the speaker offset to one side is an excellent solution in many circumstances.

John C

[Steveruger45]

While sound results can be very subjective It seems John's ears and mine are hearing much the same.
Just one extra thing I have found is that putting a 9x16 speaker in a less than 750-800mm3 enclosure doesn’t sound as good as an 8x12 in an enclosure of the same volume as the aforementioned..  At least that’s what I thought when I squeezed in a 9x16 in a shallow enclosure of 4.5mm tall (giving internal height of 4mm and capacity of about 575mm3) as compared to an 8x12 mounted offset in a similar sized long shallow enclosure filling the same space.

[daniel_leavitt2000]

If I needed to use a baffle-less speaker like the first GP15 attempt, would it be better to use a 8x12 or a 9x16 speaker?

[peteski]

If I needed to use a baffle-less speaker like the first GP15 attempt, would it be better to use a 8x12 or a 9x16 speaker?

I wouldn't use any speaker without a baffle/enclosure.  The sound will *SUCK*!!!  Honest!

Quoting https://en.wikipedia.org/wiki/Loudspeaker_enclosure

The primary role of the enclosure is to prevent sound waves generated by the rearward-facing surface of the diaphragm of an open speaker driver interacting with sound waves generated at the front of the speaker driver. Because the forward- and rearward-generated sounds are out of phase with each other, any interaction between the two in the listening space creates a distortion of the original signal as it was intended to be reproduced. As such, a loudspeaker cannot be used without installing it in a cabinet of some type, or mounting it into a wall or ceiling.

[Steveruger45]

If I needed to use a baffle-less speaker like the first GP15 attempt, would it be better to use a 8x12 or a 9x16 speaker?

The flat piece of styrene glued over the front of the speaker is a baffle of sorts in that it does separate the front and rear sound waves and for sure sounds better than nothing at all.  As I found out a long while ago when upgrading the non baffled onboard speakers on some MRC decoders.  Nonetheless, not only is this style physically flat, it sounds real flat too compared to the same speaker in an enclosure of suitable volume.
IMHO I believe the loksound decoder deserves the better solution.