I had a question about my 21" if the larger box is better. My answer soon became 'dual 18s > single 21'. I figured I'd post it here to see your input.

I just copied and pasted my reply:

The larger box does preform well, but be honest for the price of one MCM 21", you could get 2 MCM 18"s or this other 18".

Lets do a little math:

The Sd of the 21" = 0.1706 m^2

The Sd of the both 18's = 0.1232 m^2

Xmax of the 21" = 7mm

Xmax of the 55-2954 18" = 4mm

Xmax of the 55-2964 18" = 6mm

We'll double the Xmax to show the max air the driver can move linearly:

1x 21": (0.1706 (m^2)) * 14 mm = 2.39 liters

2x 55-2954 18"s: 2 * ((0.1232 (m^2)) * 8 mm) = 1.97 liters

2x 55-2964 18"s: 2 * ((0.1232 (m^2)) * 12 mm) = 2.96 liters

If we go by air movement the 55-2964 (Other 18") 'wins'.

Now the best way to find out is to put them next to each other:

Sadly I have the dual 18's taken apart right now. The 18's in the picture are the cheaper MCM 18's. I did give them a quick test out there, the dual 18's were louder, but they are in half space.

Here's the SPL curves of them:

Single 21" (55-2985):

Dual 18" (55-2954):

Dual 18" (55-2964):

I just copied and pasted my reply:

The larger box does preform well, but be honest for the price of one MCM 21", you could get 2 MCM 18"s or this other 18".

Lets do a little math:

The Sd of the 21" = 0.1706 m^2

The Sd of the both 18's = 0.1232 m^2

Xmax of the 21" = 7mm

Xmax of the 55-2954 18" = 4mm

Xmax of the 55-2964 18" = 6mm

We'll double the Xmax to show the max air the driver can move linearly:

1x 21": (0.1706 (m^2)) * 14 mm = 2.39 liters

2x 55-2954 18"s: 2 * ((0.1232 (m^2)) * 8 mm) = 1.97 liters

2x 55-2964 18"s: 2 * ((0.1232 (m^2)) * 12 mm) = 2.96 liters

If we go by air movement the 55-2964 (Other 18") 'wins'.

Now the best way to find out is to put them next to each other:

An externally hosted image should be here but it was not working when we last tested it.

Sadly I have the dual 18's taken apart right now. The 18's in the picture are the cheaper MCM 18's. I did give them a quick test out there, the dual 18's were louder, but they are in half space.

Here's the SPL curves of them:

Single 21" (55-2985):

An externally hosted image should be here but it was not working when we last tested it.

Dual 18" (55-2954):

An externally hosted image should be here but it was not working when we last tested it.

Dual 18" (55-2964):

An externally hosted image should be here but it was not working when we last tested it.

I've had the question the question, "Is having two 18's better than one 21?" in my head for almost 2 years. I've been leaning to one side and then to the other, never able to make up my mind. Well I fixed that 18", and now answered the question. Even though the 21" will move 2.39 liters, and the dual 18's will only move 1.97 liters, thedual 18's are still louder.

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