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MultiWay Conventional loudspeakers with crossovers 

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5th October 2008, 08:19 PM  #1 
diyAudio Member
Join Date: Mar 2008

Mmd Vs Mms
Just a quick question.. Does anybody know if it is possible to deduce Mmd From Mms?
Hornresp requires Mmd, but most specsheets only quote Mms.. or is the difference really insignificant? 
5th October 2008, 11:31 PM  #2 
diyAudio Member

Yes this is possible. First it is important to understand what Mmd and Mms are. Mmd is the effective moving mass of the mechanical system. Mms is the effective moving mass of the mechanical system plus the air on the front of the driver. Thus to get Mmd from Mms we need to know what the effective mass of the air in front of the driver is.
What's going on here is that the cone sees an impedance from the outside world called the radiation impedance. For a piston, at low frequencies the reactive part of the impedance looks like a mass this is the mass added to Mmd to get Mms, and it is given by: m = (8/3)*rho*r^3 where rho = density of air r = piston radius Thus to get Mmd from Mms you need to compute this mass and then subtract it from Mms to get Mmd. Source: Fundamentals of Acoustics by Kinsler and Frey pages 184187 
6th October 2008, 08:20 AM  #3  
diyAudio Member
Join Date: Jun 2007

Re: Mmd Vs Mms
Quote:
Simply doubleclick on the Mmd text box in edit mode, and enter the fs value given on the specification sheet instead. Kind regards, David
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www.hornresp.net 

6th October 2008, 08:20 PM  #4 
diyAudio Member
Join Date: Mar 2008

Hey, this is great, two definitive answers!
One shortcut for the lazy (me) in Hornresp, and one formula for general application! What more could one ask for! Thank's guys, much appreciated! PS: Regarding the formula; should the answer be multiplied by two since the cone has two sides, both of which I anticipate will se a mass loading from the air? 
7th October 2008, 03:16 AM  #5  
diyAudio Member

Quote:
However, if the driver is in an infinite baffle radiating into half space on both sides, the answer is yes (at least as an approximation). 

7th October 2008, 08:54 PM  #6 
diyAudio Member
Join Date: Mar 2008

Thanks for that last clarifying answer, makes good sense!

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