Compression driver topology

Greg Cameron

Greg Cameron

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Jan 11, 2011
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Mackie posted the user guide and specs on their new SRM series speakers. I noticed that the specs state the horn is using a 1" titanium diaphragm with a 1.4" "horn entry". I've never seen a compression driver where the diaphragm was smaller than the exit, always the other way around. It seems to me that with an exit larger than the diaphragm, you wouldn't really have a "compression" driver. Am I wrong here? I'm by no means a driver designer, but I'd like to play one on TV someday.

Thanks,
Greg
 
Re: Compression driver topology

I just means that the driver is designed to fit onto a 1.4" horn, and doesn't really say anything about the throat's narrowest part.
 
Re: Compression driver topology

Here's what the user guide says:
 

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Re: Compression driver topology

With the 3kHz crossover point (yech) it seems that they're doing what I think they're doing.
 
Re: Compression driver topology

Per Søvik said:
I just means that the driver is designed to fit onto a 1.4" horn, and doesn't really say anything about the throat's narrowest part.
Click to expand...

I see what you're saying, they might possibly be using a narrower throat past the entry, like a .75" throat?
 
Re: Compression driver topology

EV used to have a driver (I don't remember the model) that was a 1 3/8" screw on driver-but had an adapter that screwed onto it and had "plumbing" that was about 6" or longer and ended up with a 2" "exit".

It looked like the adapter was part of the actual driver. It was very well made.

So sometimes things are not as they first appear.
 
Re: Compression driver topology

Ivan Beaver said:
EV used to have a driver (I don't remember the model) that was a 1 3/8" screw on driver-but had an adapter that screwed onto it and had "plumbing" that was about 6" or longer and ended up with a 2" "exit".

It looked like the adapter was part of the actual driver. It was very well made.

So sometimes things are not as they first appear.
Click to expand...

Do you remember the diaphragm size on that driver Ivan?
 
Re: Compression driver topology

Greg, I think you might be looking for compression in the wrong places. In a typical compression driver with an annular phase plug, much of the compression and expansion are taking place in the concentric apertures of the phase plug; after the diaphragm and before the throat. If you look at a phase plug's cross section, it is a series of overlaid circular "horns."

Having said that, a 1" diaphragm loading a 1.4" throat is kind of goofy. A lawn tractor pushing a hay wagon. Sounds like a combo of too many leftover parts to be used up, and marketing doublespeak.
 
Re: Compression driver topology

Mike Smith said:
Greg, I think you might be looking for compression in the wrong places. In a typical compression driver with an annular phase plug, much of the compression and expansion are taking place in the concentric apertures of the phase plug; after the diaphragm and before the throat. If you look at a phase plug's cross section, it is a series of overlaid circular "horns."

Having said that, a 1" diaphragm loading a 1.4" throat is kind of goofy. A lawn tractor pushing a hay wagon. Sounds like a combo of too many leftover parts to be used up, and marketing doublespeak.
Click to expand...

Thanks Mike. I'm aware of the phase plug slits, usually the better designs have 3 as opposed to 2. I thought that the diaphragm to exit ratio was part of the equation as well, but I'm not studied on that aspect. I am aware that larger throats tend to get louder and can go lower - if parts before the exit are up to the task. Thanks for the input.
 
Re: Compression driver topology

RYAN LOUDMUSIC JENKINS said:
What did they say wen you called them to ask? Looking at both images you posted I would guess that it is a typo. Seeing as how about 100% of all audio manufacturers have typos in their manuals, it seems like the most plausible explanation.
Click to expand...
I would agree.

If you look at all the various "numbers" 3K xover 1" and 1.4", I would suspect a 1.4" dia voice coil a 1" exit.

Yes typos happen all the time.
 
Re: Compression driver misprint

Greg Cameron said:
Do you remember the diaphragm size on that driver Ivan?
Click to expand...
The EV DH2A was the driver Ivan mentioned, it uses a 2" diaphragm and a 6" long throat adapter from a thread on terminating in a 2" exit.

The Mackie SRM 350 uses a 1.4" diaphragm and a 1" exit, the reverse is a misprint.

A 2" diaphragm has more than double the surface area of a 1.4" diaphragm, hence the high crossover point required to keep the little bugger from hammering the phase plug.

Art
 

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Re: Compression driver misprint

IME no manufacturer has their literature proofread before publication any more. Besides being rather expensive to have it done properly I suspect they figure that very few RTFM these days anyways and those that do and give a shit will let them know for rev 1.1 - AKA free proofreading :?~:-?~:???: .
 
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