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B&C DCM50 Response "Anomaly"


John Warren

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Oh dear, when I am about to order a pair of DCM50 based on everything else I read good abput this driver, now I see this @@

 

It seems obvious to me that the DCM50 is likely a pretty good driver that would sound quite good. The K-400 and K-500 midrange horns themselves introduce their own irregularities in FR and if you were using other midrange horns, you'd see different irregularities in those horns, too.

 

For instance, the Beyma CP25 tweeter is, IMHO, very much superior to the K-77 in terms of how it sounds relative to its corrected FR and phase, its inherent harmonics, and its coverage angles vs. frequency.  But I've found that it really needs to be EQed, preferably by an active digital crossover, so that its output FR is smoothed a bit.  This makes a significant difference in the sound of the driver/horn assemblies.  Simple (and correctable) FR irregularities are typically the difference between diaphragm material types.

 

YMMV.

 

Chris

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The attached are scans from Beranek's Acoustics 2cd ed.

 

Although for a cone loudspeaker, it's still informative.  The number labels on the response plot associate with the corresponding nodal patterns shown in the second attachment.  The nodes associated with radial nulls and are responsible for relative minor ripples in the response. 

 

The circumferential nulls are more significant and are responsible for both reinforcement and cancellation effects.. 

post-864-0-65020000-1447366848_thumb.jpg

post-864-0-13420000-1447366878_thumb.jpg

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I'd like to see response plots of this driver on other horns...anyone have them to share?

 

 

I would like to also John.

 

John do you have any polar response plots? I would be curious to see the behavior of the polar responses of the horn you are using especially in the frequency region of the dip.

 

 

miketn

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JW. Tell us your favorite 2" or smaller compression driver you recommend for dedicated midrange only. Again, what JBL driver is the FR curve on.

 

Not sure I have a "favorite" but the Radian 950 with the Materion Be-diaphragm can make "spooky good" sound on some horns.  It can't go lower than about 600Hz. 

For low end a pair/side of 12" direct radiator units (JBL, TAD).  For HF a ribbon, one of the really expensive ones. 

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A comparison of the B&C response plot provided with the driver to a measurement of the raw driver response with the mic sniffing at the tip of the phase-plug.

 

The diaphragm begins to deviate from true piston-like behavior above about 2kHz.  The arrows identify where the sensitivity peaks at each node.  The red plot is the driver with no network.

 

(p.s. Beranek has a nice treatment on this behavior for cone drivers and (I think) there's a JBL white paper on this related to compression drivers.  The Be diaphragms push these nodes out at higher frequencies).

 

The B&C response plot comes from an exponential horn, not a driver in free space. I could see the loading on the driver playing a significant role here...especially since we're looking at a composite acoustic response versus measuring the diaphragm stiffness directly.

 

One thing not mentioned by Beranek in regards to bell modes is that the suspension can have resonances too. I had a problem with a 15" driver a while ago and no amount of EQ'ing could fix the problem. I've found that it's typically best to leave these behaviors alone because the mechanisms at play are often very non-linear, so they manifest themselves differently depending on the source material. In other words, the amount of ringing and its decay shape depends heavily on how it was stimulated - and music is a complex arrangement of multiple frequencies. All of the "steady state measurements" only apply to aspects of the system that are always constant with time - and those things can definitely be addressed with EQ.

 

These are interesting plots John.

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Guest David H

I am not sure what the point of this thread is, but the DCM-50 is a great sounding driver.

 

Every driver available has dips and peaks, some more than others. I think it all comes down to the sound.

 

I have seen a lot of graphs, and to this date I still can't hear them.

 

I have also heard systems EQ'd near ruler flat - (lifeless) Ill take a bit of deviation any day over that.

 

 

May be I should stick with my k55v ( double phase plug version ) for now. @@

 

The K-55 is a good driver as well. If you are happy with the sound you are getting then stick with it.

 

 

Dave

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I have also heard systems EQ'd near ruler flat - (lifeless) Ill take a bit of deviation any day over that.

 

You were good until that statement, IMHO.  Floyd Toole, Sean Olive, and even I will disagree (except perhaps a small rise in bass response SPL in small listening rooms like those that exist in any home). 

 

I believe the problem is the state of the recordings that you're listening to, which are "pre-EQed" to something that is, in fact, insane.

 

Chris

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May be I should stick with my k55v ( double phase plug version ) for now. @@

Don't be swayed away from this driver, It does a nice job and is well regarded. I use an Edgar 300hz tractrix home built horn and I cant complain. I hear a very natural and convincing tonality that far exceeds the 400 horn and k55 v. I have used the k-55 on a 2" horn with an adaptor before and it was pretty darn good. When I went to the B&C the natural, easy sound they make won me over big time. Their may or may not be better out there but the B&C is definitely worth going after in my opinion for whatever that's worth.

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Guest David H
Their may or may not be better out there but the B&C is definitely worth going after in my opinion for whatever that's worth.

 

Furthermore the B&C DCM-50 is an exceptional value.

 

Dave

Edited by GotHover
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I am not sure what the point of this thread is, but the DCM-50 is a great sounding driver.

 

Every driver available has dips and peaks, some more than others. I think it all comes down to the sound.

 

I have seen a lot of graphs, and to this date I still can't hear them.

 

I have also heard systems EQ'd near ruler flat - (lifeless) Ill take a bit of deviation any day over that.

 

 

Dave

When someone EQs and it sounds worse that is proof of the improper use of Equalization.

This often happens because many are inexperienced and don't understand how to properly apply EQ by measurement as well as listening.

Knowing how to properly interpret measurement combinations of Frequency, Polar, Phase along with Cumulative Spectral Decay and other test along with Listening will lead one to the proper application of Equalization and an optimized Loudspeaker and Listening Experience.

As far as the purpose of this thread some of us on the forum like to have a deeper understanding of when and how measurements and the listening experience correlate.

Also people need to not be so defensive just because this driver isn't perfect because none exist but some sure are better than others. :-)

miketn

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If we were really that concerned with flat response, we wouldn't be using compression drivers and horns.

 

I believe that I understand your intent here, but I'll offer the following experience, suggested by Greg Oshiro, and taking me some time to get it completed (learning some things along the way about in-room measurements).  My response to Greg's tasks is found below his.  See point #5. 

 

In a nutshell, I found that getting the FR as flat as you can made a really huge difference in the sound.  In other words, I found that Floyd Toole is actually correct on this point - EQing flat is one of the most important tasks that I've done to increase the performance of my setup.

 

Just because compression drivers and horns tend to have uneven FR doesn't mean that we shouldn't do all we can to correct it.

 

Chris

Edited by Chris A
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