Which 8" coaxial ?

Status
Not open for further replies.
Jump to Latest
#64
#65
The 508/2B below is the Stamped Steel Basket version of the 5208C which uses a Cast Frame. Both are for SR.
 

Attachments

  • RADIAN 508_2B.jpg
    RADIAN 508_2B.jpg
    41.2 KB · Views: 465
#66
Later on today I will have access to my other PC where I have stored my measurements of some experiments that I recently did with a Beyma 8cx300nd. As expected - the frequency response was quite rugged and it is best used with an active solution. My measured response is also less smooth than what the data-sheet suggests. I am not content yet with the (measurement-) results that I have achieved so far and I will use a different crossover topology as soon as I have time to do so. But I could get it sounding quite smoothly from my subjectieve point-of-view (I particularily like the voice reproduction of it).

The goal was to develop a small point-source for nearfield listening that is transient "perfect". Therefore I opted for a driver that has reasonable x-max and a protruding horn. The latter helps reducing FM distortion but has the disadvantage of a slightly more rugged response compared to the ones where the woofer cone is acting as tweeter waveguide. I don't know how accurate my measurements actually are but it seems that (due to the "detour" the midrange frequencies take around the horn) there is only a minor path delay between tweeter and woofer. This is actually a slight disadvantage for making a time-aligned or transient improved design - although many might belive that the contrary is the case. But a "mechanically delayed" (i.e. offset) tweeter is actually your friend when it comes to crossover design.

There is a protective screen that can easily be removed by unscrewing the horn (simply turn it counter-clockwise). When I have too much time on my hand I will also measure with this one removed. Maybe this will give a slightly smoother HF response - but beware of doing this for stage applications (especially wedge monitors).

So far I have only listened to one speker at once - I will soon be able to test them is stereo. At the moment they seem to lack in bass punch (they are in a EQed closed box) even for the nearfiled application. If they are good enough for the task as a pair I will continue like that. But if not I will add a woofer and a third amp channel and use them as a mid-field speaker.

A sidenote: The build quality of the driver is very good - as you would expect from a professional device that is manufactured by a company like Beyma. From my experience I think that it makes a good speaker for voice and acoustic guitar only. If you have the ability to alter the response onthe fly according to your application - even better.

Regards

Charles
 
#68
phase_accurate said:
The goal was to develop a small point-source for nearfield listening that is transient "perfect". Therefore I opted for a driver that has reasonable x-max and a protruding horn. The latter helps reducing FM distortion but has the disadvantage of a slightly more rugged response compared to the ones where the woofer cone is acting as tweeter waveguide. I don't know how accurate my measurements actually are but it seems that (due to the "detour" the midrange frequencies take around the horn) there is only a minor path delay between tweeter and woofer. This is actually a slight disadvantage for making a time-aligned or transient improved design - although many might belive that the contrary is the case. But a "mechanically delayed" (i.e. offset) tweeter is actually your friend when it comes to crossover design.

Charles
Click to expand...

I'm not sure there is any "path delay" because of the tweeter horn. Air is a compressible media, so it just squishes around the horn. I would think that the presence of the horn would provide a small amount of acoustical load to the woofer, possibly improving sensitivity in the same sort of way that horn loading does for other woofers.
 
Last edited:
#69
dirkwright said:
So, you are referring to the original Radian 508/2 when you say that you use it as one of your reference speakers?
Click to expand...

Yes, the early models, the ones with the polypropylene cone. I just rechecked the label. It only says 508 (without the /2). I think the 508/2 is the early SR version and the 2B is the updated ones. All very confusing.

The model I'm using is the Radian 508.
 
#70
@dirkwright

I don't belive that the squishing you describe might accelerate the propagation but maybe you are wright. ;-)
From the mechanical distance between the farthest part of the cone and the compression driver one should assume at least about 90 us of delay but it was less than that (around 20 us).

But with the horn effect you may be right. Beteen ftc and the most sensitive point in the midwoofer response is a bigger difference than the effect of Qtc and BSC would suggest IIRC.

Regards

Charles
 
#71
Here's another kind of coaxial: the B&C DCX50. Frequency range is 400Hz to 16KHz. It's two compression drivers so it needs a horn that goes down to at least 400Hz. Since it has been recommended that these 8" coaxials be cut off at about 300Hz, then this driver seems to be in a similar range of performance. They are not cheap.... about $600 each...
B&C SPEAKERS
 
#72
dirkwright said:
Here's another kind of coaxial: the B&C DCX50. Frequency range is 400Hz to 16KHz. It's two compression drivers so it needs a horn that goes down to at least 400Hz. Since it has been recommended that these 8" coaxials be cut off at about 300Hz, then this driver seems to be in a similar range of performance. They are not cheap.... about $600 each...
B&C SPEAKERS
Click to expand...

I kindof would like to know the difference in sound between one of these 8" coaxials and the DCX50 with something like a JBL 2385A 500Hz horn. I would guess that the JBL horn would have better controlled dispersion down to 500Hz than the 8" coaxials, but I'm not an expert. Still, we're talking about $900 in parts vs. around $300 for an 8" coaxial.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=294-426
There is a Selenium horn that goes down to 400Hz also:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-329
 
Last edited:
#78
David dP said:
It is in my list, and would be my favorite to try out, if not for the really high Fs, the low Xmax (and admissible power)... and the high price tag !

I'm afraid it even more a midrange unit than any of the competitors...
Click to expand...

OK, but you've been given the advice to high pass any of these 8" coaxials at about 300Hz, so it's no problem to have a high Fs and low Xmax. There doesn't seem to be any way around requiring a 3 way loudspeaker based on the these coaxial drivers.
 
Status
Not open for further replies.
Top Bottom