Suitable midrange cone, for bandpass mid in Unity horn

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#1,301
re
"Originally Posted by JLH
The path length of the BMS 4550 is 6.7cm.
The path length of the BMS 4552 is 5.1cm.
The path length of the Selenium D220ti-omf-8 is 3.65cm
The path length of the RCF N350 is 3.95cm
The path length of the RCF ND350 is 2.25cm"

I was planning to use the BMS4550 on a 90x40 horn but its path length forces me to place mid holes too close to the horn apex.

Do you know the path length of the DE250? Can you suggest an alternative to the BMS4550 that supports a >1200 hz xover on a wide horn?

Thanks,
Jack
 
#1,302
Vandersteens

My first "audiophile"setup included a pair of Citation 2's wired in mono driving Vandersteen 2C's...yeah the imaging was pretty deep behind the speakers as well as (on certain recordings anyway)wall to wall(12'X16' room,speakers on the long wall.)Yeah,STOOPID ME- sold the Citations back in the early 2000's...
Joe
 
#1,303
nc535 said:
re
"Originally Posted by JLH
The path length of the BMS 4550 is 6.7cm.
The path length of the BMS 4552 is 5.1cm.
The path length of the Selenium D220ti-omf-8 is 3.65cm
The path length of the RCF N350 is 3.95cm
The path length of the RCF ND350 is 2.25cm"

I was planning to use the BMS4550 on a 90x40 horn but its path length forces me to place mid holes too close to the horn apex.

Do you know the path length of the DE250? Can you suggest an alternative to the BMS4550 that supports a >1200 hz xover on a wide horn?

Thanks,
Jack
Click to expand...

If I recall correctly, Tom said he crosses the BMS 4550 at 900Hz. I think this is due to a combination of the driver being capable of 900Hz, and its long path length. I don't have a DE250 to measure, but a rough guess would be about the same as the Selenium D220Ti
 
#1,305
JLH said:
If I recall correctly, Tom said he crosses the BMS 4550 at 900Hz. I think this is due to a combination of the driver being capable of 900Hz, and its long path length. I don't have a DE250 to measure, but a rough guess would be about the same as the Selenium D220Ti
Click to expand...

Thanks John,

I already have the BMS4550s, which I bought on TomD's recommendation. Now with his endorsement of a 900 Hz crossover, I think I won't give up on them, yet. Sketchup says I can just get to a 900 hz null/xover with the Aura NSW2 mids, so I will try them first. If I don't like the result, I can still look for a CD with a shorter path.

Jack
 
#1,310
John, of course you're right, but currently my samples are buried in another diy Synergy speaker, not easy to get to.

Much of an impedance curve can be flattened by adding an additional network in parallel to the crossovers' input. In only works for bringing impedance peaks down though, can't pull up the low spots.
 
#1,311
RE: Question

Thanks John and Bill for your answers. It looks like the impedance curve on the Danley SH-96 is close(above 100 hz). If I spec'd my single ended (no-feedback) tube amp output impedance to 7 ohms I would be close with that design of speaker.(gonna use multiple subs for the bottom anyway)
Other than a more complex crossover, what would the trade-offs be for adding additional networks be ?(there usually is no free lunch)
thanks,
dennis

http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/04/SH-96-spec-sheet2.pdf

this is the flattest design of his I could find....
 
#1,312
Looks like the minimum impedance is 6 ohms at about 435Hz. If you're going custom output transformer, I would have it wound for 6 ohms. Then again, the difference between 6, 7 and 8 ohm taps is not likely to be audible.

One very good trade off is inserting a second order 16.5KHz lowpass filter on the compression driver. This will boost the highs to combat the conical horn's roll off. The trade is lower impedance. However, even with tube amps the impedance down in the bass is more important than what it is above 1KHz.
 
#1,313
bwaslo said:
John, of course you're right, but currently my samples are buried in another diy Synergy speaker, not easy to get to.

Much of an impedance curve can be flattened by adding an additional network in parallel to the crossovers' input. In only works for bringing impedance peaks down though, can't pull up the low spots.
Click to expand...

Agreed. Due to the nature of the conical horn's decreasing power response with raising frequency, the compression driver is going to set your overall sensitivity. 99.9% of the time you have to pad the mids down to match the compression driver. I use this as an opportunity to keep the impedance across the mids even and high by inserting some series resistance as needed. The real challenge is the crossover between the mids and the woofers in a 3-way Synergy. What I've found is overlap in the crossovers almost always leads to dips in impedance. To avoid this you have to try to get most of the driver roll offs acoustically by the design of the horn, entry ports, driver spacing and front chamber volumes. When the crossovers do not overlap, the impedance can stay nice and high without having a peak in frequency response at the crossover point.
 
#1,314
Got a UPS shipment notice from Parts Express. The B&C Speakers DE120 compression drivers should be here on Monday. Of course the first order of business is to take them apart and measure the path length... er… check for shipping damage. Yes, I’m checking them for shipping damage.
 
#1,316
All you have to do is remove the diaphragm and slip a piece of paper through the phase plug slits. Measure the distance the paper goes from the top of the phase plug to the edge of the exit. Add about a 1mm for the space between the phase plug and diaphragm. This will give you a good enough number to model with. This number will give you the worst case in the model because the acoustical center of the driver actually occurs slightly forward of the diaphragm. To measure the actual acoustical path length you need to do an impulse test and calculate it based on the speed of sound.
 
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#1,318
The B&C Speakers DE120 drivers came today. However, one of them has an open voice coil. :sad: I'll be contacting Parts Express in the morning and get the defective one exchanged. I did measure the path length through the phase plug. They are 2.5cm long. 😎

That means with the DE120 I should be able to get a 1370Hz crossover on a 65 X 45 horn using the Visaton M10. Or, I can get a 1390Hz crossover on a 55 X 40 horn using the Misco RDC3T-A.
 
#1,320
In trial fitting a bunch of different mids on my horn drawing this weekend I realized that with the 90 degree horn, I can actually get the mid holes closer to the apex than with a 60 degree horn because the 90 degree horn walls take longer to move a given perpendicular distance down the throat from the apex.

Comparing notes:
I figured I could get the Misco RDC3T holes within .672" of the physical apex. With a .25" mounting plate, I get the 1/4 lambda null at 1774 hz with the DE120. However, if I go DE250 and its path length is indeed 37mm, then I have the null at 1421 Hz. The benefit though is its closer to the recommended crossover. The BMS4550 comes in at 950 and is above its recommended minimum but I wonder if the close-in mid holes for it won't compromise the high end ...
 
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