Horn vs. Waveguide

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#1,462
Just posted some results of the JBL 354267-001 and Pyle PH612 horns with a BMS 4540ND on my Drivervault. No full polars as I just didn't have the time. The JBL looks much better now. The Pyle doesn't take the BMS driver well, there is a 1/8" gap between the throat and the driver exit. I did have a chance to use a real JBL 338800-001 but the driver center was a bit off center so I figured it didn't really matter how it performed if the QC is hit and miss. Maybe I'll grab another one anyway just to see.
 
#1,465
Yeah the BMS fits the JBL 354267-001 and 338800-001 fine (other than being off center), so the Pyle seems like it's got a problem. I would look into it further but I think Zilch has had no luck getting anything to work without the 12khz notch anyway, so what's the point? I may do more measurements on the 354267-001, and maybe get a real 338800-001 just to see how they perform with the BMS.

EDIT: Strange thing is the Selenium adaptor fits the Pyle horn ok.
 
#1,466
Several of us have now found the Pyle insert undersize. JBL 2408H and 2414H don't go on easy, either.

I don't have a bottoming finish tap that size to open them up, either.

Don't worry about the lack of concentricity on the JBL PTs. It doesn't seem to matter....
 
#1,467
ZilchLab said:
Several of us have now found the Pyle insert undersize. JBL 2408H and 2414H don't go on easy, either.

I don't have a bottoming finish tap that size to open them up, either.

Don't worry about the lack of concentricity on the JBL PTs. It doesn't seem to matter....
Click to expand...

Thanks for the info. Yeah the BMS was a bit tough to get on the last few turns, I used anti-seize for fear these would end up permanently mated together.

So the off center throat is common? That's not real reassuring.
 
#1,468
"I don't have a bottoming finish tap that size to open them up, either."

In a pinch I just grind down the nose of the tap I have on hand, and get another one the next time I'm at the building center.

Not sure how close to the bottom a real bottoming tap gets, but this gets a lot closer.
 
#1,469
The Behringer analog crossovers I've heard were pretty transparent to my ear and they use the same chips.
Click to expand...

Iv'e had a few problems with the Behringer "analogue" crossovers locking up and needing "rebooting". Which is kinda weird if they are truly analogue but yeah a powering down/up seems to get them going again. I'm not sure if the pots that select the crossover frequency are VCA or multi-gang. If they are not VCA I would question the accuracy between the tracks, knowing the issues with volume controls in general.

I try to avoid having more than one piece of Behringer equipment in a rack. Nowadays I hand build my active crossovers hardwiring the frequency/crosses using all 1% tolerance components. If your pushing a compression driver to it's lower limits it's nice to know that it is crossing where you plan it to cross.

Soon I will be receiving a Behringer DSP1124P which has a very cost effective 2 x 12-band parametric eq. I'm hoping this will be a good combination with my crossovers for tuning in waveguides.

col.
 
#1,470
18 Sound XT 1086 and Beyma CP-385Nd?

Has anyone here mated the 18 Sound XT 1086 waveguide with the Beyma CP-385Nd compression driver with good effect?

Are there any problems in mating the throat of the horn to the compression drivers exit?

Are there any measurements taken from this pair of components available for study?

Thanks

NW
 
#1,472
ZilchLab said:


Yes, but if you look closely in the 3D version, there's a "bump" on the top of the plateau which shows as a hotspot in the spectrogram. Clearly, the issue is not entirely resolved as, while the resonance is well suppressed now, the region is still "fat." My intent was to discover if EQ alone had promise to mitigate it. Answer: "Yes," but there's more to do.




I'll migrate to your filter, most likely. What I have presently is a proof of principle kludge. The ancient relic Altec Model 19 crossovers are merely what I use for initial testing of various combinations, because they have the facility to dial in varying levels of HF comp. My own version of that has even greater versatility, but it is otherwise occupied presently.

We got our first look at the Geddes crossover in member DougSmith's Abbeys recently, below. It incorporates three notch filters to smooth the DE250 response. To achieve the result I show, I did the same using DEQ2496, much as Col has just suggested. None of them is more than 2.5 dB deep, as I recall, and could be implemented passively using series LRC notches in a final design, if required....
Click to expand...


This appears to be a first order filter on bass and HF, and the three mentioned notch filters?

Russellc
 
#1,475
ZilchLab said:
Yes, with a Zobel in the LF.
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More likely, that's a 2nd order electrical lowpass (who knows what the acoustical response is) with the resistor doing some response shaping. Here's a theoretical 2nd order lowpass with a 1.5mH inductor and a 6uF cap. The red line adds 10 ohms in series with the cap.
 

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#1,477
ZilchLab said:
AKA "quasi-" 2nd order.... :yes:
Click to expand...

A quasi 2nd order is where the poles are spread far apart in frequency so it starts off as 1st order and later turns 2nd order. I doubt that's what's going on here. Earl is going for an unknown acoustical response (maybe 3rd order, maybe 4th order) and the resistor is just a tool to help get it done. Bottom line, it's a 2nd order electrical filter giving some acoustical response that's steeper than that.
 
#1,478
It's my understanding that the resistor is to reduce the peak in the woofer's response around that region. It's how I use it in my own crossovers and I believe Dr. Geddes said the same. Having built his speakers, I have the values of these LCR's in the tweeter, but would rather let him post them if he wants to. However, I do know that due to my and I believe Marcus building these very publicly, the values are posted in a round about way. I think I may have inadvertently posted a form of the crossover schematic too. It's also available on his website I believe.

When I talked with Dr. Geddes on the function of each LCR (I had assumed that two if not all three were serving to reduce the impedance peaks in horns), I was told that one serves to flatten the impedance, and two serve more as EQ's. One as an EQ in the 2-4k range and one to shape the crossover response. The crossover is acoustically like a 3rd order filter I believe, but electrically it's really a 1st order. If you look at the phase response, it looks like what it basically is, a 1st order filter. There is no parallel inductor without the addtion of a capacitor and resistor, and as a result, there is a very small phase change. The acoustic phase response of his speaker is excellent, really excellent. I think it's at the expense of frequency response some, which is usually the tradeoff I face when I try and balance the two.
 
#1,479
8 kHz crossover

Pos,
In post #938 you said,"This is the PT wave guide I am going to use as a tweeter with a 2407H above 8khz."
Would you please give me a description of that waveguide & driver?
I don't see any reference to 2407H in JBL's listing.
Thank you in advance,
Frank
 
#1,480
Re: 8 kHz crossover

dobias said:
Pos,
In post #938 you said,"This is the PT wave guide I am going to use as a tweeter with a 2407H above 8khz."
Would you please give me a description of that waveguide & driver?
I don't see any reference to 2407H in JBL's listing.
Thank you in advance,
Frank
Click to expand...

Hi

That horn was presented by Zilch here, starting at post #11
http://www.audioheritage.org/vbulletin/showthread.php?t=24280

it is a small square PT waveguide.
The 2407 has been replaced by the 2408, and now by the 2414 it seems (althougth that one seems to be even smaller).

The 2407 was a BMS design, identical to the 4540
 
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