Experience with PT Wave Guides

[Guido]

I have not listened to them yet or finalized the network so I still have a bit of work to do.

Rob

Glad that the 2435 Diaphragm deal worked out.

Please keep us posted with the crossver design. In what combination do you plan to use those nice drivers?

[Robh3606]

Hello Zilch

They measure better on PT waveguides than the specs would dictate.

Thanks for posting the link. First thing I did is drop in some pink noise and look at the RTA. I got very similar results. You have more resolution than I do with my older 8024.

They measure better on PT waveguides than the specs would dictate.

Yes they do. It was a pleasant surprise.

Didya see what was "two-stage" about it?

No I tried to back light the driver through the phase plug. Maybe Steve will jump in on that one.

Rob

[Robh3606]

Hello Guido

Glad that the 2435 Diaphragm deal worked out.

Yes they did and thank you for them

In what combination do you plan to use those nice drivers?

Right now I am going to swap out my 2344/2425 combo in my main active set-up. I am hoping for an easy swap. My main concern is the PTH1010 horn. It sure looks good but I won't know until I get it all working. That will team them up with E145's and 2123 midranges. I am planning on crossing them over at 1.5K.

Rob

[Robh3606]

Just tried some capacitor value changes. I was trying to find the value where I wouldn't depress the low end response as much and still maintain a relatively flat curve from about 1.5k and up. The 1.6 Uf in the original curves actually give you a rising response relative to the low end of the drivers range. I wanted to get a slightly rolled off upper octave response. I tried 3uf and 5uF series caps and you can see the sensitivity and balance changes with each value. The measurements are all at the same level from the same set-up so the level changes are due only to capacitor value changes.

Rob

[johnaec]

Rob - could you identify which values go with which colors in your charts? It looks like green is a different value in the lower one?

Thanks - John

[Zilch]

Hi, Rob.

We need to know the circuit you're working with.

If you're going to cross at 1.5 kHz, I'm not sure I appreciate the point of trying to flatten between 1.5 and 2 kHz, though I believe it can be done.

Do you have Spice to assist with tweaking?

[Robh3606]

Rob - could you identify which values go with which colors in your charts? It looks like green is a different value in the lower one?

Hello John

Sorry I didn't even realize I changed up the colors on the traces. On both graphs the top is 5uf middle is 3uf and lowest is 1.6uf. The larger the series cap value the higher the sensitivity.

Hello Zilch

It is a modified AM621200 crossover, with a series cap and the notch filter. The notch filter values are L4 .05uh R1 2.5 and C2 is 6uf

If you're going to cross at 1.5 kHz, I'm not sure I appreciate the point of trying to flatten between 1.5 and 2 kHz

I am not going to at this point. I want to try it first and see how much of an anomally I get through the crossover point using the active crossover. I can always bring it up 100Hz or so.

Do you have Spice to assist with tweaking?

No but I should spend some time to learn to use one of the programs. As off yet I have been putting it off but down the road I will need it. I have Micro Cap I have played around with and Cross Over Pro 3 so I could have but starting with JBL's crossover and having Clio makes it real easy to just change the series cap values and take actual measurements. Clio is a real pleasure it's so easy to use.

Rob

[Zilch]

It's not changing the area of interest.

You're missing a key component.

The series cap and shunt inductor in combination determine the highpass frequency and "Q".

Adjusting the notch can alter the "Q" somewhat.

I'd set 1 kHz where I want it, then contour the rest with the notch, if possible.

I'm not familiar with MicroCap, but you can do this in Xover3P.

You'll need to put in the response curve of the driver and horn, tho.

With some assumptions, Spice sim of your voltage drives:

[Robh3606]

It's not changing the area of interest.

You're missing a key component.

The series cap and shunt inductor in combination determine the highpass frequency and "Q".

Adjusting the notch can alter the "Q" somewhat.

I didn't change the notch. I felt it was fine. Overall the response it is smoother than the 2307/2425 to 2405 integration in my 4344's. Take a look at the response of the 4344 over the same range. The top end of the 4344 sounds good warts and all. I used my experience dealing with the 2344 before I was biamped. When you have a single series cap on a compression driver you can manipulate the curve by changing the value. If you look at the curves the relative level in the 10K-20k region gets lower as you increase the value. That was the region of interest to me. I wanted to lower the energy in that band a bit relative to the rest of the curve. You also gain sensitivity as well which never hurts. It's hard to see but it also help raise the level in the notch at 1K. To try to get the 1K-2K region flat won't work cause of the wave guide loading. All of the graphs for just the 1010 show a hinge around 1.5K where the loading changes. We are looking at this from 2 different angles. I would rather adjust the cap as I gain sensitivity, get a little more energy in the 1-2K region and roll off a bit above 10K which is what I wanted to do.

Rob

[Zilch]

Ahh, yes. I see it now. The 2344A is down somewhat in that region as well.

You're apparently far enough along with this it's fair to ask, "How does it SOUND?"

[Robh3606]

Ahh, yes. I see it now. The 2344A is down somewhat in that region as well.

You're far enough with this it's fair to ask, "How does it SOUND?"

Exactly!! I didn't want a voiceing change when I dropped this new horn and driver combo in place.

How it sounds is the $64,000 question. I plan on building network tonight and getting them in on the weekend. I have my fingers crossed I will like it better than the 2344/2425 combo.

Rob

[Earl K]

Fascinating !

- The resonance point for that LCR notch-filter looks to be centered about an octave lower than what the text-book formula would predict ( 4600 hz vs around 9190 hz for the standard formula) .

- Can anyone offer an explanation to this ? ( plus maybe offer up a new formula that includes the modifiers / this has me stumped )



- "Known Formula" is given as ; Notch Frequency = 1 / ( 2 * Pi * sqrt ( L * C ))

- L is in Henries, C is in Farads, F is in Hertz .

[Zilch]

Hiya, Earl.

Notch in the sim is at 9.152 kHz, graphically.

I'd say your known formula is correct.

[It rings quite nicely when I lower R to 0.025 Ohms.... ]

[Earl K]

Thanks Zilch for the clarification !

- I now realize that I was mis-reading your pics' log scale .

[Zilch]

Per Rob's request, 4 X 2435HPL on PT-H1010, AM filter:

http://audioheritage.org/vbulletin/s...3&postcount=19

2435HPL on 2352 uses same circuit, but with 0.08 mH in the notch.

#9 and #10 need their gaps cleaned and ferrofluid recharge, looks like....