QSC Waveguide project, XOs (active and passive)

[soho54]

Yeah, with the other programs the negative values can not be displayed. PCD for example.

In HOLM Impulse you just save the file, then add 90dB to the window, (the curve will no longer show, but the data is still there) and finally "save as" with a new name. Now you have a clean HI txt, and a fully frd compatible file (minus the header.)

[penngray]

If Im actually going to do a passive XO for this speaker should I first rear mount the woofer, like everyone else is doing in their passive designs?

Up to now, I have been just trying to learn how to even build an XO design but I guess I should do it right If I want a passive XO version.

[Saurav]

It would reduce the acoustic offset, which would probably make the crossover design simpler. If the relative positions of the drivers are similar to one of the other designs, the chances are better that one of the other crossovers will just work.

[penngray]

I guess I should determine the depth difference between the TD12M and the other drivers.

[Saurav]

Oh, good point, I forgot you were using a different woofer from everyone else. My bad

[penngray]

Yeah, Im starting to think I should have went with the popular Eminence choices. They have more sensitivity and they are almost 1/2 the price for similar performance.

Plus I could piggy back all those XOs for the woofer. The PCD XO seem to work okay with my TD12M though.

I tried to do a quick measurement to get the depth of the QSC152i waveguide and its 5 1/2"

here are the dimensions for the TD12M

http://www.aespeakers.com/news.php?start=0&news_id=21

It looks like the depth is 3.93 inch (99.71 mm)

so my difference is 1.57 inch (39.99 mm )

If that is right then a double 3/4" baffle would be perfect for rear mounting the woofer.

[A9X]

here are the dimensions for the TD12M

http://www.aespeakers.com/pdfs/TD12-dimensional.pdf

It looks like the depth is 3.93 inch (99.71 mm)

so my difference is 1.57 inch (39.99 mm )

6.656" from the rear of the flange to the rear of the magnet and the flange + gasket is close to 3/4" on my 15X's.

[penngray]

The site might have bad specs?

[A9X]

The site might have bad specs?

I took it off my saved copy of the TD12 dims .pdf.
Just D/L from link and it's the same 6.656

[soho54]

Nah, they match up pretty good for this.

It looks like the depth is 3.93 inch (99.71 mm)

What are you calling the AC?

[soho54]

You just want to center the VCs midpoints on the same line, yes?

Edit
I just got time to work it out. I still can't follow your numbers, but I get to about the same place. When adding the B&C in.

That is a bit deep. Got any really large chamfer bits? :twisted: I might skip that second baffle panel, or go double 1/2". These are pretty close, and should be no problem for a passive xover to cope with.

[Dennis H]

Back in the HOLM thread, doing the ARTA excess phase thing, I got about .35 ms or about 4.5" that the AC of the Celestion tweeter was behind the AC of the woofer. That's just for that tweeter and that mic position but it at least gives you an idea of what you're dealing with.

Time to buy an ARTA license, Penn, so you can do this stuff yourself and save the results. Stop being a cheapskate.

[soho54]

What were the physical offsets using VCs?

[Dennis H]

Why would you use the VC? Extreme example, say there's a 12" tube connecting the VC to the cone. The AC would be somewhere up near the cone, not back by the VC. We've got all these cool tools like ARTA to measure that stuff so there's no need to guess.

[soho54]

Going by the VC mid point is how it has been done for years. I see no reason to throw it out yet. All you have to do is get close.

Since these are 12" woofers as mids, as opposed to say 6"ers there will be a little more slop in the old school rule of thumb, but it won't be anything you can't work out passively.

I bet more people will screw it up worse with trying to measure it than just going the easy route. With a passive xover who cares if it's off. Tweak till it's right. :T

[soho54]

I guess I should add a little more. There are two reasons to be worried about AC. They are time alignment and phase alignment.

If you have TA you have PA. The reverse is not true.

The crossovers will twist phase between the drivers, so what was phase aligned is no more.

Unless you are going for first order slopes with an eye on physical TA and PA religiously, I would just get the drivers close to TA, and let the chips fall were they lay. I would be more worried about slight off axis performance myself.

[Dennis H]

Sure, all that's true. With ARTA (and other good measurement software) you can measure the time difference exactly. Or you can guess at it by taking a tape measure to the drivers and trying to decide which point on the driver is the 'acoustic center'. We're trying to advance the SOTA here so using good (and cheap) software tools makes the most sense to me. Just like using LspCAD/PCD/SE to design a crossover makes more sense than using a textbook internet calculator.

[soho54]

The OP was tape measuring it. :

I haven't seen an example where the AC was so far off the old school method wasn't good enough.

[Dennis H]

The OP was tape measuring it. :

I haven't seen an example where the AC was so far off the old school method wasn't good enough.

So what AC offset do you come up with using the tape measure method? The horn is 5.5" front to back and the TD drivers have dimensional drawings posted.

[soho54]

LOL, we are derailing here.

I don't have them on hand, so I will use pdfs.

Lets see, the WG is 5.5", CD is around 2.4". The CD motor midpoint seems to be ~.75" That gives us an AC of ~6.25" in.

This TD12m is around 7.2" overall, and an AC ~5" from the front lip.

The popular 3012LF at 6" overall, would put the AC around 4.75"

This would work out to ~1.25" for the td12, and ~1.5" for the 3012.

I just thought about this, but a CD diaphragm is reversed in relation to a normal driver, on top of being on the opposite side. In this case I would add the other half of the motor back in play, and maybe half of the remaining CD. This will give you ~2.5" for the td12, and ~2.75" for the 3012. That's a ~.09ms difference. The extra thoat loading on the driver might not be worth the small correction with a xover this low.

Can this die now? I'm tired of thinking about it. ;x( :B

[penngray]

Back in the HOLM thread, doing the ARTA excess phase thing, I got about .35 ms or about 4.5" that the AC of the Celestion tweeter was behind the AC of the woofer. That's just for that tweeter and that mic position but it at least gives you an idea of what you're dealing with.

Time to buy an ARTA license, Penn, so you can do this stuff yourself and save the results. Stop being a cheapskate.

lmao, now its just on principle

btw, I remember the .35 ms and it being 4.5" so Im just more confused.

[penngray]

LOL, we are derailing here.

I don't have them on hand, so I will use pdfs.

Lets see, the WG is 5.5", CD is around 2.4". The CD motor midpoint seems to be ~.75" That gives us an AC of ~6.25" in.

This TD12m is around 7.2" overall, and an AC ~5" from the front lip.

The popular 3012LF at 6" overall, would put the AC around 4.75"

This would work out to ~1.25" for the td12, and ~1.5" for the 3012.

I just thought about this, but a CD diaphragm is reversed in relation to a normal driver, on top of being on the opposite side. In this case I would add the other half of the motor back in play, and maybe half of the remaining CD. This will give you ~2.5" for the td12, and ~2.75" for the 3012. That's a ~.09ms difference. The extra thoat loading on the driver might not be worth the small correction with a xover this low.

Can this die now? I'm tired of thinking about it. ;x( :B

Thanks and sorry, Im just trying to figure it out so that I can do future projects with fewer noob moments.

[soho54]

Crap, I forgot to add that this is on an axis centered between the drivers. If you want to have the CD at say ear level (and you are terribly worried about TA) you need to account for the path difference. It could be over 1/2" with these large driver spacings, and you would need to breakout the tape measure if you wanted to get closer.

Sorry, done now. I want to go back to sleep. :Z :cry:

[soho54]

btw, I remember the .35 ms and it being 4.5" so Im just more confused.

I remember augerpro using ~.2ms on top of his 1.2" baffle, so ~4" total. He was using the 3012HO which is ~.5" shorter that the LF. Using the above method you get a 3.25" offset. A .05ms difference.

I don't remember if measurements were done at center level or not, but that makes a difference. All in all in is pretty close.

EDIT: that should be 1.5" baffle on the NQs. :T

[penngray]

Thanks Soho, Im going to be cutting the wood this weekend for the new box build. Im thinking of having a 2" thick baffle (remounting the TD12M) that I can round over 3/4" on the front (maybe that will look nice??).



I also finally have the foam cut for my waveguides. I found out that an electric knife cuts its really easy and smoothly.

I would like to get the foam in place and the new box build before I continue with passive measurements.

In the meantime Im going to just spend some time listening to the BMS4550 active setup. Avatar tomorrow will be the first movie using them.

[Paul Spencer]

Thanks for sharing the process, it's a good read, including your other thread.

I also finally have the foam cut for my waveguides. I found out that an electric knife cuts its really easy and smoothly.

Did you buy this electric knife, or is it something you've rigged up?

[penngray]

Thanks, I just used a Black & Decker electric knife from Walmart ($10), it cuts its really easily.

I should update my project with the new boxes I built including bass bins using AV15X drivers.

[JoshK]

What are you guys using for surrounds? I am finishing up my Geddes Abbey clones (with the TD12M). I don't really feel like building surrounds given the number of things I have to get done, plus pro audio fixed application speakers seem cheap. Been looking at these:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=245-544

Any other good thoughts?

[penngray]

You have Abbey 12" OS WG???

do you have a build thread? I would love to read about it and how the CTC is an issue on the vertical axis. I have had some discussion recently on that and there are two camps on the issue. Im thinking it just another fussy/nitpicking type thing that is not really audiable since I have seen many designs with larger CTC then the QSC or JBL waveguides. Designs like the Emerald Physics and Duke Audiokensis stuff.

As for my surrounds. Currently I use Tannoy V8s, their mounting flexibilty is great for me and I found them on Ebay for $100 each so I couldnt resist. Not sure if they are still on Ebay but I love mine for surround duty. NOTE: I measured them and the measurements are not that great but still the sound is just fine. I actually use a pair every Saturday at a friends Gator football tailgate. Pretty impressive speakers for what I found them for.


If you want to buy something then maybe consider the Berhinger B2031P, I think they are on PE too (http://www.parts-express.com/pe/show...mber=248-6042). They have been measured by Geddes and others. The recently had a blind comparison to SL Orions and for that tests listening goals they won so they can not be that bad.

[JoshK]

I bought the waveguide a long long while ago (actually the first I think) when he sold them seperate. I've seen Brandon's measurements and Zilch's opinion on vertical lobe. Still I've heard the Summa's and I can't say I wasn't impressed.

I'm sure the xo is going to take some work. Geddes gave me his xo schematic that I can use for the HP at least, but since I use the TD12M, I'll need to revise myself anyhow.

[penngray]

The measurements are for the smaller waveguide, in the Geddes waveguide thread on diyaudio. I recently posted that I think some people focus more on that lobe then others do.

The list of speakers that have greater CTC then the QSC choices are quality speakers.
Summas, Abbeys, Duke's Audiokenesis designs, Emerald Physics, etc.

There are things that can be done in the XO to minimize the issue and in the end I think everyone agrees overall sound is more important then any measurement flaw. Like you said, the Summas sound incredible, I have not heard them but there isnt a person that has ever posted that the Abbey or Summa designs suck because of some null at a certain degree on the vertical axis....Its a lot about nothing IMO.

btw, I would to buy those 12" WGs off you if you feel the measurement lobe issue is too important

[JoshK]

I think the questions raised were in an effort to advance the state of the art. Any design can be improved, but at what cost? All designs are a balancing act to meet a set of priorities, and Geddes' priorities aren't necessarily those of others.

In the end its the sound that counts. If your inclined to be bothered by a narrow vertical lobe, then you might look to something else. I get Zilch's criticism and his rationale, but I've paid my money and I took my chances. I am not upset about it either.

[penngray]

I want both

If you ever want to sell those 12" WGs send me a PM.

I think Im going to now buy the Beyma CP380 CD. I dont remember the exact model # that Augerpro uses but Im going to build again using his passive XO design with the Beyma/TD12M combo.

All my passive design attempts never get anywhere. I just like active too much to bother.

[augerpro]

Hold off on the Beyma purchase if you intend to use them on the QSC. I have to do an A/B test to confirm, but going from the DE160 to CP380M then back to the DE160, I'm not sure the CP380M is the best match with the QSC horn. At least crossed at 1450hz, it gets some shrillness earlier than the DE160. I could cross it higher but then the lower crossover point was the whole reason for using them over the DE160 for the standard version of the NQ. Still isolating all the variables for now (nothing appears to be wrong with the drivers themselves) so I'm not going to make an statement on what exactly is the issue right now, but consider that before buy some. Now if you are using a different horn, than hold off a bit and I may have some barely used CP380M's for you.

BTW I sent you an email a while back to get your feedback on those crossovers. How do they sound? Any issues?

[noah katz]

What are you guys using for surrounds? ....

Any other good thoughts?

I'm using and like B&C 8CX21 with their XO-1

http://www.prosoundservice.com/Search_Results.html?m9:cat=/BRANDS/B%26C%20SPEAKERS&i1613287:page=6

the XO's aren't on their site but they have them