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post #181 of 603 Old 09-02-2009, 12:12 PM - Thread Starter
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There's Dennis! Thought you were sick or something

I was wondering what they meant by trapezoid, as the baffle looked rectangular to me. You could saw off the flange, use a flush trim bit to trim it up, then glue another layer to it and finish it off with a roundover. Dealing with it isn't impossible, just takes more time. Adn to me that is the only benefit of these, as you said anyone who has the skill to make the mods certainly has teh skill to build it from scratch in the first place.
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post #182 of 603 Old 09-02-2009, 12:28 PM
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Quote:
Originally Posted by catapult View Post

You could make it work but it would be a kludge.

Kludge?

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post #183 of 603 Old 09-03-2009, 07:48 AM
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Quote:
Originally Posted by augerpro View Post


On the top of your speaker can you still see the seem between your baffle and the box?

If you cant did you use bondo or woodfiller to smooth it over? Or maybe just a good primer?

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post #184 of 603 Old 09-03-2009, 08:12 AM - Thread Starter
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Between the baffle and the top? I actually cut the baffle and back panel a bit oversized then used a flush trim bit to trim it flush with the sides and top after they are glued on. In addition I always run a quick swipe of bondo over the seams and sand to 200 grit so there is no chance of seeing a seam through the paint.
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post #185 of 603 Old 09-03-2009, 11:20 AM
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Quote:
Originally Posted by augerpro View Post

Between the baffle and the top? I actually cut the baffle and back panel a bit oversized then used a flush trim bit to trim it flush with the sides and top after they are glued on. In addition I always run a quick swipe of bondo over the seams and sand to 200 grit so there is no chance of seeing a seam through the paint.

Thanks, my mistake of not doing enough with my wood filler and I didnt do any bondo. Im use to veneering which never requires this type of detail.

Live and learn....time to bondo and sand again.


I would like if Bondo would stick to my primer then I wouldnt have to sand down that area.

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post #186 of 603 Old 09-08-2009, 03:11 PM - Thread Starter
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Well I'm working the crossover now and hit a snag on the No Quarter. The DE160 acoustic center is back much farther than I was hoping compared to the woofer, even with the LP in place. At any given distance the DE160 phase is wrapping very fast so it and the woofer share a small area where they are in phase - with textbook slopes. Since I can now see far off axis at a 10 degree resolution I may be able to get creative with assymetric slopes. There are some other tricks I know but they usually center around lessening the woofer's phase wrap for the same rolloff (damping the shunt cap) or ladder delays for the tweeter. Trying to find some similar tricks for the DE160 but the difference is pretty large.

Outside of that I'm investigating mounting the driver to the back of the baffle, but that will require a new test box as I have no removable panel to do it and it won't fit through the horn cutout. I will be using a DCX2496 for prototyping so I can adjust the delay, but this project will have a passive crossover in the final version so I have to figure something out.

For those that are already building this I would make provisions for the possible rear mounting of the woofer. Or wait a little bit until I figure out what I'm going to do.

Oh yeah, I scratched the front of my pretty baffle moving a saw stand around too...

The BBV2 project is promising though. Not real far on the crossovers, but everything looks like it will work out well.
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post #187 of 603 Old 09-08-2009, 07:31 PM
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Are you saying that if the woofer is 3/4" back it would be okay?

If we mount the woofer to the back of the baffle, we should round over the woofer hole on the front of the baffle with maybe 3/4" roundover?

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post #188 of 603 Old 09-09-2009, 05:59 AM - Thread Starter
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More like 3" or 4", not 3/4" We don't need them exactly aligned, a lot can be fixed in the crossover. The lower and steeper you cross the less misalignment is an issue so I thought I'd be ok, if only just barely. But now that I'm actually modeling it looks like I'll have to shift gears.

I'm looking at rear mounting the full 1 1/2" thickness of the baffle. With maybe a 1" roundover or so. The frequencies covered by the woofer should be low enough not to have any diffraction problems from the lip, but then, I could be surprised again. Active XO will obviously make it a moot issue, but it didn't plan on this being an active only speaker. I'm also looking at a ladder delay circuit. Results are promising so far, but I've lost about 5dB sensitivity with it.
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post #189 of 603 Old 09-09-2009, 06:49 AM
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Quote:
Originally Posted by augerpro View Post

I'm also looking at a ladder delay circuit. Results are promising so far, but I've lost about 5dB sensitivity with it.

Ouch.

What about using a different horn? I realise that's basically starting over, but if you're having too many problems with this horn's depth, would a more shallow horn work?

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post #190 of 603 Old 09-09-2009, 07:56 AM - Thread Starter
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I haven't seen anything shallower that I like. I'd rather change the box to work with horn than change the horn to work with the box.
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post #191 of 603 Old 09-09-2009, 08:21 AM
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Is sticking the horn out in front of the baffle a possibility?

YID DIY
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post #192 of 603 Old 09-09-2009, 10:53 AM
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Brandon,

Just put a capacitor, and possibly also a resistor, in series with the shunt inductor in the tweeter HP filter. This makes a series RLC notch filter. If you place this about 1 octave below your desired crossover frequency, you can use it to change the phase of the tweeter output at the crossover frequency. By varying the exact frequency and depth of the notch, you can adjust the exact phase shift.

If you need to move the phase the other way, you can replace the woofer shunt capacitor with an RLC also.

The big advantage to these circuits is that you only have to change one or two parts to tweak the phase at the crossover frequency. When you switch from 3rd to 4th order on one driver to get the same effect, you are talking about lots of different part values. In your case it also has the big advantage of killing extra output right where the compression driver has its worst behavior.

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post #193 of 603 Old 09-09-2009, 01:50 PM
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Quote:
Originally Posted by Looneybomber View Post

Is sticking the horn out in front of the baffle a possibility?

That would kill all the work put into managing diffraction.

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post #194 of 603 Old 09-09-2009, 06:35 PM - Thread Starter
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Jack thanks for the advice. So essentially you are suggesting an elliptic type filter for the tweeter HP? I've used them woofers before but never really tweeters.
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post #195 of 603 Old 09-09-2009, 07:10 PM
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Brandon,

Yes an elliptic filter. Although if you need more delay on the woofer, you should actually put the elliptic filter on the woofer LP, not the tweeter.

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post #196 of 603 Old 09-09-2009, 07:25 PM
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What about swapping in the Celestion 14XX CD? It's lower cost right?

Regards,
Dan
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post #197 of 603 Old 09-09-2009, 07:51 PM
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Tough spot. Kind of bass ackwards, to have to move the woofer back(farther away)to get the acoustic centers (closer). What happens if you simulate moving the woofer down by a similar amount?

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post #198 of 603 Old 09-10-2009, 06:19 AM - Thread Starter
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Dan I'm not following you on switching the CD, the problem is the horn depth.

I've calculated how much delay is needed to bring things in alignment and I'll be testing some things out soon.
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post #199 of 603 Old 09-10-2009, 08:54 AM
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Quote:
Originally Posted by augerpro View Post

More like 3" or 4", not 3/4" We don't need them exactly aligned, a lot can be fixed in the crossover.

I ran into that problem before a long time ago. Not being very skilled I couldn't get it to work very well. Since I was using an expensive horn with a cheap woofer, I bought a new larger woofer. I went from a 12" to a 15", and it had 2.5" more depth. It was definitely an improvement, except for the beaming because I was crossing over at 1200hz.

Since then I've replaced the driver with a TD15M, which has a depth 8.5". I recently bought a pair of the QSC horns, based on your measurements, to see how they will work with the TD15Ms, even though I probably won't get around to it until after the new year.

The TD15Ms sound great, but they are effing heavy. I actually use mine in a PA system, but I plan on phasing them out and using them in a two channel system for home only. They are just too heavy to lug around.

It's one thing when your young or have lots of help. It's another when you're old and do most of it your self. Setting up isn't too bad, but after a gig, when it's late and you're tired, dragging heavy equipment around is a real pain. I've recently replaced the alcino drivers in my guitar cabinet with neo drivers. I cannot believe the difference in weight. From now on, neo only if I have to transport it.

Good luck Brandon. I hope you get these and your high end version to work. If you do, I plan on building both. The high end for home, but using my TD15Ms, and the neo version for on the road.

Thanks for all your hard work,
John
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post #200 of 603 Old 09-10-2009, 09:45 AM
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Quote:
Originally Posted by Jack Hidley View Post

Brandon,

Just put a capacitor, and possibly also a resistor, in series with the shunt inductor in the tweeter HP filter. This makes a series RLC notch filter. If you place this about 1 octave below your desired crossover frequency, you can use it to change the phase of the tweeter output at the crossover frequency. By varying the exact frequency and depth of the notch, you can adjust the exact phase shift.

If you need to move the phase the other way, you can replace the woofer shunt capacitor with an RLC also.

The big advantage to these circuits is that you only have to change one or two parts to tweak the phase at the crossover frequency. When you switch from 3rd to 4th order on one driver to get the same effect, you are talking about lots of different part values. In your case it also has the big advantage of killing extra output right where the compression driver has its worst behavior.

I sent a PM asking about this, but I thought a few others may be interested in any response, so I'll ask here as well on this one. Very interesting, these circuits that can shift the phase at crossover.

My question is VERY basic, as one who is just now getting together measurement equipment.( Dayton mic, and REW and synRTA ) How is the phase difference/correction determined, and what equipment would I need to do so?

Thanks for any dumbed down assistance you could lend.

Russell50
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post #201 of 603 Old 09-10-2009, 09:49 AM
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Never heard of synRTA, looks very interesting because its free!

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post #202 of 603 Old 09-10-2009, 09:51 AM
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Originally Posted by augerpro View Post

Dan I'm not following you on switching the CD, the problem is the horn depth.

I've calculated how much delay is needed to bring things in alignment and I'll be testing some things out soon.

So the problem is with the physical depth of the horn itself? I dont know how this was handled by Wayne over at the PI speaker forum, but the H290 horn he uses is even a little longer than the QSC. Or is there something I'm missing? (very likely the case) Sorry to be so inquisitive, I just cant help myself.

Thanks for the time,
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post #203 of 603 Old 09-10-2009, 09:54 AM
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Originally Posted by penngray View Post

Never heard of synRTA, looks very interesting because its free!

That was one of the main things that interested me in it. Plus, I've had a lot of people advise it and especially REW. As soon as I get mic pre, phantom power and maybe a new sound card, I will begin trying them out. Hopefully it will answer more questions than it asks

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post #204 of 603 Old 09-10-2009, 11:01 AM
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Have you tried ARTA (free just can't save)?

or

HOLMImpulse (New, free and has a great following on DIYaudio right now. Geddes says its awesome and its the first software package to make him switch in 20 years).

found here
http://www.diyaudio.com/forums/showthread.php?t=145662

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post #205 of 603 Old 09-10-2009, 11:43 AM
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Russell,

Step 1) Measure the frequency and phase response of both drivers in the system without moving the microphone.

Step 2) Compare the measured phase values of the two drivers at the desired crossover frequency. Whichever driver has more phase shift at that frequency means that driver is more delayed. For example, the tweeter is 136 degrees and the woofer is 276 degrees at 1.8kHz. 276-136=140 degrees. At 1.8kHz a phase shift of 140 degrees is a path length difference of 2.95". ((1,800*140)/(13,680*360)). 2.95" is how far you would need to move the woofer forward to make the phase difference zero at 1.8kHz.

Step 3) Model a crossover with an RLC parallel notch filter that is shunted to ground. Here is an example of one used in the woofer circuit:

http://zaphaudio.com/XDS-crossover.gif

The RLC filter is formed by C7, L8, R9. In the case above you want to put the RLC circuit in the tweeter section, since you need to delay the tweeter output to match that of the woofer. The RLC circuit increases the steepness of the crossover function. This always causes more delay (phase shift) as a result.

Here is the transfer function of the crossover above:

http://zaphaudio.com/XDS-transferfunction.gif

You can see the notch at 8kHz and the very steep slope that adds delay from 3-6kHz. When using this circuit to add phase shift, you don't really care how deep or where the notch is per se. You adjust the notch parameters until you get the desired phase shift at the crossover frequency.

Step 4) How do I figure out how to achieve the 140 degrees of phase shift at 1.8kHz? You must have some modeling software such as LSPCad for this. You import the drivers impedance, frequency and phase responses. Build a Spice model of the crossover in the software. The software will then show you what the resulting phase response of each output will be. I'm not hip to all of the latest freeware/shareware crossover modeling software, so others will have to offer suggestions. Having access to crossover modeling software is absolutely essential to building a loudspeaker. Doing it by trial and error/calculator method will take 10 times as long and will nearly always result in a significantly inferior result.

Jack Hidley
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post #206 of 603 Old 09-10-2009, 11:49 AM - Thread Starter
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I don't know what Wayne does, or Geddes for that matter, who must have the same issues given the depth of his waveguides. The may not do anything. The JBL horn on the econowave probably wouldn't have much of an issue since it is relatively shallow. Just eyeballing it the nominal acoustic center of the little JBL probably lines right up with a typical 12" woofer. Others just don't care if the phase is alignable in a very narrow passband. Like I said I knew it had the potential to be an issue, I just didn't think it would be very big. I've been working on some ideas so I'm not too concerned. I'm just bummed that I have to do more woodwork since that stuff takes me forever and I find it really tedious. And contrary to some comments on other threads this is not an attempt at a time aligned design, and there is no confusion on what minimum phase is. Everyone who has measured and designed a speaker before understands what the problem is. The cool thing is this has forced me to look at the active solutions more closely adn there should be some cool variations for this design when all is done.

I should probably post some pics of what is going on to make it clearer to people following along. Keep in mind I tend to be a perfectionist about this sort of thing, so others may not see this as a big deal at all.
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post #207 of 603 Old 09-10-2009, 11:56 AM - Thread Starter
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Jack's explanation of the issue is right on. Jack one question: I'd already tried a small cap in parrallel with the woofer's first series inductor, basically another form of notch similar to the LCR shunt. Assuming similar resulting slopes (or even just using higher order roll off in the first place) does the LCR shunt on the woofer wrap phase more? Seems to me it should be about the same?
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post #208 of 603 Old 09-10-2009, 11:57 AM
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Quote:
Originally Posted by penngray View Post

Have you tried ARTA (free just can't save)?

or

HOLMImpulse (New, free and has a great following on DIYaudio right now. Geddes says its awesome and its the first software package to make him switch in 20 years).

found here
http://www.diyaudio.com/forums/showthread.php?t=145662

Meaning to look at ARTA, and have been reading about HOLMimpulse, looks like it may be the ticket......and the price is right.

Russellc
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post #209 of 603 Old 09-10-2009, 12:00 PM
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Quote:
Originally Posted by Jack Hidley View Post

Russell,

Step 1) Measure the frequency and phase response of both drivers in the system without moving the microphone.

Step 2) Compare the measured phase values of the two drivers at the desired crossover frequency. Whichever driver has more phase shift at that frequency means that driver is more delayed. For example, the tweeter is 136 degrees and the woofer is 276 degrees at 1.8kHz. 276-136=140 degrees. At 1.8kHz a phase shift of 140 degrees is a path length difference of 2.95". ((1,800*140)/(13,680*360)). 2.95" is how far you would need to move the woofer forward to make the phase difference zero at 1.8kHz.

Step 3) Model a crossover with an RLC parallel notch filter that is shunted to ground. Here is an example of one used in the woofer circuit:

http://zaphaudio.com/XDS-crossover.gif

The RLC filter is formed by C7, L8, R9. In the case above you want to put the RLC circuit in the tweeter section, since you need to delay the tweeter output to match that of the woofer. The RLC circuit increases the steepness of the crossover function. This always causes more delay (phase shift) as a result.

Here is the transfer function of the crossover above:

http://zaphaudio.com/XDS-transferfunction.gif

You can see the notch at 8kHz and the very steep slope that adds delay from 3-6kHz. When using this circuit to add phase shift, you don't really care how deep or where the notch is per se. You adjust the notch parameters until you get the desired phase shift at the crossover frequency.

Step 4) How do I figure out how to achieve the 140 degrees of phase shift at 1.8kHz? You must have some modeling software such as LSPCad for this. You import the drivers impedance, frequency and phase responses. Build a Spice model of the crossover in the software. The software will then show you what the resulting phase response of each output will be. I'm not hip to all of the latest freeware/shareware crossover modeling software, so others will have to offer suggestions. Having access to crossover modeling software is absolutely essential to building a loudspeaker. Doing it by trial and error/calculator method will take 10 times as long and will nearly always result in a significantly inferior result.

Thank you for this informative post. This helps explain this topic quite well, and hopefully others were wondering as well, hope I didnt divert too much from the original thread.

Very much appreciated,

Russellc
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post #210 of 603 Old 09-10-2009, 10:19 PM
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Quote:
Originally Posted by Jack Hidley View Post

Russell,

Step 1) Measure the frequency and phase response of both drivers in the system without moving the microphone.

Step 2) Compare the measured phase values of the two drivers at the desired crossover frequency. Whichever driver has more phase shift at that frequency means that driver is more delayed. For example, the tweeter is 136 degrees and the woofer is 276 degrees at 1.8kHz. 276-136=140 degrees. At 1.8kHz a phase shift of 140 degrees is a path length difference of 2.95". ((1,800*140)/(13,680*360)). 2.95" is how far you would need to move the woofer forward to make the phase difference zero at 1.8kHz. ....

Jack,
Thanks much for this info.
When measuring the phase of an individual driver connected in the system, is it necessary to place a dummy load in the other driver's place? (Assuming a 2-way system.)

And when determining the x-o frequency for doing the calculation above, is it right to use the acoustically measured x-o frequency observable from a FR measurement? (Invert polarity of one driver.) Or is it necessary to look at the voltage drive of the crossover?

Sorry to intrude here, thanks again.
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