1st Solo flight - questions

[tom_s]

Thanks to Wolf's great blog entries, I think I am finally ready to graduate from 1st grade. I wanted to design a cheap, simple MT using drivers that Zaph had measured. I chose the Peerless 830656 and the Vifa BC25SC06-04, since I already have a pair on the shelf. If I didn't screw something up here, I plan on building these with my 12 year old daughter. She's been pushing me to build something in the shop and this is could be a nice little project that will teach her how to use some basic tools.

One major issue has me scratching my head- The 830656 exceeds X-max at only 11 watts above 40Hz when modeled in WinISD Pro Alpha. I am using 14L tuned to 45Hz. Below the tuning frequency, it's beyond X-max with anything greater than 1 watt, so I am assuming that's normal? But could that be why it has no power handling to speak of - a flat line at zero watts?

Beyond that, any advice or critique would be more than welcomed. I'm not quite certain on the driver offsets yet. Won't really know how much to use until I actually buy the woofers.

Thanks, Tom

[edlafontaine]

Re: 1st Solo flight - questions

It is normal and to be expected...it will still play louder than you will tolerate in "her" room for extended periods. This just means it won't provide great amounts of bass...no surprise considering the size.

Proceed

Welcome to the club

[tom_s]

Re: 1st Solo flight - questions

It is normal and to be expected

I was hoping that was the case. I modeled the TB W5-704 with the same volume and tuning that Wolf used in his Canvas project and noticed they also exceeded X-max in about the same way.

Anyone have comments or tips on the crossover model? I am wondering if the slope on the tweeter is steep enough to keep it out of trouble with that 2K crossover point?

[Wolf]

Re: 1st Solo flight - questions

I was hoping that was the case. I modeled the TB W5-704 with the same volume and tuning that Wolf used in his Canvas project and noticed they also exceeded X-max in about the same way.

Anyone have comments or tips on the crossover model? I am wondering if the slope on the tweeter is steep enough to keep it out of trouble with that 2K crossover point?

If you have the offsets entered in the PCD, then it looks decent to me. Posting the impedance would help as well. I would possible recommend 3rd elec on the tweeter to protect it more at 2 kHz, but the acoustic phase is fine as-is. I would also place a resistor in series with the 10uF cap or the 0.33uF cap to keep this from looking like a short at high frequencies. 1-2 ohms in the woofer will help tame that small hill below the xover, or use it in the tank of about 4-5 ohms.

Not bad!
Wolf

[tom_s]

Re: 1st Solo flight - questions

Wolf, I used your blog to get through Response Modeler. I never would have figured that out without your directions. I guess I owe you a beer...or three! But at this point I am using Speaker Workshop for the network. (A big thanks to Roman is also in order for his tutorial that taught me how to set a project up in SW.) I still have a little to learn about setting things up in PCD. Like where to add a cap for the tank (elliptic?) circuit and what measurements to use for the design axis. I'm sure it would help if I just read the user guide :p PCD is much slower on my old desktop than Speaker Workshop. This computer is not the fastest thing in world. I am betting it will run better on my laptop.

I hope the final impedance will be OK. The topology is similar to the HDS project that Jay designed, so I have my fingers crossed. I still don't know how to generate the total Z & phase in SW. I can generate the chart, but there is no usable data. I am guessing that I need to apply a signal somewhere....

Thanks for the tips on the crossover! I added a 2 ohm in series with the cap in the LP and it did bring that hump down a bit. It's still there, but I can play around a bit more and see if I can flatten that even more. My phase tracking gets further apart as I flatten that hump. Is that an issue & what will solve that...or do I just need to keep them parallel through the intersection? Response also starts to drop in the 2.5K range as I add more resistance. That's to be expected, so is this an instance where you would use a shallow notch filter?

I do need to look into my offsets, but without having the woofer in hand to examine, it's just a guess based on the spec sheet. I think I had too much on this first try, so I changed them to reflect 13mm difference between the W & T. I'll play with a 3rd order a bit more on the HP. I had tried it a bit earlier today but I still don't have a good feel for what role each component plays in shaping the curves. 2nd order isn't too tough, but 3rd order is still a bunch of guessing & clicking for me at this point. I know...practice, practice. It's the only way to get better. This is quite fun, Kind of like doing puzzles I guess.

So many questions...and I'm sure I'll have more!

Thanks again. I'll keep pluggin away.

Tom

[jbruner]

Re: 1st Solo flight - questions

There was a similar project posted here. I remembered because I saw almost the same network in your design. It might help to compare. The woofer is different, but apparently not much different.

[tom_s]

Re: 1st Solo flight - questions

jbruner- good memory!

I actually built a pair of those and use them daily at work in my video editing suite. They are in some really ugly boxes!! :eek: But at least no one would steal them if I left my office unlocked. They are what led me to choose this as my 1st real solo design. Jay is partly responsible for getting me started with modeling in Speaker Workshop. I learned a bit from playing around with the files that he posted.

[tom_s]

Re: 1st Solo flight - questions

Here's where I'm at now. The added resistance to the tank and Cap on the LP should help. I'm not sure I like the dip at 2.5K though. Can anyone tell me how to get summed impedance data from the total frequency plot in Speaker Workshop? I must be missing a data set somewhere.

Thanks,
Tom

[curt_c]

Re: 1st Solo flight - questions

Looks good from here, Tom.

Assuming the impedance and phase plots look alright, I'd say you are ready to build the first iteration of the design and start the voicing process. The 'BBC dip should make for a nice laid back presentation, and I'd guess the tweeter may sound a little hot unless you plan to listen to it off axis. You might try modeling it without the tweeter zobel too, as I suspect its not having much effect.

You can only get them close with the software. Your ears will take the design the rest of the way...

Nicely done!

C

[Zero the Hero]

Re: 1st Solo flight - questions

Here's where I'm at now. The added resistance to the tank and Cap on the LP should help. I'm not sure I like the dip at 2.5K though. Can anyone tell me how to get summed impedance data from the total frequency plot in Speaker Workshop? I must be missing a data set somewhere.

Thanks,
Tom

right click your network, go to Properties, in the General tab check on Network Impedence in the Generate box

[Dirk]

Re: 1st Solo flight - questions

Tom, you may want to shrink the box down some. Yes, it's going to cost you your nice low F3, but if you're willing to take an F3 in the mid-50's you can probably double the power handling.

[tom_s]

Re: 1st Solo flight - questions

Thanks Zero! That pointed me in the right direction. Looks like the total Z is fine.

Dirk, thanks for the input. How much smaller should I go? 12L? 9L? I realize that these are not going to produce serious low bass, but where is the point that they start sounding like satellites missing their sub?

Tom

[Zero the Hero]

Re: 1st Solo flight - questions

curious to see the outcome of these, as this is the woofer I was planning on using for my first project. I'm going to use LspCAD however, so learning the ropes of that program first. Are you planning on taking measurements or just using sims? Pretty well-behaved drivers, I don't foresee any real issues with sims...

[jkim]

Re: 1st Solo flight - questions

A quick note, Tom. Which impedance file do yo use for the tweeter? I realized that the manufacturer's impedance chart of one of these Vifa tweeters is off the mark---too low. That caused some of my previous modeling work to underestimate the tweeter's SPL, and I remember in your previous build you padded the tweeter much more than predicted by my modeling. Take a look at the impedance window for the tweeter in SW. Place the cursor around 4 kHz and read impedance in the bottom status bar. If it is below 3 ohms (e.g., 2.8 ohms), it's too low. Scale it using the Scale menu under Transform. If it's between 3.3 - 3.5 ohms, you're good to go. In case you need to scale it, you'll also need to change the tweeter Zobel component values, 10 uF in a tweeter Zobel is too large. It's not in line with the concept of budget design, either Even the 6.0 uF in Caleb's crossover is a bit too large---I wanted to use it since he already had it. Try 4.7 uF.

By the way, you're using the horn-loaded Vifa (BC25SC06-04), aren't you? In this case, drivers' relative acoustic offset should be very small. You extracted minimum phase from the midwoofer's response, didn't you? What value are you using for the midwoofer's driver offset value in SW? Tweeter offset should be set at 0.

Jay

[Dirk]

Re: 1st Solo flight - questions

Thanks Zero! That pointed me in the right direction. Looks like the total Z is fine.

Dirk, thanks for the input. How much smaller should I go? 12L? 9L? I realize that these are not going to produce serious low bass, but where is the point that they start sounding like satellites missing their sub?

Tom

I just looked at that SDS woofer. I didn't realize the Qts was so high. Personally, I'd be inclined to seal them in about 8L. You'd be surprised what an 80hz F3 sounds like with proper BSC. Your 14L vented will probably be very fun to listen to. Just don't forget that it's a single 5.25" woofer. ;)

What are these going to be powered by?