Hello, and My Second 3-Way

[Brian B]

I'm looking for a fairly simple way to finish these 1.7 cu. ft. MDF towers. They aren't going to be in a prominent place in the house, so nothing fancy is needed. Something somewhat subdued like a satin or textured paint (in a lighter color).
I was thinking of using a sanding sealer to seal the MDF edges. Any particular primer that works well over that? How about the final coat? Will some type of latex enamel work well?

Thanks in advance for any suggestions.

[Brian B]

I have both boxes built and fully assembled now, including the crossovers. I wasn't able to get the additional software to work with Open Office (I don't have Windows Office), so I'm limited to WinPCD for now. The crossover is basically unchanged from before (all 2^nd order with some padding). The modeled response using the published specs looks like this (using Win PCD):



I'm enjoying the sound of these speakers. They seem pleasing across the audio spectrum.

I've been listening to:
Wynton Marsalis – Joe Cool's Blues
Sting – Nothing Like the Sun
Dire Straits – Brothers In Arms
Holly Cole – The Best of Holly Cole
Donald Fagen – The Nightfly
Metallica – Black Album
Adele – 25
Mark Knopfler – The Ragpicker's Dream
ZZ Top – Tres Hombres
The Police – Synchronicity
Grand Funk Railroad – Some Kind Of Wonderful (song)
plus some of Waylon's songs and a small variety of other stuff.

These speakers seem to do especially well with vocals (both male and female), and brass instruments. Electric and acoustic guitar seem good as well. The bass seems both tight and reasonably strong and it seems to go deep enough for most recordings. I do prefer the sealed bass sound to ported bass even though the latter generally goes deeper.
They do seem a little harsh on some of the head-banging stuff. A little more tweeter padding largely corrected that, so I added an extra 2 ohms to the tweeter pad. I also added a shorting switch to remove the extra padding when desired. With the extra padding, the modeled response looks like this:




For the time being (and since the boxes buttoned up for the time being), I'll probably leave the crossovers alone and just enjoy listening to them for awhile. Should I find something notably lacking, or acquire better tools, I may revisit the crossover.
I also need to decide how I'm going to finish these. They are fairly large and will probably stay out of the living room, so I'll probably go with something simpler than veneer. Perhaps some sort of texture paint. I may also need to add some grill cloths to keep the grandkids from poking the neat circles.

[Brian B]

I'll plan to look at those additional tools.

In the mean time, I've worked more with the crossover and have it sounding pretty good (to my ears). It's all simple 2^nd order stuff at this point. WinPCD says it should produce a SPL like this:




And maybe it does. At any rate I'm liking it.

I have tailored the crossover a few different ways that produce a flatter SPL in PCD, but the octave to octave balance of the one above sounds more pleasant and natural to me than the those others. There obviously could be some things going on that I'm ignorant about (and/or that are outside the model), so for now I'll probably stop the crossover tweaking in order to review the other software tools suggested.

As an aside, I had enough scrap MDF to put together an Overnight Sensation over the last couple of days. Impressive sound for such a small speaker. But everyone knows that already.

[Millstonemike]

I don't have many loudspeaker design “tools” at this point. I used two free software programs to calculate the enclosure volumes from the woofer and midrange driver parameters. Since both the midrange and woofers were going to be in sealed enclosures I didn't feel I needed high accuracy for the calculated volumes.

I downloaded FPGraph Tracer and WinPCD to help with the crossover work. It took a little while, but I'm getting use to using that software. I imagine it would be more useful (accurate) if I had my own measured data rather than simply using the driver manufacturer published data.

I have one internal brace left to finish, plus the top, and the enclosures will be done except for gluing (and finishing). I'm saving the bottom and cutting in the terminal plate on the back until I get further along with the crossover work.

Two out of three ain't bad ...

You need the third leg of XO design: Response Modeler.
Response Modeler will allow you to account for BSC (and diffraction which can cause humps above nominal dB at certain freq.'s) as well as including the lower freq.'s of the box model (and min phase).

Trace the graph, process with Response Modeler, input the Response Modeler output into WinPCD. If the driver spec's are accurate, the model will be good.

Bullittstang's comment on BSC is right on.

[scottvalentin]

Those are great drivers in all respects, with some work and some help here you will have a very capable speaker. As Chris and Dynamo allude to, those breakups will need flattening and single order probably won't cut it on the F5, you will want a steeper slope. This also helps the XT25 as well, although at 3k it should work pretty good.

With FPTrace and PCD you should be able to come up with a pretty good sim that will be able to help you notch out the breakups and get the drivers to work together pretty good. Check out this writeup on how to piece together a sim using traces:

https://sites.google.com/site/undefinition/simulated-measurements

If you follow these steps with the manufacturer data sheets, you should get pretty close and will then be able to tweak it to your liking.

[dynamo]

Seems like a combo that could sound pretty nice but like Chris pointed out will need some good attention in the crossover. Not sure what you set your z axis at without being able to measure it, but if you left all drivers at zero in your crossover design software you may want to take a WAG and throw at least some approximate numbers in and see what your phase and fr look like after the change. My WAG would be -20mm for the mid and -40 for the woofer, with the tweeter at zero. Could be way off though.. I’m assuming you modeled the baffle diffraction effects. If not I would suggest that as well.

[Chris Roemer]

That F5 has 2 pretty bad breakups, one near 1.5kHz (notch) and again near 5k (don't take it that high).

[Brian B]

It's Alive!

The tweeter will need some padding as expected. The mid is considerably hotter than desired above 1-2K. So the WinPCD 1^st pass crossover (based on published graphs) isn't very pleasant sounding (not really a surprise). But it definitely shows promise.

[bullittstang]

...Never been a big fan of BSC either because of the losses. Of course, the use of a port (with the "gain") helps offset the loss in a BSC circuit

This statement illustrates you really should read some more about the finer points of designing a competent Speaker/XO design, IF you want the best sounding speaker possible. We would all love to ignore BSC too, but it's PHYSICS, you CAN ignore it, but your design will suffer because of it.

Decent choice of components - you really should optimize the XO and get the most out of them you possibly can.

[Brian B]

I'll give some consideration to a port, but I generally prefer sealed designs. I know ported designs have been pretty much standard for many years now, but they can sound somewhat tubby or one-note to me at times. I may try it once I get these speakers making noise. Conversely, I don't like the approximate 3dB loss that comes with a sealed design.

Never been a big fan of BSC either because of the losses. Of course, the use of a port (with the "gain") helps offset the loss in a BSC circuit.

I beginning to sense how important the overall efficiency is to a lively speaker. It seems like the less sensitive a speaker is, the less dynamic it is, no matter how much power is thrown at it.

[Chris Roemer]

Even in only 1.6cf, adding a (3" x 9" long "Precision") port will drop your F3 by 10Hz (50 down to 40) as well as add a dB or 2 of "lift" near 100Hz, which could be used as part of your BSC.

[Brian B]

I don't have many loudspeaker design “tools” at this point. I used two free software programs to calculate the enclosure volumes from the woofer and midrange driver parameters. Since both the midrange and woofers were going to be in sealed enclosures I didn't feel I needed high accuracy for the calculated volumes.

I downloaded FPGraph Tracer and WinPCD to help with the crossover work. It took a little while, but I'm getting use to using that software. I imagine it would be more useful (accurate) if I had my own measured data rather than simply using the driver manufacturer published data.

I have one internal brace left to finish, plus the top, and the enclosures will be done except for gluing (and finishing). I'm saving the bottom and cutting in the terminal plate on the back until I get further along with the crossover work.

[westrock2000]

Good start. It took me a while to get the software stuff. I have Dayton Omnimic and DATS combo and it's great. Very simple to use and really adds a whole other dimension to the hobby. I have also tried REW (using the Omnimic mic) and it does work and it's free (plus cost of a USB mic), but I like the Omnimic interface better. But REW does have some cool features, like making a very tight frequency sweep that allowed me to find the exact frequency a panel was vibrating at.

[Brian B]

Finished the cuts on the front, back, and side panels, and have them assembled together temporarily with drywall screws. They measure 38.5” tall, 11.25” wide, and 10.25” deep. Next up are cutting and fitting the interior panels and braces, followed by the top.

[Brian B]

OK. The Drivers are as follows:
Woofer – Dayton DA270-8
Midrange – HiVi F5
Tweeter – Peerless XT25TG30-04
My intended internal enclosure volumes are approximately 3.1L for the mid/tweeter and 45L for the woofer. 3/4” MDF will be used for the sealed enclosure. I'm planning 2^nd order crossovers all around at approximately 300Hz and 3000Hz.