Blaupunkt Subwoofer Idea

[bwilkinson]

I have a couple of ACS1021 4 ohm subwoofers that have been sitting around for nearly 20 years, doing nothing. It's time to have some fun with them.

I'm working on designing cabinets for them. My goal is to receive low end boost (from 30 Hz to 50-60Hz) boost with these. I will never use them at "high" volumes, so I'm less concerned about over-excursion of them.

One will be used with a pair of Polk 5jr bookshelves. Those are pretty good to 50Hz, and I'm just looking for some "bump" in the bottom. I started a design of the cabinet using WinISD beta version, and the cabinet will have inside dimensions of 18"x18"x20". I will be creating a bottom rectangular vent 18" wide x 1.25" high, and with the .75" MDF it will take up a total of 2" of the cabinet. This should give me 3.375 cubic feet inside the the cabinet. The outside dimensions will be 19.5x19.5x21.5. So far, so good.

What WinISD showed me is that from 30-50Hz, it is pretty flat at -7dB, then efficiency rises.

Here's my question. I have no experience with crossover design. What do I want to do to get it to create a low pass filter at 60Hz, with a fourth order response (just for phase issues)?

Thanks!
Bob

 

[highfigh]

I have a couple of ACS1021 4 ohm subwoofers that have been sitting around for nearly 20 years, doing nothing. It's time to have some fun with them.

I'm working on designing cabinets for them. My goal is to receive low end boost (from 30 Hz to 50-60Hz) boost with these. I will never use them at "high" volumes, so I'm less concerned about over-excursion of them.

One will be used with a pair of Polk 5jr bookshelves. Those are pretty good to 50Hz, and I'm just looking for some "bump" in the bottom. I started a design of the cabinet using WinISD beta version, and the cabinet will have inside dimensions of 18"x18"x20". I will be creating a bottom rectangular vent 18" wide x 1.25" high, and with the .75" MDF it will take up a total of 2" of the cabinet. This should give me 3.375 cubic feet inside the the cabinet. The outside dimensions will be 19.5x19.5x21.5. So far, so good.

What WinISD showed me is that from 30-50Hz, it is pretty flat at -7dB, then efficiency rises.

Here's my question. I have no experience with crossover design. What do I want to do to get it to create a low pass filter at 60Hz, with a fourth order response (just for phase issues)?

Thanks!
Bob

If the surround is foam, I don't think I would do this. 20 year old speakers probably won't last long, at just about any level because the foam may look OK, but it deteriorates badly. Don't bother using a passive crossover. That's about the least efficient way to do it and if you consider the insertion loss, it's like using a 25W amp compared with a 100W amp. This is about 6dB of loss
just from the crossover if you go with a 4th order filter.

If you really want to do this, get the Theil/Small parameters for the drivers. That will make it possible to at least build the "correct" box.

 

[bwilkinson]

You make very good points. However, I look at it this way - wood is cheap (I have a bunch sitting in a barn currently doing nothing), the woodworking is fun - even if the result is a failure - and my options are either to use these drivers for something or have spent money on something so long ago that is now useless money. I originally bought them as a teenager for a car, and never used them. When I moved out for college, they sat at my parents' house, and I forgot about them. While cleaning up a bit of my parents' basement, I found them again. So why not have some fun...

I will agree that a passive crossover makes no sense - an active crossover with an amp makes more sense. I assumed that since the driver is such an old one that the T/S parameters used by WinISD were close enough to correct for my uses. I also agree that it is a horribly inefficient use of the driver, as it begins dropping off in a smaller box with a smoother response at 50Hz. It's the reality of the situation.

However, I can either use the drivers, or do nothing at all. Considering the room it's going to be used in (a three season front porch where the volume will never be above 70-75dB SPL) it should do fine. If I happen to smoke the drivers, it's 40 bucks to recone them. If I nuke them beyond repair, I've lost nothing - I have no other use for them.

 

[highfigh]

You make very good points. However, I look at it this way - wood is cheap (I have a bunch sitting in a barn currently doing nothing), the woodworking is fun - even if the result is a failure - and my options are either to use these drivers for something or have spent money on something so long ago that is now useless money. I originally bought them as a teenager for a car, and never used them. When I moved out for college, they sat at my parents' house, and I forgot about them. While cleaning up a bit of my parents' basement, I found them again. So why not have some fun...

I will agree that a passive crossover makes no sense - an active crossover with an amp makes more sense. I assumed that since the driver is such an old one that the T/S parameters used by WinISD were close enough to correct for my uses. I also agree that it is a horribly inefficient use of the driver, as it begins dropping off in a smaller box with a smoother response at 50Hz. It's the reality of the situation.

However, I can either use the drivers, or do nothing at all. Considering the room it's going to be used in (a three season front porch where the volume will never be above 70-75dB SPL) it should do fine. If I happen to smoke the drivers, it's 40 bucks to recone them. If I nuke them beyond repair, I've lost nothing - I have no other use for them.

If WinISD has the parameters, ge ahead. I didn't know they were in the database.

You might consider making an isobaric box. That way, it won't be as big and it will still hit pretty hard.

 

[bwilkinson]

I will look into the isobaric box. I have no experience or understanding with that design at all - I'll take a look across the web for information on them.

 

[highfigh]

I will look into the isobaric box. I have no experience or understanding with that design at all - I'll take a look across the web for information on them.

You can model it in WinISD.

 

[bwilkinson]

I saw that. I, however, wanted to get a little better idea behind the isobaric design rather than simply throwing numbers in.

In doing this, I noticed that WinISD shows the isobaric design as two drivers face to face, coupled together, out of electrical phase with each other and in acoustic phase with each other - as one driver pushes "outward", the other pushes "inward". This, of course, is necessary to keep from drastic changes in pressure in the sealed area between the cones.

Another sketch I saw online had the two drivers coaxially aligned, but in the same direction with a second box coupling the airspace together. In this case, they were wired electrically in phase with each other, and the air inside this separate box was the "shared" space.

http://www.danmarx.org/audioinnovation/theories.html

What is the difference, other than complexity? What is the preferred design?

Also, I did check the drivers today, and you are correct - the foam surrounds are deteriorating. I will check into the cost of refoaming them - either myself, or hiring it done. This project may end before it starts. That would kill a whole lot of fun, though, I was in the mood to make a lot of dust!

 

[highfigh]

I saw that. I, however, wanted to get a little better idea behind the isobaric design rather than simply throwing numbers in.

In doing this, I noticed that WinISD shows the isobaric design as two drivers face to face, coupled together, out of electrical phase with each other and in acoustic phase with each other - as one driver pushes "outward", the other pushes "inward". This, of course, is necessary to keep from drastic changes in pressure in the sealed area between the cones.

Another sketch I saw online had the two drivers coaxially aligned, but in the same direction with a second box coupling the airspace together. In this case, they were wired electrically in phase with each other, and the air inside this separate box was the "shared" space.

http://www.danmarx.org/audioinnovation/theories.html

What is the difference, other than complexity? What is the preferred design?

Also, I did check the drivers today, and you are correct - the foam surrounds are deteriorating. I will check into the cost of refoaming them - either myself, or hiring it done. This project may end before it starts. That would kill a whole lot of fun, though, I was in the mood to make a lot of dust!

Re-foam kits are pretty cheap- Parts Express has them and they come with an instructional video.