Re: OT: Subwoofer project to support your Altecs.
Got 'em done.
http://www.hostboard.com/forums/hbmc...2013/08/13.jpg
It was quite a saga. I first tried painting them, but nothing sticks to this plastic. These had Walmart logos on them and that didn't even stick. So I guess I'll live with WM blue until I find some black ones.
The second issue was the Crown amp. I guess this is a pro level amp and not designed for home audio. My 12dB Grounded Grid preamp would not drive it. Even though Crown support says it has a 1.4V input sensitivity and my main amp is 2.2V and it drives that one just fine. Hum...
Every one else that has used this amp uses high level inputs paralleled off the main amp speaker outs with an inline resistor to knock the voltage down rather then the low level RCAs. I started with a 2.2K Ohm and ended up at only 220 Ohm to get the gain right. Here's a pic of the experimental cable I used while switching out resistors:
http://www.hostboard.com/forums/hbmc...2013/08/14.jpg
So now that I had output, I set off to trim it out. I've settled on 53Hz. The volume is about 8.5 of 10. At that level I can't 'hear' the subs when they're on, but the bottom drops out when they're off. That's the way I want it. Like adding salt to my soup. I want to bring out the flavor, but I don't want to taste the salt.
The blend is uncanny. My old KLH gave up some sub sonics, but it sounded dry and monotone. More of a vibration than a musical note. These sound sweet and smooth and very musical. I really can't tell where my Altecs end and these begin...until I turn off the Crown. Then..."oh, where'd all that nice deep bass go?" When I turn it back on, I can't really hear the bass come back...until I turn it off again. Nice.
Re: OT: Subwoofer project to support your Altecs.
Awesome job, Alan.
My first bucket is nearly complete - waiting for the concrete to hydrate.
While I am waiting for that, I played around with some box calcs for this Peerless 8" sub:
http://imageshack.us/a/img9/8155/y36c.png
This plot shows that sub in my sealed box (0.5 CF is about what's inside the bucket), and in a 3 CF vented box. What a difference!
What I don't know is what WinISD is doing regarding box shape and how it would differ if it could model a cylinder.
Perhaps the next experiment is to take a 40 gallon brute trashcan and try out a 12" LoL!
Re: OT: Subwoofer project to support your Altecs.
Quote:
Originally Posted by
Alien_Shore
Perhaps the next experiment is to take a 40 gallon brute trashcan and try out a 12" LoL!
I was thinking the same thing! Then I thought of the amount of concrete required...
There's a funky component going on with the bucket too. It certainly is not rigid. The whole thing vibrates. Ed strongly urges to resist stuffing with fill or damping it in any way. The bucket itself becomes a passive radiator of sorts. So sound waves certainly shoot out the top, but they must also radiate 360* around as well.
What was also not expected is that they can take a punch. I was cranking out some old Madonna and the whole floor was shaking. And they're sitting on 3 rubber feet!
Re: OT: Subwoofer project to support your Altecs.
Most programs just define the cab's air mass as having a uniform particle density in an infinitely rigid cab, i.e. has no resonant modes, so shape is irrelevant and the vent's output is in the same location as the driver. MJK's more recent MathCad software is a bit better as it adds another dimension in length to include its 1/4 WL resonances and an adjustable driver and vent location along it, but still no 3D [width x depth] modes. AFAIK, of the programs available to the DIYer only AkAbak does 3D.
In short, as long as the cab's LxWxD are all near the same and the driver , vent on the same vertical side, then the programs are pretty accurate if measured outdoors on a large flat area.
The 'breathing' bucket lowers the speaker's effective Qtc [Qtb if vented], so can really 'tighten up' its transient response, so no need for any internal damping.
A 40 gal. trashcan has enough of a high aspect ratio to require using MJK's or similar software to more accurately sim it, though none can sim the 'breathing' cab's variable Q damping.
Even though the driver is upward firing, its BW is so large acoustically [80 Hz is a ~54" diameter 'sphere'] that it will still mirror image as a vertical 2pi [half] space radiator, though through the XO BW it may sound more 'airy' if it doesn't have a steep slope order.
GM
Re: OT: Subwoofer project to support your Altecs.
Quote:
Originally Posted by
GM
A 40 gal. trashcan has enough of a high aspect ratio to require using MJK's or similar software to more accurately sim it, though none can sim the 'breathing' cab's variable Q damping.
GM
That explains why when I drop one of my 40 gallon trash cans back onto the floor after emptying in I get one hell of a bass note from it, especially in the bathrooms. :D
- - - Updated - - -
Quote:
Originally Posted by
GM
A 40 gal. trashcan has enough of a high aspect ratio to require using MJK's or similar software to more accurately sim it, though none can sim the 'breathing' cab's variable Q damping.
GM
That explains why when I drop one of my 40 gallon trash cans back onto the floor after emptying in I get one hell of a bass note from it, especially in the bathrooms. :D
- - - Updated - - -
Quote:
Originally Posted by
GM
A 40 gal. trashcan has enough of a high aspect ratio to require using MJK's or similar software to more accurately sim it, though none can sim the 'breathing' cab's variable Q damping.
GM
That explains why when I drop one of my 40 gallon trash cans back onto the floor after emptying in I get one hell of a bass note from it, especially in the bathrooms. :D
Re: OT: Subwoofer project to support your Altecs.
Re: OT: Subwoofer project to support your Altecs.
Quote:
Originally Posted by
GM
Even though the driver is upward firing, its BW is so large acoustically [80 Hz is a ~54" diameter 'sphere'] that it will still mirror image as a vertical 2pi [half] space radiator, though through the XO BW it may sound more 'airy' if it doesn't have a steep slope order.
GM
The Crown XLS1500 has selectable crossover points between 50Hz and 3kHz on 1/12 octave centers. They use 4th order Linkwitz-Riley filters.
Re: OT: Subwoofer project to support your Altecs.
As it turns out, my first Crown amp was a dud. I got it off ebay supposedly new, but who knows. I have a feeling someone hooked it up and blew out the inputs. My preamp that can produce a 12dB gain at RCA level couldn't get a whisper out of it. I had to run high level outs, paralleling off my main amp to get it to do anything.
The replacement came today and ...wow. Just wow. I'm bridging it mono and paralleling the two buckets subs at 4 Ohms. I'm guessing thats somewhere around 525W into each sub. Peter Tosh never sounded so good. I'm crossing over at 59Hz right now. It seems right.
Re: OT: Subwoofer project to support your Altecs.
Hostboard was screwing up not me. :D
Re: OT: Subwoofer project to support your Altecs.
Regarding low and high level inputs, the few guys that have made these and tested them extensively all say the same thing: that they sound better running high level inputs paralleled off the main amp instead of low level (RCA, XLR) inputs. It's not just a gain issue, the claim is that they blend better in that configuration.
I guess that kind of makes sense since you're taking the sub inputs right off the main outputs. Whatever characteristics that are inherant in the main are translated to the sub amp.
