New DIY Subwoofer Project (1 Viewer)

[Greg P]

Conrad I also have an SVS, a 25-31(which Im selling). I am kind of in the same boat to start off with, but a soon as I finish my sealed 1503 I want to build something else. My problem with the SVS is not output, but integration, and figuring out that I like sealed alignments and a bit higher Q. I listen to mostly rock music. I have found from listening to several subs that I like a Q of .647 to .707 better than the very low Q (.54-.577) of the SV's. I also like that tight "pop" off of notes, a characteristic that sealed subs have. The SVS is very good for hometheater, but for music, and my tastes its a bit too dry.

Conrad, you also seem to be set on making a ported sub. I know after talking a lot with Tom V. he kind of got me in the mode that porting a sub is the only way to go.(No disrespect to TV, he is great and very knowledgable) This is not true and a very subjective matter. I have found actually that I like the sound of sealed better. Porting seems to not be an option with this sub. If you put these guys in a sealed sonotube with one of the amps I talked about, it will easily CRUSH a pair of the regular SV's.

 

[Vince Bray]

If you want more output I think you need ported or PR design. The reality is that a sealed sub is not going to give you the spl you want with 500 watts per channel. 500 watts to the 1203 will yield (for two subs together) 100db at 20hz, 106db at 30hz, and 111db at 50hz. Using a vented or PR box (they are equivilant efficiency-wise) you can get 112db from about 22hz up, and be down 1db to 110 at 20hz. This is two PR18 (custom massed to 2050g) and two BP1203 in a box 110 liters. That's roughly the size of the 15.2 cube, about 22" cubed.

Just for fun, to get 110db from the 1203 took 8000 watts. You might fuse the VC at some point just before you hit 8000. The sealed box is great for SQ, but if you're wanting more than an SVS, you might want to go ported/PR. I would guess that the SVS can best the sealed design we're looking at, at least in terms of output.

Vince

 

[Conrad_S]

Interesting, you two have opposing opinions on the sealed box. Could someone else throw their opinion on whether a sealed sonotube with dual 1203's powered by ~1000 watts RMS can "handle" an SVS in output?
Greg, could you elaborate on Q a bit more?

 

[Greg P]

I agree that one ported SVS will beat a sealed below 30hz. However there is no comparison above 30hz the blue print will blow it away. If your talking about average spl from 60 - 25hz (the most important) you would have the blueprint probobly being the winner. I believe 2 sealed blueprints with 1000 watts each together will reach about 110db (anechoic) at 22hz. Thats nothing to sneeze at. You could do this project for around $1000. Honestly you would have had a better deal going with sealed 1503's. Also require a small box and you would gain quite a bit of output. (around 115db at 22hz in a sealed encolsure.)

Conrad I would advise you to go to diysubwoofers.org to learn more about speaker design.

Qtc or "Q" is the dampening of the driver. How much air your giving each woofer. The lower the Q the better transient response the woofer will have and the greater lower end output as well as reduced group delay. However the woofer sacrifices higher frequencey output and will also tend to loose fullness to the sound. Some schools of thought believe in the butterworth alignment (QTC = .707) this is the point where the woofer has its flatest signal responce. Others believe in a critically damped alignment which is the Bessel (.5777) where the woofer has its lowest group delay. Before you build your sub you need to figure out what "Q" and align ment you desire. Once you have the airspace you know you need though remember you need to also subtract any bracing in the sub, as well as the flange, and the space of the motor structure. (Blueprints 03 motors are .24 ft^3)

 

[Conrad_S]

Thanks for the link. I'll try reading up before this weekend. (1203's arrive Friday) I'm here to build an enjoyable subwoofer and to learn at the same time, so I don't mind building a few boxes...

The two reasons I chose the 12's were that I didn't have room for an 18" sonotube in my room, (16" was the max I could fit) and the 12's are a faster subwoofer - due to the smaller driver area I assume.

 

[Jack Gilvey]

and the 12's are a faster subwoofer - due to the smaller driver area I assume.

This is a fallacy.

 

[Conrad_S]

Wow, that's news to me! It made sense since the 15" has to move more air than a 12", hence it will have more air resistance in both directions. Are there any articles that explain why this is a fallacy? (diysubwoofers.org didn't have any links pertaining to it)

 

[Vince Bray]

Jack is right. When you get the thing working you'll see. That motor will be in total control of the cone, it is a very powerful motor and with lots of juice it'll blow you away.

Give a bit more detail as to why I'm building a DIY. I have an SVS 20-39CS paired with a Samson S700. It sounds great, but it really lacks in output

Ok, this sounds like you want some pants-flappin'.

Even if you port with a 4" flared port, I think you'll be happier with that design. The Arial SW12 uses a 4" port I believe and it is working for it... just use flares. Again, the PR design would overcome the compression issue totally. Using two PR18 from stryke, I get something like 115db from 20hz on up. That's a big difference down low where it counts in movies. The frequencies between 20 and 30 are crucial to that grab-you-by-the-kahones-make-you-say-holy-sh@t quality you want for movie listening. Also I am very pleased with my 15.2 for music and everything else. Listening to Fantasia 2000 the bass in the Firebird suite is amazing, as is the Pines of Rome passage. Very clean and very loud

What kind of music do you listen to?

Vince

 

[Conrad_S]

Even if you port with a 4" flared port, I think you'll be happier with that design.

What about making a single 33" sonotube with a curved 53" long 4" port, braced of course? (It would fit the requirement for port length at 20hz)

 

[Anthony_Gomez]

curved 53" long 4" port

I think that 53" sould be long enough to cause problems. I am sure that someone else will explain why better than I can, so I will leave it to someone else.

 

[Conrad_S]

Would putting several ports solve the problem then? (ie. CS+/Ultra) I'm not looking for the sonotube to be as efficient as the passive radiator, but 1/3 of the performance is quite a hit...

 

[Anthony_Gomez]

Multiple ports do not help..actually they can hurt by creating more surface area for air friction.

Port length is a fuction of box volume, tuning frequency and port cross section. ie. for a given tunnine/Fb, a 4" port would need to be x inches long. now, you can use 4x 2" ports and they would also each need to be x inches long

cross sectional areas:

4"=pi*(4/2)^2=4pi

4x1"=4*pi*(2/2)^2=4pi

Also, PR's and ports are for the most part the same (functionally). The advantage of the PR is that you can avoid 52" long ports, you end up with a smaller box (since you no longer have to subtract the port volume displacement), and you have no port noise. The down side is the cost.

 

[Jack Gilvey]

Also, PR's and ports are for the most part the same (functionally). The advantage of the PR is that you can avoid 52" long ports, you end up with a smaller box (since you no longer have to subtract the port volume displacement), and you have no port noise. The down side is the cost.

All true, but I think maybe the most important benefit is the alleviation of dynamic port compression, which I believe occurs well before noise becomes a problem.