My first stab at a subwoofer

[Moset]

Hi!

I've built a pair of Cheap Trick 237 bookshelf speakers a while back and am now considering building a subwoofer to go with them. The CT237 go down fine to around 50-60 (the Internet mentions 48 Hz at -8db, for some reason), so I'm looking at something to cover just the last bit from about 50Hz down. I'm not looking for a huge SPL, rather lower Hz.

I've been looking at a couple of different Seas Prestige woofers, L22RN4X/P H1208 and CD22RN4X H1192, they are priced about the same, both 8" and have Fs of 21 Hz and 20 Hz respectively. They go for about €100, which is around what I'm willing to spend on the driver.

I've put together a couple of plots in WinISD below. I can get Fs-3 to around 27 Hz, about 25 Hz with filtering (the max is about 1,5dB lower if you disregard everything above about 50 Hz).

I'm looking at a box at 46 L tuned to 26 Hz. Is this sane? The response levels out in those graphs. Good or bad? Any comments are appreciated!

[revboden]

Questions: Is this just for music, what kind of music? How big is the room? What amp are you planning to use with it and does it have a "rumble filter/ HP filter"? Do you have a spl meter, what is your average listening level?

[Arty]

Te predicted responce curve is just one of the factors.
Consider powerhandling and cone excursion too,along with group delay.

A lot depends on where You place the subwoofer, and room gain helps too.
A flat sub curve -if it is flat till roomgain kicks in- can sound very boomy.
So some rolloff is not a problem at all.

Extended low frequency subwoofer
this article can be verry helpful if You read it
contains links for verry nice projects.

[Moset]

It's primarily for music. I have a pair of MLTLs as my main system, this is going to be hooked up to the computer. It might get some games played through it, but I'm not that interested in huge explosions, but perhaps drum & bass, dubstep or whatever plays really low bass nowadays.

I don't have an amp for the sub yet. I'm considering getting a decent plate amp. I've built a couple of chipamps, so I could probably put together an active subsonic line-level filter if the amp doesn't have one.

The room is about 15 sq meters.

[Moset]

Originally Posted by revboden

Do you have a spl meter, what is your average listening level?

I don't have an SPL meter but I'm powering my speakers from an LM1875 chipamp, which puts out about 20 W. The Internet (Loudspeaker Kit CT 237 by Klang+Ton specifically) mentions a sensitivity of 81dB @ 1W/m, so about 90-ish if I max out, though I'm sitting closer than 1m.

[revboden]

Are you using WinISD pro? if so switch to "cone excursion" then fiddle with signal levels.

[revboden]

Once you have a signal level for that design, switch to "SPL" graph to see if the output will be adequate.

Note: I've looked around for T/S parameters for that driver (CD22RN4X H1192). The Xmax is 7mm.

[Moset]

Cone excursion and SPL below. I've added a third order lowpass filter at 65 Hz to model how it will likely be used. The plots are for 40W input power and I'll get an SPL in the high 90s, around 98, depending on frequency.

[Moset]

Also adding a third order highpass at 22 Hz gives the plots below. It keeps us within the 7mm linear excursion at all times (at 40W).

[Moset]

I should add that the plots below are for L22RN4X/P H1208. They modeled very similarly, although L22RN4X/P showed a slightly louder transfer function.