Subwoofer Issues

[jb]

Guys, I need your help!

I built my first sub for my HT using 3 Dayton SD315-88 12" DVC Shielded subwoofers (295-490) powered by a Dayton SA240B 240w amp with boost (300-805) in a 2.9 cubic foot sealed cabinet.

The subwoofers are wired with the individual DVC's in series and the three speakers in parallel for a theoretical resistance of 5.33 ohms (measured to be 4 ohms in box).

The HT room is approximately 20 by 16 with an average ceiling height of 9 feet.

Issue 1: humming sound with amp on and connected to the AV receiver - no hum with amp on and disconnected. Have plugged sub amp into same outlet as the receiver to insure a common ground source, but it still hums.... I read the earlier posts on this - not sure they will solve this one?

Issue 2: excitedly put Jurassic Park into the DVD player, turned on the sub and listened to several passages that should have blown the windows out - very subdued bass response... T-Rex footsteps were seen more than heard/felt...

I'd really appreciate any input as I'm frustrated after all the work and to have these performance issues.

Thanks in advance for any suggestions! I really enjoy this new found hobby - your technical guidance is most appreciated!

[bill]

> Guys, I need your help!

Comments inline

> I built my first sub for my HT using 3
> Dayton SD315-88 12" DVC Shielded
> subwoofers (295-490) powered by a Dayton
> SA240B 240w amp with boost (300-805) in a
> 2.9 cubic foot sealed cabinet.

How did you figure the size of the cabinet? WinISD says that optimal size for three of those drivers is a bit over 5 cubic feet.

> The subwoofers are wired with the individual
> DVC's in series and the three speakers in
> parallel for a theoretical resistance of
> 5.33 ohms (measured to be 4 ohms in box).

That's fine.

> The HT room is approximately 20 by 16 with
> an average ceiling height of 9 feet.

> Issue 1: humming sound with amp on and
> connected to the AV receiver - no hum with
> amp on and disconnected. Have plugged sub
> amp into same outlet as the receiver to
> insure a common ground source, but it still
> hums.... I read the earlier posts on this -
> not sure they will solve this one?

You've probably got a ground loop from the cable feed or some other external connection. Go to Radio Shack and get a 270-054 ground loop isolator. Connect it in series with the input to the sub. Presto, no more hum.

> Issue 2: excitedly put Jurassic Park into
> the DVD player, turned on the sub and
> listened to several passages that should
> have blown the windows out - very subdued
> bass response... T-Rex footsteps were seen
> more than heard/felt...

Well, that's to be expected. The F3 of those subs in your box is 50 Hz, not exactly "feel it" territory. They'd work a lot better in a bigger box, preferably vented. The other issue is that you may not have the sub amp gain high enough, but I'm thinking low end extension is your biggest problem.

> I'd really appreciate any input as I'm
> frustrated after all the work and to have
> these performance issues.

> Thanks in advance for any suggestions! I
> really enjoy this new found hobby - your
> technical guidance is most appreciated!

HTH,
Bill

[natediggidy]

> Guys, I need your help!

> I built my first sub for my HT using 3
> Dayton SD315-88 12" DVC Shielded
> subwoofers (295-490) powered by a Dayton
> SA240B 240w amp with boost (300-805) in a
> 2.9 cubic foot sealed cabinet.

> The subwoofers are wired with the individual
> DVC's in series and the three speakers in
> parallel for a theoretical resistance of
> 5.33 ohms (measured to be 4 ohms in box).

> The HT room is approximately 20 by 16 with
> an average ceiling height of 9 feet.

> Issue 1: humming sound with amp on and
> connected to the AV receiver - no hum with
> amp on and disconnected. Have plugged sub
> amp into same outlet as the receiver to
> insure a common ground source, but it still
> hums.... I read the earlier posts on this -
> not sure they will solve this one?

> Issue 2: excitedly put Jurassic Park into
> the DVD player, turned on the sub and
> listened to several passages that should
> have blown the windows out - very subdued
> bass response... T-Rex footsteps were seen
> more than heard/felt...

> I'd really appreciate any input as I'm
> frustrated after all the work and to have
> these performance issues.

> Thanks in advance for any suggestions! I
> really enjoy this new found hobby - your
> technical guidance is most appreciated!

Well, right now you have just about everything working against you. Just curious. Where did you come up with a volume of 2.9 cu-ft sealed? That gives you a net volume of .88-.90-ish cu-ft per driver. with those subs, that would give you a F3 of around 65Hz and a system Qt of around .91. Hardly suited for HT use.
These drivers are better suited for bass-reflex or PR alignments anyway.
The amp's bass boost is centered at 30Hz and with the drivers response so far down at that point, all that boost is doing is eating up amp power.
Then you've split the amps output among three drivers which isn't helping either.

Sorry to say it but, it's time to go back to the drawing board, or rather the modeling program on this one.

[Chris Roemer]

> Guys, I need your help!

> I built my first sub for my HT using 3
> Dayton SD315-88 12" DVC Shielded
> subwoofers (295-490) powered by a Dayton
> SA240B 240w amp with boost (300-805) in a
> 2.9 cubic foot sealed cabinet.

> The subwoofers are wired with the individual
> DVC's in series and the three speakers in
> parallel for a theoretical resistance of
> 5.33 ohms (measured to be 4 ohms in box).

> The HT room is approximately 20 by 16 with
> an average ceiling height of 9 feet.

> Issue 1: humming sound with amp on and
> connected to the AV receiver - no hum with
> amp on and disconnected. Have plugged sub
> amp into same outlet as the receiver to
> insure a common ground source, but it still
> hums.... I read the earlier posts on this -
> not sure they will solve this one?

> Issue 2: excitedly put Jurassic Park into
> the DVD player, turned on the sub and
> listened to several passages that should
> have blown the windows out - very subdued
> bass response... T-Rex footsteps were seen
> more than heard/felt...

> I'd really appreciate any input as I'm
> frustrated after all the work and to have
> these performance issues.

> Thanks in advance for any suggestions! I
> really enjoy this new found hobby - your
> technical guidance is most appreciated!

I've got that amp (but w/o the boost).
Mine hummed when I got it too, until I got a $.29 cheater plug adapter (3 prong to 2 prong) which people seem to frown upon.

I'll split the difference. Your too small box is giving you a 0.6dB boost at 105Hz. 3dB down from there puts your F3 in the mid 50's. Now, my BR-1 clones can hit 40Hz, so I feel your pain.

If you plugged 2 of the 3 driver holes, and put a 4" id PVC port tube 11" long in one of these "plug plates", your sub would now be capable of low 30's. That's now exactly one octave of extension, but it's maybe 5/6?

Just for a quick fix, try the cheater plug on your amp (you've probably got one around the house SOMEWHERE - usually on the end of an extension cord), and disconnect 2 of the 3 drivers from the amp (leaving those drivers "open"). They should act like expensive PR's giving you the equivalent of a vented box, but with who knows what kind of tuning frequency?

Once again, <A HREF="http://www.linearteam.org">www.linearteam.org</A> .

[unknownuser]

I am doing the same thing with 3 8" Dayton DVCs but it is ported and tuned way down low @ 22 Hz in a 2.6 cubic ft box. Just experimenting with Curt C's theory???? Anynways if it does'not work I can just plug the holes!


(Originally posted by: Jo)

[Chris Roemer]

> I am doing the same thing with 3 8"
> Dayton DVCs but it is ported and tuned way
> down low @ 22 Hz in a 2.6 cubic ft box. Just
> experimenting with Curt C's theory????
> Anynways if it does'not work I can just plug
> the holes!

Your box, also, is too small. F3 in the high 30's (not knowing what your "boost" situation is). Now, plug ONE driver hole, and shorten your port tuning to 27 Hz, and you'll do upper 20's.

[jb]

Thanks Guys - I did model the cabinet in BassBox Pro - realized it was tight but the amp has a nice boost in the 30 hz range and with floor/room coupling I was hoping for a little more oomph...

I will try venting the cabinet and the other suggestions presented.

Best regards!

[keithfeasley]

> Guys, I need your help!

> I built my first sub for my HT using 3
> Dayton SD315-88 12" DVC Shielded
> subwoofers (295-490) powered by a Dayton
> SA240B 240w amp with boost (300-805) in a
> 2.9 cubic foot sealed cabinet.

> The subwoofers are wired with the individual
> DVC's in series and the three speakers in
> parallel for a theoretical resistance of
> 5.33 ohms (measured to be 4 ohms in box).

> The HT room is approximately 20 by 16 with
> an average ceiling height of 9 feet.

> Issue 1: humming sound with amp on and
> connected to the AV receiver - no hum with
> amp on and disconnected. Have plugged sub
> amp into same outlet as the receiver to
> insure a common ground source, but it still
> hums.... I read the earlier posts on this -
> not sure they will solve this one?

> Issue 2: excitedly put Jurassic Park into
> the DVD player, turned on the sub and
> listened to several passages that should
> have blown the windows out - very subdued
> bass response... T-Rex footsteps were seen
> more than heard/felt...

> I'd really appreciate any input as I'm
> frustrated after all the work and to have
> these performance issues.

> Thanks in advance for any suggestions! I
> really enjoy this new found hobby - your
> technical guidance is most appreciated!
sell your subs, seal the 12" holes, cut one 15" hole, drop in a quatro, and DUCK!!!

[damkor]

> Issue 1: humming sound with amp on and
> connected to the AV receiver

> Issue 2: very subdued
> bass response... T-Rex footsteps were seen
> more than heard/felt...

Granted that the comments by others are true concerning the box size, but I doubt that is the whole problem.

I would check the RCA cable, make sure each end is plugged all the way in, check the connections on the sub plate amp and the receiver, try the cheat plug, try the settings on the receiver and the plate amp, make sure the output is the mono subwoofer output and set everything to 100Hz, for use with small satellites. Even with sealed F3 around 60Hz, you should get plenty of boom from the sub if the xover is 100Hz.

Finally: not hearing footsteps? Forget hearing for a moment. Does the cone vibrate strongly against your fingers when there are loud effects? It should.

[Dirk]

> Thanks Guys - I did model the cabinet in
> BassBox Pro - realized it was tight but the
> amp has a nice boost in the 30 hz range and
> with floor/room coupling I was hoping for a
> little more oomph...

> I will try venting the cabinet and the other
> suggestions presented.

> Best regards!

The problem is that your room (17x20...and we'll assume an 8' height), you won't see much room coupling. Your longest axial wavelength of 20' amounts to about 28hz. That means that reinforcement will gain about 12dB/oct *below* 28hz. Above that, you're on your own. Or more, the subs are on their own. The +6dB of boost @ 30 hz won't help save the sinking ship.

However, if you were to defeat the bass-boost of the plate amp, seal 2 of the 3 driver holes, and place a 3" x 6.25" port (or 4" x 12" if you can fit it), you'll have an F3 if 30hz and you'd be doing it at a respectable 105dB, excursion limited. You could also create two cabs, wire each DVC up for 16-ohm operation and then just jumper the two cabs together so they run in parallel. That'd give you about 170W out of the plate amp, and honestly, that's about all that two 12" shielded DVCs can take. THAT should be good for over 110dB, which is more than enough for most circumstances.

I've had really good success with this driver. I built a sub for a buddy of mine and paired it up with the 100W plate amp in a 3ft^3 ported cab. Best "Sub-$150 sub" I'd ever heard.

[Dirk]

> Granted that the comments by others are true
> concerning the box size, but I doubt that is
> the whole problem.

> I would check the RCA cable, make sure each
> end is plugged all the way in, check the
> connections on the sub plate amp and the
> receiver, try the cheat plug, try the
> settings on the receiver and the plate amp,
> make sure the output is the mono subwoofer
> output and set everything to 100Hz, for use
> with small satellites. Even with sealed F3
> around 60Hz, you should get plenty of boom
> from the sub if the xover is 100Hz.

> Finally: not hearing footsteps? Forget
> hearing for a moment. Does the cone vibrate
> strongly against your fingers when there are
> loud effects? It should.

Excellent point. Even in a box with a Q of .85 or so, the cones should be flapping in the breeze with the jurassic footsteps. These ARE very efficient drivers.

I'd also track down some hiphop or house/trace with a good constant beat. It may help to play that while you're troubleshooting.

[damkor]

[Dirk]

[jb]

Guys, lots of great ideas. I installed all 3 units identically in the box with the terminals in symmetrical alignment - easy to keep straight - so I'm certain about the coils being in phase - they move in synch as well.

They do move when a signal is passed through them - just not loud and the constant hum. There is a definite thump but very weak.

I'll try the arrangement with just one speaker hot and the other two acting as passives to see what difference that makes - it will also give me an idea as to how it might work vented.

The plug adapter and filter ideas also will be tested.

My experience in this has been a great learning opportunity and everyone's ideas have been most helpful - Thanks All!

[tomzarbo]

Moving in and out at exactly the same time?
The reason I ask is I have a multi-driver sub in my attic, and it houses (4) 12" Titanic MK2's. When I play sine sweeps the woofers do not all move the same. Some vibrate wildly, while others move much less, indicating that some of them may be acting as passive radiators, even though they are active. If you haven't already started tearing things apart, just for fun, try running a low 20-40 hz sine sweep, and look at them to see if they are all in sync.

If I ever do a multiple driver subwoofer again, I will divide the cabinet into separate chambers so this doesn't happen.

Good luck,
TomZ

[wingnut]

My money is on this answer. I think there are multiple issues causing weak output as others have pointed out, but even with a box about half the optimum size and an F3 of 50, the T-Rex footsteps should be heard and felt. Lots of bass energy above at and above about 45 hz including harmonics that should be coming through.

JB: As Dirk and Damkor indicated, your drivers are probably wired incorrectly. Double check your wiring. Good luck.

Cheers.

[jb]

> Thanks Tom! Yes, they truly appear to be in close synchronization - no evidence of passive behavior.

Wiring checks out too - I screwed the cabinet together (no glue) for purposes of prototyping this beast. I can open it up, change the baffle, stuffing, padding, wiring,etc...

Looks like that flexibility will be needed to get this sub to perform as I had hoped.

[jb]

> If someone can tell me how to post pictures I have several that show the unit in various stages of assembly.

[marlboro]

WHILE you have connected them accurately, are you sure that they were labeled accurately. You might check them for polarity.

Marlboro

[jb]

> WHILE you have connected them accurately,
> are you sure that they were labeled
> accurately. You might check them for
> polarity.

> Marlboro

Good idea - hope to have some time this weekend to test all the suggestions.

[johnastockman]

You can get a photobucket account for free...I think they have the URL next to the pic once it's uploaded. Just paste it into the image URL box...make sure there isn't two "http://" in there. There are other hosting sites, but photobucket is pretty popular for the guys here.

John A.

[jb]

> You can get a photobucket account for
> free...I think they have the URL next to the
> pic once it's uploaded. Just paste it into
> the image URL box...make sure there isn't
> two "http://" in there. There are
> other hosting sites, but photobucket is
> pretty popular for the guys here.

> John A.

Thanks John, I'll set up an account this weekend. One of the best things about this tech page is seeing everyone's good work - even that of us amateurs! ;-)

[johnastockman]

Provided Link: http://custom.smugmug.com/gallery/115064/1#4114714


> Thanks John, I'll set up an account this
> weekend. One of the best things about this
> tech page is seeing everyone's good work -
> even that of us amateurs! ;-)

Us amateurs do pretty good, huh? Looking forward to seeing some of your pics! Here's a link to my host site with some photos of just a small portion of speakers I've put together over the past few years. Some were duds (I didn't know enough about getting the XO "right"), but since I've been hanging around here, my skills have improved tremendously.

John A.

[jb]

> Us amateurs do pretty good, huh? Looking
> forward to seeing some of your pics! Here's
> a link to my host site with some photos of
> just a small portion of speakers I've put
> together over the past few years. Some were
> duds (I didn't know enough about getting the
> XO "right"), but since I've been
> hanging around here, my skills have improved
> tremendously.

Thanks John! Your web site is an excellent testimonial to an outstanding DIY'er! Awesome work! The crossovers are models of efficiency - wish I could get mine to look half that good!

Hats off to you!

> John A.

[johnastockman]

> Thanks John! Your web site is an excellent
> testimonial to an outstanding DIY'er!
> Awesome work! The crossovers are models of
> efficiency - wish I could get mine to look
> half that good!

> Hats off to you!

I really appreciate the compliment...if I would've had a digital camera back when I first started, you could see how my earlier XO's looked! They were huge! I didn't have a grasp on how to get from a schematic to something on a board, so I laid out the components physically just like the diagram. This cap horizontal...this coil vertical...and so on. I finally got to the point where I learned how to conserve space and bend the pieces around on the board so they would actually fit in the cabinet. Curt has a terrific write-up on this at:

<A HREF="http://www.geocities.com/cc00541/nodal_analysis.html">http://www.geocities.com/cc00541/nodal_analysis.html</A>

I wish I had that when I did some of my first XO's. Hope to see some of your stuff in the near future!

John A.