New Project - The Pottery Barn Subwoofer

[AlanH]

Hi all,

A recent visit to a friend in Indiana left me feeling a little inadequate in the subwoofer department (I only have a Polk PSW303 with an 8" driver and a 100W plate amp). I tried, but there was no way I was going to talk my wife into a seven-foot-tall sonotube sub...

After looking around on this site I was inspired by Darren Thomas' sub, which has the outward appearance of a mild-mannered cabinet. Then I saw Thomas recommending the Tempest-X 15" subwoofer to many builders on the site, so I thought it would be a perfect match. I got my wife's blessing and now I'm ready to start.

My plan is to build a big sealed sub. Following the application notes on the DIYCable site, I figured I'd shoot for a volume of 200L (my current drawings are coming in at ~185L after the driver and bracing volume is subtracted). I can't go too much larger. I could go smaller, but given the faux-cabinet design there isn't too much point to that either.

Before I get too far along, I'd like to toss out a couple of questions with the hopes that you folks will give me a few pointers.

First, does the above plan sound reasonable? If you were tackling this project what would you do differently?

Second, in their application notes the DIYCable guys recommend the 500W amp from PE and say that the 1000W amp won't be needed. Should I heed this advice? Will the extra $100 on the 1000W amp just be wasted money or do I actually have to worry about destroying the driver? I was always under the impression that more power is better when it comes to subs.

On a related note, how does everyone feel about the 500W PE plate amp (HPSA500)? Should I be looking at the 500W Keiga amp at Madisound instead? Is there another that would be better?

Last question for now. The driver will fire down. Is there a rule for how much distance I should allow from the floor to the baffle? From Darren's pictures it looks like he left about four inches or so.

Okay, that's it for now. I continue to update and post pictures as I progress!

Thanks!

Alan

[WillyD]

I'd go with the Oaudio 500W amp.

https://www.oaudio.com

[Silversmoky]

I agree with Willy. I used the Oaudio 500W amp a while ago in a sub project and have been very impressed with it. It was paired with a 10" TC1000 in a 1 cubic foot sealed box and it really performs. More power and performance than I was imagining. Lots of adjustments possible too.

[peter_m]

A little less power then what you might want but it's on special: http://www.mcminone.com/product.asp?...me=MCMProducts

Once you add it to your basket, the price drops to 89$ Not bad for 300W

Peter

[ThomasW]

The Oaudio amp is the appropriate match for the quality of the Tempest-X.

4" of clearance is fine...

[---k---]

200L is really BIG. I just looked over the application notes. The differences between the 120L, 160L, and 200L are small (FS=27.5, 26.4, and 26hz). I wouldn't sweat it if you can't reach 200L.

Other than that, sealed is pretty easy. Just build a good, solid box.

[AlanH]

I'd go with the Oaudio 500W amp.

www.oaudio.com

Hi Willy,

Thanks for the recommendation. :T Looks like others agree with it as well!

-Alan

[AlanH]

A little less power then what you might want but it's on special: http://www.mcminone.com/product.asp?...me=MCMProducts

Once you add it to your basket, the price drops to 89$ Not bad for 300W

Peter

Hi Peter,

Wow! 89$ for 300W seems pretty cheap...Errr, sorry, I mean inexpensive! After looking at the Oaudio amp though, I like the idea of having built-in EQ to control room modes.

Anyone have a feeling for how useful or effective those controls are? My processor also has adjustable notch filters for controlling room modes. I guess the advantage there is that I can adjust the filter using the remote and the OSD!

[AlanH]

200L is really BIG. I just looked over the application notes. The differences between the 120L, 160L, and 200L are small (FS=27.5, 26.4, and 26hz). I wouldn't sweat it if you can't reach 200L.

Other than that, sealed is pretty easy. Just build a good, solid box.

Hi Ryan,

I guess if the guy with the 'small speaker suck!' signature says something is BIG, I need to worry. Looking at my sketches I was figuring on a pretty wide cabinet. I could make it significantly narrower I suppose.

How important is the golden ratio here? I could make the box 25"x25"x16" and get to about 140L (after substracting the driver volume and bracing). The cabinet will be a little bigger with the legs and top and trim and such, but is a symmetric cabinet okay?

Thanks,

Alan

[---k---]

I wasn't trying to talk you out of a big box. As Thomas always says, build as big of a box as you can. If you're getting ~140L net, I would build whatever looks best in your room.

Don't worry about the shape. The wavelengths are really long. But asymetical is probably better.

You might want to check your math. I'm getting 124L gross, so say 100L net. I think you're using exterior dim instead of interior. And, you're going to want to double the baffle thickness to 1.5".

[AlanH]

I wasn't trying to talk you out of a big box. As Thomas always says, build as big of a box as you can. If you're getting ~140L net, I would build whatever looks best in your room.

Don't worry about the shape. The wavelengths are really long. But asymetical is probably better.

You might want to check your math. I'm getting 124L gross, so say 100L net. I think you're using exterior dim instead of interior. And, you're going to want to double the baffle thickness to 1.5".

Yeah, my math is always suspect. State school, what can I say?

In this case, the dimensions I gave were actually the interior dimensions of the box. So the external box dimensions would be more like 26.5W x 27.25H x 18D. My 'big' version is simply wider at 34".

I figured I should use double thickness on the baffle. I expect the driver will move quite a bit, not to mention that the darned thing weighs something like 40 lbs by itself!

[AlanH]

Hi all,

So here are a couple of drawings to try and describe the box I'm envisioning. Dark brown is 3/4" MDF, tan is 2"x2" braces (so actually 1.5x1.5) and gray is the driver.

What do you guys think of the bracing? What I've tried to draw are 2x2 corner braces with a several cross braces. I figured I would just use half-lap where the braces cross. This seems easier to me than making shelf braces.

My only concern is that this beast will be heavy, so I want to make sure I get it right!

Thanks!

[ThomasW]

Looks fine, the driver needs 4" of clearance.

Half-laps aren't really necessary, you can just place the bracing at 90 degrees to each other then use screws/glue to create the 'joint/connection'.

There are very few 'style' points awarded for interior construction after the box is closed up....

[chasw98]

Alan:
Did you see a large sonosub at a major university in Indiana? perhaps??

As far as the Oaudio amplifier, I have tested it with my equipment and it is a very good plate amp. I have used these units 2 or 3 times and they work very well. The EQ that is included is very good for a plate amp.

BUT! It is a plate amp. You might want to look into some of the larger professional power amps that some people have used in the past. You can pick up Behringer A500's, EP1500's, and EP2500's relatively inexpensively these days. You can also add a BFD (DSP1124P) equalization unit for less than $100 and you will get a lot more control over your sub and its sound quality.

I can see that you got the wife's blessing like a lot of us do. That usually means that you will not being putting the sub where it performs best in the room but you will be putting it where it 'fits in' best. This is why you might want to think of the better eq unit. BTW, that is an excellent driver to use.

Chuck

[AlanH]

Looks fine, the driver needs 4" of clearance.

Half-laps aren't really necessary, you can just place the bracing at 90 degrees to each other then use screws/glue to create the 'joint/connection'.

There are very few 'style' points awarded for interior construction after the box is closed up....

Hi Thomas,

Thanks for the feedback and the pointer about driver clearance. I guess I should look to maximize my style points on the finishing job, huh?

[AlanH]

Alan:
Did you see a large sonosub at a major university in Indiana? perhaps??

Hmmm...major university? I thought it was an ag school!

As far as the Oaudio amplifier, I have tested it with my equipment and it is a very good plate amp. I have used these units 2 or 3 times and they work very well. The EQ that is included is very good for a plate amp.

BUT! It is a plate amp. You might want to look into some of the larger professional power amps that some people have used in the past. You can pick up Behringer A500's, EP1500's, and EP2500's relatively inexpensively these days. You can also add a BFD (DSP1124P) equalization unit for less than $100 and you will get a lot more control over your sub and its sound quality.

In our current house my space to house components is somewhat limited so I think using the plate amp is the best solution for now. But if (when?) my wife and I move, we want to have a theatre room where I won't be so limited.

I can see that you got the wife's blessing like a lot of us do. That usually means that you will not being putting the sub where it performs best in the room but you will be putting it where it 'fits in' best. This is why you might want to think of the better eq unit. BTW, that is an excellent driver to use.

Yeah, it will be located in a corner at the front of the room, so that's not too bad, though it'll excite a very bad room mode at about 40 Hz. (Of course right now that mode is the only thing that give the illusion of deep bass from my little Polk sub!) The mode filter on my AV processor does a pretty good job of taming that now and with the Oaudio plate amp I'd have two options.

A lot of people here (at HTG) seem to like the Tempest-X. I'm excited to get a box together so I can hear it. What's odd though is some folks on another DIY site were really tearing into a 15" driver that had VERY similar T/S parameters (I won't name the site but you guys can probably guess it). They started to rant a little too much for my taste and no one seemed to bring real facts to the discussion, so I stopped reading.

[Kevin Haskins]

T/S parameters really only point you to the type of box/application that a driver is suited for. Better or worse depends on the needed application. If your aiming for a driver that works well in a large box and goes deep, the Tempest-X fits the bill. If your looking for a small box driver or a high efficiency midrange, they don't. Its as simple as that. For people trying to descern some sound quality differences based upon T/S parameters, they are lost in the dark to begin with. Playing with the parameters is a balancing game you play to achieve a design goal, nothing more.

[---k---]

Hmmm...major university? I thought it was an ag school!

I TAKE OFFENSE TO THAT!

:P

You better watch it, there are a bunch of us around the forums.

[AlanH]

I TAKE OFFENSE TO THAT!

:P

You better watch it, there are a bunch of us around the forums.

Fair enough! Actually I'm an ag school (oops I mean major university) alum too, about 240 miles to the east.

[chasw98]

In our current house my space to house components is somewhat limited so I think using the plate amp is the best solution for now. But if (when?) my wife and I move, we want to have a theatre room where I won't be so limited.

Well, at least look into the possibility of not mounting the plate amp in the enclosure. That way if you do want to upgrade you won't have it mounted in the box. You will also only have one wire going to the box if you put the plate amp outside the enclosure.

Chuck

[JonW]

Cool looking project, Alan. :T

I can't really help out too much. My sub is just a copy of another design. But the resident gurus here are saying it looks good. Listen to Chuck (chasw98 ) on the amps- he knows his amps very well.

Alan:
Did you see a large sonosub at a major university in Indiana? perhaps??

It's quite possible. :B

Hmmm...major university? I thought it was an ag school!

And we train the occasional engineer, too, once in a while.

A recent visit to a friend in Indiana left me feeling a little inadequate...

If only I were more mature, I might be able to let such a comment go... must... keep... sarcasm... in... check... :P

[AlanH]

T/S parameters really only point you to the type of box/application that a driver is suited for. Better or worse depends on the needed application. If your aiming for a driver that works well in a large box and goes deep, the Tempest-X fits the bill. If your looking for a small box driver or a high efficiency midrange, they don't. Its as simple as that. For people trying to descern some sound quality differences based upon T/S parameters, they are lost in the dark to begin with. Playing with the parameters is a balancing game you play to achieve a design goal, nothing more.

Hi Kevin,

Thanks for your input. That's exactly what I thought I knew about T/S parameters from reading the good work here. In the end I think the guys just wanted a sub using a big driver stuffed into a small vented box. In that case a driver like the Tempest-X is not it, but I hope it will work well in a big box!

[AlanH]

Cool looking project, Alan. :T

I can't really help out too much. My sub is just a copy of another design. But the resident gurus here are saying it looks good. Listen to Chuck (chasw98 ) on the amps- he knows his amps very well.

Thanks for checking in! It's nice to see you're keepin' it real while on the left coast.

If only I were more mature, I might be able to let such a comment go... must... keep... sarcasm... in... check... :P

If only...

[AlanH]

BUT! It is a plate amp. You might want to look into some of the larger professional power amps that some people have used in the past. You can pick up Behringer A500's, EP1500's, and EP2500's relatively inexpensively these days. You can also add a BFD (DSP1124P) equalization unit for less than $100 and you will get a lot more control over your sub and its sound quality.

I was just looking at the Behringer amps. They look nice! I still don't think I'll use one for this project, but...Why wouldn't I buy 3 of the A500 amps instead of an expensive multi-channel amp (like I did this summer :cry: )