Sub's all done

[CharlieM]

Hello All,

This project began when a friend commented that my DIY hybrid electrostats were a bit lacking on the bottom end-- I couldn't just let that slide, right? (subwoofer now required)
I opted for a Dayton reference HF 12" driver and Dayton 240W plate amp in a sealed box. A WinSd calculator gave 2.8 ft3 as optimum volume so that was my starting point. The plastic box around the plate amp looked a bit flimsy so I configured the box with a separate recessed enclosure for the plate amp. The box walls are a whopping 1.5 inches thick; consisting of a layer of 3/4" mdf glued to a layer of 1/2" mdf with a layer of 1/4" red oak plywood on the outside. Before bonding on the plywood, I bored holes thru the box and glued in (4) 1" hardwood dowel rods to further stiffen the box: (1) top/bottom, (1) front/back and (2) side/side. Finally, the edges of the box were notched on the table saw to accept the quarter-round oak molding edge closeouts. Hidden magnetic grill guides are located just under the plywood surface on the front baffle. All inside surfaces lined with gray urethane open-cell acoustic foam and the box is stuffed with 36 ounces of poly-fill. Box dimensions are 13"x15"x25.5" inside and 16"x18"x28.5"; which give a starting volume of 2.9 ft3. Deducting displacements for the amp box, bracing and woofer motor, the final volume is about 2.6 ft3. All this with 1.5" wall thickness make for a pretty big box but I'm not married so it doesn't matter.

How does it sound? It feels tight and clean at reasonable volumes and I need only crack the throttle a hair to fill in the lower octave below my hybrid electrostats. Cranking it up to half throttle will bust up drywall and make you puke :-)

Thanks to all of you here for inspriration!

Charlie
pic links below:

http://img9.imageshack.us/my.php?image=s5000691lg7.jpg
http://img12.imageshack.us/img12/7360/s5000688ji8.jpg
http://img14.imageshack.us/my.php?image=s5000699as4.jpg
http://img357.imageshack.us/my.php?i...yesl022ef1.jpg

[jamikl]

Hi charlieM, both the subs and the ESLs look wonderful. How low do those subs go?
jamikl

[CharlieM]

Thanks for the compliment! The sub was pretty much straightforward and easy and fast to build but I spent 5 months designing and building the hybrid transmission line/beam-splitter ESL's. I had actually underestimated the efficiency and output capability of the ESL panels and the 10" bass drivers just don't move enough air to keep up at high volume levels. I think the TL-loaded 10" Aurum Cantus Mk II woofers in the hybrids actually output as low as my new Dayton sub but they can't match its authority and excursion capability. I really didn't need much to augment the hybrids anyway-- merely cracking the throttle on the sub fills in the lowest octave nicely.

[back to your question:]
I don't have any means to actually measure the frequency response of the sub but the WinSd program calculated the 3db down point (f3) at 37 hz and f5 at 30 hz. The Dayton SA240-B plate amp is equalized to add 6db of boost at 30hz so I'm thinking the actual f3 is certainly under 30 hz... maybe as low as 25 hz(?)

In retrospect, I'm thinking I could have used less box volume without significantly compromising the f3; thereby improving the esthetics of the box and probably allowing the woofer to accept more power and output more upper bass before reaching X-max (as it is, the driver approaches x-max at about 1/2 throttle on the Dayton boost amp). A really knowledgeable guy here on this forum advised me that, with my large box volume and for just playing music, I didn't really need or want the "boost" version of the Dayton plate amp... I'm thinking he was right about that but I had already ordered the thing and so decided to live with it. Anyway, the sub still sounds great at any reasonable/tolerable spl-- just need to NOT GET CRAZY on the throttle (just because I can).

[MaVo]

I like a little boost in the lowest octave, especially at smaller listening levels it makes the sound bigger. I apply up to 9db boost at 20hz depending on my mood.