AV15 Subs (design & construction)

[ShinOBIWAN]

Just finished designing a pair of subwoofer to be used with my mains.

Each design features a single Acoustic Elegance(formerly Stryke) AV15 mkII driver in downward firing configuration and Linkwitz Transform alignment. Each driver features 4.6cm of peak-to-peak excursion with a radiating area of 830sq cm so there's plenty of displacement for the really low frequencies. More info can be found here: http://www.stryke.com/AVseries.html

And a couple of pictures of the driver:





The subs will feature a 500w into 4ohm plate amp. The driver is a dual 2ohm voice coil design and these will be wired in series to provide a 4ohm load. The power rating of each driver is 500w continuous so the BK amp is the ideal partner. More info here: http://www.bkelec.com/MODULES/bsbpv500.htm

Here's the scale drawing used to form the cutting list for the MDF and also check for proportions and fitment. The drawing doesn't have the dimesions shown as it made it look even more confusing. The different colours used in diagram aren't there to bring anything in the way of art but actually just help me to identify the individual panels since the colour coding is carried across through each perspective. Also the cross hatched section is the sub-enclosure for the amp. All cabinet wall are just over 1" thick (9mm + 18mm MDF), except the driver baffle which is 1.5" thick (2x 18mm MDF).



And finally here's a few plots from the predicted performance model. These are anechoic and are for a single sub. Performance will increase with a pair and in-room. The -3dB is at 15hz and inroom I expect that this will be flat to 15hz. Predicted maximum SPL at 20hz is something like 108dB if I remember correctly, a pair in room should have no problems reaching 115dB.



Not done anything other than all the preliminary work. The nice thing about building subs compared to speakers is that they only tend to take a few of weeks to build as opposed to nearly a year :lol: More to come later but rest assured that these pair of 15" will almost certainly satisfy the need for deep deep bass at 100dB+ and with low distortion (<10% THD).

I'll pop back with more info as I start and eventually post measurements of a finished sub for distortion, frequency, group delay etc etc. If anyone see's any real problems please let me know. Its only a rough starting point and I'd love to hear suggestions to improve things but I am restricted in terms of overall cabinet volume since I'm building two of these.

[pinkmouse]

What are the overall dimensions, Ant?

[ShinOBIWAN]

Sorry, thought I'd mentioned it.

Its 55h x 45d x 70w cm. These are external dimensions. Net volume is approx 95ltrs (3.5cuft) after deducting amp compartment and bracing volumes.

Talking of bracing is there enough? The pictures hard to make out at first glance but do make sense in the end, I hope

[pinkmouse]

Pics are fine! I would put another horizontal brace between the red panel and the outside wall, and possibly one from midway along that to the top panel. But I just like playing with my table saw.

[ShinOBIWAN]

I'll drop those in as suggested.

Hope I'm going to be able to lift this

[ssabripo]

have you double checked your box design? it took several passes for me to get it just right...here is the final results:



and here are the drawings:
wire frame:


rendered outside:


rendered internals (braces, no driver no amp added):


I played with downfiring designs as well, but it just took too much net volume to get the desired FR without walking on port noise boundaries...

[ShinOBIWAN]

Hi ssabripo

I notice that you've gone ported - good choice if you've got the space. 7cuft is roughly twice as large as my design and since I'm planning on using two then it will have to say that way.

The alignment I'm using is completely different to a ported design. Its sealed 95ltrs with a Linkwitz Transform circuit to artificially lower the box Q and driver Fs, just think of this as precision EQ which is tailored to the driver and box volume. The tradeoff here is power handling, maximum SPL and excursion, these are worse compared to a similar ported or much larger sealed design. The upshot is much smaller size for the depths the sub is cabable of reaching and better groupdelay and phase in the audible range.

As I already pointed out, you tend to use MUCH more excursion with an LT, take a look at the excursion graph and you'll see that at 20hz its 2mm one-way already and this is at the drivers rated sensitivity or ~91dB. For every 3dB increase in sound pressure your looking at twice the excursion and twice the required power from the amp. Its easy to see that this is a rather inefficient design but when pair with big excursion and robust drivers like the AV15 then these drivers tend to take it in their stride. As further headroom I'm building two identical subs so I'll effectively be increasing the output by 6dB over a single one should the subs be located close together (they will), then factor in room gain and it starts to look much better.
I've conservatively predicted that I should have a max SPL of ~115dB at 20hz in room and with both subs running. Way more than I need but I want low distortion so making the subs work less by doubling the number of them is always a good thing for this.

[ShinOBIWAN]

Almost forgot about this thread.

The panel amps arrived a couple of days ago, so I now have all the bits needed, I've just got to cut and build the enclosures.





Planning on getting these up and running within a fairly short period of time. Will post more as I progress.

[pinkmouse]

Have those plate amps got LT built in, or are you going to add a piggyback circuit?

[ShinOBIWAN]

Unfortunately there's no LT on them Al. It might be a good thing because to really get the maximum accuracy and therefor benefits from the whole LT idea, you must have fairly precise cap and resistor value's in the LT circuit and these values are determined by box resonance and driver TS parameters. As you can imagine, this all changes rather abruptly should you swap drivers around and box volumes, making the circuit near useless.

All the panel amps I've seen with built in LT circuits have been rather generic and non tailored for any specific driver or box. I really don't think that's the best way to go about designing an LT alignment.
Its impossible to implement a fully variable analogue interpretion of an LT circuit, so you have to make do with the generic stuff if you have the functionality build into a panel amp.

So the short answer is yes, I'm going to be using a piggyback type system.