CSS SDX12 Build Thread

[GO-NAD!]

I'll take a crack at this one in a day or so. Been too tied up as of late. In the last two-three months I have had a promotion, relocation, house hunting, a new baby and volleyball tournaments for my (oldest) daughter to boot.

It looks to me like you don't have your priorities straight - you should've been on this as soon as I made the first post.

Honestly, I appreciate whatever time you can take for this. I was thinking of a low-ish tuning, but as Isiberian pointed out, I'll lose some headroom as a result and the enclosure volume creeps up. I don't know if I'm asking too much from a 12" driver?

 

[GO-NAD!]

Messing around in WinISD seems to point to 85 litres and 22 Hz tune which gives an F3 of 21.1 Hz. That seems to give the best balance of size, extension and output. Does that make sense? Further questions:

1)I'm not sure about the vent dimensions. They can be manipulated in WinISD, so how can I tell what is correct?
2)How does volume, tuning and the vent affect power limits?
3)How do you determine the appropriate HPF?

 

[annunaki]

So in doing some modeling, assuming the T/S parameters are correct, it appears as though this driver was designed for sealed/PR use. The reason I say that is because the size enclosures required from a vented standpoint. The issue I see in going vented is the vent length, at nearly 80" to keep vent velocity below compression with 500 watts RMS in a 95L enclosure. The response looks great with an F3 around 17.5 hz and an upper -3db point of 87.4hz with a 4th order low pass at 80hz.

Going the PR route can put you at a smaller net enclosure volume (no need for vent displacement) and yield nearly the exact same performance as a vented application. Below is the SDX 12 modeled in 3.50ft^3 with APR15s (purple trace). Xmax is well in line and the lower and upper -3db points are nearly identical to vented without the hassle. The other big advantage here is that you would avoid vent resonance issues which would likely be entirely present with the vented application unless using a VERY steep filter on the low pass.

In either application it would be advised to add a 2nd order infrasonic filter at 14hz, which will have minimal impact on response and f3, perhaps pushing it up by about 1hz or so but would greatly help to protect the woofer.

If these are my drivers, I bite the bullet and go the PR route...

 

[GO-NAD!]

So in doing some modeling, assuming the T/S parameters are correct, it appears as though this driver was designed for sealed/PR use. The reason I say that is because the size enclosures required from a vented standpoint. The issue I see in going vented is the vent length, at nearly 80" to keep vent velocity below compression with 500 watts RMS in a 95L enclosure. The response looks great with an F3 around 17.5 hz and an upper -3db point of 87.4hz with a 4th order low pass at 80hz.

Going the PR route can put you at a smaller net enclosure volume (no need for vent displacement) and yield nearly the exact same performance as a vented application. Below is the SDX 12 modeled in 3.50ft^3 with APR15s (purple trace). Xmax is well in line and the lower and upper -3db points are nearly identical to vented without the hassle. The other big advantage here is that you would avoid vent resonance issues which would likely be entirely present with the vented application unless using a VERY steep filter on the low pass.

In either application it would be advised to add a 2nd order infrasonic filter at 14hz, which will have minimal impact on response and f3, perhaps pushing it up by about 1hz or so but would greatly help to protect the woofer.

If these are my drivers, I bite the bullet and go the PR route...

Can I assume that you are talking about a pair of APR15s per sub? That'll cost me $400! I really wasn't counting on that and it's an awfully big bullet to bite. I'm willing to go with a higher tune, if I can avoid chucking out that much more cash. How would the 3ft^3, 22Hz tune, as I mentioned above, look in a vented enclosure?

 

[annunaki]

I know not what you were expecting...

Another option you could look at is what I had sent in your PM:
4.0ft^3 net volume with a slot vent of 2.75" x 12.5" x 58.25" and REQUIRES a 13hz high pass filter 2nd order. Your first vent resonance is at 116hz here so a good 4th order high pass/cascaded filter should work. Remember this was simmed with 500 watts of RMS input power.

If power goes up, vent size has to increase to stay below 17m/s. and that is where everything gets tricky because the length increases with the surface area, as does the displacement and then the vent resonance keeps creeping down to a more audible range.

 

[GO-NAD!]

Well, in the end, I took Annunaki's advice and I've gone the PR route. They worked out the final specs for the SDX12 and based on those, Jeff Bagby came up with the PR model. He has a reputation for knowing his stuff, so I went with that. The model is quite different from Annunaki's, because he based his on the preliminary specs, which were all he had to work with at the time. If the performance of these subwoofers is even close to Jeff's model, I am going to be very happy. If not, well, I'll take 'em apart and start over. Here's the model: http://creativesound.ca/pdf/Q12XC.pdf.



I followed the plans from CSS for the PR model and have a couple of 18" cubes. Although you will see two enclosures in the photos, I actually built three. After I had finished assembling two enclosures, I had them sitting side-by-side and noticed that they didn't look quite identical. After staring for a couple of minutes, I figured it out - the bracing in one of them was out of position by 90°. I knew it would be futile to try to disassemble it, but I didn't have anything to lose by trying. Of course, I destroyed it as the joints were very strong. Oh well, I'm glad that MDF is cheap...

One slight variation that I have included, is to rotate the enclosures forward 90°, so that the drivers are now downfiring and the SPA500's are on top. Since these subs will be placed behind the PJ screen false wall and with just 22" of space between it and the front wall, it's the only way I'd have access to the amps. Bob, at CSS assured me that these drivers are suitable for a downfiring configuration, so that's my solution. I just finished the flat black paint yesterday, so I think I'll give them a couple of days extra drying time before installing the drivers, PR's & amps.

 

[GO-NAD!]

Here's one more photo of a finished product. I hope to fire it up this evening.

 

[annunaki]

Very cool! Glad you got a better set of specs to use than the prelims. True tested specs always produce a more reliable model. Looking pretty good though. Be sur eto let us know how they sound!

 

[GO-NAD!]

Very cool! Glad you got a better set of specs to use than the prelims. True tested specs always produce a more reliable model. Looking pretty good though. Be sur eto let us know how they sound!

I have them both assembled and after ensuring they were both functional, placed them in their new home last night. I ran YPAO, then ran through some test tones to see what I'm getting for a FR. I have not yet added the 3db of boost suggested by Jeff, which is supposed to give an F3 of 15Hz. I stopped at 18Hz, with no sign of drop off, although there were a couple of 5db-ish troughs at 28Hz and 56Hz, if memory serves. I hope to be able to flatten that a bit, by playing with phase and maybe some lateral position adjustments. We'll have to see how I fare with that. I haven't checked for max output yet, but my first impressions are very positive.

 

[caper26]

Freakin sweet dude! Dual SDX 12's ! I want to replace the trio12 in my 24" cube with one of these puppies. Now that the numbers are ironed out, I will email BoB.
You are a lucky dog!

 

[GO-NAD!]

Oh yeah, I'm quite happy with the results! I just did some more testing. After reversing the phase on the left one, the very low FR evened out some. The problem is - if you want to call it a problem - there is so much room gain, I have the SPA500s turned down to "3". I zeroed the SPL meter at 40Hz, and when you look at these numbers, it looks like there is a null around 80Hz. But actually, I took readings well up the scale to 6300Hz and 80Hz looks to be about -3 or -4db. Which means from 63db, the spl just takes right off! If I were to turn both subs gain to above "6", I'm sure things would start falling off the walls! I have no regrets whatsoever, in making this purchase. Bob had advised that I probably wouldn't need the SPA1000s to power them and he was absolutely right. Hey, if you want a demo, just let me know. You're welcome to come buy. By the way, you wouldn't know anyone in the market for a Velodyne DPS12 and/or a Reel Acoustics RSW1215, would you?

FREQ

RAW SPL

SPL (comp)

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</TBODY>

16	66	78.7
18	70	80.6
20	70	79.1
22	71	78.6
25	72	78.5
28	74	79.3
31.5	77	81.4
36	79	82.6
40	80	83.0
45	75	77.4
50	73	75.0
56	69	70.6
63	67	68.3
71	62	63.1
80	62	63.0

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</TBODY>

 

[caper26]

I may take you up on that offer sometime I am in the city! Do you have the "Subwoofer Mix" mp3? After you listen to it for a minute or 2, anything else that you thought had bass will sound like it doesn't

 

[GO-NAD!]

I may take you up on that offer sometime I am in the city! Do you have the "Subwoofer Mix" mp3? After you listen to it for a minute or 2, anything else that you thought had bass will sound like it doesn't

Subwoofer Mix? Never heard of it. If you have it, bring it along if you're coming to Metro.

 

[annunaki]

Very cool stuff!

Glad you are pleased with the results. What type of output are you generating near reference volumes with those? And, is your response remaining linear at those volumes as well?

 

[GO-NAD!]

Very cool stuff!

Glad you are pleased with the results. What type of output are you generating near reference volumes with those? And, is your response remaining linear at those volumes as well?

Well, after placing and connecting both subs, I set the gains at "6", then ran YPAO. YPAO set the sub level at -4.5 db. Then I ran the test tones. Picking 1600Hz as my 0db point @ 80db, I went down the scale. By the time I got to 63Hz, output was 100db, and 40Hz was 110db! The low bass FR was pretty uneven too. So, I turned back the amps' gain to "3" and to see what I could do about flattening the lowest frequencies I reversed the phase on the left-hand sub, which seemed to do the trick.

I haven't tried to determine reference level output yet, but it would appear that I'm getting a wicked amount of room gain at the bottom end. I have no doubt that after I apply some EQ, I'll have no problem getting in the 110db range from 80hz, right down to 16hz. I have no idea what kind of output I'd get if I set one up outside. Sorry to say, that will be unlikely, as these things are heavy!

As for determining linearity, I don't think I'm at all qualified to make that judgement.

 

[Adam]

Sweet! I don't know how I missed this thread for three months. I've got some reading to do...and then maybe ask some questions.

 

[GO-NAD!]

Sweet! I don't know how I missed this thread for three months. I've got some reading to do...and then maybe ask some questions.

Thanks!
What - not happy with the SVS?

I still have some tweaking to do with these. If I play around with the SPAs' EQ and gain, I'm sure I can improve the performance. There's plenty of headroom to play around with.

 

[Adam]

What - not happy with the SVS?

Oh, I sure am. One of my questions might be, "why not just buy an SVS?"

 

[GO-NAD!]

Oh, I sure am. One of my questions might be, "why not just buy an SVS?"

You're funny.

 

[caper26]

imagine what you will be getting if you crank the master volume control up? I got something like 119 dB on my Trio12 at 20 Hz with volume around -6 on my receiver. (SPL meter at about 10 feet) from woofer cone.

I think you should pick a "base frequency" that will be inside the curve that you will be using for your measurements. Pick something like 40 Hz, then set your volumes, etc, to get about 80 db on the meter, then run your tones and take measurements.