24" Stealth Build: Stereo Integrity Audi A4 Avant

J

JasonInAugusta

Noob
So the story to this is a bit crazy.

A couple of years ago I was at the Sundown show in North Carolina with the Chevelle. This show was where we had to go for the Virginia State Finals.

I threw the car together to get it playing and hit the road.

At one point a guy introduced himself as "Nick, from Stereo Integrity".

Aside from the forums I knew nothing about him or his products. I DID have a BM MK IV at the house that belonged to another forum member, but I never did any testing with it.

We chatted for a bit and that was that. I recently told him that I couldn't remember if he listened to the Chevelle that day or not and he said "I didn't get the chance, Bertholomey wouldn't come out" :lol:

So fast forward to last November. Nick and Josh came to the meet I had here. I never listened to the Passat - too busy.

He saw the van build I have here and told me he had some subs that would walk all over the 13W7s. I thought "He's in sales mode now" and filed that bit of info away to memory.

So time goes by and we end up talking about these subs. HST-15s. I told him I'm not convinced. All I see is an SPL sub. We talked about things and I told him that I wanted to be able to test these against the 13W7s before telling the customer that this (buying SI 15s) was the better route to take. I had modeled it, but wanted to hear it.

I made the trip to his place and tuned the Passat as much as I could with the processor and other issues we had that day. Brought a HST-15 back for testing.

Long story short, I'm a believer in the SI subs. The HST-15 is a lot like the 13W7 in regard to specs, but Nick was right, the HST-15s out-perform the 13W7s, sound better (shorting rings that the W7 doesn't have make a difference) and don't need as much enclosure space to get their output.

So...I was sold on the HST-15s for the van and Nick asked me if I'd be interested in doing a stealth build in his Audi.

"Sure. Stealth builds are kinda my thing."

We went over plans and discussed the build. The initial plan was a simple stealth install with a SQL-15 in the 2ft^3 sealed enclosure in the spare tire well with his components up front with Sundown's prototype SALT amplifiers powering everything.

Originally the car was going to be here and built so it could get to Bertholomey's meet on May 1st and then...pandemic. :daniel: Everything got put on hold.

Finally the time comes that things work out and Nick decides to bring the car. He also brought a pair of HS-24s for me to play with. No idea what I'll destroy with those, but they're in the arsenal now. :lol:

For those of you that haven't been around a 24" sub, they dwarf everything else. The DD Audio 3015ESPs I have for the Chevelle look small - and DD uses a 18" cone to build the ESP 15s.

So I moved the Audi in and started going over the car to see how well what I wanted to do would work. The idea of stealth mounting the 3" drivers behind the factory tweeter location wasn't going to work so I nixed that idea and put my plan for the doors on hold while I thought about what to do up front.

While thinking over the front of the car I got to work at the rear. To build the 2ft^3 enclosure for the SQL-15 I would need to remove the large hump in the middle of the spare tire well. That hump, on the underside, houses the EVAP canister. I knew that would need to be relocated so I unbolted it and disconnected the lines.

After that I got to work with the drill and drilled out the spot welds for that hump in the spare tire well. After they were drilled I had to crawl under the car, cut through the seam sealer, and separate the hump from the floor pan.

At some point I sliced myself open. Had not idea I was cut, but for some reason my hand felt slimy.

So..I bled on it. It's officially a project now. :lol:
 
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It was at this point I realized how big of an opening there was in that spare tire well now.

While returning the dead blow hammer to the tool box I walked past the 24s on the other side of the shop. (For those that haven't been here before I have a 3-car bay and a 2-car bay. The Audi is in the middle of the 3-car bay and the subs are all stored in the 2-car side.)

So I see the 24s sitting there and the idea my mind is set on convincing Nick to go with a 24 in an infinite baffle setup instead of the SQL-15 in 2ft^3 sealed.

Didn't take any convincing at all. As soon as he saw the opening he was thinking the same thing.

So the first major change happened after the first bit of tear-down. The idea of a SQL-15 in a sealed enclosure was nixed and I would install a 24.

But it will stay a stealth build.

A couple of pictures of the 24s for size reference.

I am not a midget.
 
With the plan finalized to go ahead with the 24 in infinite baffle I got to work making a template for the baffle. I needed to locate the sub at a happy medium where I had plenty of room between the surround and full excursion and the bottom of the floor of the cargo area. I also needed to be mindful of the motor and how much of it was below the bottom of the floor pan.

As luck would have it the surface of the factory metal floor in the back of the wagon is perfect. With the dimension between the floor and metal floor known, I made a layout block and got to work marking cut lines on the factory plastic floor liner.

After that I made a template from some hardboard for the baffle and made a ring that would give me the mounting hole diameter of the 24 as well as the outer diameter of the basket.

With the template located, I centered the ring on the car, traced it's location, then template taped it down and cut the opening on the router.

This gave me the template I would need to take to the metal shop.
 
When I saw the pics on FB, I was wondering if you were working on Nick's car. I can't wait to see what you do with it.
 
So then it was time to hit the local metal shop. I got lucky and the guy that runs the CNC plasma was geeked out about the project. I knew that asking them to transfer my template to a CNC file would be a PITA but he spent time trying to get it right. When he was done he etched the file to the surface of the metal and it was close, but not 100%.

Since I needed the piece to be as close to perfect as I could get, he cut the center hole as well as another ring from the center, and we laid the template on the steel to trace the perimeter. With the perimeter traced it was time to shear everything off the perimeter that I didn't need.

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Back at the house I got to work with my handheld plasma to get the detail cuts made in the baffle. Safety Sandals: Engaged

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At that point my template and the steel were a close match. It'll take a bit of work with a grinder to finalize fit, but this will do.

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At that point I HAD to drop one of the 24s here into the hole to get a visual...

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I called Nick told him to look at the pics on Facebook. The initial laugh upon seeing the pictures was awesome and came back around every so often as he scrolled through the pictures. I could hear him smiling the entire call. I wish I had recorded it for the YouTube channel. :banghead:

So these pics brought about a ton of comments on social media about how there's not enough airspace, there's not enough room between the sub and the bottom of the floor, the motor is going to get damaged, and so on.

Out of curiosity I grabbed one of the HS-24s here, threw it in the car, and connected it to the IM-SG.

The baffle isn't welded and is just laying there. The sub is just laying on the baffle.

94.1dB at 20Hz. Measured 0 watts. :lol:

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So with the 24 going in some sound treatment was in order. Nick contacted Eric from Second Skin and a shipment of products arrived. Some Damplifier Pro, Mega Zorbe (hydrophobic melamine foam), and Overkill Pro (CCF). These combined with the roll of MLV I have here should make things a bit quieter and hopefully keep everything from rattling with the 24 gets going.

Also pictured here are the prototype SALT amplifiers from Sundown. Full range Class D amps made to produce their power at 12v. Not 14.4. Not 16. They ALL over-achieve. The monoblock SALT amps are silly. The SALT 12 is doing 18,000w into 1 ohm at 12 volts. Something like 21,000w at 14.4v.

The 200.4 is rated for 200w x 4 channels at 4 ohms and 600w x 2 channels at 4 ohms.

The 300.4 is rated for 300w x 4 channels at 4 ohms and 900w x 2 channels at 4 ohms.

The other amplifier is the yet-to-be-named SALT 6-channel. It has staggered outputs.

Channels 1&2: 100x2@4
Channels 3&4: 150x2@4
Channels 5&6: 200x2@4

Channels 5&6 can also be bridged and will do "1200 watts or so" at 2 ohms.

The plan for power in the car is to use the 300.4 as a two channel and send 900w to each coil of the IB-24.

The 6-channel will run the components.
 
Awesome.

Let's see an underneath picture,you're wrapping the back of the cone in the old spare tire well (while still allowing a large enough hole to impement IB. Is that why some people didn't think there would be enough airspace ?
I've always wanted an IB 18" but this is mental.
 
preston said:
Awesome.

Let's see an underneath picture,you're wrapping the back of the cone in the old spare tire well (while still allowing a large enough hole to impement IB. Is that why some people didn't think there would be enough airspace ?
I've always wanted an IB 18" but this is mental.
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I have a picture of the bottom with the HS-24 in. It has a mounting depth of 13 1/2".

The IB-24 has a mounting depth of 11 3/4". That will put the bottom of the magnet about 8 1/4" off the ground. The low point on the mufflers? 7" off the ground.

I'll build a piece for the bottom of the car when the IB-24 is here. Hydrophobic mesh, stainless, mesh, and some other stuff. The sub will be protected.

And, since the motor is nickel plated (looks like chrome) the exterior of motor was clear coated to prevent corrosion.
 
Reading the title of the thread I'm thinking "a stealth build with 24" wheels or something?" but no ... it's even more better.

subscribing....
 
Justin Zazzi said:
Reading the title of the thread I'm thinking "a stealth build with 24" wheels or something?" but no ... it's even more better.
Click to expand...
I don’t know if you’ve had a chance to hear the HS-24 but it is a special driver. I know it is physics and a 70 lb magnet motor can pretty much do whatever it wants with a 1 lb cone but it is still amazing how something so large plays so deep, clean, and accurately.
 
dgage said:
I don’t know if you’ve had a chance to hear the HS-24 but it is a special driver. I know it is physics and a 70 lb magnet motor can pretty much do whatever it wants with a 1 lb cone but it is still amazing how something so large plays so deep, clean, and accurately.
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I don't think anyone on this site has any lack of desire for a 24" subwoofer - I know I don't !
 
Hey, I recognize that car :lol::D


JasonInAugusta said:
I called Nick told him to look at the pics on Facebook. The initial laugh upon seeing the pictures was awesome and came back around every so often as he scrolled through the pictures. I could hear him smiling the entire call. I wish I had recorded it for the YouTube channel. :banghead:
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Having run a 10" sub in there for years before Nick bought the car, I let out the same laugh at seeing the 24" sitting in there. Was talking to Nick on the phone and telling him how much I love the complete stealth look and how he can have a little fun with demos telling people there is no sub installed.

JasonInAugusta said:
So these pics brought about a ton of comments on social media about how there's not enough airspace, there's not enough room between the sub and the bottom of the floor, the motor is going to get damaged, and so on.
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Plenty of room under the floor, IIRC there is at least 2" under the initial wooden floor.


Been following the build on Instagram, can't wait to see it all finished and get a demo.
 
Justin Zazzi said:
Reading the title of the thread I'm thinking "a stealth build with 24" wheels or something?" but no ... it's even more better.

subscribing....
Click to expand...

It's an interesting build for sure.

dgage said:
I don’t know if you’ve had a chance to hear the HS-24 but it is a special driver. I know it is physics and a 70 lb magnet motor can pretty much do whatever it wants with a 1 lb cone but it is still amazing how something so large plays so deep, clean, and accurately.
Click to expand...

They're definitely not a novelty subs like others that have been made.

BigAl205 said:
Jason, you should make a speaker 'grille' out of an old Samsonite suit case

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There will be no grille.
 
JasonInAugusta said:
Hydrophobic mesh, stainless, mesh, and some other stuff. The sub will be protected.
Click to expand...
Staying tuned - probably wouldn't ever be practical knowledge for me, here in Buffalo NY with our weather extremes, but always wondered about doing something like this - think it'll end up working more like an aperiodic membrane?
 
going off topic a little here, but having studied AP setups a bit and used them for door woofers, I've often contemplated where the line is crossed between AP and IB. The first thing I think of is that an IB woofer should be somewhere in the .7 qts range whereas an AP driver is better suited for < .45 based on my research. But one thing that is very difficult about measuring/comparing AP is the relative size of the "port", and the density of the stuffing within. All of this makes it very difficult to model or compare. Say you have a sealed box and drill a tiny hole in it - that is one type of AP. As the hole gets bigger at some point it will just be "IB". The other interesting aspect is that AP reduces your Q peak but the anectdotal way of understanding that is that it does so by suppressing the low end output overall. Yet we know with IB, low end extension is very good as there is no air spring resistance on the driver. All of which leaves me a little confused about what is happening on the "boundary" of AP and IB !!

Anyway sorry for the digression, none of which is applicable here, as I think its clear the OP is building only a water resistant membrane not any kind of resistant port.
 
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