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-   -   Sunfire/Boston Acoustics Frankenstein Experiment (https://www.hometheatershack.com/forums/sealed-subwoofer-build-projects/65733-sunfire-boston-acoustics-frankenstein-experiment.html)

Nitrofreakman 02-20-13 03:47 PM

Sunfire/Boston Acoustics Frankenstein Experiment

Hi all,

I've never really though about building my own home sub until the last couple of weeks ( looking at some of the builds here really propelled me in that direction ) The biggest motivator was the voice coil coming apart from the spider in my Sunfire MKII sub..a real downer. I was going to buy another driver, and that got vetoed by my better half, so I thought about sending my current driver out for repair but couldn't decide.

I have a Boston SPG555 car subwoofer in 1cu/ft, 3/4"MDF sealed enclosure, that I built in a hurry without any care other than it was sealed well ( read: it's ugly :dumbcrazy:). This sub was pretty impressive when I had it in my car, it was the best sub that I had owned after owning a multitude of car subs from my younger days..I really did forget just how impressive:R

It will handle 1000w RMS, and as mentioned, fits in a 1 cu/ft sealed box, and has more surface area than a 12" sub.I really wish I had the know-how to use the specs in the manual to custom design a box for this particular build. Since I don't, I though I would experiment with whatever I currently have at my disposal. Here is the sub:


I decided to hook up the Sunfire amp to the Boston sub, I was a little worried at first because of what I'd read about the circuitry in the amp/crossover/voice coil work together utilizing the high back EMF of the Sunfire woofer's monster magnet. The boston has a large neodymium magnet, and so I thought 'why not ?':scratch:

..and I tried it:bigsmile: At first at low to medium volume, and soon enough, I turned it up. I was pretty shocked with the result, it was louder and tighter than the MKII..unfortunately, I now have a few annoying vibrations in my room that this sub brought out:R . In fact, some music that never sounded right with the MKII ( Tupac, some metal music ) all of a sudden sound great, and the speed of a fast kick drum in metal music has never hit so hard and fast as it does now. I really loved my MKII, and didn't want to ever part with it, now I'm rethinking that idea.

Well yesterday, I had the day off and decided to try phase 2 of this experiment. I took the passive radiator out of the Sunfire, and put it on the opposite side of the boston. I was a little worried that this may be taking things too far, because I really don't know anything about designing a sub box, especially one with a round passive radiator on an oval sub:coocoo: ( if somebody is willing to help with this, please post here ). I also lack tools/space to build a decent enclosure.


Here's the MKII beside the ugly block:


After trying it, it appears to be a good move. I don't have a db meter or test equipment ( yet ), so I used the db meter on my iPhone, and I gained just over 3db on my phone:scratch: It also seems to play lower frequencies louder than just a sealed box( not sure if this box is still considered sealed ? ) Yet it's still tight.

The sub amp volume is turned down lower than before( a couple notches lower than midpoint ) but the thing seems louder than ever before, and my room has less nulls, where before, the bass relied heavily on proper placement because my room has a strange ceiling design. I decided not to fix the Sunfire, and instead build a nice enclosure for my Frankenstein setup instead. The only lingering question, can someone design an enclosure that would better exploit the full potential of my equipment ? I'm sure there is, and I hope they aren't shy about posting, you're help will be appreciated.

Nitrofreakman 02-20-13 03:48 PM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

...hmm, not sure why my Photobucket pics didn't post?

**edit** problem solved

Nitrofreakman 02-26-13 01:23 AM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

Well, after living with this sub for a few days, I like it more than the Sunfire. In fact, I may put my Supercube up for sale, and buy another Boston, and build two sealed enclosures instead. Apparently, Boston makes a weight-tuneable radiator for this sub ( same shape ), but I can't find one anywhere. They claim a 3db gain with their radiator, in the same enclosure..about the same result I got with the Sunfire's radiator, mind you, I was using my iPhone's db meter ( it looks like the Radio Shack model ), which may be questionable. My RS db meter quit working after lending it to a friend, the needle won't move anymore.

I was hoping to get some feedback from fellow forum members on this. I really want to start building an attractive, solid version of this box, but can't help but wonder how this sub would sound in a slightly larger enclosure ( 1.3-1.6 sq/ft v.s. the current 1sq/ft enclosure ) I don't know how to use all the specs in the manual to figure out the ideal enclosure( I'm still learning ), one more suited to a home environment, that could dig maybe down to 15-16Hz (if that's possible), while still playing as tight and loud is it currently does. As it sits, it does rumble my couch, floor and pants..but I can't help but think that it's capable of more yet.

I also read threads where it mentions the Q of a sub, and some DIYers alter the Q ( one method I read was by stuffing the enclosure with pillow stuffing, but I'm not sure what it was supposed to do ?? ) So what is Q ? What does altering it do ? There are 3 Q specs in the manual, Qts (0.80), Qes (0.86), and Qms (11.66).

If anyone can help, please post away, I'm really eager to get this build started. Thanks in advance.

Nitrofreakman 02-26-13 11:49 PM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

:unbelievable: wow..170 views, and zero advice, well it was worth a shot. Gonna start this box tomorrow since I'm off.

gperkins_1973 02-27-13 01:43 AM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

Hi there,

I have managed to actually find the T/S parameters on this driver. Naturally being a car audio driver and probably works well in the boot of a car it won't work very well as a HT sub hence why they say a 1 cu ft box. This will give you a qtc of 1.2 which is way too high and won't sound that great personally.

To try and get the best out of it, I am getting 8 cu ft sealed which gives you a qtc of 0.899 which is still EQ'able but a little high. This only needs 600 watts input power and gives you 102db at 20hz. To be honest a $200 Dayton ultimax 15" driver will have 3db over this at 20hz.

Then 100db is still pretty loud in the scheme of things.

Put this driver in a 4 cu ft box and tune to 22hz you will get 113db at 20hz with 1000 watts input power.



Nitrofreakman 02-27-13 01:42 PM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

Hi Graham,

Thank-you for your reply, I just read it after getting back from getting my lumber cut:doh: I have all the TS parameters for the sub, but I just don't have the know-how to use them. Before I started this thread, I did try the WinISD's web applet (iMac user), but I'm not sure if I'm doing it correctly because it gives me a negative value for the 'optimal' for 'Closed Vb' of -6.41 with and a QTC of 0.7

I'm assuming the -6.41 is the volume, but I don't understand why the negative value, so I walked away confused, and thought that I'd maybe try using the program again when I have a better understanding of the related terminology and when I learn the significance of the individual values that I'm inputting( Vas, Qts, etc. ). Unfortunately, due to my lack of free time, this quest has been futile. I may also end up with result that don't sound as good in the physical world ( sometimes the data and ears don't agree ).

As it sits in the 1cu/ft enclosure ( only 3/4 MDF, no internal bracing, read: I can feel the box flex quite a bit at moderately high volume ), it does sound fantastic with all the music I've played through it ( a very wide variety ), it's a very, very tight sub, and very fast. It plays clean and loud ( louder than I can remember my Sunfire playing, and my wife and son both seem to think so lol ). It is much louder throughout the whole house, all the way to the second floor ( not good )where the bedrooms are. My good friend has a 15" Elemental Design sub, I don't know the model, but it's a great sub, and when he heard this Boston, he thinks it puts out no less than his 15, and higher for some frequencies, yet plays tighter. He also helped in my final decision to go ahead and stick to the current dimensions. I wonder how many others have tried ( or thought about trying ) car audio subwoofers, and were as pleasantly surprised as I am. It's an idea I got from Totem, they used a 10"( I think it was a 10 )PPI car subs in one of their speakers, and it would dig down to 10 or 12Hz if I remember correctly. I can say this, my new Supercube is going up for sale, and I'll be looking for another Boston..the difference between the two is like comparing a pop gun to a shotgun lol.

The final box will be 2 layers of 1" MDF on all sides, all glue, no screws, all corners rounded..I figure this way I shouldn't need internal bracing, but it should still be fairly solid. I'll likely paint it piano black to match my towers.

Thanks for your help Graham! Is there any links that can help me better understand the T/S parameters ? Just so that I can try to make sense of the numbers.

vroentgen 11-17-13 11:17 AM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

Hi. I purchased the matching passive radiators for the spg555 from Boston Acoustics recently. They cost 74 dollars or so. 201.762.2099. They have a warehouse of parts.

Nitrofreakman 11-17-13 11:23 PM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

THANK-YOU for the heads-up! I've been wanting one since I built this beast. I will have to call Boston and order one ASAP. This sub never ceases to amaze me, it absolutely rocks with the Sunfire sub amp. It puts out much more bass than the True Sub that it replaced, at a lower volume setting on the sub amp..the volume knob goes from -15 to +15 with 0 being the centre point. With the original sub, I had it between 0 and +5, with this Boston sub, it sits at -6, and still makes more bass, digging quite deep and remaining very tight. The sub volume on my processor is set at -6.5 ( I like to run my bass on the hot side, about 10db-15db, sometimes for different music/movies and negative 6.5 seems to give me a PLENTY of bass, and it's a nice adjustable volume range, if I need more bass without going above zero on my processor, though I rarely turn it up past -3..it's just way too much bass once I get to -4 ) For the most part, -6.5 is where it stays though.

I haven't been around here for a while, I feel like I'm not wise enough( audio wise lol ) to be here haha. When I read some of posts here, I'm dumbfounded by the knowledge of HTS's members. Some of these are really amazing, but unfortunately for me, it can get quite confusing when I read through some threads. There are som many acronyms and terms that are used here that I'm not familiar with. This makes it hard to apply much of the information I read to my own setup. It would be great to have an ' acronym/terms ' thread for guys like me lol. This is by far the most impressive AV forum that I've dabbled in, I just wish I had more time to read and figure things out lol.

I have upgraded some of my system since coming around though. I bought a Sunfire Cinema Grand amp, something I've wanted for many years. This upgrade alone was instantly noticeable in the sound while using my Yamaha's pre outs for the processing. It felt as though I'd upgraded my speakers. This upgrade was worth every penny.

The week after buying the Sunfire amp, I came across a Marantz AV8300 pre pro at a price I couldn't resist. The former owner bought it with the intentions of building a big, component based theatre room, but things didn't pan out, and it sat, new in the box, until I bought it from him at a killer price. I sold my Yamaha receiver to my brother, and replaced it with a Marantz. It's older than the Yamaha, and lacks some of it's features, but it really does sound great. I feel as though I'm listening to my music for the first time again in 2 channel stereo. I kept thinking that my centre channel speaker was on because the vocals are now dead centre ( appearing to come from my TV screen ) and with the Sunfire amp driving my BP10s, they are putting out some quality bass, reaching subwoofer-like bass, though not the kind of bass I require:yes:

As for movie watching, this processor really images very, VERY well, and steers like an indy car..I find my eyes flying off the screen when the sound moves from the screen and 'into the walls', what blows my mind the most is the way it puts the sub-bass where it belongs in the room. I can feel bass moving, up and down, panning side-to-side over my head and below my feet moving across the floor. I could always feel the bass everywhere before with my Yamaha, but with the Marantz, the bass goes where it belong and moves with the picture on the screen...th Hulk actually runs through my living room and steps on my feet as he runs by:yikes: I'm not sure if most of that made any sense, but in short, I'm quite happy with it. Next will be a 2 channel amp to get my 7.1 setup back, but I'm in no hurry because I'm enjoying this for now. My room is small ( 10 x 14 ) so the SB speakers really aren't a necessity.

I also treated my room with a corner bass trap and along with 2'x4' panels for the side walls, two on each side prior to my hardware upgrades. I still have to build some for the ceiling and front wall. I was pretty shocked at what the 4 panels and bass trap did to my sound and specifically the imaging. This was a very worthwhile project, and I can't wait until I find the time to make the rest of them. This forum has been a great motivation for my man cave.

I really do appreciate you telling me about the radiator, and I will certainly put it at the top of my list. I's sure love to find another SPG555 for a nice price to build another killer home sub.

Mike P. 11-18-13 03:49 AM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

There is a member here who built a HT sub with the Boston driver.


Nitrofreakman 11-18-13 04:01 PM

Re: Sunfire/Boston Acoustics Frankenstein Experiment

Thanks for the link Mike..I thought I was the only one that tried this sub. I'm glad to see another member try it. The boxes he built are HUGE..I was always curious what this sub would sound like in a big sealed box, I imagine they should still sound good with the ports. ? I'm thinking that he will be quite pleased with the performance, especially with 2 of these beasts.
My box is 1cu/ft (internal), and it puts out a shocking amount of bass, it plays tight and low, and loud ( Perhaps the Sunfire amp has something to do with this?? ) I never got around to building the other box, and ended up paying a private woodshop to build it, unfortunately, it's been nearly 1 year since I payed him, and still no box. I'd say that it's time to do something about that, I've been pretty patient/nice for too long..

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