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Boston Acoustics SPG-555 Bandpass design...did I do it right??

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vernors

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Hi,

I've run a lot of subwoofers through WinISD to find the right one which met the needs of the audio system being installed in the car. The goal was to produce a very deep subwoofer that drove 25 hz to 80 hz effectively. In looking at over a dozen drivers I came up with the Boston Acoustics SPG-555 2 ohm. It's going to be run in a 2009 BMW 535i, but needs to be ported through either the rear seat arm rest or up through the rear deck. The car has a lot of steel and really deadens any sound in the trunk, so I felt I'd lose too much sound quality unless it was ported into the cabin. The last car I had, the previous gen E39, ran a JL Audio W7 firing through the ski pass, but that wasn't an option on this car unless I cut the whole for it...which I want to avoid.

So, do any of you have WinISD and can look at the attached file to provide some feedback on the performance graph and if I did everything correctly? 

For those of you who don't have access to WinISD I have attached a bunch of photo's showing graphs and specs.....

Does this look like a good set up? Am I missing/forgetting anything? Thoughts, concerns, impressions?

Thanks for the feedback, appreciated!

View attachment BA SPG 555 2 Ohm.wpr

WinISD SPG555 Performance Graph.jpg

WinISD SPG555 Enclosure Sizes.jpg

WinISD SPG555 Port Size.jpg

WinISD SPG555 Parameters.jpg

WinISD SPG555 Advanced Parameters.jpg

WinISD SPG555 Group Delay.jpg

BA SPG 555 Manual Driver Technical Specs.jpg

Click to read more...
 
I would tune a little higher like 47 or 48hz. With cabin gain you're going to have a big peak around 30hz then it will roll off by 60hz. You should try using bass box pro for a more accurate plot. It can estimate cabin gain unlike winisd. 

 
Interesting, that's something I hadn't checked for or thought of. I see Bass Box Pro is $150, but they have a 'lite' version. Do you know if the lite version would allow for cabin gain? If I have to pay for software, I'd rather spend the least I can and definitely not drop $150 just to do one box build. I'm not a shop which will monetize the investment. But, thanks for the suggestions, totally makes sense to estimate a cabin affect.

 
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Also, I see when I tune it for 48 hz my low side performance increases from 25 hz to 27hz, but the Group Delay drops significantly. I assume that is what you noticed indicating the peaky sound the sub would cause around 30 hz? Do I assume that music depth will be cut off at 27 hz, or does that just mean it's still efficient at 27 hz but may still produce low 20 hz frequencies? 

48 hz Group Delay.jpg

 
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Also, someone said on another post that a DSP can be used to correct the in-situ gain


I've got a Mosconi 6to8 DSP

Here are the other components.

Focal 4" ES Component Front
Focal 130KRC Rear
Custom Audio X-Ion 8" underseat drivers
Technic Wiring Harness
Focal 900.6 amp (all but sub)
Kicker cx1200.1 amp for sub

The whole goal is to frequency match the sub as best as I can...but tune it as deep as possible. The rest of the system is solid down to 35/40 hz or so
 
I definitely prefer having as smooth of a frequency response to gain/SPL as possible without needing to offset via DSP....assuming I'm understanding the issue correctly.

 
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Thank you so much, and I hope 4:20 was good to you today :  )

Also, do you need to know the free-air space of the vehicle's cabin? I have no idea if I can track that down, but will try if needed.

 
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Red line is your original design without cabin gain figured in

Black line is your original design tuned to 41hz with the addition of cabin gain. Note the HUGE difference below 50hz which is why I'm always preaching that winisd is useless below 50hz. 

Green line is a tune to 48hz with cabin gain. Note the difference over the black line above 35hz. 

Depending on the power, a 4 inch port might be a bit too small and will cause compression and port noise. 

View attachment spg555 4th order.pdf

 
Wow, what a difference and completely see what you mean about WinISD. Great to know about the affect of cabin gain, the charts clearly show that the higher tune frequency is the way to go. Was 47 hz the best all around choice for this set up....and does that graph show that this setup would kick out 20hz at +6 DB?

I've got a bit of a problem to figure out with the port and it helps if it's smaller rather than larger. I'd prefer to cut through the backseat wall within the armrest, but if that isn't possible I have to go up through the rear deck. Armrest option is problematic because the sealed enclosure portion of the bandpass exceeds half the box...and the armrest is pretty much square in the middle. Possible to angle the inside of the enclosure, but will see. Trying to minimize the size of the box due to limited trunk space. 

Any way to check how much power I can push without issues? 

Also can I continue to use WinISD with the assumption that a 47 frequency tune is the base line? I can model different size ports to check options. 

Thanks for checking on the set up, major difference and great advice.

 
I followed the advice and bought Bassbox 6 lite, but since this is my first time using this software I wanted to get opinions from others to see if I did this correctly.

How does this design look overall? Any issues that you see? Air Velocity too high?

Thanks for the advice, appreciated!

 
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Ok, so I just picked up a dayton audio DATS speaker analyzer and one of the things that the software requires is the diameter of the piston. It says to measure from center of surround to center of surround....however the SPG-555 is an oval shape.

Here's what I did, and am not 100% I did the right thing based on what the software wants, but I measured the circumference and then divided by 3.14. It turns out the SPG is 33 inches around and that works out to 10.5 ish. So, I used 10.5 as the diameter of the piston area. If that's how to do it great. Or  if someone knows the actual diameter value I'll plug that in.

The numbers compared to the original OEM specs seem quite different than those I got when using the DATS. Does this look right to any of you? This is the 2 ohm version.

SPG Measured Thiele Small Paramters.jpg

BA SPG 555 Manual Driver Technical Specs.jpg

 
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You can check for yourself by working out the area of a circle 10.5" and comparing to the 555cm^2 published..

Or to save you the time, yes, your piston area is correct.    For the record, when using DATS if you're using added mass method make sure you use a large enough mass (I usually use 500g or so) and make sure you do measurements in a quiet room (fans running or breeze will give you very strange looking results), and sit the sub up on something so that the pole vent isn't restricted if the woofer has a pole vent.

 
Specs actually look pretty good and close to what BA quotes. A lot of times manufacturer tsp numbers are an average from multiple samples off the production line so minor variances are to be expected. How much has the sub been used? Imo it looks like it hasnt been broken in, hence the stiffer suspension (higher vas and fs.) Play it free air for a few hours on 10-15hz on low power and it should loosen up.

How low do you want the box to play? Its nearing xmax just under 30hz. The other plots look good. It looks like you added the cabin gain boost in the plots.

 
Thanks for the feedback folks. I actually don't know how much the sub has been used, it looks to be in perfect shape. Also, I used the SPL selection in DATS..... 

Here's the updated charts with both Cabin Gain and without. I actually don't know what to think about the cabin gain factor within BassBox. It makes a huge difference to frequency response....but without it the results show it won't be very effective at 20 hz....

what do you think real-world affect will be? Does this look like a good baseline sub? I'm going to use a digital processor to tune the speakers, but want to start off with a solid foundation.

The goal of the sub is to play 20hz to 70 hz (or so). The car has twin 8" mid bass drivers that play easily down to 40 hz, so I'm focusing the sub to drive deeper bass.

Looking at the chart without Cabin Gain included and the roll off at 0 db is around 35 hz.....is real world use cut off at this point, or will the sub be able to drive 20 to 25 hz frequencies?

Thanks, I appreciate any advice offered.
 
View attachment DATS SPG555 With Cabin Gain.pdf

No Cabin Gain.jpg

With Cabin Gain.jpg

 
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