Designed 4th Order Bandpass....did I do it right??

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Got a vehicle with some serious sound deadening and the only way to really get good sub tones into the cabin is by porting in.

After reviewing more than 12 subwoofers I ended up selecting the Boston Acoustics SPG555.

Modeled an enclosure using Bassbox 6 (first time using this software) and wanted to get your opinions on final specs.

Anyone see problems with this set up? One of the issues seems to be potential air cavitation using the 6 in port, not sure what is 'too fast' for air to travel without distortion.

Charts, settings, etc....included. Any issues? Adjustment suggestions? Thanks!
 

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I don't see inductance mentionned...it's add a big low pass in this kind of speaker box. Do you have this parameter value for this speaker ?
Got +/- the same result as you with hornresp with 1400 w (taking account of speaker real resistance), and with inductance of 2mH (seems me reasonnable). Group delay is not too bad.

40m/s vent air velocity on port (lot higher than more reasonnable 15-20m/s) means lot of chuffing, and port compression, very bad thing.

I really encourage you to measure your own speaker parameters.
With 4th bandpass, it is very sensitive to speaker parameter variation.

There is not really a good solution with 4th bandpass to avoid chuffing since bigger port means longer, means lower frequency reasonnances. Or you can replace the port with a passive radiator.

And around 1000w in one closed back speaker, is a pretty bad idea => Heat => power compression + speaker parameter variations.

To not loose power with such wattage, you need to got for tapped horn, with motor vented by output mouth. It will be bigger.
 
The 22" vent should be ok, I'm going to run it either through the rear parcel shelf or through the arm wrest area of the back seat. I may need to add a bend within the box to take up some of the total length.

There are two underseat 8 inch drivers that will play clean below 40 hz so having it roll off at around 70 hz should be a good match

Yes, I was worried about vent air resonance and the 1000 watts was at maximum output for the speaker. I doubt I'd push it that hard, but wanted to design a box, if possible, that will play fairly cleanly at that level.
 
Have you experienced chuffing/port compression, power compression ? there will be a point (and a lot sooner than what you can expect) where leveling up power will no more add lows, but a bit of noise. 6" vent is just too small.
I'd like to see coming a "Hi all" + "FYI:" + "b" suggestion ^^
 
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I'm not familiar with Bass Box, but I'm wondering why the first graph shows the response leveling off at 0 dB to the left, all the way down to 5 Hz and beyond. For a 4th Order Bandpass, I would expect a plateau (or peak), with a roll off slope on each side.

Also, I'm wondering about the value and units given for the Bl product in your attachments. The spec sheet that I found on line gives BL = 11.58 T*m for the 2-ohm version. (What is lb/A?)

What "band" of frequencies are you hoping to target? As an example, if you have a 6.5" coax that plays down to 70 Hz, you might want the bandpass to run from 30 to 70 Hz.
 
The software has a cabin gain algorithm which significantly affects some of the graphs. It flattens them out a lot.

You got it, the box is tuned for 20-70 hz as the car has 8" midbass drivers that supposedly can push cleanly below 40 hz.

I just ordered a dayton audio DATS to pull the actual thiele parameters from the sub driver to really dial in the box. A number of people have independently stated that this is a key part for a good box design. It will be interesting to see the shift in numbers over the last 10 years.
 
car audio, including cabin gain, is something I haven't looked at that much. (I prefer to concentrate on sound quality at home :) )

I agree, accurate measurements that apply to the specific driver really is the best way to get good results. And from past experience, the volumes on a 4th order bandpass can be very finicky. If there's room for it, it's easy to build a box that is a little bit oversized, and use some solid filler material to adjust as needed. Especially if you have some measurement equipment to verify.
 
Yeah the software has another feature which can help optimize cabinet size while calculating fill material. I've been told to go with Roxul wool insulation and will be using it because I need the smallest cabinet possible, yet with the most equivalent high volume.

Understood on the home side, I've never built any speakers for home use but instead have just bought good gear. It's addicting, unfortunately.

We'll see how this all works out, the car stereo being installed is the trickiest I've ever done, and this subwoofer is causing extra effort due to complexity of placement and sizing.

Thanks for the advice, appreciated.
 
The 22" vent should be ok, I'm going to run it either through the rear parcel shelf or through the arm wrest area of the back seat.

FWIW, you could build a sealed or vented box, with an additional "coupling chamber" that directs the output through the entire arm wrest area. There should be several examples of such a configuration available via Google search on the Internet.

I once tried the bandpass with vent through the rear package tray approach. It sounded like crap, due to the location and the use of a vent that was too small (the output of a 4th order BP enclosure changes significantly at different levels if the vent is too small).
 
That sounds like an option as well. I'll know more which way to proceed once I can get an accurate measurement of it's parameters and plot out the box.

I've had to move up to a 6 inch port due to air velocity issues, it's tricky to build but will model and decide. I don't mind a challenge, but don't want to bet on something that the odds say won't work.

Thankfully bassbox seems to be pretty robust.
 
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