Repercussions of Oversized Sealed Subwoofer Enclosure (Inferior Boominator)

[jonsow84]

Hello,

Quick Question:
What are the repercussions of having an oversized sealed subwoofer enclosure, double the volume in this case? I am specifically interested in optimizing efficiency/sensitivity and volume in this case, so how will it effect these factors? Is there an easy and inexpensive way to reduce the enclosure volume to optimize these factors?

Detailed Background:
I am brand new member here, but I was inspired to build my own portable speaker after reading through the boominator thread. However, I did not do a very good job designing my system.

During the initial design of my speaker system I kind of ignored the efficiency/sensitivity of the system all together. I really did not think it was a factor I needed to consider in much depth because the original boominator was stated to last up to about 50 hours without a charge using relatively small batteries, powering I believe a total of four 10" drivers and four tweeters. Given this fact I thought if I just used larger batteries I wouldn't need to really design for efficiency and I would still have a significant run time, but I was very wrong. At close to full volume my unit dies after only about 3 hours.

Anyways.... I am now trying to redesign my system to make it a little bit more efficient, and put in even bigger batteries (35AH, freaking huge I know, but this is how I'm remedying my terrible design lol). To do this I purchased some more sensitive drivers, two polk db521 (93dB/W) and a single polk MM1040 (91dB/W), probably not very sensitive drivers in your eyes, but I believe they are pretty efficient for car audio drivers.

However, I originally designed the entire enclosure for a different set of drivers, so the volume is way out of wack. I never optimized the volume for the 5-1/4 inch full range drivers, because I didn't have any of the necessary info to do so, but the subwoofer sealed enclosure is currently 1.26ft^3 and the new Polk sub is optimized for a sealed enclosure of 0.65ft^3 according the the spec sheet (0.44ft^3 according to the calculator on this website Speaker Box Enclosure Designer / Calculator).

Here is the current equipment that I have installed in my system:

Battery: 12V 18AH Sealed Lead Acid Battery

Amp: Sony XM-GTX6041 4/3 Channel Amp 600W Peak Power with a current drain of 31 Amps at max power

Full Range Drivers: 2x Sony XS-R1345 5 1/4" 4-Way Speakers 35W RMS with a sensitivity of 85dB/W

Subwoofer: 1 x Sony XS-GTX101LW 10" Subwoofer 300W RMS with a sensitivity of 84dB/W

Here is what I'm replacing:

Battery: 12V 35AH Sealed Lead Acid Battery

Full Range Drivers: 2 x Polk db521 5 1/4" Two Way Speakers 45W Max RMS with a sensitivity of 93dB/W

Subwoofer: 1 x Polk MM1040 10" Subwoofer 350W Max RMS with a sensitivity of 91dB/W

I estimated that making these changes will, at the very least, double my run time (6hr) at max volumes. I am hoping that it will increase my run time to closer to 8-10hrs at max volume. However, it is very obvious that my system isn't even close to being optimized. It is significantly heavier, has a much larger battery, and fewer drivers than the Boominator, and it still will probably only have about 20% of the run time of the Boominator. I'm obviously missing some information/knowledge about how to increase the efficiency of my system (is it the back to back drivers?), but I have no idea what could be making such a huge difference. If you guys have any recommendations for this amateur, they would be much appreciated.

Thanks,
Ben

 

[weltersys]

Hello,

Quick Question:
1)What are the repercussions of having an oversized sealed subwoofer enclosure, double the volume in this case?
2) I am specifically interested in optimizing efficiency/sensitivity and volume in this case, so how will it effect these factors?
3)Is there an easy and inexpensive way to reduce the enclosure volume to optimize these factors?


Here is the current equipment that I have installed in my system:
Battery: 12V 18AH Sealed Lead Acid Battery
Amp: Sony XM-GTX6041 4/3 Channel Amp 600W Peak Power with a current drain of 31 Amps at max power
Full Range Drivers: 2x Sony XS-R1345 5 1/4" 4-Way Speakers 35W RMS with a sensitivity of 85dB/W
Subwoofer: 1 x Sony XS-GTX101LW 10" Subwoofer 300W RMS with a sensitivity of 84dB/W
Here is what I'm replacing:
Battery: 12V 35AH Sealed Lead Acid Battery
Full Range Drivers: 2 x Polk db521 5 1/4" Two Way Speakers 45W Max RMS with a sensitivity of 93dB/W
Subwoofer: 1 x Polk MM1040 10" Subwoofer 350W Max RMS with a sensitivity of 91dB/W

4)I estimated that making these changes will, at the very least, double my run time (6hr) at max volumes. I am hoping that it will increase my run time to closer to 8-10hrs at max volume. However, it is very obvious that my system isn't even close to being optimized. It is significantly heavier, has a much larger battery, and fewer drivers than the Boominator, and it still will probably only have about 20% of the run time of the Boominator.
5)I'm obviously missing some information/knowledge about how to increase the efficiency of my system (is it the back to back drivers?), but I have no idea what could be making such a huge difference. If you guys have any recommendations for this amateur, they would be much appreciated.

Ben,
1) Low frequency sensitivity will be increased, less power will be required to reach Xmax.
2) Using a ported alignment or a tapped horn could increase sensitivity by 3 to 6 dB.
3) Reduction of size will reduce sensitivity, but is easily done by partially filling the enclosure with Styrofoam.
4) Doubling the battery amp hour rating will reduce the Peukert's effect, at minimum that alone will more than double run time. Increasing sensitivity by 7 dB will increase run time by more than 4 times at the same sound pressure level, your recharge time should increase from 3 hours to over 24. If you really want some battery improvement, try using the GBS-40Ah from http://evolveelectrics.com/GBS.html

Four in series are nominally 12.8 Volts, weigh only 12.4 pounds, cost $248.
The amazing thing is you can pull peaks of 400 amps out of the pack with hardly any sag.
You can get by with much lower rated Ah LiFP04 than lead acid because they have virtually no Peukert's effect.
5) "Back to back drivers" generally would be an isobarick loading, which reduces the cabinet volume for a given F3, but uses twice as much power to achieve the level that could be achieved with the larger enclosure.

Art

 

[bitSmasher]

Your amplifier is the weakest link. Car audio, especially speaker drivers, has terrible efficiency.
Get a class-d car amp at the minimum, or look at "chip amps" as made by Sure or the like - a bit more DIY but worth the effort

 

[just a guy]

Welcome to the world of car audio where you have to search hard for the specs and hope and pray they actually mean something.

I checked the Polk website but this page didn't give an exact Re - MM1040 DVC - Polk Audio
So I kept looking and found the manual here - Polk Audio MM1040 Owner's Manual (Page 10 of 16)

I simulated based on the svc 10 inch model.

Then I found the Sony specs here - https://www.manualowl.com/swfviewer...e&FitWidthOnLoad=false&ZoomTime=0.5&Scale=0.6
They didn't list an actual number for Sd so I just used 350 sq cm, same as the polk.

I can't figure out what Polk is talking about with 91 db sensitivity. Even if you sim the 4 ohm svc driver at 2.83 volts it's still nowhere near 91 db.

Anyway here the comparison sim showing that if sensitivity is key the Sony is king in this case. Unless I made a huge mistake somewhere. Check my inputs for mistakes.

Both simulated with 1 actual watt into Re. Both simulated in your 1.26 cu ft sealed box size.
Bottom graph shows both overlaid, the Sony is the one with higher sensitivity.

The moral of this story is never EVER trust car audio specs. Ever.

I'd expect the same type of gamesmanship with the little drivers too, sensitivity is probably measured at 2.83 volts (for a 4 ohm driver) and measured at a peak in response (maybe at a cone breakup peak). NEVER trust car audio specs.

[IMGDEAD]http://i63.tinypic.com/2igeu6g.png[/IMGDEAD]

 

[just a guy]

You probably should put a port in the box and buy an actual high sensitivity driver instead of car audio crap if your number one goal is sensitivity.

 

[sreten]

Hi,

Just add a port tuned to 40Hz, you should be good to go.

rgds, sreten.

 

[jonsow84]

Ben,
1) Low frequency sensitivity will be increased, less power will be required to reach Xmax.

I'm kind of surprised by this, not really what I was expecting. I'm happy that I don't have to fill the volume in my box to increase the sensitivity.

2) Using a ported alignment or a tapped horn could increase sensitivity by 3 to 6 dB.

Would this just increase the sensitivity across a narrow band of frequencies, or would it increase it across the entire frequency range of the sub? Either way I probably won't be modifying my box at this point. I think I'm too far in the hole at this point to make modifications that large worthwhile. I'd be better off stating from scratch. [/QUOTE]

4) Doubling the battery amp hour rating will reduce the Peukert's effect, at minimum that alone will more than double run time. Increasing sensitivity by 7 dB will increase run time by more than 4 times at the same sound pressure level, your recharge time should increase from 3 hours to over 24. If you really want some battery improvement, try using the GBS-40Ah from http://evolveelectrics.com/GBS.html

Four in series are nominally 12.8 Volts, weigh only 12.4 pounds, cost $248.
The amazing thing is you can pull peaks of 400 amps out of the pack with hardly any sag.
You can get by with much lower rated Ah LiFP04 than lead acid because they have virtually no Peukert's effect.

I was not aware of the Peukert effect, I will have to look into it. I'm not really worried about recharge time too much. I will probably be using this over the course of a long weekend, and then not touching it for a month, so I'll have plenty of time to recharge it. However, weight is an issue so the LiFPO4 batteries would definitely give me a huge advantage there. They are about 5 times the cost of an SLA with similar ratings though, so I probably won't be using them in this design.

Thank you for all this information. I probably won't be using it to modify this speaker, but I do plan on building a better one at some point in the future.

 

[jonsow84]

Your amplifier is the weakest link. Car audio, especially speaker drivers, has terrible efficiency.
Get a class-d car amp at the minimum, or look at "chip amps" as made by Sure or the like - a bit more DIY but worth the effort

Could you go into a little bit more detail into how to pick an amp? I assumed that the amp was my weakest link, but I had a really hard time finding information on amp efficiency. I believe the amp I chose is a class D amp, at least that's how it was listed when I purchased it. I was under the impression that class D was the most efficient type of amp, and that all class D amps have similar efficiencies, but this is probably a faulty assumption. I made this assumption because I could never find any efficiency specs on any of the amps that I looked at.

 

[jonsow84]

Welcome to the world of car audio where you have to search hard for the specs and hope and pray they actually mean something.

I checked the Polk website but this page didn't give an exact Re - MM1040 DVC - Polk Audio
So I kept looking and found the manual here - Polk Audio MM1040 Owner's Manual (Page 10 of 16)

I simulated based on the svc 10 inch model.

Then I found the Sony specs here - https://www.manualowl.com/swfviewer...e&FitWidthOnLoad=false&ZoomTime=0.5&Scale=0.6
They didn't list an actual number for Sd so I just used 350 sq cm, same as the polk.

I can't figure out what Polk is talking about with 91 db sensitivity. Even if you sim the 4 ohm svc driver at 2.83 volts it's still nowhere near 91 db.

Anyway here the comparison sim showing that if sensitivity is key the Sony is king in this case. Unless I made a huge mistake somewhere. Check my inputs for mistakes.

Both simulated with 1 actual watt into Re. Both simulated in your 1.26 cu ft sealed box size.
Bottom graph shows both overlaid, the Sony is the one with higher sensitivity.

The moral of this story is never EVER trust car audio specs. Ever.

I'd expect the same type of gamesmanship with the little drivers too, sensitivity is probably measured at 2.83 volts (for a 4 ohm driver) and measured at a peak in response (maybe at a cone breakup peak). NEVER trust car audio specs.

Most of this info is waaay over my head, but thank you from doing the work What I take away from this is that the spec sheets are highly inaccurate and that the Sony 10" sub is actually significantly more sensitive than the Polk sub? How confident are you in this conclusion?

 

[jonsow84]

You probably should put a port in the box and buy an actual high sensitivity driver instead of car audio crap if your number one goal is sensitivity.

Adding a port to the box seems like it might be more work than it is worth at this point. It seems like there are so many faults in my design/choice of equipment that I'd be better off just starting at the beginning.

Even though the system didn't turn out the way I wanted it to, I'm still very happy with it. It's incredibly loud and I had a lot of fun making it. I just wish I didn't spend so much money on it lol. I think at this point I've put somewhere between 600-800USD into it. I would have been way better off buying higher quality components from the beginning.

I'm definitely going to build a better unit in the future starting my design over from scratch. All of this info will help me redesign a better system. Anyone have some recommendations for audio websites I can use to research/buy components in the U.S.?

Here are a couple pictures of my project as it stands now, if anyone is interested.

 

[chris661]

I'd definitely try to add a port to the box.

You can get extendable ones. Mount it with the port sticking out, play music, adjust the length. Once you're happy with the sound, mount the port inside the cabinet and you're good to go.
You'll get more SPL for <$10, and cutting a single hole. Very much worth it IMO.

Chris

 

[sreten]

Hi, You need to seal off the upper drivers, and add a port, rgds, sreten.

 

[jonsow84]

Hi, You need to seal off the upper drivers, and add a port, rgds, sreten.

The upper drivers are sealed off. Each driver has it's own compartment.

You guys are really pushing for this port ;p What frequency do you think I should try to tune it to? Any recommendations for the easiest way to accomplish this?

I was convinced that the Polk drivers were much better than the Sony's, but now you guys have got me worried. Which drivers would you recommend that I install?

 

[just a guy]

The easiest way to install a port is to use a 3.something inch hole saw and then jam a 3 inch (internal) abs pipe length into the hole. It fits so tight you will probably need a hammer to get it in the hole. You don't need to glue it or anything, it won't go anywhere and it won't leak around the edges. Just cut the hole with the hole saw (attached to a drill) and pound the abs port into the hole.

I would recommend that you install the driver that sounds better after you listen to both of them.

 

[chris661]

Tune for 40Hz, maybe 50. Make it boomy and then EQ it down --> free headroom.
Forget about doing low bass outdoors - it doesn't come easily.

Chris

 

[BIGlep]

Look into Turnigy LiPO packs, their made in china so their cheap, but have been shown to be reliable. You can get huge capacity and current for dirt cheap compared to LiFePO4. LifePO4 has it's place in maximum performance applications, but standard Lithium Ion have the edge in price and weight. You will need a balance charger however.