That would be going bass-ackwards. What you should have told him was that he needs a highpass filter before his amp. 4th order at 60Hz should do nice.
@ v-bro
I apologize. When I first read the article about the backpack system made at 41hz, I did only that. Read the article... I didn't notice the link at the bottom that takes you to the thread where it was originally posted! A lot of good info there, which I'll try to get to when I can.
Anyways, yeah, one larger woofer would work the best for my price-range i think. But you're right, I guess I need to plan around my box size... which, incidentally, is looking to be coming in around .75 cu.ft, if I go with a box 12" wide, 8" deep, and about 14" high.
on that same track, I really like the look of that Goldwood speaker! (nice price!) However, I wish it had a frequency response graph like the others I've looked at. Unfortunately, when I tried to put the specifications into winISD (which I'm slowly learning how to use), it wouldn't let me create a new driver, because apparently the specifications didn't make sense... And what are sonotubes? just ports with pvc on them?
Also, upon further digging, I've seen several places that recommend using CTS piezo tweeters... so if i was going to use that Goldwood, a KSN-1141 would work well, right?
Interesting... so everything below 60-75hz is unnecessary? huh... wouldn't have thought that! so much to learn...
And mfong, I'm not entirely sure what you're getting at...
PVC enclosure? huh?
I apologize. When I first read the article about the backpack system made at 41hz, I did only that. Read the article... I didn't notice the link at the bottom that takes you to the thread where it was originally posted! A lot of good info there, which I'll try to get to when I can.
Anyways, yeah, one larger woofer would work the best for my price-range i think. But you're right, I guess I need to plan around my box size... which, incidentally, is looking to be coming in around .75 cu.ft, if I go with a box 12" wide, 8" deep, and about 14" high.
on that same track, I really like the look of that Goldwood speaker! (nice price!) However, I wish it had a frequency response graph like the others I've looked at. Unfortunately, when I tried to put the specifications into winISD (which I'm slowly learning how to use), it wouldn't let me create a new driver, because apparently the specifications didn't make sense... And what are sonotubes? just ports with pvc on them?
Also, upon further digging, I've seen several places that recommend using CTS piezo tweeters... so if i was going to use that Goldwood, a KSN-1141 would work well, right?
Interesting... so everything below 60-75hz is unnecessary? huh... wouldn't have thought that! so much to learn...
And mfong, I'm not entirely sure what you're getting at...
PVC enclosure? huh?
backpack as enclosure
The enclosure itself doesn't have to be hard-sided. If you mount the drivers on the backpack, you can use the inside of the backpack (maybe stuffed with foam) as your enclosure to deal with cancellation from the back wave (the real main reason we build a box at all). Most people hear upper bass and think it's deep bass. If you cut below 75hz, you can get much louder since you won't be trying to produce frequencies that you can't actually produce with that kind of setup anyway. A lot of car stereos have a lot of apparent bass, but it's really mid to upper bass played really loud and over-equalized. The size of the bass wave tends to be bigger than the compartment of the vehicle which means that there are often all sorts of crazy things going on below 100hz.
Anyway, it also saves on weight and expense.
The enclosure itself doesn't have to be hard-sided. If you mount the drivers on the backpack, you can use the inside of the backpack (maybe stuffed with foam) as your enclosure to deal with cancellation from the back wave (the real main reason we build a box at all). Most people hear upper bass and think it's deep bass. If you cut below 75hz, you can get much louder since you won't be trying to produce frequencies that you can't actually produce with that kind of setup anyway. A lot of car stereos have a lot of apparent bass, but it's really mid to upper bass played really loud and over-equalized. The size of the bass wave tends to be bigger than the compartment of the vehicle which means that there are often all sorts of crazy things going on below 100hz.
Anyway, it also saves on weight and expense.
You put them in the wrong order.
The length of the low bass waves IS longer than the length of the car interior - which is precisely why cars have so much low bass. Also, because there's a smaller space to pressurize, any woofer will sound louder and lower in a car than in a room. And as i said, i'd lower the cutoff freq of the highpass filter to 60Hz, cutting at 75 might be a little bit extreme. Make the filter 4th order otherwise it'll still be a waste of power.
The "room gain" area with car audio is (depending on the vehicle) in the order of 60~80 Hz; below that you get a natural increase in frequency response that is at least 3dB/octave but in practical terms you may see response that is often higher due to the nature of subwoofer frequency responses (ie ... not flat). There is a certain corollary to that (probably not the right word but ...) in that, even though you will measure a higher response than flat in the low bass, it sounds fine since you are, in effect, sitting inside the enclosure. In other words an elevated response in a car sounds "more right" where it might sound elevated in a conventional room.
This is all kind of dancing around the issue with your application, but to tie it all together it's common with music intended for popular consumption as compared to, say, Beethoven's Fifth, to elevate the second/third harmonics of the low bass frequencies with a DSP application in the studio when mastering the bass and drum tracks, so that the fundamental isn't really that important anyway, at least in terms of getting an enjoyable musical experience out of a song.
If you can get even close to 60 Hz in free air you will be fine; it won't sound bass shy. By way of example, a typical laptop's built-in speakers have virtually nothing below 200 Hz, yet pop music played back on one (try a YouTube video) has recognizable bass notes, apparently. That's all you really need. A driver with a bump in your box in the 100 Hz+ area would be quite effective, subjectively. You can always take the backpack off and put it into a corner, elevating what bass you do have, and taking advantage of how the typical modern disk is mastered.
Driver efficiency is probably one of the critical areas to look at, and I mean that in the sense that you should prefer efficiency over low frequency response when making a driver choice; not only is it "free power' in terms of your limited amplifier choices, the more you can run at lower current demands, the longer the batteries last.
Piezos have a bit of a bad rap, since they "can" be run without a crossover as they have a natural low cutoff but tend to sound harsh near that frequency, but if you do employ a "real' crossover taking that a bit higher, they sound decent. They are stupid efficient.
I mentioned the CTEK chargers earlier for SLA batteries specifically because I have had excellent results from them. CTEK is from Sweden; if you buy a BMW, Mercedes, or Yamaha branded charger, it's a CTEK. Ripple below 100 mV, I can use a Tripath based amplifier with the charger in the circuit with the penalty of a very slight audible hum only, and your SLA will definitely last more than a few years with one.
I've personally used the CTEK 3300 to bring "dead" car batteries back to serviceable life that other chargers would not even initiate a charge cycle on. They make a less expensive model, the 3300 has a cycle for "Optima" style batteries that I need. I've sold all my other Lead Acid battery chargers; they're not in the same league.
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Yeah, PVC enclosure! 
Simple, cheap and works really fast when you choose a driver that fits nicely...
Here are some examples of things I have built over the past few years:
Mounted on my bike:
Backside with the inputs and 12V power socket, a mains socket for the built in PS...
Finally with power switch and led:
Mini active speaker:
The first little dark brown PVC speaker is the most impressive of them all using a 41hz AMP32 and two SPH-30X drivers. I have pulled some passive preamp tricks out of my sleeve that make it sound extremely impressive. Also highpass at around 80hz, it's got isolated audio inputs, so you can power the source from the same PS and it won't suffer from ground loop noise. For a system so small and light (700 grams!) and waterproof it is extremely good sounding and loud!! I have sold a few of them, the last one to a guy in the US and he recently mailed me back how impressed he and his friends are by the way it performs....
I've got similar speakers, but a bit more shabby in my car. It's a larger diameter PVC sewage pipe with Monacor SP-60, which is a pretty cheap 4"driver that sounds several times as good as it costs. As tweeters I have used the DT-284, which is also an amazing silky soft sounding tweeter, excellent for car audio. You might think I am a salesman for Monacor or something, well I have been using them for about 20 years and they never let me down and they have such a good price/performance ratio....
My humble car speakers:
Simple, cheap and works really fast when you choose a driver that fits nicely...Here are some examples of things I have built over the past few years:
An externally hosted image should be here but it was not working when we last tested it.
Mounted on my bike:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Backside with the inputs and 12V power socket, a mains socket for the built in PS...
An externally hosted image should be here but it was not working when we last tested it.
Finally with power switch and led:
An externally hosted image should be here but it was not working when we last tested it.
Mini active speaker:
An externally hosted image should be here but it was not working when we last tested it.
The first little dark brown PVC speaker is the most impressive of them all using a 41hz AMP32 and two SPH-30X drivers. I have pulled some passive preamp tricks out of my sleeve that make it sound extremely impressive. Also highpass at around 80hz, it's got isolated audio inputs, so you can power the source from the same PS and it won't suffer from ground loop noise. For a system so small and light (700 grams!) and waterproof it is extremely good sounding and loud!! I have sold a few of them, the last one to a guy in the US and he recently mailed me back how impressed he and his friends are by the way it performs....
I've got similar speakers, but a bit more shabby in my car. It's a larger diameter PVC sewage pipe with Monacor SP-60, which is a pretty cheap 4"driver that sounds several times as good as it costs. As tweeters I have used the DT-284, which is also an amazing silky soft sounding tweeter, excellent for car audio. You might think I am a salesman for Monacor or something, well I have been using them for about 20 years and they never let me down and they have such a good price/performance ratio....
My humble car speakers:
I built a truly portable system like you are thinking about, but in a 16 liter cooking pot. The cost and time adds up if you are not careful.
I've found that digital crossovers will save a lot of time and make speakers more efficient (no resistors in the crossover turning energy into heat).
The "Econowave" inspired speakers below should be crossed around 1.2 kHz and will sound very, very good. Econowave is a speaker designed by people on the discussion boards who like to test speakers and aim for wide dispersion. I've included the horn they use.
- Crossover and amp ($150)
MiniAmp/MiniDSP combo:
MiniDSP - miniAMP
(Alternately, for the same price and a little bit more wiring you can get a 100 watt tripath amp from Sure and the DSP board without the amp)
- Battery holder: 10 AA battery holder ($10)
Battery holder for 10 AA batteries with wire leads.
- adapter to connect iphone to minidsp/amp ($5)
- Eneloop AA batteries X 10 ($25) for 12V system
- wire /extension cord to cut up ($5)
Econowave inspired speaker :
-Waveguide ($13)
Dayton Audio H6512 6-1/2" x 12" Waveguide 1" Threaded | Parts-Express.com
(the famous waveguide)
- Eminence alpha 6 ($40) does 94db/watt and will work ok in enclosures down to 5 liters:
Eminence Alpha-6A 6" Midrange 8 Ohm | Parts-Express.com
(you can port it to get down to 100 Hz at high volume, or 80 Hz at around 12 watts with these. It will be plenty loud at 12 watts)
-Horn driver ($25)
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-204
(or pay a $50 and get nicer highs with this: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-270)
-Sonotube enclosure for alpha 6, some crossbraced thin plywood, or use a cooking pot as an enclosure ($15) (see my speaker here: http://www.flickr.com/photos/72376551@N00/5051992190/in/set-72157624970380057/ )
-The volume control is your ipod, so all you really need is a plug between the battery pack and the speaker to turn it off and on (or wire a switch).
I've found that digital crossovers will save a lot of time and make speakers more efficient (no resistors in the crossover turning energy into heat).
The "Econowave" inspired speakers below should be crossed around 1.2 kHz and will sound very, very good. Econowave is a speaker designed by people on the discussion boards who like to test speakers and aim for wide dispersion. I've included the horn they use.
- Crossover and amp ($150)
MiniAmp/MiniDSP combo:
MiniDSP - miniAMP
(Alternately, for the same price and a little bit more wiring you can get a 100 watt tripath amp from Sure and the DSP board without the amp)
- Battery holder: 10 AA battery holder ($10)
Battery holder for 10 AA batteries with wire leads.
- adapter to connect iphone to minidsp/amp ($5)
- Eneloop AA batteries X 10 ($25) for 12V system
- wire /extension cord to cut up ($5)
Econowave inspired speaker :
-Waveguide ($13)
Dayton Audio H6512 6-1/2" x 12" Waveguide 1" Threaded | Parts-Express.com
(the famous waveguide)
- Eminence alpha 6 ($40) does 94db/watt and will work ok in enclosures down to 5 liters:
Eminence Alpha-6A 6" Midrange 8 Ohm | Parts-Express.com
(you can port it to get down to 100 Hz at high volume, or 80 Hz at around 12 watts with these. It will be plenty loud at 12 watts)
-Horn driver ($25)
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-204
(or pay a $50 and get nicer highs with this: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-270)
-Sonotube enclosure for alpha 6, some crossbraced thin plywood, or use a cooking pot as an enclosure ($15) (see my speaker here: http://www.flickr.com/photos/72376551@N00/5051992190/in/set-72157624970380057/ )
-The volume control is your ipod, so all you really need is a plug between the battery pack and the speaker to turn it off and on (or wire a switch).
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Too cool. Did you line that pot with fiber ior foam of some kind to cut down the resonance?
I just installed a MiniDSP in my boombox, just as an equalizer, as it's a full-ranger (CHR 70). Really easy to do, and replaced a pile of passive components both at the line and speaker level. Sounds better now, with much better bass. Great product and really easy to use.
--Buckapound
I just installed a MiniDSP in my boombox, just as an equalizer, as it's a full-ranger (CHR 70). Really easy to do, and replaced a pile of passive components both at the line and speaker level. Sounds better now, with much better bass. Great product and really easy to use.
--Buckapound
That would be great...
I have a 9vEQ with low cut @75hz ($50 behringer) but have not noticed a huge increase in run times with a 12v T-amp. EQ and compression of the MP3's made more of difference. DSP and HP filters are not essential for good sound with a nice driver/box IMOHO.
I have a 9vEQ with low cut @75hz ($50 behringer) but have not noticed a huge increase in run times with a 12v T-amp. EQ and compression of the MP3's made more of difference. DSP and HP filters are not essential for good sound with a nice driver/box IMOHO.
Resonances were not a problem in the end. These steps I took may have been overkill:
1) Used a super heavy commercial aluminum stockpot from cooking.com . The stiffness raises the resonances to very high frequencies.
2) One cross-brace attached with plumbers epoxy
3) Pink insulation
In the end, the cabinet was incredibly dead, rugged, and rigid.
I totally agree that the Mini-dsp will produce better bass!! It uses fewer resistors and has more capacity to direct amplifier energy to where it will be used the most effectively.
Protecting the woofer from breaking up when it reaches full excursion is half the battle. Bass-box pro can identify that frequency, and there probably is a free program somewhere that can do that.
A bass boost right before the low frequency cut-off can also flatten out the bass. This is what ported subs typically use (also open baffle and and super-small enclosures need EQ lovin).
You haven't mentioned the slope of the low cut. The reason why EQ'ing the music files themselves worked is because you can do very steep cuts with digital EQs. If you had the same in hardware, like the miniDSP mentioned by someone else, you would get the same increase in run time without having to edit every MP3.
My design is a bit different, I used four 13 cm full-range drivers from Visaton FR 13 4 Ohm version and did a small line array because I wanted directional sound and they don't need a crossover. I used a cheap car audio amp which I had available (I would prefer any D-class amp). Batteries are lipo (will be changed for a stronger ones, also lipo), box is made from fiberglass and carbon and so everything comes together around 5 kilograms of weight.
Sound is very nice for a simple setup and because it uses four drivers it can play very loud. As mentioned in thread, when used with players that have equalizer I usually set to minimum frequencies below around 60 Hz, it doesn't effect sound much, but it can play louder and longer.
After all I'm satisfied with result, but if I did it again I would use 10 cm drivers instead of 13 cm to get a bit smaller backpack.
And here is a video of backpack in action YouTube - wwwrolanjeeu's Channel
It is easy enough to carry it around for two hours without problems, well that is the longest time I did carry it.
Sound is very nice for a simple setup and because it uses four drivers it can play very loud. As mentioned in thread, when used with players that have equalizer I usually set to minimum frequencies below around 60 Hz, it doesn't effect sound much, but it can play louder and longer.
After all I'm satisfied with result, but if I did it again I would use 10 cm drivers instead of 13 cm to get a bit smaller backpack.
And here is a video of backpack in action
YouTube - wwwrolanjeeu's Channel It is easy enough to carry it around for two hours without problems, well that is the longest time I did carry it.
Attachments
Here is my portable party backpack I have been perfecting this for the last 10yrs. It weighs 12lbs total, backpack, speakers, amp, and battery. Has great sound and gets pretty loud. I ski with it.
Speaker Backpack - YouTube
In the wild Copper Mountain Colorado.
Perfect Spring Day at Copper Mountain April 2013 - YouTube
Speaker Backpack - YouTube
In the wild Copper Mountain Colorado.
Perfect Spring Day at Copper Mountain April 2013 - YouTube
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