Too small sealed box, driver size.

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Too small sealed box, driver size. doing it properly now

Quick dumb question, I think it is more relevant to Subwoofers than car audio, at least academically so that's why i've posted the question here and not there.

If I was to build a sealed subwoofer box small enough to fit under, oh I don't know a seat in a car, would I get better low frequency performance using a 10" woofer or an 8" woofer?

I think the easy thing to do is buy an 8" woofer, buy a 10" woofer, make two boxes as big as I can, stuff them, then try both. the winner can go in my car, the loser can go in my wife's car.
 
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It's a question that unfortunately the answer to is "it depends". It all comes down to the parameters of the drivers that are available to you.

It is possible - choosing the best mix of parameters - to get a box that the 10 inch performs better than some other 8 inch driver. But equally it is possible for an 8 to outperform a 10. Very generally speaking, it will take a more expensive driver to outperform as the suspension will need to cope with extra travel and the voicecoil will need to cope with more power.
 
ended up building these, bought some 8" sherwood carbon fibre woofers off ebay as cheap speakers arent common in AU that do a pretty good fullrange impersonation. boxes are 9mm MDF (i hate MDF) as it was free, light and will give (marginally) more internal volume. had to rear mount the drivers due to space restrictions.

the boxes are wedge shaped as they had to go behind the seats, not enough room under them (they are in a small pickup truck)

bit too much midrange now so i'm kludging a low pass filter, the inductors I need cost about as much as the drivers did so i'm using some out of an off the shelf crossover, will add capacitor/s too.
 
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Get a used car amp with low pass filter built in. Probably cost about the same as the inductors but far better results.

I've got a spare I've been testing various crossover configurations with, it has a LP filter which confirms you are right, don't want to use it unless I have to as I can't be bothered running the power/ground/RCA cables for it and it runs the portable sound system for my projector.

I think i'll get there with the inductors I have and the capacitors that are on the way.
 
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bit of an update, have been running two of these in my small pickup, in general they sound "bad" and surprisingly don't go much lower than the 4" coaxials in the dash.

did a bit of tinkering today, first of all I holesawed a hole in the baffle of one, sounded marginally louder but definitely lost bass, then liberated that driver from the box and kludged an isobaric enclosure with the other one. Definitely has more low frequency response but still sounds bad.

might see if I can make another box to go with the isobaric theme, but space is pretty limited. might try building a box with the 10" sub out of my harman kardon HT sub that blew up its plate amp.

and a photo of my handiwork so far for anyone's amusement, rear mounting the loudspeakers had predictable consequences.

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In order to produce satisfying bass from a small cabinet you will need a driver with more motor strength .... You can derive motor strength figures by comparing the "BL factor" to the "Re" (voicecoil DCR), the formula is BL^2/RE , these numbers (BL and Re) should be provided by the manufacturer of any decent speaker .... If these parameters are not listed or not made available by the manufacturer then it is probably not a very good speaker , at least not good enough for critical applications such as this ....


Your best bet is too explore the options in "shallow mount" subwoofers for car audio ..... Some car audio subs are made specifically with "small box" parameters (strong motor and tight suspension) , because a small box is precisely what you are trying to accomplish here ...


as an example (even though these aren't all made specifically for car audio) : Dayton Audio LS10-44 10" Low Profile Subwoofer Dual 4 Ohm

or

http://www.parts-express.com/tang-band-w8-2022-8-rbm-subwoofer-8-ohm--264-955

or

http://www.sonicelectronix.com/item_95305_Infinity-REF1000S.html

or

http://www.sonicelectronix.com/item_36298_Rockford-Fosgate-R2SD4-10.html
 
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In order to produce satisfying bass from a small cabinet you will need a driver with more motor strength .... You can derive motor strength figures by comparing the "BL factor" to the "Re" (voicecoil DCR), the formula is BL^2/RE , these numbers (BL and Re) should be provided by the manufacturer of any decent speaker .... If these parameters are not listed or not made available by the manufacturer then it is probably not a very good speaker , at least not good enough for critical applications such as this ....


Your best bet is too explore the options in "shallow mount" subwoofers for car audio ..... Some car audio subs are made specifically with "small box" parameters (strong motor and tight suspension) , because a small box is precisely what you are trying to accomplish here ...


as an example (even though these aren't all made specifically for car audio) : Dayton Audio LS10-44 10" Low Profile Subwoofer Dual 4 Ohm

or

Tang Band W8-2022 8" RBM Subwoofer 8 Ohm

or

Infinity REF1000S 800W 10" Reference Series Shallow Mount Single Voice Coil Selectable Smart Impedance Car Subwoofer

or

Rockford Fosgate R2SD4-10 10" Shallow Prime Stage 2 Subwoofer

Thanks for that, the tang band looks great, oddly lowish power rating though.

keeping with the low budget theme I tried fitting a 10" sub from a ported HT sub I had lying around (amp blew up long ago) but it was too big to fit behind the seat.

I bought one of these via ebay as it was cheap and should just fit (Fusion isn't exactly a well regarded brand in Australia but I was going to buy a generic sub anyway) which was $40 AUD 10? Subwoofer (EN-SW101) | FUSION Entertainment

they recommend 15 litres for a sealed box, which should be doable, have roughed out a design but won't do more until it arrives as they don't have a drawing for it.
 
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oculi;... $40 AUD [url=http://www.fusionentertainment.com/car/products/subwoofer-encounter/en-sw101 said:
10? Subwoofer (EN-SW101) | FUSION Entertainment[/url]

they recommend 15 litres for a sealed box, which should be doable, have roughed out a design but won't do more until it arrives as they don't have a drawing for it.

Hi oculi,

Have a look at my :2c: of Sims and Calculations:

b:)

PS: The 15 Liter Sealed Box needs an Amp. with a built in PEQ.
 

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Hi oculi,

Have a look at my :2c: of Sims and Calculations:

b:)

PS: The 15 Liter Sealed Box needs an Amp. with a built in PEQ.

wow thanks! I only understand about half of that but I appreciate the effort.

it will have a conventional car amp (bridged for the sub and has an LP and HP filter) until the cheaper smaller stuff i order from ebay arrives. unless a parametric equaliser is very cheap i won't be employing one, but my standards and expectations are pretty low and I don't plan to measure the T/S parameters for this thing let alone correct anything.


using this calculator

I did some experimenting to see the effect of box volume on Qtc and was surprised at the large changes in volume required to change Qtc much, and determined that the 15 litre box with this driver will have a Qtc of 1.45 (very similar to your numbers) so if anything I need to make the box as bigger as I can, originally I thought I could get away with making it smaller, because I foolishly assumed the recommended volume would have a Qtc of 0.707 - 1.1 or so.

Forgive my noobness but the PEQ is to get rid of the 4dB hump at ~70 hz instead of using a bigger (just a bit bigger at 15000 litres or so) box? I was briefly considering an infinite baffle setup but didn't want to cut a hole in the cabin :)

This is basically a cheap learning exercise that gets to live in a cheap vehicle, I want to make a pair of sealed subs for my home stereo some day plus some other bits and this is a good stepping stone. A friend did all of the calculations for the last sub box I built, didn't realise the calculators were so simple to use.

Thanks again!
 
Hi oculi,

Have a look at my :2c: of Sims and Calculations:

b:)

PS: The 15 Liter Sealed Box needs an Amp. with a built in PEQ.


Don't forget to include the effects of the car's cabin gain. HornResp does provide the option to include a "room gain profile", and for a car this can be a few dB @ 80 Hz, reaching to over 24 dB @ 20 Hz. So, for car audio subwoofer design, the import part is what's happening between 80 Hz and below, and its power handling through that frequency range.
 
Sub arrived, looks fine. i'm starting to get a feel for T/S paramaters, which I have never paid much attention to until now (as per the first post in this thread) and it is starting to make sense, more on that when I do the next project.

It is going to be a tight fit, but should end up with a volume of a bit more than 15 litres and the passenger seat will still slide and recline all the way back.

Did some mockup with one of the old boxes with bits of plywood nailed to it, I considered MDF but I have 12mm ply lying around so I'm using that. Will be adding bracing, mostly externally.

Not sure if I should use normal woodglue or cinstruction adhesive to old everything together, considering using caulk to seal the joins, but woodglue seems to do this fine too.

anyway, progress. I could have got a bit more volume by removing the jack bracket but I don't really want to cut it out.

I think a better technique would be to make a very simple box and then cut it down until it fits, this is taking ages.

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those slimline amp/8" subs are looking pretty good now, if I had more money than time that's what I would be doing.
 
Baffle (3 overlapping panels which probably isn't ideal but needed to be done for clearance while maximising volume, and I didn;t have any single sheets big enough) glued up, the tricky side is glued up, goign to use the box as a saw guide to trim the baffle so it will fit in. Will finalise the position of the driver before mounting the baffle to the box.

I have some sheep's wool I might use to stuff this with if there is enough of it.

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construction update, turning into an exercise in something, not obsession exactly but it is taking a while.

baffle trimming went well, I've been using small nails to hold bits of wood where they need to go, they are then removed, glue slathered on and the nails lined up with the old holes to position them correctly. this doesn't always work, but is helpful often enough.

pic dump

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haven't checked the fit with the driver in yet, I put it as high as I dared without it poking out bast the back of the box (had to cut a hole in the panel and plate it as it was) so the seat cushion will get close to the cone, might have to add some standoffs to keep it (the cushion) away from it (the cone)

don't think I would use this method of construction again, too fiddly. an air compressor would make the job easier, my brad nailer is pretty unhelpful without one.

Still have to add two or three internal braces and lots of external bracing where it will fit. Not really sure what the volume is now, but close to 15 litres, which keeping in the spirit of the thread title is too small.

Apart from the warped bits plywood is much nicer to work than MDF!

and a winisd plot, assuming i'm using it right box volume would need to be 100 litres or so to get a "nice" shape, at 10,000 litres Qtc is 0.81 (and doesn't improve with more volume) so I'm wondering what this driver was designed for.

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Apart from the warped bits plywood is much nicer to work than MDF!

and a winisd plot, assuming i'm using it right box volume would need to be 100 litres or so to get a "nice" shape, at 10,000 litres Qtc is 0.81 (and doesn't improve with more volume) so I'm wondering what this driver was designed for.

Yeah, my woodworking/speaker building hobby began before MDF became available, so no-void [marine grade] plywood is what I was 'weaned' on for quality construction plus being involved in the electrical power distribution engineering part of the first plant here in the Deep South, all I learned about its manufacture was enough to keep it out of my life for the most part and wear a suitable respirator combined with plenty of ventilation when building with particle board in general and especially with M/HDF.

Open or infinite baffle, TL/BLH, Linkwitz-Riley Transform [LRT] sealed alignments [basically what bjorno posted] and 'boombox'/'one note' mobile audio apps.

GM
 
probably the last update for this, more shots of my, err, "workmanship" for anyone who is interested.

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Mounted the amplifier under the driver's seat, had to make some line level cables out of stuff I had lying around (the sub cables are yellow) should have just made Y cables as while the headunit has two sets out outputs they are, or might as well be wired in parallel. (can adjust L/R balance but not F/F fade)

I can adjust cutoff/gain from the drivers seat which is useful if you need something else to distract you while driving.

wired everything up, the 4" speakers in the dash are a poor match for the subwoofer but it works pretty well. Listened to it briefly before stuffing it moderately with slightly greasy sheep's wool.

from a cost perspective I'm pretty happy with it, but it took way too long to build. don't see much point painting it but I might to see how badly all the glue runs show up in case I make something else out of plywood.
 
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