The Most efficient DIY sub under 2cft

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I've been following alot of subwoofer builds in the last few months, and have grand plans to build different sub woofers for my room, my car, etc. I even have a few drivers waiting. But a few things went wrong, and now I'm going in a completely different direction - I now need something as efficient as possible.

SO here is my question - for those who have been keeping their eyes on recent DIY efforts for subwoofers, at or below 2 CUBIC FEET - 50 L, for freq 30-80Hz which are the MOST EFFICIENT designs?

The reason for such requirements are that this sub will be powered by only about 50-70W RMS, and I listen loud. Its going in a car, so the < 2cft, cabin gain helps, but I would like a "rising response" as described by The Subwoofer DIY Page - Projects : A car subwoofer with cabin gain compensation instead of a flat one. I only really NEED 40-80Hz, which is only 1 octave, but going lower would be nice. I'm thinking, minimum 95db per w. but higher the better

I've done a bit of research. High efficiency brought me to look at horns, and the best designs fall to BFM's tuba family of FLH. But its a bit big and it really just goes down to 40Hz.

Wanting a little smaller and lower brings me to read up on all the recent tapped horn efforts, with the TB w6, MCM8, Jbell's single sheet, the unhorn, insubnia. etc.

But the problem with reading DIY forums on speaker designs is that I don't have the knowledge and experience to tell just exactly how efficient each design is - some of them are measured, but not many of them can be compared directly. Further more, a few of these designs, seem to not even beat ported designs of comparable size with a larger driver.

So here I come and ask you sub masters, what can I expect from 2cft in terms of efficiency - in the BW of 30-80Hz only. Is 95db per w or more possible in a car?

But I did not post this is the car forum, because if I find something that works, I'm going to be building one for my room too :)
 
After many TH, FLH, etc high efficiency pa designs... and the last xxx years in car audio before going pa... I'm still of the opinion that a small sealed sounds best in-car. That's not to put down unhorn, ported, bandpass, or any of the other interesting designs out there.

To show my point: Here's a simple sim of the lowly 55-2421. (ok, 8 of them) That fit your requirements. Even a 3015lf in a 50liter sealed will accomplish your stated goal.

I've put some thought into this as well of late -- I now have a new tundra crewmax that I'm in the process of putting stereo in. Yea I have room to do a TH, and it looks better spl-wise in hornresp... but the 50hz response (that is flat in 2pi space) just sticks out WAY too much and makes it sound way too 'one note.' After much thought, a sealed quad of 55-2421 with a massive nanoblock was the smallest, loudest design I could come up with -- without sacrificing any behind seat space.

Years ago, there was a saying I'd heard: "For sq, at some point everyone will come back to a sealed 10." There's a lot of wisdom in that saying.
 

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Thank you Jbell for your insight, I'm honored to listen to your advice, from all the horn subs I have read, you seemed to have achieved the best.

I have only tried ported and sealed in my car - and I was always happy with my 2x10" ACI SV10 sealed in 1cft. Very happy in fact. I was steal reading all the TH and whatnot, it was fun, but then disaster happened. Somehow my headunit decided to have huge noise problems with the pre-outs. Some grounding problem somewhere I assume, I reinstalled amps, cleaned up wires, moved things around, and whatever I do, I can't fix the noise problems - The amps on their own are fine, but once the RCAs are connected, popping sounds, high/low freq noise, whines, everything comes through in huge volume.

My temp solution - I hooked up the Headunit speaker outputs for the first time, bypassing the amps, then I built simple 1st order passives XO for my front speakers, no sub.

I have tried everything, the only I have left to do is to get a new HU, but I have one of those $1k nav computer touch screen headunit which I can't just ditch and get a new one. So, my solution - to simply. Use the 20w RMS x4 from the HU to power everything. I am almost happy with my front end with just 20W per channel - I was using 100W before! As long as I high pass the mids high enough - right now at 80Hz.

The rear 20x2W output can be bridged into 70W rms into 2ohms. This, is what I planned to power my "still non existent sub"

The problem is that I do listen to music very loud in my car - as in clubbing level. In fact, thats the only place where I can enjoy real electronic/trance music in full blast other than in a club - thanks to cabin gain. I can't achieve that in home. Obviously I love the horn sound in clubs. So what that means is that I am not aware any sealed alignment that will be efficient enough to satisfy my thirst for loud bass with a mere 70W!

And then the next thing is that if I can find something that is efficient enough, be it a TH or FLH or what not, I have friends who are on super tight budget that would love to get a nice sub in their trunk - without having to spend time and money on high power amps and upgrade electrical systems etc. And those head units I bet I cant even bridge the rear - so a mere 20W might be all I get!

So, thats why I need something 95db+, preferably 100db per watt, that means i can get up to 110-120db with 70W. I got a feeling that I am asking for something impossible, not in 2cft anyway. But it doesnt hurt to ask right? But if I can't get 100db per watt in 2cft, what CAN I get? Whats the best I can find? One thing that helps is that I really only need 1 octave of bass - 30-80, maybe even 40-80, or 30-70. Something along those lines....

What do u think, am I thinking this the wrong way?

btw, are u saying that 8xMCM8" in 2cft or a 3015lf in 2cft will get me 110-120db with 70W RMS at 2ohms?

best regards
 
I have had to sit on what you said for a few days. Really think about it.

I have tried using the high lvl outs, doesnt seem to help. I used these:

High To Low Adapter with Male RCAs | Parts-Express.com

I have also considered sealed with many many smaller drivers to increase efficiency, and looked at sealed for large pro drivers like the one you suggested. The problem is, the roll off just seems too early. All of these drivers want to be vented at the least. The roll off probably helps to get flat response with cabin gain, but with an F3 of 80Hz or so just seems awfully early. I just keep thinking with sealed I am not using the driver's capabilities, almost wasteful, and I thought this would be a great chance for me to try the horn sound everybody has been raving about. Mind you, I am so tempted to just order a 3015LF and use it sealed for now until I get a horn design I can use for the car. In the meantime I can see if I actually like that sealed idea, and also, I would have the perfect excuse to build one of your monster tapped horns using the 3015LF for HT. But that thing is not cheap....and most importantly, a 3015LF is 8ohms, so thats 10W of clean power my HU will be putting out.....that will not work.


The thing is, I DO have eq at 40Hz and 80Hz from my headunit, so I do have a little response shaping power.

Have you implemented the quad 55-2421 in your truck yet? If so, how is it working out? How many watt are you feeding it before excursion runs out? And is it "clean bass" like the horns you have built?

You seriously think that as of now, theres nothing out there horns wise that is worth putting into a car? Even with the extra efficiency and SPL capabilities? I know thats the first thing you said in your first replay, but its just so hard to believe! But if its from the guy who has built the most successful horns, how can i argue!

mwmkravchenko has kindly agreed to help me, he is also trying to optimize a design that is small and efficient. we'll see what we can come up with. Whatever it is, I'm long way to having bass in my car!
 
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And just for fun, here's a design using a little 8 inch mid-bass driver (Eminence Alpha 8A) that delivers the goodies.

An amp capable of 10W into 8 ohms (or 20W into 4 ohms) can drive it to Xmax in band and close to Xlim out of band, so it's ideal for those little bridge amps that run straight off the "12V" battery.

I've no idea how "room gain" works with horns in cars though.
:Pawprint:

p.s. I've been thinking about this for home use - 115dB over 2 octaves with a 10 watt amp - yum!
 

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I have had to sit on what you said for a few days. Really think about it.

I have tried using the high lvl outs, doesnt seem to help. I used these:

High To Low Adapter with Male RCAs | Parts-Express.com

I have also considered sealed with many many smaller drivers to increase efficiency, and looked at sealed for large pro drivers like the one you suggested. The problem is, the roll off just seems too early. All of these drivers want to be vented at the least. The roll off probably helps to get flat response with cabin gain, but with an F3 of 80Hz or so just seems awfully early. I just keep thinking with sealed I am not using the driver's capabilities, almost wasteful, and I thought this would be a great chance for me to try the horn sound everybody has been raving about. Mind you, I am so tempted to just order a 3015LF and use it sealed for now until I get a horn design I can use for the car. In the meantime I can see if I actually like that sealed idea, and also, I would have the perfect excuse to build one of your monster tapped horns using the 3015LF for HT. But that thing is not cheap....and most importantly, a 3015LF is 8ohms, so thats 10W of clean power my HU will be putting out.....that will not work.


The thing is, I DO have eq at 40Hz and 80Hz from my headunit, so I do have a little response shaping power.

Have you implemented the quad 55-2421 in your truck yet? If so, how is it working out? How many watt are you feeding it before excursion runs out? And is it "clean bass" like the horns you have built?

You seriously think that as of now, theres nothing out there horns wise that is worth putting into a car? Even with the extra efficiency and SPL capabilities? I know thats the first thing you said in your first replay, but its just so hard to believe! But if its from the guy who has built the most successful horns, how can i argue!

mwmkravchenko has kindly agreed to help me, he is also trying to optimize a design that is small and efficient. we'll see what we can come up with. Whatever it is, I'm long way to having bass in my car!

First:
Your high level to low level converter looks to be the resistor dividing kind, and does not have an isolation transformer. Meaning -- whine&noise in = whine&noise out. A $10 high to line level with noise isolation (transformer) should kill any noise and/or ground loops to your amps. I would always fix the original problem first... I've even used these successfully: Amazon.com: PAC SNI1 Noise Isolator: Automotive The fact that your high level to line level converter shows the exact same issues as your preouts tells me your pres are fine. It's just a grounding issue, or even an amp issue.

Second:
Mark is a great guy, and has spent lots of time on various designs, if he's helping out, you're in good shape. The fact that I've had some success in designing some PA cabinets, does not necessarily make my opinion any more valid than any one else. There are MANY on this board that have a wealth of knowledge, and are willing to share.

Third:
My take on sealed subs in car audio is based on the fact that you have a somewhat 'sealed' cabin. The entire idea of a horn is based on acoustically coupling the air to the sub driver (high pressure/low volume to low pressure/high volume) so that you can effectively create a wave that will transmit bass in an unenclosed space. Where you have a somewhat enclosed space, a sub design that only presents one side of the driver to the cabin, can actually change the pressure inside that cabin. It's this pressure change that you can feel, and is why (my opinion) a sealed sub always sounds different than any other design in car. That is not to say that ported, bandpass, hybrid, tapped, front loaded, or even rear loaded horns can't be used effectively in car.

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While I appreciate your desire to come up with a sub design that will work based on low wattage, it's not the problem you should 'really' be addressing. Car audio in my experience has always been about the battle of the 1/4 inch... What works best is what fits -- first and foremost. There are huge compromises you have to live with. I just got my polks installed in my front doors last weekend, and they are within 1/8" of not fitting, as an example. (no the quad mcm is not installed yet.)

fix your whine/ground issue -- that's the real solution here.
 
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