help making a decision to buy a new subwoofer or not

Hello all,
Wondering if I could get some opinions here (what better place to go right?)
First I apologize for the long post.
Iam currently running a QSC 1400 in bridged mode ( 500 watts mono into 8 ohms) to a JBL 2235H 15" low frequency driver in a 5 cubic ft. enclosure tuned to 30 hz.
For both home theater and music listening the results are pretty impressive although I have somewhat of a hard time mating it with my full range ported towers.
Someone told me that the JBL is not by definition a true sub and I would need to get a "real" sub to get the appropriate results.
Here is what I am considering:
Dayton Titanic MkIII 15" sub in a 3 cubic ft sealed enclosure, using my QSC in bridged mode ( now 800 watts into 4 ohms)
Does anyone think this is a good idea? I've heard good things about the Titanic I am just not sure if I should change what I now have.
I have also heard people talk about a sealed box being quicker and punchier than a ported one . Does anyone with some experience in this have some good suggestions? (BTW for home theater - 80 hz, and down, for music 40 hz. and down using the x-over in my Acurus ACT 3 pre pro.


Any opinions would be greatly appreciated

Dave.
 

SpeakerBob

Member
2002-08-15 6:21 pm
UK
Your JBL models well against the 2226G used in the almighty subwoofer project here.

http://member.newsguy.com/~stigerik/almighty/index.html

Maybe you could try lowering the tuning freqency and building a slightly larger box.

As Bill said, 2 would be even better.

Cheers,

Rob
 

Attachments

  • jbljbl.jpg
    jbljbl.jpg
    42.3 KB · Views: 233
RobWells said:
Your JBL models well against the 2226G used in the almighty subwoofer project here.

http://member.newsguy.com/~stigerik/almighty/index.html

Maybe you could try lowering the tuning freqency and building a slightly larger box.

As Bill said, 2 would be even better.

Cheers,

Rob

Hi Rob
Do you think making the box bigger and lowering the tuning frequency will give me better performance? JBL reccomends a 5 cubic ft, box with 30hz, tuning, maybe this is good for full range use and not sub use?
fs on the driver is 20 hertz, should I be tuning towards fs instead?
Thanks Dave
 

SpeakerBob

Member
2002-08-15 6:21 pm
UK
fazman said:


Hi Rob
Do you think making the box bigger and lowering the tuning frequency will give me better performance? JBL reccomends a 5 cubic ft, box with 30hz, tuning, maybe this is good for full range use and not sub use?
fs on the driver is 20 hertz, should I be tuning towards fs instead?
Thanks Dave

Yes I do. JBL recommened enclosure is probably for PA use - doesn't factor in room gain. Lowering the tuning, and increasing the box size a bit will give you an EBS type roll off - should give you good extention, hopefully only 5 or 6dB down at 20Hz. Do a search for mike.e 's 2226 EBS on this forum to give you an idea.

A search on EBS and room gain should give you lots of info so you can make your own mind up.

Cheers,

Rob
 
RobWells said:


Yes I do. JBL recommened enclosure is probably for PA use - doesn't factor in room gain. Lowering the tuning, and increasing the box size a bit will give you an EBS type roll off - should give you good extention, hopefully only 5 or 6dB down at 20Hz. Do a search for mike.e 's 2226 EBS on this forum to give you an idea.

A search on EBS and room gain should give you lots of info so you can make your own mind up.

Cheers,

Rob

Rob, Thanks for this info- I have never heard of an EBS alignment before. Just did some reading on it and it seems to make sense when designing a ported sub to go deep in a typical living room.

I'm starting to see the light and that there may be some NEW life given to my JBL. (BTW I do own a second 2235H but it is not in an enclosure, just don't have the physical space for it in my room)

I have had this sub for approx. 6 years now and although I liked it I just couldn't get myself to love it's really deep bass performance. Maybe the 30 hertz tuning frequency is why I am having trouble mating it with my mains?

I lack the skill/sosftware to design a new enclosure for them - is there anything you or any one could reccomend for box size and port tuning to get to my 20hertz tuning frequency?
I will be reworking my existing cabinets (adding more enclosure space)
Esthetics is not an issue as the box is hidden out of sight

Very much appreciated you guys know your stuff
 
How big can you go?

10 cu.ft internal net tuned to about 18.4 Hz with two 4" diameter Precision Port would be perfect but that's too big for most people hehe!

EDIT: I see you have a 2nd JBL 2235H, go isobaric my friend!
You can keep your enclosure as is. Just put a woofer bolted on the front of your enclosure exactly in front of your other woofer. You wire it out of phase so it's in phase with your other woofer. You will need to change the tuning of your box, use a single full-length 4" diameter flared Precision Port, for a nice 18.4 Hz tuning, remove the old port and put this one instead. You might need to block the old hole and drill a new one because the Precision Port is 18 inches long and need clearance behind it if possible.
 
simon5 said:
How big can you go?

10 cu.ft internal net tuned to about 18.4 Hz with two 4" diameter Precision Port would be perfect but that's too big for most people hehe!

EDIT: I see you have a 2nd JBL 2235H, go isobaric my friend!
You can keep your enclosure as is. Just put a woofer bolted on the front of your enclosure exactly in front of your other woofer. You wire it out of phase so it's in phase with your other woofer. You will need to change the tuning of your box, use a single full-length 4" diameter flared Precision Port, for a nice 18.4 Hz tuning, remove the old port and put this one instead. You might need to block the old hole and drill a new one because the Precision Port is 18 inches long and need clearance behind it if possible.
simon5
Interesting!
But I thought only woofers that typically work well in sealed enclosures work well in isobaric configurations ( high xmax huge rubber surrounds etc) Theres no doubt these JBL's were designed for ported enclosures.
Do you really think this kind of design would work well for what I have?
If so, Do I need to leave any space between the two woofers, won't the surrounds on the woofer interfere with each other?
Also , my cabinet now has 2 four inch diameter ports each 11 inches in length.
How long would I have to make this 4 inch precision port you talk about?
I like where you are going with this as I don't have to get out my wood working tools to completely change my box around.
I can just here my 2 year old now "DADDY DADDY COME PLAY WITH ME! NO MORE SPEAKERS NO MORE SPEAKERS!

Can any of you relate to this one!

Simon5 waiting to hear from you on this issue!
Any one else think this is a good idea?
 
You would need to leave maybe 1/4 of an inch between drivers surrounds. Since anyway, when one is moving forward, the other one is moving backward.

Yes I think this design will work well, especially because you have already too much power with this beefy amplifier. You will need about 500W to get good output and you have 800W. You will lose some output, but the frequency response will be flatter and your subwoofer will go deeper. You will also get less distortion because of the isobaric operation.

For the ports, are they flared? If not, remove them.

If your box is really 5 cu.ft internal net, if the box dimension is approximately 22 inches long or more where one port hole is, then you can use one old hole for this new port :
http://www.creativesound.ca/details.php?model=4FP
This new port is 18" long and need 4" of clearance if possible.
Then close the other hole. If not, you might need to close two holes and drill a new hole somewhere.

If your ports are flared, just replace one of the center tube with a longer one, so it's around 18" long total with the flared ends. Remove the other port and close the hole.

It's not going to cost you alot of money, about 22$+shipping for the port and that's it. If you don't like it, then you can try something else.

Advantages : Same size box, deeper bass, flatter FR, less distortion.
Disadvantages : Power hungry, less SPL.
 
simon5 said:
You would need to leave maybe 1/4 of an inch between drivers surrounds. Since anyway, when one is moving forward, the other one is moving backward.

Yes I think this design will work well, especially because you have already too much power with this beefy amplifier. You will need about 500W to get good output and you have 800W. You will lose some output, but the frequency response will be flatter and your subwoofer will go deeper. You will also get less distortion because of the isobaric operation.

For the ports, are they flared? If not, remove them.

If your box is really 5 cu.ft internal net, if the box dimension is approximately 22 inches long or more where one port hole is, then you can use one old hole for this new port :
http://www.creativesound.ca/details.php?model=4FP
This new port is 18" long and need 4" of clearance if possible.
Then close the other hole. If not, you might need to close two holes and drill a new hole somewhere.

If your ports are flared, just replace one of the center tube with a longer one, so it's around 18" long total with the flared ends. Remove the other port and close the hole.

It's not going to cost you alot of money, about 22$+shipping for the port and that's it. If you don't like it, then you can try something else.

Advantages : Same size box, deeper bass, flatter FR, less distortion.
Disadvantages : Power hungry, less SPL.

Simon5
Thanks for this suggestion. I will try this with the second woofer .
For the ports for now I will close one of them off and extend the other using a coupler or elbow to get a finished length of 18 inches. I can always get the precision port later if I like the results, I may just experience a bit of port chuffing until then but at least I'll get the idea for now, because it is just black PVC piping.

Do you reccomend that I bridge the amp into a mono 4 ohm load running the 2 JBL's in parallel (one out of phase right?) or should I just use the 2 channels of the amp, one channel to one woofer and the other channel to the other woofer? This would give me 200 watts to each JBL.

If you are interested I will post the results when I'm done.

Thanks again Dave.
 
The Precision Port need to be 18 inches long because of the two flared ends. If you have no flares, just make it 17 inches long.

I don't know how you will separate the two woofers, I guess you'll figure out how to do a good airtight gasket hehe.

I guess since you need 500W, it would be better to run a mono 800W signal because you'll have at least some headroom versus 2x 200W. I think it's not that important, one or the other, the easier for you the better.

Yes, one need to be out of phase.

Yes, I'm interested by the results if you don't mind.

Good luck!
 
simon5 said:
The Precision Port need to be 18 inches long because of the two flared ends. If you have no flares, just make it 17 inches long.

I don't know how you will separate the two woofers, I guess you'll figure out how to do a good airtight gasket hehe.

I guess since you need 500W, it would be better to run a mono 800W signal because you'll have at least some headroom versus 2x 200W. I think it's not that important, one or the other, the easier for you the better.

Yes, one need to be out of phase.

Yes, I'm interested by the results if you don't mind.

Good luck!

simon5
just completed a makeshift version of the isobaric configuration of the 2 JBL's- plugged one port and added an elbow to the other although the exact port length is a little longer than the required 17 inches, also the 2 drivers' surrounds may be touching cause I'm gettings some noise- will have to devise some sort of gasket but man what a difference!
Absolutely NO overhang at all and HOLY DEEP!
Can't wait till the wife and kid go shopping so I can let this beast loose.
My sub never sounded like this before with just the one driver in the ported box.
I'll update with some more critical evaluations once I get everything done the way it should be done but if this is any indication I think I'm off to a great start.

simon5... You the man!
Thanks for your suggestions and thanks to everyone who responded, you all convinced me to keep my JBL's
 
Here's a few things I've learned.
With isobaric loading the FR is the same as that of a single speaker in double the enclosure volume. This is due to a halving of VAS while the other speaker parameters stay the same. The maximum SPL should be the exact same if not higher than that of a single driver in the excursion limited power region and +3db in the thermal limited power region.

If you mount your woofers clamshell(which I assume you did) the even order harmonic distortion will be canceled, although the amount by which distortion is lowered is probably less than using the two speakers seperate(using double cone area excursion is decreased and there's also mutual coupling benifits).

If you mount the woofers vertically the cone sag of both drivers will slightly INCREASE excursion due to the coils being both slightly off center(one speaker gets an extra millimeter or two of positive excursion, the other gets an extra millimeter or two of negative excursion and they add together). The effect is very similar to JBL's Differential drive technology.
 
fazman :

I'm happy that you like the results so far.

How did you do the gasket?

Pictures?

Check that noises aren't coming from the port. More air is moving than before from that port hehe!


BassAwdyO :

Moving mass is doubled, so you need to quadruple the power imput to stay at the same SPL. Why? I don't know exactly. Just model it in WinISD Pro and several websites on the web can probably explain this better.
 
well modeling in winISD shows that you do need 4 times the imput on a isobaric enclosure with the same sealed Q as a single speaker. But it does show some nasty inductive effects which makes me think theyre using series wiring.

I guess I had that backwards then, you lose 3db in the thermal limited power region, but the excursion limited region will the the same if not higher.
 
simon5 said:
fazman :

I'm happy that you like the results so far.

How did you do the gasket?

Pictures?

Check that noises aren't coming from the port. More air is moving than before from that port hehe!


BassAwdyO :

Moving mass is doubled, so you need to quadruple the power imput to stay at the same SPL. Why? I don't know exactly. Just model it in WinISD Pro and several websites on the web can probably explain this better.

simon5

I'm pretty sure the noise is coming from the two surrounds because they are definitely touching each other plus I didn't here any chuffing from the port although I haven't had it really loud yet.
I'm still yet to construct the gasket but I know what I will be doing- I will use half inch mdf and cut a ring that is the same width as the part of the woofer that that the screw holes are located- use a little silicone on both sides so it seals both woofers and send a long *** screw through the whole thing and into the cabinet. I think this should do it if you follow where I'm going with this!

One thing I will need to experiment with is whether or not to have the drivers facing the floor or to have them fire conventionally into the room (maybe some floor bounce/reinforcement will give better results we'll see.

When I get the thing completed I'll try to take some pictures although I don't have any intentions of painting it cause it's located ina storage room under the stairs firing into the room through acoustic grill cloth in the wall (pretty trick set up)

I'm just glad that I can finally use that second JBL that was sitting doing nothing
 
I don't recommend using them facing the floor unless if JBL said they are ok for up/downfiring operation.

You'll still get boundary reinforcement if they are not downfiring. Most reinforcement you'll get is in a corner of the room.

To test them, you just bolted the other woofer directly onto the other? Hehehe! Yeah, you'll be better with a gasket or it might damage the surrounds on the long run. Use a reasonably sized gasket, too thick the isobaric effect is not as good, not thick enough and the surrounds are in contact with each other.

Yeah, this is a very good setup because that JBL was doing nothing, you already had a 5 cu.ft box and you have already alot of amplifier power. You will now have a -3 dB point in room of about 16 Hz.

If I was you, after this is done, crank the amplifier and watch again the Balrog scene in the 1st Lords of the Ring if you're a fan hehe!