4th Order Bandpass pictures of design... port/sub placement...

[rickymac21 10+ year member]

Well I finally decided to go with the 4th order bandpass for my trunk install... Basically I have the cu ft for both sealed and ported chamber... Now I just need help deciding on the two options shown below.

This first picture is a TOP view looking down into the box... The sub and port are firing in the same direction which if in the trunk would be into the cabin of the car... This was my first idea but after reading apparently having the port right in front of the sub like this isn't a good idea as it'll mess with performance output ... Any thoughts on this one??



This second picture is a SIDE view of a different design than the one above ^^. In this design the sealed section has the sub firing up, while the port direction stays the same as the first desing (port fires into cabin)...



Both boxes are would have the same dimensions externally, but the sealed chamber changes obviously. Regardless, the number of cubes per chamber wouldn't fluctuate between design, nor would the tuning. The only change is the sub firing direction and my question is which is going to be better?

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[rickymac21 10+ year member]

Bueler......Bueler

 

[Buck 5,000+ posts]

You could do #2 and have a 45 degree slanting baffle so you won't have that awkward gap above the sub.

 

[bbeljefe]

The second design is good, the first is not. But, with the second design for a 15, you'll need bracing in the center of the box because the top, which needs to be removable, will be a large panel. It would also be good to laminate that panel for added strength.

Oh and, I've modeled a few boxes for that driver so far but haven't had much luck getting a wide enough passband. I'm thinking that driver wants to be in a 6th order, as the EBP is somewhere around 75. But, I'll keep trying on the 4th order.

 

[rickymac21 10+ year member]

The second design is good, the first is not. But, with the second design for a 15, you'll need bracing in the center of the box because the top, which needs to be removable, will be a large panel. It would also be good to laminate that panel for added strength.
Oh and, I've modeled a few boxes for that driver so far but haven't had much luck getting a wide enough passband. I'm thinking that driver wants to be in a 6th order, as the EBP is somewhere around 75. But, I'll keep trying on the 4th order.

I had someone else tell me they've used the xfl in a 4th order with success. But I'm kind of open to options for the sub. As long as its not too pricey ($300 give or take). Do you have any other options? If I can get 2 lower end 15's (AB tnt's... AB xd's... Sdc2.5) or even an 18 would be good. RE SX 18... Hdc3 18... Fi ssd.

Those are just what I've found in that price range. You have any idea what would work well in the 4th order?

 

[bbeljefe]

I had someone else tell me they've used the xfl in a 4th order with success. But I'm kind of open to options for the sub. As long as its not too pricey ($300 give or take). Do you have any other options? If I can get 2 lower end 15's (AB tnt's... AB xd's... Sdc2.5) or even an 18 would be good. RE SX 18... Hdc3 18... Fi ssd. Those are just what I've found in that price range. You have any idea what would work well in the 4th order?

Success is a subjective term, especially where loudspeakers are concerned. If you're looking for extreme SPL in a narrow bandwidth, then the boxes I've modeled so far would be great. But if you're looking for sound quality (wide passband) then we haven't had any yet.

The graph above shows a few boxes I've modeled for the AB driver you selected. The light blue graph is the widest bandwidth possible and is the box WinISD recommends for this driver. It's flat and has a reasonably wide passband but it's -3dB at 29hz, which means it isn't going to be very efficient on the lows. It's also a pretty small box at just over 3 cubes total. Using the same ratio WinISD recommended, I modeled two others (actually, I've modeled about 8) at a lower frequency and larger volumes, with opposite ratios for Fb & Fr. They both slam the low 30s but as you can see, they fall off steep on both ends. The problem here is that this driver has a high EBP (Efficiency Bandwidth Product).

EBP is derived by dividing the driver's Fs by its Qes and here's what it tells us:

1-50 = Driver should be used in sealed or 4th order box.

51-99 = Driver can be used in either sealed/4th order or ported/6th order.

100+ = Driver should be used in ported/6th order.

That's a rule of thumb I've heard a lot but I've found that drivers above 50 don't usually work well in sealed/4th order alignments. That said, there are other factors so it's not a waste of time to model a driver with an EBP higher than 50. The XFL1544 is at 56 so it should be okay in a 4th. And to clarify, I think I said 74 in another post but clearly, I didn't do my math correctly so, I'm sorry about that confusion.

In any event, if 4th order is the best alignment for you, I'd recommend a driver with a low EBP. The TNT1544 has an EBP of 50.8. The XD1544 is 46 and the Sound Qubed Sdc2.5 15 is also 46, so either of those would be a likely choice.

Here are those two drivers:

Teal and green graphs are WinISD recommended for the SQ and AB drivers, respectively. Yellow and white are my modeling for them. Each box is:

Vf - 3ftⁿ

Vr - 6ftⁿ

Fb - 36hz

Vent = 6" x 14.82"

The SQ has a higher acoustical peak (+7dB @ 36) and both hit -3dB at 23hz, so they will play the lows well. The SQ also extends slightly higher than the XD but both of them hit -3dB on the high side at 56hz.

If you're looking for loud, I'd go with the SQ but if you're looking for a more smooth response curve, the XD would be better. And, if you're looking for pure sound quality, I'd go with WinISD recommended volumes for either driver. Although, the SQ does extend a bit lower on recommended volume.

 

[rickymac21 10+ year member]

I can't thank you enough Bbeljefe... I appreciate you going out of your way to give me such a detailed answer and information. You just taught me so much in that one post and that's why I love this forum..

Never the less, I think I might go ahead and try out the sdc2.5's seeing as it appears it'll play a relatively similar range as the xd's, just a bit louder... Yes? ....

3 cu ft sealed TOTAL I'm assuming? so 1.5 cu ft per 15?

6 cu ft ported TOTAL.

tuned to 36 hz (Is this just a unique driver for bandpass? I've read most people end up having to tune to 45 hz in bandpass)

Thanks again for the help.. I hope when this thing is all said and done it just rips people apart..

 

[rickymac21 10+ year member]

In any event, if 4th order is the best alignment for you, I'd recommend a driver with a low EBP. The TNT1544 has an EBP of 50.8. The XD1544 is 46 and the Sound Qubed Sdc2.5 15 is also 46, so either of those would be a likely choice.

Here are those two drivers:

Teal and green graphs are WinISD recommended for the SQ and AB drivers, respectively. Yellow and white are my modeling for them. Each box is:

Vf - 3ftⁿ

Vr - 6ftⁿ

Fb - 36hz

Vent = 6" x 14.82"

The SQ has a higher acoustical peak (+7dB @ 36) and both hit -3dB at 23hz, so they will play the lows well. The SQ also extends slightly higher than the XD but both of them hit -3dB on the high side at 56hz.

If you're looking for loud, I'd go with the SQ but if you're looking for a more smooth response curve, the XD would be better. And, if you're looking for pure sound quality, I'd go with WinISD recommended volumes for either driver. Although, the SQ does extend a bit lower on recommended volume.

BbelJefe, I am going to be constructing this 4th order here within the next week and just wanted some clarification. Were these graphs modeled with (2) 15" woofers??? If so according to your specs I should give each TNT 15 a sealed chamber of 1.5 cu ft and the shared ported chamber should be 6 cu ft... Is this right? I'm assuming so as 3 cu ft sealed seems like a lot for a single 15, but then again I've never done a 4th order before... Appreciate the help

 

[Jroo 10+ year member]

somebody correct me if Im wrong, but a 4th order tuned to 36hz wont play up to 50 after roll off. Depending on application, it might not even play up to 45. So unless you have hella midbass that digs down below 50, you are building a box that basically will only play 45 down. This could also be what you want, dont know?

 

[bbeljefe]

BbelJefe, I am going to be constructing this 4th order here within the next week and just wanted some clarification. Were these graphs modeled with (2) 15" woofers??? If so according to your specs I should give each TNT 15 a sealed chamber of 1.5 cu ft and the shared ported chamber should be 6 cu ft... Is this right? I'm assuming so as 3 cu ft sealed seems like a lot for a single 15, but then again I've never done a 4th order before... Appreciate the help

Yes, those boxes are plotted assuming two woofers.

 

[bbeljefe]

somebody correct me if Im wrong, but a 4th order tuned to 36hz wont play up to 50 after roll off. Depending on application, it might not even play up to 45. So unless you have hella midbass that digs down below 50, you are building a box that basically will only play 45 down. This could also be what you want, dont know?

If you look at the above graphs you'll notice that all of the models are flat at or very close to 50 Hz and the two flattest ones don't go -3dB until ~60 Hz.

So no, there is no rule that says 4th orders tuned low can't play above 45. And yes, depending on the application, some will play well above 50 and others not so much. That's why it's a good idea to model a lot of different boxes for the same driver before making a final decision... so you can get the maximum bandwidth. Unless you're building a burp box, of course.

 

[rickymac21 10+ year member]

Most music listened to the bass rarely exceeds 55 hz anyways (rap that is). And if it did, why would anyone want to hear such a noise? Notes that high sound like a boat horn and are in no way pleasurable to listen to. Just my opinion. I'd much rather have a shorter bandwidth that digs down into the 20's so I can shake someone else's mirrors at a red light, and still peak at a solid 35- 40. No need for the highs if I don't want em. It'll "sound" louder tuned lower anyways, even though the term lab will say different

 

[Beatin' 10+ year member]

And if it did, why would anyone want to hear such a noise? Notes that high sound like a boat horn and are in no way pleasurable to listen to.

Oh man, I love bass up to at most 100hz. Sounds great to me! I'm in the process of building a 4th that will play from +2db 100hz to -3db 47hz.

 

[rickymac21 10+ year member]

Oh man' date=' I love bass up to at most 100hz. Sounds great to me! I'm in the process of building a 4th that will play from +2db 100hz to -3db 47hz.[/quote']
Really? To each his own I suppose. Personally I feel like bass is meant to be played low and move a lot of air. MAYBE if I was building a comp box I'd tune up there, but for everyday listening, no way... But that's why we design and build it ourselves, get what we really want out of it.