Looking to build 2x18" enclosure - PPSL?

[norman bates]

so, you have 2 x 18's in a 7ft3 box (sealed).

Ideally qtc .707 calls for Vb=5.9ft3 (each) for F3=Fsb=31hz.

But you have 2 in a 7ft3 box, yielding Qtc = .86, Fsb = 38.5hz, and F3 = 32.8hz.

Should be fine, you may want to add some boost, maybe not.

I wouldn't worry about too small of a plenum for the drivers.
Good luck mounting those drivers after the box is made.
I'd have the guy making it mount the subs.

 

[turbodawg]

Even with a pair of 18's, a sealed box isn't going to get you good output in the low teens. Why are you not building a ported box....???

 

[djk]

Because the port required for the huge x-max would make an already large cabinet huge.

If you have the space it could be done.

I made a 24x30x48 cabinet for a single 18 many years ago, it was installed in another room with a wall cut-out for ducting the sound into the listening room.

Another install had two 48" tall dual 15 enclosures and a 50" television mounted flush in the living room wall with the cabinets all inside a bedroom closet behind the living room. It made cable changes very easy, you just went into the bedroom closet. The ports for the dual 15 enclosures had to be huge, they went from the front to the rear, then through two 45° bends and halfway up the back of the enclosure. The bass was incredible, tight, detailed, and deep.

 

[MemX]

Thanks for the confirmation on the likely massive box sizes in a ported configuration, djk, I suspected as such! Your builds sound like they were pretty crazy 🙂

Even with a pair of 18's, a sealed box isn't going to get you good output in the low teens. Why are you not building a ported box....???

I have an SVS with 16Hz tune at the moment and it is good but I just feel I'm missing some 'weight' to some scenes on certain Blurays, so I was hopeful that I would achieve decent single-digit Hz output with a reasonable sized total cabinet volume with the above setup 🙂

The WinISD modelling I posted in post #8 of this thread seems to suggest the potential for 108dB @ 10Hz?
http://www.diyaudio.com/forums/subwoofers/242665-looking-build-2x18-enclosure-ppsl.html#post3639716
Hopefully that would be enough?

I will have to have a play with WinISD to see what box sizes it would give for really low ported boxes!

so, you have 2 x 18's in a 7ft3 box (sealed).

Ideally qtc .707 calls for Vb=5.9ft3 (each) for F3=Fsb=31hz.

But you have 2 in a 7ft3 box, yielding Qtc = .86, Fsb = 38.5hz, and F3 = 32.8hz.

Should be fine, you may want to add some boost, maybe not.

I wouldn't worry about too small of a plenum for the drivers.
Good luck mounting those drivers after the box is made.
I'd have the guy making it mount the subs.

You may be right about fitting... I will double check driver dimensions to make sure I've not messed up and they will definitely squeeze in. The guy is unfortunately the other end of the country so it would be a mission to get up to him with the drivers 🙁 I'm thinking a stubby screwdriver and lots of swearing will be needed... lol 😛

Audyssey should provide me wih some boost 🙂 I will just have to see how it goes once they are in-room and consider options if I need more!

 

[djk]

"I'm thinking a stubby screwdriver and lots of swearing will be needed... "

I've never had a problem with that. You could always use allen-headed cap screws and a small rachet-drive.

 

[MemX]

Ah, of course! That's an excellent idea, thank you 🙂

 

[MemX]

Well, I don't know how it's now December... this year is disappearing quickly!


I have just re-modelled in WinISD because I have learnt on another forum that WinISD sets your box 'leakiness' (the QI value) to 10 ('very leaky', the Red line) whereas I would presume that most boxes are much nearer a QI value of 50 ('no leaks'), therefore I have amended this value and re-graphed, as attached below.

Having done so I have seen the cone excursion drop drastically from the original modelled response, and the drivers should hopefully now remain within XMax all the way down to 3Hz, so they should be safe from over-excursion and always within XMech, even with 5kw of power!

I guess the main concern now will be cooking voicecoils from extended ultra-low bass scenes in movies...


I also played with the QA (interior stuffing) values as well - going from minimal fill (QA value of 80, the Green line) to lined walls (QA of 20, the Blue line) to totally stuffed (QA of 5, the Yellow line) has reduced the box Q from 0.841, to 0.815, and then down to 0.726 (so much nearer to 0.707) but I am a little worried that too much stuffing will make it sound 'muffled'?


I may work to the Blue line and line the walls fairly well, while making sure the box is as airtight as possible!


Any comments or thoughts are gratefully received 🙂 I am pretty happy with the results so just want some reassurance really! lol

 

[MemX]

Hey all 🙂

Just a quick update!

I've played with Sketchup and you can see on the attached my proposed stacking at 1/4 and 3/4 heights, which I think I have read will help with some room modes, hopefully? 😕

I also played with the Linkwitz Transformer section of WinISD and it looks like if I implement an LT using a MiniDSP or similar, I should be able to reduce current draw and cone excursion (and hence improve driver safety) at the expense of only a couple of dB, which I hopefully wouldn't notice. 🙂

The amp rolloff is -3dB at 5Hz so running these with no filters or anything, I should only be constrained by the amp and any other signal chain rolloff, and I shouldn't ever be pulling the full 1250w to each driver the amp could give (hopefully).


Hopefully that's all ok, any input is more than welcome! 🙂

 

[MemX]

My box builder guy has made a start on the boxes - going from the amount of MDF dust, I'm glad I didn't attempt this in my apartment!

 

[MemX]

Last pic for the moment 🙂

There will be additional risers at the top, bottom and in the middle, which should locate the centreline of the drivers at quarter and three-quarter heights of the room (which I believe is a good thing? 😱)


They are Dual 2Ohm drivers. Just to check, I should wire each driver's coils in series (because of potential manufacturing differences between drivers?) and then the two drivers in parallel to get 2Ohm shown to the amp?

 

[MemX]

Bit more progress 🙂

 

[weltersys]

They are Dual 2Ohm drivers. Just to check, I should wire each driver's coils in series (because of potential manufacturing differences between drivers?) and then the two drivers in parallel to get 2Ohm shown to the amp?

Yes, series parallel wiring of four 2 ohm coils results in a nominal 2 ohm load.

 

[norman bates]

I am so excited for you !!!!!!!

2 (stereo integrity 18) drivers in how many cubic feet sealed ?




something like this may be on my horizon by x-mass. Maybe qtc 1.1 with boost for a flat to 20hz, oa qtc .707 without boost. Measured specs from data bass (Data-Bass) make the F3's higher and the box smaller compared to the manufacturors.

data bass ------------- st integrity
Qts .296 ------------ .38
Fs 15hz ------------- 17hz
Vas 465 ------------- 411 Lit

.707 sealed (anechoic)
Vb 3.5ft3 --------------- 5.9ft3
F3 = fsb 36hz --------------- 32hz


Norman

 

[MemX]

Yes, series parallel wiring of four 2 ohm coils results in a nominal 2 ohm load.

Thanks for the confirmation, Welter 🙂

 

[MemX]

I am so excited for you !!!!!!!

2 (stereo integrity 18) drivers in how many cubic feet sealed ?




something like this may be on my horizon by x-mass. Maybe qtc 1.1 with boost for a flat to 20hz, oa qtc .707 without boost. Measured specs from data bass (Data-Bass) make the F3's higher and the box smaller compared to the manufacturors.

data bass ------------- st integrity
Qts .296 ------------ .38
Fs 15hz ------------- 17hz
Vas 465 ------------- 411 Lit

.707 sealed (anechoic)
Vb 3.5ft3 --------------- 5.9ft3
F3 = fsb 36hz --------------- 32hz


Norman

Aaargh, I just wrote a really long reply and this damn computer refreshed on its own and lost it, grrr..


Anyway, as I was trying to say, each 2-driver subwoofer has approximately 7.5 cubic feet of internal space. I left the bracing up to the guy building it so I haven’t calculated it, but as AVS Forum has several large SI-driver based builds running with c.3.5 to 4 cubic feet per driver and similar, c.1kw, power, whether I end up a little over or under my 7.5cuft target should not matter too much 🙂

I think SI are re-starting production of the HT series in the next few months so I will be interested to see your far-more-expert-than-mine thoughts if you do utilise them – I have read that they are already a ‘clean’ sounding driver, but I’ve only heard them in an 8x18” forward-firing setup so the drivers were not really pushed! I will be interested so see how mine come out, I’ve not heard a PPSL before so I will hopefully like it... lol. I reckon I will, but I will report back either way, probably a little while after I’ve managed to re-adjust to the low distortion sound, as I'm coming from my current, ported SVS sub!

The data-bass review did comment on the fact that the driver was already well run in, having been a demo driver (IIRC?) so it’s hard to know whether it is just an isolated difference, whether the SI measurements are perhaps slightly out, or whether all the drivers start out with SI specs but loosen up to data-bass specs! I think I would have preferred to run my setup in larger boxes and less power, to reduce risk to the coils, and ideally setup an IB in the loft above, but seeing as I live in a relatively small top floor flat (the open-plan kitchen/living/dining room they are going in is 20'x14'x8') that is surrounded by other blocks of flats in close proximity, I don’t think they would appreciate hearing the bass outside as loud as I have it inside 😛 (and I don’t have the skills to build an enormous, effectively IB, box in the loft!)

My biggest current issue is needing to run cables through a wall into a cupboard so I can get the amp out of the room (the CV5000 is noisy as hell as it has two 100cfm fans in it, IIRC) and also that I need to find some willing victims, er, volunteers to help lift the stack into place – each subwoofer is going to end up about 100kg / 17 stone, going from the guy building it's calculations!!

 

[Zero D]

Originally Posted by MemX

Aaargh, I just wrote a really long reply and this damn computer refreshed on its own and lost it, grrr..

I got burned like that years ago on another forum with the same vB software. So what i've done ever since is, compose & save my posts in notepad etc first, then post. It never fails 🙂

 

[MemX]

I got burned like that years ago on another forum with the same vB software. So what i've done ever since is, compose & save my posts in notepad etc first, then post. It never fails 🙂

I do try to do that too 🙂 but, sadly, it's only when I haven't that things crash! 😛 lol

 

[MemX]

Couple more pics, progress is coming along nicely.

 

[norman bates]

wow.

your neighbors are going to hate you !!!!!!!!!!!

 

[MemX]

The guy building them sent me the attached pic of the first one in his garden. Is it bad that I think they look reasonably small...? lol


Fortunately my apartment block appears to be concrete block and steel girder construction, with a concrete skim over the floor joists. I only really have a downstairs neighbour as I am on the end (and he is young and out a lot), and 'next door' is not connected to my lounge/diner/kitchen room except by one row of blocks that join one corner of the alcove these are going in, so fingers crossed I won't get a noise abatement order watching action films of an evening! 😛