DIY Sub - Advice Needed Please....

[theritz]

Hi,

I've got a BKElec 100W panel and 12" Speaker on their way - intending to make a Q100e/RTP12/RELinquish/Relax/etc clone (take your choice......). One small fly in the ointment, the depth of the design isn't exactly ideal for the location in my movie room, something nearer 300m would be handier. Can I maintain the other dimensions of the sub enclosure and use polyfil to make the enclosure "appear" bigger, or do I have to adjust the dimensions to maintain a 50 litre enclosure volume ? If the volume is smaller than 50l, what will the effect be ?

Thanks in advance,


Sean G.

If it's a sealed sub then polyfil will lower the box Q a bit. Have you modelled the driver at original volume, and newer volume. ? If it goes from say, a Q of 0.7 to 0.75 then I doubt you'd notice the difference.


Cheers,

Rob

[theritz]

Rob,

Thanks for the response........... unfortunately your talking to someone who will have absolutely no prob constructing the box, but who is mystified by the terms (Q, Qts, Vas etc) which accompany the dark art of subwoofery. I've tried modelling it (it will be sealed) using Winisd, but as the BK site doesn't list Xmax (which I understand) I fear that I haven't all of the parameters correct. It recommends something like a 67l box when I try it.......... definitely out.

As far as the stuffing was concerned I was operating under the impression gleaned from lots of Googling that I could get the box to appear about 25% bigger by using the correct amount. This is not a "mission critical" issue, really, but I don't want to go down this path if the result is going to sound "choked" or if it limits the low frequency performance of the sub.


Would be grateful for any further advice.


Sean.

Any further

[ShinObiWAN]

Hi,

I've too recently built the q100e clone. Not bad at all for £150 worth of parts.

Is it possible to build the box say 32cm (w) x 32cm (d) x 55cm (h) and downward fire the unit? Or you could still forward mount it near the bottom, may look a little strange though. These are external dimensions and the final internal volume will be approx 50ltr. With this sort of shape you will have something that resembles a Rel Storm.

If I were you I wouldn't worry terribly about the volume if its 45ltr then I think you'll be fine, less and you may start to notice.

[theritz]

Shinobiwan,

Thanks............. I thought about having it that shape, but I don't think the driver is suitable for down-firing ( vague recollection of Retro posting something about this in the dim distant past...). If anyone would have a look at the specs of the driver and say whether they think it would perform ok down firing I'd be interested - I tried writing a spreadsheet based on an Adire paper, but found it rather difficult as I wasn't familiar with the metrics used in the specs.

Funny you should mention the Storm, I had one on extended loan from another member and it really rocked..... the sound stage is a bit (!) anaemic without it, now that it's returned to it's rightful home, hence the DIY route. I'm not gone mad on having that shape front-firing..... I may just end up sticking with the proven volume/shape.

The big downside is it would mean losing my current arangement - the screen wall in my movie room is false, made with black velvet covered panels and hides variable masking for the screen, with the hcpc, amp etc and front L C R speaker all out of sight and we really like it that way. The Storm fitted out of the way behind the screenwall (just !), but there's just a little over 12" clearance which means the Q100e dimensions won't fit.

Love your work on the sub and the vistathon speakers, btw, class workmanship.......

Sean G.

[IronGiant]

The specs for the BK driver don't easily fit into WinISD as they are labelled up differently. With some lateral thinking you can get most of them in, but WinISD will still suggest a bigger box. I figured that if I'm building a clone and know less about subwoofer design than REL, I'd stick with their internal dimensions (outer dimensions were adjusted for the thicker MDF I was using). So long as you stay to the same internal volume I doubt it will matter if you change the actual dimensions of your box to fit your space (within reason)

Dave

[GaryG]

Originally Posted by theritz

Can I maintain the other dimensions of the sub enclosure and use polyfil to make the enclosure "appear" bigger

Yes, up to a point.

http://www.win.net/audtatious/audio/fiber.html

If the volume is smaller than 50l, what will the effect be ?

The response will have a slight peak just before the corner frequency at which it starts to roll off, for HT use this is probably beneficial. Most people prefer the sound of a high Q sub for HT use, it has a 'punchier' sound. Also, the output below the corner frequency will be lower as the 'roll-off' is steeper. In other words, the bigger the box, the more output you will get at the lowest frequencies for a given amount of input power.


If you feel that you need the lower Q response provided by a larger cabinet here are two possible options you can do.

1. Use electronic equalisation

2. Use 2 drivers and go for an isobaric design, which requires half the cabinet volume for a given Q compared to a single driver (at the expense of lower efficiency).

If you have bought a BK amp with bass boost that will probably be sufficient.

What drive unit are you using ?

Rob

[theritz]

Dave,

Thanks for that...... I think I'll have a play with the dimensions and see how close I can get.....

Gary,

That link was the one which prompted the idea about the filling.......

I'm very grateful for the rest of you're reply, but must confess that most of it went gently whooshing over my head....................

The response will have a slight peak just before the corner frequency at which it starts to roll off, for HT use this is probably beneficial. Most people prefer the sound of a high Q sub for HT use, it has a 'punchier' sound. Also, the output below the corner frequency will be lower as the 'roll-off' is steeper. In other words, the bigger the box, the more output you will get at the lowest frequencies for a given amount of input power.

I'm assuming that this means that a smaller enclosure will mean that it won't have as good a response at the lower end of the scale as it would with an appropriately sized enclosure.

Any view on the suitability for down-firing ??

I'm heartened by the response and advice of the sub "regulars" - I'll reflect on this a bit longer, hoping the panel and sub might make it here by the weekend, (fingers crossed). I think I might go for the smaller enclosure (screwed together temporarily) with filling; if it doesn't perform as well as I might hope, I'll make a new enclosure - I'll be able to re-use the back, front and brace....

Thanks again for the advice, guys.........


Sean.

[GaryG]

No offence, but given the low cost of that driver I wouldn't worry about down firing. It's most likely you will have moved onto bigger and better things before you will notice any sag in the cone.

For testing the difference in cabinet volume try and get hold of a big cardboard box from a retail park (discarded appliance box) and cut a hole in it for your driver and add mass (bricks, magazines etc) to it to lower the volume to get a feeling for the difference it makes. You will need to keep the amp volume down to stop the cabinet vibrating too much but it will give you an idea of what the final cabinet will sound like.

[theritz]

Gary,

Missed the question about the driver in your earlier post, soz, and no offence taken - I know it's the lower end of the foodchain, but selected on the basis that the match of components is well proven from diyérs experience here. I wouldn't have a clue about picking a driver (and there's bugger all available here - would always have to import....) and for a first try this seems like a reasonable approach.

As for moving onwards, if this produces a decent result, I'll be keeping it, pursuing audio perfection etc is not on my upgrade path, more interested in upgrading the projector and doing some room improvements - fabric panneled walls etc.

I might give it a go in a sealed Storm-sized enclosure firing downwards...... I can see a couple of sheets of MDF disappearing into this


Thanks again


Sean.

[theritz]

Rob,

Sorry, only noticed that it was your post asking which driver - it's a BSB-12 from Bkelec, specs here - as used in the Q100e and clones mentioned above. I incorrectly thought GaryG had asked........


Sean G.

[ShinObiWAN]

Originally Posted by theritz

Gary,

Missed the question about the driver in your earlier post, soz, and no offence taken - I know it's the lower end of the foodchain, but selected on the basis that the match of components is well proven from diyérs experience here. I wouldn't have a clue about picking a driver (and there's bugger all available here - would always have to import....) and for a first try this seems like a reasonable approach.

As for moving onwards, if this produces a decent result, I'll be keeping it, pursuing audio perfection etc is not on my upgrade path, more interested in upgrading the projector and doing some room improvements - fabric panneled walls etc.

I might give it a go in a sealed Storm-sized enclosure firing downwards...... I can see a couple of sheets of MDF disappearing into this


Thanks again


Sean.

Glad you've got some plans laid down now, its always a pain when your unsure how to progress to the next stage, but you sound like a man with a purpose now

If you get stuck then pop back here and I'm sure we'll all chip in with advice. Don't forget to post some pictures of your progress too!

[theritz]

Shin,


"A man with a plan" - more like a man with three plans !!!!! I'll think more about it tomorrow, and I'll come back and report the results when it's built. I intend to get the parts pre-cut by my local suppliers, they're brill at cutting stuff to spec, so it'll be a bit of routing and assembly. I might run it for a few weeks in it's chosen format before finishing it - particularly like the effect you got with the black/veneered sides, but I'm inclined towards a painted finish all over - it'll be out of sight so a classy finish is not necessary.


Thanks again,


Sean.

I wouldn't worry too much about the smaller enclosure. Just use the polyfil.

I've attatched a pic with the response for 40L, 50L, winisd recommended vol. 67L, and my fav. - Q=0.5 (ish)

See how as the box gets bigger the low end comes up ? notice how it starts to roll off earlier higher up though..

Cheers

Rob