Pair of small subs, TH?

[chris661]

Hey guys,

I'm thinking of making a pair of small subwoofers, for a bedroom system. My mains are a pair of Fostex FE126eNs, driven by either a 6EM7 SET amplifier, or an amp6-basic from 41Hz. The Fostexes cut off around 80Hz, so that'd be an ideal starting point.

I have available 4 ofthese, so I'd preferably use 2 per side. I know they may not be ideal, but if I could get something decent out of them, that'd be good.

I have drivers such as the TB W6-1139SG available to me, too (though at £70/pr, they'd need to be right for the job, not just something that might work).
Anyway, I'd like them to be ~700mm tall, less than 300mm wide, 300mm deep at a maximum. I'd like extension to cover 30Hz comfortably, SPL isn't a huge issue, as it'd need to keep up with a practice guitar amp (played at sane levels), not much more, in a small room (2.3mx2.8mx3.4m hwd). The speakers are ~half way along the longer wall, ~1.5m apart.

I've never built a tapped horn before, but I think it'd be something interesting to try.

I've tried Hornresp a few times, but never been able to get anything remotely usable out of it. If someone was to post sims, a brief explanation of the reasoning behind it would be much appreciated. I've read through a few tutorials, but none of them have explained it as you would to a teenager such as myself.

Nearly forgot - the amplifier would be initially a 25w/ch stereo amp (rated, before I upgraded the PSUs), bridged with a large PSU (2x200VA transformers, 2 bridge rectifiers and 18000uF of capacitors for each rail ~+/-34v - basically 2 near identical PSUs in parallel). The plan is to get a more powerful (likely switching, likely stereo) amplifier later on.

Musical interests vary, but I've tracks that go to 30Hz, so that's the initial target. The end result should beat a pair of these in a 40L cabinet with Linkwitz to get an f3 of ~28Hz (severely SPL limited in the lower regions). In reality, they go into harmonics before reproducing such frequencies at a decent level, so an upgrade is in order.

Anyway, if you've read this far, thank you very much. I'm looking forward to suggestions.

Chris

PS - the wood will likely be CNC cut, ply or MDF. The latter is preferred due to budget reasons...

Edit - the cabinet could be physically deeper, to maybe 500mm at a push.

[chris661]

Decided they'll be powered by a stereo 100w/ch@ 4ohm amp from 41Hz, but only because I have a power supply ready.

[steviedon]

The only design I can offer that almost meets (413mm deep, but fits all the other size criteria) your goals is- http://www.volvotreter.de/pics/TH_38...fold_klein.jpg
plans-http://www.volvotreter.de/downloads/TangBand_W6-1139SC_38Hz_TH_Rev_1.pdf

[chris661]

I was thinking the along the lines of another design suggested by jbell in another thread...

Reed Exodus Anarchy 25hz Tapped Horn - AVS Forum

But I'd like to know if I can get decent results with the Visaton drivers I already have.

I've seen the sims etc for the TB subwoofer, looks promising...
AVS Forum - View Single Post - Reed Exodus Anarchy 25hz Tapped Horn

[bjorno]

Originally Posted by chris661

..But I'd like to know if I can get decent results with the Visaton drivers I already have..

Hi, Your room is small and if comes with one closed door and widow: The passive 'room gain' could be wide-band and large and low end contributions from the Visaton's are IMO more than enough: See the first picture.

FYI, a couple of simulations:

b

[chris661]

Bjorno, thanks for that.

A couple of things...

1) - is there any chance they could go lower? I know there's a few conflicting rules about how low THs can go. Some say half Fs, others say 0.7*Fs... Anyway, ideally I'd be able to use them for movies, too, so I figure the extra extention could be useful.
2) - the graph for the Tang Band (that I posted above) looks less-than-optimal... I've looked around a bit, but can't seem to find anything suitable. Maybe I'm just looking in the wrong places... What would be your opinion of making the one I listed, then playing with eq'ing out the 25Hz peak?

In think in the end, I'd like to mess around with some bonkers drivers, so the TBs are likely to be the one's I'll get...

Cheers again,
Chris

[chris661]

I'm going to build the recommended Th for the Visatons.

If it works, then I've spent a minimal amount of money for something decent. If it doesn't work so well, I haven't wasted much money (just the wood).

So, a couple of questions on that design.

1) The schematic shows only one driver. Would I be right in thinking that I could simply double the area for the second driver?

2) How should I go about folding this design?

I think I've worked out what all the numbers mean. It's not L23 (as in twenty-three), it's L Two-Three, ie, the distance between the indicated areas of S2 and S3.

3) I suspect I ought to use a double folded design (look at me, using the proper language...), as a single fold would result in a design that's too tall (Mum already complains occasionally)... Am I over-complicating things, or is this feasible?

4) (and it's only a minor one, I'll probably speriment anyway), would stuffing/lining be needed anywhere? I've seen some with lining on the folds, others without.


Thanks all,
Chris

[tb46]

Hi chris661,

As to the Visaton W130S: the old way of specifying Xmax=(Winding Height minus Front Pole Plate Height)/2, in other words 2.25mm, and even the Excursion limit (Xmech?=8mm) is not very big. I feel that this may be a little limiting for a sub. It is real easy to bottom out such a sub, even when the overall levels are quite benign. Bye the way, just in case you are not aware of it: bjorno's Rec. enclosure (on the left) is not a tapped horn.

The best way to learn about tapped horns I can think of is to take known working designs and plug them into Hornresp, then make changes and note the results. Take bjorno's tappedhorn (the one on the right), and change it into a four section model, and play around with it until you have a flat response from 34 to 100 Hz, or, for example look at (admittedly, one of my favorite threads) geitmans' thread on a dual 8" tapped horn:

Dual 8" tapped horn = TH-SPUD

,here you have a Tom Danley design, and a good example of how to build, and measure a dual tapped horn; then plug that one into Hornresp, and see what you can do with it to make it smaller, how different drivers affect the response, etc..

Anyway, its the journey ....

Regards,

[chris661]

I had failed to take into account that the sims posted above were the maximum SPL the drivers would do, while the 25Hz TH is at 1 watt, so the driver would have plenty of excursion reserves. This puts a new light on things, so I'm unsure now of what to do.

Despite my protests, Hornresp isn't giving out the same graph as bjorno's recommended design, though I've checked all the input parameters twice. My design gives a peak at ~32Hz before dropping off. Changing the design to look like the schematic helps a little, though the cutoff has gone up to 40Hz.

confused...
Chris

[MaVo]

Originally Posted by bjorno

Hi, Your room is small and if comes with one closed door and widow: The passive 'room gain' could be wide-band and large...

b

Or you could say it this way: Your room is small and has little leaks, the resulting room modes will lead to deep notches in the response, lowering the usable output by a large amount (what use have those pesky high q spikes in the response, that look like room gain with a low enough frequency response resolution, if the nulls inbetween are deep?). Now, whats the truth? If it lies somewhere in between, then that means you could simply ignore room gain and get reasonable results. The principle at work here is: Never be too optimistic, concerning the results of your work, or you may have to redo it completely. Thats why one should think of room gain as a nice addition, but not as granted.

While you are in the planning stage, i highly recommend googling "harman white paper" and look at the subwoofer placement ones. Great stuff to know, easy to implement, makes the resulting speaker setup sound much better.