DIY Sub

Hi,

My suggestion is to IGNORE commercial designs.

Simply take a set of 4pcs of reasonably long throw (+/- 1/4") 10" drivers with a high Fs and lowish Qts, place the 4 drivers into 4 of the 6 surfaces of a 13" cube made from 1" MDF and use a big but cheap and convection cooled Pro-Amp to drive this, equalise via double integrator.

This is called "URPS" (under resonance principle subwoofer) and has been all the rage in Germany in recent times and are considered as (to quote) "faster than klipschorns", "deeper than velodyne" and so on.

By operating the Driver only below resonance and in a small box most problems with woofer systems just go away. What remains is the need for loads of power and drivers with a reasonably long throw. The non-linear air cushion in the box adds at VERY HIGH LEVELS some "Maxx Bass" effect style harmonics.

Here a german page with such a beasty explained, this uses the legendary soviet russian made "S-90" woofer, this is around Fs 40Hz, Qt = 0.4, Vas 100L.

http://www.weidinger-online.de/urps/allgem/urps.htm

More details and the explanation of the "Maxx Bass" part are there, in German sadly.

Ciao T

 

The URPS that T is describing is the principle behind the bag-end subs with a big reputation in the US.

If a box is very small for a sub then even harmonic distortion is generated because the air pressure inside is non linear [eg you will travel less excursion into the box than outward for a force from the voice coil]. Can be fruity and fun.

I doubt if your DEQ will like the necessary amount of slope needed to get the sub flat. 'Double integrator' means 40dB decade slope - or in a 70s context 'bass on full, followed by another bass knob on full, plus the loudness button on.....'

those where the days..

Sod Volt drivers from Wilmslow. How many [better] Peerless XLS 10 can you buy from BKelec for those prices??

 

Hi,

Most commercial Subs use various custom or at least custommed parts (I'm just involved in the development of two different ones, one for 3D Sonics to complement our open baffle speaker and another sharing a lot of tech for a DIY Kit open Baffle speaker Kit. No way you will ever be able to buy our drivers off the shelf, even though they share basket, magnet, cone and suspension parts with other drivers made for Car audio which will make them superficially identical to certain car drivers, the performance is entierly different though. And I may be not entierly wrong in stating that the system bears some resemblance to URPS....

Yes, you get the cone surface of a 15" driver from 4pcs 10", but usually much more motor strength and excursion than most 15" Woofer drivers. The principle is to use fairly high efficiency, medium throw Driver, with a fairly high Fs.

A URPS cannot quite sustain high level sinewaves at very low frequencies, BUT music usually does not contain much high level sub 40Hz sinewaves....

However low you want. Bagend in the US tunes their systems for 8Hz/-3db, I tend to suggest a tuning to 16Hz/-3db, the tuning is via electronic EQ, either using integrator (Bag End, earlier 70's german designs by a number of companies) or using a multipole EQ filter (usually called Linkwit Transform, though not really invented by my fellow German Siegfried Linkwitz).

If you commit enough cone surface (say a tower with 4 X 10" in each side, so 16 X 10" Drivers in a 13" X 13" X 52" tower) you can get material SPL's even at something as low as 4Hz....

One of the key merits of the URPS is the elimiation of traditional resonances within the Audio Range, all other systems (in nother words systems that utilise sound output above a driver or driver/box, or driver/box/vent combination will settle at their fundamental tuning frequency (the highest Q one).

With an URPS the settling is determined by the resonance which is ABOVE the operational band, meaning for once the driver settels much faster than the LF signal applied, so that it can "track" the signal well....

I would recommend a Sub processor (ananlog), which combines a Linkwitz Transform circuit with a single integrator (best compromise on group delay) and if the Sub is going to be used at frequencies within the modal range of the room a 3 or 4 way basic parametric EQ, cut only, Q tied in with level of cut). Can't buy that, DIY it....

Ciao T

 

Hi,

I think "rich and savoury" may be more appriate, like the Duck we had at the Magic wok....

Not really. You might wish to consider either old stock or used EV 30W (the 30 is the diameter in inch) or a new Fostex FW-800 (the 800 is the diameter in mm). Maybe doubling up for a little headroom and stereo bass is a good idea....

In quantities of at least 250pcs you can probably get something WAY BETTER. Otherwise you may be able to find something that appears the same, but probably has a different thickness magnet top plate and voice coil, making it a completly different driver.

Ciao T

 

Hi,.

You sepcify it.... For 250pcs many a chinese factory will make you your own driver. You name it, multiple neodymium stick magnet, 6" Voice Coil, 1" throw and 12 diameter is not that hard to do, add a profiled Aluminum Cone (for stiffness while light)d a symmetrical voice coil with dual gap, adjust T/S parameters to exactly suit your job.

Of course, the resulting Sub is not competetive on price, so selling 250 may proove difficult.... And you need a custom driver which is really maxed out to get "there"....

Ciao T

PS, meanwhile, while pondering the ineffeable and the limitations of reality, consider this device.... It is really good....



PPS, I'm not suggesting your'e a moron, anyway, among cat's "moron" is a term of endearment....

 

Thorsten

How does this equate with your previous recommendations for bass dipoles?

(I haven't bothered to refer back to any previous posts so if I've mis-remembered or other wise distorted any of your previous comments/suggestions then I apologise in advance)

Ta

Chris

 

Hi,

As suggested, a speaker system should be dipolar or unipolar in the rooms modal range, usually above 25...40Hz. Tenson wants a Sub that will work below the modal range, meaning a sealed (or other monopole) sub is recommended.

It is invariably horses for courses. It seems you (and others) take my specific comments and interpret them as general unqualified recommendations, which they are not.

Ciao T

 

And any suggestions for (affordable) drivers?

 

erm... No!

A good way of ensuring you understand (I have found) is to ask questions that ensure there is no confusion. Which is what the response in your 1st paragraph provided. Your second sentence above was unnecessary and inappropriate. At no point have I implied that you have been inconsistent (in fact I find your observations to be the opposite). The alternative (for me) would have been to have gone back and read through all your previous (and scattered throughout the Internet) references to speaker design, dipoles, speaker behaviour at different frequency ranges and room modes and not ask the question...

Not surprisingly it was quicker and easier to ask a simple (and non-provocative) question

 

Hi,

Pretty much any sensible 10" Driver (sweet spot on cone stiffness vs. motor strength) with a big motor which will give a build in Qt of under 1 when placed into 5L sealed will do.

A good outside bet on an affordable 8" driver for the job is the Apexjr.com Super 8. They also have a decent Plate Amp (which could be placed in one of the two remaining surfaces, I'd say below the 13" cube), the Apex Senior that would do a decent job driving this shooting match and is affordable as well.

My current own URPS uses a pair of Eminence Delta 12LF Pro drivers in a 15" cube with a Thomessen 220W Plateamp...

Ciao T

 

Hi,

Which would probably have taught you a lot more than my current answer. I do recommend it.

Ciao T

 

I know that - i've already read them (at least once).

Your current answer (or rahter the 1st paragraph of it) provided the approriate summary (based on my question)

 

I built a sub around the late seventies. It was a transmission line encloseure, very long and large with 4 10" 16 ohm speakers firing at the floor. I made it into a window seat. MMM all those vibes. It was pretty good but let down (in hindsight) by my amplifier. It was called the "Basset" a magazine design or something. It did manage to extend the bass as low as my room would allow and was quite smoot and detailed - easy to listen too, even across the road!