Roofspace horn

[Stentor]

Hello from Stentor. For anyone else whose Greek mythology is a little rusty, Homer said "his voice was as powerful as fifty voices of other men". Not Homer Simpson, the other one.

To explain my name choice: I have 2 x 42" high x 30" wide x 24" deep homebrew VOTT copy cabinets in a fetching shade of Beech veneer. They have 1 x 15" Wharfedale drivers each, mid boxes atop with 8 x 4" Wharfedale drivers each, le tout ensemble iced with 2 off 8 x 1" Wharfedale Mylar tweeters.

I'll go into the graphic eqs, electronic x-overs, amps, etc when you've reawoken.

Meantime I need some inspiration please for a roofspace-mounted 1 x 18" subwoofer, preferably in a horn enclosure. I have lots of space and an available mouth perimeter in the ceiling of about 9' (but more could be made available). I have about 250W to drive it, but I like LOTS of headroom - say 20dB - so a target input power of 25W would be very nice. X-over point and passband is open at the moment.

Any ideas?

 

[Brett]

LF horns are usually a major compromise and it's going to be a major PITS to build in a loft space. There's the tapped horn thread here, but I'd suggest an infinite baffle. More expense for some drivers, but much less work and similar performance.
http://ibsubwoofers.proboards51.com/

Otherwise, build some LABhorns and extend the mouths.

 

[Rademakers]

I recently did build a 2 x 18" tapped horn in just under two days, and demolished it in one day (at 141 cubic ft. I say it was biggish but at the same time kinda small), so I would definately say build a 'frikkin' huge tapped horn (it didn't sound slow-ish as I orginally espected). Or if you build anything else, make it 'frikkin' huge.

Wkr Johan

 

[chops]

and demolished it in one day

 

[Rademakers]

It was a build for a stand at a weekend festival (Solar, project Halfspace) with materials I required at the spot. As it was roughly 366 x 125 x 100 cm (12.2' x 4.2' x 3.3'), it was to big to transport it back to my place, so I had to use my circulair saw as it was mostly glued
Don't worry tho, it's parts have now become a vip-balcony/room at our ..ehm...squat.

Anyway, it's intended use and size seem pretty much the same as the OP has in mind, so it might be usefull as some inspiration as it was big, easy to construct and ehh.. big. Hornresp simulated it as 97...100 dB/2,83V/m (1/2-space) from 15 Hz (f3) and up (that was all the inspiration I needed )

Wkr Johan

 

[Stentor]

Rademakers/Johan:

Your horn sounds just the job. I have only the one driver (8 Ohm/18") although I can source another. I'll have to be careful if a 4 Ohm load is being presented to the amp.

The mouth area sounds just right without rejigging my ceiling joists overmuch (the existing joist ends can act as mouth stiffeners) and I can put twists/folds in the gradually reducing horn sides to exploit the 5m-wide x 2m high x 5m long bisected cube space available. The apex included angle is 90deg.

Love the idea of 15Hz and your achieved efficiency of 97-100dB @ 1W/1m will fit nicely within the tweak range of my sub bass x-over/amp and match the VOTTs.

Can you point me at plans/curves for the taper please? Are the drivers in compression chambers? I have fair woodworking skills and all the power tools necessary. And a BIG pot of glue.

Thanks for responding. On a good day, you might hear me in NL. My path is only about 400km straight across the North Sea. I can often work PAs on 2m/70cm/23cm ham radio. Ruth and I really enjoyed our last visit to den Bosch and Venlo. There was a JS Bach carrillon recital from den Bosch cathedral the last time we were there. We listened to it from a pavement cafe - delightful. Definitely one of my favourite countries.

John GM1TDU

 

[Rademakers]

What works best for your driver depends on the driver. The tapped horn I build was designed around a specific driver. Depending on the (mis)match between the drivers parameters this tapped horn would work for your driver or might not perform well. It design parameters are however pretty common.

Got any T/S-parameters for the driver you want to use? We might be able to suite it up.

Hornresp:







Some pics during the build:







Fold style:

http://img155.imagevenue.com/view.php?image=05613_Tapped_horn_Hornresp_122_1037lo.JPG

On a good day, you might hear me in NL

Looking forward to it

Wkr Johan

 

[Stentor]

Hello Johan

Here is all the data I have including the T-S parameters. It's in German but I wouldn't think that will be a prob for you

OMNITRONIC AL-1800
Allgemein: Thiele-Small-Parameter:
Gesamt-Außen-Durchmesser: 450 mm FS: 29,9469 Hz
Befestigungs-/Lochkreis-Durchmesser:
440 mm (8 Schrauben) Re: 7,2000 Ohm
Einbauloch-Durchmesser: 425 mm Qms: 8,3143
Einbautiefe: 190 mm Qes: 0,6767
Bass-Kalotte-Durchmesser: 125 mm Qts: 0,6258
Magnet-Durchmesser: 185 mm mit
25 mm Bohrung für
Schaumstoff-Staubfilter
Vas: 518,4930 l
Impedanz: 8 Ohm No (Ref efficency):
1,9898 %
Leistung: 200 Watt RMS (sinus) Sd: 0,1195 sqm
Schalldruck: 96 dB
Frequenzbereich: 25 - 3.000 Hz

Motor Impedance Parameter:
Levc (Induc at 1 kHz): 1,3702 mH
Levc (Induc at 20 kHz): 0,6482 mH
Krm (Resistance Cons): 9,2922 mOhm
Kxm (Reactance Cons): 12,1807 mH
Rem (Res at 1 kHz): 4,3991 Ohm
Rem (Res at 20 kHz): 36,2865 Ohm
Erm (Resist. Expont): 0,7043
Exm (React Expont): 0,7502

When I have time (3 small sprogs permitting) I'll try cranking the
T-S figures into the calc you posted.

Your observations would be welcome.

Thanks for your kindness.

J

 

[Rademakers]

Because of the T/S-parameters I would have another look at the Infinite Baffle, as Brett suggested. Qts is very high which would reinforce the usage as IB. However only a (tapped) horn of the mentioned size would get close to the mentioned sensitivity, that low.

In the same enclosure the Omnitronic AL1800 wouldn't perform quite well as is shown in the next sim (grey is a single 18LW1400, black is the AL1800):



It would need much less compression and shorter length for better results, this is the best I could came up within the time I had:





By enlarging S4 you would get higher sensitivity @ 30 Hz and up, making the response flatter as well as lowering overall excursion needs.

Too bad Xmax is not stated as this is one of the more important parameters when it comes to reproducing subfrequencies. Due to the missing Xmax it's unclear what the mechanical powerhandling would be. However with 99% of today's music and 25 input power I wouldn't expect much problems, tho it might.

Wkr Johan

 

[AndrewT]

What works best for your driver depends on the driver. The tapped horn I build was designed around a specific driver. Depending on the (mis)match between the drivers parameters this tapped horn would work for your driver or might not perform well.Hornresp:

Hi,
the Hornresp shows a flat response from ~15Hz to ~50Hz.
A bit less than 2octaves. Is this typical of the passband of a tapped horn? What would this design sound like if the response was rolled off at 100Hz?

 

[Stentor]

Hi AndrewT and hi again Johan

Here's what I can do at the low end of my graphic eq:

+/- 12dB centred at: 20 25 31.5 40 50 63 80 100 & 125 Hz
rolled up/down @ 12dB/octave centred on the above frequencies.

I plan to cross the subwoofer actively at about 80Hz and pass the remainders to the next stages, with the 15" bass element in my VOTT crossing to the mids at 800Hz and thence to the trebles at 3000 or 5000Hz, each driven by separate amps.

I feel the response dips and peaks posted above can be "ironed out" with the graphic.

Comments please?


J

 

[Rademakers]

Hi,
the Hornresp shows a flat response from ~15Hz to ~50Hz.
A bit less than 2octaves. Is this typical of the passband of a tapped horn? What would this design sound like if the response was rolled off at 100Hz?

Typical for any horn loaded enclosure is that it's usefull for about 3 octaves. Most tapped horns I've seen sims or measurements (DSL) of where give or take 2,5 octaves. With the possibility to gain effciency at the cost of bandwidth.

Because there is basically no typical reference for the sound of electronical music (drum and bass at the Solar festival by the time it was finished), it's hard to say if it sounded unnatural or not.
I've had subs that dropped off at 6 dB/octave, were kinda flat, or with a small "bump" in the response that all sounded OK up to about 80 - 100 Hz (not just with electronical music).
Usually 100 Hz and above is where the trouble starts.

From what I've heard, Hornresp seems to overdo the big peaks a little, compared to sims.

I feel the response dips and peaks posted above can be "ironed out" with the graphic.

The dips and peaks as seen above will probably be small compared to the influence of the room but with such EQ you should have no problems.

Excursion peaks at ~27 Hz and below ~15 Hz.

Keeping the 1kHz-3 kHz region crossover free is generally a good idea.

Wkr Johan