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In the Forum: Horn-Loaded Speakers
In the Thread: New speaker system

Post Subject: New speaker systemPosted by guy sergeant on: 3/16/2010

I recently completed some upper bass horns which I'm now enjoying very much. Sadly I lack the skills of someone like Jessie so my efforts are crude in comparison, but they are working well for me which is the main thing.

I already had some old frontloaded, folded horn cabinets so had a 3 way system of sorts running a while ago. I'd already chosen the JBL 2405 Alnico as my preferred tweeter & had acquired a pair from a church in the US. I'd been using the Vitavox S2 mid driver in a Vitavox 4 cell exponential horn until about 18 months ago when I bought some of the cast resin tractrix 400 Hz horns from Stereolab. These sounded more natural & played higher (being shorter) even if they are less impressive in some ways.

My problem was that both the S2 and the 2405 needed padding down quite alot, and that the folded front loaded 'bass' horn didn't really get up to 500 never mind 800Hz which was where I wanted to run the S2's from. The folds seemed to introduce uneveness in the response, arguably just behaving as a series of tapered sections each with its own problems. Such a folded horn also can't readily be time aligned with the mid horn although I suppose if digital were the only source, a digital x-over with delays to the mf & hf could allow for it.

The intention was therefore to make a straight horn & choose a driver which would get up to and beyond where I needed it to. Such a horn would also allow all 3 drivers to be physically time aligned. The mouth area was set by dimensions which would allow it through a typical doorway and the length was set by being at least a quarter wavelength of the frequency I wanted it to play down to. I also thought it would be interesting to apply the Macondo axioms where possible.

The free software Hornresp was used to try several drivers & various horn profiles. I opted for a square section Salmon type horn (aka Hypex) and eventually settled on a particular Eminence 12" driver that seemed to give the required result.

The horn was made from MDF in 3 sections, 30, 40 & 50 cm long but approximates closely enough the profile that was modelled particularly when the joins are filled & filed smooth.

Back chamber

With driver installed

Initial testing

Some paint goes on.

I was pleased that the measured performance of the driver in the horn matched the predicted performance fairly well. The rolloff it does introduce has allowed me to simply series feed the MF & HF drivers via appropriate caps without any padding.

an early response plot, on axis with the S2 & stereolab horn.

The back chamber is sealed & partly filled. Adjusting this volume adjusts the Fs of the driver & how it reacts with the horn. I need to play with this some more. The back box is double thickness. Ideally the rest of the horn would perhaps be more massive but it seems to work well enough. It is pretty substantial where the pressure is highest. I perhaps also need to treat those drivers to some nicer series capacitors at some point.

Here in the UK we have a forum run show where enthusiasts can take their own equipment and set up systems. There were perhaps 45 rooms at the recent event so I and a couple of friends took a largish room (250 Cubic Meters) and set the horns up to play there. We used a home built 3W amplifier using the 6B4G to drive the horns and then a smallish XTZ subwoofer below. This Sub-woofer was really somewhat underpowered for the room, but despite that the result was good and the horns seemed well received. It did illustrate very clearly the demands a large room makes on LF systems. The horns had no difficulty filling that room but the bass system really needed to fill out beneath them would have to be quite large & capable.

I now need to find a relatively compact LF solution to go with them. I'm currently using a single, small active sub-woofer which just about manages in my 4.5 x 5m room. A proper LF will then give me the opportunity to high pass these horns and unload the bottom of what they do. I suppose the options include conventional active subwoofers, possibly tapped horns (although I'd like to hear some first ) but any other suggestions would be gratefully received.

I wish I was a better woodworker, but I can tolerate their appearance. These aren't the kind of project I'd pay a cabinet maker to do on the offchance that they would work properly. So I had to do it myself.

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