OT optimised for a bass horn amp

Design and use of the various types.
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mseddon
Posts: 35
Joined: Thu May 05, 2005 12:04 pm
Location: perth australia

OT optimised for a bass horn amp

Post by mseddon »

Hi Dave,

What might an OT optimised for a bass horn amp look like? Horn used up to Fc of around 320 Hz and 100 - 104dB sensitive.

To narrow things down a bit I have a nice quad of SV811-10s and a power trannie. willing to try pentodes. Have been thinking pp - but open minded. At present using a ss amp on the bottom. Bi-amp on top has been SE of many vaieties, but also find I like PP.

Would like to design for the horn and driver (and sound), rather than impose preconcieved ideas. Control / damping factor probably high on agenda.

moolah your way if something comes of it.

Thanks and best rgds,

martin
reVintage
Posts: 365
Joined: Fri Sep 07, 2007 9:54 am
Location: Sweden

Post by reVintage »

If the horns are Hypex made according to Leach findings they need to be driven from a very low output impedance. If not, the horns need adjustment by adding the output impedance to Re of the driver when calculating. I have made a simple Excel-spreadsheet, www.eflatjump.se/subbasshorn.xls , where you can input the Radd.
Brgds
Lars
mseddon
Posts: 35
Joined: Thu May 05, 2005 12:04 pm
Location: perth australia

Post by mseddon »

Hi Lars, I found your website - looks great - but cant get the to the spreadsheet. Can you post it to me at mseddon@eftel.com.au ?

My bass horn is designed using McBean to a 0.6 Hypex : have a look on azurahorn.com

Not sure I undersand why one needs very low impedance - can you explain? But In fact the ss amp I now use gives much better dymnamic performance than my 300B SE amp - so I guess this is true.

rgds,
martin
reVintage
Posts: 365
Joined: Fri Sep 07, 2007 9:54 am
Location: Sweden

Post by reVintage »

Sorry Martin,
Wrong spelling :oops: ! Do not have the file in this (work)computer so try the link again: www.eflatjump.se/subbashorn.xls . Can mail it when I get back home!

Brgds
Lars
Brgds
Lars
mseddon
Posts: 35
Joined: Thu May 05, 2005 12:04 pm
Location: perth australia

Post by mseddon »

Nice spreadsheet Lars, thanks.

I wondered if this is about horns not transformers, and we should take it off line - but realised this is exactly where the transformer design should start - as part of an acoustic / electrical circuit of the horn / tranducer / transformer. Unfortunately the maths is over my head, but I can understand that the horn loading would increase driver R because driver is working harder in terms of force x distance.

However isnt the driver Radd in series with the amp output R? ie so it is no different from amp output R. But I guess this is really ac impedances adding vectorially and there's a lot more involved.

Why does HornResp does not show Radd on the Impedance output model?

I had always thought that highish output impedance tube amps with no NFB were well suited to driving horns becuse of the constant Zo in the pass band. Would one in fact benefit from lowering Zo using NFB?

rgds, martin
reVintage
Posts: 365
Joined: Fri Sep 07, 2007 9:54 am
Location: Sweden

Post by reVintage »

Good thinking! Of course a horndesign should be begin and be done for a specific amp and driver.

My intention is that you should input your amps Zout(in which RDC usually is a big part) into the Radd. You might also input the added DCR of filter-components.

And of course NFB makes output impedance lower.

One might even think of using an amplifier feedback with negative Zout .

So this thread is just partly OT :wink: .

For a basshorn I would go for a PP-amp with parallelled triodes, with moderate NFB. Also wound with the heaviest possible wire to get RDC down.

I am also interested in the transformer/amp subject as I am currently making a concrete/brick horn in my new listening room. Have not decided about amp yet.

I am anxious to hear what Dave recommends.
Brgds
Lars
mseddon
Posts: 35
Joined: Thu May 05, 2005 12:04 pm
Location: perth australia

Post by mseddon »

I had a look at the Hornresp impedance plot vs the spl plot and pretty clear the 'ripples' are in opposite phase. So I guess 'negative output impedance' amp would be a good thing to to try.

ie at frequencies that draw less current from the amp (and have less horn spl) due to higher acoustic and driver impedance there is less NFB (voltage) to the amp input. So the amp drives these frequencies harder.

Interestingly higher amp Zo seems to work in our favour here if driver and amp Zo sum positively.

Sorry if my ignorance is painfully obvious - know just ust enough to be dangerous.

Interested to know how you would achieve 'neg output impedance' (which I suspect is a misnomer). I have seen a scheme that uses a transformer to sense current in the lead to the speaker.

Could this sensing trannie be part of the output winding? There are various feed back schemes that use this.

Rgds, martin
reVintage
Posts: 365
Joined: Fri Sep 07, 2007 9:54 am
Location: Sweden

Post by reVintage »

Try adding a negative Radd and do some simulations i Hornresp to see what happens. An idea could be to add just as much negative Rout to an amp to make its Zout 0 ohm.

Schematic from an old AES-paper:
Attachments
negout.JPG
negout.JPG (48.22 KiB) Viewed 15708 times
Brgds
Lars
slowmotion
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Location: Norge

Post by slowmotion »

SE amps with output impedance of 8-16ohms work fine for me with mid and high horns .... I prefer this to amps with low output impedance when driving horns. Don't know if this is a speacial case or not. I'm not going back, tho ...


:wink:
reVintage
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Location: Sweden

Post by reVintage »

Heja Norge!
You are absolutely right about driving mid and high with no feedback SE triode amps.

What we are talking about here is only applicable to bass horns constructed according to Leach findings.

But it should not be a bigger problem to add negative output impedance to a SE than a PP subwoofer amp :wink: .

Brgds
Lars
Brgds
Lars
lanshan75
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Post by lanshan75 »

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