My Swansong speaker build

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#16 Re: My Swansong speaker build

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Nick wrote: Sat Jul 23, 2022 9:34 pm Yes, that's all I was saying, it seemed to me, to shine a light on the perspective of the speaker designer versus that of someone coming from the amp side.
It's Culture Wars !
No .. but seriously... I will say that you have to spend money to make an autoformer sound as good as a good resistor.
I found that the BI planar resistors were significantly better than the 50% nickel autoformers that Dave S made for me ; at least when knocking 10dB or more off the compression drivers.
What did you use for the tweeters, Nick ?
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#17 Re: My Swansong speaker build

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#18 Re: My Swansong speaker build

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Yes , very good.
+ your point about the bass drivers being driven separately of course.
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#19 Re: My Swansong speaker build

Post by Toppsy »

I have now re-drafted the driver layout similar to the layout to the photo in post #6. This places both the Revelator bass drivers within the same shared volume. After speaking to Scott regards this layout he advised to design the bass volume as a double chamber reflex, hence the reason for the 2 separate chambers with connecting port tubes. There will likely be some minor tweaks to adjust these volumes, ideally I believe the total volume should be split into 3 with 2/3 for the lower chamber and 1/3 for the upper, but for now this layout seems to work and Lynn is happy with the aesthetic looks of the revised front baffle. Also allows better positioning of the Hypex amp. So a win-win result.

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#20 Re: My Swansong speaker build

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Neat. :)
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#21 Re: My Swansong speaker build

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Nick wrote: Sat Jul 23, 2022 9:34 pm
That being the case, the midrange and HF have to be padded anyway to the level of the bass units
I thought Colin was talking about using a Hypex amp for the LF?
Yes, but for level matching (ignoring everything else for a moment) there are two ways of going about it with a semi-active system. You can raise the output of the bass drivers, or you can pad down the midrange & HF to match them. Both work, & within reason, assuming you don't have a completely limp-wristed amplifier on one leg (most likely the midrange / HF) the difference in that narrow sense is mostly just a question of implementation & method. Whichever you do, your ultimate limit in this sense is always defined by the dynamic headroom and distortion performance of the least efficient element, which is inherent to the driver[s]. Not everybody will agree with this, but for me, overall system level-matching is not the main advantage to a semi-active system; their primary scoring points are greater flexibility for adjusting to room position etc., and avoiding needing some extremely large and expensive components necessary for a passive equivalent -especially inductors, since low DCR is pretty much mandatory to keep the filter functioning as intended & not cripple damping.

Re autoformers -I like the idea, but (correct me if I'm wrong -it's been a long time since I used them) while they are fine for adjusting overall SPL and / or impedance, they'll do just that and nothing more. But since these are drive units, not resistors, their impedance load varies with frequency and some of the impedance peaks need to be damped down to ensure the passive filters function properly. For example, the midrange units for this box will have roughly a 25ohm peak relative to the nominal level at 200Hz, which is right around the (passive) midrange high-pass filter frequency. If that peak isn't flattened out, the drivers will start to roll off, and then either level off, or peak back up again, which will affect power-handling / distortion, and ultimately the overall speaker response. Within reason (it's not always possible / practical) the simplest way of damping the peak down & ensuring the filter behaves as its supposed to is with a resistive shunt. The more complex alternative is to use an LCR Zobel, but that's three components rather than one. Sticking with this example, since the midrange impedance load will be about 12ohms, which is a little higher than ideal for a lot of amplifiers, we could then add an autoformer to address that, and what level adjustment, if any, is desired. But if (if ;) ) you can get the necessary damping of the impedance peak and also drop the level a couple of ohms with a simple shunt resistor -it strikes me as a valid (and cheaper) solution. Since current / power demands tend to drop as frequency rises too, it shouldn't be causing excessive waste, especially if you're starting from a reasonably high efficiency in the first place.

More generally (and this is just a personal thing) -I tend to think that within reason, you can get 'better' results if you make the speaker load as unreactive as possible, even if this means sacrificing a touch of sensitivity or drawing a little more current, than if you maximise sensitivity, but end up with a highly reactive impedance load & electrical phase angles. Context is obviously critical as it's going to depend on a bunch of factors that need to consider in the design stages. Nick -I'd be interested to hear your take on that as an amplifier designer; what sort of load would you prefer? Presumably a flat-line impedance with the highest possible sensitivity, but if we're having to make some compromises -which direction would you take?
Last edited by Scottmoose on Sun Jul 24, 2022 1:37 pm, edited 1 time in total.
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#22 Re: My Swansong speaker build

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Very interesting design and it prompts a couple of questions - as ever!

I experimented with ring circle small drivers myself and found it can work well, it did have some lobbing measurable but not audible to my ears.

Questions that occurred to me are:
1) What were your thoughts on time aligning the drivers with a stepped baffle?
2) What drove the decision for the CHN50 compared to the CHN40?

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#23 Re: My Swansong speaker build

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JamesD wrote: Sun Jul 24, 2022 1:37 pm Very interesting design and it prompts a couple of questions - as ever!

I experimented with ring circle small drivers myself and found it can work well, it did have some lobbing measurable but not audible to my ears.

Questions that occurred to me are:
1) What were your thoughts on time aligning the drivers with a stepped baffle?
2) What drove the decision for the CHN50 compared to the CHN40?

James
James, interesting your experiments in the past. Lobbing is something Scott and I have discussed. Good to know to your ears the measurable lobbing was not audible to you.
In answer to your questions:
1) To be honest James, not a lot really. Without some redesign of the simple box cabinets I don't think the driver layout lends itself to a stepped baffle and maintain the existing aesthetic appearance. A very big consideration to the choice of this design was WAF and I think the flat baffle works aesthetically and makes the build simpler. Lynn likes the look of the simple box format.
2) Again one of aesthetics. Price wise there is not a lot in them and both Scott and Stefan at KJF thought the CHN50 would work better in this design layout. The circular frame of the CHN50 is just a 1mm smaller in diameter than the frame diameter of the Satori Beryllium dome tweeter. The squarish frame of the CHN40 looked a little odd when I drafted these as a polar array around the tweeter.
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#24 Re: My Swansong speaker build

Post by Daniel Quinn »

What are the theoretical and empirical benefits of multiple drivers covering the same frequencies . Is it room size dependant ?
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#25 Re: My Swansong speaker build

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Nick -I'd be interested to hear your take on that as an amplifier designer; what sort of load would you prefer
Been thinking about this. I guess my answer would have to be it depends. As before, if you are making something that has to survive in the wild, then my instinct is to assume the worst, size and choose the output device(s) and add SOA limiting to ensure that everything will be fine. Then test into a 1R load and make sure it behaves. Then pick the compensation such that when you add a 1uf cap to that 1R load its still fine. Then punish the SOA limiting by grounding one input of one of the amplifiers, then drive the other one to 70% or so with a input signal, then connect the two outputs together and see if anything bad happens. However that's the making a pick up truck method, where it just has to keep working. If on the other hand you are making a racing car where the goal is it falls apart as it crosses the line, you throw all that away and I guess that's the condition from where you are asking the question. Not sure there is a single answer, but if I was designing a amp for use with a speaker, which is the DIY situation, my preference is assume the amp can handle the impedance swing, you can do that if you know what it is in advance, and size everything to match, increased sensitivity would be a good thing in that it will make it simpler to handle the reactive load. My instinct is to keep the output stage of the amp as close to the drivers as possible, which would mean the amps see more of the drivers oddness, but conversely the amps can control the drivers better. There is an argument that matching the amp to the speakers allow you to avoid a lot of things that you may want to do without, GFB for example, having a solution without that, that manages a low impedance output by just doing heavy lifting in the output stage (high current, lots of and/or big devices) would probably be a interesting thing to try.

All of the above is very much from a solid state perspective, some may be also valid for transformer coupled output as well.

One thing I just thought while typing all that. There is a lot of history of high sensitivity loudspeakers and valve amps, and low sensitivity speakers and SS amps, but other than folk like Nelson P, there is not as much about solid state outputs and high sensitive speakers. Generally when there is the idea of a high sensitive speaker in that context its something above 92dB/W. Maybe when I get the workshop here sorted out so I can get the new OB's in use outside shows, I should play with solid state amps and 98dB/W speakers and see what door's that opens. When I tried the OB's at Colins we started with the P6's and then Colin suggested using the 300b's. I was expecting a big change in sound, but in fact all I heard was just the extra bit of 2nd harmonic. You heard a much bigger change for example using the Eadindales going between those two amps as it was taking far more from the 300b's. Likewise at the show last month, the 100W mono's driving the OB's was a lot more neutral than I expected (which was good, but still not what I had expected based on other speakers). In fact, thinking about it, Chris tried his PA amps driving them at the last Owston, and again there was no obvious mismatch which again I expected, and had a pocket of excuses ready about the amp and speakers being a bad match, but they stayed in my pocket.

The last bit is somewhat off topic, but maybe not that far off. Maybe Scott has something to add to the stream of conscious ranting.
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#26 Re: My Swansong speaker build

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ps. it's 'lobing' not 'lobbing'.
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#27 Re: My Swansong speaker build

Post by vinylnvalves »

I have listened to a speaker with a similar driver spacing, it was very enjoyable to listen to, the impact of a big midrange driver without the beaming issues, obviously a reasonable combined sd. This speaker used BMR drivers, which have a flat wave front, which minimises lobing. They were 2.5” little drivers, but he used a lot of them.
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#28 Re: My Swansong speaker build

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Scottmoose wrote: Sun Jul 24, 2022 1:34 pm
For example, the midrange units for this box will have roughly a 25ohm peak relative to the nominal level at 200Hz, which is right around the (passive) midrange high-pass filter frequency.
Surely you would do this on the input of the mid/high amplifier - could the output transformer be optimised for mid/high work? Doing it on the output would also mean that it was virtually open circuit at low frequencies - would this affect a (likely) valve amplifier?

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#29 Re: My Swansong speaker build

Post by Scottmoose »

Amplifiers are Nick's solid state monoblocks.

No, a damping resistor, whether part of a fixed L-pad (https://sound-au.com/articles/l-pad-calc.htm) for level adjustment, or by itself for helping to flatten a midrange or HF driver's impedance peak, is a perfectly conventional feature in literally millions of loudspeaker crossovers. Nothing unusual here. Nominal impedance for a given leg with a damping resistor is the same calculation used for dissimilar parallel resistors (R1*R2)/(R1+R2).

So if we assume for e.g. a driver with an Re of 8ohms & a damping shunt resistor of 10ohms, then (8*10)/(8+10) = 4.44ohms [nominal]. The point about these damping shunts is that while they lower the overall impedance, they have a significantly greater impact on peaks -for e.g. those around resonance. That's a major reason for using them.
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#30 Re: My Swansong speaker build

Post by Scottmoose »

Re your post Nick, many thanks for that -lots to take away. Will look over properly in the morning as I don't want to miss anything, but on a quick skim re the 2nd half, personally I see nothing wrong with high power SS amps and high efficiency speakers, providing they're quiet enough. All other things being equal, I'd always rather have as much clean power (or power with any desired type of HD) as possible. I know a few over in the US in particular who do just that. I'll put a few thoughts together tomorrow, for whatever they're worth.
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