Speaker Motors

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Scottmoose
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#16 Re: Speaker Motors

Post by Scottmoose »

There are a few examples of that; Wilson have / have had a few designs with dissimilar sized LF units sharing the same cabinet volume. As far as loading goes you can create a set of compound T/S values for low frequency modelling purposes; Thorsten did that a few years back. Works OK so long as you don't go crackers and the drivers aren't ridiculously far apart. Above the mass-corner frequency Fhm it gets more involved as electrical filter analogies (a la Small) are only useful in the driver's rising response (acceleration) BW.

Dissimilar loads with the same type or different types of drivers is a related field. About 20 years back there were a few attempts at running two drivers in two differently sized expanding QW / horns, the shorter one being intended to fill in the harmonic nulls of the longer. Horst does a variation on this with some of his horn designs. Works to a point, and you get some interesting loading effects on the series (or parallel) wired drivers also.
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#17 Re: Speaker Motors

Post by Nick »

If you used two identical speakers in series, you've doubled the impedance seen by the amplifier at all frequencies. Perfect potential divider.
Yes, all very true, but in this case irrelevant as he is not.
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#18 Re: Speaker Motors

Post by Mike H »

Nick wrote: Thu Feb 28, 2019 11:55 pm I would expect the resistor and the speaker coil will generate identical amounts of heat.
Er, so would I ack-shirley ..... speakers are actually quite inefficient so a lot of power goes to making heat.

I also dare to mention the NVA amp is not the OTL that you are doing this for. I think? But, as a sperrymint, to mess about with stuff, OK. :D
 
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#19 Re: Speaker Motors

Post by Mike H »

chris661 wrote: Fri Mar 01, 2019 10:00 am My inclination would be to play with adding mass to the internal driver to make sure its resonant frequency matches the Fane's.
Yes.

Image
 
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#20 Re: Speaker Motors

Post by Cressy Snr »

Mike H wrote: Fri Mar 01, 2019 5:40 pm
Nick wrote: Thu Feb 28, 2019 11:55 pm I would expect the resistor and the speaker coil will generate identical amounts of heat.
Er, so would I ack-shirley ..... speakers are actually quite inefficient so a lot of power goes to making heat.

I also dare to mention the NVA amp is not the OTL that you are doing this for. I think? But, as a sperrymint, to mess about with stuff, OK. :D
Yes I like messing about with stuff. :D
On the resonance front, I twiddled my sig gen to find the Fane's Fs and yep, it visibly increased its excursion at about the frequency it says in the spec.
Connected up my extra speaker motor on its own and kept adding strips of self-adhesive window lead tape to the dustcap of the motor until it too increased its excursion at the same freq as the fane. It took four lead strips to bring it down sufficiently.
Put the two back in series and they both bounced up and down in unison at the same frequency. Harmless fun. Main driver makes the noise, the internal speaker motor is the 'silent' partner and gives me the 16 Ohm impedance I want.

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#21 Re: Speaker Motors

Post by Mike H »

I've obviously led (pun) too sheltered a life I had to look up self-adhesive window lead tape - oo-er!

Is it real lead tho? Well obviously heavy. I'm thinkng Blutack should work also.
 
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#22 Re: Speaker Motors

Post by Cressy Snr »

Mike H wrote: Fri Mar 01, 2019 6:09 pm I've obviously led (pun) too sheltered a life I had to look up self-adhesive window lead tape - oo-er!

Is it real lead tho? Well obviously heavy. I'm thinkng Blutack should work also.
Aye, Blu-Tak would work , but that lead window tape damps like buggery and is heaaavy.
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#23 Bob Carver Challenge

Post by rowuk »

Back in the day, Bob Carver challenged the audiophile press, claiming that he could replicate the transfer function of a tube amp with his SS power amps.
https://www.stereophile.com/content/carver-challenge
Bob Carver won. One of the major factors was adding a resistor to the output to dramatically reduce the damping factor. With many speaker types (including his dipole "Amazings", this also increased the apparent LF extension.
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#24 Re: Bob Carver Challenge

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rowuk wrote: Sat Mar 02, 2019 11:23 am Back in the day, Bob Carver challenged the audiophile press, claiming that he could replicate the transfer function of a tube amp with his SS power amps.
https://www.stereophile.com/content/carver-challenge
Bob Carver won. One of the major factors was adding a resistor to the output to dramatically reduce the damping factor. With many speaker types (including his dipole "Amazings", this also increased the apparent LF extension.
Yes, I read about that a few years ago. Thing is I'm using a reactive element in my own speakers as the 'silent' partner to the main driver, simply to get an nominal impedance of 16 Ohms, to make life easier for my forthcoming single tube OTL.
IME as I said earlier, adding resistors in line to the main driver, more often than not, will ruin the bass performance of the system.

Series resistors can have their uses, eg, forcing low Qts (around 0.2) drivers to produce some semblance of bass when put in transmission line cabinets, though why you'd want to do that is another matter; however people do do it. Apart from that, IMO resistors should be restricted to attenuating tweeters, where they do the job they are asked to without audible side effects.

Now then, after crudely synchronising the Fs of the 'silent motor' and the Fane full ranger yesterday, I've had a chance to listen properly this morning, and the overall tone of my speaker system is fuller, richer, with more saturated colours. Solo piano is very good, as is any kind of guitar based music. Bass instrumentation is nice and tight and what extension there is with my sealed boxes rammed against the walls is kept firmly under control in my small 12 x 13 x 8'6" high room.

The straight 8 Ohm Fanes, do sound slightly arid in comparison. It's not night and day, but the 16 Ohm setup is usefully better and provides an easy listening experience, that can be enjoyed for hours. A more conventional method of creating a 16 Ohm system would be a second set of Fane 12" full rangers, series wired in an isobaric arrangement. That, obviously would mean building a new set of cabinets and I may do that eventually.

For now though I think this 'silent motor' partner arrangement, stolen from the guitar amp world, does work extremely well. I could never have thought of such a thing independently, so it's a bit of fortuosity that my daughter bought me a guitar amp book.
Last edited by Cressy Snr on Sat Mar 02, 2019 1:21 pm, edited 1 time in total.
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#25 Re: Speaker Motors

Post by IslandPink »

Can you get more power out of the OTL if it's set up for 16-ohm load ?
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#26 Re: Speaker Motors

Post by Cressy Snr »

IslandPink wrote: Sat Mar 02, 2019 12:39 pm Can you get more power out of the OTL if it's set up for 16-ohm load ?
Maybe (I^2R and all that) but my primary objective, rather than to try to increase power, is to ease the pressure on the 13E1s. The higher impedance load, should reduce distortion a tad and give the 13E1s an easier time. I should, because of increased efficiency with the higher load, be able to reduce the idle current a bit, which ought, in theory, to prolong the life of the tubes.
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#27 Re: Speaker Motors

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Cressy Snr wrote: Sat Mar 02, 2019 1:03 pm Maybe (I^2R and all that) but my primary objective, rather than to try to increase power, is to ease the pressure on the 13E1s. The higher impedance load, should reduce distortion a tad and give the 13E1s an easier time. I should, because of increased efficiency with the higher load, be able to reduce the idle current a bit, which ought, in theory, to prolong the life of the tubes.
You'll be able to experiment with the amount of feedback too, I know Wolfgang uses a potentiometer for exploring different feedback levels.
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#28 Re: Speaker Motors

Post by rowuk »

It would be interesting to see/hear if the LCR equivalent of that speaker would provide similar results (without compression effects due to the voice coil getting hot).
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#29 Re: Speaker Motors

Post by Nick »

It might be interesting to try the primary of a 115-115 torroid as a autoformer to connect the speaker to the amp.
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#30 Re: Speaker Motors

Post by Cressy Snr »

I'll try it this week or next and report back.
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