SET Friendly Confusion

[Mike C]

As you know, I'm looking into upgrading my speakers to be used with a 300B
SET amp. I have enough volume from the present 88dB ones, but conventional
wisdom suggests a bit more efficiency may improve the sound quality.

Package and WAF considerations pretty well limit me to 6.5inch drivers (as the
current S3TLs).
In looking for more efficiency, paralleling up the mid/bass drivers is a common way
to do this and evidently it can work very well. But here's my confusion.

Paralleled drivers will have half the impedance, right?
So if the bass drivers are simply paralleled, the speakers Z will be about 8 ohm
above Xover freq and about 4 ohm below it.
If one driver is rolled off above say baffle step frequency, then Z will be about 8 ohm
above this and about 4 ohms below it, I think.
And I guess that, in most cases, 'about 4 ohm' will mean in fact a minimum of perhaps
3 ohms or so?

This really doesn't look good, when SETs are said to like a moderately high and
fairly constant Z.
So how is it that one of the most SET friendly speakers, the Living Voice Avatar,
uses this configuration and gets away with it?
And the Eros at speakerbuilder.net seems a very good unit for a SET (and looks
a really fine speaker to boot).
Also there is the Ariel, very much designed for SETs.

Anyway, I'm confused. My thinking up to now has been to reject speakers with
such highly variable and low impedance, but it seems this may be wrong!

My choice to date for a design has been a small TL (6.5inch driver) similar to
my present speaker which I like a lot. But I guess I should add d'appolito bass
reflex designs to my list of contenders?

Any comments to help clear my confusion are welcomed!

[leadbelly]

Originally posted by Mike C
This really doesn't look good, when SETs are said to like a moderately high and
fairly constant Z.
So how is it that one of the most SET friendly speakers, the Living Voice Avatar,
uses this configuration and gets away with it?
And the Eros at speakerbuilder.net seems a very good unit for a SET (and looks
a really fine speaker to boot).
Also there is the Ariel, very much designed for SETs.

Anyway, I'm confused. My thinking up to now has been to reject speakers with
such highly variable and low impedance, but it seems this may be wrong!

Don't know about the Living Voice Avatar, but the Eros and Ariel have versions of the crossover specifically for SET use. The Eros MkI is a parallel crossover version with a 2.85 ohm dip, and the MkII is the series crossover version Wayne uses with his SETs. Similarly, the Ariel has a impedance correction portion of the crossover specifically designed to keep impedance more constant (between 3.5 and 8 ohms). So to answer what I think is the crux of your question, no, you are not seeing applications of "highly variable and low impedance" speakers to SETs.

[planet10]

A real set friendly speaker would turn a x.5-way speaker with a mid bass & a 0.5 driver into a 3 way with a single driver above the baffle-step & 4 of the same drivers below it... this gives constant load & BSC compensation. Also improves the midrange because that driver is no longer excursing to cover the bass.

dave

[leadbelly]

Originally posted by planet10
A real set friendly speaker would turn a x.5-way speaker with a mid bass & a 0.5 driver into a 3 way with a single driver above the baffle-step & 4 of the same drivers below it... this gives constant load & BSC compensation. Also improves the midrange because that driver is no longer excursing to cover the bass.

dave

I thought you were allergic to that many drivers

But I'm not sure I understand. So one version of this would be 1 fullrange at the top and 4 identical drivers beneath it with top rolled off at the baffle step? But how does that help impedance if 4 replace 1 driver, since 4 wired series/parallel you wind up at the same nominal impedance as 1?

[planet10]

Originally posted by leadbelly
I thought you were allergic to that many drivers

You never saw my 4-way system with 4x15", 2x6.5", tweeter + super-tweeter... each side driven with 2 Bryston 4bs & a Bryston 3B -- 1-way or mostly full-range 3-ways are just work out a bit better at home.

But I'm not sure I understand. So one version of this would be 1 fullrange at the top and 4 identical drivers beneath it with top rolled off at the baffle step? But how does that help impedance if 4 replace 1 driver, since 4 wired series/parallel you wind up at the same nominal impedance as 1?

the 4 drivers would have the same impedance & sonic characteristics as the single driver, but with 6 dB more sensitivity... XO can be simple & seemless. I have 10 surplus Kipsch (?) 6" + a wave-guide loaded VIFA tweeter (somewhere) for just such a project -- should be 96 dB midband -- i'll bi-amp with a couple 1.25 W 50EH5 amps.



dave

[HiFiNutNut]

Dave,

May I ask how you connect the 4 woofers? I have a WWMTMWW speaker and whenever I tried serial connection of 2 woofers the sound sucked while parallel connection was OK. Common practice is 2 pairs of 2 woofers connected in series then parallel but I could never get that working well and the bass was totally unacceptable. I have temporarily abandoned the top WW and the SPL of the bottom WW happens to match well with the MTM. But ultimately, using the additional top WW will halve the excursions and hopefully distortions but this is an expensive way to do it because I think I need one more power amp in order to preserve the parallel connection, i.e. 2 separate sets of 2 woofers, each connected in parallel. If I could find the right way to connect them without sound degradation and without requiring an additional amp it would be great.

Regards,
Bill

[planet10]

Originally posted by HiFiNutNut
Common practice is 2 pairs of 2 woofers connected in series then parallel but I could never get that working well and the bass was totally unacceptable

That's it.

A bass reflex? Or did you get the phasing wrong? Or one of the drivers with dramatically different impedancce curve?

dave

[HiFiNutNut]

Dave,

It is a BR. I have not tried connecting 4 woofers. My experiments told me 2 woofers connected in parallel sounded substantially better than connected in series. It was night and day. So I did not bother connecting 4 woofers. I guess the reason could be doubling the inductance vs halving the inductance. When connected in parallel, the inductance is only 1/4 comparing to serial connection. My amplifier has a 200,000uF capacitor bank and a huge transformer (plus massive heatsinks of course) so should be capable of driving drivers in either connection. This may not be due to back EMF as Svante proved somewhere in this forum that back EMF is the same with either connection.

Regards,
Bill

[planet10]

Originally posted by HiFiNutNut
My amplifier has a 200,000uF capacitor bank and a huge transformer (plus massive heatsinks of course)

And will have about 4 x as much distortion driving 2 ohms as opposed to 8 ohms...

My recent experiences (with tube amps mind you) is that series connection sounds better.

dave

[HiFiNutNut]

Dave,

Thanks for your replies and I will certainly do my tests once again.

Regards,
Bill