Tubes driving dipole mids

[rick57]

My belated SL Phoenix is 80% done. I was going to drive them with LM3886 chip amps with high quality parts, but recently heard an SE 845 triode amp made with high quality parts. The latter was far more expensive, but sounded far more seductive, without being at all soft.

How well do you think a similar 20 watt SE 211 triode amp – maybe based on the Ongaku - would drive the Phoenix midranges (99 dB above 250 Hz, decreasing to 92 dB at 100 Hz)?

Linkwitz says:
The Phoenix main panel should work really well with low power tube amplifiers, because of its high sensitivity over the midrange and the generally low power requirements on most program material for the tweeter. The drivers represent an easy, low reactance load to the amplifier output transformer due to the restricted frequency range used. The output impedance should be low (<0.4 ohm) to maintain tight control over the voice coil motion.

Anyone heard tubes driving dipole midranges?

Thanks

 

[CLS]

With 99dB, I doubt you'd need 20W in a normal living space, especially within a limited spetrum.

Except bloody loud heavy metal & explosions in the movies, I think you would be happy with 8~10w on this midrange.

I've been using Focal Audiom 7k midrange for years. It's nominal sensitivity is 98dB/2.83V. I had tried 3W 2A3 SE on them & my ears was overloaded far earlier than they were.

Now the mid drivers are working with Oris horn without back chamber. I haven't measured the sensitivity. They sound much louder anyway.

I'm using 300B SE with them now. Headroom is much more than I need.

 

[rick57]

It’s 99 dB above 250 Hz, BUT decreasing to only ** 92 dB at 100 Hz

So in a largish room, a 300B would I think be somewhat marginal.

A little more power than 20 W would maybe add an effortlessness.
Options that occur to me are a KT88 (6550) PP, or an Aleph 30 watter.

 

[CLS]

I just thought you need this amp only for 99dB midrange after the active xover? 200Hz~4kHz or the likes?

 

[jeff mai]

It’s 99 dB above 250 Hz, BUT decreasing to only ** 92 dB at 100 Hz

I thought the Phoenix was EQ'd flat.

 

[rick57]

The Linkwitz Phoenix www.linkwitzlab.com/builtown.htm mids run 100 – 1500 Hz on an open baffle, and efficiency declines (but is balanced by EQ) below 250 Hz.

So the amp needs to handle the least efficient 92 dB part.

Effective load impedance is 3.5 ohms for the midrange.

 

[rick57]

> I thought the Phoenix was EQ'd flat.
Yes it is. The “99 dB above 250 Hz, decreasing to 92 dB at 100 Hz” is a quote off SL’s site, apparently pre EQ.

As I understand it, when you EQ boost, you lose some efficiency "off the peaks". I’m not sure what that would translate to, but would think that the efficiency *after EQ, would be (over the operating range) between 92 – 99 dB.

 

[CLS]

Well, yes.
You may need bigger amp to deal with the less sensitive portion.

However, 2 more considerations:

1) normally, limited spectrum needs less power to deal with
2) drivers on open baffle hit mechanical limit far earlier than thermal limit.

[ LR mentioned in his web page, in the open baffle bass, 20~30w would be enough to "bottom" most drivers around fs. ]

So, I suggest you still can try some little amps for yourself. If you could borrow them from someone, just open your mind and try.

I bet you'll love the low power simple amp better than those bigger one

 

[rick57]

> You may need bigger amp to deal with the less sensitive portion.
You’re not suggesting turning a 3 way into a 4 way?

> 1) normally, limited spectrum needs less power to deal with
> 2) drivers on open baffle hit mechanical limit far earlier than thermal limit.
Yes

When you said
LR mentioned in his web page, in the open baffle bass, 20~30w would be enough to "bottom" most drivers around fs.

I recall that was in connection with the bass, not the mids.

> try some amps for yourself. If you could borrow them from someone, just open your mind and try.

A good idea The ones I want to try most are a 211 and an Aleph!

> I bet you'll love the low power simple amp better than those bigger one

Are you hinting that a 300B might be enough?
The 300B midrange is liquid/velvet, the 211 midrange - if like an 845 – should be muscular/velvet– I prefer the latter.

Cheers

 

[CLS]

I was not suggesting 4ways, too complicated.

I meant, in your whole midrange operation, for the less sensitive portion, you'd need more power (for particular occasions at least).

"Big" tubes often sound 'stronger'.

However, a good design of 300B or even 2A3 SE amp can also be fast with richness & full strength. No problem at all.

 

[derf]

[ LR mentioned in his web page, in the open baffle bass, 20~30w would be enough to "bottom" most drivers around fs. ]

I've always wondered why Linkwitz didn't use 2 x 18" drivers per side, rather than 2 x 12". One 18" has twice the surface area of a single 12", usually around the same fs. The drivers are only being used to 100-150hz, so what's the need for a high excursion 12's?

Surely moderate excursion 18's would be more appropriate, cause less distortion etc. It seems it might of ended up this way purely for aesthetic reasons

 

[rick57]

What SE circuit & parts do you think would give the most strength/ effortless powerful sound?

> wondered why Linkwitz didn't use 2 x 18" drivers per side

Cost? The XLS 12 was $US 120? How much would a 18" of comparable Vd and distortion be? And yes aesthetic reasons – ie small size.

I agree moderate excursion 18s would be more appropriate, cause less distortion etc. Do you know any suitable – pro-sound eg P Audio or JBL?


Thanks

 

[derf]

Cost? The XLS 12 was $US 120? How much would a 18" of comparable Vd and distortion be? And yes aesthetic reasons – ie small size.

I suppose you could find something for slightly above $200. VD would be quite a bit better with almost any 18" I'd suspect, due to the massive rise in surface area(double that of a 12"). TBH, I don't think the aesthetic impact would be that huge(what's 6 inches between friends?) and what you end up with is twice the surface area per side...

I just think the upsides outweigh the down, even from a marketing perpective. I'm kinda suprised SL didn't come to this conclusion aswell...

 

[rick57]

The rise in surface area would be 2.25 times that of a 12", but I think Xmax would be lower, as the XLS is designed to maximise that, and pro drivers are more about efficiency. It could be 50-100% more Vd.

But he does say in different places if you want more, either double the diploes or – I think better – cover below about 40 Hz with a sealed box – his Thor.

I agree the aesthetic impact would not be huge and if you had a big room that would be better.


But to return to topic - has anyone used or heard a 20 watt SE 211 or similar triode amp – or say a 30 watt Aleph – to drive 95 db speakers?

 

[CLS]

18" Dipole Bass

...

I did make one of these

I use 2* EV DL18W in a W baffle, just large enough to wrap around them. ( HxWxD is 536x752x550mm )

Or you may see the old post for the picture.

The EV 18" PA woofer has only 5.6mm Xmax & low Q. With such a 'small' baffle, amazingly, only 5~6dB of EQ is enough to work quite well. Measured by RTA, it extends flat to around 30Hz by this setting, somewhat attenuated in 20~25Hz region, but still there. I believe they can handle more EQ to make it flat all the way down, I just take it conservative.

In normal real use, the diaphragms barely move, can be felt but can not be seen. I've tried 8Hz dinosaur foot steps, then the movement could be seen, but still not much. The bass is more than enough to shake the windows & ceiling.

If you got good energy in 30~50Hz region, the strength of sound pressure would be very impressive & enough to shake most things in the house. Below that, it turns to mostly 'body feel' & much less 'hearing'.

I think LR chose 12" Peerless for both good Xmax & low Fs. So they can be tuned to fit most normal listening habits & living spaces.

But if you got some PA woofers lying around, don't be afraid to put them on open baffle just because the small Xmax & low Q. They are just too strong for home use. Just EQ them, feed them power, then they will sing

Talking about effortless dynamics, PA drivers rule! Especially those big ones.

 

[CLS]

Oops, sorry I made a mistake.

In the posts above, when I said LR, I meant Mr. S. Linkwitz.
I mixed the name with both Linkwitz & Riley....

 

[derf]

I think LR chose 12" Peerless for both good Xmax & low Fs. So they can be tuned to fit most normal listening habits & living spaces.

Although this is gross simplification, excursion = distortion. Like I said before, if it's only to 100-150hz, 18's have the surface area not to require the Xmax, is 6 inches really that much of a problem in any listening space that'll allow dipoles in the first place?

At any rate, sounds like you have a cool setup, CLS

Back on topic, never heard those kind of amps driving 95db speakers, I'm sure aslong as you don't run out of wattage, you'll be fine with whatever you choose to go with

 

[rick57]

> is 6 inches really that much of a problem in any listening space that'll allow dipoles in the first place?

I don’t think so at all, it’s probably SL’s view of SAF + cost:

I’m not saying there aren’t any, I’d love to hear of some, but what 18 inch driver available now beats the XLS?

> sounds like you have a cool setup, CLS

Agreed

> Back on topic

Thank you!

I'm sure as long as you don't run out of wattage, you'll be fine with whatever you choose to go with

Probably right. As a 211 SE may cost $US 1000 – 1500, I thought I’d seek opinions . .

 

[derf]

Probably right. As a 211 SE may cost $US 1000 – 1500, I thought I’d seek opinions . .

For me, that's quite a bit of money to drop on an amp. Even if does make an improvement, it'd have to be an awfully noticable one for me to be fully satisfied.

Granted, I'm obviously not as flush as you. So there may just be a little, tiny bit of jealousy creeping in there, somewhere...

I’m not saying there aren’t any, I’d love to hear of some, but what 18 inch driver available now beats the XLS?

Not trying to tread on SL's toes here or bash the XLS, but I think almost any *good* 18" with around 5mm+ excursion will out do the XLS in this application, by virtue of it being an 18" driver.

Yes, the VD may be within only 50-100% more than with the XLS, but the 18" attains that VD via being big and moving a little , whereas the XLS does it by being smaller and moving more.

Also, as the design we're talking about only needs to go up to 100-150hz, any low Q driver is going to be 5 or 6 db down(if not more) by 100-150hz(in comparison to at 500hz or so), which means less eq needed to get flat down to fs, making qts less of an issue.

I'd check out the Eminence range of 18" drivers, I'm sure one of there cheaper models would be more than enough for this application.

 

[rick57]

I agree - Eminence or P Audio might do the trick.


> that's quite a bit of money to drop on an amp

I agree, absolutely. But YMMV – on a local forum someone said today $A 2500 ie US$ 1800 is “peanuts” for 30 watts class A(!). He’s right for an 845, but for just about anything else, including DIY class A, it’s not.

I heard a commercial 845 amp for about an hour, and to me it was awfully noticeable.

Still, I’m surfing etc to see that it really is best bang for buck –is there a cheaper option of lower cost.
(Joe Net Archives may have an answer).

What's the views here? KWV? Frank?

Cheers