12 inch driver?

Dedicated to those large boxes at one end of the room
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10040
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#16 Re: 12 inch driver?

Post by IslandPink »

It seems to me that if you're going to use the same approach, it needs to use a roughly similar base driver ( pun only accidental ).
From what I've seen, Richard's approach to 'doping' the driver involved quite a lot of material, such that it -
1. damped a lot of the potential HF energy that could come from the cone
2. Provide a mechanical low-pass effect due to the damping and the extra mass
3. Increase the driver Qts so that it was more suitable for a sealed box

So, you really need to have a rough idea of what driver was used. I'm assuming it was a non-whizzer driver ?
"Once you find out ... the Circumstances ; then you can go out"
User avatar
Nick
Site Admin
Posts: 15483
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#17 Re: 12 inch driver?

Post by Nick »

I think its more a question of what would you do without damping given the box and preference for simple xover. From what I can see it was a QTX driver of some sort, but if I could find TS parameters for them (which I cant), the doping would throw that out the window anyway.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
JamesD
Old Hand
Posts: 997
Joined: Tue Oct 09, 2007 4:26 pm
Location: North Yorkshire

#18 Re: 12 inch driver?

Post by JamesD »

This suggests that something like the SB Acoustics SB34NRX75-6 might work well as it has a relatively heavy cone to get the very low Fs of 19Hz for the driver and although an ideal sealed box for the driver is larger than the existing box, the 50 litres or just under of Daniels sealed box yields an F3 of 37Hz at the cost of a Qtc of just over 0.9. Cost of the SB driver is £145 from Falcon Acoustics... Sounds like a possibility except for the relatively extended frequency response of up to 5KHz so it would probably need a roll off from the crossover as it gets a bit slow on transients and peaky above 2Khz

ciao James
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8597
Joined: Mon May 21, 2007 9:42 pm

#19 Re: 12 inch driver?

Post by Paul Barker »

Glad youre dropping in James.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8597
Joined: Mon May 21, 2007 9:42 pm

#20 Re: 12 inch driver?

Post by Paul Barker »

Daniel I doped lowther alnico 8” after the late Sukuma San. Cant recall any magic. A man came to the house to collect all such drivers and recondition them for me. He never returned and I lost his details. Oops! Sure he was cosha (however thats spelled), maybe he died of a heart attack and his wife couldnt fulfill his orders. He claimed Lowther supplied him new baskets etc. On reflection, I might have been conned.

cut the whizzer off another of same ilk. That sounded horrible.

So my very limited experience of doping wasnt great.

But glad its working for you. I very much get youre sentiment on crossovers though. Im ok with these speakers I use having only the tweeter 6db’d which is beautiful at midrange as its a celestion paper mid/tweet alnico motor. Best alriund tweeter Ive auditioned. If I could only support my system to communicate with bats and young people Id be done. I might only hear detrimental additions to frequencies I dont want messing with. So I dont play music to bats at home. I found just the two types of drivers blend magically in the midrange, thats perfect. Beautiful integration. super tweeters ive tried upset that beauty, and give pesaz thats not timbred right.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
Daniel Quinn
Old Hand
Posts: 804
Joined: Thu Jan 05, 2017 9:19 am

#21 Re: 12 inch driver?

Post by Daniel Quinn »

The ts parameters for a sealed box are not crucial so I’m lead to believe . The volume is 50 litres .

The cabinet is lined with 15mm Perspex and 6mm Steel and there are wooden rods to between surfaces to brace .
JamesD
Old Hand
Posts: 997
Joined: Tue Oct 09, 2007 4:26 pm
Location: North Yorkshire

#22 Re: 12 inch driver?

Post by JamesD »

That depends on what one means by "crucial"...

Any simulation result is only informative and not, in practice, definitive but information is often all we have to base our decisions on...

The ts parameters when entered into the sealed box equations via modelling software (could be done by hand or excel if you are perverse enough) would tell you how the driver is likely to perform in a sealed box of a given volume - so the SB driver mentioned above in your box of 50 litres would have an F3 of about 37 Hz and so will reproduce almost all modern music properly and most classical music too with regard to bass frequency response. The Qtc (Driver and Cabinet Q) of 0.9 ish tells us that the bass will be under damped to some degree and so transients will suffer a little compared to a bigger box. For instance the same SB driver in a 450 litre box has an F3 of 24Hz and a Qtc of 0.5 for perfect transients but a slightly dry sound in comparison. The maximally flat response is from a 120litre sealed box and yields an F3 of 34Hz for the, generally considered, most musically even response...

Whoever stated that TS parameters are not crucial to sealed biox modelling was literally correct but somewhat misleading to you...

ciao

James
Daniel Quinn
Old Hand
Posts: 804
Joined: Thu Jan 05, 2017 9:19 am

#23 Re: 12 inch driver?

Post by Daniel Quinn »

Interesting James .

I’ve never noticed a lack of transients , but you never know. Plenty to ponder , thanks for your informative post.
User avatar
Nick
Site Admin
Posts: 15483
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#24 Re: 12 inch driver?

Post by Nick »

Just remember that in the above when James talks about transients he means how the 12" driver and box responds to a step change of signal. In your case the two other drivers will also be be adding to the edge. In the case of the heavy doped driver (if it's anything like the one Richard sent me to try) it will be responding so slowly it will be so different because of the extra mass.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Daniel Quinn
Old Hand
Posts: 804
Joined: Thu Jan 05, 2017 9:19 am

#25 Re: 12 inch driver?

Post by Daniel Quinn »

There is always a trade off .

I’m still of the opinion that doping is better than passive components in terms of what I hear .

Again I’m concerned there may be a difference between the theory and what I hear.

It’s all very well sitting there thinking he theory and measurements on this speaker are brilliant. I’d rather listen to the music
User avatar
Nick
Site Admin
Posts: 15483
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#26 Re: 12 inch driver?

Post by Nick »

The speakers Richard sent me did do something good (once I replaced the incorrect tweeter cap, that's another conversation some time) but the problem I had with them was they were so inefficient that there was very little dynamic range between too quiet and burning driver out levels. The thing theory alone won't give you is what you prefer but once you calibrate that against theory I find it works just fine. That's what James is talking about with the varying system Q.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Daniel Quinn
Old Hand
Posts: 804
Joined: Thu Jan 05, 2017 9:19 am

#27 Re: 12 inch driver?

Post by Daniel Quinn »

Your description is not something I recognise as a problem.

It may be the language?

For instance , in the air tonight . It goes from Collins voice to explosive drums effortlessly and dynamically .

I listen to 70s rock music and these speakers give (gave 😂) me the best experience so far. But everything is temporal so I accept that better may be available.

Also I use a 3 way with the midrange in its own enclosure with an inductor and cap.
User avatar
Nick
Site Admin
Posts: 15483
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#28 Re: 12 inch driver?

Post by Nick »

Your description is not something I recognise as a problem.
I don't mean within the context of playing a piece of music, but if I wanted say a extra 10dB of sound in the room for some rock I was not sure the driver would take it. It was however a much smaller driver in question in a small two way speaker, maybe Mission something.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Post Reply