Cut the driver holes in the cabinets this evening:
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An externally hosted image should be here but it was not working when we last tested it.
Hi, driver specs ... some ideas
It would be fun if we could forget real world and just design a dreamdriver going low and loud
But you need a efficient driver, so lowend will be a bit restricted
Played a bit and found some realistic parameter
VAS 80 ltr. ........fs 30hz ........Qts 0.4
It gives a box=30 ltr. netto, roughly -3db/50hz and -6db/40hz
With fs=25hz rolloff would be 5hz lower - but will it be possible to maintain good efficiency, I cant say really
It would be fun if we could forget real world and just design a dreamdriver going low and loud
But you need a efficient driver, so lowend will be a bit restricted
Played a bit and found some realistic parameter
VAS 80 ltr. ........fs 30hz ........Qts 0.4
It gives a box=30 ltr. netto, roughly -3db/50hz and -6db/40hz
With fs=25hz rolloff would be 5hz lower - but will it be possible to maintain good efficiency, I cant say really
ShinOBIWAN said:
Considering that this driver is still in the midrange, well lower midrange, my key concern would still be linear decay - more specifically linear decay within at LEAST the first 8-12 db (for the entire midrange section (around 80-90Hz to at least 500 Hz), WITH OUT using dampening fiber to make things look "pretty". In that range I want it to drop within half a milisec. (less=better). I'd prefer if it was down to a very low 40 db within this range, but I know better and it isn't that audibly important in this passband.
I realize this isn't a T/S parameter, never the less its what I'd be most concerned with.
The next thing I'd be looking for is high force AND efficiency. I'm aware that the two are effectively opposing choices, but I'd still be looking for something that was at least dealing with 10 Bl, moderate mass (for its sd) - i.e. below 20 grams of mms, and at *least* 93 db (nominal 8 ohms) at 150 Hz infinite baffle. Do NOT rely on simply paralleling the drivers to obtain greater perceived efficiency. There is clearly an audible difference in favor of a greater eff. for a driver (and in this passband this will truely define the "tarantism" quality you seek).
Considering the above factors I'd almost have to think you'll be using a ported design (because the driver's resulting fs will be fairly high), but as you have found - ported done correctly can actually sound quite good (..depending on the driver and the amplifier).
Try running these requirements past Per, and see what he suggests for a resulting driver's T/S. Then do some modeling and see what you can come up with, remembering of course that you have room gain and some additional port gain if coupling the port near the floor (and of course this will likely only be possible for one port). Note that even with a high fs driver you can get good extension from a non-aligned port and room gain. I'd probably be looking for a port tunning freq. of about 30-35 Hz with such a driver where little "fundamental" energy resides with most recordings.
If he needs to get eff. up with another magnet as Troels did here, then spec. it..
http://www.troelsgravesen.dk/HES_II.htm
(..and in fact that is an excellent article that should be read and re-read by any loudspeaker diy'er - there are a LOT of subtle things going on with that design that result in not so subtle performance)
m0tion said:
Energy is building up exciting all shorts of room modes and structural resonances. Deep bass needs big room to be reproduced effortlessly.
Rather than choking it is better to avoid it in small rooms. Shooting for efficiency from 40Hz-100Hz is a better plan in my experience. Leads to a quicker more dynamic speaker for rooms no larger than 30sqm with 3m ceilings.
ScottG said:
Thanks Scott. Thing is, Per is very realistic about what can and can't be done. I pretty much spec'ed a sort of similar driver to what you propose and it quickly became apparent that it would have great strengths but also great weaknesses - not a well rounded driver in other words.
I believe getting the decay down to those levels you specify will necessitate a cone material, surround and spider change which is very expensive. Think more like £2k for four 8" drivers! Its likely that new cone geometry will need to be spec'd for the new material and this involves costly jigs to create and test the profiles to ensure controlled breakup and also to check that were heading in the right direction. Despite Per's experience I don't think he would be happy, nor I, with a one shot at getting it right so clearly there's going to be some testing to be done there - extra expense.
Per did say that he'd include the new Kapton/Alu hybrid VC former which offers both extra midrange clarity and the mechanical break nature when reaching excursion limits.
If going vented he suggested a QB3 alignment for best transient nature without compromising driver efficiency through lowering Fs or using EBS alignments.
For sealed high BL is counter productive to extension because Qts quickly drops as Qes becomes 'stiffer'.
And basically it went on like this for a good few emails, with me being unrealistic and Per patiently trying to guide me in the right direction. In the end I was so confused, enlightened and downright tired that I gave up and said I would get in touch again once I had the money to order the driver so as not to waste anymore of his time.
I'm now considering being cheeky and asking to buy a single driver to test and then order the other 3 after I'm happy with the proviso that I still qualify for the 15% discount. So I'm looking to start searching for the perfect 8 again.
ShinOBIWAN said:
I believe getting the decay down to those levels you specify will necessitate a cone material, surround and spider change which is very expensive. Think more like £2k for four 8" drivers! Its likely that new cone geometry will need to be spec'd for the new material and this involves costly jigs to create and test the profiles to ensure controlled breakup and also to check that were heading in the right direction. Despite Per's experience I don't think he would be happy, nor I, with a one shot at getting it right so clearly there's going to be some testing to be done there - extra expense.
I'm now considering being cheeky and asking to buy a single driver to test and then order the other 3 after I'm happy with the proviso that I still qualify for the 15% discount. So I'm looking to start searching for the perfect 8 again.
Hmm, you might want to look back at the troels page I posted..
hint, hint:
http://www.hoejttalerbutikken.dk/product.asp?product=295&sub=11&page=1
with the extra magnets of course..
Even with a smaller volume and a higher tunning freq.. I'd bet you would be considerably better off - AND have a LOT more cash in your account. Heck, you could even go with a compound configuration sealed and STILL have more cash (but freq. extension would of course be lessened). (.. all provided of course they still have enough of these drivers left.)
I know, I know - you are still shooting for AT 8"s though.
ScottG said:
Hmm, you might want to look back at the troels page I posted..
hint, hint:
http://www.hoejttalerbutikken.dk/product.asp?product=295&sub=11&page=1
with the extra magnets of course..
Even with a smaller volume and a higher tunning freq.. I'd bet you would be considerably better off - AND have a LOT more cash in your account. Heck, you could even go with a compound configuration sealed and STILL have more cash (but freq. extension would of course be lessened). (.. all provided of course they still have enough of these drivers left.)
I know, I know - you are still shooting for AT 8"s though.
I've read Troels work... honest!
You know me Scott, half the fun is spending over the odds and being happy about it. So forgive me if I don't want to use a crusty 15 year vintage Vifa C20 woofer, Troels lies anyway.
What I really need to do is just break loose of this damned aesthetic illness I have and go with 15 or 18's, that would solve a ton of issues straight away. But it would kill me to ever build a baffle wide enough to house one of those... no seriously it would, I feel ill just thinking about it.
'kin hell.
I'm sure Per will be thrilled when he see's my mail in his inbox tomorrow. Lets hope he's made a revelatory driver advance since our last contact. Scott can you mail him, tell him to lie and just to let me know what I want to hear? I think that approach could yield the best results yet.
ShinOBIWAN said:
I've read Troels work... honest!
You know me Scott, half the fun is spending over the odds and being happy about it. So forgive me if I don't want to use a crusty 15 year vintage Vifa C20 woofer, Troels lies anyway.
What I really need to do is just break loose of this damned aesthetic illness I have and go with 15 or 18's, that would solve a ton of issues straight away. But it would kill me to ever build a baffle wide enough to house one of those... no seriously it would, I feel ill just thinking about it.
'kin hell.
I'm sure Per will be thrilled when he see's my mail in his inbox tomorrow. Lets hope he's made a revelatory driver advance since our last contact. Scott can you mail him, tell him to lie and just to let me know what I want to hear? I think that approach could yield the best results yet.
Yeah.. vintage is just another word for tired..
And damn that Troels, seems to make more speakers than you do - whats he trying to do, make everyone else feel like mud? (except possibly TonyG.) ..miserable SOB.
Yeah a couple of 15 or 18's and something larger than a coffin! I know, only when you are ready to be buried.
Now I wouldn't do that to Per..
Might berate him for the high expense with VERY custom drivers though.
I mean, isn't it his DUTY to advance state-of-the-art.. and to hell with the costs (his cost)?
ScottG said:Yeah.. vintage is just another word for tired..
And damn that Troels, seems to make more speakers than you do - whats he trying to do, make everyone else feel like mud? (except possibly TonyG.) ..miserable SOB.
Yeah but subjectively speaking and I'm speaking subjectively about an under current of subjectives that are lost amongst other subjectives that in turn are wholey subjective, he builds cabinets that my mother would approve of.
Yeah a couple of 15 or 18's and something larger than a coffin! I know, only when your ready to be buried.
Now you've got me thinking... reckon there's money to be made in that? The coffins with subs thing I mean.
Looks like Tannoy beat me to it 50 years ago though.
Now I wouldn't do that to Per..
His wife clearly holds the cheque book. I'm betting he'd do all this for now't given his own volition.
ShinOBIWAN said:
Ah, but then you just have to think like a lawyer and spin to him so he could spin it to her.
i.e.
Doing this advances the state of the art.
As only your company has this technology - more private (and more importantly) commercial enterprises will want this.
This will allow those companies to sell more product with your product.
Any initial expense will be more than made up with increased sales of your product (..and quickly as well).
Ergo, you will make a LOT more money by doing this.
i.e. its really an investment.
In fact you should probably pay me for suggesting such a course of action that will make you so much money.
I'll tell you what - just start in on it as quickly as possible and you'll owe me one.. but we won't worry about payment just now.
ScottG said:
Ah, but then you just have to think like a lawyer and spin to him so he could spin it to her.
i.e.
Doing this advances the state of the art.
As only your company has this technology - more private (and more importantly) commercial enterprises will want this.
This will allow those companies to sell more product with your product.
Any initial expense will be more than made up with increased sales of your product (..and quickly as well).
Ergo, you will make a LOT more money by doing this.
i.e. its really an investment.
In fact you should probably pay me for suggesting such a course of action that will make you so much money.
I'll tell you what - just start in on it as quickly as possible and you'll owe me one.. but we won't worry about payment just now.
Ever noticed that its only men who go to law school? That's because women are born with those skills intrinsically bred into them from years of BS from men dating all the way back to when we threw spears for our food, caught 3 Deers, selfishly ate one on the way home and then told our other half we only caught two. This still happens today only the Deers are now your paycheck and the one you selfish ate is a pub, a bunch a mates and a bandit(electronic gambling machine thats programmed to fleece money from idiots).
So she'd see right past all that. What you need to do is make this appeal to women by perhaps throwing in a years supply of cellulite cream and telling her she looks great each and every day for the rest of eternity. Now that they would buy into.
ShinOBIWAN said:
At my school it was about 50/50. Not a pretty girl in the bunch though.
And I'd even question the sex of a few. Oh I forgot that at almost the same time Per is mentioning all this to his wife (immediately prior to this) he should give her something shiny that sparkles. (It really works like a *charm*.) (Of course in my case she gets it appraised a few weeks latter, but by then its too late.
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