Designing a 2-way bookshelf speaker
- Thread starter tcpip
- Start date
Please check the Unibox box model spreadsheet in one of the earlier posts? I've also attached screenshots of the graphs and data.
Last edited:
When I measure the impedance of the SM16IH-4 6.5" drivers for my TM design, I get nice curves, which are very closely matched:
The resonant peak happens at about 54Hz, and the published documentation mentions 49Hz. Close enough (unlike the TL26 tweeter). But ARTA LIMP hangs when I try to calculate the basic T/S parameters with this data. If I reduce the frequency range to start from 35Hz instead of 20Hz, then the T/S parameter calculation goes through.
This of course means that I can't use the added-mass method to calculate Vas, because adding mass lowers the resonant peak frequency, which means that limiting the range to 35Hz and upwards won't work. So I'll have to use the closed-box method, which raises the resonant peak. In that case, I'll probably be able to keep to the shorter frequency range and make it work, who knows?
Now to cut a fresh baffle for this driver to fit my Vas measuring box (yes, I have a reusable box with a removable baffle, from my Asawari 1 days). So, some more delay.
Did I tell you I love ARTA LIMP?
The resonant peak happens at about 54Hz, and the published documentation mentions 49Hz. Close enough (unlike the TL26 tweeter). But ARTA LIMP hangs when I try to calculate the basic T/S parameters with this data. If I reduce the frequency range to start from 35Hz instead of 20Hz, then the T/S parameter calculation goes through.
This of course means that I can't use the added-mass method to calculate Vas, because adding mass lowers the resonant peak frequency, which means that limiting the range to 35Hz and upwards won't work. So I'll have to use the closed-box method, which raises the resonant peak. In that case, I'll probably be able to keep to the shorter frequency range and make it work, who knows?
Now to cut a fresh baffle for this driver to fit my Vas measuring box (yes, I have a reusable box with a removable baffle, from my Asawari 1 days). So, some more delay.
Did I tell you I love ARTA LIMP?
Last edited:
Actually, I think the resonant peak on the phase graph is, I think, the point where the curve changes direction -- the inflection point. That point matches well with the peak on the impedance curve. This point on the phase graph may not be the zero crossing point.
If you use any measurement software it does not show resonance at the point where the curve changes directions, but at the place where the phases changes at zero deg imo. But in most cases this difference is only a few Hz and should not matter.
Ok, I have good news. The problem I was facing with the impedance measurement of the 6.5" driver is now licked. See this thread on DIYaudio for the full details. The problem was with the sound card (USB audio interface) I was using.
I'm so glad.
I'm also sleepy. Good night. Got to wake up at 5 AM tomorrow.
I'm so glad.
I'm also sleepy. Good night. Got to wake up at 5 AM tomorrow.
The 6.5" driver details
I did the T/S parameter measurement of the two SM16IH 6.5" drivers:
and this is what I got:
I consider this fairly tight consistency of parameters. I'll take the average of each value and model the box accordingly.
I did the T/S parameter measurement of the two SM16IH 6.5" drivers:
and this is what I got:
I consider this fairly tight consistency of parameters. I'll take the average of each value and model the box accordingly.
keith_correa
Well-Known Member
Depending upon the surround type the parameters may change on break-in. The spider gets loose with break-in and this changes the Fs and the mechanical Q [which impacts associated params]. Some people press the cone in and out a couple of times to achieve this and some break it in with a few hours of playing a low bass track. When the VC heats up, the parameters change too but usually revert back on cool-down.
Break-in = Run-in
Break/Run-in <> Burn-in
Yes, I too believe this in theory. In practice, I haven't seen this happen. I suspect all driver makers worth their salt do some driving of each new driver on the test bench. This, I suspect, is the reason further break-in doesn't seem to change the parameters in all the cases I've seen.
Why do so many audiophiles believe that drivers, and earphones, and headphones, are shipped from factories without break-in and associated reliability testing? Even cars these days don't need break-in ( warnings like "drive the first 5,000km at 40km/hr" are history) these days.
However, I'm willing to believe that some boutique drivers, or very delicate full-range drivers, specially those which are hand-made using very specialised materials in very small quantities, may in some cases be shipped without adequate break-in at their factories. Ditto, those post facto cone treatments which some people apply. Their makers may not have the resources to do good break-in. In all other cases, I'd like to see some measurable evidence.
If you see published T/S parameters, many manufacturers put percentage ranges for piece-to-piece variations of key parameters. Even Fs often comes with a +/-10% tag attached. So, a "nominally" 45Hz Fs can be anywhere between 41Hz and 49.5Hz, just like that. If the break-in has to show statistically significant changes, it needs to move the measured value beyond random piece-to-piece variations, on a sufficiently large sample set. Are you sure break-in does this for most drivers?
Just take a step back and think of the practical implications of your belief. Your belief seems to imply that hundreds of different driver models, if picked off the shop shelf and tested, will likely not have T/S parameters matching the published spec. Imagine what this does to the manufacturer's reputation. Note that the manufacturer never says anything on the spec sheet like "If you want to verify our published spec, you need to burn the driver in for X hours at Y Watts with Z frequency mix first." So, either the manufacturer is willing to risk large percentages of their drivers being off-spec, or their drivers are on-spec while on the shop shelf and they have done what's needed to get them there in the factory itself. Which of these are you inclined to believe?
Let's look at this belief from the opposite end. Let's assume that this belief is correct. If you believe that your 100 hours of break-in change basic T/S parameters in addition to whatever burn-in testing it's gone through before it reaches you, then where does it stop? Do we then believe we need to keep re-measuring T/S parameters after every 500 hours while we use the driver? For how long? The first 6 months? The first 2 years? After every monsoon? If not, then why do we all feel so certain that the first X hours make important changes to the driver, which the manufacturer is not competent or not willing to do in the factory, but no further changes will ever be seen later? Where do we get this confidence from? Where does this stop?
This entire belief seems quite illogical to me. And I haven't yet read a single report where someone has done such break-in of a good quality, mainstream mass-produced driver and recorded statistically significant changes to measured T/S parameters. But the belief continues, much like the belief of skin effect of electricity in audio cables.
I found the following article interesting: http://www.wired.com/2013/11/tnhyui-earphone-burn-in I like the first sentence: earphone makers seem to be too polite to speak the plain truth.
They know the facts. But they have chosen to let the audiophile world enjoy their little myths. But then, in audio, as I keep saying: whatever floats your boat. Choose your own poison. Or words to that effect.
hyeah:EDIT: I just read your signature in the post above. If that's how you see things, then of course, I understand your beliefs.
Last edited:
keith_correa
Well-Known Member
Irrespective of my beliefs and past experiences, I would rather invest in a couple of hours of break-in and then judge for myself whether break-in affected THAT PARTICULAR driver. If params change, I'm that close to being accurate, if they don't, so be it.
I would not hang on to my old beliefs/experiences and let that rule my current and future. Everything is not cut and dry.
I would not hang on to my old beliefs/experiences and let that rule my current and future. Everything is not cut and dry.
Last edited:
I will never use a 1st order crossover in any situation other than situations where a crossover is not necessary at all. I'm referring to 1st order acoustic, not 1st order electrical.
Let me explain.
A first order low-pass will apply to a midrange or midbass driver only when the upper end of the driver is so extended and so smooth that I don't need to suppress the upper regions at all. What sort of driver will this be? The only answer is a very good full-range driver, which I can play without a crossover. Remember that with a 1st order low-pass, I'm allowing my midrange or midbass driver to be clearly audible even four octaves beyond Fc, because at 4 octaves out, it's down by only 24dB. In fact, it'll be audible right till the end of its natural frequency curve.
A first-order high-pass will apply to a tweeter when it has the construction to handle low frequencies thrown at it, and still not blow. A first-order high-pass hardly cuts the low frequencies, and an average tweeter will be damaged if it's played at anywhere remotely near its rated power with such a filter. (That's why power rating measurements on tweeters are done only after applying a 3rd order or 4th order filter first, if you read the fine print. It protects them from blow-outs.) Therefore, what sort of tweeter will be able to handle a 1st order high-pass and still survive? My guess is that some of those (very expensive) larger ribbons, which can handle frequencies down to 500Hz at full power, will survive with a 1st order at 3KHz or so. In essence, here too, we are allowing the tweeter to be audible almost till the bottom of its frequency range, just tapering the bottom end down a bit.
Therefore, in my eyes, a 1st order filter is not a "crossover", because there's no frequency beyond the Fc where the sound actually "crosses over". Both drivers practically remain audible through their entire audible frequency ranges, playing in parallel, and their responses are just being shaped by the crossover, very gently. These need very special drivers to sound good. I accept that a lot of paper cone or poly cone midbass drivers can be driven with just a 1st order low-pass (LP), but then those drivers can also be driven without a crossover. (Hence my initial remark -- I'll use a 1st order where I actually don't need a crossover at all.)
If I do a 1st order crossover, I'll be restricted to only these very special drivers, or else I'll have to live with the stresses, strains, resonances, and distortions which come when a driver is pushed beyond its "comfort zone". I choose to increase my choice of drivers, by using "normal" drivers, and I choose to use my crossover to shape their responses such that they are restricted to their "comfort zones" and can perform at their best. That's what crossovers are for, IMHO. I can imagine using a 2nd order LP for a very, very well-behaved mid-bass driver. And in the case of tweeters, I never use anything less than a 3rd order slope, because I want to protect tweeters against damage.
I want to do good engineering first, and esoteric audio second. I find no merit, for instance, in a design which sounds wonderful, but where I can only play the music upto 2 Watts of power, where an accidental turning up of the volume will blow the tweeter. I also don't see any point in using a 7" midbass driver in such a way that it is audible even at 8KHz, so that is beaming sound (all drivers beam at frequencies too high for their diameter) merges with the widely dispersing sound from the tweeter to create weird dispersion profiles.
I know that 1st order crossovers have a huge fan following. To each his own, I guess.
In the graphs, the mismatch is very visible. In actual use, I am not sure this mismatch will make an audible difference. We need to see how much the impedances differ in the range in which the tweeter will be used, and that will be probably above 2.5KHz. I think in that range, the difference will be small enough to be ok.
However, the impedance of one tweeter is showing some irregularities, the curve is not as smooth as it should be. I'll wait to take the SPL measurement of that tweeter, and if I see corresponding differences in the SPL curves, then the tweeter is defective and I'll need to buy another one. One more good reason to not buy Peerless India drivers.
After many years of designing the first order crossovers, i am slowing coming to the conclusion with my Metronomes that having no crossover is better with the full-range drivers. Also in my ribbon tweeter i have removed all other components and now have only a single pole high pass filter to only block the low frequencies. Luckily the fostex and audiopur have similar SPL and i did not have to use any attenuation circuit.
IMO, too many passive components used in the crossovers alters phase, transfer functions, linearity and coherence which is difficult to construct once lost. Agreed your peerless drivers may not be able to do without a second order or higher crossover because their limited bandwidth. Also you are using a MTM design which requires steeper slopes compared to a conventional 2 way design.
I strongly believe that crossover is a necessary evil and if you can avoid it or keep a minimilast approach it will be the best design ever. But again the drivers should allow that kind of design.
I thank Prem and Sumanta to come over last month to review my speakers and share some insights in subjective reviewing of speakers which i should agree I am not too very familar with. This helped me in out of box thinking and leave all conventional wisdom of crossover design aside and look at the overall perspective of what needs to be done to achieve the subjective choices. I still did lot of simulations and measurements to not be very off target but the end result was very satisfying.
Having said that, it will be interesting to have one weekend listen session of your speakers after its build to see how true are my findings.
Last edited:
Agreed.
I am reminded of Einstein's quote: "Everything should be made as simple as possible, but not simpler." I wholeheartedly agree with this statement. I am often saddened to see how often the last three words are forgotten from the sentence. I guess, to each his own.
Agreed. This leaves us with drivers which are very-wide-range or full-range, without any harsh cone breakups or other distortion-inducing flaws within 4+ octaves of the crossover points.
Glad you're having fun.
As you know, we never managed to meet up the last time. Will look forward to your visit.
In a strange coincidence, I found a leaflet with the Fostex FF225 drivers which I'd ordered, which arrived 2 days back. This leaflet gives speaker designs for complete (multi-way) speakers you can make using the Fostex FF series. I found it interesting that arguably the most well-known manufacturer of full-range drivers offers designs for multi-way speakers using their drivers. This zip file contains the full leaflet. It was printed in 2011 in China, and at least one tweeter mentioned in it, a Fostex ribbon, is now no longer available. But the designs are interesting to study nevertheless. I thought that the designs are very relevant for our first-order discussion. I found five crossover designs in this leaflet:
The language is either C, J, or K, but one can understand what the xo designs are by just Googling for the parts -- they are all Fostex FF series drivers or Fostex tweeters. The following observations stand out:
- All the full-range drivers are allowed to run to the bottom of their natural in-box frequency ranges -- no HP filter on them anywhere.
- Some of the full-range drivers have a LP filter to shape their top end. Others are allowed to run full-range to the top of their frequency curve.
- All the LP filters, all of them are first order.
- Whenever a tweeter is used, it has an HP filter to limit its bottom end. And these HP filters are always second-order electrical, which means they are at least 2nd order acoustic. No just-a-single-cap filter on any tweeter.
So, I came to the following insights, right or wrong, I don't know:
- First-order crossovers, or even natural-rolloff crossovers, are popular with full-range drivers.
- Tweeters, as I had believed earlier, should never be used with anything less than a 12dB/oct HF filter. I believe (without the Fostex pamphlet saying so) that this is to protect the tweeter from low frequency excursion damage. If (arguably) the world's most famous full-range driver brand baulks at using a just-a-cap HP filter on their tweeters, I think it's something we need to note.
I agree with, and respect, your "physics", your conceptual foundation. You and I are choosing different tradeoffs, that's all that is different between our perspectives, I think. On a separate note, I intend to build a 2-way standmount design using the FF225 and the G2Si ribbon tweeter. I intend to use a 2nd order HP for the tweeter, as you can guess by now. For the FF225, I was thinking of using a 2nd order LP to drop its top end. I now think I'll first try a 1st order for its LP and see how it goes. It'll be fun to build a 2-way floorstander using the very inexpensive Boston Acoustics 8" drivers which DIYAudioCart is selling, and mate it with a tweeter. One can try a 1st order for the LP of the 8", and just a simple 2nd order on the tweeter. One can use any tweeter, even the 19mm Vifa ring radiator, I suppose.
Last edited:
I use Recron brand from Reliance. They are available in 3 density. I usually go for medium density. It's available for around Rs,200/- per KG with some reputed Gadiwalas. Don't go for unbranded stuff as the fiber density usually is not uniform with Nalla brands.
This is interesting. Where do you get it from? I have always bought a Recron pillow and cut it up.
That way the cost goes up.
Thanks I agree not sure the density of which I am currently using. What should be the ideal density?
Or getting acoustics material is better
I have used the below Foam i is 1.5 inch thick, I got it here from a shop where they make Sofas & other type of furniture. This foam is very light weight & has a medium density. I have observed that this foam is more efficient in absorbing the mids & high frequencies. By putting ear on the vents I didn't heard any mid's or highs coming out from vent.
Sadik
Sadik
Buy from India's official online dealer!
Similar threads
