What I built, impressions and solutions?

[GM]

OK, just looked at a pic and assuming it mirrors your drivers, then the first driver tweaks are to trim down the tall gasket till it's flush with the metal frame, do the $0.98 tweak, i.e. adding a damping ring around the whizzer and damp the basket, motor. These should 'open up' the sound considerably by reducing their excessive cavity resonances.

GM

 

[IG81]

What exactly is the $0.98 tweak? I read something about polyfil around the whizzer, is that right? How would you make it hold in place?

EDIT - Ok, I found an archived post in which you linked to a place with explanations, it's missing s couple of pictures, but I get the gist of it. I would guess not too dense open cell foam? - /EDIT

Bass is smoother without the series resistor, and does sound more like it's critically damped. I would simply not think that a mere 4.7 ohm would make it sound as boomy as it was.

 

[IG81]

$0.98 mod worth it weight in unobtainium

Ok, so I took of that cardboard ring surround thing, which I had been meaning to do since I got them but never got around to. And I added a foam ring as suggested to damp the whizzer and it's noticably better! It took out some of what I did not like in the mids although it's not all gone.

Weekend project will be damping the basket-magnet assembly and re-arranging the stuffing inside.

I was told that speaker burn-in changes some parameters but in a complementary manner, in a way that does not invalidate an enclosure alignement. But what about the subjective sound? Does anything in the mids to highs typically change with increased use?

Thanks again for the help everyone!

 

[IG81]

WRT converting them to a MLTL, adding a 3" i.d. diameter x 2" long vent 31.5" down from the top sims usable output to 40 Hz and if it sounds 'boomy', damp the vent as required, then dial in some series R to flatten it.

GM

Keeping my enclosure as it is, I would get a L of 47.5", thus quarter wave resonance of ~71Hz, pretty much dead on my driver's Fs, good coincidence!

I have some 2.75" diameter, 3" deep plastic ports just lying there not being used, could that do, I could even shorten them if necessary.

BTW, if anyone has a useful link or read for me on Helmoltz resonance and how to apply it to enclosures, I'd like to know more about that, I'm never happy with just using box softwares, I wanna know the mechanics behind! I failed to find anything relevant on that so far...

 

[GM]

Assuming 2.75" i.d., then 1.5" long, though try them at 3" just to get a frame of reference. Insert the vent in baffle, but don't push it in all the way, so you can pull it back out to shorten if desired. Use some type of putty to seal them to the baffles though, such as Blu-tac, Play Doh modeling clay, etc. to ensure a good seal that's easily cleaned up.

Google Helmholtz resonator, audio speaker vents or similar, though you'll have to read MJK's docs to learn how 1/4 WL cab resonances impact the performance of a vent's 1/2 WL ones.

GM

 

[IG81]

Assuming 2.75" i.d., then 1.5" long, though try them at 3" just to get a frame of reference. Insert the vent in baffle, but don't push it in all the way, so you can pull it back out to shorten if desired. Use some type of putty to seal them to the baffles though, such as Blu-tac, Play Doh modeling clay, etc. to ensure a good seal that's easily cleaned up.

Google Helmholtz resonator, audio speaker vents or similar, though you'll have to read MJK's docs to learn how 1/4 WL cab resonances impact the performance of a vent's 1/2 WL ones.

GM

Thanks for the info GM!

 

[IG81]

Re: Re: Re: Re: What I built, impressions and solutions?

If it's the cheap patchwork of scraps, it's called 'rebond'. Regardless, all foam carpet padding is closed cell, ergo reflective, so open cell is required for lining speakers and is probably contributing to how they sound. Try 3/8" thick felt or 1" acoustic fiberglass insulation instead or just the minimal stuffing I suggested.

Hmm, if the mids/HF don't sound good on a baffle this big, then you may have to make do with adding a tweeter.

OK, the dims you listed implied only an 11.5" offset which yielded a hard to cure dip, but at 16" it's close enough for the negligible dip to be inaubile with the minimal stuffing I suggested.

GM

- or make that the hammer is hitting the smiley's head (me)!

My driver is not 16" down the line like I said, it is in fact ~12.25" down the line. I got mixed up with other dimensions...

I therefore did not try the port since it would probably not work like you modeled now. Would that make the port dimensions and location change and can anything be done with that "hard to cure dip"?

Duct sealing the basket/magnet assembly seemed to help a bit more.

 

[GM]

Greets!

Ah well, spiff happens...........

So, with the tweaks is the 'telephony' gone?

In a MLTL, the closed pipe dip becomes a vent peak that typically fills in a bit where the driver is beginning to roll off, so a plus, not a minus WRT response.

Anyway, same vent, just shift it down to ~35.25" from the top.

GM

 

[GM]

Oops! Forgot the sim...... 2 ohm series R shown and again, if any peaking at Fb is audible, then it can be easily dealt with by damping the vent.

GM

 

[IG81]

Greets!

Ah well, spiff happens...........

So, with the tweaks is the 'telephony' gone?

In a MLTL, the closed pipe dip becomes a vent peak that typically fills in a bit where the driver is beginning to roll off, so a plus, not a minus WRT response.

Anyway, same vent, just shift it down to ~35.25" from the top.

GM

Telephony is still there, but mucho reduced thanks to all these simple mods.

My front baffle gave me a sim'd baffle step peaking at ~7dB from ~500Hz to a bit above 1000Hz, quitle flat, then back to 6dB all the way up the FR. So uncompensated, it is very telephony yes, but with some EQ to counter the stepped response, it's better. I still get that not-too-lively midrange, but I have realistic expectations of a rather no-name-ish 25$ driver. At least things got better.

Ok, I'll try that new vent position and re-stuffing when I get a chance. Thanks!

 

[chris661]

The last bit may be solved by bedding them in properly

Unless it's a different part of your set-up

Which amp are you using???

 

[GM]

You're welcome!

Another good tweak, though it shouldn't affect any 'telephony': http://fullrangedriver.com/singledriver/images/press-screw.gif

The baffle only supports a > ~160 deg 'half space' and since driver beaming begins at around 1 WL across it's effective diameter this equates to ~3390 Hz where it starts narrowing up on axis.

Hmm, is the mids 'not too lively' or is the lower HF too strong? This is the usual situation with small, cheap whizzer drivers having a fairly strong stepped response. If so, an only semi-reversible tweak is knead the starch out of the whizzer to damp it and coat them to 'taste' with cheap lacquer hairspray if it either doesn't help and/or you overdo it. Shown is an extreme example of small driver whizzer 'shout' centered at ~2 kHz:

GM

 

[IG81]

The last bit may be solved by bedding them in properly

Unless it's a different part of your set-up

Which amp are you using???

Yamaha M45.

You're welcome!

Another good tweak, though it shouldn't affect any 'telephony': http://fullrangedriver.com/singledriver/images/press-screw.gif

The baffle only supports a > ~160 deg 'half space' and since driver beaming begins at around 1 WL across it's effective diameter this equates to ~3390 Hz where it starts narrowing up on axis.

Hmm, is the mids 'not too lively' or is the lower HF too strong? This is the usual situation with small, cheap whizzer drivers having a fairly strong stepped response. If so, an only semi-reversible tweak is knead the starch out of the whizzer to damp it and coat them to 'taste' with cheap lacquer hairspray if it either doesn't help and/or you overdo it. Shown is an extreme example of small driver whizzer 'shout' centered at ~2 kHz:

GM

What is that pressure screw tweak supposed to accomplish?

Adding a port at 35.25" down the line did wonders! Opened up the low end nicely. It's much more tonaly balanced now. Still some lingering telephony, but I wasnt expecting it to go away with that of course, it's just better proportionned now.

Can't wait to see what a couple hundreds hours of play will do in terms of break-in...

I'll borrow the Quest sound level meter from work and see if I can isolate a peaking in the FR and notch it out. My EQ is nice and all, but not quite precise, having full octave bands. I'll be looking into Rod Elliot's line BSC circuit, so a sole notch in the boxes should not be too hard to implement.

The speakers I had at the beggining of the week and what I have now are a couple orders of magnitude appart, thanks to this wonderful forum and it's users!

 

[GM]

You're welcome! Glad you're actually trying our suggestions and giving feedback. Too often I feel like I'm wasting my quality time talking to myself.

So, are you saying that the simmed Fb peaking isn't an audible issue, i.e. bass sounds 'tight'/'accurate' (~critically damped) as opposed to 'loose'/'sloppy'/'resonant' (under-damped)?

If I'm right and these are PA/car audio drivers, then they'll probably never break-in on their own WRT cone flex as they're heavily doped for atmospheric protection and long life without losing their ability to project the lower HF in a high noise ambient and why I suggested manually doing it at least to the whizzer.

Anyway, the screw brace is used to mass load the driver to the much higher mass of the cab and since with increased mass comes increased rigidity it improves the driver's electro-mechanical-acoustic efficiency a little bit to a lot depending on the various component's constructions. Ideally, the driver should be either rear mounted or attached to a separate mounting ring, then the ring attached to the baffle, but putting a slight tension on mounting screws works good enough with small drivers.

Basically, you apply pressure very slowly (fractions of a turn at a time once snugged up to the motor) as you play some simple acoustic music or vocal solos and you should hear a slight tightening up (increased definition) of the presentation as you dial it in and once you hear no improvement, then stop. If you hear no difference then use your judgment as to how tight is 'tight' without risking damaging the driver, i.e. bending weak flanges and/or causing a VC misalignment on the more flimsy framed units.

Note that most folks tend to over tighten the driver's mounting hardware, severely limiting and/or literally crushing the gasket's ability to isolate/damp any spurious resonances from either it or the baffle, i.e. the mounting hardware should be tightened in a pattern and should never crush the gasket > ~1/4 its thickness, IOW just enough to seal properly and keep the hardware from loosening up.

GM

 

[IG81]

You're welcome! Glad you're actually trying our suggestions and giving feedback. Too often I feel like I'm wasting my quality time talking to myself.

So, are you saying that the simmed Fb peaking isn't an audible issue, i.e. bass sounds 'tight'/'accurate' (~critically damped) as opposed to 'loose'/'sloppy'/'resonant' (under-damped)?

If I'm right and these are PA/car audio drivers, then they'll probably never break-in on their own WRT cone flex as they're heavily doped for atmospheric protection and long life without losing their ability to project the lower HF in a high noise ambient and why I suggested manually doing it at least to the whizzer.

Anyway, the screw brace is used to mass load the driver to the much higher mass of the cab and since with increased mass comes increased rigidity it improves the driver's electro-mechanical-acoustic efficiency a little bit to a lot depending on the various component's constructions. Ideally, the driver should be either rear mounted or attached to a separate mounting ring, then the ring attached to the baffle, but putting a slight tension on mounting screws works good enough with small drivers.

Basically, you apply pressure very slowly (fractions of a turn at a time once snugged up to the motor) as you play some simple acoustic music or vocal solos and you should hear a slight tightening up (increased definition) of the presentation as you dial it in and once you hear no improvement, then stop. If you hear no difference then use your judgment as to how tight is 'tight' without risking damaging the driver, i.e. bending weak flanges and/or causing a VC misalignment on the more flimsy framed units.

Note that most folks tend to over tighten the driver's mounting hardware, severely limiting and/or literally crushing the gasket's ability to isolate/damp any spurious resonances from either it or the baffle, i.e. the mounting hardware should be tightened in a pattern and should never crush the gasket > ~1/4 its thickness, IOW just enough to seal properly and keep the hardware from loosening up.

GM

Your welcome, I wouldn't want to make anyone lose their time by asking for solutions and doing nothing!

Bass reaches lower now with the vent added. I haven't cut it down to 1.5" also. It does sound a bit boomy, but nothing too bad. I did not try with a 2ohm resistor yet, I'll see after cutting the vent, but series resistance would only aggravate boominess as I see it.

About the driver being a car/pa unit, in the current Q-component catalog, it is simply listed there as a fullrange driver. But I did look at an older McBride paper catalog I had lying somewhere and there it was, same part#, with a car audio mention, but with somewhat differing T/s parameters. So I'm not sure what to think... It would explain some things though!

Good info on that pressure screw, thanks!

 

[IG81]

Hmm, is the mids 'not too lively' or is the lower HF too strong? This is the usual situation with small, cheap whizzer drivers having a fairly strong stepped response. If so, an only semi-reversible tweak is knead the starch out of the whizzer to damp it and coat them to 'taste' with cheap lacquer hairspray if it either doesn't help and/or you overdo it. Shown is an extreme example of small driver whizzer 'shout' centered at ~2 kHz:

GM

So far I've tried a bunch of reversible mods that have all made small improvements. Although the mental image I have of what the whizzer might look like after the de-starching process is scary (flabby mass of paper flailing around!), I'm considering it right now, as it's probably not that bad! They are not expensive drivers and have responded well to tweaks so far as I said.

I think I'll cut out the dustcap and make some phase plugs as well. Might take some shrill out of the highs, not that it's terrible right now. I think a slight reduction of HF radiating area and change in radiation pattern might be welcome. I just figure I might as well go the whole nine yards tweak-wise.

And for those of you who have seen a pic of this driver, the whizzer is something else, very long! At least so it seems to me compared to most FR units we see around here. It's higher than the surround in a way that I cannot put it face down on a flat surface since gasket removal. How about a trim? Any opinions towards that? This should be done before making a phase plug, as the latter's lenght is a function of whizzer height, correct?

Thanks!

 

[IG81]

I measured my whizzer cone at 2" outer edge diameter. This is the wavelenght for ~6700Hz. Perhaps frequencies around a radiating cone's size get a bit peaky. I remember reading something about this, but can't recall what/where exactly. It would also explain why I cannot EQ it out completely, as my EQ has 4kHz and 8kHz bands, the offending frequency falling right in between... So if the previous is correct, trimming the whizzer would transfer this effect up the FR until whizzer is ridiculously small. I'll abstain from any trim for the moment.

I also came upon a nice thread on fullrangedriver.com on phase plugs for Pioneer B20's. The user described a certain "honkiness" which does not seem too far from what I experience. Consensus seemed to be DC removal and plugging in a... well... phase plug! It was a good read for me. Also featured Planet10's blue/yellow creature!

 

[GM]

Just a quick note, but the whizzer mouth frequency is a lot lower, more like ~1652 Hz with its end correction factored in.

More to come as time permits...........

GM

 

[IG81]

Armed with patience and a sharp Xacto knife, I performed a succesful dustcapectomy on my McBride drivers last night. I then headed off into the shop and assembled the sketchiest of makeshift wood lathe ever in order to turn 1" hardwood dowels down to ~0.95" and have phase plugs.

It made a difference in the highs, although not as big as I'd have thought, but it's on the good side at least!

I also bought some damar varnish to coat the whizzer as mentionned in so many places. I just wanna be sure I got the right stuff. I tried it on paper, but it did not seem to dry as what I'm acustomed to regarding varnishes does. It's Lefranc & Bourgeois Ultra Fine Damar varnish, with turpentine. Did I get the right stuff? Maybe it just takes longer to dry than I assumed.

Other thing I should do, that I should have done sooner is play with the stuffing. I'm puting my hopes on that now!

Last resort after that is a notch filter if I'm able to identify a peak in the FR.

IG

 

[GM]

Adding series R reduces Fb peaking, just not as efficiently as stuffing the vent, not to mention a tonally balanced (maximally flat) system tends to ameliorate minor Fb peaking as long as Fb is low enough and/or room gain doesn't severely under-damp it and why speakers placed in a small room near one or more boundaries need to have a relatively high F3.

With such a long whizzer, it's definitely optimized for PA/car audio.

WRT kneading it, you don't do the whole thing, just the mouth to damp its bell modes. That, or rim it with foam, though finding the right density is a tedious affair, so some folks just coat them with rubber cement, but kneading them works best overall IME.

Right, to have max effectiveness, the phase plug must extend beyond the whizzer to at least its height + its radius *0.613, so if it's 1" high from the pole piece and has a 2" i.d. bell, then the phase plug minimum height = 1 + (1*0.613) = 1.613" with its shape being the inverse of the whizzer's flare as a first approximation to fine tune from there.

The whizzer has horn action along with transmitting the signal through its material, so reducing its height/mouth area raises its cut-off and reduces its directivity, so depending on its FR it could cause an audible notch as well as increasing its polar response down low (in the whizzer's BW), which may/may not be a good thing overall, so without a measured response to make an educated guess as to what to do with it, this one-way tweak may force you to cut it all off and add a tweeter.

GM