I think that my bass-reflex box is too big. The bass is boomy and it rumbles. Instead of building a recommended and tested enclosure of 28l I made it of 40 liters. Now, making some simulations I got to the conlusion that shortening the port is equivalent to lowering the box vulume: the SPL resp extends a bit lower but with faster rolloff, the peak power handling due to maximum cone displacement gets bigger. There is a slight difference in transient response but I think it will not be audible. But something tells me that I'm missing something since removing the port completely seems to make it even "boomier". I'll experiment but I'd like to know what is it that I'm missing. Also, other suggestions that might help me get rid of the boomy sound are welcomed.
I suck at describing sound, but maybe boomy is not the exact word, but also slow, at least this is how I perceive it. Does boomy bass come with slowness too?BillFitzmaurice said:
Can this be because of room gain? Also, could the fact that I haven't broken-in the drivers be of any importance? I've read an article on the Visaton webpage where they state that the effect of breaking-in is practically inaudible, and prove it with measurements and theoretical explanations. And, if this persists with more damping material, should I shorten the port or extend it? I'm pretty confused, theory and practice are starting to contradict each other.
Tomac said:
http://www.visaton.com/english/artikel/art_457_1_19.html
I used published specs.as I was assured times and times again that Visaton is very strict on parameter deviations and I trust this brand. I could measure them of course but right now I don't have a low distorsion amp to do that.
What are the dimensions of the box you are currently using?
dimensions of port?
Judging by the simulation it shoud work without "boominess" in 40 l box.
But if the parameters are quite different than the published ones,than this simulation has no use. I do own pair of W170s which were measured to have Qts of 0.7
. I didn't measure it but I trust this guy who did measurements.
If this driver also has higher q than it was published ,it might cause bass to sound without control.
Overdamp your box and make a port longer.This should help.Without measurements it is hard to guess the solution,becuse first you should guess about the cause...
put lot of damping in that box
if there will be no improvement,than you'll have to measure T/S again.
don't be desperate,even if you find out it has higher Q you can put it in closed box,or you could make a TL.
Report us on your progression
dimensions of port?
Judging by the simulation it shoud work without "boominess" in 40 l box.
But if the parameters are quite different than the published ones,than this simulation has no use. I do own pair of W170s which were measured to have Qts of 0.7
. I didn't measure it but I trust this guy who did measurements.If this driver also has higher q than it was published ,it might cause bass to sound without control.
Overdamp your box and make a port longer.This should help.Without measurements it is hard to guess the solution,becuse first you should guess about the cause...
put lot of damping in that box
if there will be no improvement,than you'll have to measure T/S again.
don't be desperate,even if you find out it has higher Q you can put it in closed box,or you could make a TL.
Report us on your progression
Sorry for not giving all the details from the beginning.
The BR tube: http://www.visaton.com/english/bildgross/144_azeichnung1.html
I haven't cut it.
Dimensions of the box: 1mx20cmx20cm. The woofer is placed approx 20 cm from the top. The port is cca 10cm from the bottom.
You can find all the details here (scroll down to GM's first post): http://www.diyaudio.com/forums/showthread.php?s=&threadid=37778 I only made very small adjustments to what is listed there. Don't be confused by the title, I hardly think of it as a TL, it's too short.
I will measure the drivers tonight, even if this will mean going to bet at 3 AM That huge deviation you measured is very scarry.
The BR tube: http://www.visaton.com/english/bildgross/144_azeichnung1.html
I haven't cut it.
Dimensions of the box: 1mx20cmx20cm. The woofer is placed approx 20 cm from the top. The port is cca 10cm from the bottom.
You can find all the details here (scroll down to GM's first post): http://www.diyaudio.com/forums/showthread.php?s=&threadid=37778 I only made very small adjustments to what is listed there. Don't be confused by the title, I hardly think of it as a TL, it's too short.
I will measure the drivers tonight, even if this will mean going to bet at 3 AM
That huge deviation you measured is very scarry.
mr_push_pull said:
Shortening the port will make the tuning frequency higher, this makes the air velocity higher and less linear. Also, as you noticed the transient response worsens.
If you are getting boomy sound the last thing you want to do is make the port shorter.
This driver has Qts a little on the high side, and Vas a little on the low side, for use in a vented box. It may well not be the tightest sound that you can hope for.
What diameter port are you using? What frequency are you tuning it to?
Oh ... the infamous W170S! 
It's well-known that Visaton's published Qts values are rather on the low side, sometimes too low.
The older version of the 4 Ohm W170S had Qts values from 0.6 to 0.7. This was also confirmed by measurements by the German Klang&Ton magazine years ago. There has been a product modification in the meantime, so that it's possible that drivers from current production batches have lower Qts, but I doubt that they have got a stronger magnet now (- for the same price )
It's well-known that Visaton's published Qts values are rather on the low side, sometimes too low.
The older version of the 4 Ohm W170S had Qts values from 0.6 to 0.7. This was also confirmed by measurements by the German Klang&Ton magazine years ago. There has been a product modification in the meantime, so that it's possible that drivers from current production batches have lower Qts, but I doubt that they have got a stronger magnet now (- for the same price
)Sorry mr_push_pull, I didn't want to sound arrogant. Should have written "well-known among the more experienced DIYers around here"...
Well... the Visaton forum... the knowledge level of its users and the fanaticism for their brand is one of the reasons I don't read there anymore... It used to be a great forum some years ago.
Well... the Visaton forum... the knowledge level of its users and the fanaticism for their brand is one of the reasons I don't read there anymore... It used to be a great forum some years ago.
Hertzschmerz said:Sorry mr_push_pull, I didn't want to sound arrogant. Should have written "well-known among the more experienced DIYers around here"...
Well... the Visaton forum... the knowledge level of its users and the fanaticism for their brand is one of the reasons I don't read there anymore... It used to be a great forum some years ago.
No, problem, I didn't imply that you were arrogant. I'm glad to have that information about the Visaton forum, even if it's too late.
Well, it's possible that I was too nervous because of my failure and I wasn't thinking straight. There was some bass, but not enough to justify such a big box, I would expect that kind of bass from a bookshelf enclosure, not a 1m tall tower. I'll be back tomorrow with T/S measurement reports, hopefully.adason said:
Just some other suggestions (while I still don't trust the Visaton specs):
Do you use an amplifier with high output impedance? Coupled to the complex impedance response of your speaker, this will also lead to boomy bass. Do you use low resistance coils in series with the woofer?
Making the port longer in order to shift resonance lower was already mentionend. Another possibility would be reducing the port diameter, if that is still an option (i.e. port is wide enough).
Using lots of damping stuff behind the driver can lower Qm at the expense of linearity.
If you need to lower Qts of the driver another possibility would be to stick a second magnet in repelling orientation to the back of rear plate of the driver. Such magnets can be ordered as compensation magnets or salvaged from broken drivers.
Good luck!
Do you use an amplifier with high output impedance? Coupled to the complex impedance response of your speaker, this will also lead to boomy bass. Do you use low resistance coils in series with the woofer?
Making the port longer in order to shift resonance lower was already mentionend. Another possibility would be reducing the port diameter, if that is still an option (i.e. port is wide enough).
Using lots of damping stuff behind the driver can lower Qm at the expense of linearity.
If you need to lower Qts of the driver another possibility would be to stick a second magnet in repelling orientation to the back of rear plate of the driver. Such magnets can be ordered as compensation magnets or salvaged from broken drivers.
Good luck!
Even in closed box this driver should have some reasonable deep bass (f3 round 50 hz). I know that you were eager to have deeper bass,but I think this can be sufficient for most forms of music..Maybe you have some other version of W170s than me. I wonder if anyone has one which is close to published specs 
?
I think it is pretty arrogant of Visaton to have such deviations in their parameters.If i was the one who bought their driver and measured such deviations of 100% I would return the drivers to factory and would ask a refund. 0.33 to 0.7, my god it is theft.
But I heard this not only problem with cheaper series,but with more expensive ones also (AL series)
I wonder how high Q have drivers with Q specified already as high as 0.7. They must have 1.5 or something
Anyway I think their drivers aren't bad but it is no use of making any plans without measuring them.
How many of you found such irregularties in their parameters?
?I think it is pretty arrogant of Visaton to have such deviations in their parameters.If i was the one who bought their driver and measured such deviations of 100% I would return the drivers to factory and would ask a refund. 0.33 to 0.7, my god it is theft.
But I heard this not only problem with cheaper series,but with more expensive ones also (AL series)
I wonder how high Q have drivers with Q specified already as high as 0.7. They must have 1.5 or something
Anyway I think their drivers aren't bad but it is no use of making any plans without measuring them.
How many of you found such irregularties in their parameters?
Measurement report
My measurements (I actually went to bed at 3 AM, although I was hoping I exaggerated):
Published params:
Qes = 0.51
Qms = 2.16
Qts = 0.41
Fs = 36
Measured T/S params:
Qes = 0.65
Qms = 2.5
Qts = 0.52
Fs = 39.5
I'll repeat the measurements today using another amplifier, just to make sure. Tomac, I tend to agree with you. Building a small closed box out of chipboard for testing is not such a big deal. I would also like to know if these problems persist with more expensive Visaton drivers. I wondered many times if T/S deviations are not just a myth and I got to learn that they aren't the hard way. After all, why do these parameters deviate with different batches? I read somewhere that they sometimes change the materials, without notice. This IS arrogant.
Edit: I measured the other unused driver (I only tested a box). I'll break it in for a while, and repeat the measurements afterwards.
My measurements (I actually went to bed at 3 AM, although I was hoping I exaggerated):
Published params:
Qes = 0.51
Qms = 2.16
Qts = 0.41
Fs = 36
Measured T/S params:
Qes = 0.65
Qms = 2.5
Qts = 0.52
Fs = 39.5
I'll repeat the measurements today using another amplifier, just to make sure. Tomac, I tend to agree with you. Building a small closed box out of chipboard for testing is not such a big deal. I would also like to know if these problems persist with more expensive Visaton drivers. I wondered many times if T/S deviations are not just a myth and I got to learn that they aren't the hard way. After all, why do these parameters deviate with different batches? I read somewhere that they sometimes change the materials, without notice. This IS arrogant.
Edit: I measured the other unused driver (I only tested a box). I'll break it in for a while, and repeat the measurements afterwards.
Your measured TSP deviations aren't that bad, at least not as bad as I had expected after your sound description. fs and Qts will further decrease somewhat with break-in.
More expensive drivers like AL130 or GF200 are also reported to have frequently higher than published Qts. I have no personal proof for this as I was never tempted to try these flashy drivers - they are too expensive for what they offer, IMO.
More expensive drivers like AL130 or GF200 are also reported to have frequently higher than published Qts. I have no personal proof for this as I was never tempted to try these flashy drivers - they are too expensive for what they offer, IMO.
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