Substituting 8'' woofer with greater Fs

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Hello! I've built a pair of loudspeakers using the woofer Vifa M21WO39-08 in a 60 litres bass reflex cabinet tuned at about 35 Hz. The towers have a very good low extension but lacks of incisiveness and impact in the bass region of the "acoustical" musical instruments, as bass guitar and drums, like saying they are a little limp and not very engaging on that yield. In other words I'm looking for a crispier and more detailed response in the 50-150 Hz band.
For more than one year I've tried to improve this decreasing internal volume, shortening the vent tube, attenuating tweeter, but what I got was always boomy effect and need to return to the original configuration.
My question is now: can I expect improvement in the sense I want by replacing the woofer with one characterized by a lighter cone and a stiffer suspension (and thus greater Fs) but equal Qts and efficiency? I'm referring in particular to a Seas Excel W22NY001E0045, which has a Fs of 33 Hz and a Vas of 72 liters against the corresponding 28 Hz and 105 liters of Vifa, while the Qts values of 0.30 and the sensitivity of 90 dB are identical for both drivers.
In case, what may I expect from the different inductance value Le, that goes from 1 mH of the Vifa to 0.61 mH of the Seas? Must I change something in the crossover?
Thank you!
 
Vas, Fs and Qts define the bass alignment (volume and tuning). For the crossover to act equally on a new woofer you need equal FR and impedance. A lower inductance means a lower rise in impedance, so probably not an easy drop-in replacement.

About your issue, are you sure that the crossover is dealing correctly with the baffle step effect? Ignoring the baffle step effect makes the bass thin, as is some dB (6 or slightly less) lower than the mid and tweeter.

Ralf
 
assuming you've dealt with baffle step correctly,
re:"shortening the vent tube - how much did you change the box tuning? Tuning the box higher will give you more bass level, at the expense of low extension. The trick is not to over-do it (a 1-2 dB hump) to avoid the boominess (assuming everything else is OK, the box is not too big, is properly damped etc.) This is easily simmed in Unibox. A quick sim shows me that the peak bumps up quite quickly, so you can't tune much higher than ~40Hz, which will give a hump about ~1.75dB

re:"looking for a crispier and more detailed response in the 50-150 Hz band" - you're looking in the wrong place, detail is higher up
 
google it
first match: Baffle Step Compensation
fourth match: bafflestep
Forget about the equalization as explained in those links, it is properly done with an appropriate oversized low-pass inductor. If your speaker has a text-book crossover then surely the baffle step has not been taken into account. For an example on how to properly deal with the effect see this project: Zaph|Audio and in particular the transfer function: http://www.zaphaudio.com/audio-speaker17-modeled-transferfunction.gif (look at the 200-1500Hz region).

Ralf
 
The New Vifa Tower by MurphyBlaster, what do you think about its low-pass filter?

Based on a simulation the New Vifa Tower seems to have a hump of 3 dB around 100 Hz. Cause is the large woofer coil of 3 mH in the crossover. I'm not sure if that explains the issue with your speaker, perhaps someone else can tell more. :confused:

The Excel woofer certainly is not a drop-in replacement for the Vifa, you would have to redesign the woofer filter completely IMO.
 

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So can I resolve this problem without substituting driver?

Difficult to say. Of course, the hump at 100 Hz is caused by the crossover and can be eliminated completely with a filter redesign. But that doesn't necessarily mean the problem is solved. Vented box design always is a trade-off between low frequency extension and transient response. A Vifa M21WO-39-08 in 60 liters clearly is an alignment in favour of low frequency extension and at the expense of transient response. That's a basic fact which doesn't change. Hence I'm very unsure what to expect from a crossover modification. :scratch1:

If you share more information about your speaker (cabinet size, driver placement, vent size (a picture usually answers many questions:))) I might come up with a crossover modification proposal. You don't really have the old Vifa D25AG-35-06 tweeter, do you?
 
Thank you very much just want to say that we're probably taking the wrong path.. I think that my problem is due more to the "vocal" features of the Vifa rather than output level, because of this I'd want to replace it, I think so just for the negative result obtained by reducing loading volume, made thinking that maybe 60 litres were too much for a QTS of 0,30.
An expert friend of mine told me that for more punch and precision in middle-bass area woofer must have highest possible Qms and BxL and suggested me Peerless 830869 HDS woofer. In effect Vifa has minor values for that, probably every hi-fi driver is so for a wanted reason to ensure more transparency, that is s what I DON'T want in the middle-bass!
This could probably be the right way but I still fear that it might work bad in 60 litres, because projects using that are often based on 20/30 litres. So:
1) could Peerless work well however in my 60 litres box?
2) if not, could I use a couple for each box,considering that in New Vifa Tower tweeter (ScanSpeak 9500) is attenuated? Could I use a 4 ohm nominal impedance woofer line and a 8 ohm tweeter line? Obviously redesigning crossover filter completely..:(
3) if yes for the point 1, can you help me redesigning lowpass filter for the Peerless leaving as is the highpass for the ScanSpeak, just adjusting if necessary the L-pad attenuator?

For a picture I must return to home,around 7° of January. Thank you very much, wish you a happy new year!
 
Hello! I've built a pair of loudspeakers using the woofer Vifa M21WO39-08 in a 60 litres bass reflex cabinet tuned at about 35 Hz. The towers have a very good low extension but lacks of incisiveness and impact in the bass region of the "acoustical" musical instruments, as bass guitar and drums, like saying they are a little limp and not very engaging on that yield. In other words I'm looking for a crispier and more detailed response in the 50-150 Hz band.
For more than one year I've tried to improve this decreasing internal volume, shortening the vent tube, attenuating tweeter, but what I got was always boomy effect and need to return to the original configuration.

Greets!

Just from its specs, the Vifa seems an excellent choice for the performance you’re wanting and absent a listening test would have chosen a ~76.4 L/28 Hz tuning to keep group delay low, efficiency high in the [mid] bass passband, i.e. a ‘fast’ [over-damped] transient response since the room typically dominates a system’s response up to ~250-300 Hz; so considering the fact that it always sounds better when going back to ‘stock’ it seems like at least a lower tuning to Fs or just 'stuffing a sock' in the port to ~seal it up should be tried first.

GM
 
Many thanks, I've realised that Vifa's problem regards its timbre, in the sense that it's too "light" and diaphanous for my taste. I've tried everything, even socks stuffed in the port but nothing helped. So I've decided to try sobstituting driver.
I apologize for my moving this thread to the italian forum Audiofaidate because there I discovered many friends that don't go round here, it's not cross-posting, hope..
However this is the list of driver, in order of preference, I selected as possible substitute:

01) Visaton GF200 (2 coils in serie: Qms 4.12 - BxL 9.2Tm - Fs 30Hz);

02) Dayton ST210-8 (Qms 4.99 - BxL 10.5Tm - Fs 51.7Hz);

03) Peerless 830869 (Qms 5.7 - BxL 9.1Tm - Fs 30Hz);

04) Ciare XH201 (larga banda Qms 6.41 - BxL 6.6Wb/m - Fs 53.4Hz);

05) Beyma CM-8B (Qms 13.46! - BxL 9.8N/A - Fs 73Hz);

06) Eminence Beta_8A (Qms 4.65 - BxL 9.6Tm - Fs 65Hz);

07) Eminence Alpha_8A (Qms 4.60 - BxL 7.8Tm - Fs 73Hz);

08) Visaton B200 (largabanda Qms 8.39 - BxL 3.9Tm - Fs 40Hz).

Here WinISD simulations and datasheets, every comments, advice or suggestions will be much appreciated.
Thank you very much : )
 
Looking at the crossover, it's a bass heavy design.
MurphyBlaster Productions

3mH is way more than I would use. That's going to create very intrusive "Here I am" bass which will overwhelm the midrange.

The Vifa M21WO-39/08 bass driver looks rather good and flat:
M21WO-39/08 - Vifa 8 inch woofer magnesium chassis coated paper cone - Europe Audio

I'd try about 1.5mH or less, with some impedance correction like 4.7uF and 4R shunt. That simple. And change C2011 to about 4.7uF for a higher 3kHz crossover. That's gonna be close to BW3, so either polarity might work, but I'd go negative polarity. You'll need less attenuation on the tweeter too, because smaller coils make for more efficiency and a more direct sound. Keep it around 8 ohms load to the filter. You could lose that 2R in series with the tweeter coil too.
 
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Oh, I could mention that unwinding coils to reduce inductance is easy enough. Inductance is proportional to the square of the number of turns. So to convert a 3mH to 1.5mH, you take out about a quarter of the turns. It helps to measure the effect with a good mH multimeter as you go along. Then scrape the enamel off the bare end for soldering. :cool:
 
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You very rarely apply more than a couple of dB bafflestep, not the full theoretical 6dB, and room gain tends to swamp it into boom anyway. Which is what is going on here, IMO.

How come Troels gets away with 0.82mH here?
TQWT-

The smaller the coil, the more slam the speaker has. No need for a new driver at all. It's the crossover that is plain useless. Whoops, outspoken again. :D
 
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