Hello all,
I am a student considering a very modest 2-way speaker system using a 3" cone tweeter crossed over first order at 6,880 hz (2.2 mf capacitor @ 10.5 ohms) along with an 8" stock mid bass unit.... Fs 56 hz, Vas 25 l, Qts 0.8, Xmax 2 mm.
Case: The above configuration is intended to be used in a sealed box with Vb 40 litres (quite larger than its Vas and hence lightly loaded).
WinIsd shows the excursion limits will be reach with just 10 watts with reference to the band 60 hz and below.
Questions -
1. If i drive it past Xmax (say at 20 watts) long term and regularly, would its spider suffer fatigue and end up getting irreversibly looser?
2. Also would that effectively raise the Vas significantly, including effect irreversible changes in other T/S parameters?
3. If Vas does increase, then it would also take the system Qtc higher. Is it likely to happen?
4. In case of 3 above, would it have any effect on the excursion limited power handling 60 hz and below?
I hope to gain some guidance through the inputs by insightful designers here!
Thanks and regards,
Sujat
I am a student considering a very modest 2-way speaker system using a 3" cone tweeter crossed over first order at 6,880 hz (2.2 mf capacitor @ 10.5 ohms) along with an 8" stock mid bass unit.... Fs 56 hz, Vas 25 l, Qts 0.8, Xmax 2 mm.
Case: The above configuration is intended to be used in a sealed box with Vb 40 litres (quite larger than its Vas and hence lightly loaded).
WinIsd shows the excursion limits will be reach with just 10 watts with reference to the band 60 hz and below.
Questions -
1. If i drive it past Xmax (say at 20 watts) long term and regularly, would its spider suffer fatigue and end up getting irreversibly looser?
2. Also would that effectively raise the Vas significantly, including effect irreversible changes in other T/S parameters?
3. If Vas does increase, then it would also take the system Qtc higher. Is it likely to happen?
4. In case of 3 above, would it have any effect on the excursion limited power handling 60 hz and below?
I hope to gain some guidance through the inputs by insightful designers here!
Thanks and regards,
Sujat
It is unwise to exceed manufactures data. If you want out and out volume some Professional PA drivers are probably the way to go.
You could play with the box dimensions to maximise the low frequency power handling.
Listening to music 20 watts at 60Hz is going to be pretty loud. What does its sensitivity suggest.
I imagine driven at 20 watts the Low frequencies from your chosen driver will be distorting and rattling quite nicely. Not a faithful reproduction of your music
I haven't answered your questions because the outcome is unknown. Either they will degrade slowly or die suddenly. Not what you want.
You could play with the box dimensions to maximise the low frequency power handling.
Listening to music 20 watts at 60Hz is going to be pretty loud. What does its sensitivity suggest.
I imagine driven at 20 watts the Low frequencies from your chosen driver will be distorting and rattling quite nicely. Not a faithful reproduction of your music
I haven't answered your questions because the outcome is unknown. Either they will degrade slowly or die suddenly. Not what you want.
Thank you for your response, RaymondJ.
The sensitivity quoted is 87 db @ 2.83 Volts @ 1m.
The sensitivity quoted is 87 db @ 2.83 Volts @ 1m.
Suppose I don't know how much power/current I am actually feeding the speakers at a given amplifier volume knob setting, is there a way i can detect distortion (excursion > Xmax) in audible terms and without any measuring device?
From my experience in such things it's pretty noticeable. In fact many (cheaper/smaller) drivers will audibly distort before xmax is reached due to a variety of different distortion mechanisms.
Ok, then it seems I should not really be worried about not being able to notice the driver working under strain. Thank you for your response, Gtimes! 🙂
WinISD should allow you to input power and explore excursion limits in the signal settings window.
In system input power play with power levels and see how it eats into your displacement limit. with the parameters all entered correctly maximum SPL should show as well.
With 20 watts drive in the midrange around 1Khz you will probably be hitting 100dB SPL without a crossover on the 8 inch. The crossover inductor should be sized to flatten the response and remove the diffraction loss produced by placing the speaker in a cabinet. Typically this reduction will be in the 3-6 dBs range so you would be making 97-94 dBs or so. This is basically loud enough. Not Bengaluru night club levels though.
Don't get too concerned by power and volume, typically listening to music you may be cruising along at a few watts or so for most of the time.
You should be able to discern overdriving quite easily as a change in overall sound, with muddiness and compression, a flattening of the sound setting in, there is an effect called doubling where the second harmonic level rises high enough that it is easily discernible. When people start knocking on your door you have definitely reached the limit.
In system input power play with power levels and see how it eats into your displacement limit. with the parameters all entered correctly maximum SPL should show as well.
With 20 watts drive in the midrange around 1Khz you will probably be hitting 100dB SPL without a crossover on the 8 inch. The crossover inductor should be sized to flatten the response and remove the diffraction loss produced by placing the speaker in a cabinet. Typically this reduction will be in the 3-6 dBs range so you would be making 97-94 dBs or so. This is basically loud enough. Not Bengaluru night club levels though.
Don't get too concerned by power and volume, typically listening to music you may be cruising along at a few watts or so for most of the time.
You should be able to discern overdriving quite easily as a change in overall sound, with muddiness and compression, a flattening of the sound setting in, there is an effect called doubling where the second harmonic level rises high enough that it is easily discernible. When people start knocking on your door you have definitely reached the limit.
Thanks a lot for your considerate and elaborate response raymondj.
I do get the clues regarding the audibility of distortion, as well as exploring WinISD.
There is one doubt though.
"you would be making 97-94 dBs or so. This is basically loud enough. Don't get too concerned by power and volume, typically listening to music you may be cruising along at a few watts or so for most of the time." - This is at 1 metre. Now in a room 16' x 20' the distance from the speakers could easily be 4 metres. I have been informed that with a monopole speaker I would be experiencing a 6 dB fading of acoustic pressure every 1 metre. So at 4 metres, the spl should be 79 dB. Now would that be sufficient for usual Beethoven 5th symphony 3rd movement sized orchestral works? Or even for chamber works that include the prominent energy of a viole de gamba?
Am I being a bit too ambitious with an entry level 8" driver?
I do get the clues regarding the audibility of distortion, as well as exploring WinISD.
There is one doubt though.
"you would be making 97-94 dBs or so. This is basically loud enough. Don't get too concerned by power and volume, typically listening to music you may be cruising along at a few watts or so for most of the time." - This is at 1 metre. Now in a room 16' x 20' the distance from the speakers could easily be 4 metres. I have been informed that with a monopole speaker I would be experiencing a 6 dB fading of acoustic pressure every 1 metre. So at 4 metres, the spl should be 79 dB. Now would that be sufficient for usual Beethoven 5th symphony 3rd movement sized orchestral works? Or even for chamber works that include the prominent energy of a viole de gamba?
Am I being a bit too ambitious with an entry level 8" driver?
The inverse square law dictates a loss of 6db per doubling of distance, so you would be in the range of 12db lower output at 4m as opposed to 1m
This would put you in the range of around 85db at four metres.
I can't say what your driver can do as I don't know them, but a decent 8" can move some air, and even a cheap one should be capable of good midbass response in my mind, but I'm no expert.
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You are correct about -6dBs level change for a doubling of distance from a monopole source.
Your room will not be anechoic, you can obtain a boost at LF from walls and corners. Then add in the other speakers contribution and it will probably be somewhat better 🙂
Not great if you want to experience the majesty of the large scale classical works. We all have to start somewhere however. My first system would have had the same volume limitations and that was with the technology of forty years ago.
You will basically get what you pay for with your entry level 8 inch driver. What is its actual power handling?
Typical a good quality 5 inch drivers with 1" voice coil usually manage at least 30 watts or so theses days. If the basic 8 inch has a small 1 inch coil and a paper former then maybe it too can only handle a few watts. Are there any local posts by people using that driver to advise you?
Going to a better specified driver will cost more and you will have to look carefully for one that allows you to crossover at 6KHz or so. Typically for an 8 inch people would be looking at crossing over below 2Khz and that too requires a well specified tweeter to match. Getting tricky now.
How about a second hand buy.
Your room will not be anechoic, you can obtain a boost at LF from walls and corners. Then add in the other speakers contribution and it will probably be somewhat better 🙂
Not great if you want to experience the majesty of the large scale classical works. We all have to start somewhere however. My first system would have had the same volume limitations and that was with the technology of forty years ago.
You will basically get what you pay for with your entry level 8 inch driver. What is its actual power handling?
Typical a good quality 5 inch drivers with 1" voice coil usually manage at least 30 watts or so theses days. If the basic 8 inch has a small 1 inch coil and a paper former then maybe it too can only handle a few watts. Are there any local posts by people using that driver to advise you?
Going to a better specified driver will cost more and you will have to look carefully for one that allows you to crossover at 6KHz or so. Typically for an 8 inch people would be looking at crossing over below 2Khz and that too requires a well specified tweeter to match. Getting tricky now.
How about a second hand buy.
I quite understand raymondj. But 85 dB at 4 metres; would that beffectively loud enough for smaller Mozart sized orchestras or largish folk music ensembles?
I understand the trickiness here, raymondj! 🙂
1. These are 30+ years old drivers seemingly in nice condition except for the brittle rubber gaskets that have come off.
2. Yes, quite probably a 1" voice coil. Not sure if the former is paper or nomex. But the continuous thermal power handling is 40 watts. Regardless of the thermal power handling, a much lower load sustenance makes sense to me, for as per WinIsd plots, it reaches peak excursion at 8 watts @ 50 hz in a 42 litre box with Qtc around 1.08. A 20 litre box offers twice the support - I.e. 16 watts @ 50 hz, but the system Q rises to > 1.3 which fails to serve my taste! 🙂
3. There is no local contribution on these drivers.
4. A used speaker system is always possible, but there is none available that is paper cone drivers, 2-way, and this simple. Besides, the satisfaction of using a self-designed pair of speakers is going to be unmatched.... always! 🙂
I hope this helps a bit.
Thanks a lot for your valuable energy and your kind contributions, raymondj. I see it as a blessing for novices and students like me. 🙂
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Sujat, thank you for the kind words.
You also explain your predicament over the loudspeaker design, all information helps.
The Q of 1.3 could be a bit of a boom box or it might just sound fulsome.
Generally I tend to use SB drivers a lot these days. There are some paper coned Peerless SDS series that can be purchased cheaply, and at the same time they offer great potential. Unfortunately they don't seem to make an 8 inch paper as far as I am aware.
I have used a vifa a paper 8 inch, some 20 years ago and just recently. Unfortunately it is expensive approx. £80.
It is becoming very difficult to find good paper coned 8 inches for use in sealed enclosures.
SB Acoustics do a papyrus paper cone, but definitely this needs crossing over around or below 2Khz in a 8 plus 1 design. Which means an equally expensive tweeter.
The fibreglass Scanspeak works in a similar sized sealed enclosure and sound good, again a low crossover is probably best
I imagine heybrook HB3, JPW or AR 18 speakers are impossible to find locally. They will have rotted foams but can be re foamed to offer a good sound.
Hopefully somebody will jump in here and suggest a faital pro or some other similar professional speaker that could fit the bill.
I need some more time to investigate different manufacturers myself, I will update you if I spot an interesting design.
Stay Safe.
You also explain your predicament over the loudspeaker design, all information helps.
The Q of 1.3 could be a bit of a boom box or it might just sound fulsome.
Generally I tend to use SB drivers a lot these days. There are some paper coned Peerless SDS series that can be purchased cheaply, and at the same time they offer great potential. Unfortunately they don't seem to make an 8 inch paper as far as I am aware.
I have used a vifa a paper 8 inch, some 20 years ago and just recently. Unfortunately it is expensive approx. £80.
It is becoming very difficult to find good paper coned 8 inches for use in sealed enclosures.
SB Acoustics do a papyrus paper cone, but definitely this needs crossing over around or below 2Khz in a 8 plus 1 design. Which means an equally expensive tweeter.
The fibreglass Scanspeak works in a similar sized sealed enclosure and sound good, again a low crossover is probably best
I imagine heybrook HB3, JPW or AR 18 speakers are impossible to find locally. They will have rotted foams but can be re foamed to offer a good sound.
Hopefully somebody will jump in here and suggest a faital pro or some other similar professional speaker that could fit the bill.
I need some more time to investigate different manufacturers myself, I will update you if I spot an interesting design.
Stay Safe.
How does this model in WinISD
8″ SB20PFCR30-8 / Paper – Sbacoustics
I haven't used it, and again I think your first order Xover at 6Khz is definitely out of reach
Eight audio in Hyderabad should be able to supply I think. I do not know how much import tax they will get in your country, but they would be a sensible good value buy.
Value being a relative thing.
Maybe pair with a 3-4" full range unit instead of a tweeter and crossed low for a woofer assisted wideband.
8″ SB20PFCR30-8 / Paper – Sbacoustics
I haven't used it, and again I think your first order Xover at 6Khz is definitely out of reach
Eight audio in Hyderabad should be able to supply I think. I do not know how much import tax they will get in your country, but they would be a sensible good value buy.
Value being a relative thing.
Maybe pair with a 3-4" full range unit instead of a tweeter and crossed low for a woofer assisted wideband.
I value your efforts, Raymondj; thanks a lot again. You have been going out of the way to help, which I should feel ashamed of. I feel grateful.
I will surely evaluate the sbacoustics driver you have suggested. At the moment i do not feel inclined to invest in new components. But i do have two pairs of these same 8" drivers, and a workable way out seems to be having 2 pairs of speakers (2 pairs of boxes with identical volumes) constructed and connected parallel. I will get roughly 20 watts of mechanical load sustenance with both pairs working together with the added flexibility of placing 1 pair well near room corners for augmentation below 100 hz.
Fortunately, I am single and not constrained by the universally dreaded WAF! 🙂
Thanks once again! 🙂
Be well; stay safe.
Regards.