Hi,
I did not want to start a new thread but could not find a specific answer.
Just wanted to ask whether there is a general guideline to ascertaining how a sealed fullrange drivers recommended box volume can be reduced when you filter out the lower frequencies in order to use a subwoofer.
For example, if a box volume is given as 80 litres to yield 50Hz and you apply a filter to limit this to 100-150 Hz how far, if possible can you reduce the box volume?
Thanks
I did not want to start a new thread but could not find a specific answer.
Just wanted to ask whether there is a general guideline to ascertaining how a sealed fullrange drivers recommended box volume can be reduced when you filter out the lower frequencies in order to use a subwoofer.
For example, if a box volume is given as 80 litres to yield 50Hz and you apply a filter to limit this to 100-150 Hz how far, if possible can you reduce the box volume?
Thanks
Greets!
Hmm........... assuming this math is correct: Closed Subwoofer Box Equations Formulas Design Calculator fc System Resonance Frequency
............and this program is accurate: Solve linear and quadratic equations with Step-by-Step Math Problem Solver
.........and I used it correctly [don't assume], then:
a = [[Fc-Fs]*[Fc+Fs]]/Fs^2
Vb = Vas/a
Hmm........... assuming this math is correct: Closed Subwoofer Box Equations Formulas Design Calculator fc System Resonance Frequency
............and this program is accurate: Solve linear and quadratic equations with Step-by-Step Math Problem Solver
.........and I used it correctly [don't assume], then:
a = [[Fc-Fs]*[Fc+Fs]]/Fs^2
Vb = Vas/a
Thanks ‘Waxx’ and ‘GM’
I’ll post the T/S parameters of a particular driver that I have and see what you think. They are on another computer.
I’d like to reduce the box volume as much as possible for an acceptable response from my wife so am considering ‘Aperiodic’ loading along with limiting the bottom end.
I’ll post the T/S parameters of a particular driver that I have and see what you think. They are on another computer.
I’d like to reduce the box volume as much as possible for an acceptable response from my wife so am considering ‘Aperiodic’ loading along with limiting the bottom end.
Assuming all you're bothered about is the approximate transfer function, WinISD (at least, the old pro-alpha version, I don't have the latest loaded at present) can give a very rough indication. Not ideal, obviously, and the details are not accurate, with impedance etc. shifting under passive filtering, but enough to provide an idea. Using the above example, just size a sealed box for a Qtc = 1.0, or your choice of peaking Qtc, then set the highpass in the EQ/filter section to 1st order for the same Fb. You'll need to calculate the cap value by hand or another piece of software. Most of the time for these transcap loads, the approximate nominal is used as a starting point. For e.g. the attached. Same driver & sealed box, nominal Qtc 1.0. Yellow = as is, blue with 1st order high pass @ Fb. As I say, not hugely accurate but suffices for a general idea.
Attachments
This article can be a guide, use high Qts value drivers such as the Peerless TC and PLS ranges and in any reflex calculator do a small volume + desired f3 (if you use a port, be sure to increase a lot the csd, or else the vent velocity will be absurd, but the response will be similar).
I use the SY-DAP1002 from 3e audio (excelent thread of it in the class D forum) which has a programmable sigmadsp chip, and the sound is excellent, the bass extension from the famed PLS-P830987 from the TABAQ thread is similar on a 4,5L desktop monitor (50hz-ish) with even higher max SPL from the corrections applied digitally increasing useful displacement.
I use the SY-DAP1002 from 3e audio (excelent thread of it in the class D forum) which has a programmable sigmadsp chip, and the sound is excellent, the bass extension from the famed PLS-P830987 from the TABAQ thread is similar on a 4,5L desktop monitor (50hz-ish) with even higher max SPL from the corrections applied digitally increasing useful displacement.
SB also have a short piece. A bit generic, but it serves as a guide if you can't either simulate or measure it: https://sbacoustics.com/wp-content/uploads/2018/05/Capacitor-Tuning.pdf
Hi,
thanks for all your offerings. All very useful. Have not been able to access my old computer as I think it has died, and it has my Winisd and Dayton speaker measurement software on it.
The drive units I have in mind are the Cotswold Sound System 6.5” BMR (BMR128DD) which I purchased a little while ago. I have used the Tectonic 2.5” drivers and I really like them for near field listening and also the 4.5” Neo drivers offered by ‘Overkill Audio’ on this site a couple of years back.
The T/S specs for the 6.5” BMR from the manufacturer but check out well with Winisd
Re: 4.1
Le: 0.031
MMS: 13.52
Cms: 0.704
VAS: 19.724
Fs: 51.6
Qms: 2.986
Qes: 1.152
Qts: 0.831
Sd: 141 cm
SPL: 88.4
Xmax: 14mm (pk-pk)
I’ll just ask the question. How best to use this driver? I need to keep the box volume as low as possible, hence my initial question about how to reduce box volume if limiting the low end frequency requirements.( I have no limit to bass reinforcement provided by two subwoofers using Peerless Xs 10” subs powered by Gallo plate amps)
Open baffle may be an option. Aperiodic loading another. I’d like to get this right so I need some expertise to make the best of these drivers.
I should add that to the best of my knowledge the only speakers that use these drivers are made by ‘Curvi HiFi’ which are transmission line loaded of a unique design. They are reviewed on ‘Stereonet.co.uk’
Cheers
thanks for all your offerings. All very useful. Have not been able to access my old computer as I think it has died, and it has my Winisd and Dayton speaker measurement software on it.
The drive units I have in mind are the Cotswold Sound System 6.5” BMR (BMR128DD) which I purchased a little while ago. I have used the Tectonic 2.5” drivers and I really like them for near field listening and also the 4.5” Neo drivers offered by ‘Overkill Audio’ on this site a couple of years back.
The T/S specs for the 6.5” BMR from the manufacturer but check out well with Winisd
Re: 4.1
Le: 0.031
MMS: 13.52
Cms: 0.704
VAS: 19.724
Fs: 51.6
Qms: 2.986
Qes: 1.152
Qts: 0.831
Sd: 141 cm
SPL: 88.4
Xmax: 14mm (pk-pk)
I’ll just ask the question. How best to use this driver? I need to keep the box volume as low as possible, hence my initial question about how to reduce box volume if limiting the low end frequency requirements.( I have no limit to bass reinforcement provided by two subwoofers using Peerless Xs 10” subs powered by Gallo plate amps)
Open baffle may be an option. Aperiodic loading another. I’d like to get this right so I need some expertise to make the best of these drivers.
I should add that to the best of my knowledge the only speakers that use these drivers are made by ‘Curvi HiFi’ which are transmission line loaded of a unique design. They are reviewed on ‘Stereonet.co.uk’
Cheers
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Depends. However, as far as boxes go, if you used roughly Vb = Vas, then assuming a voltage source amplifier with about 1/2ohm series R for wire loop, connection losses, a sealed box will likely put you somewhere in the Qtc 1.0 - 1.2 region depending on the damping. The latter was roughly what the LS3/5a had. You could vent it, nominally Fb = Fs, and then stuff the vent to provide heavy flow-resistance.
If you wanted to use a series cap on the sealed, then something like 650uF - 1000uF should do reasonably & allow you some room for adjustment as desired.
Thiele's last ever AES paper was in fact on this very subject, & entitled 'Closed-Box Loudspeaker with a Series Capacitor'.
If you wanted to use a series cap on the sealed, then something like 650uF - 1000uF should do reasonably & allow you some room for adjustment as desired.
Thiele's last ever AES paper was in fact on this very subject, & entitled 'Closed-Box Loudspeaker with a Series Capacitor'.
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As a series capacitor is effectively ac coupling the speaker, in a situation where an amplifier was dedicated to such a speaker (e.g. an integrated powered speaker) then presumably it would be OK to use a single ended amplifier?
(I have been thinking about this since reading about some well regarded amplifiers using ac coupling - e.g. the original Creek amplifiers and more recently HEED)
(I have been thinking about this since reading about some well regarded amplifiers using ac coupling - e.g. the original Creek amplifiers and more recently HEED)
A series capacitor blocks low-frequency sounds at a rate of 6dB per octave. ie, if the -3dB point is 100Hz (the -3dB point is typically defined as the crossover frequency for first-order filters), then 50Hz will be at -9dB, 25Hz is -15dB, etc etc.
That does mean AC coupling, I suppose, but that's more a term for amplifiers than speaker design: all the signals a speaker should be receiving are AC.
In terms of amplifiers, I suspect "single-ended" might be the wrong term: there are lots of amplifiers (I have two of them in my line of sight) which are single-ended, but don't require any DC blocking. They're simple class AB designs where the positive terminal is driven, and the negative terminal is grounded. That works because they have a positive and negative power supply rail, and the output can move between those rails.
I suspect the designs you're referring to use a "single-ended" power supply, and don't operate BTL. ie, without a DC-blocking component (transformer or capacitor), the speaker output will sit at half the power supply voltage. Simple class A amps are often done this way.
Chris
That does mean AC coupling, I suppose, but that's more a term for amplifiers than speaker design: all the signals a speaker should be receiving are AC.
In terms of amplifiers, I suspect "single-ended" might be the wrong term: there are lots of amplifiers (I have two of them in my line of sight) which are single-ended, but don't require any DC blocking. They're simple class AB designs where the positive terminal is driven, and the negative terminal is grounded. That works because they have a positive and negative power supply rail, and the output can move between those rails.
I suspect the designs you're referring to use a "single-ended" power supply, and don't operate BTL. ie, without a DC-blocking component (transformer or capacitor), the speaker output will sit at half the power supply voltage. Simple class A amps are often done this way.
Chris
Hi Chris, yes I was having a flight of fancy about combining an amp with a single supply rail (so the live terminal would sit at half supply voltage without blocking cap - the original Creek amps were like this as well as the modern HEED designs) with a speaker like this and using the cap for two purposes -blocking dc and allowing a smaller box. There would be no good reason apart from you could possibly make a powered speaker slightly cheaper as single ended amps are a bit simpler usually...
Anyway Sorry for the OT!
Anyway Sorry for the OT!
Greets!
Personally would want a ~max flat alignment with max power handling, so raise it to a 2 Qt, then LR 4th order at 2x Fc = ~ 4.116 L/124.186 Hz Fc, ~248.371 Hz XO. max's out 7 mm/120 W from ~85 Hz/105 dB/2pi.
Now I got me a fine 'phone' BW reproducer or 500 Hz horn driver.
