need advice about Monacor drivers

[steph_tsf]

hello, what Monacor drivers would you advise for :

- a 4th-order Bandpass (35 Hz to 120 Hz) (5" to 8" diameter)
- a Bass-Reflex box (120 Hz to 6 kHz) (3" to 5" diameter)

Thanks

 

[Inductor]

Hi Steph. The MONACOR SPH 130 seems to be the best mid. Of course you and others, will have to pay me a lot of cash for this information.

 

[Inductor]

I would also test/simulate the Monacor SPH-200KE (against the Monacor SPH-176) for the bass 4th-order Bandpass. Regards😎

 

[steph_tsf]

Here is Monacor SPH-200KE + SPH-130 combination simulated with LTspiceIV, including the active filters. See attached .zip.

 

[steph_tsf]

Here is Monacor SPH-265 + SPH-130 combination simulated with LTspiceIV, including the active filters. See attached .zip.

 

[Inductor]

It's an active xover right? You have the drivers in phase (0º phase/same phase) I suspect. Now if there is a difference like a relative offset between the woofer and the tweeter in which the AC of the woofer is located behind that of the tweeter, how do you deal with the phase alignments.😕

Note: In the case, a more complex, 4th-order Bandpass phase (does it matter or only for higher frequencies in this case for the tweeter).
(1. Time aligned, Phase coherent, Phase aligned, Transient accurate, What's up with that? - Kreskovs)
(2. The Evolution of JBL’s Large Format Monitor Loudspeaker - JBL)

 

[steph_tsf]

If there is a difference like a mechanical position offset between the woofer and the tweeter in which the AC of the woofer is located behind that of the tweeter, how do you deal with the phase alignments ?

Yes, that's absolutely true. If you put the tweeter on the same plane as the bass-midrange driver, then there is indeed a mechanical offset between the tweeter and the bass-midrange, as showed on the two pictures you have provided. Nowadays you can find loudspeaker simulation programs able to take this mechanical offset in account. They allow you to specify a mecanical offset. Then you see the disastrous consequences when summing up the tweeter and bass-midrange acoustic pressure. During the last 30 years I have played with complicated crossover fllters for blending the bass-medium with the tweeter. About 10 years ago I've discovered a better way to filter and blend the bass-medium with the tweeter. In order to use this improved method, you need a small size bass-medium driver "man designed" able to deliver a smooth acoustic response until 6 kHz or 8 kHz. When I say "man designed", I mean a transducer that got designed and optimized by a specialist, able to control the membrane break-up above 4 kHz. There are not many drivers like this on the market. Fortunately, the Monacor SPH-130 looks to be such "man designed" driver. For the treble range, you need a modern miniaturized dome tweeter like Visaton CP-13 (13 mm dome - limited to moderate listening levels) or Monacor DT-284 (28 mm dome - better suited to loud listening levels). You will then use a 1st order crossover filter : a coil for the SPH-130 (low pass), and a capacitor for the CP-13 or DT-284 (high pass). You put the crossover frequency at 6 kHz in case of a CP-13 or 4 kHz in case of a DT-284. This guarantees the complementary of the two signal branches, with a linear phase response when adding the two acoustic responses. Other solutons like 2nd order low pass filtering of the bass-medium may exist, but the tweeter high-pass becomes then alot more complicated than just a capacitor in series, for getting the complementary amplitude and phase response. Now you will ask : "yes, okay, let us go for a 1st order crossover filter, but how to compensate the mechanical misalignment ?". My answer is : "use a delay line in the tweeter". Such delay line is not complicated. The components values are not critical. Later on I'll do a simulation of such delay line if you want. If the mechanical misalignment is 35mm, the delay is 103µs with the sound speed equal to 340m/s. At 5 kHz, the sound wavelength is 68mm. Now you understand how a 35mm misalignment can ruin a crossover : this is equivalent to a 185 degree phase shift at 5 kHz ! If you don't put the delay line, you'll get a huge dip in the acoustic response. And if you invert the tweeter polarity, then you'll get a localized boost at 5 kHz preceded and followed by weird amplitude variations. Of course, you surely have realized that in the context basing on phase accuracy, it is mandatory to use a MTM arrangement : tweeter positionned in the middle, between the two bass-medium drivers. If you don't use a MTM arrangement, you'll never be able to attain the objective of phase accuracy.

It's an active xover right? You have the drivers in phase (0º phase/same phase) I suspect. In the case, a more complex, 4th-order Bandpass phase, does it matter or only for higher frequencies ?

The active crossover simulation around 100 Hz can be considered as accurate. At 100 Hz, the wavelenght is 3.4 meter. That's quite a lenght compared to an eventual subwoofer / bass-midrdange mechanical misalignment. Say the misalignment is 17 cm. This is equivalent to a 18 degree phase shift. That's quite neglectible. So yes, you will get a flat acoustic response from 40 Hz to 6 kHz with the combination that's simulated. But wait a moment. Look to the resulting phase response. Although the low frequency response is essentially flat between 40 Hz to 200 Hz, there is a -300 degree phase shift developing between 40 Hz and 200 Hz. Now you will ask me "How is this possible : flat amplitude but phase buildup ? Are you sure ?". My answer is "Yes, absolutely sure". You'll need some maths to figure out what's happening. But we can bypass this painful necessity. Let's act practical. If you want both a flat amplitude and a zero phase buildup, then you'll need a far more elaborate active crossover at 100 Hz. You'll need an electronic copycat circuit of the 2nd low pass subwoofer acoustic behaviour, kind of steep 2nd order lowpass at 100Hz. Actually, it is more complicated than this because in reality, it is the negative edge of a 4th bandpass filter. We may use 1 or 2 two opamps, so that's realizable. On top of this we need to add the crossover behaviour : a 2nd order lowpass at approx 250 Hz. This is one extra op-amp. So, with an electronic circuit containing 2 or 3 opamps, we can get an electronic image of the subwoofer low-pass acoustic response, when filtered. If you want to get a fully complementary crossover, all you need to do is to put a substractor. Take the input signal, and substract from it the anticipated subwoofer low-pass acoustic response, when filtered. At the end of such circuit, you get your beloved complementary high-pass signal. You'll discover that it has a slope of +6d/oct, like it was a 1st order high-pass, but with a added boost at the 100 Hz corner frequency. Oops : this is maybe too much for a Monacor SPH-130, because of limited excursion ... You may then think that the mission is completed, feeding the Monacor SPH-130 with this. Unfortunately, that's not the case. You'll need to reverse-equalize the SPH-130 acoustic response, making it appear like a perfectly flat driver from 50 Hz to 100 Hz, both in phase and amplitude, before actually feeding it with the beloved complementary high-pass signal. You'll need 1 or 2 more opamps for doing this empirically. This is the same kind of job as with the subwoofer, but now with an acoustic response inversion as target. And doing so you increase the excursion stress on the Monacor SPH-130 ... You may need an intelligent high-pass filter, with a variable corner frequency, for limiting the Monacor SPH-130 excursion in function of the deep bass content.

Then you realize what kind of electronic monster you are developing, and you may want doing the exact same in digital domain using minDSP or SynthMaker.
Regarding miniDSP we need to wait the release of a "free world IIRs + delays" plugin. "Free world IIRs" because as you may have noticed, the "bare hands" crossover filters we are designing here have nothing to do with Butterworth, Bessel and Linkwitz. "Delays" because a delay line is needed when dealing with the tweeter crossover. And I doubt miniDSP will ever be able to execute an intelligent high-pass filter, with a variable corner frequency, for limiting the Monacor SPH-130 excursion in function of the deep bass content.
Regarding SynthMaker, we need to wait the release of a Windows 7 Sound System -> VST bridge.

Want to do a practical workshop during this summer ?

 

[Inductor]

Want to do a practical workshop during this summer ?

What's that, where?😀
I'm not very much into active multiple systems, (but) more on passive components.🙂

 

[steph_tsf]

Anywhere in Cascais. 33% of the time would be me and my wife at the beach, 33% eating and sleeping in a hotel, and 33% you and me designing, assembling and measuring some elaborate audio system. Need to find a decent hotel at a decent price in Cascais. Topics : measuring T/S drivers parameters using AudioTester3 (added mass method), simulating free air, closed box, bass reflex and 4th order bandpass speakers enclosures with LTspiceIV, simulating passive filters and multiway speakers enclosures with LTspiceIV, simulating active crossovers and multiway speakers enclosures with LTspiceIV. Aso with LTspiceIV : positive resistance drive, negative resistance drive, motional voltage extraction and feedback, acceleration piezo disc sensor and feedback.

 

[steph_tsf]

Here is Monacor SPH-250KE + SPH-130 combination simulated with LTspiceIV, including the active filters. See attached .zip.

 

[steph_tsf]

Here is Monacor SPH-176 + SPH-130 combination simulated with LTspiceIV, including the active filters. See attached .zip.

 

[Mission720]

Hello - I've stumbled across this thread after a search engine result... looks like some very good technical advice, so just wondering if anyone able to help:

I have a Monacor SPH-250KE and SPH-102KEP plus looking at a suitable tweeter to combine in a 3-way speaker design. Monacor and other sites suggest a bass reflex design so I'm struggling with various designs suggesting certain 'golden ratios' for box dimensions, internal baffling/bracing, whether to add 'polyfill' or not, and finally the choice of x-over, being a 3-way of course - but with Zobel network across just tweeter or all drivers?

I am an engineer but not in the audio industry so am overwhelmed with the help and advice, being quite varied, out there...

Many thanks in advance....

 

[steph_tsf]

Hello - I've stumbled across this thread after a search engine result... looks like some very good technical advice

Hi, this thread is quite old, dating back from 2010. If I remember, the aim was to rely on a 4th-order bandpass enclosure as subwoofer (deep bass down to 34 Hz @ 3dB), and determine if is feasible to hook a bass-reflex on it for the midbass. This, without ending up in trouble because of the relative phases. As you can see, this is feasible in the context of an active filter. Bear in mind however, that in a bass-reflex, there is a phase mismatch between the vent output, and the membrane output.
Some hate this. They say it causes the air making circles (vortexes) in the room, instead of imprinting soundwaves into the room.
Some like this. They say that the vortexes help stimulate the room, here and there, better than a planar soundwave.

For the ones wanting to benefit from a deep bass extension (like coming out from a 4th-order passband enclosure), and wanting to benefit from planar soundwaves in the bass range, a solution could consist of relying on :
- a 2nd-order active lowpass filtering the 4th-order enclosure for getting a Linkwitz-Riley 4th-order lowpass edge at say 100 Hz (thus : 30 Hz to 100 Hz @ -6 dB)
- a 2nd-order active highpass filtering a closed box for getting a 4th-order Linkwitz-Riley highpass edge at say 100 Hz (thus : 100 Hz to 1700 Hz @ -6 dB).

Please note, the closed box must reproduce 100 Hz @ -6 dB. This means that we cannot rely on some "medium driver" optimized for the 340 Hz-3400 Hz range having a small Xmax. We must rely on a high-quality midbass driver exhibiting a decent Xmax and exhibiting a smooth frequency response extending to 3400 Hz (twice the crossover frequency), and featuring a wide radiating angle at 1700 Hz.

I recommend two Vifa Tymphany Glass Fiber 10 cm TG9FD-10-04 that you wire in series for attaining a 8 ohm impedance, defining a MTM configuration. You mount a small tweeter in the middle, as close as possible to the two 10 cm midbass drivers. The sensitivity at 1 kHz will be something like 87 dB for 2.83 Veff at the input.

In case you dislike the MTM idea, there is the Vifa Tymphany Glass Fiber 10 cm TG9FD-10-08 (8 ohm impedance) approaching the TG9FD-10-04 specs. Please note the somewhat degraded high frequency response of the TG9FD-10-08. The sensitivity at 1 kHz will be something like 84 dB for 2.83 Veff at the input.

You can find a proper tweeter from Tangband. Look for Tangband 25-1414SC and Tangband 25-1719. Their frequency response extends in the low, down to 850 Hz or so. They won't cause trouble. Their sensitivity is something like 90 dB for 2.83 Veff at the input. You shall rely on a passive attenuator, for reducing their sensitivity to 87 dB or 84 dB for 2.83 Veff at the input. They both feature a 66 mm outer diameter. You can interchange them, according to your taste. Make sure you mount the tweeter as close as possible to the midbass driver.

There can be a passive crossover between the midbass driver and the tweeter. Over there, a LR2 (Linkwitz-Riley 2nd-order) may suffice in case you don't listen at very loud levels.

In case you opt for the MTM, and you don't listen at very loud levels, you may try a 1st order passive filter : a coil in series with the two Vifa Tymphany Glass Fiber 10 cm TG9FD-10-04 in series, and a capacitor in series with the Tangband tweeter.

A small analog delay line (aka Inductor-Capacitor pure phase shifter) may be required what's regarding the tweeter, for phasing it with the midbass.

 

[nimo_jon]

Hi steph_tsf

Great comments in 2010 (!). Three items caught my attention:
1. Use of Monacor Driver
2. *Time delay of Tweeter in 2 way design
3. Linkwitz-Riley 4th-order active filtering

My question may take this discussion thread off topic. I am currently modifying a KEF 104aB into active biamp. As the KEF is already 45 years old the 8in driver is already out of spec due to age. I am using a Monacor SPM205/8 to replace the B200 SP1039 (8in 8ohms).

The HF T27 and B200/SPM205 are mounted on the same plane. The interference pattern is understood. KEF used a 3rd order filter @3khz and inverted the phase of T27. On axis the speaker sounds great, but if off axis the speaker can sound strange. It also demand careful speaker placement.

I intend the run the HF and LF in phase and introduce a time delay. The difference between the acoustic center is about 35mm, and the time delay should be about 175us for 3000Hz by calculation.

Questions:
1. Monacor SPM 205/8 response is up to 5khz. B200 is only 3500hz. I expect the SPM 205 to handle well at 4khz region. Can I cross the frequency at 4khz higher so that the T27 and SPM 205 can integrate better? Crossing at 3khz in the original design is placing the B200 at the edge of its frequency response capabilities.

2. How do you introduce time delay? Just cascading all pass op amp filters? Attached is Texas Instrument Filter pro to come up with a 175us 3rd Bessel all pass time delay.

3. Can I ignore the box frequency response order and directly use a 4th order LR active filtering? Note that the bass driver is also coupled with a passive radiator.

Thank you so much 🙂

"My answer is : "use a delay line in the tweeter". "

 

[steph_tsf]

I am replying with pleasure, albeit the three questions being off-topic.

1. Monacor SPM 205/8 response is up to 5.0 kHz. B200 is only 3.5 kHz. I expect the SPM 205 to handle well at 4.0 kHz region. Can I cross at 4.0 kHz so that the T27 and SPM 205 can integrate better? Crossing at 3.0 kHz in the original design is placing the B200 at the edge of its frequency response capabilities.

Graph the magnitude and the phase of the bare woofer, and the bare tweeter. Observe the frequency response of the woofer. Determine the frequency where cone breakup occurs. Determine the frequency where the -30 degree response departs significantly from the on-axis response. Set the revised crossover frequency (actually, the overlap frequency) at 0.7 times the frequency where the woofer becomes imperfect. Do not allow the crossover frequency to become smaller than 3.0 kHz otherwise the tweeter will overload. Eventually, grab a better woofer, I mean a woofer that's less prone to cone breakup and less prone to off-axis degradation. Keep in mind that the goal of Kef with the aB revision, was to obtain a 3rd-order Butterworth high-pass acoustic response, what's regarding the filtered tweeter acoustic response. Acoustic means measuring with a mike. I don't know how Kef managed to filter the woofer, for the (low-pass filtered woofer + high-pass filtered tweeter) acoustic magnitude response to become essentially flat. I don't know to what extend, the (low-pass filtered woofer + high-pass filtered tweeter) acoustic phase response was imperfect.

2. How do you introduce time delay? Just cascading all pass op amp filters? Attached is Texas Instrument Filter pro to come up with a 175 us 3rd Bessel all pass time delay.

Excellent ! This is more effective than cascading identical delay cells. Make sure the resulting delay is essentially constant on the whole audio band. Try maintaining the delay from 100% to 70%, from DC to 15 kHz. You may need a higher order Bessel delay structure.

3. Can I ignore the box frequency response order and directly use a 4th order LR active filtering? Note that the bass driver is also coupled with a passive radiator.

Are you talking about the woofer-tweeter crossover that's operating at say 3.5 kHz? Are you talking about replacing the genuine Kef aB crossover concept, by some 4th-order Linkwitz-Riley crossover concept?

 

[nimo_jon]

Hello steph_tsf


Thanks for the reply!


1. After reading your post I studied the trace on SPICE again on the 104aB cross over simulation. The KEF 104aB have the 3rd order high pass set at *4khz in reality, which is the 3.3u/0.3mH/10uf CLC filter into 8 ohms. The down slop curve of the tweeter meets the woofer trace at about 3khz (very close at the default setting). The woofer crossover is set at about 1khz (!) using 2.7mH/5uf/0.3mH 3rd order. The final measured acoustics amplitude summed up well at the 3kHz region. The measured acoustic pass band meets the +/-3dB requirement. The test report of KEF 104aB shows above 3khz the tweeter was not very smooth. Electrically, the trace for woofer starts to fall off rapidly from the 1khz region. If I use the Monacor SPM model the curve is more straight. I am not sure what is the real life trace of the B200, but I expect it to have a big hump near the 2-3khz before it breaks off at 3.5khz.


For the Monacor to cross at 3khz, the low pass has to revised to 1.5mH/8uf/0.3mH which is about 1.5khz. This is the problem with passive cross over, no flexibility. (Anyway the Monacor has a Qt of 0.7, not very suitable because 104aB has a ABR design 🙁 ... the B200 has a Qt of 0.4 I will have to experiment when I have the drivers next week).


2. Thanks for the tips on the Bessel all pass delay!


3. I intend to drive the new configuration using Op amp 4th-order Linkwitz-Riley (built) and cross at 4khz and drive individual tweeter/woofer by 2 dedicated Class D amplifier. As it is LR4, I expect the interaction between the tweeter and woofer will be much less. The purpose of doing this to upgrade the performance assuming the Monacor SPM 205/8 is a more accurate and better driver than the 40 years old B200 SP1039.


The 104aB makes me very puzzled. How the 104aB achieve a final lobe makes me very confused. Like what you said, have to measure the output using the computer/microphone to check.