Monitor Audio Gold 300 loudspeaker Measurements

Sidebar 4: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Monitor Audio Gold 300's frequency response in the farfield and an Earthworks QTC-40 mike for the nearfield responses. I left off the loudspeaker's grille for the measurements.

Although Monitor Audio specifies the Gold 300's sensitivity as 90dB/W/m, my estimate was almost 3dB lower, at 87.3dB(B)/2.83V/m, perhaps due to the fact that the Gold 300's impedance is specified as 4 ohms. (An input of 2.83V is equivalent to 2W into 4 ohms.) The impedance magnitude (fig.1, solid trace) does stay close to 4 ohms from the upper bass through to the mid-treble, with minimum values of 3.7 ohms at 117Hz and 3.57 ohms at 1kHz. There is a current-hungry combination of 5 ohms and –39° electrical phase angle (dotted trace) at 77Hz, and the phase angle exceeds +40° above 10kHz, presumably due to the inductance of the MPD tweeter's drive system. The Monitor Audio needs to be partnered with an amplifier that is comfortable driving low impedances.

1019MAG300fig1

Fig.1 Monitor Audio Gold 300, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).

The impedance traces are free from small discontinuities that would imply the presence of panel resonances, and the enclosure did seem inert to the knuckle-rap test. When I investigated the cabinet's vibrational behavior with a plastic-tape accelerometer, only the areas of the sidewalls level with the upper woofer had resonant modes in the midrange (fig.2). On the back panel, a strong mode was present just below 800Hz (fig.3), but the area affected, between the top of the cabinet and upper port, was small.

1019MAG300fig2

Fig.2 Monitor Audio Gold 300, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of back panel (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

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Fig.3 Monitor Audio Gold 300, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of sidewall level with upper woofer (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

There is a saddle in the impedance magnitude trace between 30Hz and 40Hz, which suggests that the tuning frequency of the two ports lies in this region. (Both ports behave identically, as do the two woofers.) The woofers' nearfield response (fig.4, blue trace) has its minimum-motion notch at 37Hz; this is the frequency at which the back pressure from the port resonance holds the cones stationary. The output of the ports (red trace) peaks broadly between 25Hz and 65Hz, implying excellent low-frequency extension, and while some midrange spuriae are present, they are low in level.

1019MAG300fig4

Fig.4 Monitor Audio Gold 300, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield woofer (blue) and port (red) responses respectively plotted below 355Hz and 650Hz.

The woofers cross over to the small-diameter midrange unit (fig.4, green trace) close to the specified 650Hz, with what appears to be a third-order filter slope, and their upper-frequency rolloff is free from peaks. The output of the midrange unit and tweeter on the tweeter axis is impressively flat, though there is a slight depression in the presence region and a second-order rolloff above 18kHz. Fig.5 shows the Monitor Audio's farfield response, averaged across a 30° horizontal window centered on the tweeter axis. The trace below 300Hz shows the sum of the nearfield woofer and port outputs, taking into account acoustic phase and the different distance of each radiator from a nominal farfield microphone position. The rise in response in the upper bass is due almost entirely to the nearfield measurement technique, the Gold 300's reflex tuning being maximally flat. The speaker might sound bass heavy in small rooms.

1019MAG300fig5

Fig.5 Monitor Audio Gold 300, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the complex sum of the nearfield woofer and port responses plotted below 300Hz.

The Monitor Audio Gold 300's horizontal dispersion, with each trace normalized to the tweeter-axis response, is shown in fig.6. The contour lines in this graph are evenly spaced in the midrange and low treble, which implies stable stereo imaging, and a slight excess to the sides balances the lack of presence-region energy in the on-axis response. The speaker becomes increasingly directional in the top two octaves, which might make the highs sound a little too mellow in large rooms. In the vertical plane (fig.7), the Monitor Audio's on-axis balance is maintained over a relatively wide listening window, but 15° above the tweeter axis a suckout starts to develop in the lower crossover region.

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Fig.6 Monitor Audio Gold 300, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

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Fig.7 Monitor Audio Gold 300, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 15–5° above axis, reference response, differences in response 5–15° below axis.

Turning to the time domain, the Gold 300's step response on the tweeter axis (fig.8) indicates that the tweeter and midrange unit are connected in negative acoustic polarity, the woofers in positive polarity. (I confirmed this by looking at the individual nearfield outputs.) More important, the decay of the tweeter's step blends smoothly with the start of the midrange unit's step and the decay of that driver's step blends smoothly with the start of the woofers' step. The outputs of the Gold 300's drive-units may not be coincident in time, but they are time-coherent, which suggests optimal crossover implementation. The Monitor Audio's cumulative spectral-decay plot (fig.9) is clean overall.

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Fig.8 Monitor Audio Gold 300, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

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Fig.9 Monitor Audio Gold 300, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

Monitor Audio's Gold 300 offers excellent measured performance.—John Atkinson

COMPANY INFO
Kevro International
US distributor: Monitor Audio USA
902 McKay Road, Suite 4
Pickering, ON L1W 3X8, Canada
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COMMENTS
beave's picture

From the review: "The design's benefits are a largely resistive load, no significant inductance (dome tweeters have an inductive voice-coil that complicates crossover design)..."

From the measurements: "...the phase angle exceeds +40° above 10kHz, presumably due to the inductance of the MPD tweeter's drive system."

JRT's picture

Air Motion Transformer tweeters exhibit flat resistive impedance response with respect to frequency in the audible frequency range. Not sure about impedance a decade or two higher.

Look at the data sheets of the Dayton Audio AMT series of tweeters.

http://www.daytonaudio.com/index.php/loudspeaker-components/loudspeaker-drivers-by-series/amt-series.html

beave's picture

That's what the review says.

But the measurements show a significant phase angle in the impedance in the highest frequencies.

Bogolu Haranath's picture

That significant phase angle you are mentioning (above 10 Khz) is not the region of the cone upper midrange frequency ........ It is in the MPD ribbon tweeter frequency range :-) .........

beave's picture

My post referenced the tweeter, not the midrange.

JRT's picture

I'm not sure what they might be doing in the crossover in the tweeter's filter network to clean up the tweeter's wave guide response, and what they might be letting happen in the ultrasonics to reduce component count. It does seem to exhibit a high Q low pass rolloff in the top octave, the high Q peak providing a little lift and associated rininging, the peak visible in figures 4 and 5. The associated peaking filter in that top octave shows as a sag in the rising impedance curve in figure 1.

edit: It was pointed out to me that JA1's measurements include some resonance present in the top octave in all of his loudspeaker measurements, and that seems to be obfuscating the behavior of the low pass here.

Bogolu Haranath's picture

There is a little peak at appox. 16 to 18 Khz region in the frequency response, but it is not anything significant ........ I have seen worse 'oil can resonance' peaks and dips in the frequency response of some metal dome tweeters ....... But those peaks and dips are usually above 20 Khz :-) ......

JRT's picture

With exception of a slight psychoacoustic dip in the range of 2kHz to 4.5_kHz, the response appears to be within a few dB of nominal above the baffle edge diffraction step and associated correction.

Bogolu Haranath's picture

That is the famous 'BBC dip' in that frequency ....... But that dip is not much in this speaker ....... Usually that dip is purposefully engineered to be -5 db or more :-) .......

JRT's picture

Psychoacoustic dip at the link:

https://www.linkwitzlab.com/models.htm#H

Bogolu Haranath's picture

Yes .... Your reference mentions the name 'H.D Harwood, BBC research department 1976' ....... Anyway, that dip is popularly known as 'BBC dip' :-) ........

beave's picture

I see a similar response in the datasheets for the drivers you linked to previously from Dayton Audio. I think it's inherent in the driver and not due to any crossover design.

But I don't see any ringing in figure 9. Isn't that little black slice always there in JA's plots and something he has mentioned as being the line rate of his monitor?

JRT's picture

...for pointing out the issue of the monitor.

Bogolu Haranath's picture

Also, that significant phase angle is not in the crossover region between upper midrange and MPD tweeter, which is 3 Khz :-) .........

JRT's picture

Look in the top octave, not the crossover frequency. They are shaping response up there.

Bogolu Haranath's picture

True ..... There is significant drop-off of FR, say from above 18 to 19 Khz ....... I don't know whether that makes any significant audible difference ...... Look at the TJN's in-room FR measurements ........ There is a lot of drop-off of the FR in the top octave :-) .........

JRT's picture

If the high frequency low pass response exhibits high Q, then the associated peak near the corner of that low pass would provide some lift in the response, and there would be some ringing associated with that.

Note that graphics show eight curves while the keys at the bottom of each identify nine. Regardless that error in identifying curves, the graphics are good enough to show Q affecting peaking and ringing. The brown curves look like textbook 2nd order Butterworth (Q=0.7071) and the yellow curves look like textbook 2nd order Linkwitz-Riley (Q=0.5000).

Source of graphics: https://e2e.ti.com/blogs_/b/analogwire/archive/2015/06/12/is-your-op-amp-filter-ringing-look-at-q

edit: It was pointed out to me that JA1's computer monitor causes a problem that falsely shows some resonance present in the top octave in all of his loudspeaker measurements, and that seems to be obfuscating some of the behavior of the low pass here.

beave's picture

Again, as mentioned above, hasn't JA said that it's an artifact of his video monitor?

JRT's picture

I do appreciate that you pointed that out to me, but did not see your comment before this morning. My comment has been edited to reflect that problem associated with the monitor. I would not want to mislead anyone with erroneous observations.

Bogolu Haranath's picture

BTW ..... Hi-Fi News has reviewed the Monitor Audio Gold 100 bookshelf/stand-mount speakers (EISA award winner) which probably use similar type of tweeters ....... Hi-Fi News measurements show similar type of peak around 15-16 Khz, with a sharp drop-off of FR above 20 Khz :-) ........

Bogolu Haranath's picture

If you want to see how 'oil can resonance' looks like (which I mentioned above), see the Hi-Fi News measurements of KEF R11 (EISA award winner) ......... But, those peaks and dips are way above 20 Khz ...... KEF is one of the companies, which uses Aluminum domes for tweeters :-) ........

Bogolu Haranath's picture

Another example ...... There seems to be some type of filter being used for high frequency roll-off for the GoldenEar speakers ....... GoldenEar also uses ribbon tweeters ....... Look at the FR measurements of GoldeEar Triton Reference by Hi-Fi News ......... There is a sharp drop-off of FR above 20 Khz :-) ........

Bogolu Haranath's picture

Here comes the 'king' of all FR measurements ......... See Hi-Fi News measurements of Dali Callisto 6C ...... Nice 'BBC dip' in the presence region and a sharp drop-off above 20 Khz ...... Very 'dramatic' FR :-) ........

Bogolu Haranath's picture

Interestingly TJN used +1 db boost in the treble frequency :-) .......

JRT's picture

Its a subjective choice in voicing the crossover.

Bogolu Haranath's picture

Goes to show the usefulness of tone controls/EQ :-) ........

JRT's picture

Al₂O₃ aluminum oxide, aka Corundum, aka Alumina ceramic, and in single crystal natural gemstone or synthetic is Ruby and Sapphire.

Al₂O₃ is also the surface coating result of aluminum anodization.

https://sundoc.bibliothek.uni-halle.de/diss-online/04/04H055/t2.pdf

MIL-A-8625
Type I chromic acid anodizing
Type II sulphuric acid anodizing
Type III sulphuric acid hard anodizing

There are processes that can produce a significantly thicker anodize, and some might refer to that as ceramic coating. It probably sells better than anodized aluminum. The Alumina ceramic is more rigid and more brittle than the aluminum substrate. It is more difficult to get a consistent thick layer of Alumina on a thin substrate of aluminum of a controlled shape without breaking the resulting item, because it can be fragile. Ask anybody who suffered through breaking an Accuton diaphragm, not inexpensive.

https://accuton.com/en-home/produkte/lautsprecher/keramik

Bogolu Haranath's picture

Revel is one example company, which uses DCC (deep ceramic composite) Aluminum cones :-) ........

Bogolu Haranath's picture

Additional note ........ The Beryllium dome tweeters used in Revel speakers show almost flat frequency response to 20 Khz :-) ........

Bogolu Haranath's picture

Time for Stereophile review of Polk Audio Legend L800 floor-standing speakers, with SDA technology ..... About in the same price range, $6,000/pair ....... See S&V review :-) .......

ringmeraudioguy's picture

I don’t understand the above commenters, seemingly trying to show their knowledge of test results and exhibiting blatant, ‘I know better than you’ statements. Such pedantry is boring. Just listen to the music!!

Chris Gramer's picture

These "Monitor Audio Gold 300" speakers look markedly different than those being sold by Crutchfield. Does MA reuse model names for multiple generations of speakers?

Example:
https://www.crutchfield.com/p_893G300PB/Monitor-Audio-Gold-300-Piano-Black.html?cc=07&tp=185

Just wondering. Thanks!

beave's picture

The model under review here is the 5th generation of Monitor Audio's Gold series, so it's sometimes referred to as the Gold 300 5G.

The one in your Crutchfield link is the previous generation Gold 300 (although it was just known as the Gold 300, not the Gold 300 4G).

Usually Monitor Audio doesn't reuse model names for multiple generations of speakers. But in this case, they sort of did.

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