Q Acoustics Concept 300 loudspeaker Measurements

Sidebar 4: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Q Acoustics Concept 300's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield and in-room responses.

Q Acoustics specifies the Concept 300's sensitivity as 84dB/W/m. My estimate was slightly higher, at 86dB(B)/2.83V/m. The Concept 300's impedance is specified as 6 ohms, with a minimum value of 3.7 ohms (on the website) or 4.7 ohms (in the product's white paper). My impedance measurements, which I took with MLSSA then checked with Dayton Audio's DATS V2 system, tell a different story. The impedance magnitude (fig.1, solid trace) only drops below 6 ohms in the lower midrange and above 10kHz. The minimum magnitude—4.9 ohms between 175Hz and 200Hz—is higher than both specified values. Though the electrical phase angle (dashed trace) reaches –57° at 90Hz and +54.5° at 23Hz, the magnitude at those frequencies is high, mitigating any drive difficulty. The Q Acoustics is not a particularly demanding load to drive. With the port sealed, the impedance has a single peak in the bass (fig.2), indicating that the Concept 300 behaves as a sealed box tuned to a relatively high 67Hz.

120Q300fig01

Fig.1 Q Acoustics Concept 300, electrical impedance (solid) and phase (dashed) with port open (2 ohms/vertical div.).

120Q300fig02

Fig.2 Q Acoustics Concept 300, electrical impedance (solid) and phase (dashed) with port blocked (2 ohms/vertical div.).

I measured the Concept 300's impedance first with it supported by upturned cones at the corners of the enclosure, then with it sitting on the Tensegrity stand. I didn't find any differences. The very slight discontinuity between 400Hz and 500Hz in the impedance traces, which suggests there is a panel resonance in that region, was the same with both measurements. However, when I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer, I found that a fairly high-level mode at 473Hz on the sidewalls with the speaker mounted on upturned cones (fig.3) was reduced by 5.4dB when the speaker was placed on its dedicated stand (fig.4). This mode was the only one present on any of the panels; it is sufficiently high in frequency and Q (Quality Factor) that even without the attenuation provided by the speaker's sprung base, it probably wouldn't have any audible effects.

120Q300fig03

Fig.3 Q Acoustics Concept 300, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of sidewall with speaker supported on upturned cones (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

120Q300fig04

Fig.4 Q Acoustics Concept 300, cumulative spectral-decay plot calculated from output of accelerometer fastened to center of sidewall with speaker sitting on its dedicated stand (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

The port on the Q Acoustics' rear panel is tuned to 44Hz, this indicated by the fact that the impedance-magnitude plot has a saddle centered on that frequency. The blue trace in fig.5, which shows the woofer's nearfield response, has its minimum-motion notch at 44Hz. (This is the frequency at which the back pressure from the port resonance holds the cone stationary.) The nearfield response of the port (red trace) peaks between 30Hz and 60Hz; while its upper-frequency rolloff is clean, there is a significant peak just above 800Hz. The woofer's output has a slight peak in the upper bass, which will be due in part to the nearfield measurement technique, which assumes the drive-unit is firing into half-space rather than in all directions. The woofer's balance is flat before it starts to cross over to the tweeter (green trace) just below the specified 2.5kHz. The crossover appears to be configured with symmetrical, ultimate 18dB/octave slopes. (Each drive-unit's rollout is slower than that for an octave or so below and above the crossover frequency.) The tweeter's response appears identical to that used in the floorstanding Concept 500 (footnote 1).

120Q300fig05

Fig.5 Q Acoustics Concept 300, acoustic crossover on tweeter axis at 50", corrected for microphone response, with nearfield woofer (blue) and port (red) responses respectively plotted below 350Hz, 1kHz.

The black trace below 300Hz in fig.6 shows the sum of the Concept 300's nearfield woofer and port outputs, taking into account acoustic phase and the different distance of each radiator from a nominal farfield microphone position. The output is down by 6dB at the port tuning frequency, below which the speaker rolls off with the usual 24dB/octave reflex slope. The Q Acoustics' farfield response, averaged across a 30° horizontal window centered on the tweeter axis, is shown as the black trace above 300Hz in fig.6. The balance is superbly flat and even up to the mid-treble, above which there is a very slight rising trend. This graph was taken with the Concept 300's rear-panel jumper set to Normal. Changing the jumper settings as indicated in the manual raised or lowered the level by exactly 0.5dB, as specified. The frequency responses of the two Q Acoustics Concept 300s matched very closely.

120Q300fig06

Fig.6 Q Acoustics Concept 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.

Fig.7 shows the Q Acoustics' horizontal dispersion, referenced to the response on the tweeter axis, which thus appears as a straight line. Other than a very slight flare at the bottom of the tweeter's passband, the contour lines in this graph are even throughout the midrange and treble, implying stable stereo imaging. This graph also shows that the Concept 300 becomes quite directional in the top audio octave, which will work against the audibility of the small peak in the same region in the on-axis response in all but very small rooms. In the vertical plane (fig.8), a suckout develops in the crossover region 10° above and 15° below the woofer axis. The Q Acoustics speaker will sound at its best with the listener's ears level with the tweeter. Fortunately, the Tensegrity stand places the Concept 300's tweeter 36" from the floor, which a 1990s survey by my colleague Thomas J. Norton indicated was the average ear height for listeners sitting in regular chairs (but not in folding "director" chairs).

120Q300fig07

Fig.7 Q Acoustics Concept 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.

120Q300fig08

Fig.8 Q Acoustics Concept 300, vertical response family at 50", normalized to response on tweeter axis, from back to front: differences in response 45–5° above axis, reference response, differences in response 5–45° below axis.

The red trace in fig.9 shows the Concept 300s' spatially averaged response with the grilles on in my room. This is generated by averaging 20 1/6-octave–smoothed spectra, taken for the left and right speakers individually using a 96kHz sample rate, in a vertical rectangular grid 36" wide 18" high and centered on the positions of my ears. For reference, the blue trace shows the spatially averaged response of the KEF LS50s I purchased following my review in 2012. The in- room response of both loudspeakers is very similar in the midrange, with a slight rising trend evident between 150Hz and 800Hz. Both roll off slowly below 100Hz, but the Concept 300s excite the lowest-frequency mode in my room at 32Hz to a significantly greater extent than the KEFs. At the other end of the spectrum, the slightly sloped-down output of both speakers is due to the increased absorptivity of the room's furnishings as the frequency rises. While the LS50s have more presence-region energy than the Concept 300s, the latter have more output in the top two octaves of the audioband. (The in-room responses of both speakers drop like a stone above 20kHz; this is because I performed the measurements using the NAD M10 amplifier, which digitizes its analog inputs with a 44.1kHz sample rate.)

120Q300fig09

Fig.9 Q Acoustics Concept 300, spatially averaged, 1/6-octave response in JA's listening room (red) and of the KEF LS50 (blue).

Turning to the time domain, the Concept 300's step response (fig.10) indicates that the tweeter and midrange unit are connected in positive acoustic polarity. The decay of the tweeter's step, which arrives first at the microphone, smoothly blends with the start of the woofer's step. This implies optimal crossover implementation. The Q Acoustics Concept 300's cumulative spectral-decay plot (fig.11) is superbly clean overall, cleaner even than that of the Concept 500. This may well correlate with the extremely transparent window the pair of Q Acoustic speakers offered into recorded spaces.

120Q300fig10

Fig.10 Q Acoustics Concept 300, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).

120Q300fig11

Fig.11 Q Acoustics Concept 300, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

The Q Acoustics Concept 300 offers excellent measured performance, indicative of equally excellent loudspeaker engineering.—John Atkinson


Footnote 1: See fig.4 here.
COMPANY INFO
Q Acoustics
Stortford Hall Industrial Park
Dunmow Road, Bishop's Stortford, Hertfordshire CN23 5GZ
England, UK
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ARTICLE CONTENTS

COMMENTS
Ortofan's picture

... bypass or mechanically short-circuit the suspension effect of the stands, particularly if the cables are relatively thick and/or inflexible and especially if the speakers are bi-wired?

For example, the set-up of Linn LP12 turntable requires that the tonearm lead be dressed in a specific manner to prevent the operation of the suspension from being compromised.

Did JA1 make separate sets of frequency response measurements with the port open and with the foam bung installed?

John Atkinson's picture
Ortofan wrote:
How does one avoid having the speaker cables bypass or mechanically short-circuit the suspension effect of the stands, particularly if the cables are relatively thick and/or inflexible and especially if the speakers are bi-wired?

Good question. For the measurements I used very floppy cables, for this very reason. For my listening, I suspended the cables so that they shouldn't have short-circuited the stand's sprung suspension.

Ortofan wrote:
Did JA1 make separate sets of frequency response measurements with the port open and with the foam bung installed?

No, but the bass response with the port blocked can be inferred from the relevant impedance graph, fig.2, which shows that the speaker then behaves as a closed box with a fairly high tuning frequency.

John Atkinson
Technical Editor, Stereophile

Bogolu Haranath's picture

It is about time JA1 reviews, B&W Formation Duo Wi-Fi speakers ($5,000/pair with stands) and/or KEF LS-50 wireless Nocturnes ($2,500/pair ) :-) .......

Bogolu Haranath's picture

Ortofan needs to take classes in mechanical, electrical and acoustical engineering :-) .......

Bogolu Haranath's picture

Regarding speaker isolation from vibrations, JCA once mentioned about isoAcoustics isolation devices used in Focal loudspeaker demonstration (Munich 2019) :-) .........

Charles E Flynn's picture

https://www.qacoustics.com/concept-300-bookshelf-speaker-pair-stands.html

Charles E Flynn's picture

From https://www.whathifi.com/reviews/q-acoustics-concept-300 :

But while we’re accustomed to a Q Acoustics speaker that favours warmth and refinement over outright liveliness, these fall short of the Dynaudios when it comes to rhythmic drive and dynamic expression. At this level, we would expect more.

Playing Drake’s Headlines, the Dynaudios immediately spring into action with enthusiasm. They hotfoot the synths with a militant timing and almost habitual cohesion that’s missing in the Q Acoustics. The Qs don’t quite hurry things along or grip a rhythm as well as the Dynaudios, which tightly tie everything together like the end of a Sherlock novel. Dynamically, while far from static or uninteresting, they fail to soar and sink to such effective levels, too.

The Concept 300s respond with greater calculation, unrivalled breadth and a textured warmth that fleshes out the midrange, but we find their rivals a more transparent and emotive listen. Ultimately, that seals their four-star fate in this review.

John Atkinson's picture
Charles E Flynn wrote:
From https://www.whathifi.com/reviews/q-acoustics-concept-300: "But while we’re accustomed to a Q Acoustics speaker that favours warmth and refinement over outright liveliness, these fall short of the Dynaudios when it comes to rhythmic drive and dynamic expression."

I reviewed the Dynaudio Special Forty loudspeaker, which the What HiFi? reviewer preferred to the Q Acoustics Concept 300, in September 2018; see www.stereophile.com/content/dynaudio-special-forty-loudspeaker. Overall, I very much enjoyed my time with the Dynaudios but one thing I couldn't get past with piano recordings was a slight amount of congestion in the midrange.

John Atkinson
Technical Editor, Stereophile

Charles E Flynn's picture

Mr. Atkinson,

Thanks for posting the link to your review of the Dynaudio Special Forty. I suspect few people are as familiar with the sound of both live and recorded piano as you are. I fondly recall the concert in Providence at which you introduced Hyperion Knight.

There are a few copies left of this Knight recording:

https://elusivedisc.com/hyperion-knight-the-magnificent-steinway-cd/

Page 2 of your review of the Dynaudio has this typo: Zeptember

John Atkinson's picture
Charles E Flynn wrote:
Thanks for posting the link to your review of the Dynaudio Special Forty.

You're welcome.

Charles E Flynn wrote:
I suspect few people are as familiar with the sound of both live and recorded piano as you are.

The sound of the solo piano is tough for loudspeakers to reproduce, as there is very little masking in the midrange. If a reviewer doesn't play any piano recordings, he may well miss a problem.

Charles E Flynn wrote:
I fondly recall the concert in Providence at which you introduced Hyperion Knight.

Although I am a big fan of Hyperion's playing, that would have been erstwhile Stereophile contributing editor John Marks.

Charles E Flynn wrote:
Page 2 of your review of the Dynaudio has this typo: Zeptember

Ah, that was a feeble attempt at humor, as I was using a Led Zeppelin recording for a review to appear in the "Zeptember" issue.

John Atkinson
Technical Editor, Stereophile

Charles E Flynn's picture

Mr. Atkinson,

Thank you.

I thought it was possible that the "Zeptember" was deliberate, but then I did not recall any other examples of such an attempt at humor.

I hope I am never called to give eyewitness testimony about who was present at a concert.

Pianist Hyperion Knight to Perform in Providence RI February 25, 2018

https://positive-feedback.com/audio-discourse/pianist-hyperion-knight/

02-05-2018 | By John Marks | Issue 95

You make a good point about the value of piano recordings for evaluating speakers. I will try to remember that better than I remembered who introduced Hyperion Knight.

Bogolu Haranath's picture

$5k is somewhat expensive for a 2-way passive bookshelf speakers ........ There are several 2-way bookshelf speakers listed in Class-A and Class-B in Stereophile recommended components, some of which costing less than half the price of Q300 ......... For $5k one can get any of those bookshelf speakers plus two powered subwoofers ........ B&W Formation Duo Wi-Fi capable speakers are $5k with stands, BTW :-) .........

tonykaz's picture

and assessment ?

Should we consider a Pair of Devialet Phantom 900s for about $3,500 ( made in France ) : a Stunning Music System.

Why would we consider a pair of spindly Mini-Monitors ( Asia Made ) costing $5,000 ?

I can't help noticing that these tiny things need Higher Authority comparisons from Wilson & Magico, etc. ( betcha these outfits aren't happy to be favorably compared like this, I wouldn't ).

So, I beg to ask: How can a technical outfit like Devialet produce 21st Century Electronic Transducer Devices ( in France ) and still charge considerably less. Why would Brit. Engineers source in Asia?

Something smells >)))))'>

Tony in Iowa frrrrreeeeezzzzzzzzzzz'n

ps. should we now expect our LS3/5a to be made in China ? What tragedy is befalling our Island friends?

ps. I know people spending serious money for Isly Single Malt that favorably compares to horrible ( my, not useful, opinion )

Bogolu Haranath's picture

I'm waiting for Asian made Scotch whisky for $5 a gallon :-) .........

tonykaz's picture

How can Scotch be made in Asia?, isn't it Scotch from being made in Scotland???

Tony lost in the fruited planes

Bogolu Haranath's picture

(Recipe) designed in Scotland, made and bottled in Asia ....... That is a good possibility ..... BTW, they are now making Tesla cars in Shanghai :-) .......

Bogolu Haranath's picture

What is a 'fruited plane'? :-) .......

tonykaz's picture

The great Mid-West was described as a "Fruited Plane" by the 1850s emigrants ( whilst still in the Old-Country ) prior to making a decision to immigrate and inhabit places like Kansas and Iowa where Land was deeded ( for free ) as an inducement to Build America into a White Man's Paradise.

Of course, the Native Indigenous population were escorted/forced out & down the "Trail of Tears" to their New Mexico Homes ( reservations ).

My ancestors were part of the 1850s group of Europeans that traversed the Erie canal to claim their Acreage recently vacated by the Native Indians, they then prepared to fight the Civil War to right the wrongs of Slavery.

The Fruited Plane is that vast track of land now known as America's Bread Basket : Flat Farm Land West of the Mississippi River where the Buffalo roam and Grasslands became Wheat Fields and Kellogg Cereals .

Tony hoping to return to Venice

Bogolu Haranath's picture

The spelling may be 'Fruited Plains' (grassland, flatland) ........ Google search :-) ........

tonykaz's picture

Yes, not hard to agree with you, thanks. I sit, corrected ( stand ).

Its a dam cold place.

But...

If they were giving me a homestead of free acreage I'd probably accept too.

A curious thing is that these folks are identical to everyone I've ever met anywhere in the World, they seem to want the same things and even look pretty much the same. I might've thought that they'd look like Hee-Haw TV Show Farmers, they don't, they could easily look like people walking down the street in San Fransisco or anywhere else.

I'm looking forward to the Deep South Campaign tour. I've heard that those people look the same too. Everyone seems kinda wonderful, I wasn't expecting that. ( being from angry-finger waving Michigan )

Tony out in the cold

Bogolu Haranath's picture

In one of the recent polls, Iowa was ranked as the number one ideal state to retire ........ Florida was ranked as one of the top ten states :-) .........

tonykaz's picture

Hmm, kinda illustrates the problem with Polling Data or suggests the Poll was hired by the Iowa Real estate developers association.

Of course, if a person likes vast panoramas of windy flowing grasslands or has a group-home overlooking the John Deere Combines at harvest time, this place could be a peaceful home.

then again,

who can retire now-a-days? or afford to retire ? Siemens abandonded Iowa workers for the Czech republic and a non-union workforce.

Tony out somewhere

Bogolu Haranath's picture

Another poll shows, Nebraska as the number one state and Iowa as number two ideal state to retire ....... New York State and California are at the bottom of the list ....... Not surprising :-) .......

soundcents's picture

The the Trail of Tears refers to the forced removal of native peoples as a result of Andrew Jackson's "Indian Removal Act" of 1830 (ending in 1850). Although many of the groups were marched through the mid-west on their way to "Indian Territories" (modern day Oklahoma) the groups were actually from the south east. The Chickasaw, Choctaw, Creek, Seminole, and Cherokee people were marched from modern day Mississippi, Alabama, Georgia and Florida.
The trail of tears was over 5,000 miles long, resulted in the death of more than 16,000 native people and the loss of 22 million acres of their land. The name refers to a quote from a Choctaw leader who referred to the forced marches and relocation as a "Trail of Tears and Death"

tonykaz's picture

How can Scotch be made in Asia?, isn't it Scotch from being made in Scotland???

Tony lost in the fruited planes

Ortofan's picture

... Hong Kong?
https://6moons.com/audioreviews2/rogers/1.html

Want to consider an even less expensive speaker?
Try the KEF R3:
https://www.youtube.com/watch?v=5esoOMgzfUo

tonykaz's picture

Ouch, this one hurts.

Tony out in the freezing winds

Anton's picture

After the review of the Crystal Cable Arabesque Minissimo Diamond speakers, I expect these to have a "$$$" next to their name in the next Recommended Components.

Four pairs of these = one pair of the Crystal Cable.

Jack L's picture

...... structures that will influence its sound in unpredictable ways,.." quoted Jim Austin.

Yes, that's why I have my KEF 2-way standspeakers isolated from their spiked steel tubular tripods (full stuffed with lead shots & baked fine fine sand to increase their mass) with 4 dense cushion pads each. This should reduce substantially any loudspeaker box vibration from passing down on to the concrete floor underneath through the tripod spikes.

It sounds obviously cleaner to my ears than without.

listening is believing

Jack L
Canada

Charles E Flynn's picture

It is always interesting to see what products covered in specialized Websites manage to gain the attention of Websites geared to a wider audience:

https://gearpatrol.com/2020/02/12/best-bookshelf-speakers

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