Q Acoustics Concept 500 loudspeaker Measurements

Sidebar 4: Measurements

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Q Acoustics Concept 500's frequency response in the farfield, and an Earthworks QTC-40 microphone for the nearfield responses. Q Acoustics specifies the Concept 500's sensitivity as 90dB/W/m; my estimate was close to that, at 89.2dB(B)/2.83V/m, which is usefully higher than average. The Concept 500's impedance is specified as 6 ohms, with a minimum magnitude of 3.7 ohms. Fig.1 shows how the Concept 500's impedance and electrical phase varied with frequency with its reflex port open. Though the magnitude does drop below 6 ohms in the midrange, with a minimum value of 3.9 ohms at 193Hz, and there is a current-demanding combination of 5.5 ohms and –39° electrical phase angle at 99Hz, the Concept 500 will not be a particularly difficult load for an amplifier to drive. With the port blocked with the supplied foam plug, the impedance plot (fig.2) indicates that the Concept 500 behaves as a sealed-box design with a woofer tuning frequency of a relatively high 59Hz.


Fig.1 Q Acoustics Concept 500, electrical impedance (solid) and phase (dashed) with port open (2 ohms/vertical div.).


Fig.2 Q Acoustics Concept 500, electrical impedance (solid) and phase (dashed) with port blocked (2 ohms/vertical div.).

When I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer, it seemed relatively inert. Fig.3 shows a cumulative spectral-decay plot calculated from the accelerometer's output when it was fastened to the front baffle midway between the lower woofer and the speaker's base. I did find some resonant modes in the midrange on all surfaces, but these are all low in level.


Fig.3 Q Acoustics Concept 500, cumulative spectral-decay plot calculated from output of accelerometer fastened to front baffle halfway between lower woofer and base (MLS driving voltage to speaker, 7.55V; measurement bandwidth, 2kHz).

With the port open, the impedance plot has a saddle in the magnitude trace centered on 42Hz (the lowest note of the four-string double bass and bass guitar), which suggests that this is the woofers' reflex tuning frequency. The two woofers behaved identically, and when measured in the nearfield had the expected minimum-motion notch in their outputs at 42Hz (fig.4, blue trace). The port's output (red trace) peaks between 30 and 90Hz, but its upper-frequency rolloff is disturbed by a shelf at around 150Hz, the frequency of a small bump in the impedance-magnitude trace. There is also a sharply defined resonance at 710Hz in the port's output, but this is 20dB down compared with the woofer's level, and its audibility will be further reduced by the fact that the port fires to the speaker's rear. Higher in frequency in fig.4, the woofers (blue trace) are crossed over to the tweeter (green) at the specified 2.5kHz.


Fig.4 Q Acoustics Concept 500, acoustic crossover on tweeter axis at 50" with port open, corrected for microphone response, with the nearfield woofer (blue) and port (red) respectively plotted below 350Hz and 900Hz.

In fig.5, the black trace below 300Hz shows the complex sum of the nearfield woofer and port responses, taking into account acoustic phase and the different distances of each radiator from a nominal farfield microphone position. The nearfield measurement technique assumes that the drive-unit is mounted in a true infinite baffle—ie, one that extends to infinity in both the vertical and horizontal planes—and this results in a peak in the upper bass with a speaker that is actually maximally flat in the bass. The Concept 500 has only a small bass peak, which implies that its woofer tuning is optimized more for definition than for weight, as TJN found. However, the boundary reinforcement in the low bass, due to the fact that the port is placed close to the floor, will result in a better balance of clarity and weight in the low frequencies.


Fig.5 Q Acoustics Concept 500, 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 with the port open (black), and the woofer response with the port closed (red), both plotted below 300Hz.

The red trace in fig.5 shows the nearfield output of the woofers with the port sealed. It rolls off below 80Hz with the expected 12dB/octave slope compared with the reflex tuning's 24dB, but this suggests that the speaker will sound lean with the port blocked.

Above 300Hz in fig.5, the black trace shows the Concept 500's farfield response, averaged across a 30° horizontal window centered on the tweeter axis. It is superbly flat. This graph was taken with the rear-panel jumper set to its Normal position. With the jumper set to More Treble or Less Treble, the tweeter's output was respectively raised or lowered by approximately 0.5dB.

The plot of the Concept 500's horizontal dispersion (fig.6) indicates a well-controlled radiation pattern. The evenly spaced contour lines in this graph suggest that a pair of these speakers will offer stable stereo imaging, due to the fact that their direct sound and the reflections of that sound from the room's sidewalls will not have different characters. In the vertical plane (fig.7), the Concept 500 is not fussy about having the listener's ears the same height from the ground as the tweeter (37" with the speaker on its spikes).


Fig.6 Q Acoustics Concept 500, 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.


Fig.7 Q Acoustics Concept 500, 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 5–10° below axis.

In the time domain, the Concept 500's step response (fig.8) indicates that the tweeter and woofers are connected in positive polarity. The decay of the tweeter's step blends smoothly with the start of the woofers' step, suggesting optimal crossover design. The Q's cumulative spectral-decay plot (fig.9) was superbly clean.


Fig.8 Q Acoustics Concept 500, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).


Fig.9 Q Acoustics Concept 500, cumulative spectral-decay plot on tweeter axis at 50" (0.15ms risetime).

I was impressed by the Concept 500's measured performance. It exemplifies textbook loudspeaker design.—John Atkinson

Q Acoustics
Stortford Hall Industrial Park, Dunmow Road
Bishop's Stortford, Hertfordshire CN23 5GZ
England, UK
(855) 279-5070

Long-time listener's picture

"The nearfield measurement technique ... results in a peak in the upper bass..."

I've noted that a dip almost always occurs just above that peak--in this case, a very shallow dip between 300-500Hz. Is that also an artifact of the measurement technique? Just curious, since you have never commented on these dips. Why would so many speakers have a dip in the lower midrange?

Bogolu Haranath's picture

Look at TJN's in-room response, before and after EQ :-) .........

Long-time listener's picture

I'm not sure what conclusion I'm supposed to be drawing. In one of those, I do see the dip in the same place, and does your post answer my question about the typical appearance of this dip in the measurements? Thanks...

Bogolu Haranath's picture

No ....... I was just mentioning TJN's in-room response ...... The dip doesn't seem to be that significant after EQ :-) ...........

Jason P Jackson's picture

The dip between ~150hz to ~350hz that is common in loudspeaker measurement at listening distance ie.2-3 metres is nearly always caused by cancellations due to room reflections. The main reflection being the floor- "floor bounce cancellation" and the side walls. The tendency of most hi-fi owners is to place their speakers along the short-wall of the room, bringing the side-walls closer to the speakers, exacerbates this problem. The bottleneck in performance of most 2 driver speakers (apart from the recording) in most rooms is usually due to these reflections, which is also the reason for why most speakers to sound remarkably similar to one another when auditioning in hi-fi stores when placed at the same height and in the same room. In this case, the in-room measurements shows a reinforcement at these frequencies and can be caused by the same reasons as described above. Ironically, I hasten to add cancellations can be less of a problem in smaller rooms. As for the near-field measurements (1.5 metres or 50", averaged across 30 degrees) of the Q-Acoustics 500, of which done by a man who knows how to properly measure loudspeakers in-room John Atkinson, the small dip in the midrange (~450hz) is most likely caused by the losses at those frequencies as a characteristic of the width of the baffle i.e "baffle step" and "baffle diffraction". These issues (baffle step and diffraction) are nearly always accounted for at least in part in the design of the crossover and baffle (the front panel of the speaker). The picture would and nearly always does look very different at listening distance. These are well designed speakers.

Bogolu Haranath's picture

Some of the apparent 'dip' is due to the port(s) adding bass reinforcement in bass-reflex designs ....... Look at the measurements before and after adding the port contribution to the bass frequencies .. Fig 4 and Fig 5 in the measurements :-) .......

Long-time listener's picture

This is the best response I've received so far. I was hoping that the person who did the measurements might respond, since this phenomenon is seen in almost all measurements, but he so far hasn't.

Bogolu Haranath's picture

"If you want clean, powerful, deep bass at realistic levels from most full-range speakers, use one or more subwoofers" :-) ........

Jason P Jackson's picture

Now that would make a nice system.

Long-time listener's picture

Even if you can accept the circular base on these speakers aesthetically (I can't, and frankly don't care for their looks in other respects), the fact that they extend so far outward past their spikes will only make placement awkward and difficult. Why on earth was this done? This seems like a poorly thought-out -- and completely unnecessary -- choice in an otherwise well-designed loudspeaker. And, umm, why put the redwood veneer on the BACK of the speaker, where no one will ever see it? ?!?! Q Acoustics, please hire someone competent at visual design.

mrkaic's picture

Especially red veneer at the back.

Long-time listener's picture

I guess if you stand behind your speakers all the time as you listen, then you can certainly enjoy the red veneer. I personally don't. But anyway, these things are all quite subjective. I just don't think they look very nice. Sometimes a clean, rectangular box with a nice veneer all the way around is the best.

Ortofan's picture

... toward the rear helps ensure that they are set up correctly.
If you can't see the redwood panels from your listening position, then the speakers are aimed properly.

spacehound's picture

Q Acoustics have a very good, and well deserved, reputation for their cheaper speakers, where probably the expectations are lower. And they are good value for money.

However, yet again, as so many manufacturers, they are obsessed with 'fashion'.
So we have 'narrow' speakers. As a result the two drivers are only 6.5 inches diameter and the working area, the cone itself, is only about 5 inches diameter.

You will NEVER get good bass from speakers of such a small size and that there are two merely makes what bass there is (and everything else until the tweeter takes over) louder, it doesn't create a lower frequency response.
Additionally the two drivers will never respond identically, thus 'muddying' the sound at ALL frequencies, not just the bass. And these two have to cover both the bass and the mid range.

All in the name of 'fashion'.
And as I said, many manufacturers do it. A ten inch bass driver, a five inch mid-range, and a tweeter will be far better. The necessarily wider cabinet does NOT spoil the stereo image either.

Stick to the lower priced Q Acoustics speakers. They will be just as good and you will save 4000 dollars.
If you MUST have fashion (at the expense of sound quality) just buy the lowest priced Sonus Faber speakers instead, they will go well with your Gucci loafers. Q Acoustics stuff, while, except for these, good value, are about as fashionable as Wal Mart trainers.

Long-time listener's picture

The reviewer found their bass to be good, if not great: "Their bass impact wasn't quite as punchy, powerful, and deep as I've heard from a few other speakers in my room, but it was never less than satisfying."

Regarding baffle width, and whether good bass can be achieved with small drivers, take the old Revel M20. It had excellent dispersion despite a wide baffle, but it also had surprising bass extension and weight given its 5-inch driver. The tradeoff, however, was that it was difficult to drive well. Also, though, models such as the AudioPhysic Virgo show that it's probably EASIER to achieve outstanding imaging and dispersion with a narrow baffle.

Ortofan's picture

... (having a five-inch mid-range and a tweeter) along with a sub-woofer (having at least a ten-inch driver) meet your requirements?
Or, would the JBL L100 Classic (12-inch woofer, 5.25-inch mid-range and a tweeter) be more appropriate?

Bogolu Haranath's picture

Excellent suggestion ....... JBL L-100 cost $4,000/pair ....... Hopefully, Stereophile reviews them :-) ........

spacehound's picture

Trying to make people buy subwoofers, preferably two, one for each side, and they probably won't 'match' your existing speakers, is just 'marketing'.
Far better not to buy narrow squeaky speakers in the first place as you still have to find room for the subwoofer(s).

It's all about trying to make you buy new stuff. And unfortunately for the 'marketeers' a decent pair of speakers can last a lifetime. I use big 'traditional' Tannoy ones, which have just the one dual concentric driver, and I don't visualise ever replacing them.

The JBL L100 Classic is in the same mould, though the deaign is different.

The laws of physics are as they are and 'fashion' won't change them.

Ortofan's picture

... besides the JBL L100 Classic, what else is available that fits the mold of a tweeter + single ~5" mid-range + single 10"+ woofer?
Harbeth M40, Spendor Classic 100, Focal Scala Utopia Evo and ...

Bogolu Haranath's picture

If someone is willing to spend $8k to $10k, Revel Ultima Gem2 and KEF Reference one bookshelf speakers are other possible choices, which have 3 drivers each. They both got very positive reviews :-) .........

Ortofan's picture

... at least a 10" diameter bass driver.

Bogolu Haranath's picture

True ...... If someone is in the market for a little bit more bass extension, better midrange isolation and reduced IMD, than a typical two-way design, these are some of the other choices ....... That is the reason why I mentioned those :-) ..........

reynolds853's picture

There are many assumptions in the comments on this speaker for some reason. As someone who auditioned these in my dedicated listening room, I think they are VERY competitive at $6k. Most reviews reach a similar conclusion. It comes down to taste, system matching and room matching but I would be hard pressed to say the speaker did anything "wrong". The measurements are exemplary. I had to spend almost 2x to beat them and that was as much about preference than really being better. Build quality is great.

Comments made:
1.) Can't do strong bass: Bass was VERY healthy and tight. (I listen to all music types including EDM, Metal, Classical, Organ music, etc.) Unless you are using them in a large room or as theater speakers without a sub, it is unlikley you would want subs for music. The construction/design is top notch... see the whitepaper at their website.
2.) Wood at the back: It's subjective. It provides an illusion that the speaker is less deep than if it were all one color. I liked it. You may not.
3.) Round base: If this prohibits your placement, they are probably not placed for best sound. Unless your room requires you to shoehorn them into a slot, this should not be an issue.

They port at the back so it does take some time to find the best spot for sound. These were at Axponia this year and I was shocked at how poor they sounded (same with the Revel 228Be) vs prior auditions where both had sounded great. ANY speaker can sound "bad" without careful setup and yes, hotel rooms are especially limiting.

Customer service is great and so is their "no risk" return policy.

CraigH79's picture

LOL @ spacehound's entire comment. Clearly someone who hasn't auditioned the speakers and is just making massive (incorrect) assumptions based on the size of the drivers. Idiotic.

"you will never get good bass from speakers of such a small size"

Absolute rubbish. You will never get LOW sub-bass from 6.5 inch speakers but you can very much get tight, punchy, heavy-hitting, accurate bass reproduction from such drivers. And as an owner of the Concept 500 I can tell you they do it with aplomb. To the point where for a lot of music, I do not need to worry about using my subwoofer (Paradigm Studio Sub 12).

Also the science and R&D behind the cabinet design ensures that these "such small sized" drivers perform far beyond the realms of what you imagine they should. Funny that you mention frequency response. I bet you haven't even bothered to find the frequency response graph of these speakers. From 70hz to 20khz their response is basically flat - within 3-4db across that spectrum.

There's nothing "fashion" about these speakers at all. Their finish, while polarizing, is not gimmicky or fashionable. The build quality is nothing short of first class.

"A ten inch bass driver, a five inch mid-range, and a tweeter will be far better."

Such a silly statement. So many variables at play and at the end of the day these speakers punch well above their weight, giving pairs up to double their price a very good run for their money (yes, including pairs with 8 and 10 inch drivers in them). In Australia these first sold for AU6.3k when released. They easily compete with speakers in the AU$10-15k bracket.

"Stick to the lower priced Q Acoustics speakers. They will be just as good and you will save 4000 dollars."

I thought this was the most stupid thing your said in your post until i read this:

"at the expense of sound quality"

In short, you make it abundantly clear that you have absolutely no idea about the capabilities and performance of the Concept 500.

knaw35's picture

Well, I am Hi-End enthusiast from many years. Write article to hi-fi magazines. I have visited Dali manufacturer headquarter in Hobro/Denmark some years ago. The chief of development department gave me a long time talk to explain some loudspeaker features and how it looks on measurement diagrams. Looking at Q Acoustic 500 I can say that impedance/phase response does not promise any good advantages from these nice looking drivers. My interlocutor says simple - these speakers cannot play well. We discussed the problem based on few similar diagrams came from different models of different manufactures. The answer was clear. Fortunately, many happy owners are not even realize that the speakers they own make bad work. They play, they have bass response and silky high frequencies. Well, but where is musicality? Can they find a melody on each area and coddle one as should be? I think the best way to understand the difference is just to get as much experience as possible and listen to deepest depth. I also would trust more to manufacture with long time experience than any newcomer on the demanding market.

Summary - If you own Q acoustic 500 and you are happy then stick to it. Happiness is a great state of mind. But to be lucky buying speakers for 5000$ you should look elsewhere.

Bogolu Haranath's picture

Q Acoustics Concept 300 looks attractive, modern and a life-style product ($5,000/pair, including stands) ......... Check out Q Acoustics website for details :-) ...........