LAB­O­RA­TORY TEST RE­PORT

Australian HIFI - - ESOTERICA -

New­port Test Labs mea­sured the fre­quency re­sponse of the Q Acous­tics Con­cept 500 it had for test­ing in its acous­tic lab­o­ra­tory as be­ing 42Hz to 30kHz ±3.5dB and it is this re­sponse that is shown in Graph 1. It’s the re­sult of mea­sur­ing the speaker us­ing two dif­fer­ent tech­niques. The trace be­low 550Hz is the av­er­aged re­sult of nine in­di­vid­ual fre­quency sweeps mea­sured at three me­tres, with the cen­tral grid point on-axis with the tweeter us­ing pink noise test stim­u­lus with cap­ture un­smoothed. This has been man­u­ally spliced (at 550Hz) to the gated high-fre­quency re­sponse mea­sured at one me­tre on axis, an ex­panded view of which is shown in Graph 2. You can see that the re­sponse is ex­traor­di­nar­ily flat, with the vari­a­tions in it be­ing pri­mar­ily the re­sult of the in­evitable roll-offs at ei­ther end of the fre­quency spec­trum. For ex­am­ple, if we look only at fre­quen­cies be­tween 110Hz and 21kHz, the Con­cept 500’s re­sponse was around ±1.25dB. Be­tween 150Hz and 5.5kHz, it was even bet­ter at ±0.7dB. This level of lin­ear­ity is a stun­ning achieve­ment in a pas­sive loud­speaker sys­tem.

Note too, that the over­all spec­tral re­sponse is not skewed to favour the bass or the treble… or in­deed the midrange.

The high-fre­quency re­sponse of the Q Acous­tics Con­cept 500 is shown in greater de­tail in Graph 2, by virtue of chang­ing the hor­i­zon­tal axis to ‘zoom in’ on the re­gion be­tween 400Hz and 40kHz. This graph also adds a trace (green) show­ing the re­sponse with the loud­speaker grille in place (the black trace be­ing the re­sponse with­out the grille.) You can see that the grille is re­mark­ably acous­ti­cally trans­par­ent with the only sig­nif­i­cant dif­fer­ence be­ing that drop in level be­tween 9kHz and about 13kHz. It is in­ter­est­ing that the very mi­nor dip in the re­sponse with­out the grille (at 7.5kHz) shifts down at lit­tle to 7kHz when the grille is in place. Also in­ter­est­ing is the slight in­crease in out­put cen­tred at 2.4kHz. While I can’t ex­plain the first, this lat­ter ef­fect is no doubt cross­over-re­lated since Q Acous­tics spec­i­fies the cross­over fre­quency as be­ing at 2.5kHz.

Low-fre­quency per­for­mance is shown in Graph 3. You can see that the per­for­mance of

At ±0.7dB, the level of lin­ear­ity is a stun­ning achieve­ment in a pas­sive loud­speaker sys­tem

the bass/midrange driver Q Acous­tics is us­ing is ex­cel­lent, ex­tend­ing up­wards from 100Hz very smoothly within about ±1dB. Its re­sponse starts rolling off at 85Hz and then does so at the ex­pected rate to its min­ima at ex­actly 40Hz. As you’d ex­pect of such a large port, it de­liv­ers its out­put over a wide band­width. There’s no real ‘peak’ as such in its out­put, with the port de­liv­er­ing al­most the same out­put from 35Hz to 55Hz. Rather than rolling off smoothly above 55Hz, there’s a cu­ri­ous ‘shelf’ in the out­put be­tween 100Hz and 140Hz. As you can see, there’s also some un­wanted leak­age of higher fre­quen­cies cen­tred around 425Hz, 590Hz and 725Hz, but it’s very low in level, and the port is at the rear, which will ame­lio­rate any au­di­ble ef­fects. The im­ped­ance of the Q Acous­tics Con­cept 500 is well-con­trolled in its bass re­flex in­car­na­tion, with the two bass res­o­nant peaks at 36Hz and 78Hz, with the min­ima be­tween them at 40Hz. Ex­cept for the higher-fre­quency bass peak, the im­ped­ance re­mains above 4 and be­low 20 right across the au­dio band, ex­cept for at 200Hz, where it drops to 3.7 , which was not un­ex­pected, since Q Acous­tics flags this in its spec­i­fi­ca­tions. How­ever whereas Q Acous­tics spec­i­fies the Con­cept 500’s ‘nom­i­nal’ im­ped­ance at 6 I would per­son­ally rate the Con­cept 500 as a 4 de­sign. You can see that Q Acous­tics must be say­ing that it’s the acous­tic cross­over that’s at 2.5kHz, be­cause New­port Test Labs’ graph clearly shows that the elec­tri­cal cross­over point is some­what lower, at around 1.7kHz. I was also pleased to note that there’s a ris­ing im­ped­ance at high fre­quen­cies, which will make the Con­cept 500 very am­pli­fier-friendly, par­tic­u­larly with older Class-D am­pli­fier de­signs.

Whereas Q Acous­tics spec­i­fies the Con­cept 500 with an ef­fi­ciency of 90dBSPL at one me­tre for a one watt in­put, New­port Test Labs re­ported its es­ti­mate of ef­fi­ciency at 89dBSPL at one me­tre, for a 2.83Veq in­put. The small dif­fer­ence could ob­vi­ously be due to the dif­fer­ent mea­sure­ment tech­niques used (watts vs. volts!) as well as other fac­tors, but is in any case well within the realms of both mea­sure­ment un­cer­tainty and sam­ple-to-sam­ple vari­a­tions in pro­duc­tion. But whether it’s 89dBSPL or 90dBSPL, the Con­cept 500 is still more ef­fi­cient than the av­er­age floor-stander and thus able to de­liver high sound pres­sure lev­els even with quite low-pow­ered am­pli­fiers.

Graph 5 shows an in-room re­sponse us­ing pink noise, with the higher graph­ing limit de­lib­er­ately re­stricted to 10kHz and you can see that the re­sponse ex­tends from 300Hz to 10kHz ±0.7dB.

Graph 6 shows the ef­fect of the rear-panel jumper on the high-fre­quency re­sponse of the Q Acous­tics Con­cept 500. New­port Test Labs has lim­ited the low-end dis­play to 2kHz, be­cause be­low this fre­quency there is no ef­fect on re­sponse at all. Above 2kHz, the ef­fect on re­sponse grad­u­ally in­creases un­til it reaches its max­i­mum at around 4kHz, at which point you can vary re­sponse by ±2.5dB… or, if you pre­fer, over a to­tal range of 5dB, which is a sig­nif­i­cant ad­just­ment that will be eas­ily au­di­ble. Other than ad­just­ing level, the jumper has no other shap­ing ef­fect on the fre­quency re­sponse, which is as it should be.

When you pay one of the top speaker de­sign con­sul­tan­cies in the world to build you a high-end speaker, you ex­pect high­end per­for­mance, and I’d have to say that Fink Con­sult­ing has done a su­perb job for Q Acous­tics. I’d even have to sug­gest that a bonus might be in or­der. The Con­cept 500 is a su­perb loud­speaker de­sign. Steve Hold­ing

In the Con­cept 500 de­sign, as in other of its ‘gel-core’ de­signs, Q Acous­tics has also me­chan­i­cally de­cou­pled the 28mm soft dome tweeter from the gel-core cabi­net

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