HEDD BASS 08 Review: active 8″ studio subwoofer with Linearizer and CoP technologies

It would seem, where and why you can develop the direction of acoustic systems? All physical principles are well known, and everything that could be invented 50 years ago. It remains only to produce. But the indefatigable Germans from HEDD Audio under the leadership of Klaus Heinz do not sit still and manage to regularly invent something new. At first, these were our own revolutionary AMT emitters for high frequencies. Then their hands reached their own original midrange-tweeters.

And finally, like the icing on the cake, they developed and implemented several branded digital processing technologies in a powerful internal DSP. Moreover, HEDD chooses the audience of users who are most demanding in terms of sound quality, who are no longer satisfied with cheap mass models, but who are not yet ready to spend money on Hi-End speakers with huge dimensions and a price.



The second generation of active studio monitors HEDD MK2 replaced purely analog models and acquired several interesting branded technologies at once. The newest official video about HEDD MK2 can be viewed on the official Youtube channel:

The HEDD company has long promised, but never released active subwoofers. Subwoofers have long been requested by users. But the company’s engineers decided to wait a bit and release the subwoofers immediately on the same technological platform as the MK2 monitors.

So, now there are 2 models of HEDD subwoofers on sale: HEDD BASS 08 and HEDD BASS 12, which provide full support for DSP and all branded technologies. If for 5-7″ monitors the low-frequency range is not the main one, then for subwoofers it is a completely different matter. It is there that the phase drift due to the acoustic design of the case is a very unpleasant phenomenon, which gives, although an even frequency response graph, but smeared bass and a headache when. For home theaters this is most likely acceptable, since it is not very noticeable on special effects. But for music and video production studios, for bass register in music, the PFC curve is very undesirable. the possibility of preferring to listen to bass through multi-way speakers with as large woofers as possible. All the efforts of the Germans were thrown into solving this problem, which was previously considered inevitable and not solvable.

HEDD Bass 08 Subwoofer Specifications

  • Woofer (honeycomb diaphram) 8″ (2″ voice coil)
  • Frequency response (-3dB) 24-80 Hz (var)
  • Variable upper frequency limit 40-120 Hz
  • LF range (-3dB): normal/extended 24Hz/20 Hz
  • LFE function (LowPass filter and +10 dB gain) LP 200 Hz / +10 dB
  • Input 1: analog stereo (2 ch) / Impedance 2 x XLR / 22 kΩ
  • Input 2: AES “in” 1 x XLR
  • Output: AES “through” 1 x XLR
  • Output to satellites stereo (2 ch) highpassed @ 80 Hz L/R 4th order
  • Satellite offset @ANALOG OUT ± 2m, in .5 m steps
  • Input gain: ±12dB
  • Input sensitivity: 0 dB = 90dB SPL/1m -10/-4/0/+4 dB
  • HEDD Lineariser, disengageable, delay: 30 ms
  • Phase switch: 0/90/180/270°
  • Universal Mains: 110-240 V 300 W ICEpower
  • AD/DA Conversion: 96kHz/32bit
  • SPL max @ 1 m (half space): 105 dB SPL
  • Dimensions (H x W x D): 392 x 290x 400 mm
  • Weight: 17

HEDD Bass 12 Subwoofer Specifications

  • Woofer (honeycomb diaphram) 12″ (2,5″voice coil)
  • Frequency response (-3dB) 20 – 80 Hz (var)
  • Variable upper frequency limit 40-120 Hz
  • LF range (-3dB): normal/extended 20Hz/16 Hz
  • LFE function (LowPass filter and +10 dB gain) LP 200 Hz / +10 dB
  • Input 1: analog stereo (2 ch) / Impedance 2 x XLR / 22 kΩ
  • Input 2: AES “in” 1 x XLR
  • Output: AES “through” 1 x XLR
  • Output to satellites stereo (2 ch) highpassed @ 80 Hz L/R 4th order
  • Satellite offset @ANALOG OUT ± 2m, in .5 m steps
  • Input gain ±12dB
  • Input sensitivity: 0 dB = 90dB SPL/1m -10/-4/0/+4 dB
  • HEDD Lineariser®, disengageable, delay: 30 ms
  • Phase switch 0/90/180/270°
  • Power Amplifier /Universal Mains 110-240 V 700 W ICEpower
  • AD/DA Conversion 96kHz/32bit
  • SPL max @ 1 m (half space) 115 dB SPL
  • Dimensions (H x W x D): 595 x 380 x 610 mm
  • Weight: 37,1

From the specifications, you can see that the subwoofers have an impressive lower cutoff frequency. When using DSP, by dropping the maximum power, you can reach frequencies below 20 Hz!

We note here the completely new speakers, which we have not seen in other HEDD models. They were developed by engineers specifically for these subwoofer models and were manufactured to order from HEDD.

Model HEDD BASS 08 can be called compact by subwoofer standards. There is definitely a place for it in any of the smallest studio or listening room. At the same time, the FI ports are directed forward and are easily accessible for installing the included plugs to turn the speaker circuit into a “closed box”.


What is the main problem with the phase-frequency characteristic curve of the columns? As you know, the time and frequency domains in sound are inextricably linked. The twisted phase breaks the front of the signal; instead of a solid beat of a drum kick or a double bass part, the listener feels only a certain sound pressure at a low frequency. As a result, in a recording studio it is impossible to understand and correctly process the bass part, and the end listener does not have the same sensations as they thought when creating a sound track.

Previously, this was extremely difficult to deal with. But with the development of DSP, especially with the advent of fast and high-quality digital filters, a lot can be done. First, you can design a digital crossover with linear phase and a minimum crossover zone between the two bands. It also removes the power loss of the passive filter amplifier. Secondly, you can compensate for the inherent disadvantages of a speaker or room, for example, make a bandpass filter to compensate for the surface of a table or console. Thirdly, it is possible to measure and compensate in advance the phase response of the entire system as a whole, in HEDD this is called the Lineariser technology. In the first generation of monitors, Lineariser was supplied as a VST plug-in or filter for the entire system.


In the second generation MK2 and in Lineariser subwoofers, it is stitched into the internal DSP. This allows you to connect to monitors not only a computer, but also any stand-alone devices. This can be done both digitally and analogously. The digital option is slightly preferable, since the built-in ADC is bypassed. It is impossible to connect monitors completely by analogy. The internal multichannel DAC always works and even with all the processing disabled, the digital crossover in DSD is needed for the signal to a separate power amplifier. \

In the case of HEDD subwoofers, we have an even more interesting system. A 4-channel DAC there can be used for a signal to the internal amplifier of the subwoofer speaker and for analog output after the DAC to connect any monitors. Not just HEDD Audio. At the same time, the quality of the AKM 44-series DAC will not be inferior to the mass models of audio interfaces. While most digital monitors from other manufacturers often have DACs of 100 dB S/N, which is not at all interesting, the HEDD has a DAC of 115 dB S/N.

If the HEDD subwoofer is connected to HEDD MK2 monitors, then the correct AES loop-through will be for the subwoofer first, then all the monitors. In this case, in the monitors, you need to select the pairing mode with the subwoofer.


  • VOL (dB) – adjusts the volume of the subwoofer over a wide range
  • HEDD Lineariser – enables and disables the branded Lineariser linear phase technology by turning the knob, there is also a third asterisk position reserved by the manufacturer
  • CoP – choice of acoustic design “closed box” or “phase inverter”, while changing DSP filters
  • SAT. OFFSET (Satellite Offset) – allows you to specify the difference in distances to the listener from the satellites and the subwoofer
  • X-OVER (Crossover Frequency) – crossover frequency from 40 to 200 Hz
  • LF RANGE (Low frequency range) – extends the low frequency range by equalizing the rolloff at the lowest frequencies, which reduces the maximum SPL
  • ANALOG / AES – select MONO / ANALOG / LEFT / RIGHT input for digital or analog connection
  • INP. SENS. (Input sensitivity) – adjust the sensitivity of the analog input -10 / -4 / 0 / + 4
  • Phase – manual phase setting 0/90/180/270

In our opinion, HEDD has stuffed MK2 monitors and subwoofers with just a huge number of advanced technologies and twists, which would be enough for a few updates.

Inside HEDD BASS 08

The filling serves as a confirmation of this.

The Class D power amplifier is a ready-made ICE Power board from the Danish B&O, as in all HEDD monitors. It provides a high power of 300 watts and virtually no heating, since almost all the energy goes into sound and not into heat. This is especially true for high power amplifiers.

The board with DSP and ADC / DAC chips is located next to the amplifier. The Analog Devices SHARC DSP Chip provides powerful 32/40-bit computing capabilities. All crossovers, filters and all digital processing are calculated and programmed by HEDD engineers. ADC AK5552 and DAC AK4454, have high performance. The ADC at the analog input operates in 24 bit 96 kHz mode. The dynamic range is 115 dB. This is so far the best stuffing that we have seen in similar models of monitors with a built-in ADC + DSP + DAC.

There is no pure analog gain mode in monitors. The signal from the analog input will always go through the ADC and DSP. Crossovers are digital only. That is, it will not work to send a signal directly to the amplifiers. Therefore, in order to achieve the maximum sound quality, it is better to send the signal to the monitors directly in digital form, via the AES interface. This way you can avoid one unnecessary conversion from analog to digital and get maximum quality.

We connected both analogue balanced and digital AES connections. We liked the sound more in terms of digital, but in analogy it is also not bad. HEDD BASS 08 is not very friendly to consumer sources, as it has neither digital nor SPDIF RCA inputs. But the matter, if desired, is solved by adapters. AES digital connection has advantages even if the source has a consumer SPDIF connector. You can use a longer AES cable and the level of noise immunity due to the balanced circuit will be significantly higher, which is important for studios where a lot of different equipment is concentrated.

Lineariser technology is the main feature of the HEDD BASS 08 subwoofer. When you turn on linearization, you can immediately hear the difference. The bass ceases to be smeared and booming, it gathers into a single fist and the music immediately sounds much more impressive. Together with the Lineariser, it is imperative to match the monitors and the subwoofer, both in frequency and in the relative signal delay. With the correct setting, a very interesting effect arises – the subwoofer ceases to be localized. He seems to be standing, but not playing. The sound comes completely from the monitors. And this is exactly what is required from the 2.1 Triphonic system – to replace two huge speakers with satellites and a subwoofer. The effect is very strong.

Another thing we particularly liked was the loop-through of the monitors to the subwoofer. It is not at all necessary that the 5-7 “satellites were produced by HEDD. For the HF and MF ranges, the phase shift from the flat line is not too strong, so you can connect HEDD monitors from other manufacturers to the subwoofer. We connected ADAM 5” monitors directly to the subwoofer via analog wires, and the computer on AES only to the subwoofer, and were very pleased with the result. The crossover inside the subwoofer very accurately and efficiently cuts off the excess frequencies that the satellite cannot play, and a continuous sound is obtained without a range failure.

The disadvantage of digital technology is a signal delay of 30 ms, which cannot be bypassed in any way, because the low-pass filters take time to correct the phase. That is, for real-time monitoring and when playing in monitors on live instruments, the technology will have to be turned off. In fact, this is not a big problem, as monitoring is required in 99% of cases for vocals and instruments. And they play mainly in the mid-range register, where the Lineariser technology corrects the sound least of all, which means that there will be little difference from turning on the Lineariser in the upper range and the sound will be good anyway. In our opinion, there is no need to dramatize the moment with monitoring.

It is also quite unusual that there is an artificial expansion of the frequency response to a lower limit lower than 20 Hz, due to equalization in the DSP, due to a decrease in the power headroom of the amplifier. We tried expanding the range and did not hear a big difference, since there is little music with frequencies of 20 Hz, it needs to be specifically looked for. The second problem with record low frequencies is that they require a very large room, free of resonances and standing waves. Although we had an equipped room with bass traps and sound absorption panels, it was still not enough for proper monitoring of the 20-30 Hz range. So fans of the deepest bottoms should fork out for a room and special treatment – changing the geometry of the walls and ceiling so that there are no parallel surfaces, no zones with excess and dips of certain frequencies are formed.

We asked Klaus whether HEDD is working on correcting the frequency response of the room so that the user can somehow correct the imperfection of the room. Klaus refused to go into details, but referred to the third mode of the linearizer, which is marked with an asterisk, only said that it was still a secret. Everything is possible in the future, so we are following the company announcements carefully!

The set includes two plugs for the bass reflex ports to change the acoustic design to a “closed box” (ZYa). A threaded handle at the end is used to extract them. In the abstract, the PS has an advantage over the FI in the accuracy of sound transmission. But if we take specific columns, it can be anything. You can make a good FI and a bad PO. The opposite is possible. The chosen scheme is not a panacea and requires very high qualifications from the developer.

In our opinion, the implementation of the phase inverter in the HEDD BASS 08 in combination with the included Lineariser phase equalization is done perfectly. The transition to PS by plugging ports cannot be called unequivocally positive. It may all depend on the situation. We listened to monitors in a well-prepared room, with bass traps, so our standard switching on in the FI mode did not cause problems with mumbling. In some other rooms, everything may be different. In our opinion, the fact that the end user will in any case use speakers with a FI plays against the ZYA in the studio. Because the industry of household hi-fi speakers and studio monitors in 99.9% prefers FI, as the most effective and full-frequency scheme. Also, do not forget that when working in a ZP, the amount of distortion at low frequencies is about 10 times higher than with a PHI. This is due to the fact that with FI the speaker moves more freely and linearly, it is not loaded on the internal volume of the case. Meanwhile, ZYA gives a more collected bass, which in some situations can sound advantageous. The only thing we will advise you when choosing between Closed and Ported is to listen with your ears. It is important that the manufacturer does not impose his opinion on us, but gives the right to choose.

What can HEDD be criticized for? AES is preferred over analog. This interface is not something special, for example, we had 2 American Lynx Studio devices with this output, but still it is more difficult to find a sound source with AES output. Can be connected via Neutrik’s inexpensive SPDIF to AES adapter, which is a matching transformer. We are a little sorry that the manufacturer abandoned the modular system of its own boards with different connection methods. Thus, for Dante connection, it is now necessary to independently search for such a device in order to switch from Dante to AES. The same goes for other interfaces.

HEDD BASS 08 Frequency response measurements

We asked the manufacturer to send their own passport graphs obtained in an anechoic chamber, as in our graphs, depending on the selected measurement point, there are peaks and dips in the region of 30 Hz from the room.

Frequency response measurements

The first graph shows a mode with open ports of the bass reflex and a standard cutoff frequency of 80 Hz. The frequency response is a perfectly flat line.

Frequency response measurements

We were very interested in the graph with the extended private range mode. It really effectively adds the lowest frequencies for HEDD BASS 08.

Frequency response measurements

It is also interesting to look at the frequency response of a closed box, where the peak of the additive from the FI ports is removed. The graph, as expected, has a smoother falloff, and for the Extended mode it allows you to get a record frequency response range.


The HEDD BASS 08 is the highly anticipated studio subwoofer that Klaus Heinz and his team have a hand in. This is the quintessence of the developments of the Germans from HEDD Audio for all the previous years. When many more well-known companies rest on their laurels and release the same models for decades, the Germans constantly delight us with an innovative approach and their own excellent developments.

At the same time, subwoofers remain affordable. The user may even be faced with a dilemma – which is better to buy, Type 05/07 + BASS 08/12 or 3-way Type 20/30 monitors? In our opinion, the 3-band models are better in the quality of the upper bass, but they are inferior in the lower cutoff frequency. Also, a system with a subwoofer looks more compact in installation and more affordable.

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