SU551-RS28F – a 2-way DEQX system loudspeaker measurement study

[gornir]

Hi,

This time I’m going to share some measurement studies I have done on a test loudspeaker. I set up this loudspeaker to see how my DEQX active-crossover pre-amp behaves.

For those who are not familiar with the DEQX HDP-3 pre-amp, here is some reading on the subject:

DEQX High Definition Audio

In short it has the following capabilities and can be described as follows:

• Digital cross-over (up to 3-way or 2-way + stereo subs).
• Frequency response correction to within 0.5dB using calibrated mic.
• Phase and time response correction.
• Group delay correction.
• Precise time alignment with zero phase error.
• Linear-phase zero-distortion digital crossovers.
• High-order crossovers up to 300dB/octave eliminate driver interaction.
• Room correction.
• Digital EQ.

The DEQX unit is one of the more advanced equipment to use when going active, but there are of course others who does similar if not identical stuff like the miniDSP, Holm Acoustics DSPre 1, Beringher dcx2496, Ground Sound and more.

There will be a lot of pictures and measurement graphs etc. and I hope DEQX owners and other people who are interested in going active with similar technologies will find something interesting and useful in this thread. Please, feel free to comment and discuss.

Why go active?

Personally I think an active setup like the DEQX is as fun as doing a passive loudspeaker design, but I realize by reading many audio forums that there are different opinions which way to go – active vs. passive. My opinion is why not both? Both have it strength and weaknesses and when used right, they both can sound great.

Is it easier designing an active loudspeaker using DEQX?

I would say yes and no

Yes, it’s easier to get started with a setup like DEQX with its integrated measurement hardware and software capabilities and to get some fairly decent results.

No, the same rule of physics applies to an active setup as to a passive one. By that I mean you have to consider and deal with baffle step, baffle diffraction, driver distortion and enclosure shape and design as you would have to do in a passive design.

Both an active and a passive design require you to have a decent knowledge about your loudspeakers driver limitations and capabilities. To achieve good or great results you need to have some experience about building loudspeakers.

Because the measurement software supplied with the DEQX is a bit rudimentary, I would say that you should have a separate measurement rig to verify your results with. It also requires you to have fairly high computer knowledge since the DEQX isn’t just a stereo equipment, it also requires you to use a computer to configure it.

To sum it up, I would recommend the following when using the DEQX:

• Good computer skills and knowledge.
• Experience in loudspeaker design and physics.
• A measurement rig and equipment to verify the results.

For someone who is not that experienced in designing loudspeakers, the chances of getting a loudspeaker to sound OK is higher with a DEQX system, than building a passive loudspeaker without experience and/or measuring equipment and software. That’s just my own personal reflections

Picture 1: DEQX HDP-3 Preamp Processor (front).
Picture 2: DEQX HDP-3 Preamp Processor (rear).

Next, measurement setup and equipment……..

[chaparK]

Originally Posted by gornir

Both have it strength and weaknesses and when used right, they both can sound great.

What kind of strength do you have in mind when you think of passive systems?

[gornir]

Hi chaparK

Thanks for your input!

You're right; I was pretty vague in my description. It is not always easy to express yourself with nuances of another language.

I meant the overall concept. One advantage of a passive design is for an example that you do not need extra amps and cables = cheaper. Passive components in the filter also interacts with the driver and changes for an example the Qts value for a driver and thus changes the box size and tuning and can be used to tailor the design to your needs or liking. Likewise using different types of caps etc. can tailor the sound characteristic and your sound preference to some degree, although there are different opinions about this matter.

As I said, I think both versions are equally fun to work with, but in my experience its how they are used in a design that determines whether they sound good or not.

I hope I make some sense?

[Zodiac]

Good start - Looking forward to the rest of the write up!

[ultrakaz]

Hello gonir,

Thanks for sharing!

Great start to an interesting subject, especially for those of us that don't or have not tried active crossovers.

When I think of active crossovers I think of them either for low crossover points, ie. for subwoofers and or multi-way crossovers, ie. 4-way or more systems. And or use active as a tool to hear a high order crossover vs. low order passive.

Now in a 2-way system it would be interesting to compare active and passive. The U16 and RS28a are good drivers for a 2-way. Were you planning on building a speaker with these or were the drivers dedicated for testing purposes? Thanks.

[chaparK]

Hi Gornir (and everybody!). Thanks for answering my question, and thanks for the post in general!

Originally Posted by gornir

One advantage of a passive design is for an example that you do not need extra amps and cables = cheaper.

I was expecting that one. However is that really true? When i'm looking at the high cost of crossover components, and at the comparatively low cost of good quality amp power, i tend to think that active designs are actually cheaper...

Passive components in the filter also interacts with the driver and changes for an example the Qts value for a driver and thus changes the box size and tuning and can be used to tailor the design to your needs or liking.

These are typically things that you can achieve better with active systems via proper equalization.

Likewise using different types of caps etc. can tailor the sound characteristic and your sound preference to some degree, although there are different opinions about this matter.

Yes yes

IMHO, the big advantage of passive systems is that speakers and amps are not 'married' forever. So one can buy a sound system at a time, then upgrade to better speakers at a later time and keep the original amp.
Meanwhile active systems are more integrated. For example, if the filtering and the amps share the same power supply and the same chassis, then it's going to be harder to upgrade the speakers separately.

I'm looking forward to reading your next posts!

chaparK

[gornir]

No, I wasn’t planning on building a design using those particular drivers. I just happened to have them available at the moment. They are both nice drivers in the same price range and I think they would do fine together in a design.

In my opinion the tweeter is of a quality which would be justifiable in a design with the SEAS W16. I’m thinking perhaps about doing such a design later this summer and I might doing both a passive and active version of it, just for fun

[gornir]

Measurement setup and equipment:
This post covers a short description of the equipment and configuration used in the test.

Pre-amp processor and active cross-over:

• DEQX HDP-3
• Firmware v63.3.6
• Software v2.58
• Standard calibration kit (calibrated Behringer mic)

Amplifiers:

• 2x PopPulse T150 (class-T stereo amplifier configured as power amps) Picture 1

Loudspeaker drivers and enclosure:

• Woofer: SEAS U16RCY/P (H1520-08) Picture 2
• Tweeter: Dayton RS28F-4 (275-140s) Picture 3
• Enclosure: Parts Express 14 liter curved enclosure (302-721s) Picture 4-5

Measurement equipment (for verification):

• HolmImpulse with M-Audio Audiophile 24/96 soundcard for frequency measurements.
• EMM-8cal and MP-1r calibrated mic and pre-amp. (www.ibf-akustik.de)

Interconnects:

• Loudspeaker Cable: Supra PLY 3.4
• Internal Loudspeaker Cable: Supra PLY 2.0
• RCA Cable: Supra EFF-I + PPSL plugs

Cross-over filter and correction settings:
The following general DEQX settings are used in the test:

• Cross-over type: Linear phase
• Cross-over frequency: 2000Hz
• Cross-over slopes: 60db/oct
• Correction range: 250-20000Hz
• Measurement smoothing: 80%
• Time align individual drivers

Next, measurements……..

[doug20]

Could you comment on the steep linear phase slopes used. Any draw backs? I have wanted the DEQX for 4 years now. I have the DCX, MiniDSP, Hypex DSP solutions and Im just waiting for the best DEQX deal. I can do a 60dB slope with cascading functions on the MiniDSP but I do not think I can do a linear phase Slope

I look forward to your measurements.

[pos]

Ev dx46 Doug!