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Multi-Way Conventional loudspeakers with crossovers

John Sheerin got Apple to use horns!
John Sheerin got Apple to use horns!
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Old 7th February 2018, 11:08 PM   #11
LineSource is offline LineSource  United States
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I'm a fan of the Kii THREE speaker from Bruno Putzeys, and expect low cost Klones using single chip multi-channel DSP.
Kii Audio GmbH - High End Active Speakers for HiFi and Professional use.
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Old 12th February 2018, 03:03 AM   #12
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Apple HomePod - The Audiophile Perspective + Measurements! : audiophile

A user on Reddit did a comprehensive review with in-room measurements. Another user and I were given early access to the data. There's a lot to be impressed with (strictly on a tech level as I'm not enamoured with the Apple ecosystem personally).

The BMR driver has dome tweeter levels of distortion and smoothness. but can be crossed 2 octaves lower. This driver plus the beamforming DSP indeed gives a controlled-directivity speaker (insofar as having a consistent, smooth beamwidth), but axial response does not seem to be Beolab 90/Geddes OSWG levels of smoothness within the beamwidth. At 5ft in-room they track each other within +/- 2.5dB.

The 4" midwoofer with active compensation is SOTA in terms of power handling and distortion. Reminds me of the tiny Tang Band midwoofers with massive motors, except with no turbulence issues. SPL tops out well above 90dB at 40Hz in mono.

Unlike B&O, room calibration uses played-back music instead of test tones.

Downsides for serious usage include a built-in Fletcher-Munson contour (dips are likely artefacts) tied to the volume control. It can be circumvented by leaving Homepod volume at maximum and attenuating at the source.

Click the image to open in full size.

Circumventing this contour this way yields a 1/12-octave response at 5ft in-room as follows:

Click the image to open in full size.

1.5kHz peak is a reflection.

Last edited by Quip; 12th February 2018 at 03:11 AM.
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Old 12th February 2018, 07:01 AM   #13
Colin is offline Colin  United Kingdom
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A review of the Homepod from Kirk McElhearn

HomePod Review: When it Sounds Good, It’s Great; But It Doesn’t Always Sound Good – Kirkville
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Old 12th February 2018, 07:14 AM   #14
planet10 is online now planet10  Canada
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John Sheerin got Apple to use horns!
Quote:
the bass is a bit too strong
I womder if that is due to the built-in F-M compensation vrs us hif guys don’t usually listen that way. If it is one could well counter that by using the “homePod all th eway up, volume controlled by the external device” trick outlined in the review Quip posted?

dave
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Old 12th February 2018, 06:46 PM   #15
Patrick Bateman is offline Patrick Bateman  United States
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Click the image to open in full size.
The Reddit review indicates that the 'tweeters' in the Apple HomePod are BMRs

Tectonic Elements TEBM35C10-4 Miniature BMR(R) Driver | Medley's Musings
The BMR is likely similar to this one that Erin reviewed

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

So I designed a waveguide for the BMR and 3D printed it. It is intentionally way way too small, I basically didn't want to make a waveguide that would take two days to print in the event that the BMR wasn't suitable for horn loading.

Click the image to open in full size.
Here's the frequency response and distortion with a 500Hz highpass, on the waveguide, with no EQ. Not too shabby really. There's some high frequency 'droop', but that's normal for a CD waveguide. The sharp 'spike' and dropoff on the lowend is because I didn't bother to make an enclosure for the BMR. So you're seeing the dipole peak and then a dropoff.

Click the image to open in full size.
With a modest amount of constant directivity EQ, you get a response curve like this. It should be trivial to get the BMR to play from 500hz to 15000hz +/- 3dB with very little EQ. (You *will* need to seal off the back of the BMR.)

Getting the BMR to play past 15khz would probably need a phase plug. I'm not sure if I would bother; it's not clear if BMRs will behave like conventional drivers when it comes to phase plugs. OTOH, it might perform better! Someone should build a phase plug for a BMR and find out (That's gonna be me, isn't it?)


One thing of note, DO NOT use these BMRs without a big waveguide or some kind of boundary effect. It's not accidental that Apple put the tweeters on the BOTTOM of the HomePod, they're doing that so that the horn is dramatically extended by the surface that the HomePod is sitting on. In one of the reviews, the reviewer complained that he didn't like the sound the HomePod, but he also advised people to mount the HomePod on a speaker stand. THAT'S A BAD IDEA. The HomePod needs that surface, it's fundamental to the design.

When I did my first measurements of the BMR on this waveguide, they looked ABOMINABLE. Then I realized that these BMRs play down to 500Hz and they need a BIG waveguide or horn. Without one, it's going to be ugly.

Simply placing the waveguide on my driveway and doing a ground plane measurement cleaned everything up. And I guarantee, the response would be even better with a larger waveguide and with the BMR in a sealed enclosure. The key to all of this, is that the BMR plays quite low. We're not talking about a 1" dome that's crossed over at 2Khz, these things can go down to 500hz, 500Hz is 68cm long!

Last edited by Patrick Bateman; 12th February 2018 at 06:50 PM.
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Old 12th February 2018, 06:54 PM   #16
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by planet10 View Post
I womder if that is due to the built-in F-M compensation vrs us hif guys donít usually listen that way. If it is one could well counter that by using the ďhomePod all th eway up, volume controlled by the external deviceĒ trick outlined in the review Quip posted?

dave
I think it's that, and also this:

"One note about that. If you were interested in using a pair of HomePod as speakers connected to your computer, or on a desk, Iíd recommend putting them on stands. The tweeters are at the bottom of the unit, so the high frequencies arenít directed at ear level. This is less of a problem when itís in a room a few meters from you, but for close listening, it would sound even more bassy.

The reviewer doesn't understand that the HomePod depends on the surface it's mounted on to extend the horn loading. It's not designed to be placed on stands.

Click the image to open in full size.
This is similar in concept to the Beolab 5, where those big ol' platters are designed to constrain the radiation of their respective drivers into half-space. That's why the midrange platter is larger than the tweeter platter. The diameter of the platter is sized to constrain radiation down to the crossover point of the driver. Without the platter, the response and directivity of the entire design is compromised.
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Old 12th February 2018, 10:00 PM   #17
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Having actually reviewed the data - there is little evidence the ground plane was intended in the design, hence the recommendation. Maximal flatness was achieved with no other discernable compromise with slight elevation. Placing it on a desk/ground plane introduced FR changes (in this case 1'5kHz peak) from distinct reflections Apple's correction DSP doesn't touch.

Also, on ifixit, there has been a teardown of the Homepod - the photos are unclear but the design looks IMO transitional between BMR and Aurasound-style high-excursion 1" driver. Except with distortion and FR like a dome tweeter
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Old 12th February 2018, 10:04 PM   #18
planet10 is online now planet10  Canada
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John Sheerin got Apple to use horns!
Quote:
on ifixit, there has been a teardown of the Homepod
HomePod Teardown - iFixit

dave
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Old 12th February 2018, 10:40 PM   #19
mpmct is offline mpmct  United States
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another tear down, brutal, but can see a little more what's inside.

( I've owned lots of audio gear over 40 years, including all of Linkwitz models except the most recent, all the way back to Henry Kloss. After three days of listening, in a 26' x 28' room ... HomePod ... amazing. )

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Old 12th February 2018, 10:52 PM   #20
mpmct is offline mpmct  United States
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Quote:
Originally Posted by planet10 View Post
painful, but might be helpful to see what's inside ...

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