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Multi-Way Conventional loudspeakers with crossovers

Horn Loading BMRs
Horn Loading BMRs
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Old 10th November 2017, 05:56 PM   #1
Patrick Bateman is offline Patrick Bateman  United States
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Default Horn Loading BMRs

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Erin posted a positive review of the small BMR speakers here : Tectonic Elements TEBM35C10-4 Miniature BMR(R) Driver | Medley's Musings

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They feature wide bandwidth, flat response, low distortion, and they're cheap. (Eight bucks.)

What's not to like? Well, the efficiency is something like 78dB.

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Here's an 18 Sound XT1086

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Here's the frequency response of the BMR on that waveguide

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Here's the crossover that I used for that measurement

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Here's the EQ that I used
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Old 10th November 2017, 06:09 PM   #2
Patrick Bateman is offline Patrick Bateman  United States
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My initial plan was not to use the 18Sound. I 3D printed this waveguide.

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The waveguide that I 3D printed was basically a copy of what Follgott did here. (I only printed one, but the idea was to make an array of them.)

Line array prototype (with waveguide and CBT shading)
Here's the thread in question

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Here's the frequency response of my 3D printed waveguide with the BMR

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Here's the frequency response of my 3D printed waveguide with the Aurasound Whisper

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Here's the frequency response of my 3D printed waveguide with the BMR. This measurement has no EQ.

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Here's all three measurements.


Here's some random comments about this project:

1) The entire thing was very rushed. I put all of this together in about two hours, including the measurements. So I know this isn't a polished project, but it gives you an idea of what is possible with the BMR

2) The Aurasound Whisper holds up pretty good against the BMR.

3) The real surprise to me, without a doubt, was putting the BMR on the 18Sound. I really hadn't expected that I could use a compression ratio of four-to-one this successfully. I think that putting the BMR on a waveguide with a high compression ratio is the most interesting possibility for the BMR.

I think that the response of the BMR + XT1086 could be improved much further. I didn't spend much time at all flattening it out, I was in a hurry. It could be improved much further.

The way that horns work, the volume of air under the surface of cone acts as a high pass filter. I think that the flat diaphragm of the BMR is the reason that we're able to get response out to 20khz using a driver that can get down to 700Hz. There are many other drivers that can do that, but nothing even CLOSE to eight bucks. For instance, a TAD 2001 can do it, and it's $1200.
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Old 10th November 2017, 06:29 PM   #3
Bill poster is offline Bill poster  Thailand
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Naim use a BMR in some v expensive speakers.
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Old 10th November 2017, 06:36 PM   #4
DPH is offline DPH  United States
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Have any foam board to try out a simple 60/90 degree conical?
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Old 10th November 2017, 06:58 PM   #5
zmyrna is offline zmyrna  United Kingdom
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3" version is much more sensitive and has lower qts; better for horn loading?
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Old 10th November 2017, 09:18 PM   #6
charlie2 is offline charlie2  England
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Patrick surely your not serious about this............??
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Old 10th November 2017, 11:21 PM   #7
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by zmyrna View Post
3" version is much more sensitive and has lower qts; better for horn loading?
With an efficiency of 80dB and a power handling of 10w, even horn loading won't make a single BMR suitable for HiFi.

The idea was to make an array like this:

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I tried the 18Sound waveguide largely to see what would happened, and the BMRs seem to be pretty friendly to high compression ratios.
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Old 16th February 2018, 04:18 AM   #8
Patrick Bateman is offline Patrick Bateman  United States
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I made an axidriver sim of the BMR. This was easy to do because it's very similar to one of their demos. According to the predictions, a BMR should have fairly smooth response on a big horn. This makes sense, because it can play so low.

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Here's what the wavefronts look like at 2150Hz and 4300Hz.

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I did a groundplane measurement of the waveguide that I 3D printed. That made a HUMONGOUS difference. Compare it to the measurements earlier in this thread and you'll see; the boundary reinforcement makes and enormous difference in the response.

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Here's what it looks like with constant directivity eq

Next up: I want to see if it's possible to raise the output level with a phase plug.
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Old 16th February 2018, 08:33 AM   #9
Patrick Bateman is offline Patrick Bateman  United States
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Here's the predicted response of a 2" BMR via the "axidriver" software. This horn has a compression ration of one-to-one. IE, there's no compression.

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Here's a phase plug I threw together. It's largely a copy of the Celestion CDX1-1425 phase plug.

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Here's the predicted response, with the phase plug.

The thing that was interesting to me, is that the phase plug doesn't appear to help the high frequencies whatsoever. My assumption is that it would increase the highs, but it doesn't. And oddly enough, it raises the low frequencies quite a bit. At 1khz, the phase plug raises the output by about 8dB. That's the equivalent of raising the power by more than 5X.

Last edited by Patrick Bateman; 16th February 2018 at 08:35 AM.
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Old 16th February 2018, 08:44 AM   #10
chris661 is offline chris661  United Kingdom
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A phase plug is required to shoehorn the output from a larger diaphragm through a small hole, so the HF dispersion can stay reasonably wide. Given that the BMR occupies the horn throat anyway, I wouldn't expect much difference there.
The increase in output at the bottom of the band is useful, though.

I'm not sure large-format compression drivers are in trouble just yet, but I like where this is going.

Chris
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