Philharmonic Audio BMR Speaker Discussion

[GelbeMusik]

Bit of a strange question and directive, but I'll assume it was asked in good faith.

Sure, all best intentions!
There is no baffle step. From a technical designer perspective. Is it still o/k with You, after reading all the internet?

 

[ribosradagast]

After weeks of nightmarish manufacturer delays and working on it every night for a month, my DIY BMR project is reaching its conclusion. I don't have a favorable listening impression yet - might need to rearrange the damping material inside and actually glue on the back panel to get it into its "final state" because right now it sounds 'bass-light' to me.

Anyhow, here's some hastily-snapped eye candy from last night:

 

[R Swerdlow]

Thanks for the nice photo. I have a few questions:

Did you get the RAAL 64-10 tweeter, or the 64-10X tweeter? The crossover network for the 64-10 uses a 1.5 µF capacitor, among other parts. The 64-10X tweeter needs 2.5 µF instead. After learning that from Dennis, I got two 1.0 µF caps to add in parallel to the existing 1.5 µF caps I got with the kit.

As far as sounding bass-light to you, what speaker were you previously using?

 

[ribosradagast]

A few questions:

Did you get the RAAL 64-10 tweeter, or the 64-10X tweeter? The crossover network for the 64-10 uses a 1.5 µF capacitor, among other parts. The 64-10X tweeter needs 2.5 µF instead. After learning that from Dennis, I got two 1.0 µF caps to add in parallel to the existing 1.5 µF caps I got with the kit.

As far as sounding bass-light to you, what speaker were you previously using?

Thanks for the heads-up - I also got the corrected caps, thanks to Dennis telling Meniscus about the batch variation. Great customer service from them the whole way, I must say.

I've got a variety of other speakers: The Revel F208, the Ascend Sierra 2EX, the SVS Ultra bookshelf, Maggie panels... I'm hoping that sealing everything up and getting the stuffing further from the woofer will do the trick. I'll be doing a bunch of measurements tonight to try and find the culprit (which might very well be my ears).

 

[R Swerdlow]

I agree with you about the customer service from Meniscus Audio. They were very helpful over the phone.

I've got a variety of other speakers: The Revel F208, the Ascend Sierra 2EX, the SVS Ultra bookshelf, Maggie panels... I'm hoping that sealing everything up and getting the stuffing further from the woofer will do the trick. I'll be doing a bunch of measurements tonight to try and find the culprit.

I had wondered if you might be used to hearing speaker with exaggerated bass (high Qtc) tuning, but none of the speakers you mentioned are known for that. The BMR's bass tuning is certainly not exaggerated in any sense. Good luck with finding the culprit.

After 2 weeks away from speaker building, I'm now getting down to building my BMRs without distraction. I was in the hospital for elective surgery, not Covid-19, and I'm recovering nicely.

 

[DeruDog]

Thanks for the heads-up - I also got the corrected caps, thanks to Dennis telling Meniscus about the batch variation. Great customer service from them the whole way, I must say.

I've got a variety of other speakers: The Revel F208, the Ascend Sierra 2EX, the SVS Ultra bookshelf, Maggie panels... I'm hoping that sealing everything up and getting the stuffing further from the woofer will do the trick. I'll be doing a bunch of measurements tonight to try and find the culprit.

My kit should ship today, so any recommendations are most welcome. I will be CNC cutting cabinets, so I might deviate from the shape, but not the volume or the front baffle. That said, your speakers look great, so I may stick with the original plans. Did you use solid wood or ply? It is hard to tell from the photo. Great job!

I am curious if the kit comes with plans/directions for the placement of acoustic material inside the cabinet.

 

[R Swerdlow]

I am curious if the kit comes with plans/directions for the placement of acoustic material inside the cabinet

The Meniscus Audio kit comes with cabinet plans, cabinet stuffing material, and directions for placing the stuffing in the cabinet. I found their stuffing directions somewhat confusing. To me, their wording could be interpreted several different ways. I think it needs a good diagram.

The Meniscus Audio directions say:

"The blue Eco Core forms a "U" shape and is placed through the woofer hole and to the back of the cabinet with about 8" extending up the both sides of the cabinet. You can use a few staples or dab of hot melt glue to hold it in place. The sides will not extend up to the woofer hole as this keeps the material from interfering with the woofer cone."​

For me, this wording works better:
Form the 12"×24" piece of Blue Eco Core into a U shape. Insert it through the woofer hole. Place the bottom of the U against the back of the cabinet. Place the parallel sides of the U along both sides of the cabinet (not the top and bottom) extending toward the front. These tops of the U should reach about 8" of the distance from back to front, but they should not extend all the way to the woofer hole in the front baffle. The damping material should not interfere with the woofer cone."

When I build mine, I'll be sure to photograph this step.

 

[ribosradagast]

^^What he said.

A lot of their instructions are extremely densely packed with information - I'd suggest reading them through all the way at least 20 times and visualizing all the steps in your mind before you even start, to make sure you don't miss anything.

 

[Dennis Murphy]

Thanks for the heads-up - I also got the corrected caps, thanks to Dennis telling Meniscus about the batch variation. Great customer service from them the whole way, I must say.

I've got a variety of other speakers: The Revel F208, the Ascend Sierra 2EX, the SVS Ultra bookshelf, Maggie panels... I'm hoping that sealing everything up and getting the stuffing further from the woofer will do the trick. I'll be doing a bunch of measurements tonight to try and find the culprit (which might very well be my ears).

The best and easiest way to check for bass tuning is with an impedance sweep. Do you have the ability to measure impedance? If so, the two impedance peaks forming the saddle should be absolutely symmetrical, and the saddle should be centered on about 33 Hz.

 

[ribosradagast]

The best and easiest way to check for bass tuning is with an impedance sweep. Do you have the ability to measure impedance? If so, the two impedance peaks forming the saddle should be absolutely symmetrical, and the saddle should be centered on about 33 Hz.

Is that something that can be done with REW and a UMIK-1? If not, then... no.

 

[Dennis Murphy]

Is that something that can be done with REW and a UMIK-1? If not, then... no.

Too bad. Impedance isn't an audio output measurement. It's purely electro-mechanical and doesn't use a mic.

 

[tktran303]

Yes you can do an impedance sweep (and measure T/S parameters) with REW.
You don't use a microphone, but you do need 2 channels of audio output AND input
(eg. PC with headphone output and a separate line input eg. soundcard)

https://www.roomeqwizard.com/help/help_en-GB/html/impedancemeasurement.html

 

[ribosradagast]

I don't have a favorable listening impression yet - might need to rearrange the damping material inside and actually glue on the back panel to get it into its "final state" because right now it sounds 'bass-light' to me.

Just to follow up on this, I had some conversations with Dennis, who is extremely helpful, knowledgeable and highly recommended, and we figured out that the tonality was actually off because of the midrange enclosure not being properly sealed. That was causing it to produce way more volume than intended, which in turn made the bass weak and pale.

I can't stress enough that the midrange box must be completely airtight - use caulk to seal the inside edges and the hole for the cable pass-through, and critically damp the enclosure. Meniscus's instructions advise to use far too little of the blue eco core, I ended up tripling that amount. Also, they include gasket tape but not instructions for how to use it - you should use that to seal around the edges of both the midrange driver and the woofer.

I'm thinking I'll put up an imgur album or something with a ton of pictures and helpful tips from the build process, since I'm sure not everybody here really cares. I'll cross post to reddit too, probably.

 

[Ericglo]

This is the problem with having around a billion different forums. A member on AVS documented his build with pics. I am not sure if it is allowed, but I will attach his notes. Davidfjoh is his name.

 

[ribosradagast]

You're absolutely correct about the horror of forum fragmentation at this point: those notes would have been awesome to see before I started! Dennis replies to him directly in that thread:
https://www.avsforum.com/forum/89-speakers/1348949-philharmonic-audio-dennis-murphy-326.html

I had almost the same questions when doing my build, but I muddled through them, with help from Meniscus Mark, and lately from Dennis himself.

Also, it's buried 326 pages in, which is less than helpful. I was hoping to avoid that with this thread, and not have it pertain directly to "DIY BMR instructions" but rather "discussion of the BMR by Philharmonic Audio as a speaker entity," which is why I have recently taken most of my personal DIY talk to PMs

 

[R Swerdlow]

I was hoping to avoid that with this thread, and not have it pertain directly to "DIY BMR instructions" but rather "discussion of the BMR by Philharmonic Audio as a speaker entity," which is why I have recently taken most of my personal DIY talk to PMs

That's my interest as well. From what I read here and at other forums, I think there may be a substantial interest in people who wish to try their hand at building this kit. However, many of these people have little or no experience with speaker building at any level.

I've received both the Meniscus Audio kit and the Speaker Hardware flat pack cabinet. Neither the crossover boards nor the cabinets have been assembled by the vendors. I've just begun the assembly job. I have some experience with DIY speaker building, and I plan on writing a DIY Builder's Guide illustrated with photos, that will be published here and at other interested forums.

From what I've seen of both kits, the cabinet may require the most work and present the greatest difficulty for inexperienced builders. The instructions from Meniscus Audio for assembling the crossover boards look very good, and I don't expect problems with that. However, there may be some additional difficulty with installing the assembled crossover boards, cabinet stuffing, and wiring things up. At this time, I don't think anything will be a true show stopper, but additional guidance might help a lot of people.

That's my plan. Stay tuned. In my opinion, the BMR speakers are well worth the effort. I heard them in my home, two summers ago when Dennis Murphy sent out a pair on the "BMR Road Trip". I've heard many of his designs, and I own a few. I honestly think the BMR speaker is one of his very best efforts.

 

[Ericglo]

You're absolutely correct about the horror of forum fragmentation at this point: those notes would have been awesome to see before I started! Dennis replies to him directly in that thread:
https://www.avsforum.com/forum/89-speakers/1348949-philharmonic-audio-dennis-murphy-326.html

I had almost the same questions when doing my build, but I muddled through them, with help from Meniscus Mark, and lately from Dennis himself.

Also, it's buried 326 pages in, which is less than helpful. I was hoping to avoid that with this thread, and not have it pertain directly to "DIY BMR instructions" but rather "discussion of the BMR by Philharmonic Audio as a speaker entity," which is why I have recently taken most of my personal DIY talk to PMs

LOL, it is buried. On the other hand, the kits haven't been available that long.

The builder probably should have started a build thread in the DIY forum. Unfortunately, it probably would have gotten lost over there. DIYSoundgroup and subs seem to be of most interest on that sub forum.

 

[Adam Bernau]

@Dennis Murphy Could you, perhaps share also off-axis -15 -30 -45 measurements of the BMR that you are using? I spent a few years building active speakers with 4.5 inch BMRs as a fullrange, crossed over to small subbass section, and i must say, that there is indeed something special about their sound, also thanks to the DML/BMR principle they can take unbelievable beating given their size, but after a lot of extatic overreactions, and long time experimentations i have found out, that their biggest advantage is also their biggest weakness- you almost cannot equalise BMR driver to have reasonable radiation pattern- their response is changing wildly with each small turn from the axis. That, and also the BMR specific distortion, which is unrelated to the current SPL makes them finally disqualified from my future projects, and that is in my opinion the reason why these interesting drivers would never be widely used in high end audio.

 

[R Swerdlow]

I'm not Dennis, but I know what his answer would be – at least in part.

Several years ago there was a very long thread on another forum about some 2-way speakers, Cambridge Audio Aero 2, that used the same small Tectonic Balanced Mode Radiator driver (2" or 2½"?) as a tweeter along with a conventional 6½" woofer. The gist of that thread had it that the BMR tweeter sounded wrong unless it was 'broken in' for many dozens of hours.

Dennis got his hands on a pair of new Aero 2s, and ran one for well over 50 hours, while keeping the other inside its unopened shipping box. Then he ran frequency response sweeps on-axis and about 30° off-axis. You can easily see where the driver is breaking-up or running out-of-phase with itself above 8 kHz in the on-axis curves, and where response drops by about 5 dB above ~7.5 kHz in the off-axis curves. The results silenced the 'you must break it in' crowd.

During this demonstration that the BMR driver was not a good tweeter in a 2-way speaker, Dennis realized it had promise as a mid-range driver in a 3-way. His idea led to the BMR Philharmonitor 3-way speaker where the same BMR driver functions as a mid-range accompanied by a Scan-Speak 8545 7" woofer, and a RAAL 64-10 ribbon tweeter. See this page for on- & off-axis frequency response curves, measured by Dennis and also by the Canadian National Research Council in their anechoic chamber, plus Dennis's comments.

Done by Dennis Murphy (red is on-axis, blue is 30° off-axis, & green is 80° off-axis). The red & blue traces never diverge. You can see above 2 kHz where the green trace converges with the red & blue, and where it drops off above 8 kHz.

Here are the NRC frequency response curves, done at 45°, 60°, and 75° off-axis. (The curves done on-axis, 15° & 30° off-axis were not shown, as all three were essentially the same.)

I hope Dennis has more to add. Perhaps he has full range sweeps of the BMR driver.

 

[R Swerdlow]

I can hear people wondering, "what about that odd looking bass performance below 100 Hz in the NRC frequency response curve?" (I know Dennis is wincing as he reads this.)

Dennis swears by his calibrated test microphone that he hears no oddness in the BMR Philharmonitor's bass response, and he doesn't understand why the NRC curves show that. After lengthy discussions with the NRC technician who ran those sweeps, Dennis realized that the anechoic chamber doesn't deal with rear ported speakers very well. There's no room reinforcement, and the port output shows up as attenuated. It seems to combine with the woofer output in a strange way. This may be caused by the different distances to the mic between the woofer in front and the port in the rear, and therefore generating a difference in phase. All the technician could say is that when the chamber was constructed almost all speakers were either sealed or front-ported. He's seen similar responses with other rear-ported speakers.

I've heard a pair of these speakers in my home directly comparing them to a pair of Salk Veracity ST speakers I own. The Salks have twin 6" mid-woofers in a mass loaded transmission line tower cabinet, plus a different RAAL ribbon tweeter. The bass response of the Salks is more potent, as expected, but there was nothing wrong or odd sounding about the BMR's bass sound. I don't have Dennis's highly trained ears, but he was present and he confirmed my impression of the BMR's good sounding bass.