[WGH]

Troels Gravesen Purifi-Be speaker - First Impressions

One of the most interesting and sought after speakers is the Salk Sound BePure1 monitor, a much discussed but rarely heard speaker. The BePure1 speaker has reached mythical status because only 3 pair were made before Jim Salk retired. Larry and I went to Scottsdale, AZ in July 2024 to listen to the BePure1 and we were both impressed by the ease and clarity of the sound. I wrote a review of the Salk BePure1 speakers:
https://www.audiocircle.com/index.php?topic=189729.msg1984959#msg1984959

Larry was so impressed he wanted to build a pair but plans are not available. The Troels Gravesen Purifi-Be speaker is very close, it uses the same drivers in a similar sized cabinet but is ported instead of the two passive radiators used in the BePure1 design.

The Troels Gravesen Purifi-Be speaker uses the Purifi PTT6.5X04-NFA-01 6.5" woofer and the SBAcoustics TW29BN-B-4 beryllium dome tweeter in a 2-way stand-mount speaker.
http://www.troelsgravesen.dk/Purifi-Be.htm







One sound characteristic that was common with both the Salk and Gravesen designs was the forcefulness of the upper mids and highs. The sound wasn't analytical but more "in your face" "first row" than I'm used to with the RAAL tweeter. Many recordings sounded great, lesser recordings were a little too hot. These speakers will sound best with only the finest electronics and preferably tubed. Jim Salk recommended the McGary Audio SA1E tube amp for use with the BePure1 speakers.

The McGary Audio SA1E amp is 30 watts per channel, by coincidence the custom tube amps we listened to with the Purifi-Be speakers were also 30 watts per channel. The mono-block amps, preamp and phono amp were designed by Kevin Carter, owner of K&K Audio, who recently passed away. The amps are clean and powerful without the classic tube sound although the speakers still need to be tube friendly. I recently listened to a restored Dynaco ST-70 amp and the K&K amps sound completely different and modern.





Another common feature with both speaker designs was a lack of low bass. I was surprised since I read about the longer excursion the Purifi drivers are capable of. The Salk's do go lower courtesy of a larger cabinet and passive radiators, but not by much. At one point during our Salk listening session Steve foolishly handed me the remote control and left the room. In hindsight, perhaps I was a little overenthusiastic with the volume and accidentally blew a grill cover off one of the passive radiators. But in all honesty I still didn't hear the bass I was looking for.

Larry has an average size room and the bass from the Purifi-Be speakers by themselves was lacking, not as anemic as his previous speakers, but both the BePure1 and Purifi-Be speakers need a subwoofer to fill in the low end and balance out the abundant mids and highs.




Luckily Larry has two Rythmik Servo Subs with 12" drivers, the sub cabinets are sealed with down firing drivers. Integration with the Purifi-Be speakers was seamless. The quick sub drivers and the Purifi woofers are an excellent match. The total sound was warm with punchy bass when needed, a little too much sometimes but the speakers are new and we were having fun.

As a side note, Dennis Murphy, owner of Philharmonic Audio, uses the Purifi woofer in his HT Tower speaker ($4500 pr). The woofers have been tuned for maximum headroom rather than maximum extension and go down to only 38 Hz. The HT Tower looks like a terrific speaker for both stereo and home theater but in both applications a subwoofer will be required to hear full range sound. I find it interesting that the three Purifi speaker designs I know of need a sub to go full range.
https://philharmonicaudio.com/products/ht-tower


Earlier this year we listened to the Fritz Carbon 7 speakers at Larry's house. No sub was needed. We loved the way they sounded with the K&K electronics. The Carbon 7's are really tube friendly but will also sound excellent with any type of amp too. The Carbon 7 speakers are for music lovers, the Troels Gravesen Purifi-Be speaker are for audiophiles who want to hear absolutely everything on a recording, warts and all.

Wayne

 

[Tone Depth]

I see the Fritz Carbon 7 SE Mk2 speakers are 3 dB down at 38 Hz, per specifications on his website:
https://www.fritzspeakers.com/DreamWeaverFritzCarbon7Mk2SpecPage.asp

Do you have any idea why these didn't seem to you to need a subwoofer for full response, as compared with the two speakers using the Purifi mid/woofer?

[newzooreview]

Fritz speakers are rear ported, allowing for more boundary reinforcement of the bass. These Gravesen speakers are front ported: much less boundary reinforcement of the bass from the wall behind the speakers.

There are plenty of speakers using Purifi drivers that don't need a subwoofer: Buchardt A10, Buchardt A700 LE, and March Audio Sointuva, for example.

A non-Purifi bookshelf that doesn't need a subwoofer is the Ascend Acoustics Sierra LX. The proprietary SEAS driver in the LX has a 2.2 cm excursion. Bass on these was better than the bass from my Spatial Audio M3 Sapphires open baffle speakers. I sold the LX to upgrade to the ELX ribbon towers, which are now burning in. https://forum.ascendacoustics.com/showthread.php?7588-Introducing-the-Sierra-LX!!!

I very much enjoyed my Salk HT-1TL speakers, so I certainly appreciate the potential of the BePure1 (although I've never heard it).

[WGH]

Do you have any idea why these didn't seem to you to need a subwoofer for full response, as compared with the two speakers using the Purifi mid/woofer?

I think the difference is perceived bass compared to actual bass. A speaker with an extended high end like the BePure1 will need an extended low end to feel balanced. Room size is important too, a large room will require a lot more bass energy than a couple of 6.5" drivers can produce. Yesterday our audio club listened to a pair of new Magnepan 2.7i speakers that have a true ribbon tweeter. These speakers have the clearest, non-fatiguing mid and high frequencies I have ever heard, they are -3db at 40 Hz but still need a sub to sound balanced. We listened to the 2.7i's with a REL Gibraltar G2 sub.


All the frequency response graphs of Salk speakers have been very flat, I would expect the BePure1 to be flat also. I haven't seen a graph for the BePure1 but the Salk website has a graph for the BePure2




The Fritz Carbon 7 speakers have beautiful highs but not in the same league as the beryllium or Magnepan tweeters, notice the highs start rolling off above 10 KHz compared to the BePure speakers. The 7's have a small but noticeable bass boost from 40 - 80 Hz which will give the impression of deeper bass and when coupled with the previously mentioned bass reinforcement from the rear facing port the combination will make most listeners happy without a sub.




Another Fritz Carbon 7 review from 2020 by hild45:
https://www.audiocircle.com/index.php?topic=170117.msg1802074#msg1802074

"Because I grew up listening to Acoustic Research three-way AR 48s, which have 10” woofers, I was used to mains that could reproduce bass really well. The Carbon’s woofers are not that large, but their bass response is excellent — deep and accurate. Some recordings — such as Donald Fagen’s “Morph the Cat,” or the Towner/Peacock duo’s “Opalesque,” — surprised me with their bass extension. On “Morph,” bass was quick, effortless, controlled; drums had kick and power. On Jennifer Warnes’ “The Ballad of the Runaway Horse,” Rob Wasserman’s bass provided a detailed, rich, woody, heartbeat that propelled the folk tale forward. The Carbon’s conveyed Eno’s Apollo bass impressionistically by creating a fathomless, spatial arena. On all these tunes, the Carbons did all I could have asked for, and it was only when I turned on my REL 328 subwoofer did I realize that there was a bottom end which could be filled a bit further. Still, it was easy to listen without the sub, and I often forgot that I had it."

[Tone Depth]

Creative Sound Solutions built identical speakers with front ports, and with rear ports, to measure and listen to, They have proved that there isn't an audible difference between the two, just an audiophile myth. Their results confirm the known physics of sound waves.

https://www.css-audio.com/single-post/front-vs-rear-ports-does-it-matter

[Norman Tracy]

Excellent review of the Purifi-Be speakers Wayne. Wonderful system, those McGary Audio SA1E amps designed by Kevin Carter are choice. Also kudos for the external crossovers and components selected.

I have been working with Purifi drivers as my SOTA choice since 2020 starting with PTT6.5 and then PTT5.25 and PTT4.0 models. I displayed at LSAF 2024 using Miller Audio LLC Dyna-70 Ultimate Audio System amplifiers (https://milleraudiollc.com/new-amplifiers-for-2024/), like the SA1E a stout 30-35 jumbo tube watts per channel. The state-of-the-art low distortion and linearity of Purifi woofers let the juicy tonal richness we love from tubes shine through. So sweet, so pure.

However, be aware we are considering woofers with Sd = 132cm2 and SPL @ 2.83Vrms/1m, 300-800Hz = 88.7dB. In my experience to really activate the PTT6.5's bass slam and full in room depth more voltage swing is very handy. I call Purifi bass it's 'party trick' and accessing the full Linear excursion of Xlin = ±9.8mm and Maximum mechanical excursion, Xmax = ±14.5mm bring on some volts and amps. Used with a carefully curated tube system like Wayne's and the results are sublime. For party time bring on a few hundred class-D watts, then stand back.

[newzooreview]

They have proved that there isn't an audible difference between the two, just an audiophile myth.

If you look at the data in the URL you provided, the speaker they measured has ports about 2" off of the floor. The floor is providing almost all of the boundary reinforcement of the bass in this configuration, so the placement of the ports and distance of the speaker to the wall behind it have a minimal influence. Even so, at 40 Hz the speaker with rear ports is +2 dB compared to the front-ported speaker.

Port tuning, port diameter, and distance of the port from boundaries (including and perhaps especially the floor) are all part of the complex physics at play.



However, the speakers under discussion are stand mounted. The ports are at least two feet away from the floor, and the wall behind the speakers is the dominant boundary (as opposed to the floor).

I don't know what the tuning frequency of the ports in the Fritz and Salk speakers is, and I don't know whether there were any differences in distance the speakers were from the wall behind them in the two listening sessions. It's also unclear whether the audible differences in bass were related to the amount of mid-bass or the audible extension of the bass to lower frequencies.

At equal port height and port tuning, and distance from the wall behind the speaker, a rear-ported stand-mount speaker will have a different bass response than a front-ported speaker that is otherwise identical. It's an oversimplification that rear-porting will always be preferable, but it's not a myth that the physics of rear porting and front porting are different.

[Tyson]

If you look at the data in the URL you provided, the speaker they measured has ports about 2" off of the floor. The floor is providing almost all of the boundary reinforcement of the bass in this configuration, so the placement of the ports and distance of the speaker to the wall behind it have a minimal influence. Even so, at 40 Hz the speaker with rear ports is +2 dB compared to the front-ported speaker.

Port tuning, port diameter, and distance of the port from boundaries (including and perhaps especially the floor) are all part of the complex physics at play.



However, the speakers under discussion are stand mounted. The ports are at least two feet away from the floor, and the wall behind the speakers is the dominant boundary (as opposed to the floor).

I don't know what the tuning frequency of the ports in the Fritz and Salk speakers is, and I don't know whether there were any differences in distance the speakers were from the wall behind them in the two listening sessions. It's also unclear whether the audible differences in bass were related to the amount of mid-bass or the audible extension of the bass to lower frequencies.

At equal port height and port tuning, and distance from the wall behind the speaker, a rear-ported stand-mount speaker will have a different bass response than a front-ported speaker that is otherwise identical. It's an oversimplification that rear-porting will always be preferable, but it's not a myth that the physics of rear porting and front porting are different.

You are correct that from a measurement standpoint, there is no difference between front porting and rear porting.  However, some speakers have ports that are too small and/or don't use flared ports.  The result is port chuffing, which is audible.  A good reason to put the ports on the back is it minimizes the amount of port noise that you can hear.

[Tone Depth]

I think the CSS guys know their speakers they manufacture quite better than anyone else. They say they don't hear a difference; I believe them.

The key points, however, are that lower frequencies are essentially omnidirectional in free space. The magnitude of sound reinforcement coming out of ports is a small fraction of that coming off the fronts of the speaker cones. Once the sound waves are launched off the cones, they all start spreading out, and up to half may diffract around the external boundaries of the speaker. The rear wall first reflection sound reinforcement happens with all of the sound waves that travel towards the back of the speaker, not just the sound exiting from rear facing ports. The two speaker movement graph measurements would look very different from each other, if only the sound waves from the rear facing ports were reflecting off the back wall.

Now let's consider the floor boundary reinforcement of the low ports. That has the effect of concentrating that sound by reflecting half of it back off the floor. That reflected sound still travels to the back wall and then has a second reflection off it, as does the diffracted sound wrapping around the speaker from the front.

CSS moved their speaker(s) towards the back wall in 12" increments between measurements. As the speaker gets closer to the back wall, the sound reinforcement from the back wall increases as shown in the plot curves rising from one measurement location to the next. Chuffing, from speakers with poorly designed ports, travels a greater distance and loses more sound volume from rear facing ports before it reaches the measuring microphone, than it would from front facing ports.

Chuffing noise and low frequencies from a rear port will respond exactly as the rest of the diffracted sound moving towards the back wall before back wall reinforcement. Chuffing doesn't disappear and the rest of the sound get reinforced. As all of the sound waves travel to the back wall, reflect, and then travel back into the room, they lose volume along the path of travel. Chuffing from a front port is more clearly audible since it travels a shorter distance. A well-designed port won't transmit chuffing.

[newzooreview]

I think the CSS guys know their speakers they manufacture quite better than anyone else. They say they don't hear a difference; I believe them.

CSS tested a speaker wholly different from the stand-mounted speakers under discussion. Their data also show a +2 dB increase in 40 Hz bass in the rear-ported speaker. Other frequencies show varying or no difference. The existence of a loudspeaker design in which rear vs. front porting has a small or modest effect does not override the physics that govern how all loudspeakers work. The physics show that depending on the loudspeaker design, front or rear porting can make a substantive difference in perceived bass response.

[Tone Depth]

Prove you can hear a difference of 2 dB at 40 Hz and an average sound level of 80 dB.

[Rusty Jefferson]

....Do you have any idea why these didn't seem to you to need a subwoofer for full response, as compared with the two speakers using the Purifi mid/woofer?

There isn't nearly enough information here to make a determination about this. Just because they both use 6.5" woofers in a ported box doesn't mean they'll have the same bass response. I don't see anything in the links provided that tell us what either speaker (or its woofer) is doing in the bass region. The Troels design seems quite heavily damped, including stuffing wool in the port. It's also a 4 ohm speaker and the Fritz is an 8 ohm. The OP is using what appears to be push-pull or parallel single ended tube amplifiers that no doubt have high output impedance and may have limited capabilities with the 4 ohm speaker load. Without more information about the drivers, you're trying to compare apples to oranges. It's not about the port location.

There are also known characteristics with the Purfi woofers that make them difficult to deploy in small vented boxes. I didn't see this discussed in the Troels link but it has been discussed in the Salk circle when they were trying to figure out how to implement them. They decided to use twin passive radiators instead of dealing with the port issues.

I'm using the same 2 drivers as Troels in a similar sized box on a Joseph Crowe baffle, but sealed box with subs below. An engineer at Purifi I reached out to prior to building mine confirmed to me going sealed box was preferable. His personal diy speakers use them sealed box. I don't know why folks want these little woofers (any brand) in small boxes to play deep bass. Ports or passive radiators just add smearing, timing and phase issues to (sort of) make deeper bass, but that's a different discussion.

[WGH]

Prove you can hear a difference of 2 dB at 40 Hz and an average sound level of 80 dB.

My REL G1 MkII sub has a digital display calibrated in Hz and dB. The next time you visit I'll set the rolloff to 40 Hz then raise and lower the dB level by 2. I'll bet a dollar to a donut you will hear a difference.

[Early B.]

I'm using the same 2 drivers as Troels in a similar sized box on a Joseph Crowe baffle, but sealed box with subs below.

Please post a pic of your speakers. Thanks.

[Rusty Jefferson]

Please post a pic of your speakers. Thanks.

Sorry, I'm not able to upload an image from my phone in the vertical orientation from my gallery. I've tried to resize it and rotate it in the gallery but it doesn't take. Keeps coming up sideways. 

[WGH]

I've tried to resize it and rotate it in the gallery but it doesn't take. Keeps coming up sideways. 

If you post it (whatever the orientation), I can rotate it.

[Charles Xavier]

.

[Rusty Jefferson]

Thanks Charles!

[WGH]

Looks like a fun little (expensive) speaker. Photo looks upright to me.

[Rusty Jefferson]

Looks like a fun little (expensive) speaker. Photo looks upright to me.

Charles flipped the image. I deleted the sideways one to keep the thread clean.

Drivers cost the same as your build I imagine (less maybe, built these 3 years ago). The baffles from Joseph Crowe cost about $450 shipped from Canada. CNC cut 2.5" Walnut. The boxes are Baltic Birch. There's a video about them on his YouTube channel.

Wasn't trying to derail the Troels thread, just pointing out my familiarity with this driver combo and some of the potential issues with putting the Purifi woofer in a small box and reasons why the Troels speakers sound different from the Fritz in your friend's system.