Constant Beamwidth Transducer (CBT) Speakers

[dc655321]

First generation.

HOLOPLOT X1

HOLOPLOT X1 blends line array and electronic beamsteering technology for complete sound control. Empowered creative freedom for your boldest audio concepts.

holoplot.com

Seems fully buzzword compliant!

 

[sarumbear]

Seems fully buzzword compliant!

Also it seems it is not yet utilised in a live environment other than demos. Interesting use of array technology.

 

[abdo123]

For a line array, the result is a cylinder. It takes a square array to do a point source.

Are square arrays used in Hi-Fi applications? Feel free to share designs that you're aware off.

Directivity control is an elusive goal for most people here.

 

[Bjorn]

Some weeks ago the CBT36s got a new owner. I set up the speakers at a friend's apartment. We used the miniDSP Flex as a DSP and 4-channel amplification with Hypex UcD modules.

Tried different placements first with measurements. The speakers generally don't change much above Schroeder and also quite little above 150 Hz because it avoids the floor bounce. But obviously the lower frequencies will vary with placement.

Ended up having the speakers fairly close to the TV. The right speaker was moved further to the left than what the picture below shows.

The speakers were intially set up with a flat response. After placement was found, we added some shelving to get a response falling towards the treble.
The response on each speaker with 1/12 oct. smoothing was like the following.

I need to investigate later what's happening between 600 Hz and 1 KHz (the dip). It may be the table with all the stuff on it that's causing it. But overall, this is a very good frequency response in such a small room with no acoustical treatment. That's the result of a good speaker design that has a very uniform directivity, avoids floor reflections and minimizes ceiling reflections.

Next step now is to do some acoustical treatment. An absorber will be placed in the ceiling between the speakers and listening postion and one absorber on side wall will be added. After that, some more tuning with DSP and add some presets the owner can change between. Later, a subwoofer will be added.

Anyway, thought this could be of interest of some. While the CBT36s aren't without flaws, it's truly a remarkable speaker IMO.

 

[Newman]

Great report @Bjorn. I doubt that an absorber is needed on the ceiling, since the CBT has a 30-degree vertical beamwidth and one would expect ceiling reflections to only come into play at listening distances over 4m with a 2.4m ceiling, or 5m with a 3m ceiling.

cheers

 

[Bjorn]

Great report @Bjorn. I doubt that an absorber is needed on the ceiling, since the CBT has a 30-degree vertical beamwidth and one would expect ceiling reflections to only come into play at listening distances over 4m with a 2.4m ceiling, or 5m with a 3m ceiling.

cheers

Thanks. A ceiling absorber will improve further. There's still flutter echo going between the floor and ceiling with the CBT. Plus, the absorber will work low enough in frequency to shorten the decay and tighten up the lower midrange and bass. Very audible!

 

[Rick Sykora]

Some weeks ago the CBT36s got a new owner. I set up the speakers at a friend's apartment. We used the miniDSP Flex as a DSP and 4-channel amplification with Hypex UcD modules....

...Anyway, thought this could be of interest of some. While the CBT36s aren't without flaws, it's truly a remarkable speaker IMO.

So, which speakers are replacing the CBT36s?

 

[HarmonicTHD]

Some weeks ago the CBT36s got a new owner. I set up the speakers at a friend's apartment. We used the miniDSP Flex as a DSP and 4-channel amplification with Hypex UcD modules.

Tried different placements first with measurements. The speakers generally don't change much above Schroeder and also quite little above 150 Hz because it avoids the floor bounce. But obviously the lower frequencies will vary with placement.
View attachment 238921

Ended up having the speakers fairly close to the TV. The right speaker was moved further to the left than what the picture below shows.

View attachment 238922

The speakers were intially set up with a flat response. After placement was found, we added some shelving to get a response falling towards the treble.
The response on each speaker with 1/12 oct. smoothing was like the following.
View attachment 238923

View attachment 238924

I need to investigate later what's happening between 600 Hz and 1 KHz (the dip). It may be the table with all the stuff on it that's causing it. But overall, this is a very good frequency response in such a small room with no acoustical treatment. That's the result of a good speaker design that has a very uniform directivity, avoids floor reflections and minimizes ceiling reflections.

Next step now is to do some acoustical treatment. An absorber will be placed in the ceiling between the speakers and listening postion and one absorber on side wall will be added. After that, some more tuning with DSP and add some presets the owner can change between. Later, a subwoofer will be added.

Anyway, thought this could be of interest of some. While the CBT36s aren't without flaws, it's truly a remarkable speaker IMO.

Question: How does it avoid floor bounce ? Could you explain please?

 

[Bjorn]

So, which speakers are replacing the CBT36s?

I have many speakers since I'm into designing them. We (me and Don Keele) are also working on a new CBT speaker.

 

[Bjorn]

Question: How does it avoid floor bounce ? Could you explain please?

By using the floor as a mirror.

 

[HarmonicTHD]

By using the floor as a mirror.

View attachment 238960

View attachment 238962

Ah thanks. So they make use of the inevitable. Interesting. Does it work consistently as not all floor bounces are equal? Or should one avoid carpets etc ?

 

[Bjorn]

Ah thanks. So they make use of the inevitable. Interesting. Does it work consistently as not all floor bounces are equal? Or should one avoid carpets etc ?

I believe it works up till the frequency where the drivers sum and don't create comb filtering. So basically up 10-16 kHz area, depending on driver size that's being used. The lows will be dominated by the room and room modes.

A thin carpet will not effect this and could be used. However, a carpet is a very bandlimited treatment.

 

[HarmonicTHD]

I believe it works up till the frequency where the drivers sum and don't create comb filtering. So basically up 10-16 kHz area, depending on driver size that's being used. The lows will be dominated by the room and room modes.

A thin carpet will not effect this and could be used. However, a carpet is a very bandlimited treatment.

Thanks. Carpet was just an example of the differing floor types. But I get it. And sure it is irrelevant below the Schroeder frequency.

 

[Bjorn]

I have these CBTs in the home theater by the way. A prototype we did some years ago.

 

[HarmonicTHD]

I have these CBTs in the home theater by the way. A prototype we did some years ago.

View attachment 238968

Was something like this ever measured anechoically? (Or with Klippel?). How do you adjust for the combfilter effects between the drivers?

 

[Bjorn]

Was something like this ever measured anechoically? (Or with Klippel?). How do you adjust for the combfilter effects between the drivers?

Th removal of lobing and comb filtering is basically what the CBT technology is about. And why it's not like a tradional line array. If you're not familiar with the technology you can read AES papers or some are also shared in the videos below. In short, it's done with a combination of a shading system and the curving. It works up to about 1/4 wavelength spacing between the tweeters. Meaning comb filtering will kick in high in frequency at some point, but primarily in near field and it probably isn't audible when small drivers with close spacing is used.

https://www.youtube.com/playlist?list=PLcuMvtBVm-LAQi1wZzoZOAIenpRTT8uyR

The prototype you saw was only measured in near field, which is very close to anechoic down to a certain frequency.

 

[Rick Sykora]

Was something like this ever measured anechoically? (Or with Klippel?). How do you adjust for the combfilter effects between the drivers?

See the first post in this thread for CBT research and measurements.

 

[sarumbear]

Was something like this ever measured anechoically? (Or with Klippel?). How do you adjust for the combfilter effects between the drivers?

JBL CBT 70J-1 Review (Constant Beam Transducer)

This is a review and detailed measurements of the special JBL CBT 70J-1 (upper unit) constant beam transducer design. It was kindly purchased new and shipped to me by a member. It costs US $1047 on Amazon including free delivery. You can get it in black or white colors. Note: our company...

www.audiosciencereview.com

 

[j_j]

Great report @Bjorn. I doubt that an absorber is needed on the ceiling, since the CBT has a 30-degree vertical beamwidth and one would expect ceiling reflections to only come into play at listening distances over 4m with a 2.4m ceiling, or 5m with a 3m ceiling.

cheers

If you put the array directly adjacent to the ceiling, you can almost double the length of the array via the ceiling images, if you're pointing the array straight ahead along the ceiling.

 

[laetoli37]

I have many speakers since I'm into designing them. We (me and Don Keele) are also working on a new CBT speaker.

Are you guys also looking at low profile center speaker for acoustics transparent application? Something straight instead of curved like the JBL Pro series.