FRD File for SEAS 27TBFCG/TV

[amplus]

Does anyone have FRD measurements for this tweeter? I traced the plots from SEAS but I don't know how reliable they are. There is an odd dip in the response that doesn't show up on the non-shielded version and it seems the roll-off is a bit different on the bottom end too from what SEAS and others like ZAPH have measured on the non-shielded version. I wish I had the non-shielded but I happen to have the shielded ones The other option is I could measure it myself, but I'm not sure if I have the right setup to do that. I do have a Behringer ECM8000 mic I used to setup my home theater room but I have never done measurements on an individual speaker driver, just in-room whole systems. Any suggestions/ideas?

[DDF]

Attached, directly from a lab tech at Seas, and measured in their anechoic chamber. Measurement conditions below.

Dave


SEAS FABRIKKER AS
15.11.2004

The files in the sub-folders are frequency response and impedance data stored in .txt files.
The data is tabulator separated and listed in the following order:
Frequency Magnitude Phase

These measurements are made in a box that can be used as a 2-way speaker. It is important that you note this difference if you compare these measurements to the datasheets for our drivers. The boundry conditions are different, especially on the tweeter measurements, so here you will see diffraction effects.

The object of this project is to give our customers access to measured data that can be used to simulate a crossover. While using LspCAD for some time I have found a very good correlation between simulated and measured end-result, so I hope this will make it easier for you to construct your own speaker.

Measurement conditions
The speaker is placed on a turntable-stand in a 4-pi (free-field) anechoic chamber.
Applied voltage is 2.83 volts. Measurement system is ATB precision. All measurements are done with a stepped sine at 250 frequency points. No gating. Smoothing at 1 (lowest setting- approx. 1/12 oct.)

The microphone (B&K 4133) was placed 1 meter from the front of the speaker, on the tweeter axis. The microphone was not moved during the whole measurement session. The woofer measurements are also done with the microphone centered on the tweeter axis. The reason for doing this is that the relative phase difference between woofer and tweeter will be accurately stored in the measurements.

To verify your simulation setup you can do the following (I'm referring to LspCAD):
Go to the General menu and import the following file in the "Target SPL curve"
L18RNX_P & 27TFFC in paralell-SPL.txt
This file shows a measurement from 100Hz to 20kHz with a woofer and tweeter in paralell without any crossover components attached.
Set the measurement distance to 1 meter.
Then import the IMP and SPL_on axis files for the same drivers located in it's respective sub folder.
L18RNX_P H1224-08_IMP.txt
L18RNX_P H1224-08_SPL_on axis.txt
27TFFC H881-06_IMP.txt
27TFFC H881-06_SPL_on axis.txt

The simulated sum of these two drivers without any crossover components and connected in paralell should match the "Target SPL curve" above 100Hz.

Off-axis measurments is also included in the folders. To get a reliable result in simulation you should always import both woofer and tweeter files for the same angle. Again, this is to get the phase difference correct. All off-axis measurements are in the horisontal-plane. Now you have a chance to see both effects of driver directivity and diffraction in your simulation of an off-axis response.


Box
The box outside dimensions:
Front baffle: 20cm wide and 49.6cm high
Box depth: 29.6cm
Edges are trimmed with a roundover-bit r=12mm.

Driver placement:
Both drivers are centered on the vertical axis.
The distance between the drivers centers are 158.5mm
The distance from the top of the baffle to the tweeter centre: 65mm
The distance from the top of the baffle to the woofer centre: 223.5mm

The box has a removable tweeter baffle. This way we can measure all drivers flush mounted in the same box.
The box is approximately 18 liters and the port tuning is approximately 40Hz. All woofers are measured like this, regardless of what the T/S calculations suggest.

Good luck with your speaker building.
Remember to check that the drivers are available at your local distributor.

Bjorn Magne Idland
Lab technician
Seas Fabrikker AS
bidland@seas.no


041112

[BOBinGA]

Thank you, Dave. I am using this shielded version of the 27TBFCG in my current project and these files will be very helpful.

-Bob

[jkim]

Does anyone have FRD measurements for this tweeter? I traced the plots from SEAS but I don't know how reliable they are. There is an odd dip in the response that doesn't show up on the non-shielded version and it seems the roll-off is a bit different on the bottom end too from what SEAS and others like ZAPH have measured on the non-shielded version. I wish I had the non-shielded but I happen to have the shielded ones The other option is I could measure it myself, but I'm not sure if I have the right setup to do that. I do have a Behringer ECM8000 mic I used to setup my home theater room but I have never done measurements on an individual speaker driver, just in-room whole systems. Any suggestions/ideas?

Seas' measurements on their product sheets are usually very accurate. Upon looking at what Dave posted above, I predict that you will have a similar result if you add baffle diffraction effects to the response in the data sheet. But unless your baffle width or tweeter location is very different (e.g., more that 1"), I'd stick to the above in-box measurements.

[amplus]

Excellent info! My baffle is actually a little over 1" larger (9"). I took another look at the SEAS site and see that the measurements posted there are on a .6m x .8m (23.6" x 31.5") baffle. Would it make more sense to stick with the trace of that vs. trying to make the data here work for my slightly larger baffle?

[DDF]

Seas' measurements on their product sheets are usually very accurate. Upon looking at what Dave posted above, I predict that you will have a similar result if you add baffle diffraction effects to the response in the data sheet. But unless your baffle width or tweeter location is very different (e.g., more that 1"), I'd stick to the above in-box measurements.

I took Seas' measurements in box and on an IEC baffle, and used a diffraction simulator to see if the diffraction could be "removed" mathematically from the IEC baffle file, then a simulation in box used to "add" the diffraction simulator back on.

It works, the result was almost identical to the measurement in box.

So the message is, if you want to rejig these files using BDC, The Edge or Jeff's diffraction simulator, they all work (I tested them all against the anechoic measurements from Seas), and the accuracy is most high above 800Hz, where it matters for a tweeter.

Dave

[amplus]

Dave, took my traced plot and used Jeff's Response Modeler 3.0 with the dimensions outlined by SEAS in the above example and it is very very close. Gives me more of a warm fuzzy feeling I'm going about this the right way.

[DDF]

Dave, took my traced plot and used Jeff's Response Modeler 3.0 with the dimensions outlined by SEAS in the above example and it is very very close. Gives me more of a warm fuzzy feeling I'm going about this the right way.

The cool thing is that baffle diffraction (viewed at one point in space) is minimum phase, so you can add the diffraction sim into teh result, and then run a hilbert transform (FRD tools will do it) and you will have the correct phase. Powerful tools!

[Jeff B.]

The cool thing is that baffle diffraction (viewed at one point in space) is minimum phase, so you can add the diffraction sim into teh result, and then run a hilbert transform (FRD tools will do it) and you will have the correct phase. Powerful tools!

[jkim]

The cool thing is that baffle diffraction (viewed at one point in space) is minimum phase, so you can add the diffraction sim into teh result, and then run a hilbert transform (FRD tools will do it) and you will have the correct phase. Powerful tools!

Yes, indeed. Baffle diffraction and even room effects are minimum phase. Diffraction modeling tools are very accurate in my experience, too. The only thing off the mark is due to close woofer cone cavities which are prominent in the case of MTM. I considered a crude method to roughly estimate the effect using available tools:

http://www.geocities.com/woove99/Spk...fle_cavity.htm

Also, a tweeter with waveguide/horn loading is not much affected by diffraction.

Jay

[DDF]

The only thing off the mark is due to close woofer cone cavities which are prominent in the case of MTM. I considered a crude method to roughly estimate the effect using available tools:

http://www.geocities.com/woove99/Spk...fle_cavity.htm

Interesting stuff. I know you do a lot of modeling for people from published curves, so I can see this being a big help. I always go from measured though.

I found a nice strip of F13 McMaster Carr felt between the tweeter and woofer ameliorated a fair deal of this cavity diffraction and surround reflection. If done right in a two way, it even looks OK. Unfortunately I couldn't find a representative measurement file, but it does work.