I am trying to replicate the Revel M105 copy project from ASR, but with a different tweeter. I built the cabinets, the waveguide, mounted the speakers and am ready for the next step (crossover design). I have taken horizontal measurements of both the tweeter and woofer while mounted in the enclosure (driving each one separately).
In the case of the woofer I have collected near field measurements and the same for the port. Microphone placement was about 0.2" from the cone center, and in the case of the port, the microphone was pretty much inside. I used REW, a UMIK-1 to collect measurements all driven from a yamaha amp without changing the output volume (near field measurements were at a lower volume due to clipping).
I combined the port and woofer near field measurements and adjusted the port SPL using the appropriate formula (20Log(portdia/woofereffectivedia). I then adjusted the near field for the baffle diffraction. Once I had a cleaned/combined/adjusted near field I blended with the far field 0deg measurements to get the response shown below.
The woofer is a Scanspeak 15W/8530K00 and the tweeter is a Morel ST1108 supreme.
I have a few questions and am looking for some expert advice.
1. How do I determine what the port tuning frequency is at right now? (Jeff bagby paper references a drop in SPL, which should occur at the tuning of the enclosure, but I don't really see it). I am targeting about 40hz for enclosure tuning and cut the port length appropriately (2" diameter port).
2. What is going on with the scanspeak at the 250-3550hz range. Why is SPL dumping out? Should I be concerned? Where should I be looking to try to address this?
The enclosure is made from 1" MDF walls (2 pieces of 1/2" glued) and the front is 1.5"MDF (3 pieces of 1/2" glued). The internal is braced and I glued some melamine foam to the interior.
Here are some pictures. I appreciate any help you can provide.
Here is my attempt at a crossover.
In the case of the woofer I have collected near field measurements and the same for the port. Microphone placement was about 0.2" from the cone center, and in the case of the port, the microphone was pretty much inside. I used REW, a UMIK-1 to collect measurements all driven from a yamaha amp without changing the output volume (near field measurements were at a lower volume due to clipping).
I combined the port and woofer near field measurements and adjusted the port SPL using the appropriate formula (20Log(portdia/woofereffectivedia). I then adjusted the near field for the baffle diffraction. Once I had a cleaned/combined/adjusted near field I blended with the far field 0deg measurements to get the response shown below.
The woofer is a Scanspeak 15W/8530K00 and the tweeter is a Morel ST1108 supreme.
I have a few questions and am looking for some expert advice.
1. How do I determine what the port tuning frequency is at right now? (Jeff bagby paper references a drop in SPL, which should occur at the tuning of the enclosure, but I don't really see it). I am targeting about 40hz for enclosure tuning and cut the port length appropriately (2" diameter port).
2. What is going on with the scanspeak at the 250-3550hz range. Why is SPL dumping out? Should I be concerned? Where should I be looking to try to address this?
The enclosure is made from 1" MDF walls (2 pieces of 1/2" glued) and the front is 1.5"MDF (3 pieces of 1/2" glued). The internal is braced and I glued some melamine foam to the interior.
Here are some pictures. I appreciate any help you can provide.
Here is my attempt at a crossover.
Looking at the impedance graph it does not seem a BR enclosure unless the tuning frequence is lower than 20Hz.
You should have something like this (Vb 10L @ 39Hz)
You should have something like this (Vb 10L @ 39Hz)
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Yeah, at tuning (Fb), the woofer basically stops moving with all the output coming from the vent.
What is the cab's net volume (Vb) after deducting driver, vent, any bracing volumes? Vent design details?
What is the cab's net volume (Vb) after deducting driver, vent, any bracing volumes? Vent design details?
Thanks for both your responses.
Enclosure internal volume (after deducting woofer, tweeter, vent, and bracing) is 12.17L. Vent is a 2" diameter vent (precision port 2") with dual flared ends. Overall length is 8.66" (or maybe even as low as 7.66"...I need to open the enclosure and remove the vent to measure...my build notes are somewhat conflicting on this point). I also think when I calculated the port length I forgot to deduct woofer, tweeter, vent and bracing.... interesting point on the vent..it is sort of a chicken and egg thing. You don't know the vent volume until you make some starting assumption and calculate vent length. I suppose it becomes an iterative process.
I don't know what is up with my 6-pack plot from my initial post. it doesn't seem to look like my current plot (specifically the impedence curve, the other curves look the same. I think I grabbed it when I had tried using the manufacturers impedence curve trace.
For impedence curve, do I just use a trace of the manufacturers datasheet? If not, how do you collect that data?
Enclosure internal volume (after deducting woofer, tweeter, vent, and bracing) is 12.17L. Vent is a 2" diameter vent (precision port 2") with dual flared ends. Overall length is 8.66" (or maybe even as low as 7.66"...I need to open the enclosure and remove the vent to measure...my build notes are somewhat conflicting on this point). I also think when I calculated the port length I forgot to deduct woofer, tweeter, vent and bracing.... interesting point on the vent..it is sort of a chicken and egg thing. You don't know the vent volume until you make some starting assumption and calculate vent length. I suppose it becomes an iterative process.
I don't know what is up with my 6-pack plot from my initial post. it doesn't seem to look like my current plot (specifically the impedence curve, the other curves look the same. I think I grabbed it when I had tried using the manufacturers impedence curve trace.
For impedence curve, do I just use a trace of the manufacturers datasheet? If not, how do you collect that data?
Is there a crossover schematic?
Also, I'd like a raw midwoofer far field (1 m perhaps) spl response (.frd) and the same for tweeter, attached here.
Also, I'd like a raw midwoofer far field (1 m perhaps) spl response (.frd) and the same for tweeter, attached here.
I wonder if your measurement of the port and subsequent splicing is the reason for whatever is going on at 300Hz ?
You're welcome!
Fiddled a bit with 12.17 L net, flared port @ 8.66" long and once all end corrections are accounted for it's closer to ~4.6" long acoustically = ~55 Hz Fb, which sims near enough perfect to your measured peaking/roll off response due to being too high/under-damped for the driver's specs, though not your impedance measurement, so it's definitely wrong for whatever reason.
@markbakk Time window gate was set at 5ms (200hz). far field measurements were taken at/about 21.5" (per Bagby white paper recommendation).
The far field measurement shows the same dip at/around the 250-300hz range. So either the speaker is performing in this way, or the enclosure is causing it (maybe some sort of resonance).
@Lojzek I have uploaded the responses requested and here is a picture of the crossover as designed which is represented in the 6-pack of images. (I am not any sort of expert on this, but just took a swing at making the response look like other designs have shown).
Tweeter: Morel Hor 0 <-- measurement taken at 21.5" away from baffle.
Port: Port Near Field <-- measurement taken right at port exit. microphone was placed just about where the flare reduces to the 2".
Scanspeak: Scanspeak Hor 0 <-- measurement taken at 21.5" away from cone (maybe I should have taken this at 21.5" from baffle).
Scanspeak: Scanspeak Near Field <-- measurement taken at 0.2" away from cone (basically as close as I could get it without it contacting the cone)
I also included the combined/correct near field port and scanspeak, as well as the blended near/far response.
@GM Where do you get your impedence measurements from? I don't think I have any equipment to really collect these, other than the accurate Re measured with a multimeter.
Again... I am super appreciative of all the questions and active feedback on this.
The far field measurement shows the same dip at/around the 250-300hz range. So either the speaker is performing in this way, or the enclosure is causing it (maybe some sort of resonance).
@Lojzek I have uploaded the responses requested and here is a picture of the crossover as designed which is represented in the 6-pack of images. (I am not any sort of expert on this, but just took a swing at making the response look like other designs have shown).
Tweeter: Morel Hor 0 <-- measurement taken at 21.5" away from baffle.
Port: Port Near Field <-- measurement taken right at port exit. microphone was placed just about where the flare reduces to the 2".
Scanspeak: Scanspeak Hor 0 <-- measurement taken at 21.5" away from cone (maybe I should have taken this at 21.5" from baffle).
Scanspeak: Scanspeak Near Field <-- measurement taken at 0.2" away from cone (basically as close as I could get it without it contacting the cone)
I also included the combined/correct near field port and scanspeak, as well as the blended near/far response.
@GM Where do you get your impedence measurements from? I don't think I have any equipment to really collect these, other than the accurate Re measured with a multimeter.
Again... I am super appreciative of all the questions and active feedback on this.
What did you use for impedance measurements? Did you trace the manufactures data or did you measure the drivers your self? Sorry I missed the answer, you traced it.
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That is the impedance calculated/simulated by the VCad Enclosure tool. You have to input in the VCad main program the impedance of the SS 15W measured in your cabinet by means of REW or the Limp tool in Arta.
This is what you get in Vcad when you input your data related to your volume/vent.
This is the merging with your FRD files and the diffraction response I simulated for a baffle of 7x14" (18x35cm). It seems like the mic is catching some room/box resonance mode in the measurement of the cone.
Besides, the measurement is interrupted above 5KHz so you cannot use it for calculate your crossover, the same happens for the TW under 1KHz.
Attachments
I’m quite sure you have a strong reflection in your measuring window. That likely causes the comb filter effect. I’d check the impulse response window and adjust the gating.
@markbakk I took the measurements in a warehouse. So the 0deg measurement didn’t have a wall opposite the speaker for over 100meters. To the left and right maybe there was a support beam at about 10meters or so (at a diagonal). I will mock up my setup and post a picture later today. Maybe my stand was causing it?
Why use the scanspeak and morel drivers instead of the SB26 and SB15 that revel is actually using? The SB drivers are made for each other, and cross excellently at 2300hz.
@chargedcapacitor i had purchased the Morels for another project in mind and i was reading that the scanspeak performance is better than the SB. The ASR forum (the build I was using for reference) started with the SB and switched to the scanspeak.
This is the measurement stand I placed this on top of a filing cabinet to get the center of the woofer at/about 5ft off the ground. The cabinet stuck out about 8” to the left of the bottom of the stand.
Does it make sense for near field data to be affected by room reflections? I was under the impression that near field was so close to the speaker that it isn’t.
Does it make sense for near field data to be affected by room reflections? I was under the impression that near field was so close to the speaker that it isn’t.
Also. Port length from end to end is 8.75”. I sealed it with tape temporarily while trying to get the tuning right. I will glue it properly later.
If you're measuring in your garage, try doing a ground plane measurements, and do the measurements with the door open.
By what metric? According to measurements, the SB15 aluminum has a deeper, flatter response, lower distortion, and it cost half as much! The paper version performs similarly, but cost even less.