A new project: HDS Peerless towers

[DcibeL]

Hello,
I would like to share with you my speaker project. Currently I am (I think) completed the design stage, and will hopefully be moving forward to the building stage shortly. Here's the design goals for this project in no particular order:

-visually appealing
-deep bass without the need for a subwoofer
-quality over quantity
-2-way design (I'm not ready for a three way crossover)
-under $1000 (keep in mind I am paying someone to build the cabinets)

With these design goals I had been very impressed with Zaphs measurements of the Peerless HDS 810921 tweeter and I find the cast metal frame to look very nice. This driver will allow me to crossover at a very low frequency, which is necessary when using a large woofer. For the woofer I had to find an 8" driver that could get the deep bass response I require, and not have and cone breakup issues that would prevent it from being used in a 2-way design.

I narrowed down my choise to only a few drivers. The Peerless HDS 830884, the Seas CA22, or the Visaton GF200. I was unable to find distortion measurements of any Visaton drivers on the internet, so I scratched that one off the list. The CA22 while I'm sure it would perform very well, visually it does not catch the eye. It looks too old fashioned for me. The Peerless 830884 looks beautiful, and Zaph had provided distortion measurements in his Tidbits section so I knew it performs well. With the speakers picked out it was time to design a cabinet and simulate the speakers as best I could. Since I don't have any measurement equipment, I'm forced to rely on third party measurements and the manufacturer's datasheet to design around. I downloaded some excel spreadsheets from the FRD consortium, and went to town:

-trace frequency response and impedance
-simulate on measurement baffle
-simulate in box
-simulate baffle diffraction
-combine results and extract phase information

The result of these simulations creates a very realistic view of how the speaker will perform in a real world environment. I was a little worried about the excursion limitations, since the simulations show me that the woofer will run out of excursion with only about 30W input power. Even thought my design criteria calls for quality over quantity I would still like to have a reasonable amount of loud. I decided it will be fine. Next came the crossover.

Here came trouble. My knowledge of crossover design is very limited. I found Jeff Bagby's Passive Crossover Designer to be very helpful, as you can visually see the impact of part value changes instantaneously. However I had a problem. Because the drivers have different acoustic centers, I was able to obtain a very flat frequency response, but the driver phases didn't line up at the crossover point. I searched around for information of what to do about this, but couldn't find a concrete solution. So I opened it up for discussion on DIYAudio. See the thread here.

The end result of the crossover was a 4th order acoustic slope around 1500Hz, with closely matched phase alignment. Much of the credit for this crossover design goes to Jay_WJ. He was very helpful in every way. Below is the final simulated design:




Like (I think) any other 2-way design, there is one limitation to this crossover. With the tweeter positioned above the woofer, the off axis response is better when the listener is located below the speaker. Because of this, I was unsure of whether I should position the tweeter below the woofer or above. The best solution to me was to be able to hear it for myself and then decide. So I designed my cabined with a baffle I could flip. This is modeled after Zaphs tower design for the Vifa XG MTM found here. Here's my design. The cabinet is roughly 57 litres, and will be tuned to approximately 31Hz:



Still to be done:

-order parts
-build cabinets
-tweak crossover
-enjoy!

[Tenson]

Good luck with the build!

Out of interest, what did you draw the cabinet plans in?

[Jay_WJ]

Great cabinet drawing!

As for the listening axis, it is always a good idea, of course, to experiment before your decision. But in this case, I don't think it is really necessary, IMO. You already know what you need to consider. Assuming the tweeter is above the woofer, the crossover performance will definitely be more stable when you listen downward below the tweeter axis than when you listen above the tweeter axis.

So, you need to consider your listening habit, say, how high you ear level will be in both of your critical and casual listening.

Then you can make your decision on whether you need to filp the baffle or not.

[DcibeL]

Originally posted by Tenson
Good luck with the build! Out of interest, what did you draw the cabinet plans in?

Thanks! The plans were drawn in AutoCAD.

Originally posted by Jay_WJ
So, you need to consider your listening habit, say, how high you ear level will be in both of your critical and casual listening.

You're right. I will likely end up with the tweeter at the bottom, since the only reason I would be a considerable amount below the speaker would be if I'm laying on my couch. Also, having the tweeter below the woofer will give speakers a more unique look, straying from the norm.

[Jay_WJ]

For your information (perhaps you've already done this), I simulated the design's vertical off-axis behavior (+/- 5 to 15 degrees). The simulation was performed in PCD but the plots were done using Speaker Workshop. Here we assume that the tweeter is placed above the woofer.






As you can see, the crossover's performance is much more stable when you listen below the tweeter axis. The data also indicate that the in-phase listening axis is about 5 degree below the tweeter axis.

[DcibeL]

Yes, I did simulate that, but thanks anyway. Those graphs will serve as good reference information for others searching through the forum.

[Tenson]

Why don't you mount the tweeter as close as possible to the woofer? maybe even cut out a bit of the face plate. Should help improve vertical lobing, all those mm make a difference!

[Jay_WJ]

Looking at the predicted FR again and according to my experience of fine-tuning speakers based on xo simulation with Zaph's data, I'm 99% sure that you'll need higher padding resistance than the current 2.7 ohms.

[DcibeL]

Originally posted by Tenson
Why don't you mount the tweeter as close as possible to the woofer? maybe even cut out a bit of the face plate. Should help improve vertical lobing, all those mm make a difference!

You're right, they are too far apart. I've updated the above image to where they were supposed to be (the same distance the drivers were simulated at).

Originally posted by Jay_WJ
Looking at the predicted FR again and according to my experience of fine-tuning speakers based on xo simulation with Zaph's data, I'm 99% sure that you'll need higher padding resistance than the current 2.7 ohms.

I'll get a few different resistor values and see what I like most.

[sreten]

Hi,

You may find a full vertical brace (panel with holes cut out) more
effective than individual cross braces. It or they should slightly
offset towards the front to spread frequencies somewhat.
I would also add a cross brace between the drive units.

/sreten.