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Old 21st August 2015, 02:56 AM   #1
keilau is offline keilau  United States
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Default The crossover for a modest DIY bookshelf speaker project

It started out and a refurbishment of my main speakers. They were the Larry Hughes bookshelf as described "A DIY Bookshelf Speaker" in HiFi Answers July 1978 issue. It is a closed box 17"x10"x8" using Audax HD17B25H and HD12x9D25. Both Badger Sound and Falcon Acoustics had built crossover for it. They are 30 years old and went out of business a while back. The woofer aged, but the tweeter still sounds good. I tried a few commercial boxes and found them wanting.
But I ended up building brand new bookshelf using the Peerless Nomex 830875 and Dayton Audio RS28A-4 in a 15 litres closed box. I will post my venture sometime when it is fully completed and auditioned at the DIY forum. Attached is the crossover and response simulation using Bagby's PCD software.

xover_peerless-dayton_bafcomp.jpg response_peerless-dayton_bafcomp.gif

I chose closed over vented box for the faster transient response. I used a pair of aperiodic subwoofers so that the bookshelf lower bass extent is not as critical as the response character. The baffle compensation was simulated by Bagby's "Response Modeler" as outlined by Paul Carmody.

https://sites.google.com/site/undefi...d-measurements

The speakers have been assembled and sound pretty good to me. I am still fine tuning and adjusting the crossover. Any critique and comment are welcome.
IMG_2381.jpg

Last edited by keilau; 22nd August 2015 at 01:06 PM.
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Old 21st August 2015, 09:56 AM   #2
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The box is too big for this driver. Around 6-7L would be optimal.
As for the crossover I suspect it is too midrange forwarded, but maybe you like it that way. With the relatively high number of components you used you could tame the breakup and have better phase tracking up to 5KHz. Have a look here for an inspiration: Studio-101

Ralf
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Old 21st August 2015, 12:57 PM   #3
keilau is offline keilau  United States
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Quote:
Originally Posted by giralfino View Post
The box is too big for this driver. Around 6-7L would be optimal.
As for the crossover I suspect it is too midrange forwarded, but maybe you like it that way. With the relatively high number of components you used you could tame the breakup and have better phase tracking up to 5KHz. Have a look here for an inspiration: Studio-101

Ralf
Ralf, thank you for the feedback.

I am a little puzzle by the box size comment. First, a 6-7 litre box is unusual for a 6.5" woofer because it will be somewhat small to find a box dimension with proper baffle width. Second, the smaller box will get a much higher efficiency, a little bumpy mid bass at the expenses of transient performance. I am aware that most 6.5" closed box use 10-12 litres box. I used the "Sonic Barrier 3/4" 3-layer composite damping material" to line all the walls (not the baffle). So the effective box volume is about 11 litres (?).

What is the reason of the midrange forward and what should I do about it? The PCD shows a very uniform frequency response from 500 Hz and up and it sounds like it. I used the BSC (baffle step compensation) on woofer and the padding resistor for tweeter to get the smoothest response. I did the BSC by trial and error on the PCD software. Any better process?

I chose the Dayton Audio RS28A-A tweeter to allow me lower crossover frequency. It was first done to improve dispersion, thus the imaging. And it has the bonus of not have to worry about the woofer breakup at 5KHz when crossover low. Did I overlook something? I am familar with most of the speaker designs by Troels Gravesen. He is actually one of the reason I chose the Peerless Nomex woofer. Thank you for the link, but it is a different design. Troels used a tuned RLC to tame the woofer breakup.

I will be very happy to try it if you have specific suggestion on crossover component changes.
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Old 21st August 2015, 01:36 PM   #4
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15L is actually very close to a box Q of 0.5 which should be fine and give you a bit more bass extension. Attached is comparison of 6L and 15L. Note that the main tradeoff will be reduced power handling.

You have a bit of a shelf between 500Hz and 3Khz which will likely make the midrange a bit more prominent. Have you turned on the target responses in PCD? to me although it is simming fairly flat, it does not look to me like your drivers are rolling off at a 4th order LR acoustic slope.

Tony.
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Last edited by wintermute; 21st August 2015 at 01:38 PM. Reason: fogot attachment.
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Old 21st August 2015, 02:24 PM   #5
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Quote:
I am a little puzzle by the box size comment. First, a 6-7 litre box is unusual for a 6.5" woofer because it will be somewhat small to find a box dimension with proper baffle width. Second, the smaller box will get a much higher efficiency, a little bumpy mid bass at the expenses of transient performance. I am aware that most 6.5" closed box use 10-12 litres box. I used the "Sonic Barrier 3/4" 3-layer composite damping material" to line all the walls (not the baffle). So the effective box volume is about 11 litres (?).
The driver you chose is optimized for a relatively small vented box, in fact 15L should be close to the optimal vented box. A closed box should be stuffed and not only lined but note also that damping material has the effect of increase the volume as seen by the driver up to 20%. Finally a Q of 0.7 has no bump at all.

Quote:
Thank you for the link, but it is a different design. Troels used a tuned RLC to tame the woofer breakup.
No. He used the RLC network to flatten the response between 500Hz and 1KHz, and a RC network to tame the breakup (in parallel to the main coil). This second network cannot be simulated in PCD, something that drove me in the past away from PCD to Speaker Workshop first and then xsim.

As Tony said, you should look at the target response in PCD, LR4 for the tweeter and a shallower response for the woofer in order to align the listening axis with the tweeter

Ralf
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Old 21st August 2015, 05:46 PM   #6
keilau is offline keilau  United States
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Tony and Ralf, thank you both for the comments.

I am at work now. I will digest them more tonight before replying.

I asked pointed questions to learn. I hope that you will not take it as argumentative.

One of the thing that I would like to improve on is the BSC for the woofer.
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Old 22nd August 2015, 01:08 AM   #7
Zuhl is offline Zuhl  England
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I hope you don't mind but I've just done a sim with these drivers. I like to use as few components as I can get away with and came up with this:

Click the image to open in full size.

Frequency response:

Click the image to open in full size.

Reverse null:
Click the image to open in full size.
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Old 22nd August 2015, 03:29 AM   #8
keilau is offline keilau  United States
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Quote:
Originally Posted by giralfino View Post
No. He used the RLC network to flatten the response between 500Hz and 1KHz, and a RC network to tame the breakup (in parallel to the main coil). This second network cannot be simulated in PCD, something that drove me in the past away from PCD to Speaker Workshop first and then xsim.

Ralf
I stand corrected. I used the RL network (0.9 mh and 3 ohm parallel) for BSC to tame the rising bump between 500 Hz and 1 KHz. It is connected in series to the woofer. It seems to achieve what I want. I pad the tweeter to match the level. The price for this flat frequency response is a lower efficiency.

The RLC network that Troels used in the "Studio-101" had a narrower dip around 500 Hz. How do I tailor it for my crossover if I want to use it to replace my current series RL network?

I have the RC zobel network too which seems to do a good job flatening the impedance at higher frequency. It smooths out the response at the crossover point. The PCD seem to simulate it quite well.
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Old 22nd August 2015, 04:56 AM   #9
keilau is offline keilau  United States
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Quote:
Originally Posted by Zuhl View Post
I hope you don't mind but I've just done a sim with these drivers. I like to use as few components as I can get away with and came up with this:
Zuhl, thank you for taking the time to do the simulation.

I started out with something very, very similar to what you did. The simulation looked very smooth and the efficiency was high. But it sounded too forward for my taste.

After some more research, I found out that I need to account for the baffle step effect. I used Bagby's "Response Modeler" to do that and created the minimum phase FRD/ZMA. Once I did that, the bump around 1-2 KHz became obvious and explained the forward sounding result.

The posted crossover is my third iteration that include a BSC network and the tweeter is pad down more to match. I like the sound ok. Some comments still think that I may have a forwarded sound. I am all ears for suggestion.

Where did you get the driver character files? What did you use for the simulation? Unless we can afford custom made drivers like the big high end manufacturer, otherwise, the crossover is necessary to have compensation network(s) to account for the driver issues.

Last edited by keilau; 22nd August 2015 at 04:59 AM.
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Old 22nd August 2015, 08:48 AM   #10
Zuhl is offline Zuhl  England
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I use X-Sim for the simulation - great piece of software. I have a collection of driver files I use for sims.

If you have a forward mid then you need to increase baffle step. Sims are fine but you usually find in room tweaks necessary to get a sound you prefer and to adjust for any room acoustics. The final step should always be listening to music; though here you can get berated for suggesting such

Here is L1 at 2.0mH:

Click the image to open in full size.

Here is L1 at 2.5mH:
Click the image to open in full size.

You could also increse the size of R1 if the top end became too bright as a result of changing L1.

I like what I see of that Peerless mid/bass - I may be tempted by it myself. I'd probably mate it with something like a SEAS 27TFFC though. I don't much like the look of that Dayton response.
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