Announcing the DIYRM-B...and a request for input on the DIYRM-C - diyAudio
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Old 24th December 2015, 12:09 AM   #1
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Default Announcing the DIYRM-B...and a request for input on the DIYRM-C

Alright…so here’s the long coming followup design to my DIYRM-A design. Again an LS3/5a sized speaker, same basic construction but with a different tweeter, crossover and no need to modify the woofer. It uses the same woofer and substitutes the Tymphany H26TG45-06 tweeter for the Dayton Reference tweeter.

I’ve updated my design document, which now clocks in at 78 some odd pages….and 13,000 words. It can be found here: https://goo.gl/MXdhXl There’s now more than 65 figures, pictures, schematics and diagrams included.

To summarize the two:

DIYRM-A…..An update to the classic British mini-monitor, meant to be placed near a room boundary (put it within a few inches of the back wall). Should be listened in the nearfield (less than 5 feet) though has pleasing sound all over in many situations and can be used to fill a room with moderate volume full(ish) range sound. Stunning balance, detail and finesse. A bit tricky to build.

DIYRM-B…..Uses the same woofer, box and overall construction methods as the DIYRMA. Simplified grill/baffle construction, no need for a modification of the woofer. This is a time aligned monitor, capable of reproducing a square wave acoustically at a fixed point in space. These speakers should be used in music production applications or small office/dedicated music listening applications where the user can be at a fixed point at all times. If used for room filling/background music applications, may sound a bit off balance depending on use and placement. Overall…a bit finicky compared to the DIYRM-A. In the right application, it can exceed the performance of the DIYRM-A.

Total parts cost (drivers and crossover) should be in the $380-$400 range depending what pieces you already have in your shop. I made this set with leftover lumber from the DIYRM-A.

Next up is a question of DIYRM-C. I’ve got several ideas that have been percolating. I’m done with the two way bookshelf/mini-monitor concept for now, I’ll revisit it again I’m sure…but not for a while.

So I’m asking for input, what would you like to see? What area of speakers are there that are underserved for the DIY’er. I’ve got a couple of ideas…

Idea Number 1: An update on the grand monitor speakers of the late 70’s and early 80’s. Usually a JBL but occasionally an Altec. This style is seeing a bit of a resurgence due to the tireless work of Kenrick Sound out of Japan. Size and output wise, think JBL 4331/4333B or Altec 846B. This one would likely have the Dayton Pro PA 15” woofer (stamped frame), custom mid horn (think Edgar Horn) midrange and LTH102/PRV D290. They would be built in mirror image pairs….and construction would be complex. The horn alone will likely require a band saw, table saw and quite a bit of patience. The midrange horn might be loaded with a Dayton PA130…but there are several possible options here.

Idea Number 2: A Klipsch Heresy sized two way…using the same LTH102/PRV D290 tweeter as above, and likely a FaitalPRO 12FH530 woofer. Same sized enclosure, but a two way design, vented, and wider bandwidth. I looked high and low for commonly available (Crites doesn’t count) speakers for a sealed enclosure…but didn’t like my options. Frankly you have to use what’s available to you and I’ve used a neo FaitalPRO woofer quite happily before. The shorting ring magnet design and high output potential are intriguing on this one.

Idea Number 3: An update on the classic monitor/subwoofer two enclosure concept…popularized by Wilson. This time without the crushing 2 ohm -50 degree phase angles and a more setup friendly polar response. The drawback again will be construction 4 enclosures….massive complex bracing. I’m curious to use either the SEAS DXT tweeter or SB Acoustics SB29 series tweeters…..so this one has some appeal there.

Other suggestions?

I’m more than willing to discuss other options. At some point I’ll have to call it though…and select one. Since it’s my labor….I get to pick. ;-)

Here’s the catch though….I have too many speakers. (4 sets of bookshelf speakers, 2 sets of synergy horns, smith horn two ways, paraline PA horns....etc...) The DIYRM-C will be for sale….for parts cost + 20% upon completion. The + 20% covers the incidental costs (blade wear and tear, glue, finish and other things that are hard to put a dollar value on.) Depending on the end design choice a local buyer would be preferred. (I’m in Central Texas.)
I love this hobby…but I just can’t keep everything I make. The estimated time to completion is ~6-12 months after the design choice is finalized. I wish it was faster, but I have a full time job, and recently my former foster children have moved back in on a permanent basis, so I’m a parent again…and their needs come first. This is a good deal for someone with a bit of patience and the willingness to do a bit of driving.

The speakers will be sold on a first come first served basis….and once they are gone…they are gone.

Which brings me to my second point.

I have too many speakers. My DIYRM-B are also for sale. $350, + shipping, continental US only please. With the holidays the fastest I could get them boxed up and out the door is probably 2-3 weeks….let me know if you’re interested.

So…what do you have in mind for DIYRM-C?

I've attached a frequency response/phase comparison for DIYRM-A and B, a quick sketch for the various ideas I have....and finally the frequency response of the LTH102/D290 pair since I already own those. (Very good performance on the tweeters/horns for those...)
Attached Images
File Type: jpg DIYRM-C Options.jpg (77.5 KB, 73 views)
File Type: jpg response compare.jpg (485.4 KB, 71 views)
File Type: jpg FR Response.jpg (171.4 KB, 70 views)
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Old 24th December 2015, 12:38 AM   #2
xrk971 is online now xrk971  United States
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Nice work on the transient perfect B! First order XO slopes do have magic in them. I did one recently with a wide band aluminum full range for the tweeter (active XO) here:

FR58EX and AC130F1 micro-FAST

It does square waves too but bass is not as robust as your box. It's tough to do a passive XO to achieve this - kudos!

Click the image to open in full size.

Here is the FR and phase:

Click the image to open in full size.

Do you have a step response of the B?

Here is what mine looks like:

Click the image to open in full size.

The "C" should be waveguide tweeter like B but with a damped tapered TL on woofer to get deep bass sensitivity and good cone control while still keeping group delay low. Kind of like a transient perfect PMC style monitor.

Last edited by xrk971; 24th December 2015 at 12:47 AM.
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Old 24th December 2015, 01:07 AM   #3
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Quote:
Originally Posted by xrk971 View Post
Nice work on the transient perfect B! First order XO slopes do have magic in them. I did one recently with a wide band aluminum full range for the tweeter (active XO) here:

FR58EX and AC130F1 micro-FAST

It does square waves too but bass is not as robust as your box. It's tough to do a passive XO to achieve this - kudos!

Click the image to open in full size.

Here is the FR and phase:

Click the image to open in full size.

Do you have a step response of the B?

Here is what mine looks like:

Click the image to open in full size.

The "C" should be waveguide tweeter like B but with a damped tapered TL on woofer to get deep bass sensitivity and good cone control while still keeping group delay low. Kind of like a transient perfect PMC style monitor.

Hmmm....TL based design...I'd thought of that...I did a couple passes at a TL with the Vifa XT 7" driver...but then they stopped making them, and I shut my company down. I still have 3 of them.....but I want the C to be something people can build with readily available drivers.
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Old 24th December 2015, 01:51 AM   #4
xrk971 is online now xrk971  United States
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Sure, it doesn't take special unobtanium drivers for a TL. In fact, the current RS150P or RS170P may even work. I had great success with a lowly DC150-8. It digs deep like no other 5.25 box I have made before. Check out the performance here on my thread. Basically the C could be similar but with a waveguide and a larger woofer. I can help you model the TL in Akabak of you are interested.

Low-Cost PMC-inspired TL Monitor with DC130A and DC28F

I even designed a quasi transient perfect XO - it would require the tweeter to be in WG though.

Click the image to open in full size.

Here is measured response and phase:
Click the image to open in full size.
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