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Reckhorn Mini-Sub
Reckhorn Mini-Sub
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Old 1st October 2017, 02:30 PM   #1
Baldin is offline Baldin  Denmark
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Default Reckhorn Mini-Sub

Just got myself a Reckhorn D-165 and 2 x P-6.5 passive units.
- Home Hifi: digitale / aktive 3 wege Frequenzweiche, Subwooferverstarker, Eckhorn Subwoofer, Korperschallwandler, Bass Shaker, Standlautsprecher und Satelliten Hifi Kugellautsprecher Boxen fur Ihre Heimkinoanlage. Auto Lautsprecher und Alubutyl finden S"

Amazing build quality for the D-165 ... 30 ?!
Fast delivery and nicely packed ... good job Reckhorn

The passives are not as impressive and quite flimsy. Seem the suspension is somewhat more soft than the D-165 .. giving a lowe Fs. Comes with 3 small discs to add weight to the 20g alu cone.

Plan is to build a small active sub in a box of 11 - 15 liter.
I'm thinking AceBass, a small inexpensive but good class-d and a SMPS.

Just ran the bass on my Dayton DATS v2, and the parameters given by Reckhorn seem to be ok. Need to burn in the unit before they reach the right parameters of course.

But how to measure the passive??
Any good ideas??

Reckhorn can not provide the relevant data effective Sd, Vas, Qm and Fs.
Sd can be estimated, measuring the diameter including half of the surround.

Cms can probably be found by adding weight and measuring how far the cone moves ......

Any more ideas or experience?

/Baldin
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Old 6th October 2017, 04:26 PM   #2
Baldin is offline Baldin  Denmark
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D-165 Sub now mounted in a in a 11 liter box with vented tuning at 25 Hz.
Works as a charm and seem to go as low as advertised

50W amp mounted right now.

Does anyon have distortion measurements for the D-165 unit??
Maybe someone has the Hobby HiFi 4/2016 magazine where it was used for a similar sub .... Would like to see this.

Wondering whether it could also be used for a small 2 or 2 way speaker, e.g. with a good dome in a waveguide crossed at say 1 - 1.5kHz
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Old 28th October 2017, 11:12 AM   #3
Baldin is offline Baldin  Denmark
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Not much interest for this project I can see

But I can say I'm quite impressed by the performance of thses drivers stil.

I have no build a 10 l box and mounted the 2 passive and the one D-165.
Both the active driver and the two passives need some more time to soften up the surround and reach stable T/S parameters.

The passives for sure need more added weight to get down to the right system Fs of ca 25 Hz I'm aiming for.

The Fs now is in the range of 39 Hz. This sounds "impressevie" but is not neerly deep enough.

But output is quite impressive with ca 50W in.

Tried to make AceBass work with the class d amp, but I need to do more develoopment for it to work, as this added loop turned out to become the controlling loop of the self orcillating amp, raising the sc freq from 250 to 500 kHz ..... not intended. So need to figure out how to avoid this.

So I have made a schematics for a small preamp, giving some 4 db lift at 25 Hz and with variable low pass (40 -160Hz). Both lowpass and high pass is 2. order.
Have ordered PCBs and chose to use through hole components so that enyone will be able to do the soldering. Will make the gerber files available, when I have tested it.

Stay tuned
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Last edited by Baldin; 28th October 2017 at 11:21 AM.
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Old 28th October 2017, 03:40 PM   #4
Zero D is offline Zero D  United Kingdom
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Hi & Thanx for the info etc & update

I've been interested in AceBass for years ! Always wanted to build a circuit. With your plans etc, i hope to get round to doing it, sooner rather than later

Keep us posted
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Old 28th October 2017, 11:43 PM   #5
Brian Steele is offline Brian Steele  Grenada
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Let's see some linearity and distortion tests.

REW and a decent mike should be enough to accomplish this.

BTW, the driver looks good, but those PRs? Pegging the Bugly Meter. I'd buy some 4" dust caps and stick them on, after I've adjusted their weight to get the Fb that I want, of course.
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Old 5th November 2017, 05:41 PM   #6
Baldin is offline Baldin  Denmark
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Update:

Been playing with my mini sub.
It takes nothing less than 190 g of added weight to each passive to get the fs down to 26 Hz!
And the passive units are not really build for that. They sag/tilt quite a lot, due to only having the rubber surround and no spider!
I'm thinking of making a kind of thread suspension (a la Duelund) to level it out.

From trials with 3 different weight adding, and comparing a measured impedance with simulation in WinISD, I find the parameters for the passives to be something like this:
Vas = 70 l
Qms = 2,8
Fs =15 Hz (without any added weight)
Sd = 150 cm2

This is not exact at all, but I think near enough to do some more simulations.

It is clear that one passive is not enough at all, no surprise and why I bought 2 in the first place.
If you did anyway, using a box of 1 liter, you would get a very good response down to 25 Hz, but the passive would bottom out at something like 90 db @ 25 Hz.
In comparrison, the D-165 in a vented box of 15 liter, tuned to 25 Hz will do almost 96 db @ 25 Hz.
But you will also have to find room for a good sized port adding to the volume!

I think the best results will be to put 2 x D-165 in a 30 liter box with a port of 6 cm diameter and 40 cm long. Either as a sub or as the bottom of a 2,5 or a 3,5 way system (you need to cut one at around 100 Hz to level out the response.

But as said I'll try to make a threaded spider to hold the weight, and see how that works out.
Stay tuned
/Baldin
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Old 11th November 2017, 10:50 AM   #7
Baldin is offline Baldin  Denmark
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Ok, I found that I actually had the Hobby HiFi 6/2015 in my pile of magazines

The D-165 is tested and described on page 61, among a number of other 6.5" mid-woofers.

I'm not sure how Reckhorn did their test to come up with the freq response found on their web page, because the measurement done by Hobby HiFi is much different!

From the measurement it is quite clear that the unit will not work as a mid-woofer, as it start to roll of already from 200 Hz. If you look at the Le given at 1,195 mH, that should not come as a surprise at all, and used as a sub unit or as a low end woofer in a 3 way, this is no problem at all.
But curiously, Hobby HiFi measures Le at 1,9 mH .... I just did a measurement on my
unit and it says 1,1 mH .... so maybe the driver has been improved since 2015?!?!
Ok, will have to do measurements my self

On the bright side, it is also clear that the unit has very good distortion levels in the sub region, only rivaled by much much more expensive drivers. And the dirver just have really compelling T/S parameters.

So if not used as a small sub, for which it is excellent, I'm thinking that a 3 way with 2 x D-165 (Xover quite low ... like 200-300 Hz), a good 5" and a tweeter would be a killer speeker. Ultra low extension and a small overall box of say 30 l.
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Old 30th November 2017, 02:20 PM   #8
grahamgraham is offline grahamgraham  United Kingdom
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Hi! I am very interested in this sub. Maybe to make two 2 driver cabinets for my front room. Would these be suitable in two banks of two for home theatre and music? A medium/large size front room.

Also, do you have any of the designs from the hobby hifi you could share with me please. These drivers seem too good to be true for the price and availability. Let me know if you have any more design info, please!
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Old 2nd December 2017, 09:14 AM   #9
Baldin is offline Baldin  Denmark
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Hi graham

The D-165 is for sure impressive especially compared to price.
2 x D-165 in 22 l tuned to 25 Hz, and given a 3 db lift at 25 Hz would do great.
But all things being relative, this is no 18" and for serious home theather use you will be better of going for e.g. some 12". Right now I have 3 x 12" + 4 x 8" in the main front speakers .... and I am considering a few more

For my use as a sub for my PC, the Reckhorn is a real performer.

I'm not so impressed with the passive units though. To reach down towards 25 Hz in a 10 l box you'll need an addition of 200 g to each. This is quite a lot and especially with this passive which have no spider.
I hope I'll have time tomorrow to make a kind of spider for it and see how this works.

Also have received PCBs for my small preamp .... stay tuned
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Old 3rd December 2017, 08:41 AM   #10
grahamgraham is offline grahamgraham  United Kingdom
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Hi! Interesting, thanks! I modelled your suggestion and it looks fairly smooth. But I think you're right. I went with two Tang Band 6.5" for this application but I am really interested in this unit for a build I will be doing for a friend where cost restraints are harsh and their living space is tiny.

Yes, keep us updated on your project!
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