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Back chamber effect (Oris Horns)

by Rudy81 @, Dallas, TX, Thursday, February 21, 2013, 21:37 (1705 days ago)

While setting my new Oris 150s up today I decided to see if there was any measurable effect on response with the chamber cover removed vs. installed. I believe Bert indicated that LF would be enhanced with the back installed. Here are my results with the Tang Band 1800 driver, calibrated mic and soundcard, using REW 5.

BTW, the crossover is set up to cross at 153Hz, so you see an early roll off due to the crossover.

The green line is the back cover installed.

Bert, Thank you for all your help. I have not finished the setup, but thus far these are everything I wanted!

[image]

Back chamber effect

by Gasper @, Friday, February 22, 2013, 08:37 (1705 days ago) @ Rudy81

Hi Rudy,

I am so pleased that you show the measurements. I am also using Oris150/DX3 combination.

Did you measure Oris150 without or with crossover set at 150 Hz or you use this crossover on woofer?

Thank you very much!

Regards,

Gasper.

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Back chamber effect

by Rudy81 @, Dallas, TX, Friday, February 22, 2013, 14:42 (1705 days ago) @ Gasper

Gasper,

The measurement was taken indoors. I had wanted to test only the Oris outside to reduce room reflections, but that was not possible. The plot I posted was taken with a Tascam calibrated audio card, a Behringer calibrated mic, the Tang Band 1800 driver AND an Ashly crossover. The crossover was set at 153Hz, but the woofers were muted, so they are not part of the results. The plot does roll off early from what I believe the Oris can do due to the crossover.

The objective was simply to compare the results of the back chamber open vs. cover installed.

Soon, I hope to take the horn outside and take a full spectrum sweep to see what it can really do.

This is what I was able to achieve in my room. I have a Klipsch RSW-15 (passive) subwoofer from 20-60Hz, a ported, double 15" bass bin from 60-153Hz and the Oris from 153Hz-20kHz.

This plot is raw, unsmoothed and of course shows quite a bit of room interference. However, this is the best plot I have seen in my room with any of my setups. I also use Audyssey Pro to calibrate the entire speaker array. However, this plot was taken prior to Audyssey Pro calibration and without any EQ. I only completed set up last night, and so far this setup sounds fantastic.


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Back chamber effect

by Gasper @, Friday, February 22, 2013, 16:08 (1705 days ago) @ Rudy81

Hi Rudy,

Thank you very much. I was asking you because I use Oris150 with REF2010/bd15/bd30/Reckhorn S1 combination and AR Chronos W38 sub. I am using sub from 16-50Hz, REF2010 from 50-300Hz and Oris150 fullrange. I am trying to set the system properlly but I think I have to borrow the omnimic from a friend and made some testings to set all thinks right.

Thank you VERY MUCH for the replay and if you have any suggestion please let me know.

With best regards,

Gasper.

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Back chamber effect

by Rudy81 @, Dallas, TX, Friday, February 22, 2013, 16:52 (1705 days ago) @ Gasper

Gasper,

Your comments have really piqued my interest in finding out what the horn alone can really do. I am going to bring one down from my listening room and take it outside to try and get a semi-anechoic measurement.

You say you run the 150 full range. Does that not stress your driver when trying to go well below 100Hz or so? I am curious as to what the driver can really handle. In terms of the Tang Band, the manufacturer says it is capable of 45Hz to 20kHz. I plan on running my test from 45Hz to 20kHz. I will be using my Behringer calibrated mic, although it is not an expensive piece, it should give us a reasonable response. The Tascam audio card will be attached to my laptop via USB and REW will interpret the results.

I will post the results later today.

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Back chamber effect

by Rudy81 @, Dallas, TX, Friday, February 22, 2013, 19:01 (1705 days ago) @ Rudy81
edited by Rudy81, Friday, February 22, 2013, 19:06

Gasper,
Here is the result of the Oris 150, Tang Band 1800 driver, taken outdoors. I don't claim this to be a truly scientific test by any stretch. It just gives me a very basic idea of what the horn and driver are doing. The graph is totally raw, no smoothing or changes to the result.

Overall, I'm really impressed by what the horn and driver can do by themselves, with no EQ, or other compensation. I ran the test from 50Hz on up since the driver is rated down to 45Hz and I didn't want to chance any damage since they are new.

[image]

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Back chamber effect

by Rudy81 @, Dallas, TX, Friday, February 22, 2013, 19:02 (1705 days ago) @ Rudy81

Here is the waterfall for that reading.

[image]

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Back chamber effect

by Rudy81 @, Dallas, TX, Friday, February 22, 2013, 19:03 (1705 days ago) @ Rudy81

Here is the spectrogram, and of course the HF response is mostly due to the driver and not the horn.
[image]

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Back chamber effect

by Rudy81 @, Dallas, TX, Friday, February 22, 2013, 19:05 (1705 days ago) @ Rudy81

Since I had already set everything up, I took some rough off axis measurements just for fun. Again, not scientific, but just an idea of performance.

If anyone has access to an anechoic chamber and has run measurements with other drivers, I would love to see some more precise measurements.

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Back chamber effect

by Gasper @, Friday, February 22, 2013, 22:36 (1704 days ago) @ Rudy81

SO MANY THANKS!!!

This give me a start to begin with set up!

Regards,

Gasper.

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Back chamber effect

by Rudy81 @, Dallas, TX, Friday, February 22, 2013, 23:10 (1704 days ago) @ Gasper

Good luck with your setup. You certainly have everything you need for some great sound.

Enjoy!

Back chamber effect

by Ivo, Saturday, March 02, 2013, 16:53 (1697 days ago) @ Rudy81

That's a nice off-axis response! Clearly a very good combination between horn and driver.

Ivo

Back chamber effect

by Don Reid, Rural Northwest Georgia, USA, Saturday, March 02, 2013, 05:58 (1697 days ago) @ Rudy81

Gentlemen, I really enjoyed your exchange regarding the back chamber covers on Oris 150s. I too have Oris 150s which I drive with an AER MD3 drivers. I have also used the Lowther PM4s with AER diaphragms. My experience might not be relevant to you because my application is different from either of yours in that I use digital crossovers with very steep rolloffs of 96dB/octave for both high pass and low pass with nominal 160Hz and 7kHz crossover points in a triamplified set-up with bullet tweeters and corner horn bass cabinets. Maximum bass extension wasn't a big concern to me with this arrangment.

What prompted me write is to mention that instead of leaving the back chamber covers on or off I settled on a third alternative which I have now been using for years. When I listened to the Oris with back covers on and then with them off I heard characteristics I liked and others I disliked with both arrangments. Just as an experiment I made two new back covers from high density wool felt 19 mm thick. I cut a circular hole in each felt cover. The holes were arbitrarily cut the same diameter as the ports in the back chamber covers which came with the horns. I really liked what I heard with the felt covers. The sound had a smoothness, control and very pleasing realistic quality that I hadn't heard before.

I assumed at that time that I would keep experimenting with other sorts of back covers, but I have been pleased enough with the sound that eight years later the same felt covers still cover the back chambers.

Back chamber effect

by Gasper @, Saturday, March 02, 2013, 07:10 (1697 days ago) @ Don Reid

Hi Don,

I have similar experiance. I have to use Bert's original setup at first with thin MDF plate and bass reflex ports. Than I removed the ports and wooden plate and the sound became more opened, relaxed and smoother. Since than I use just the dampig material itself.

Best regards,

Gasper.

Back chamber effect

by fu_man @, Saturday, March 02, 2013, 10:27 (1697 days ago) @ Don Reid

HHmm interesting, I have friend who run his horns with no back and just a wool blanket over the back (with Lowether PM2's i think.
Don, IIRC you are using DEQX right? Thanks for describing your setup. Did you play around with the high pass frequency much?

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Back chamber effect

by Rudy81 @, Dallas, TX, Saturday, March 02, 2013, 15:17 (1697 days ago) @ fu_man

Very interesting idea on just using the felt covers. Once I finish my setup, I might try the changes. In my case, I too use a tri-amped system with a 48dB L-R electronic crossover. Bass performance below the crossover is not an issue for me either as my other speaker components are a dual 15" ported enclosure and a modified Klipsch RSW-15 subwoofer.

However, I would like to see optimum response at the horn crossover point.

What crossover points are you gents using?

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Back chamber effect

by Bert @, Saturday, March 02, 2013, 18:47 (1697 days ago) @ Rudy81

Hi Rudy,

Your horn/river combo shows a relative strong boost in the lower midrange. I would compensate that with a 6dB crossover set at around 500Hz and another 6dB stage around 150Hz. This will smoothen the overall response and gives a good 180Hz crossover point to match for your bass.

Just play around with some values, see what is happening and respond to that.

Measure further away from the horn mouth though (minimal the diameter itself), the extra energy measured closer to the mouth is misleading.

Cheers,

Bert

--
BD-Design - Only the Best!

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Back chamber effect

by Rudy81 @, Dallas, TX, Sunday, March 03, 2013, 14:31 (1696 days ago) @ Bert

Bert,
I'm not sure what you mean by a XO at 500Hz? My XOs are LR 48dB set at 80Hz for the sub to LF bin and 190Hz LF bin to Oris. What am I missing here?

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Back chamber effect

by Bert @, Monday, March 04, 2013, 10:11 (1695 days ago) @ Rudy81

What am I missing here?

It is about the result of the total concept (all parts connected) that matters. A theoretical crossover set to whatever value is pointless unless the driver combo is at least 2 octaves below and above the desired crossover frequency linear.

Try to give the horn/driver the full signal and aplly a capacitor in series with the combo and see what happens. If it rolls of too soon or not enough then try another value which comes closer. Next is to add a coil to make the slope steeper if needed and so forth...

Bert

--
BD-Design - Only the Best!

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Back chamber effect

by Rudy81 @, Dallas, TX, Monday, March 04, 2013, 15:21 (1695 days ago) @ Bert

Bert,

Part of the issue with those readings is that they were taken indoors and I did not gate the response before posting, so room modes and effects are part of that plot.

I did take the horns outside to do a more accurate reading. Unfortunately, I was not able to remove the back covers to take a reading with the cover removed for comparison. If you know of some trick to easily remove the back cover, let me know.

Also, in my case, I use Audyssey Pro on my entire system to smooth the response of all my speakers, so individually trying to EQ a given speaker is not necessary.

Back chamber effect

by Don Reid, Rural Northwest Georgia, USA, Friday, March 08, 2013, 04:11 (1691 days ago) @ fu_man

Hi Fu_man,

Sorry to be slow to reply.

Yes the DSP unit I am using is the DEQX HDP-3. It is a digital crossover, phase and time correction, speaker correction, room correction, etc. component. It is a substantial upgrade over the DEQX PDC-2.6 I was initially using.

The bullet tweeters I am using are Fostex T-900a. The minimum crossover frequency Fostex recommends for this driver is 7 kHz. After studying Fostex published frequency response curves for the t900a I decided to not go below 7kHz despite the steep 96dB/8vo rolloffs. One reason for this is that I like things I build to be really reliable and trouble free. No blown tweeters for me. I tried higher nominal crossovers but I liked 7kHz best.

I know that for purists such as Bert and probably most of the members of this forum think using a DSP device such as the DEQX is a sin and a destroyer of good sound. I beg to differ.

Back chamber effect

by fu_man @, Friday, March 08, 2013, 13:22 (1691 days ago) @ Don Reid

I know that for purists such as Bert and probably most of the members of this forum think using a DSP device such as the DEQX is a sin and a destroyer of good sound. I beg to differ.

heh heh, thanks for your reply and good on you! I'm sure they don’t think it's sin... they simply don't agree and share their opinions about it (being a destroyer of good sound!) And our gracious host Bert certainly has lots of opinions...for which I am always so grateful that he shares so generously here. I admire the way he works away developing new ideas then shares them so ridiculously freely. He is magnificent!

Now, I am particularly interested in your views on the DEQX... as I am also a DEQX owner! Except that I pretty much gave up on it! Not because it destroyed the sound or anything like that... i just found it too hard to work out how to use the bloody thing! Actually I still really liked it as my DAC.
I know the assistance with set up is far better these days and I'm fairly confidant I could get a lot further with it if i tried again. However right now my hifi is decommissioned. For me, listening to music is far too much of a solitary pursuit at the moment while i have a young family.

I'm still keeping my horns though and one day, maybe soon i'll be back getting the gear going again.
Hhmmm ...maybe a floor space infinite baffle project..?


PS sorry all for not keeping on topic.

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