Pushing a horn: how to measure (with an UMIK1).

[Droogne]

I recently finished building my horn-loaded cab (see pics below, dont mention all the dust and the weird positioning for now). I also got my UMIK-1 in the mail (what a great day). The builder of the horn tells me it only goes down to 30hz when pushed with EQ, and a decent mic to test. But how do I do this? I have a DCX2496 to do the equalising (or my Audyssey software in my Marantz SR7011 if that suffices). How do I know, beyond what I can hear, if I'm pushing it too low? I'm only listening at very moderate levels (for now) so 80-90db goal for now. I'm using REW for measuring, and I see it has a "subwoofer" EQ option. Is there maybe something better? And if not, how do I use this to get best results? 

 

Also, what tests could I do with this kind of gear to get the best sound from this sub? Can I use it to measure best positioning etc? 

[Ukko Kari]

Typically, horns with short path lengths are used in multiples, to extend the low frequency capability, when tightly packed.

This appears to be a front loaded horn, which below the corner where the horn is effective, is still an 18" woofer in a small sealed box, so you can apply a modest bit of eq to boost the bottom end, but will have to keep in mind the short throw of the driver. I would only recommend doing so in a domestic environment like yours, not in a dance club or other pro use.

With REW, you can play a sweep through the subwoofer from say 25 hz to 200 hz, and look at the response. I am not familiar with the UMIK-1 mic and interface, other than having read of the possibility of clipping the signal with high sound pressure level. This is dependent on the dip switch settings inside the mic on the preamp board.

http://www.avsforum.com/forum/155-diy-speakers-subs/1797489-massively-clipped-umik-1-a.html

People have received the UMIK-1 with different dip switch settings, both 12 db and 18 db.

If you do not have a sound pressure level meter, you could likely use an application with a smartphone to set the level to calibrate the level with pink noise in REW before making a sweep.

Start by measuring the time delay of the subwoofer, you will need that to tell the Marantz to delay all other channels with respect to the bass horn.

 

 

[Droogne]

32 minutes ago, Ukko Kari said:

Typically, horns with short path lengths are used in multiples, to extend the low frequency capability, when tightly packed.

This appears to be a front loaded horn, which below the corner where the horn is effective, is still an 18" woofer in a small sealed box, so you can apply a modest bit of eq to boost the bottom end, but will have to keep in mind the short throw of the driver. I would only recommend doing so in a domestic environment like yours, not in a dance club or other pro use.

Yeah, I do plan on using it in bigger situations (festival etc), but not with this kind of EQ. This is only for moderate levels, and a temporary situation too till I get my sub 35hz subs.

32 minutes ago, Ukko Kari said:

With REW, you can play a sweep through the subwoofer from say 25 hz to 200 hz, and look at the response. I am not familiar with the UMIK-1 mic and interface, other than having read of the possibility of clipping the signal with high sound pressure level. This is dependent on the dip switch settings inside the mic on the preamp board.

http://www.avsforum.com/forum/155-diy-speakers-subs/1797489-massively-clipped-umik-1-a.html

People have received the UMIK-1 with different dip switch settings, both 12 db and 18 db.

If you do not have a sound pressure level meter, you could likely use an application with a smartphone to set the level to calibrate the level with pink noise in REW before making a sweep.

Ok, will try that !

32 minutes ago, Ukko Kari said:

Start by measuring the time delay of the subwoofer, you will need that to tell the Marantz to delay all other channels with respect to the bass horn

Doesnt the marantz have time delay functions? Also, more importantly. How do I measure the time delay in REW?

[Ukko Kari]

Good question, with my duplex sound card, I use a loopback cable, in essence, returning the output of the sound card to the input. The software calculates the round trip latency and deducts that from the signal arriving from the microphone input, thus giving you your delay measurement. On one channel, the microphone is connected, on the other, the loopback cable.

Alternately, REW can use a high frequency device to calculate delay. This requires the sweep to be set full range, and it will listen for the high frequency chirp before the measurement. ( Typically only used for full range loudspeakers )

Yes your Marantz has time delay functionality. I am not familiar with Audessey products, and if utilizing it will give you an appropriate delay. Someone more familiar may be able to help you out in this regard.

Since the UMIK-1 is a USB device with no other input, you could add a second sound card with just a loop back cable in order to have REW calculate the time delay. In the drop down menus in REW, you have the option of telling the software what inputs and outputs you would like to use.

Hope that helps you.

[Ukko Kari]

Also of note, you must ensure that the settings in Windows ( I assume you are using Windows, not Mac or Linux ) match those set in REW ( 2 channel, 44.1 khz ) as these can be set differently, and your results can be wonky.

Every time I use REW, I have to change the settings for Windows under the sound device.

[Droogne]

47 minutes ago, Ukko Kari said:

Also of note, you must ensure that the settings in Windows ( I assume you are using Windows, not Mac or Linux ) match those set in REW ( 2 channel, 44.1 khz ) as these can be set differently, and your results can be wonky.

Every time I use REW, I have to change the settings for Windows under the sound device.

Good call! Did not think about that (I doubt they are the same so it's good you mention it).

[SME]

I have experience with Audyssey, and while one of its key features is automatic setup of delays, my experience is that this function performs very poorly.  When using Audyssey, I almost always achieved better results by manually adjusting the distances from what Audyssey gave.

I also do not like how Audyssey re-shapes frequency response.  It aims for a flat in-room target, which leads to a poor tonal balance including thin sound and weak bass.

Setting distance for the sub optimally can be a bit tricky, but measurements are your friend.  Do you have a good tripod for the measurement mic?  I strongly recommend investing in one.  Setup the tripod and mic at ear-level at the MLP and then run a series of sweeps, varying the sub delay/distance around 1 ms with each sweep.  Look for the delay that gives you the smoothest frequency response around the crossover frequency that you choose.  Once you've found the best distance, you can also try to incrementally adjust the crossover for an even smoother response.  Note that the optimal delay may also vary depending on the crossover.

[Droogne]

30 minutes ago, SME said:

I have experience with Audyssey, and while one of its key features is automatic setup of delays, my experience is that this function performs very poorly.  When using Audyssey, I almost always achieved better results by manually adjusting the distances from what Audyssey gave.

Will probably end up doing that for the moment, and get into some more precise methods after my exams. 

30 minutes ago, SME said:

I also do not like how Audyssey re-shapes frequency response.  It aims for a flat in-room target, which leads to a poor tonal balance including thin sound and weak bass.

What do you recommend I do? reset everything and do it all manually? I'm definitely up for that, but might need some experience first with some more straight forward projects. EQing my Klipsch LaScala tomorrow (with help from a Klipsch forum member). 

30 minutes ago, SME said:

Setting distance for the sub optimally can be a bit tricky, but measurements are your friend.  Do you have a good tripod for the measurement mic?  I strongly recommend investing in one. 

I don't have a tripod, but I do have a speaker stand that is unused and can easily function as a tripod (it has adjustable height).

30 minutes ago, SME said:

Setup the tripod and mic at ear-level at the MLP and then run a series of sweeps, varying the sub delay/distance around 1 ms with each sweep.  Look for the delay that gives you the smoothest frequency response around the crossover frequency that you choose.  Once you've found the best distance, you can also try to incrementally adjust the crossover for an even smoother response.  Note that the optimal delay may also vary depending on the crossover.

Could you maybe explain why time delay will result in a flatter response? Are you  talking about a full range sweep (where the delayed sub frequencies will arrive at the same time as the main speakers higher frequencies?)

[SME]

9 minutes ago, Droogne said:

What do you recommend I do? reset everything and do it all manually? I'm definitely up for that, but might need some experience first with some more straight forward projects. EQing my Klipsch LaScala tomorrow (with help from a Klipsch forum member). 

Yeah, manual is best.  IF you are going to EQ the LaScala by hand, that's still more reason to not use Audyssey because it will basically undo much of your work.

And yes, there is quite a learning curve for doing it manually, but I'd argue it's well worth it.  IMO, the performance of good equipment is held back considerably without good configuration.

14 minutes ago, Droogne said:

I don't have a tripod, but I do have a speaker stand that is unused and can easily function as a tripod (it has adjustable height).

The speaker stand may be OK for sub measurement, provided it holds the mic well in an upright position.  However, the tripod with boom arm is best because anything near the mic influences the measurement, especially with high frequencies.

16 minutes ago, Droogne said:

Could you maybe explain why time delay will result in a flatter response? Are you  talking about a full range sweep (where the delayed sub frequencies will arrive at the same time as the main speakers higher frequencies?)

In the crossover region, you have two transducers in different locations producing sound.  If the sound from each source arrives at different times, then there will be frequency-dependent phase shift between them.  The phase shift will cause them to not combine coherently at all frequencies.  You don't need to do a full-range sweep, but your sweep should cover at least 1 to 1.5 octaves above and below the crossover point.  It's helpful to label each sweep with the distance and/or crossover point you used and view them all together to compare.

[Droogne]

10 minutes ago, SME said:

Yeah, manual is best.  IF you are going to EQ the LaScala by hand, that's still more reason to not use Audyssey because it will basically undo much of your work.

Aight, as I'm little time restricted (but still want to EQ the LaScala as it is distracting me ), I'll probably run Audyssey, take notes of what it measured, reset everything and manually insert the distances (from the measurement). I can then maybe adjust those distances, but guess it will suffice for now right? Db levels I can easily match by ear (as I always change it after Audyssey as I'm never happy with how it turns out). 

10 minutes ago, SME said:

And yes, there is quite a learning curve for doing it manually, but I'd argue it's well worth it.  IMO, the performance of good equipment is held back considerably without good configuration.

I'm only 22, so time enough to learn  I like it a lot! Before this I was a diehard tv-show bingewatcher, but I have now transitioned from quantity to quality by investing in the top-of the line gear (for a non-working student). 

10 minutes ago, SME said:

The speaker stand may be OK for sub measurement, provided it holds the mic well in an upright position.  However, the tripod with boom arm is best because anything near the mic influences the measurement, especially with high frequencies.

It is in a pretty good position, the UMIK-1 has a little tripod itself, which sits on the speaker stand. (will snap a pic in half an hour).  Will probably invest in a dedicated tripod though. 

10 minutes ago, SME said:

In the crossover region, you have two transducers in different locations producing sound.  If the sound from each source arrives at different times, then there will be frequency-dependent phase shift between them.  The phase shift will cause them to not combine coherently at all frequencies.  You don't need to do a full-range sweep, but your sweep should cover at least 1 to 1.5 octaves above and below the crossover point.  It's helpful to label each sweep with the distance and/or crossover point you used and view them all together to compare.

Ok, that makes a lot of sense, thanks! Seems like a solid way to go about it. 

[Ukko Kari]

I concur, a boom mic stand is a solid investment when it comes to measurement gear. Here is an example from Amazon:

https://www.amazon.com/AmazonBasics-Tripod-Boom-Microphone-Stand/dp/B019NY2PKG/ref=sr_1_3?s=musical-instruments&ie=UTF8&qid=1513464419&sr=1-3&keywords=boom+mic+stand

I am sure you should be able to source one locally similar to the example. It does not need to be a heavy duty model, and the slimmer the better. ( you do not want reflections from the mic stand to reach the mic capsule )