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Boomer1950

69 yr-old guy needs advice with 1st DIY sub

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Congrats on finishing the build!  It looks real nice under the TV.

I apologize.  I hadn't noticed that the Crown XLS DSP is limits the high pass filter setting to 30 Hz.  Without a high-pass filter (HPF), preferably set a lot lower than 30 Hz (like at 16-20 Hz) heavy bass below the sub's lower limit can cause heavy distortion and damage to the sub over time.  A high-pass filter is generally recommended for vented subs; although yours is tuned low enough that you probably won't encounter issues with most content and don't turn the volume up too much.

One option to allow setting a lower HPF is an external unit from MiniDSP.  I haven't looked at their stuff for a while, but you should be able to get something very capable for ~$100.  In addition to allowing setting of a high pass filter, you can set other EQ which can help you tune the sub for the room.

Either way, I'm glad you are enjoying the new sound.  I'm pretty sure your new sub plays a lot lower and louder than the old one.  :)+

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Thanks, @SME for the kind words. I had planned to buy a Crown XLS amp, but before I bought one, I found a Crown CDi 1000 at a great price.  I have some questions about setting up the DSP correctly.  First question is about High Z & Low Z.  Here is the relevant section of the manual:

Output Mode: The options are:
• 70V (70V/high-Z mode for Ch. 1 or Ch. 2)

• High Z – Channel is configured for 70V/high-Z loads.
(A 70Hz high-pass filter is automatically enabled whenever 70V is on.) It is a 24 dB/octave Linkwitz-Riley filter in the crossover section.

• Low Z – Channel is configured for low-Z loads.

From what I've read "Low Z" would be correct for the 4 ohm (two 2 ohm voice coils wired in series) SQL-15 driver.  Is that right?

I am running it in "Bridge Mode."

My choices for Crossover settings are:

XOV (Crossover): The available crossover frequencies are: OFF, 90 Hz, 100 Hz, 1200 Hz, 1500 Hz, 2000 Hz, 2-CH SUB, CUSTOM.

With my old sub I set the crossover on the sub as high as it would go & let the AV receiver set the crossover.  What do I select as the crossover for the Crown amp?

I set the EQ to "Out" bypassing the EQ.  I set delay to "Off" letting the setup function in the AV receiver set the delay.  

There are options for a "Limiter" setting: OFF, -3dB, -6dB, -12dB. I'm not sure which setting would be best. 

Comments & advice are greatly appreciated.

 

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@Boomer1950Looks like you've done your homework, your driver falls into the low impedance category ("Low Z") and your amp seems to be 2 Ohm stable, which is why you can run it in bridge mode on the 4 Ohm load. You can let your AVR handle crossover and delay as you mentioned. I think the SI driver will be able to handle all that your amp can give, so I'd not bother with the limiter.

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I agree with @peniku8.  The high Z mode is probably for commercial/retail applications where several in-ceiling speakers may be strung together in series for one amp channel.   That makes sense given the 70 Hz high pass filter, which keeps heavy bass from overloading little speakers.

As I noted, you need a HPF down at like 16-20 Hz.  Your sub will probably do just fine without it for most content, but a few movies have strong content at 15 Hz and below which could overwork the sub even at fairly moderate volume.  I suggest being mindful of the situation and if you hear obvious distortion with bass, turn it down.

When you get around to doing measurements, one of the first things you'll want to check is where the tuning frequency is.  One way to do this is to use a tone  generator (like the REW software has), starting at like 25 Hz.  Set the volume so you can see the cone moving, but only just.  You don't want to burn out the coil by running the tones too hot.  Then gradually decrease the frequency and note the excursion.  It might increase a bit, but as you drop the frequency, it should start to decrease until the driver is almost stationary.  Below there, excursion will increase again.  Where the driver moves the least is where the tuning frequency is.  With your design, I expect it to come in roughly in the 18-22 Hz range.

Have you had more time for listening?  Feel free to share your impressions.  :)

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@SMEI've been looking into getting a miniDSP to better fine tune my sub, so your recommendation for a HPF to protect the driver will move that decision along.  I have a tone generating app that I used to do the test you suggested to find the tuning frequency.  It appeared to be about 21-22Hz.  By 18Hz the cone was moving quite a bit again.  I was shooting for 20Hz, so it will be interesting to see what it actually is, when I do measurements with REW.

Listening impressions - During the build I tried to give my wife an idea of what to expect from the new sub. It was always a difficult topic, because I wasn't completely sure what to expect.  But now that it's playing in my living room, the new sounds I'm hearing are a little easier to describe.

Both music & movies are dramatically different.  With music there is a "presence" of bass that can't be ignored.  It's not totally volume, but rather how the bass now seems to fill the room.  As the bass line gets lower there is no obvious reduction of volume which, of course, makes it louder in the lower frequency ranges & that increase in volume comes with an increase in chest-thumping vibrations.  Listening to music is a much more visceral, immersive experience now.  Even at moderate volume the ability of the sub to reach down & hit the lowest notes with authority is impressive.

Movie viewing has been radically changed - especially action movies with Dolby Atmos soundtracks.  However refined & musical it's capable of being, start Mad Max Fury Road & it becomes a sledgehammer - seriously rocking us during explosions.  The ability to reproduce loud explosions, gunshots or car crashes is stunning.  The sub never seems to be pushed anywhere near its limits - even when the soundtrack is as loud as I can stand (the ultimate measurement of the volume capability of your system - it's louder than you can listen to it) .

I don't want to sound too giddy, but I'm more than pleased - I'm thrilled.

 

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A high displacement 15" driver will do very well even at loud levels down to like 20Hz. Since most movies nowadays don't have much content below that point, a single sub like this will do the job very well. When you start with BEQ and you're aiming for a good seat-to-seat variance it starts getting ridiculous, which is why you often see guys at AVS with 4 18" drivers in huge cabs or well.. more than that.

I think that my 2x21" rig is overkill for my use, but better have too much headroom than not enough..! Adding a BOSS riser to the setup (really just a sheet of plywood with two 12" drivers mounted to it, was 30 minutes of work) was the icing on the cake, since I get no low tactile response in my room (all stone and cement).
If you're into "feeling the bass" you might want to look into that. And as I said, since it's basically just a sheet of plywood with two holes in it, it wouldn't steal much of your time. And since you're looking to get a miniDsp already, the total cost for that might be around 150 bucks. It's far less gimmick-y than it seems.

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6 hours ago, Boomer1950 said:

@SMEI've been looking into getting a miniDSP to better fine tune my sub, so your recommendation for a HPF to protect the driver will move that decision along.  I have a tone generating app that I used to do the test you suggested to find the tuning frequency.  It appeared to be about 21-22Hz.  By 18Hz the cone was moving quite a bit again.  I was shooting for 20Hz, so it will be interesting to see what it actually is, when I do measurements with REW.

So the tune is probably at 21-22 Hz then.  You'll likely get decent output down to 20 Hz with some audible bass down to ~16-18 Hz, depending on what your room is doing.

 

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