Where to start with room correction

[RonSanderson]

I have been away from the state of the art for some time now.

I have a straightforward stereo system with just two full-range speakers. My amp/preamp is an integrated Krell KAV-300i that is fully analog. I am unsure whether it has a way to output the preamp signal, modify it, and route it back in to the amplifier. (I can find out if it becomes relevant.)

Where do I even start? I think the current crossovers create a dip in the low bass output, but are exceptionally good on phase reproduction. It was a design goal.
What I want is a small 2 channel unit that will measure, then correct, the signal to restore the missing bass. Of course, I expect this is a minor subset of what can be done. But my needs are simple, I think, so where do I start looking for a simple solution?

I have about 30 threads open at the moment to study, but where do I start?

 

[NTK]

Welcome to ASR!

You can use the tape loop in your Krell integrated amp to insert the room EQ processor. A popular choice around here would be the MiniDSP Flex unbalanced.

If you want to add subwoofer(s), there would be a bit more hassle. The reason is that you'd need to control the volume using the room EQ processor, and not using the Krell. The Krell volume control, I presume, would likely be downstream of the tape loop. If you have sub(s) running off the room EQ processor, then the Krell volume control will not be able to affect the volume of your sub(s). Moreover, once you set the volume of the Krell and finished EQ'ing your system, you cannot move the volume knob on the Krell any more. However, if you are not adding sub(s) at this point, then you don't need to worry about it and adding the room EQ processor will be pretty simple.

 

[LTig]

Even without an EQ it makes sense to get a Umik-1 and free REW and start measurements using MMM. Then you can start moving the speakers around and check if this helps to fill in nulls or tame peaks in the frequency response.

 

[RonSanderson]

Welcome to ASR!

You can use the tape loop in your Krell integrated amp to insert the room EQ processor. A popular choice around here would be the MiniDSP Flex unbalanced.

If you want to add subwoofer(s), there would be a bit more hassle. The reason is that you'd need to control the volume using the room EQ processor, and not using the Krell. The Krell volume control, I presume, would likely be downstream of the tape loop. If you have sub(s) running off the room EQ processor, then the Krell volume control will not be able to affect the volume of your sub(s). Moreover, once you set the volume of the Krell and finished EQ'ing your system, you cannot move the volume knob on the Krell any more. However, if you are not adding sub(s) at this point, then you don't need to worry about it and adding the room EQ processor will be pretty simple.

Not to worry, the speakers are a transmission line design (Fried Studio V) and I won’t be needing a subwoofer. I will track down the manual for the Krell (where did I put that 25 years ago?) and check out the tape output. I did use it when digitizing some LPs several years back but I am not sure if the signal just goes out to a tape or if it can come back in, too!

 

[NTK]

Not to worry, the speakers are a transmission line design (Fried Studio V) and I won’t be needing a subwoofer. I will track down the manual for the Krell (where did I put that 25 years ago?) and check out the tape output. I did use it when digitizing some LPs several years back but I am not sure if the signal just goes out to a tape or if it can come back in, too!

Yes, it should. If you turn on the "Tape Mon" switch in the front panel, the amplifier will send the source signal the input selector selects to "TAPE OUT", and takes the signal from "TAPE IN" and send it to the volume control and then to the power amp. By inserting the room EQ processor into the tape loop, you'll be feeding the EQ'd signal to the power amp section of the Krell.

 

[RonSanderson]

Yes, it should. If you turn on the "Tape Mon" switch in the front panel, the amplifier will send the source signal the input selector selects to "TAPE OUT", and takes the signal from "TAPE IN" and send it to the volume control and then to the power amp. By inserting the room EQ processor into the tape loop, you'll be feeding the EQ'd signal to the power amp section of the Krell.

Thanks. I tracked down the manual online and you are much more helpful that it was! I will get the flashlight and take a look at the back of the unit. I did see mention of resetting an input so the unit could be controlled externally. That disables the balance and volume controls, which would mess up controlling our system with our universal remote!

S3/proc: For simplified integration of an A/V surround sound processor, the S3/proc input can be set to operate as a unity gain stage. In this Theater
Throughput mode, when the S3/proc input is selected, the KAV-300i's volume and balance controls are disabled. Volume control is transferred from the KAV-300i to the A/V surround sound processor connected to the S3/proc input. The left and right channel volume settings are now independent of the KAV-300t's volume control and the overall system level is determined by the A/V surround sound processor exclusively.
NOTE: The factory default position sets the S3/ Proc input as a standard input.
To enable this option, it is necessary to remove the top cover of the KAV-300i.
1. Unplug the KAV-300i from the AC outlet.
2. Remove the KAV-300i top cover screws with the supplied T-10 Torx wrench.
Lift the cover from the KAV-300i.
And so on…

Assuming that I can use my existing equipment, it will put me miles ahead. I would only have to choose the unit for room correction and patch it in! That’s much better than having to start replacing equipment - and training the household on new remotes and the resulting angry recriminations. (To be fair, the 300i has a dedicated preamp output, so I would have to buy a new amp and splice the EQ processor between them. Still, a hassle and expense I don’t want to deal with.)

 

[Mr. Widget]

From your title I was thinking this was going to be a thread about diffusers, absorption panels, bass traps and RT60. Don't get me wrong, adding a DSP can do wonders, but looking at the room is often an even bigger leap forward.

 

[Mtbf]

Love that amplifier. The S3 can be configured as theater throughput by setting a jumper inside.

 

[RonSanderson]

From your title I was thinking this was going to be a thread about diffusers, absorption panels, bass traps and RT60. Don't get me wrong, adding a DSP can do wonders, but looking at the room is often an even bigger leap forward.

Actually I think the room is OK. The soundstage is solid and huge. The only problem I am trying to solve is a depressed bass range.

After I bought the speakers, the manufacturer/designer sent me a new crossover that he said was better. I think, but cannot be sure, that the range covered by the bass unit is a little bit too low. I can go into technical details tomorrow.

I am diving into DACs and reading reviews, but what I have seen is too advanced for my needs.

All I need is a unit with two RCA jacks for input, and two for the corrected output. All my digital inputs have already been converted by other components. Does anyone have an idea where I could start with this bare bones unit?

 

[RonSanderson]

I bought a package that bundled a miniDSP UMIK-1 and a miniDSP HD. It has two analog inputs which I connected to the tape monitor output. I used only two of the four outputs since I have full-range speakers and no woofers. These outputs from the miniDSP went back to the tape monitor inputs. It took a little while to get all the right cables and learn REW and the miniDSP interface.

I first ran a frequency sweep of the room response for the left and right speakers.

Then I went into REW and generated room equalization filters, then copied those files to the Input PEQ filters on the miniDSP. I then re-ran the left and right room sweeps, generating new curves. I used these to generate a second set of filters, and loaded those into the miniDSP's Output PEQ filters.

Here are the left and right channels response curves. All room effects are neutralized and a significant hole in the bass response is handled. The sound has a much more solid bottom that it never had before.

That's the ticket! Mostly within 2db of level, with a tiny peak at 30db where I will never notice it.

Take a look at the 20Hz bass response - that is within 1 db of flat response. This is not out of line with its advertised response, so this is not in danger of overdriving the bass units.

I set a 15kHz rolloff - I guess the speaker would handle 20kHz if I had wanted it to. It was rated to 22kHz.

Thanks to this forum for pointing me in the right direction.

 

[rwortman]

That would sound too bright to me and most listeners. A downward slope with a kick up below 60hz is most preferrred.

 

[wacomme]

Dac - Topping 10s.

REW and the umik would be a good start - to verify that all you need to correct is the depressed base range.

 

[RonSanderson]

@rwortman - I tried using the default house curve in REW. I didn’t like it.

This is what I started with. (The right channel had mostly similar issues.)

The analysis shows an effective SPL 72.7db (at the bottom of the window) with the frequencies above 1500Hz pretty flat at about 74 db. So the new adjustment leaves me with almost the same emphasis in this region, and I am used to that after 25 years of listening to this system.

However, the SPL peak through the midrange made the sound too bright and the bass dips sucked energy and bottom out of the music. Having gained back about 12 db at the 76Hz and 102Hz dips has provided sufficient increase in the bass over what I had.

Perhaps the desire to ramp upward below 60Hz is due to listening at levels where the bass seems diminished due to Fletcher-Munsen effects. Or, perhaps it is a hangover from listening to systems where a premature bass rolloff is compensated by leaving a bass resonance boost just before the response dives.

Either way, your suggestion is a good one, but I decided for my own reasons to go against the common knowledge.